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Muscle and Joint Function After Anatomic and Reverse Total Shoulder Arthroplasty Using a Modular Shoulder Prosthesis
Abstract
Changes in joint architecture and muscle loading resulting from total shoulder arthroplasty (TSA) and reverse total shoulder arthroplasty (RSA) are known to influence joint stability and prosthesis survivorship. This study aimed to measure changes in muscle moment arms, muscle lines of action, as well as muscle and joint loading following TSA and RSA using a metal‐backed uncemented modular shoulder prosthesis. Eight cadaveric upper extremities were assessed using a customized testing rig. Abduction, flexion and axial rotation muscle moment arms were quantified using the tendon‐excursion method, and muscle line‐of‐force directions evaluated radiographically pre‐operatively, and after TSA and revision RSA. Specimen‐specific musculoskeletal models were used to estimate muscle and joint loading pre‐ and post‐operatively. TSA lateralized the glenohumeral joint center by 4.3 ± 3.2 mm, resulting in small but significant increases in middle deltoid force (2.0%BW) and joint compression during flexion (2.1%BW) (p<0.05). Revision RSA significantly increased the moment arms of the major abductors, flexors, adductors and extensors, and reduced their peak forces (p<0.05). The superior inclination of the deltoid significantly increased while the inferior inclination of the rotator cuff muscles decreased (p<0.05). TSA using an uncemented metal‐backed modular shoulder prosthesis effectively restores native joint function; however, lateralization of the glenoid component should be minimised intra‐operatively to mitigate increased glenohumeral joint loading and polyethylene liner contact stresses. Revision RSA reduces muscle forces required during shoulder function but produces greater superior joint shear and less joint compression. The findings may help to guide component selection and placement to mitigate joint instability after arthroplasty.
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... Computational modeling of RTSA facilitates estimation of muscle and joint loading, which is currently impossible to measure non-invasively in vivo. Modeling and simulation of RTSA has played a critical role in guiding implant positioning and surgical technique [19][20][21][22], prosthesis selection [23,24], implant design [25,26], and post-operative rehabilitation prescription [27,28]. To date, most modeling and simulation tools require high levels of expertise and are generally restricted to the research setting. ...
... For example, shoulder muscle forces during upper limb elevation can be calculated in several minutes using a subject-specific rigid body model ( Figure 1A) [28,31]; however, since deformation mechanics is neglected, the internal stresses and strains in the bone and implant cannot be accurately evaluated using this method. An important utility of rigid body models has been in their capacity to estimate the influence of arthroplasty on muscle moment arms, muscle and joint forces, and range of motion (ROM) at the shoulder, which are primary indicators of implant functional performance [21,23,24,[29][30][31][32][33][34][35][36][37][38][39][40]. ...
... While computational modeling may provide a basis for estimates of muscle and joint function, even the most sophisticated anatomical models are limited by the degree to which they replicate bone and joint biomechanics in vivo. Virtually all rigid body models neglect glenohumeral joint translation, and represent the glenohumeral joint as a threedegree-of-freedom constrained ball and socket or spherical joint [21,24,30,[32][33][34][35][36][37][38]40,93]. This simplification limits the degree to which such a model can predict joint stability, since joint subluxation cannot be explicitly simulated. ...
Reverse total shoulder arthroplasty (RTSA) is an established treatment for elderly patients with irreparable rotator cuff tears, complex proximal humerus fractures, and revision arthroplasty; however, with the increasing indications for RTSA over the last decade and younger implant recipients, post-operative complications have become more frequent, which has driven advances in computational modeling and simulation of reverse shoulder biomechanics. The objective of this study was to provide a review of previously published studies that employed computational modeling to investigate complications associated with RTSA. Models and applications were reviewed and categorized into four possible complications that included scapular notching, component loosening, glenohumeral joint instability, and acromial and scapular spine fracture, all of which remain a common cause of significant functional impairment and revision surgery. The computational shoulder modeling studies reviewed were primarily used to investigate the effects of implant design, intraoperative component placement, and surgical technique on postoperative shoulder biomechanics after RTSA, with the findings ultimately used to elucidate and mitigate complications. The most significant challenge associated with the development of computational models is in the encapsulation of patient-specific anatomy and surgical planning. The findings of this review provide a basis for future direction in computational modeling of the reverse shoulder.
... Prior studies indicated that the magnitude of joint forces should range between 38% and 60%, whereas the cumulative deltoid force should range between 33% and 60%. 3,16,21 Our joint and muscle forces were approximately 50% and 40% bodyweight, respectively, suggesting that the 3D simulator produced forces reasonably within the range of previous observations. Exclusion of human tissues, inferior glenoid inclination, or lack of 3D scapulohumeral rhythm in the studies may account for the broad force ranges observed previously. ...
... Comparisons between native muscle forces and rTSA showed that the overall trend was a decrease in deltoid force after rTSA (Fig. 5), which reinforces prior observations about muscle forces required for abduction. 3,17,21 Although not statistically significant in the middle and posterior deltoid, the lower forces were the most pronounced in the anterior deltoid where the rTSA was on average 20-30 N/kg less than the native forces. This is especially surprising as the motion included external glenohumeral rotation, which would be expected to increase the anterior deltoid force to abduct the arm. ...
Background
Optimal implant placement in reverse total shoulder arthroplasty (rTSA) remains controversial. Specifically, the optimal glenoid inclination is unknown. Therefore, a cadaveric shoulder simulator with 3D human motion specific to rTSA was used to study joint contact and muscle forces as a function of glenoid component inclination.
Methods
Eight human cadaver shoulders were tested before and after rTSA implantation. Scapular plane abduction kinematics from control subjects and those with rTSA drove a cadaveric shoulder simulator with 3D scapulothoracic and glenohumeral motion. Glenoid inclination varied from -20º to +20º. Outputs included compression, superior-inferior (S/I) shear, and anterior-posterior (A/P) shear forces from a 6 degree of freedom loadcell in the joint, and deltoid and rotator cuff muscle forces. Data were evaluated with statistical parametric mapping and t-tests.
Results
Inferior glenoid inclination (-) reduced S/I shear by up to 125% relative to superior inclination, with similar compression to the neutral condition (0°). Superior inclinations (+) increased the S/I shear force by approximately the same magnitude, yet decreased compression by 25% in the most superior inclination (+20°). There were few differences in deltoid or rotator cuff forces due to inclination. Only the middle deltoid decreased by ∼7% for the most inferior inclination (-20°). Compared to native shoulders, the neutral (0°) rTSA inclination showed reduced forces of 30-75% in the anterior deltoid, and a trend toward decreased forces in the middle deltoid. Force demands on the rotator cuff varied as a function of elevation, with a trend toward increased forces in rTSA at peak glenohumeral elevation.
Conclusions
Inferior inclination reduces superior shear forces, without influencing compression. Superior inclination increased S/I shear, while decreasing compression, which may be a source of component loosening and joint instability after rTSA. Inferior inclination of the rTSA glenoid may reduce the likelihood of glenoid loosening by reducing the magnitude of cyclic shear and compressive loading during arm elevation activities, although this may be altered by specific-subject body habitus and motion. These factors are especially important in revision rTSA or glenoid bone grafting where there is already a 3-fold increase in glenoid baseplate loosening versus primary rTSA.
... 21 This is especially interesting to consider in the context of the post-RSA shoulder, where the deltoid assumes a primary role to power the glenohumeral joint. 4,38 In this study, greater variability was noted for the 60-90° phase of motion at both six and twelve months post-RSA, which may point to differences in functional control throughout the motion arc. This is also consistent with literature observations of greater SHR variability during the scapular setting phase (<60°) across multiple studies. ...
... 17,35 Mechanically, post-RSA values especially with greater variability during early phases of motion may point towards differences in the musculature responsible for powering this motion in the RSA shoulder, which may have differences in supraspinatus and deltoid load sharing. 4,38 Furthermore, especially in an RSA population with variable rotator cuff integrity and soft-tissue condition, rotator cuff contribution to overall shoulder stability may be variable. For example, a lack of supraspinatus and infraspinatus to assist the deltoid in arm elevation and depression may be compounded by a dysfunctional motor pattern and may result in deltoid inhibition. ...
Background:
Reverse shoulder arthroplasty (RSA) is associated with high rates of midterm complications including scapular notching, implant wear, and mechanical impingement. Scapulo-humeral rhythm (SHR), described by Codman in the 1920's, is defined as the ratio of glenohumeral motion to scapulothoracic motion. SHR is used as an indicator of shoulder dysfunction, as alterations in SHR can have profound implications on shoulder biomechanics. The determination of SHR can be hindered by soft-tissue motion artifacts and high radiation burdens associated with traditional surface marker or fluoroscopic analysis. EOS low dose stereoradiographic imaging analysis utilizing 3D model construction from a 2D X-ray series may offer an alternative modality for characterizing SHR following RSA.
Methods:
Patients (n=10) underwent an EOS imaging analysis to determine SHR at six and twelve months post-RSA. Leveraging 3D models of the implants, 2D/3D image registration methods were used to calculate relative glenohumeral and scapulothoracic positioning at 60, 90 and 120° of shoulder elevation. Subject-specific SHR curves were assessed and midterm changes in post-RSA SHR associated with follow-up time and motion phase were evaluated. Pearson correlations assessed associations between patient-specific factors and post-RSA SHR.
Results:
Mean post-RSA SHR was 0.81:1 across subjects during the entire midterm postoperative period. As a cohort, post-RSA SHR was more variable for 60-90° of shoulder motion. SHR for 90-120° of motion decreased (0.43:1) at twelve months post-RSA. Post-RSA SHR could be categorized using three relative motion curve patterns, and was not strongly associated with demographic factors such as BMI. 50% of subjects demonstrated a different SHR relative motion curve shape at twelve months post-RSA, and SHR during the 90120° of motion was found to generally decrease at twelve months.
Conclusion:
Midterm post-RSA SHR was successfully evaluated using EOS technology, revealing lower SHR values (i.e., greater scapulothoracic motion) compared to normal values reported in the literature. SHR continued to change for some subjects during the midterm post-RSA period, with the greatest change during 90-120° of shoulder motion. Study findings suggest that future post RSA rehabilitation efforts to address elevated scapulothoracic motion may benefit from being patient-specific in nature and targeting scapular stabilization during 90-120° of shoulder motion. Level of Evidence: IV.
... While using generalized healthy shoulder motions to investigate pathology or repair is a known limitation, 3D scapulothoracic and glenohumeral motions also vary with age in healthy individuals [27]. Thus, studies analyzing procedures like reverse shoulder arthroplasty with in vitro [28][29][30][31][32][33][34] and in silico [35][36][37] models could be influenced by the assumption of healthy shoulder kinematics, affecting how physical therapists, surgeons, and implant designers assimilate findings into clinical practice. ...
... Additionally, glenohumeral axial rotation steadily decreased where others had steep initial decreases ( Fig. 2(b)). More anterior scapular tilt and glenohumeral plane of elevation could cause deltoid forces to distribute more evenly, thus higher MD and PD forces relative to AD. Cadaver C6 had the highest BMI (29) and lowest CSA (24.1), which deviated by >1 SD from the group (Table 1). Additionally, humeral torsion, inclination, and head radius were among the highest. ...
In vitro simulation of 3D shoulder motion using in vivo kinematics obtained from human subjects allows investigation of clinical conditions in the context of physiologically relevant biomechanics. Herein we present a framework for laboratory simulation of subject-specific kinematics that combines individual 3D scapular and humeral control in cadavers. The objectives were to: 1) robotically simulate 7 healthy subject-specific 3D scapulothoracic and glenohumeral kinematic trajectories in 6 cadavers, 2) characterize system performance using kinematic orientation accuracy and repeatability, and muscle force repeatability metrics and 3) analyze effects of input kinematics and cadaver specimen variability. Using an industrial robot to orient the scapula range of motion (ROM), errors with repeatability of ±0.1 mm and <0.5° were achieved. Using a custom robot and a trajectory prediction algorithm to orient the humerus relative to the scapula, orientation accuracy for glenohumeral elevation, plane of elevation, and axial rotation of <3° mean absolute error was achieved. Kinematic accuracy was not affected by varying input kinematics or cadaver specimens. Muscle forces over 5 repeated setups showed variability typically <33% relative to the overall simulations. Varying cadaver specimens and subject-specific human motions showed effects on muscle forces, illustrating that the system was capable of differentiating changes in forces due to input conditions. The anterior and middle deltoid, specifically, showed notable variations in patterns across the ROM that were affected by subject-specific motion. This machine provides a platform...(truncated to fit word count, missing text in main PDF includes R2 changes).
... It is indicative of a muscle's potential to contribute to actuation of a joint in a particular joint motion direction, and defines the role of the muscle, for example as a joint flexor or abductor. Muscle moment arm data have played an important role in validation of musculoskeletal models (Ackland et al., 2019;Holzbaur et al., 2005), and have had clinical applications in assessing the mechanical outcome of surgical interventions such as tendon transfers and arthroplasty (Ackland et al., 2010;Berton et al., 2015;Dicker et al., 2012). ...
... A cadaveric testing apparatus for moment arm measurement was developed based on a previously published design (Ackland et al., 2019). The testing rig facilitated passive motion of each MCP, PIP and DIP joint independently, while allowing simultaneous measurement of joint angles and tendon excursions (Fig. 1A). ...
The moment arm of a muscle’s force represents the muscle’s leverage or mechanical advantage in producing a joint moment. It is indicative of the muscle’s potential to contribute to actuation of a joint in a particular joint motion direction, and defines the role of the muscle, for example as a joint flexor or abductor. The aims of this study were, firstly, to measure the moment arms of the flexors and extensor muscles of the metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints, and the moment arms of the major abductors and adductor muscles of the metacarpophalangeal (MCP) of each finger in the hand using the tendon-excursion method; secondly, to assess the effect of change in joint angle on these moment arms; and thirdly, to determine if there are differences in a given flexor or extensor’s muscle moment arms between the joints it spans on a given finger, and across its tendon slips to multiple fingers. The tendon-excursion method was used to measure instantaneous muscle moment arms in nine fresh-frozen entire forearm cadaver specimens. Flexion angle was found to have significant effects on the moment arms of the extensor muscles at the MCP and PIP joints (p<0.05). In contrast, the digital flexor muscles maintained relatively constant moment arms through the range of flexion. The moment arms of the digital flexors and extensors spanning multiple joints in a finger were largest at the MCP joints and smallest at the DIP joints. The findings demonstrate greater torque generating capacity for tasks such as grasping at the proximal interphalangeal joints, and smaller torque capacity for finer movement control at the distal interphalangeal joints. The dataset generated in this study may be useful in the development and validation of computational models used in surgical planning, and rehabilitation.
... Dans la configuration inversée, l'allongement est plus important, en particulier si une grosse glénosphère est utilisée, l'allongement atteignant alors 7 à 8 cm. Malheureusement, la littérature reste pauvre concernant l'impact de l'inversion sur le comportement de la musculature de l'épaule [6,43]. ...
... Lors de l'alésage de la glène, il faut tenir compte de sa concavité. En utilisant un alésoir plat, le bord extérieur du cercle glénoïdien sera alésé en premier et affaiblira le support osseux, ce qui est le prix à payer pour avoir une bonne assise et éviter les contrainte type « cheval à bascule » [6]. ...
... found that TSA configurations led to more stressed volume and higher maximal measured stress compared with RSA configurations, probably because of an active supraspinatus muscle and the very different geometric properties compared with reverse configurations. In a biomechanical and cadaveric study using musculoskeletal modelling, Ackland et al. [2] compared stemmed TSA and RSA and found that RSA models without supraspinatus muscles produced less joint compression than TSA models with supraspinatus muscles did, which is consistent with our results. In a similar study, the same authors found that RSA with an intact or isolated supraspinatusdeficient rotator cuff produced large glenohumeral joint forces that may increase baseplate failure risk, particularly during flexion, when posterior shear forces are largest, without a significant difference between the configurations [1]. ...
Purpose
Our purpose was to quantify stresses in the bone surrounding stemless implants in various configurations.
Methods
A detailed finite element model of the glenohumeral joint was used to simulate abduction kinematics before and after arthroplasty and to measure bone stresses around the implants. Two digital patients were simulated: one healthy and one with supraspinatus muscle impairment (deficiency). Two anatomic total shoulder arthroplasty (TSA) configurations were placed in a 135° cutting plane. Two reverse shoulder arthroplasty (RSA) configurations with cutting angles of 135° and 145° were simulated with asymmetrical and symmetrical polyethylene cups, respectively, to obtain humeral neck‐shaft angles of 145°.
Results
Compared with preoperative models, TSA preserved and RSA restored abduction kinematics. The bone mechanical stresses were located mainly around the central stud of the TSA and were more peripheral to the RSA humeral components. The RSA configuration with the 145° cutting angle and symmetrical cup generated the lowest maximal bone stress and bone volume involvement. Stresses in the scapular cortical bone were highest in the supraspinatus fossa for TSA and the crest of the acromion for RSA.
Conclusion
Early stability and glenohumeral bone stress change with implant configuration and should not be extrapolated from anatomic clinical data to reverse configurations.
Level of Evidence
Diagnostic tests or criteria; Level IV.
... The overall force trajectories in the 90 o trial also appeared qualitatively different, with a sudden drop in force values at the supraspinatus position mid-cycle at 90 o . Although the other myorobotic forces were not measured in this study, this difference in kinetic profile appears consistent with findings in cadaveric studies using reverse shoulder implants, and this finding is likely explained by the fact that at 90 o ROM, other muscles such as the anterior and medial deltoid are preferentially recruited [48]. ...
Advanced robotic systems that replicate musculoskeletal structure and function have significant potential for a wide range of applications. Although they are proposed to be better platforms for biomedical applications, little is known about how well current musculoskeletal humanoid systems mimic the motion and force profiles of humans. This is particularly relevant to the field of tendon tissue engineering, where engineered grafts require advanced bioreactor systems that accurately replicate the kinetic and kinematic profiles experienced by the humans in vivo . A motion study was conducted comparing the kinetic and kinematic profiles produced by a musculoskeletal humanoid robot shoulder to a group of human participants completing abduction/adduction tasks. Results from the study indicate that the humanoid arm can be programed to either replicate the kinematic profile or the kinetic profile of human participants during task completion, but not both simultaneously. This study supports the use of humanoid robots for applications such as tissue engineering and highlights suggestions to further enhance the physiologic relevance of musculoskeletal humanoid robotic platforms.
... Cortical strain, fracture load, and stiffness are mechanical parameters related to fracture, which can be analyzed relative to pre-operative intact conditions to account for their large variability across people [15]. Finally, the risk analysis should consider, among implant loads caused by common daily activities in implanted patients, the loading conditions causing the highest risk of implant failure, to draw meaningful considerations of implant safety [10,[16][17][18]. Therefore, measuring the displacement of the bone in intact and implanted conditions under controlled load can enable a complete risk analysis of biomechanical failure. ...
Background
Reverse Shoulder Arthroplasties (RSA) have become a primary choice for improving shoulder function and pain. However, the biomechanical failure mechanism of the humeral component is still unclear. The present study reports a novel protocol for microstructural imaging of the entire humerus implant under load before and after fracture.
Methods
A humerus specimen was obtained from a 75-year-old male donor. An expert surgeon implanted the specimen with a commonly used RSA implant (Aequalis reversed II, Stryker Orthopaedics, USA) and surgical procedure. The physiological glenohumeral contact force that maximized the distal implant migration was selected from a public repository (orthoload.com). Imaging and concomitant mechanical testing were performed using a large-volume micro-CT scanner (Nikon XT H 225 ST) and a custom-made compressive stage. Both when intact and once implanted, the specimen was tested under a pre-load and by imposing a constant deformation causing a physiological reaction load (650 N, 10 degrees adducted). The deformation of the implanted specimen was then increased up to fracture, which was identified by a sudden drop of the reaction force, and the specimen was then re-scanned.
Results
The specimen’s stiffness decreased from 874 N/mm to 464 N/mm after implantation, producing movements of the bone-implant interface consistent with the implant’s long-term stability reported in the literature. The micro-CT images displayed fracture of the tuberosity, caused by a combined compression and circumferential tension, induced by the distal migration of the implant.
Conclusion
The developed protocol offers detailed information on implant mechanics under load relative to intact conditions and fracture, providing insights into the failure mechanics of RSA implants. This protocol can be used to inform future implant design and surgical technique improvements.
... 12,38 Increased rotator cuff forces are consistent with the findings of prior studies and may arise from the residual cuff becoming adductors. 1,10,11,18 Muscle excursion data also support this concept, where the subscapularis and teres minor exhibited opposite excursion directions following rTSA. Even in anatomic reverse shoulders, the rotator cuff muscle insertions are initially below the rTSA center of rotation, causing an adduction moment. ...
... According to the publication by Ackland et al., the deltoid muscle pulls with up to 175 N during an arm abduction of 40° (based on a person weighing 75 kg) [19]. Therefore, the movements of the acromion fragment were evaluated at each increment up to a load level of 175 N and in the direction of the deltoid's muscle pulling direction (Figure 3). ...
Background:
Acromial Levy III fractures after inverse shoulder arthroplasty occur in up to 7% of patients. To date, it is not clear how these fractures should be treated as clinical outcomes remain unsatisfactory. The aim of this study was to evaluate the biomechanical performance of three different plating methods of type III acromion fractures.
Methods:
Levy III fractures in synthetic scapulae were fixed with three different methods. Angular stable locking plates were placed on the spina scapula to bridge the fracture either dorsally, caudally, or on both aspects by double plating. In a biomechanical experiment, the pull of the deltoid muscle at 40° abduction of the arm was simulated by cyclic loading with increasing load levels until failure. Failure load, cycles to failure, and fragment motions were evaluated.
Results:
The results showed that double plating (350 ± 63 N) withstood the highest loads until failure, followed by dorsal (292 ± 20 N) and caudal (217 ± 49 N) plating. Similarly, double plating showed significantly smaller fragment movement than the other two groups.
Conclusions:
Double plating appeared to provide the largest biomechanical stability in type III acromion fracture under arm abduction. Caudal plating in contract resulted in insufficient fracture stability and early failure and can thus not be recommended from a biomechanical point of view.
... 10,11 During the post-operative recovery period, patients are more likely to subject the baseplate to isolated shearing forces as they adapt to the altered use of the deltoid muscle, altered compressive contraction mechanics, and increased range of motion as a result of RTSA. [10][11][12] Limited range of motion exercises are encouraged during the initial rehabilitation period and compressive forces are low, placing enhanced importance on initial resistance to shear loading in the absence of significant compressive loading. 13 Most studies focus on the application of cyclic shear and compressive loading while measuring pre-cyclic and post-cyclic displacement. ...
Background
In a reverse total shoulder arthroplasty, the altered glenohumeral joint center of rotation subjects the glenoid baseplate to increased shear forces and potential loosening.
Methods
This study examined glenoid baseplate micromotion and initial fixation strength with the application of direct shear force in a Sawbone model. The reverse total shoulder arthroplasty systems examined were the DJO Reverse® Shoulder Prosthesis, the Exactech Equinoxe® Reverse System, and the Tornier Aequalis TM Reverse Shoulder Prosthesis. Specimens were cyclically tested with increasing shear loads until 150 µm of displacement between the implant and glenoid was achieved, and subsequently until failure, classified as either 1 cm of implant/glenoid displacement or fracture.
Results
The average load withstood for the 150 µm threshold for DJO, Tornier, and Exactech was 460 ± 88 N, 525 ± 100 N, and 585 ± 160 N, respectively. The average total load at device failure for DJO, Tornier, and Exactech was 980 ± 260 N, 1260 ± 120 N, and 1350 ± 230 N, respectively.
Discussion
The Exactech implant design trended toward requiring more load to induce micromotion at each threshold and to induce device failure, most commonly seen as inferior screw pull out. This study proposes design features that may enhance fixation and suggests little risk of initial micromotion or failure during initial post-operative recovery.
... Although in vitro experimental studies can provide valuable information regarding joint loading with (Parsons et al., 2002;Dyrna et al., 2018) and without rotator cuff tears (Ackland et al., 2019), the experimental cost is not conductive to parameter research. Musculoskeletal multibody dynamics modeling provides a non-invasive strong platform for understanding in vivo biomechanics of the shoulder and the effects of joint replacement on function. ...
Anatomic total shoulder arthroplasty (ATSA) is widely used to treat the diseases of the glenohumeral (GH) joint. However, the incidence of rotator cuff tears after ATSA increases during follow-up. The effects of rotator cuff deficiencies after ATSA on the biomechanics of the GH joint are to be investigated. In this study, a musculoskeletal multibody dynamics model of ATSA was established using a force-dependent kinematics (FDK) method. The biomechanical effects were predicted during arm abduction under different rotator cuff deficiencies. The deltoid forces were increased under the rotator cuff deficiencies, the maximum deltoid forces were increased by 36% under the subscapularis deficiency and by 53% under the supraspinatus, infraspinatus, subscapularis, and teres minor deficiencies. The maximum GH contact forces were decreased by 11.3% under supraspinatus and infraspinatus deficiencies but increased by 24.8% under subscapularis deficiency. The maximum subscapularis force was decreased by 17% under only infraspinatus tear during arm abduction. The results suggested that the changes in the biomechanics of the GH joint induced by rotator cuff deficiencies after ATSA increase the deltoid muscle energy expenditure and joint instability, which result in postoperative less satisfactory clinical outcomes. The changes in rotator cuff muscle forces deserve more attention for understanding the evolution of rotator cuff tear after ATSA.
... The biomechanical test protocol consisted of a preload of 30 N [17] followed by dynamic testing with 700 cycles covering a minimum load of 30 N and a maximum load of 130 N. The first 200 cycles were used as preconditioning; therefore, results will be reported from cycle 200 onward. The maximum cyclic load based on the average muscle force of the medial part of the deltoid muscle measured by Ackland et al. for an abduction movement with a reverse prosthesis (112 N), the predicted values by Karlsson and Peterson for an abduction movement (60° with 1 kg-130 N) [18,19] and the physiological cross sectional area defined by Veeger et al. [20]. After cyclic loading, a position/displacement-controlled load-to-failure test with a displacement rate of 60 mm/min in accordance to the previous established test protocol by Spiegl et al. was performed [16]. ...
Introduction
The number of atraumatic stress fractures of the scapular spine associated with reverse shoulder arthroplasty is increasing. At present, there is no consensus regarding the optimal treatment strategy. Due to the already weakened bone, fractures of the scapular spine require a high fixation stability. Higher fixation strength may be achieved by double plating. The aim of this study was to evaluate the biomechanical principles of double plating in comparison to single plating for scapular spine fractures.
Methods
In this study, eight pairs ( n = 16) of human shoulders were randomised pairwise into two groups. After an osteotomy at the level of the spinoglenoid notch, one side of each pair received fracture fixation with a single 3.5 LCP (Locking Compression Plate) plate. The contralateral scapular spine was fixed with a 3.5 LCP and an additional 2.7 LCP plate in 90–90 configuration.
The biomechanical test protocol consisted of 700 cycles of dynamic loading and a load-to-failure test with a servohydraulic testing machine. Failure was defined as macroscopic catastrophic failure (screw cut-out, plate breakage). The focus was set on the results of specimens with osteoporotic bone quality.
Results
In specimens with an osteoporotic bone mineral density (BMD; n = 12), the mean failure load was significantly higher for the double plate group compared to single plating (471 N vs. 328 N; p = 0.029). Analysis of all specimens ( n = 16) including four specimens without osteoporotic BMD revealed no significant differences regarding stiffness and failure load ( p > 0.05).
Conclusion
Double plating may provide higher fixation strength in osteoporotic bone in comparison to a single plate alone. This finding is of particular relevance for fixation of scapular spine fractures following reverse shoulder arthroplasty.
Level of evidence
Controlled laboratory study.
... used computational models to apply discrete static loads, while Halonen et al. considered load and cartilage stress variation of a single subject in response to shoe insoles (Halonen et al. 2017), both during gait. Ackland et al. used musculoskeletal models to compliment cadaveric studies in determining muscle lines of action and forces after shoulder prosthesis implantation (Ackland et al. 2019) The objective of the current study was to use a dynamic computational model based on kinematics from 6 patients performing activities associated with post-THA adverse events to quantitatively describe and compare how variation in both THA implant geometry and implantation alignment contribute to joint stability and the overall resistance to anterior and posterior dislocation. ...
Instability and dislocation remain leading indications for revision of total hip arthroplasty (THA). Many studies have addressed the links between implant design and dislocation; however, an understanding of the impact of alignment and kinematic variability on constraint of modern THA constructs to provide joint stability is needed. The objective of this study is to provide objective data to be considered in the treatment algorithm to protect against joint instability. Joint contact and muscle forces were evaluated using musculoskeletal models of THA patients performing activities consistent with posterior and anterior dislocation. Position and joint loads were transferred to a finite element simulation with an experimentally calibrated hip capsule representation, where they were kinematically extrapolated until impingement and eventual dislocation. Cup anteversion and inclination were varied according to clinical measurements, and variation in imposed kinematics was included. The resistive moment provided by the contact force and joint capsule, and overall dislocation rate (dislocations/total simulations) were determined with neutral and lipped acetabular liners. Use of a lipped liner did increase the resistive moment in posterior dislocation, by an average of 5.2 Nm, and the flexion angle at dislocation by 1.4° compared to a neutral liner. There was a reduction in similar magnitude in resistance to anterior dislocation. Increased cup anteversion and inclination, hip abduction and internal rotation all reduced the occurrence of posterior dislocation but increased anterior dislocation. A quantitative understanding of tradeoffs in the dislocation risk inherent to THA construct options is valuable in supporting surgical decision making.
OpenSim Moco enables solving for an optimal motion using Predictive and Tracking simulations. However, Predictive simulations are computationally prohibitive, and the efficacy of Tracking in deviating from its reference is unclear. This study compares Tracking and Predictive approaches applied to the generation of morphology-specific motion in statistically-derived musculoskeletal shoulder models. The signal analysis software, CORA, determined mean correlation ratings between Tracking and Predictive solutions of 0.91 ± 0.06 and 0.91 ± 0.07 for lateral and forward-reaching tasks. Additionally, Tracking provided computational speed-up of 6-8 times. Therefore, Tracking is an efficient approach that yields results equivalent to Predictive, facilitating future large-scale modelling studies.
Reverse total shoulder arthroplasty (RTSA) accounts for over half of shoulder replacement surgeries. At present, the optimal position of RTSA components is unknown. Previous biomechanical studies have investigated the effect of construct placement to quantify mobility, stability and functionality postoperatively. While studies have provided valuable information on construct design and surgical placement, they have not systematically evaluated the importance of scapular morphology on biomechanical outcomes. The aim of this study was to assess the influence of scapular morphology variation on RTSA biomechanics using statistical models, musculoskeletal modeling and predictive simulation. The scapular geometry of a musculoskeletal model was altered across six modes of variation at four levels (±1 and ±3 SD) from a clinically derived statistical shape model. For each model, a standardized virtual surgery was performed to place RTSA components in the same relative position on each model then implemented in 50 predictive simulations of upward and lateral reaching tasks. Results showed morphology affected functional changes in the deltoid moment arms and recruitment for the two tasks. Variation of the anatomy that reduced the efficiency of the deltoids showed increased levels of muscle force production, joint load magnitude and shear. These findings suggest that scapular morphology plays an important role in postoperative biomechanical function of the shoulder with an implanted RTSA. Furthermore a “one‐size‐fits‐all” approach for construct surgical placement may lead to suboptimal patient outcomes across a clinical population. Patient glenoid as well as scapular anatomy may need to be carefully considered when planning RTSA to optimize postoperative success.
Since the Food and Drug Administration (FDA) approval nearly two decades ago, the indications for and utilization of reverse shoulder arthroplasty (RSA) have expanded considerably. Stemless RSA designs have been used in Europe since 2005, but have only recently been introduced in domestic Investigational Device Exemption trials. Potential advantages of stemless RSA are similar to those of stemless anatomic total shoulder arthroplasty, which may include fewer shaft-related complications, avoidance of stress shielding, bone preservation, and easier revision surgery. European data support similar outcomes between certain stemless RSA prostheses compared with that of stemmed RSA implants at early and mid-term follow-up. However, long-term outcomes remain to be seen and differences exist between the stemless RSA designs used in Europe and those being studied in domestic clinical trials. An understanding of the potential advantages and disadvantages of stemless RSA, differences between existing designs, and reported clinical outcomes is prudent for the safe and meaningful implementation of this new technology in the United States.
Introduction:
Indications for reverse total shoulder arthroplasty (RSA) have expanded to include individuals with intact rotator cuffs such as patients with severe glenoid deformity or with concern of future rotator cuff insufficiency. The purpose of this study was to compare outcomes of RSA with an intact rotator cuff to RSA for cuff arthropathy and anatomic total shoulder arthroplasty (TSA). We hypothesized that outcomes of RSA with an intact rotator cuff would be comparable to RSA for cuff arthropathy and TSA but with diminished range of motion compared to TSA.
Materials and methods:
Patients at one institution who underwent RSA and TSA between 2015 and 2020 with minimum 12-month follow-up were identified. RSA with preservation of the rotator cuff (+rcRSA) was compared to RSA for cuff arthropathy (-rcRSA) and anatomic TSA (TSA). Demographics and glenoid version/inclination were obtained. Pre/postoperative range of motion (ROM); patient-reported outcomes including visual analogue scale (VAS), subjective shoulder value (SSV), and American Shoulder and Elbow Surgeons (ASES) scores; and complications were obtained.
Results:
24 patients underwent +rcRSA, 69 underwent -rcRSA, and 93 underwent TSA. There were more women in the +rcRSA cohort (75.8%) than the -rcRSA (37.7%, p=0.001) and TSA (37.6%, p=0.001) cohorts. Mean age of +rcRSA (71.1) was greater than that of TSA (66.0, p=0.021) but similar to that of -rcRSA (72.4, p=0.237). Glenoid retroversion was greater in +rcRSA (18.2°) compared to -rcRSA (10.5°, p=0.011) but was similar to TSA (14.7°; p=0.244). Postoperatively, there were no differences in VAS or ASES between +rcRSA vs -rcRSA and +rcRSA vs TSA. SSV was lower in +rcRSA (83.9) compared to -rcRSA (91.8, p=0.021), but was similar to TSA (90.5, p=0.073). Similar ROM was achieved in forward flexion, external rotation, and internal rotation at final follow-up between +rcRSA and -rcRSA, but TSA had greater external rotation (44° vs 38°, p=0.041) and internal rotation (6.5° vs 5.0°, p=0.001) compared to +rcRSA. There were no differences in complication rates.
Discussion:
At short-term follow-up, preservation of the rotator cuff in RSA demonstrated similarly excellent outcomes and low complication rates compared to RSA with a deficient rotator cuff and TSA, except for slightly lower internal and external rotation compared to TSA. While multiple factors deserve consideration when choosing between RSA and TSA, RSA with preservation of the posterosuperior cuff is a viable treatment option for glenohumeral osteoarthritis, particularly in patients with severe glenoid deformity or those at risk for future rotator cuff insufficiency.
Background
The 2021 AOANJRR (Australian Orthopaedic Association National Joint Replacement Registry) report indicated that total shoulder replacement using both mid head (TMH) length humeral components and reverse arthroplasty (RTSA) had a lower revision rate than stemmed humeral components in anatomical total shoulder arthroplasty (aTSA) - for all prosthesis types and diagnoses. However, there are many factors that impact on the outcome of total shoulder replacement including stem length and polarity, polyethylene type and glenoid fixation (cemented vs cementless). The aim of this study was to assess the impact of these variables in the various primary total arthroplasty alternatives for osteoarthritis in the shoulder.
Methods
Data from a large national arthroplasty registry were analysed for the period April 2004 to December 2020. The study population included all primary aTSA, RTSA, and TMH shoulder arthroplasty procedures undertaken for osteoarthritis (OA) using either cross-linked polyethylene (XLPE) or non-cross-linked polyethylene (non XLPE). Due to the previously documented and reported higher revision rate compared to other anatomical total shoulder replacement options, those using a cementless metal backed glenoid components were excluded. The rate of revision was determined by Kaplan-Meir estimates, with comparisons by Cox proportional hazard models. Reasons for revision were also assessed.
Results
For a primary diagnosis of OA, aTSA with a cemented XLPE glenoid component had the lowest revision rate with a 12-year cumulative revision rate of 4.7%, compared to aTSA with cemented non-XLPE glenoid component of 8.7%, and RTSA of 6.8%. The revision rate for TMH (with XLPE or non-XLPE) was lower than aTSA with cemented non-XLPE, but was similar to the other implants at the same length of follow-up. The reason for revision for cemented aTSR was most commonly component loosening, not rotator cuff deficiency.
Conclusion
Long stem humeral components matched with XLPE in aTSA achieve a lower revision rate compared to shorter stems, long stems with conventional polyethylene, and RTSA when used to treat shoulder OA. In all these cohorts, loosening, not rotator cuff failure was the most common diagnosis for revision.
PurposeThe rotator cuff (RC) muscles contribute to dynamic stability and rotational actions of the glenohumeral joint. Moment arm can be used to demonstrate the potential work a muscle contributes to a musculoskeletal joint rotation. This study aimed to understand the moment arm contributions of the RC muscles and explore changes following a complete supraspinatus tear treated with either superior capsular reconstruction (SCR) or reverse total shoulder arthroplasty (rTSA).Methods
Five fresh-frozen cadaveric specimens were prepared and mounted in an apparatus where each intact RC muscle was held in tension with a line of action toward its origin on the scapula. Mean moment arms for each muscle were determined experimentally based on Optotrak data collected during cadaveric shoulder arm abduction.ResultsUsing ANOVA testing, our analysis demonstrated significant differences (p < 0.001) in infraspinatus and teres minor moment arms after rTSA compared to the intact shoulder model. After SCR, significant differences (p < 0.001) were seen in teres minor, with these differences being statistically similar to the changes seen in teres minor after rTSA. Subscapularis showed no significant difference in moment arm values between the models (p = 0.148).Conclusion
Our results illustrate that mean moment arms were preserved in the RC muscles after complete supraspinatus tear. This study also shows evidence that subscapularis function may be maintained after SCR or rTSA. After SCR, infraspinatus may maintain similar abduction ability compared to the anatomical shoulder, while teres minor ability may increase. Infraspinatus may have decreased abduction ability after rTSA while teres minor may have increased ability.
BACKGROUND
Repair of the subscapularis following reverse shoulder arthroplasty (RSA) remains a controversial topic among surgeons. Poor rotator cuff muscle quality is associated with increased musculotendinous stiffness, and the subsequent effect of compromised tissue repair on RSA functional outcomes remains unclear. The objective was to investigate the influence of subscapularis stiffness together with glenoid component lateralization on pre- and post-impingement joint mechanics during external rotation after RSA.
METHODS
A validated finite element model incorporating the Zimmer Trabecular Metal reverse system was utilized. The deltoid and subscapularis tendon were tensioned and wrapped around the joint prior to controlled shoulder external rotation. Baseline subscapularis stiffness, determined from cadaveric testing, was varied to 80%, 120% and 140% of baseline, to simulate a range of pliability associated with fatty infiltration and fibrosis. We evaluated the effects of varying subscapularis stiffness and the corresponding variation in joint tension with varying glenosphere lateralization (2, 4, 10 mm) on the torque required to externally rotate the shoulder and the impingement/subluxation risk.
RESULTS
Prior to any impingement, the torques required to externally rotate the shoulder ranged from 22-47 Nm across the range of parameters studied, with the greatest torques required for the 10 mm glenosphere lateralization. The impact of increasing subscapularis stiffness on torque requirements was most pronounced at the 10 mm lateralization, as well. A 20% increase in subscapularis stiffness necessitated a 7-14% increase in pre-impingement torque, while a 40% stiffness increase was associated with a 12-27% increase in torque. Torque was proportional to lateralization. When lateralization was increased from 2 mm to 4 mm, the pre-impingement torque increased by 10-13%, while a 10 mm lateralization necessitated a 35-62% torque increase relative to 2 mm of lateralization. Increased subscapularis stiffness did not limit impingement-free ROM or substantially decrease post-impingement subluxation in this model.
DISCUSSION
Mechanical gains achieved through lateralization may be hindered by increased torque demands, especially when a stiffer subscapularis is repaired. As lateralization increases subscapularis tension, greater torque is required to externally rotate the shoulder. The torque required for external rotation has been reported between 15-50 Nm. Subscapularis repair with the simulated increases in stiffness requires relative increases in torque that the reconstructed shoulder may not be able to physically produce to rotate the glenohumeral joint, particularly at 10 mm lateralization. These results suggest that subscapularis repair may not be indicated in cases where a lateralized glenoid component is utilized and the subscapularis is compromised.
LEVEL OF EVIDENCE
Basic Science Study; Computer Modeling
Background
The biomechanical effects of joint line medialization during shoulder surgery are poorly understood. It was therefore the purpose of this study was to investigate whether medialization of the joint line especially associated with total shoulder arthroplasty (TSA) leads to changes in the rotator cuff muscle forces required to stabilize the arm in space.
Method
A validated computational 3-D rigid body simulation model was used to calculate generated muscle forces, instability ratios, muscle-tendon-lengths and moment arms during scapular plane elevation. Measurements took place with the anatomical and a 2mm and 6 mm lateralized or medialized joint line.
Results
When the joint line was medialized, increased deltoid muscle activity was recorded throughout glenohumeral joint elevation. The rotator cuff muscle forces increased with medialization of the joint line in the early phases of elevation. Lateralization of the joint line led to higher rotator cuff muscle forces after 52°of glenohumeral elevation and to higher absolute values in muscle activity. A maximum instability ratio of >0.6 was recorded with 6mm of joint line medialization.
Conclusion
In this biomechanical study, medialization and lateralization of the normal joint line during TSA led to substantial load changes on the shoulder muscles used for stabilizing the arm in space. Specifically, medialization does not only lead to muscular shortening but also to increased load on the supraspinatus tendon during early arm elevation, the position which is already most loaded in the native joint.
Level of evidence: Basic Science Study; Computer Modeling
Background
Increased glenoid retroversion occurs in patients with severe arthritis but its effect on baseplate fixation of a reverse total shoulder arthroplasty (rTSA) is not clear. The purpose of this study is to determine the effects of increasing glenoid retroversion on baseplate fixation in rTSA using finite element analysis (FEA) modelling.
Methods
Five sets of computerized tomographic (CT) images of healthy normal shoulders were selected and segmented with Amira (Thermo Fisher Scientific) to obtain the solid geometries. Scapula FEA models with 5°, 10°, 15°, 20° and 25° retroversion angles were generated for each healthy scapula geometry and a rTSA glenoid baseplate was implanted on each model. Maximum stress at the anterior and posterior portions of the glenoid and the micromotion between the bone and baseplate were recorded. After simulation with normal scapular bone material properties (Young's modulus 4GPa and Poisson's ratio 0.3), another set of simulations was run on each subject with a 25° retroversion angle and poor bone quality (Young's modulus 500 MPa and Poisson's ratio 0.3) to study a worst-case scenario. Micromotions in each model were also recorded. All statistical analysis was done with SPSS.
Results
Simulation results of models generated from the same subject but with different retroversion angles showed a clear pattern: as retroversion angle increased, the stresses increased posteriorly and decreased anteriorly. Also, micromotion between the bone and the baseplate increased with the increase of retroversion angle. With analysis of variance (ANOVA), we found that all three values change significantly as the retroversion angle increases (p < 0.001). The simulation results also showed that micromotion was large in shoulders with small glenoid size and poor bone quality. However, even in the model with the worst-case scenario (smallest glenoid size, poorest bone quality and 25° retroversion angle), the maximum micromotion and the maximum stresses are still within the safe range.
Discussion
In all cases with both normal and poor bone quality, the stresses and micromotion stayed below the threshold to allow for bone ingrowth of the glenoid baseplate to occur. Based on these results, for glenoid baseplates with a central peg/post and 4 screws for fixation, rTSA baseplate retroversion does not need to be corrected to less than 10° to provide good initial fixation as has been recommended for a cemented glenoid component and can withstand the initial stresses and micromotion up to 25° of retroversion.
Level of evidence
Basic Science Study; Computer Modeling
Background
Instability following reverse shoulder arthroplasty is influenced by various factors such as component design, component positioning, and soft tissue tensioning. Patients may achieve glenohumeral motion beyond initial scapular impingement during activities of daily living which could further compound instability. However, instability/subluxation risk postscapular impingement is not well documented. Conventional range of motion analysis tools cannot account for the restraining effect of soft tissues or subluxation risk after impingement. Using a previously validated finite element analysis approach, the purpose of this study was to investigate the effects of glenoid component lateralization and humeral component angle of inclination (AOI), with or without simulated subscapularis repair, on postimpingement subluxation. We hypothesized that lack of subscapularis repair, a valgus humeral component AOI, and glenoid medialization would all result in greater postimpingement instability.
Methods
A FE model of the shoulder including the subscapularis tendon and middle deltoid was created, incorporating a general representation of a commercial reverse shoulder arthroplasty implant placed under the direction of a fellowship-trained shoulder surgeon. The deltoid and subscapularis were tensioned and wrapped around the reconstructed glenohumeral joint prior to simulating motion. Humeral rotations were then prescribed to simulate external rotation (neutral to 50°), extension (neutral to 50°), adduction (neutral to 30°), and abduction (neutral to 90°). The effects of three glenosphere lateralization offsets (2, 4, and 10 mm) and 2 humeral liner angles of inclination (varus-150° and valgus-155°) on subluxation propensities were investigated with and without the subscapularis tendon present.
Results
Simulated subscapularis repair resulted in 21%-34% less postimpingement subluxation. Presence of the subscapularis provided stability over a greater range of abduction. Impingement-free range of motion was similar regardless of the presence or absence of the subscapularis. The valgus AOI resulted in 23% less subluxation during abduction. During other motions however, the valgus AOI resulted in 67%-110% greater postimpingement subluxation (subscapularis present), which further worsened without the subscapularis.
Conclusion
Implant design modifications to improve stability may not be beneficial for all motions, highlighting the importance of directionality when investigating instability. Liner-bone impingement appears to compound instability/subluxation and the subscapularis appears to restrain postimpingement instability.
Level of evidence
Basic Science Study; Computer Modeling
Rotator cuff tears are known to affect clinical outcome of reverse total shoulder arthroplasty (RSA). This study aimed to use computational modelling to quantify the effect of rotator cuff tear severity on muscle and joint forces after RSA, as well as stresses at the glenosphere, base‐plate, fixation screws, scapula, and humeral components. A multi‐body musculoskeletal model of the glenohumeral joint was developed comprising the scapula, humerus and 9 major upper limb muscles. Simulations of abduction and flexion were performed after RSA with the intact rotator cuff and tears to (i) supraspinatus (ii) supraspinatus and infraspinatus (iii) supraspinatus, infraspinatus and subscapularis. The intact and supraspinatus deficient rotator cuff resulted in the largest calculated muscle forces, glenohumeral joint contact forces and implant stresses. Peak glenohumeral joint forces during flexion were lower than those during abduction in all cases; however, substantially more posterior joint shear force was generated during flexion than abduction. A combined supraspinatus and infraspinatus tear reduced glenohumeral joint forces by a factor of 8.7 during abduction (603.1 N) and 7.1 during flexion (520.7 N) compared to the supraspinatus deficient shoulder. RSA with an intact or supraspinatus deficient rotator cuff produces large glenohumeral joint forces that may increase base‐plate failure risk, particularly during flexion when posterior shear forces are largest. Infraspinatus tears after RSA greatly reduce glenohumeral joint compression and may ultimately reduce joint stability. Given the inherent uncertainty of musculoskeletal model calculations, future research ought to focus on experimental validation of subject‐specific muscle recruitment strategies and joint loading after RSA. This article is protected by copyright. All rights reserved
The aims of this study were to determine the survival of anatomic total shoulder arthroplasty with uncemented metal-backed (MB) glenoid components with a polyethylene (PE) insert in primary osteoarthritis, to assess the reasons for revision surgery, and to identify patients and diagnostic factors that influence failure rates.
Between 1994 and 1999, 165 patients (mean age, 68 years) with primary osteoarthritis were treated with anatomic total shoulder arthroplasty using an uncemented MB/PE glenoid component. Outcomes were assessed both clinically and radiologically with a minimum of 2 years of follow-up. A prosthetic survival curve was constructed with the end point defined as either partial or complete revision, using 100% confidence intervals.
Survival rate free of revision was 46% (100% confidence interval, 32%-54%) at 12 years. At a mean follow-up of 8.5 years (range, 2-16 years), revision was required in 61 patients (37%); 80% of shoulders undergoing revision (49 of 61) had evidence of PE wear. Glenoid loosening (because of osteolysis secondary to wear debris), soft tissue deficiency, and prosthetic instability were the most common modes of failure. Younger patients and biconcave glenoids (with posterior humeral subluxation) have a negative effect on implant survival. Proximal humerus osteolysis was significantly more frequent in shoulders with PE wear. Exchange of the PE insert (with conservation of the MB tray) was possible in only 3% of the revised shoulders.
Uncemented MB glenoid resurfacing is not a viable long-term therapeutic option because of accelerated PE wear leading to early revision surgery. Conservation of the MB tray with reinsertion of a new PE insert is rarely possible because of glenoid bone loss, implant loosening, soft tissue deficiency, and prosthetic instability. Younger patients and biconcave glenoids have a negative effect on implant survival.
Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
The management of irreparable rotator cuff tears associated with osteoarthritis of the glenohumeral joint has long been challenging. Reverse total shoulder arthroplasty (RSA) was designed to provide pain relief and improve shoulder function in patients with severe rotator cuff tear arthropathy. While this procedure has been known to reduce pain, improve strength and increase range of motion in shoulder elevation, scapular notching, rotation deficiency, early implant loosening and dislocation have attributed to complication rates as high as 62 %. Patient selection, surgical approach and post-operative management are factors vital to successful outcome of RSA, with implant design and component positioning having a significant influence on the ability of the shoulder muscles to elevate, axially rotate and stabilise the humerus. Clinical and biomechanical studies have revealed that component design and placement affects the location of the joint centre of rotation and therefore the force-generating capacity of the muscles and overall joint mobility and stability. Furthermore, surgical technique has also been shown to have an important influence on clinical outcome of RSA, as it can affect intra-operative joint exposure as well as post-operative muscle function. This review discusses the behaviour of the shoulder after RSA and the influence of implant design, component positioning and surgical technique on post-operative joint function and clinical outcome.
Purpose:
Revision of a shoulder arthroplasty to a reverse arthroplasty is a highly demanding procedure. The aim of this study is to report the clinical results of hemi and total shoulder prosthesis revisions to reverse implants without removal of the humeral stem, using a modular shoulder replacement system (SMR Lima LTD). We retrospectively reviewed 26 patients who underwent an operation from 2004 to 2009.
Methods:
The patients were divided into two groups: in Group I, 18 patients underwent a revision of hemiarthroplasty implanted for fracture; in Group II, eight patients underwent a revision of anatomical total prosthesis. All patients were evaluated at a mean follow-up of 32.3 (±12.7) months using the Constant score rating scale and by range of motion evaluation, EQ-VAS, X-ray and CT scan.
Results:
The Constant score of each patient was 47.88 (±5.88) after the revision. The EQ-VAS improved from 40 (±20) to 70 (±10). All patients improved in terms of range of motion. The radiographs and CT scans obtained after revision showed good integration and no signs of loosening of the implant. The mean time of surgery was recorded as 62' (±8'), with a maximum blood loss of less than 300 ml in all cases.
Conclusions:
Our study demonstrates that using a full modular system at the time of the first implant allows avoidance of the step to remove the humeral stem and metal back in cases of shoulder prosthesis revision to a reverse prosthesis, resulting in a short operative time, few intraoperative complications and a satisfactory clinical outcome at medium-term follow-up.
Our goal was to evaluate the objective and subjective midterm outcome after revision of a failed shoulder arthroplasty with a reverse design prosthesis. Twenty consecutive patients with 21 revisions of a primary shoulder arthroplasty using reverse shoulder prosthesis Delta III(®) were followed up postoperatively for a mean of 46 months including clinical and radiological examination. Complications were recorded and Constant score, DASH and SF36 were assessed. With the numbers given a significant reduction of pain was achieved from 8.7 to 3.0 (p < 0.001). There was a significant improvement of active flexion from 43° to 97° (p < 0.001) and active abduction from 44° to 90° (p < 0.001). However, at the same time, active external rotation with an adducted humerus decreased significantly from 26° to 12° (p = 0.012). The constant score improved significantly from 16.7 to 55.9 (p < 0.001). Sixteen patients (84%) rated their shoulder better or much better than before. In 43% an intraoperative and in 38% a postoperative complication occurred including two late stage infections which required prosthesis removal. Our results support the use of the reverse prosthesis as revision prosthesis. The reverse design helps to compensate functional deficits due to severe soft-tissue damage except active external rotation. Nevertheless, the revision is a technically demanding procedure reflected in a high rate of intraoperative complications. The rate of secondary infections of 10% remains a special concern.
The objective of the present study was to measure the lines of action of 18 major muscles and muscle sub-regions crossing the glenohumeral joint of the human shoulder, and to compute the potential contribution of these muscles to joint shear and compression during scapular-plane abduction and sagittal-plane flexion. The stabilizing potential of a muscle was found by assessing its contribution to superior/inferior and anterior/posterior joint shear in the scapular and transverse planes, respectively. A muscle with stabilizing potential was oriented to apply more compression than shear at the glenohumeral joint, whereas a muscle with destabilizing potential was oriented to apply more shear. Significant differences in lines of action and stabilizing capacities were measured across sub-regions of the deltoid and rotator cuff in both planes of elevation (P < 0.05), and substantial differences were observed in the pectoralis major and latissimus dorsi. The results showed that, during abduction and flexion, the rotator cuff muscle sub-regions were more favourably aligned to stabilize the glenohumeral joint in the transverse plane than in the scapular plane and that, overall, the anterior supraspinatus was most favourably oriented to apply glenohumeral joint compression. The superior pectoralis major and inferior latissimus dorsi were the chief potential scapular-plane destabilizers, demonstrating the most significant capacity to impart superior and inferior shear to the glenohumeral joint, respectively. The middle and anterior deltoid were also significant potential contributors to superior shear, opposing the combined destabilizing inferior shear potential of the latissimus dorsi and inferior subscapularis. As potential stabilizers, the posterior deltoid and subscapularis had posteriorly-directed muscle lines of action, whereas the teres minor and infraspinatus had anteriorly-directed lines of action. Knowledge of the lines of action and stabilizing potential of individual sub-regions of the shoulder musculature may assist clinicians in identifying muscle-related joint instabilities, assist surgeons in planning tendon reconstructive surgery, aid in the development of rehabilitation procedures designed to improve joint stability, and facilitate development and validation of biomechanical computer models of the shoulder complex.
The purpose of this study was to describe the outcome after reversed Delta III shoulder prosthesis in patients with rheumatoid arthritis (RA) and irreparable rotator cuff tear. Fifteen patients (17 joints) were prospectively analysed using the Constant-Murley score (CS). Comprehensive outcome measure was carried out by means of four widely used questionnaires as well as clinical and radiographic examinations at an average of 24.3 months postoperatively. The CS improved significantly from 19 to 59.5 points. The mental (MSC) and physical (PCS) component summary score of the Short Form 36 (SF-36) reached 108% and 77%, respectively, while the DASH (Disabilities of the Arm, Shoulder, and Hand) was 58% of a comparative norm population. Remaining deficits were documented by SPADI (Shoulder Pain and Disability; 54.4 points) and ASES (clinical and patient-orientated American Shoulder and Elbow Surgeons; 84.3 and 61.3 points, respectively). No radiological signs of loosening were found, but scapular notching occurred in four cases. Reversed arthroplasty provides a substantial improvement of shoulder function in patients with RA. The high incidence of notching is of concern.
We used an inverted shoulder arthroplasty in 43 consecutive patients with a mean age of 78 years (65 to 97) who had sustained a three- or four-part fracture of the upper humerus. All except two were reviewed with a mean follow-up of 22 months (6 to 58).
The clinical outcome was satisfactory with a mean active anterior elevation of 97° (35° to 160°) and a mean active external rotation in abduction of 30° (0° to 80°). The mean Constant and the mean modified Constant scores were respectively 44 (16 to 69) and 66% (25% to 97%). Complications included three patients with reflex sympathetic dystrophy, five with neurological complications, most of which resolved, and one with an anterior dislocation. Radiography showed peri-prosthetic calcification in 36 patients (90%), displacement of the tuberosities in 19 (53%) and a scapular notch in ten (25%). Compared with conventional hemiarthroplasty, satisfactory mobility was obtained despite frequent migration of the tuberosities. However, long-term results are required before reverse shoulder arthroplasty can be recommended as a routine procedure in complex fractures of the upper humerus in the elderly.
Reversed shoulder prostheses are increasingly being used for the treatment of glenohumeral arthropathy associated with a deficient rotator cuff. These non-anatomical implants attempt to balance the joint forces by means of a semi-constrained articular surface and a medialised centre of rotation. A finite element model was used to compare a reversed prosthesis with an anatomical implant. Active abduction was simulated from 0° to 150° of elevation. With the anatomical prosthesis, the joint force almost reached the equivalence of body weight. The joint force was half this for the reversed prosthesis. The direction of force was much more vertically aligned for the reverse prosthesis, in the first 90° of abduction. With the reversed prosthesis, abduction was possible without rotator cuff muscles and required 20% less deltoid force to achieve it.
This force analysis confirms the potential mechanical advantage of reversed prostheses when rotator cuff muscles are deficient.
The moment arm of a muscle represents its leverage or torque‐producing capacity, and is indicative of the role of the muscle in joint actuation. The objective of this study was to undertake a systematic review of the moment arms of the major muscles spanning the glenohumeral joint during abduction, flexion and axial rotation. Moment arm data for the deltoid, pectoralis major, latissimus dorsi, teres major, supraspinatus, infraspinatus, subscapularis and teres minor were reported when measured using the geometric and tendon excursion methods. The anterior and middle sub‐regions of the deltoid had the largest humeral elevator moment arm values of all muscles during coronal‐ and scapular‐plane abduction, as well as during flexion. The pectoralis major, latissimus dorsi and teres major had the largest depressor moment arms, with each of these muscles exhibiting prominent leverage in shoulder adduction, and the latissimus dorsi and teres major also in extension. The rotator cuff muscles had the largest axial rotation moment arms regardless of the axial position of the humerus. The supraspinatus had the most prominent elevator moment arms during early abduction in both the coronal and scapular planes as well as in flexion. This systematic review shows that the rotator cuff muscles function as humeral rotators and weak humeral depressors or elevators, while the three sub‐regions of the deltoid behave as substantial humeral elevators throughout the range of humeral motion. The pectoralis major, latissimus dorsi and teres major are significant shoulder depressors, particularly during abduction. This study provides muscle moment arm data on functionally relevant shoulder movements that are involved in tasks of daily living, including lifting and pushing. The results may be useful in quantifying shoulder muscle function during specific planes of movement, in designing and validating computational models of the shoulder, and in planning surgical procedures such as tendon transfer surgery.
Background:
Glenoid loosening is a common mode of failure after total shoulder arthroplasty (TSA). Newer cementless glenoid components have been introduced to promote biological fixation with the aim to decrease glenoid loosening. Limited data are available comparing revision rates between cemented and cementless glenoid fixation in TSA. The study aim was to compare the revision rates of cemented and cementless design glenoid components used in conventional TSA performed for the diagnosis of osteoarthritis. The secondary aim was to compare various subclasses of glenoid components.
Methods:
Data were obtained between April 16, 2004, and December 31, 2016, from the Australian Orthopaedic Association National Joint Replacement Registry. Within the study period, 10,805 primary conventional TSAs were identified. The analysis was undertaken for the diagnosis of osteoarthritis, which represented 95.8% of all conventional TSA procedures.
Results:
At 5 years, in patients with primary TSA procedures, those with cemented glenoids had a lower revision rate than those with cementless glenoids: 3.7% versus 17.9% (hazard ratio for entire period, 4.77). The most common revision diagnosis for primary conventional TSA with cementless glenoid fixation was rotator cuff insufficiency (4.4% for cementless vs 0.4% for cemented), instability and/or dislocation (3.8% for cementless vs 0.8% for cemented), and loosening and/or lysis (1.1% for cementless vs 1.1% for cemented).
Conclusions:
Cementless glenoid components in conventional TSA had a significantly higher revision rate than cemented glenoid components. The loosening rates between cemented and cementless glenoid components were similar. Glenoid design and fixation are important considerations when selecting a prosthesis for TSA.
Background:
Rotator cuff tears following anatomic total shoulder arthroplasty increase with duration of follow-up. This study aimed to evaluate contact pressure between the rotator cuff tendons and prosthesis after anatomic total shoulder arthroplasty and compare these with the tendon-contact pressures in the native shoulder.
Methods:
Eight entire upper extremities were mounted onto a testing apparatus, and simulated muscle loading was applied to each rotator cuff tendon with the shoulder positioned in abduction, internal rotation, and external rotation. Pressure-sensitive film placed between each tendon and bone was used to measure the resultant tendon contact pressures. Experiments were repeated after anatomic total shoulder arthroplasty using standardized implant sizes, and pressure-sensitive film was used to evaluate tendon-prosthesis contact pressure.
Results:
Both joint angle and shoulder joint replacement surgery had significant effects on the maximum contact pressure measured between the humeral head and all rotator cuff tendons (P < .05) except the teres minor. The supraspinatus demonstrated a significantly larger peak tendon contact pressure after surgery at 45° of abduction relative to that in the native shoulder (mean difference, 0.2 MPa; P = .031), while the subscapularis had a significantly larger maximum contact pressure at 10° of abduction (mean difference, 0.45 MPa; P = .032) and 90° of abduction (mean difference, 0.80 MPa; P = .008) postoperatively.
Conclusion:
Anatomic total shoulder arthroplasty results in significantly larger tendon contact pressures relative to those in the native shoulder. High tendon contact pressures may ultimately predispose rotator cuff tendons to postoperative wear-induced damage and tearing.
Aims:
Controversy about the use of an anatomical total shoulder arthroplasty (aTSA) in young arthritic patients relates to which is the ideal form of fixation for the glenoid component: cemented or cementless. This study aimed to evaluate implant survival of aTSA when used in patients aged < 60 years with primary glenohumeral osteoarthritis (OA), and to compare the survival of cemented all-polyethylene and cementless metal-backed glenoid components.
Materials and methods:
A total of 69 consecutive aTSAs were performed in 67 patients aged < 60 years with primary glenohumeral OA. Their mean age at the time of surgery was 54 years (35 to 60). Of these aTSAs, 46 were undertaken using a cemented polyethylene component and 23 were undertaken using a cementless metal-backed component. The age, gender, preoperative function, mobility, premorbid glenoid erosion, and length of follow-up were comparable in the two groups. The patients were reviewed clinically and radiographically at a mean of 10.3 years (5 to 12, sd 26) postoperatively. Kaplan-Meier survivorship analysis was performed with revision as the endpoint.
Results:
A total of 26 shoulders (38%) underwent revision surgery: ten (22%) in the polyethylene group and 16 (70%) in the metal-backed group (p < 0.0001). At 12 years' follow-up, the rate of implant survival was 74% (sd 0.09) for polyethylene components and 24% (sd 0.10) for metal-backed components (p < 0.0002). Glenoid loosening or failure was the indication for revision in the polyethylene group, whereas polyethylene wear with metal-on-metal contact, instability, and insufficiency of the rotator cuff were the indications for revision in the metal-backed group. Preoperative posterior subluxation of the humeral head with a biconcave/retroverted glenoid (Walch B2) had an adverse effect on the survival of a metal-backed component.
Conclusion:
The survival of a cemented polyethylene glenoid component is three times higher than that of a cementless metal-backed glenoid component ten years after aTSA in patients aged < 60 years with primary glenohumeral OA. Patients with a biconcave (B2) glenoid have the highest risk of failure. Cite this article: Bone Joint J 2018;100-B:485-92.
Robotic-assistive exoskeletons can enable frequent repetitive movements without the presence of a full-time therapist; however, human-machine interaction and the capacity of powered exoskeletons to attenuate shoulder muscle and joint loading is poorly understood. This study aimed to quantify shoulder muscle and joint force during assisted activities of daily living using a powered robotic upper limb exoskeleton (ArmeoPower, Hocoma). Six healthy male subjects performed abduction, flexion, horizontal flexion, reaching and nose touching activities. These tasks were repeated under two conditions: (i) the exoskeleton compensating only for its own weight, and (ii) the exoskeleton providing full upper limb gravity compensation (i.e., weightlessness). Muscle EMG, joint kinematics and joint torques were simultaneously recorded, and shoulder muscle and joint forces calculated using personalized musculoskeletal models of each subject’s upper limb. The exoskeleton reduced peak joint torques, muscle forces and joint loading by up to 74.8% (0.113 Nm/kg), 88.8% (5.8%BW) and 68.4% (75.6%BW), respectively, with the degree of load attenuation strongly task dependent. The peak compressive, anterior and superior glenohumeral joint force during assisted nose touching was 36.4% (24.6%BW), 72.4% (13.1%BW) and 85.0% (17.2%BW) lower than that during unassisted nose touching, respectively. The present study showed that upper limb weight compensation using an assistive exoskeleton may increase glenohumeral joint stability, since deltoid muscle force, which is the primary contributor to superior glenohumeral joint shear, is attenuated; however, prominent exoskeleton interaction moments are required to position and control the upper limb in space, even under full gravity compensation conditions. The modeling framework and results may be useful in planning targeted upper limb robotic rehabilitation tasks.
Background:
Despite the increasing numbers of reverse total shoulder arthroplasty (RTSA) procedures, the long-term results have been rarely reported. We previously reported early outcomes of a cohort of patients treated with a Grammont-style RTSA. The purpose of this study was to evaluate the outcomes after a minimum of 10 years, and to document prosthetic survival and complications.
Methods:
Clinical outcome assessment was based on the absolute and relative Constant scores and the active range of motion. Radiographic evaluations of scapular notching, tuberosity osteolysis, and periprosthetic radiolucent lines were done as well. Complications and revisions were compiled, and a Kaplan-Meier survival analysis was performed.
Results:
The original report included the outcomes for 186 patients (191 RTSAs) who had been followed for a mean of 40 months. In the present study, in which the mean duration of follow-up was 150 months, follow-up clinical evaluations were available for 84 patients (87 prostheses) and radiographic assessments were available for 64 patients (67 prostheses). Seventy-seven patients (79 prostheses) had died before the 10-year follow-up, and 17 patients (17 prostheses) had been lost to follow-up. The mean absolute and relative Constant scores (and standard deviations) were 55 ± 16 points and 86 ± 26 points, respectively, with both having decreased significantly compared with the scores at the medium-term follow-up evaluation (at a minimum of 2 years) (p < 0.001 and p = 0.025, respectively). Forty-nine shoulders (73%) exhibited scapular notching. Forty-seven complications (29%) were recorded, with 10 cases (10%) occurring after 2 years. Sixteen (12%) of the original patients underwent revision surgery. The 10-year overall prosthetic survival rate using revision as the end point was 93%.
Conclusions:
Despite a high arthroplasty survival rate and good long-term clinical results, RTSA outcomes showed deterioration when compared with medium-term results. The cause of this decrease is probably related to patient aging coupled with bone erosion and/or deltoid impairment over time.
Level of evidence:
Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.
Kinematics of the shoulder girdle obtained from non-invasive measurement systems such as video motion analysis, accelerometers and magnetic tracking sensors has been shown to be adversely affected by instrumentation measurement errors and skin motion artefact, yet the degree to which musculoskeletal model calculations of shoulder muscle and joint loading are influenced by variations in joint kinematics is not well understood. A three-dimensional musculoskeletal model of the upper limb was used to evaluate the sensitivity of shoulder muscle and joint force. Monte-Carlo analyses were performed by randomly perturbing scapular and humeral joint coordinates during abduction and flexion. Muscle and joint force calculations were generally most sensitive to changes in the kinematics of the humerus in elevation and of the scapula in medial-lateral rotation, and were least sensitive to changes in humerus plane of elevation and scapula protraction-retraction. Overall model sensitivity was greater during abduction than flexion, and the influence of specific kinematics perturbations varied from muscle to muscle. In general, muscles that generated greater force, such as the middle deltoid and subscapularis, were more sensitive to changes in shoulder kinematics. This study suggests that musculoskeletal model sensitivity to changes in kinematics is task-specific, and varies depending on the plane of motion. Calculations of shoulder muscle and joint function depend on reliable humeral and scapula motion data, particularly that of humeral elevation and scapula medial-lateral rotation. The findings in this study have implications for the use of kinematic data in musculoskeletal model development and simulations.
Upper limb muscle force estimation using Hill-type muscle models depends on musculotendon parameter values, which cannot be readily measured non-invasively. Generic and scaled-generic parameters may be quickly and easily employed, but these approaches do not account for an individual subject?s joint torque capacity. The objective of the present study was to develop a subject-specific experimental testing and modeling framework to evaluate shoulder muscle and joint function during activities of daily living, and to assess the reliability of generic and scaled-generic musculotendon parameters in predicting muscle and joint function. Three-dimensional musculoskeletal models of the shoulders of 6 healthy subjects were developed to calculate muscle and glenohumeral joint loading during abduction, flexion, horizontal flexion, nose-touch and reaching using subject-specific, scaled-generic and generic musculotendon parameters. Muscle and glenohumeral joint forces calculated using generic and scaled-generic models were significantly different to those of subject-specific models (p<0.05), and task dependent; however, scaled-generic model calculations of shoulder glenohumeral joint force demonstrated better agreement with those of subject -specific models during abduction and flexion. Muscles in generic musculoskeletal models operated further from the plateau of their force-length curves than those of scaled-generic and subject-specific models, while muscles in subject-specific models operated over a wider region of their force length curves than those of the generic or scaled-generic models, reflecting diversity of subject shoulder strength. The findings of this study suggest that generic and scaled-generic musculotendon parameters may not provide sufficient accuracy in prediction of shoulder muscle and joint loading when compared to models that employ subject-specific parameter-estimation approaches.
If a modular convertible total shoulder system is used as a primary implant for an anatomical total shoulder arthroplasty, failure of the prosthesis or the rotator cuff can be addressed by converting it to a reverse shoulder arthroplasty (RSA), with retention of the humeral stem and glenoid baseplate. This has the potential to reduce morbidity and improve the results.
In a retrospective study of 14 patients (15 shoulders) with a mean age of 70 years (47 to 83) we reviewed the clinical and radiological outcome of converting an anatomical shoulder arthroplasty (ASA) to a RSA using a convertible prosthetic system (SMR system, Lima, San Daniele, Italy).
The mean operating time was 64 minutes (45 to 75). All humeral stems and glenoid baseplates were found to be well-fixed and could be retained. There were no intra-operative or early post-operative complications and no post-operative infection.
The mean follow-up was 43 months (21 to 83), by which time the mean visual analogue scale for pain had decreased from 8 pre-operatively to 1, the mean American Shoulder and Elbow Surgeons Score from 12 to 76, the mean Oxford shoulder score from 3 to 39, the mean Western Ontario Osteoarthritis of the Shoulder Score from 1618 to 418 and the mean Subjective shoulder value from 15 to 61.
On radiological review, one patient had a lucency around the humeral stem, two had stress shielding. There were no fatigue fractures of the acromion but four cases of grade 1 scapular notching.
The use of a convertible prosthetic system to revise a failed ASA reduces morbidity and minimises the rate of complications. The mid-term clinical and radiological results of this technique are promising.
Cite this article: Bone Joint J 2015;97-B:1662–7.
Background:
The substantial increase in the utilization of shoulder arthroplasty in the United States during the past decade is partly attributable to the growing acceptance of reverse shoulder arthroplasty (RSA). This study compared the national utilization of and indications for shoulder hemiarthroplasty, total shoulder arthroplasty (TSA), and RSA.
Methods:
The Nationwide Inpatient Sample was used to identify shoulder arthroplasty procedures performed in the United States in 2011. Indicating diagnoses, demographics, and hospital characteristics were identified for each shoulder arthroplasty procedure. Multivariable regression identified factors associated with long hospital stays.
Results:
An estimated 66,485 shoulder arthroplasty procedures were identified (33% RSA, 44% TSA, and 23% hemiarthroplasty). Common diagnoses for RSA were rotator cuff tear and arthritis (80%) and proximal humerus fracture (10%). TSA was performed for osteoarthritis in 93% of cases. Hemiarthroplasty was performed for osteoarthritis (45%) and proximal humerus fracture (38%). One quarter of proximal humerus fractures treated with arthroplasty received RSA compared with 69.8% that underwent hemiarthroplasty. Mortality occurred in 0.08% of patients with atraumatic diagnoses but in 0.53% of patients with proximal humerus fractures (P < .001). Older patients with comorbidities often had longer hospital stays, as did those with government insurance.
Conclusions:
RSAs accounted for one third of all shoulder arthroplasty procedures in the United States in 2011. Whereas the majority of RSAs are performed for rotator cuff tear arthropathy, one quarter of proximal humerus fractures are treated with RSA, suggesting the strong uptake of this relatively new procedure in the United States.
Anatomical data necessary for the analysis of human motion are presented on the total living body segmented into sixteen parts. Cadaver data from Dempster (1955) are applied to water displacement data obtained on 135 living subjects (35 men and 100 women) to obtain the weight, center of gravity, and radius of gyration for the segmented extremities. Thirty-three of these subjects (15 men and 18 women) were used to obtain the weight of the segments of the trunk, using the water displacement method, and sixteen of these subjects (7 men and 9 women) were used to locate the center of gravity of each trunk segment. A lead model was constructed using the trunk data to obtain the radii of gyration in both the sagittal and frontal planes. A single male cadaver was dissected to compare the trunk measurements with the lead model results.
Anatomical data obtained from cadavers and from water displacement studies with living subjects were used to determine the weight, center of gravity, and radius of gyration for 16 body segments. A lead model was used to study movement patterns of the trunk section of the body. (Authors/PP)
Purpose:
The number of shoulder arthroplasties has increased over the last decade, which can partly be explained by the increasing use of the reverse total shoulder arthroplasty technique. However, the options for revision surgery after primary arthroplasty are limited in cases of irreparable rotator cuff deficiency, and tuberosity malunion, nonunion, or resorption. Often, conversion to a reverse design is the only suitable solution. We analysed the functional outcome, complication rate and patient satisfaction after the revision of primary shoulder arthroplasty using an inverse design.
Methods:
Over a ten-year period 57 patients underwent revision surgery for failed primary shoulder arthroplasty using a reverse design. Of the 57 patients, 50 (mean age, 64.2 years) were available after an average follow-up of 51 months. Clinical evaluation included the Constant Murley Score, the UCLA score, and the Simple Shoulder Test, whereas radiological evaluation included plain radiographs in standard projections. Patients were also requested to rate their subjective satisfaction of the final outcome as excellent, good, satisfied or dissatisfied.
Results:
Compared to the preoperative status, the overall functional outcome measurements based on standardised outcome shoulder scores improved significantly at follow-up. The overall mean Constant Murley score improved from 18.5 to 49.3 points, the mean UCLA score improved from 7.1 to 21.6 points, and the mean simple shoulder test improved from 1.2 to 5.6 points. The average degree of abduction improved from 40 to 93° (p < 0.0001), and the average degree of anterior flexion improved from 47 to 98° (p < 0.0001). The median VAS pain score decreased from 7 to 1. Complications occurred in 12 cases (24 %).A total of 32 (64 %) patients rated their result as good or excellent, six (12 %) as satisfactory and 12 (24 %) as dissatisfied.
Conclusion:
In revision shoulder arthroplasty after failed primary shoulder arthroplasty an inverse design can improve the functional outcome, and patient satisfaction is usually high. However, the complication rate of this procedure is also high, and patient selection and other treatment options should be carefully considered.
Patients with total knee arthroplasty (TKA) frequently exhibit changes in gait biomechanics post-surgery, including decreased ranges of joint motion and changes in joint loading; however, the actions of the lower-limb muscles in generating joint moments and accelerating the center of mass (COM) during walking are yet to be described. The aim of the present study was to evaluate differences in lower-limb joint kinematics, muscle-generated joint moments, and muscle contributions to COM accelerations in TKA patients and healthy age-matched controls when both groups walk at the same speed. Each TKA patient was fitted with a posterior-stabilized total knee replacement and underwent patellar resurfacing. Three-dimensional gait analysis and subject-specific musculoskeletal modeling were used to determine lower-limb and trunk muscle forces and muscle contributions to COM accelerations during the stance phase of gait. The TKA patients exhibited a 'quadriceps avoidance' gait pattern, with the vasti contributing significantly less to the extension moment developed about the knee during early stance (p=0.036). There was a significant decrease in the contribution of the vasti to the vertical acceleration (support) (p=0.022) and forward deceleration of the COM (braking) (p=0.049) during early stance; however, the TKA patients compensated for this deficiency by leaning their trunks forward. This significantly increased the contribution of the contralateral back extensor muscle (erector spinae) to support (p=0.030), and that of the contralateral back rotators (internal and external obliques) to braking (p=0.004). These findings provide insight into the biomechanical causes of post-operative gait adaptations such as 'quadriceps avoidance' observed in TKA patients.
Background:
The aim of this study was to evaluate the midterm results and complications of a total shoulder arthroplasty implanted with a metal-backed, bone-ingrowth glenoid component.
Materials and methods:
In total, 62 patients (65 shoulders) diagnosed with primary osteoarthritis were treated with total shoulder arthroplasty with a cementless glenoid component. The mean age was 66 years (range, 54-85 years). Fifty-three patients were evaluated after a mean of 64 months (range, 26-85 months). Functional results were documented by use of the age- and sex-adjusted Constant score. Radiolucent line (RLL) assessment of the glenoid component was performed by use of true anteroposterior and axillary views.
Results:
The Constant score improved significantly from 49% preoperatively to 89.8% postoperatively (P < .0001). Active range of motion improved significantly for flexion (from 118° to 146°), abduction (from 87° to 133°), and external rotation (from 21° to 44°) (P < .0001). In 3 cases (5.7%), RLLs of 1 mm or less were present, and 1 case (1.8%) had an RLL of 2 mm or less in 1 zone. Glenoid component loosening occurred in 5 cases (9.4%) because of breakage of the cage screw. Four of these patients presented preoperatively with a type B1 glenoid and one patient with type A2. Two of the patients who underwent revision also had a complete tear of the rotator cuff. The revision rate was 11.3% (6 patients) after a mean of 68 months.
Conclusion:
After midterm follow-up, clinical outcomes of patients operated on with a cementless, metal-backed glenoid implant improved significantly. However, an unacceptable rate of complications and revisions was found. Glenoid loosening predominantly occurred in patients with preoperative eccentric glenoid morphology and was also related to cranial migration of the proximal humerus during the follow-up period.
The purposes of this study were to determine the contributions of each shoulder muscle to glenohumeral joint force during abduction and flexion in both the anatomical and post-operative shoulder and to identify factors that may contribute to the incidence of glenoid component loosening/failure and joint instability in the shoulder after reverse shoulder arthroplasty (RSA). Eight cadaveric upper extremities were mounted onto a testing apparatus. Muscle lines of action were measured, and muscle forces and muscle contributions to glenohumeral joint forces were determined during abduction and flexion of the pre-operative anatomical shoulder and of the shoulder after arthroplasty. Muscle forces in the middle deltoid during abduction and those in the middle and anterior deltoid during flexion were significantly lower in the reverse shoulder than the pre-operative shoulder (p < 0.017). The resultant glenohumeral joint force in the reverse shoulder was significantly lower than that in the pre-operative shoulder; however, the superior shear force acting at the glenohumeral joint was significantly higher (p < 0.001). Reverse total shoulder arthroplasty reduces muscle effort in performing lifting and pushing tasks; however, reduced joint compressive force has the potential to compromise joint stability, while an increased superior joint shear force may contribute to component loosening/failure. Because greater superior shear force is generated in flexion than in abduction, care should be taken to avoid excessive shoulder loading in this plane of elevation.
No clear recommendations exist regarding optimal humeral component version and deltoid tension in reverse total shoulder arthroplasty (TSA).
A biomechanical shoulder simulator tested humeral versions (0°, 10°, 20° retroversion) and implant thicknesses (-3, 0, +3 mm from baseline) after reverse TSA in human cadavers. Abduction and external rotation ranges of motion as well as abduction and dislocation forces were quantified for native arms and arms implanted with 9 combinations of humeral version and implant thickness.
Resting abduction angles increased significantly (up to 30°) after reverse TSA compared with native shoulders. With constant posterior cuff loads, native arms externally rotated 20°, whereas no external rotation occurred in implanted arms (20° net internal rotation). Humeral version did not affect rotational range of motion but did alter resting abduction. Abduction forces decreased 30% vs native shoulders but did not change when version or implant thickness was altered. Humeral center of rotation was shifted 17 mm medially and 12 mm inferiorly after implantation. The force required for lateral dislocation was 60% less than anterior and was not affected by implant thickness or version.
Reverse TSA reduced abduction forces compared with native shoulders and resulted in limited external rotation and abduction ranges of motion. Because abduction force was reduced for all implants, the choice of humeral version and implant thickness should focus on range of motion. Lateral dislocation forces were less than anterior forces; thus, levering and inferior/posterior impingement may be a more probable basis for dislocation (laterally) than anteriorly directed forces.
Revision shoulder arthroplasty represents a complex and difficult problem for the treating surgeon, with multiple potential complications. In the setting of a well-fixed humeral component, removal can lead to fractures and compromise the outcome of the revision. The current study describes and evaluates the results of a novel vertical humeral osteotomy (VHO) for stem extraction. We hypothesized that the VHO will enable successful stem extraction without perioperative or postoperative fractures.
Twenty-seven patients were retrospectively identified who had a VHO for revision shoulder arthroplasty, with 23 patients available for final follow-up. Records and radiographs were reviewed for postoperative complications. Final follow-up was completed with the inclusion of shoulder scores.
There were no perioperative or postoperative fractures on clinical examination and radiographic review at an average follow-up of 41 months. Average American Shoulder and Elbow Surgeons (ASES) score was 64.7 (contralateral ASES, 76.9), average Simple Shoulder Test was 6.3, and the visual analog score pain average was 1.3. There were no instability events.
The glenoid is the more common site for failure in both hemiarthroplasty and total shoulder arthroplasty. This can lead to a difficult revision procedure if the ingrown or cemented humeral stem requires removal.
In the current study, we found the VHO was an effective tool for the removal of the humeral prosthesis with no perioperative or postoperative fractures.
The objective of the present study was to determine the instantaneous moment arms of 18 major muscle sub-regions crossing the glenohumeral joint in axial rotation of the humerus during coronal-plane abduction and sagittal-plane flexion. The tendon-excursion method was used to measure instantaneous muscle moment arms in eight entire upper-extremity cadaver specimens. The results showed that the inferior subscapularis was the largest internal rotator; its rotation moment arm peaks were 24.4 and 27.0 mm during abduction and flexion, respectively. The inferior infraspinatus and teres minor were the greatest external rotators; their respective rotation moment arms peaked at 28.3 and 26.5 mm during abduction, and 23.3 and 22.1 mm during flexion. The two supraspinatus sub-regions were external rotators during abduction and internal rotators during flexion. The latissimus dorsi and pectoralis major behaved as internal rotators throughout both abduction and flexion, with the three pectoralis major sub-regions and middle and inferior latissimus dorsi displaying significantly larger internal rotation moment arms with the humerus adducted or flexed than when abducted or extended (p < 0.001). The deltoid behaved either as an internal rotator or an external rotator, depending on the degree of humeral abduction and axial rotation. Knowledge of moment arm differences between muscle sub-regions may assist in identifying the functional effects of muscle sub-region tears, assist surgeons in planning tendon transfer surgery, and aid in the development and validation of biomechanical computer models.
This study examined national trends and projections of procedure volumes and prevalence rates for shoulder and elbow arthroplasty in the United States (U.S.). This study hypothesized that the growth in demand for upper extremity arthroplasty will be greater than the growth in demand for hip and knee arthroplasty and that demand for these procedures will continue to grow in the immediate future.
The Nationwide Inpatient Sample (1993-2007) was used with U.S. Census data to quantify primary arthroplasty rates as a function of age, race, census region, and gender. Poisson regression was used to evaluate procedure rates and determine year-to-year trends in primary and revision arthroplasty. Projections were derived based on historical procedure rates combined with population projections from 2008 to 2015.
Procedure volumes and rates increased at annual rates of 6% to 13% from 1993 to 2007. Compared with 2007 levels, projected procedures were predicted to further increase by between 192% and 322% by 2015. The revision burden increased from approximately 4.5% to 7%. During the period studied, the hospital length of stay decreased by approximately 2 days for total and hemishoulder procedures. Charges, in 2007 Consumer Price Index-adjusted dollars, increased for all 4 procedural types at annual rates of 1700.
The growth rates of upper extremity arthroplasty were comparable to or higher than rates for total hip and knee procedures. Of particular concern was the increased revision burden. The rising number of arthroplasty procedures combined with increased charges has the potential to place a financial strain on the health care system.
A major requirement to design an implant is to develop our understanding of the applied internal forces during everyday activities. In the absence of any basic apparatus for measuring forces directly, it is essential to rely on modelling. The major aim of this study was therefore to understand the biomechanical function of subjects with the reversed anatomy Bayley-Walker prosthesis, using an inverse dynamic shoulder model. In this context, the muscle and joint forces of 12 Bayley-Walker subjects were compared to those of 12 normal subjects during 12 activities of daily living. Maximum glenohumeral contact forces for normal and Bayley-Walker subjects were found to be 77% (+/-15) and 137% (+/-21) body weight for lifting a 2kg shopping bag, and the least forces 29% (+/-4) and 67% (+/-8) body weight for reaching to opposite axilla, respectively. For normal subjects, middle deltoid, supraspinatus and infraspinatus were found to be the most active muscles across the subjects and tasks. On the other hand, for implanted subjects with a lack of rotator cuff muscles, the middle deltoid and coracobrachialis muscles were found to be the most active. The biomechanical model can therefore be used in order to gain knowledge about the pathology as well as possible post surgical rehab for subjects with reversed shoulder replacement.
Reverse total shoulder arthroplasty is known to increase the moment arm of the middle subregion of the deltoid during shoulder abduction; however, at present, comprehensive data regarding the shoulder muscle moment arm through the full range of abduction and flexion are not available. The purpose of this study was twofold: (1) to measure the instantaneous moment arms of thirteen subregions of major muscles spanning the glenohumeral joint during abduction and flexion of the shoulder after reverse total shoulder arthroplasty and (2) to compare these data with the muscle moment arms previously measured preoperatively in the anatomical shoulders.
Reverse total shoulder arthroplasty was performed on eight entire cadaveric upper extremities. The specimens were mounted onto a dynamic testing apparatus, and the instantaneous abductor/adductor and flexor/extensor moment arms of subregions of the deltoid, latissimus dorsi, pectoralis major, teres major, and subscapularis muscles (a total of thirteen subregions) were measured with use of the tendon excursion method. These muscle moment arms were compared with those measured preoperatively in the anatomical shoulders.
Reverse total shoulder arthroplasty resulted in significant increases in the abductor moment arms of the anterior subregion of the deltoid (mean increase = 10.4 mm; 95% confidence interval = 7.5 to 13.3 mm) and the middle subregion of the deltoid (mean increase = 15.5 mm; 95% confidence interval = 10.8 to 20.3 mm) as well as recruitment of the posterior subregion of the deltoid as an abductor. The superior subregion of the pectoralis major (the clavicular fibers) and anterior subregion of the deltoid were the most effective flexors and had a substantial potential to initiate flexion. The adductor and extensor moment arms of the teres major, latissimus dorsi subregions, and inferior and middle subregions of the pectoralis major increased substantially after the arthroplasty. The subscapularis subregions behaved as extensors, abductors, and adductors after the arthroplasty; this was in contrast to their roles in the anatomical shoulder, in which they were mainly flexors and adductors.
Reverse total shoulder arthroplasty increases the moment arms of the major abductors, flexors, adductors, and extensors of the glenohumeral joint, thereby reducing muscle effort during common tasks such as lifting and pushing.
Dislocation is the most common serious complication after reverse shoulder arthroplasty. One theorized cause is subscapularis insufficiency because the tendon cannot be repaired at the time of surgery. There are no documented risk assessments of reverse total shoulder arthroplasty dislocation related to this cause. The study objective was to quantify the risk of postoperative dislocation after reverse total shoulder arthroplasty in patients with a subscapularis tendon that was irreparable at the time of surgery.
A prospective evaluation was done of 138 consecutive reverse arthroplasties performed through a deltopectoral approach by a single surgeon (average follow-up, 36 months).
The subscapularis was reparable in 62 patients and irreparable in 76 at the conclusion of the procedure. Seven postoperative dislocations occurred; all dislocations were in patients whose subscapularis was irreparable (P = .012). Dislocations were more likely in patients with complex diagnoses, including proximal humeral nonunion, fixed glenohumeral dislocation, and failed prior arthroplasty.
This report documents that an irreparable subscapularis tendon at the time of reverse total shoulder arthroplasty using a deltopectoral approach results in a statistically significant risk for postoperative dislocation.
Level IV, Case Series, Treatment Study.
Background: Reverse anatomy shoulder prostheses, in which a partial sphere is attached to the scapula and a socket to the humerus, have become popular for the treatment of arthritic shoulders with severe rotator cuff arthropathy. While they have been in relatively common use, their biomechanical aspects have not been fully investigated.
This study uses an adaptation of a 3D biomechanical shoulder model to describe the DELTA reverse prosthetic shoulder geometry and to investigate its properties. The muscle configuration was modified to represent the pathology and joint contact forces were computed for standardised activities.The model also uses a contact detect algorithm to record the impingement of the prosthesis with the scapula.
Results showed that the reverse design increases the deltoid function compensating for the dysfunctional rotator cuff muscles by providing sufficient moment arm (increased by 42%) to elevate the arm. It also restores joint stability by reversing the envelope of the joint contact forces and reacting to the increased shear forces. Despite these advantages, the model also confirms impingement and predicts bone notches from the contact of the prosthesis with the scapula border. Results indicate that optimised fixation and design alterations can reduce the problem but is difficult to eliminate it without compromising the joint stability.
The study provides a deep understanding of the function of the reverse designs highlighting their advantages in irreparable rotator cuff arthropathy but also the associated problems that compromise their use. Despite the limitations results indicate that reverse designs can be optimised to provide maximum functionality.
The objective of the present study was to determine the instantaneous moment arms of 18 major muscle sub-regions crossing the glenohumeral joint during coronal-plane abduction and sagittal-plane flexion. Muscle moment-arm data for sub-regions of the shoulder musculature during humeral elevation are currently not available. The tendon-excursion method was used to measure instantaneous muscle moment arms in eight entire upper-extremity cadaver specimens. Significant differences in moment arms were reported across sub-regions of the deltoid, pectoralis major, latissimus dorsi, subscapularis, infraspinatus and supraspinatus (P < 0.01). The most effective abductors were the middle and anterior deltoid, whereas the most effective adductors were the teres major, middle and inferior latissimus dorsi (lumbar vertebrae and iliac crest fibers, respectively), and middle and inferior pectoralis major (sternal and lower-costal fibers, respectively). In flexion, the superior pectoralis major (clavicular fibers), anterior and posterior supraspinatus, and anterior deltoid were the most effective flexors, whereas the teres major and posterior deltoid had the largest extensor moment arms. Division of multi-pennate shoulder muscles of broad origins into sub-regions highlighted distinct functional differences across those sub-regions. Most significantly, we found that the superior sub-region of the pectoralis major had the capacity to exert substantial torque in flexion, whereas the middle and inferior sub-regions tended to behave as a stabilizer and extensor, respectively. Knowledge of moment arm differences between muscle sub-regions may assist in identifying the functional effects of muscle sub-region tears, assist surgeons in planning tendon reconstructive surgery, and aid in the development and validation of biomechanical computer models used in implant design.
We determined the outcome of 113 total shoulder replacement arthroplasties performed with a Neer prosthesis between 1975 and 1981. The operations were performed for the treatment of osteoarthritis, rheumatoid arthritis, and old fractures or dislocations with traumatic arthritis. The probability of implant survival was 93% after 10 years and 87% after 15 years. Complications requiring reoperation developed in 14 shoulders. Seventy-nine patients with 89 replacements were available for follow-up a minimum of 5 years after the operation (mean 12.2 years, range 5 to 17 years). Relief from moderate or severe pain was achieved in 83% of shoulders. Active abduction improved by an average of 40 degrees to an average of 117 degrees. The amount of elevation that was regained was related to the amount of rotator cuff disease. Seventy-five glenoid components developed bone-cement radiolucencies, and 39 (44%) glenoid components had radiographic evidence of definite loosening. Glenoid loosening was associated with pain. A shift in position of the humeral component occurred in 49% of the press-fit stems and in none of the cemented stems. Humeral component loosening was not associated with pain.
Despite its importance for the understanding of joint mechanics in healthy subjects and patients, there has been no three-dimensional (3D) in vivo data on the translation of the humeral head relative to the glenoid during abduction under controlled mechanical loading. The objective was therefore to analyze humeral head translation during passive and active elevation by applying an open MR technique and 3D digital postprocessing methods. Fifteen healthy volunteers were examined with an open MR system at different abduction positions under muscular relaxation (30-150 degrees of abduction) and during activity of shoulder muscles (60-120 degrees ). After segmentation and 3D reconstruction, the center of mass of the glenoid and the midpoint of the humeral head were determined and their relative position calculated. During passive elevation, the humeral head translated inferiorly from +1.58mm at 30 degrees to +0. 36mm at 150 degrees of abduction, and posteriorly from +1.55mm at 30 degrees to -0.07mm at 150 degrees of abduction. Muscular activity brought about significant changes in glenohumeral translation, the humeral head being in a more inferior position and more centered, particularly at 90 and 120 degrees of abduction (p<0.01). In anterior/posterior direction the humeral head was more centered at 60 and 90 degrees of abduction during muscle activity. The data demonstrate the importance of neuromuscular control in providing joint stability. The technique developed can also be used for investigating the effect of muscle dysfunction and their relevance on the mechanics of the shoulder joint.
Combined destruction of the rotator cuff and the glenohumeral joint may lead to a painful and pseudo-paralyzed shoulder. In this situation a nonconstrained shoulder prosthesis yields a limited functional result or may even be contraindicated. Previous constrained prostheses (ball-and-socket or reverse ball-and-socket designs) have failed because their center of rotation remained lateral to the scapula, which limited motion and produced excessive torque on the glenoid component, leading to early loosening. The reverse prosthesis designed by Paul Grammont, unlike any previous reverse ball-and-socket design, has introduced 2 major innovations that have led to its success: (1) a large glenoid hemisphere with no neck and (2) a small humeral cup almost horizontally oriented with a nonanatomic inclination of 155 degrees, covering less than half of the glenosphere. This design medializes and stabilizes the center of rotation, minimizes torque on the glenoid component, and helps in recruiting more fibers of the anterior and posterior deltoid to act as abductors. Furthermore, the humerus is lowered relative to the acromion, restoring and even increasing deltoid tension. The Grammont reverse prosthesis imposes a new biomechanical environment for the deltoid muscle to act, thus allowing it to compensate for the deficient rotator cuff muscles. The clinical experience does live up to the biomechanical concept: the reverse prosthesis restores active elevation above 90 degrees in patients with a cuff-deficient shoulder. However, external rotation often remains limited, particularly in patients with an absent or fat-infiltrated teres minor. Internal rotation is also rarely restored after a reverse prosthesis. Failure to restore sufficient tension in the deltoid may result in prosthetic instability. The design does appear to protect against early loosening of the glenoid component, but impingement of the humeral cup on the scapular neck can lead to scapular notching and polyethylene wear. This is a cause for concern, especially as the notch is often more extensive than can be explained by impingement alone. Bony lysis of the scapula may also be related to a polyethylene granuloma. Further follow-up is required to ensure that loosening does not become a problem in the long term, and it has been recommended to limit its use to elderly patients, arguably those aged over 70 years. Despite these concerns, the reverse prosthesis, based on the biomechanical Grammont concept, offers a true surgical option in several situations where only limited possibilities were previously available: cuff tear arthrosis, persistent shoulder pseudo-paralysis due to a massive and irreparable cuff tear, severe fracture sequelae, prosthetic revision in a cuff-deficient shoulder, and tumor surgery. Finally, surgeons must be aware that results are less predictable and complication/revision rates are higher in revision surgery.
The Delta III reverse-ball-and-socket total shoulder implant is designed to restore overhead shoulder function in the presence of irreparable rotator cuff deficiency by using the intact deltoid muscle and the stability provided by the prosthetic design. Our purpose was to evaluate the clinical and radiographic results of this arthroplasty in a consecutive series of shoulders with painful pseudoparesis due to irreversible loss of rotator cuff function.
Fifty-eight consecutive patients with moderate-to-severe shoulder pain and active anterior elevation of <90 degrees due to an irreparable rotator cuff tear were treated with a Delta III total shoulder replacement at an average age of sixty-eight years. Seventeen of the procedures were the primary treatment for the shoulder, and forty-one were revisions. The patients were examined clinically and radiographically after an average duration of follow-up of thirty-eight months.
On the average, the subjective shoulder value increased from 18% preoperatively to 56% postoperatively (p < 0.0001); the relative Constant score, from 29% to 64% (p < 0.0001); the Constant score for pain, from 5.2 to 10.5 points (p < 0.0001); active anterior elevation, from 42 degrees to 100 degrees (p < 0.0001); and active abduction, from 43 degrees to 90 degrees (p < 0.0001). The patients for whom the implantation of the Delta III prosthesis was the primary procedure and those who had had previous surgery showed similar amounts of improvement. The total complication rate, including all minor complications, was 50%, and the reoperation rate was 33%. Of the seventeen primary operations, 47% (eight) were associated with a complication and 18% (three) were followed by a reoperation. Of the forty-one revisions, 51% (twenty-one) were associated with a complication and 39% (sixteen) were followed by a reoperation. Subjective results and satisfaction rates were not influenced by complications or reoperations when the prosthesis had been retained.
Total shoulder arthroplasty with the Delta III prosthesis is a salvage procedure for severe shoulder dysfunction caused by an irreparable rotator cuff tear associated with other glenohumeral lesions. Complications were frequent following both primary and revision procedures, but they rarely affected the final outcome. The procedure has a substantial potential to improve the condition of patients with severe shoulder dysfunction, at least in the short term.
This study examines long-term outcomes of total shoulder arthroplasty (TSA) via survivorship analysis, patient questionnaires, and minimum 10-year physical examinations. The study group consisted of 320 consecutive TSAs performed in 267 patients between 1974 and 1988. Diagnoses included rheumatoid arthritis (69%), osteoarthritis (22%), and juvenile rheumatoid arthritis (4.7%). Minimum 10-year physical examination follow-up was obtained on a subset of 72 TSAs at a mean (+/- SD) of 14.0 +/- 2.7 years. A Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire was obtained from 80 patients with 103 TSAs at a mean of 15.4 +/- 3.4 years after the index procedure (range, 10.4-23.2 years). Kaplan-Meier survivorship rates with revision as the endpoint at 5, 10, 15, and 20 years were 98%, 93%, 88%, and 85%, respectively. Of the shoulders, 22 (6.9%) required a revision, most commonly for loosening of one or both components (15 shoulders). Dislocation occurred earlier than other causes of revision or complication (P < .05, analysis of variance). Minimum 10-year physical examination follow-up revealed lasting, significant improvements in range of motion and strength. The patients' subjective assessments of TSA were favorable in that 92% felt that their shoulder was "much better" or "better" after TSA. The mean DASH score was 49 +/- 25; no significant differences were found among diagnoses. Long-term analysis of the Neer-type TSA revealed survivorship rates comparable to other joint replacements. The significant improvements in relief of pain, shoulder range of motion, and strength are associated with a high degree of patient satisfaction.
Development of a rotator cuff tear after shoulder arthroplasty can adversely affect outcome. To assess the results of a subsequent procedure to repair the torn cuff, we reviewed all shoulder arthroplasties performed at our institution to identify patients who had a subsequent operation for cuff repair with or without component revision. We identified 19 patients and 20 involved shoulders. One patient was lost to follow-up, and one was excluded because the subsequent cuff repair could not be adequately accomplished. Patients were studied retrospectively a mean of 9.1 years after cuff repair by analysis of prospectively collected data supplemented by use of a questionnaire (10 shoulders). The presence of the tear was diagnosed preoperatively by physical examination or routine radiographs in 13 shoulders, an arthrogram in 3, and surgical exploration in 2. The tear involved the subscapularis in 7 shoulders, the supraspinatus in 15, and the infraspinatus in 8. Rotator cuff repair was successful in only 4 shoulders and was unsuccessful in the remaining 14. Pain was absent in 4 shoulders, slight in 6, occasionally moderate in 5, and moderate in 3. The mean visual analog pain score was 5.6. Range of motion was limited, with mean values for elevation of 78 degrees and external rotation of 54 degrees . Because results of subsequent cuff repair are poor, every attempt should be made to repair the cuff securely and carefully direct postoperative physical therapy.
We report the use of the reverse shoulder prosthesis in the revision of a failed shoulder hemiarthroplasty in 19 shoulders in 18 patients (7 men, 11 women) with severe pain and loss of function. The primary procedure had been undertaken for glenohumeral arthritis associated with severe rotator cuff deficiency.
Statistically significant improvements were seen in pain and functional outcome. After a mean follow-up of 44 months (24 to 89), mean forward flexion improved by 26.4° and mean abduction improved by 35°. There were six prosthesis-related complications in six shoulders (32%), five of which had severe bone loss of the glenoid, proximal humerus or both. Three shoulders (16%) had non-prosthesis related complications.
The use of the reverse shoulder prosthesis provides improvement in pain and function for patients with failure of a hemiarthroplasty for glenohumeral arthritis and rotator cuff deficiency. However, high rates of complications were associated with glenoid and proximal humeral bone loss.