ArticleLiterature Review

Interplay of the Static and Dynamic Restraints in Glenohumeral Instability

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Abstract

Anterior glenohumeral instability is a common, yet complicated orthopaedic disorder. During the past few years, basic science research has improved the understanding of the glenohumeral joint stabilizing systems. The current authors review new contributions specifically detailing study of the interplay between the static and dynamic restraints. Simulation of the shoulder muscles in a recent study also has manifested the powerful contribution of the joint reaction force to concavity-compression. Continued advances, such as these, will improve the understanding, and allow better outcome, in treatment of glenohumeral instability.

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... Multidirectional shoulder instability (MDI) is a symptomatic condition of the glenohumeral joint, in which the humeral head cannot be maintained within the glenoid fossa [1,2], which leads to recurrent involuntary shoulder (sub)luxations. MDI is associated with symptoms ranging from discomfort and apprehension to chronic shoulder pain [3][4][5][6]. ...
... Taken together, the EMG results suggest that individuals with MDI may have [1] an increased or prolonged activity of muscles that stabilize the humeral head; [2] a reduced or shorter activity of muscles that move or accelerate the arm and shoulder girdle; [3] and increased or prolonged activity of muscles that decelerate or eccentrically control the movement of the arm and shoulder girdle. Which muscles accelerate or decelerate the arm depends on the specific arm movement under evaluation. ...
... To illustrate the first part of the hypothesis [1], several studies reported increased [30,37] or prolonged [31,32,38] infraspinatus activity and prolonged supraspinatus activity [31,32,38] in MDI individuals during elevation in the scapular plane. Because these rotator cuff muscles create compressive forces that prevent excessive glenohumeral translations [23,44,45], their increased or prolonged activity presumably reflects an attempt to control the humeral head better and longer [46]. ...
Article
Background: Several studies reported the importance of glenohumeral and scapular muscle activity and scapular kinematics in multidirectional shoulder instability (MDI), yet a systematic overview is currently lacking. Objective: This systematic review evaluates and summarizes the evidence regarding muscle activity and shoulder kinematics in individuals with MDI compared to healthy controls. Method: The electronic databases PubMed and Web of Science were searched in September 2020 with keywords regarding MDI (population), muscle activity, and glenohumeral and scapular movement patterns (outcomes). All studies that compared muscle activity or scapular kinematics between shoulders with MDI and healthy shoulders were eligible for this review, except for case reports and case series. All articles were screened on the title and abstract, and remaining eligible articles were screened on full text. The risk of bias of included articles was assessed by a checklist for case-control data, as advised by the Cochrane collaboration. Results: After full text screening, 12 articles remained for inclusion and one study was obtained by hand search. According to the guidelines of the Dutch Institute for Healthcare Improvement, most studies were of moderate methodological quality. We found moderate evidence that MDI individuals show increased or prolonged activity of several rotator cuff muscles that control and centre the humeral head. Furthermore, we found evidence of decreased and/or shortened activity of muscles that move or accelerate the arm and shoulder girdle as well as increased and/or lengthened activity of muscles that decelerate the arm and shoulder girdle. The most consistent kinematic finding was that MDI individuals show significantly less upward rotation and more internal rotation of the scapula during elevation of the arm in the scapular plane as compared with controls. Finally, several studies also suggest that the humeral head demonstrates increased translations relative to the glenoid surface. Conclusion: There is moderate evidence for altered muscle activity and altered humeral and scapular kinematics in MDI individuals as compared with controls. Keywords: electromyography; kinematics; muscle activity; scapula; shoulder instability.
... Among them, the negative intraarticular pressure has the greatest importance. The dynamic restraints are composed of the muscular structures around the shoulder [62,63]. The list of the restraints is given in Table 1.1. ...
... 1.10 and 1.11). With the help of the labrum, the depth of the glenoid cavity is increased by approximately 50% [62,63]. Superiorly, it's continuous with the tendon of the long head of the biceps brachii muscle that serves as one of the dynamic restraints of the glenohumeral joint by changing the orientation according to the rotational movements of the upper extremity. ...
Chapter
The shoulder is a complex structure which is comprised of various bones, joints, muscles, nerves, and vessels. It has the importance of being the only true connection between the axial skeleton and the upper extremity, and it plays the key role for upper extremity movements. In order to make the positioning of the upper extremity properly, all structures forming the shoulder must be intact and interoperate. Knowing the anatomy of the shoulder is essential for surgeons who want to evaluate the pathologies correctly and avoid the possible complications while performing surgical procedures. In this chapter, we will review the basic anatomy of the shoulder.
... The dynamic and static balance of the supraspinatus and infraspinatus components of the rotator cable, particularly the supraspinatus, is critical for anterior stabilization. [5] The long head of the biceps tendon, which is tightly supported by the supraspinatus and subscapularis tendons, also plays an active role in stabilizing the humeral head. It reflects the objective of this study to examine the role of stiffness of these soft tissues on stabilization in the shoulder joint, which is so well supported by soft tissues. ...
Article
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Objectives: This study aims to evaluate the soft tissue stiffness which has a prominent role in shoulder instability using ultrasound (US) shear wave elastography (SWE) and to compare the results with healthy shoulders. Patients and methods: Between December 2018 and January 2020, a total of 33 male patients (mean age: 26±4.3 years; range, 18 to 35 years) who underwent arthroscopic repair for traumatic isolated anterior glenohumeral instability were included in this prospective study. The shoulder girdle was evaluated with US SWE in patients with traumatic anterior instability. Deltoid (D), supraspinatus (SS), infraspinatus (IS), subscapularis (SSC), and long head of biceps (LHB) tendons forming the shoulder girdle and anterior labrum (L) were evaluated with SWE. The elasticity and velocity of the tissues were quantitatively measured. The operated shoulders of 33 patients due to isolated traumatic anterior instability were named Group 1, while the healthy shoulders of these patients were named Group 2. Thirty volunteers with healthy shoulders were considered as the control group (Group 3, n=30). Results: All three groups were compared in terms of SS, D, LHB, and SSC tendon velocity and elasticity; however, no statistically significant difference was observed among the groups (p<0.05). The anterior labrum of these three groups did not significantly differ in terms of SWE measurements (p<0.05). Conclusion: The stiffness of shoulder girdle muscle tendons and labrum measured with US SWE does not constitute a risk factor for traumatic anterior shoulder instability.
... When the shoulder joint is in motion, passive tension in the rotator cuff provides compressive stress between the articular surfaces, which forms concavity compression to stabilize the joint (Halder et al., 2001). Additionally, the coordination of rotator cuff muscle contraction keeps the stress in balance in all directions, which is conducive to the stability of the shoulder joint (Lee et al., 2000;Abboud and Soslowsky, 2002). In our study, all patients had their entire humeral head and most of the rotator cuff preserved. ...
Article
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Background: Tumorous bone defect reconstructions of the proximal humerus with joint sparing is a challenge. Numerous reconstruction methods have been proposed but the proximal residual humerus is commonly sacrificed because of its extremely short length. To preserve the proximal humerus and improve clinical outcomes, we designed a three-dimensional (3D) printed uncemented prosthesis with a porous structure to treat tumorous bone defects of the proximal humerus. Methods: Our analysis included seven patients treated between March 2018 and July 2019. A 3D model was established, and related data were obtained, including the diameter of the humeral head, the resection length, and the residual length. A prosthesis was designed and fabricated based on these data. Functional and oncologic outcomes were recorded, and complications and osseointegration were evaluated. Results: The mean age of the patients was 20.3 years, and the median follow-up period was 26 months. The lengths of the residual proximal humerus were 17.9 mm on average. All the patients had preserved humeral heads and most of the rotator cuff was intact. The average postoperative range of motion (ROM) of the affected shoulder was 83.8°; flexion was 82.5°, extension was 43.8°, and adduction was 16.3°. The average Musculoskeletal Tumor Society score (MSTS) was 94.3%. Good osseointegration was observed on the interface between the bone and prosthesis. Conclusion: A 3D printed porous prosthesis with cone-like structures successfully achieved joint-sparing reconstruction of proximal humeral tumorous defects with satisfying functional outcomes. The preservation of the rotator cuff and humeral head plays an essential role in the function of the shoulder joint.
... The dynamic stability needed for this highly mobile joint is made possible through joint concavity compression due to rotator cuff (RC) muscle contraction [1][2][3][4]. Thus, to maintain stability, RC muscles must efficiently contract to maintain joint congruency when forces act on the shoulder joint in the different positions of the elevation arc [4,5]. The activity of RC muscles changes when the arm is held at different angles and in different planes [3,6]. ...
Article
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Introduction Muscle fatigue is a leading cause of rotator cuff (RC) pathologies. Scapular orientation affected by changes in the thoracic spine account for differences in body postures leading to altered RC muscle activation. This posture-related alteration in RC muscle activation and its fatigue response needs to be analyzed. Materials and methods This study included 50 healthy shoulders with no coexisting spine pathologies. Raw data were recorded using electromyography sensors for RC muscles during two isometric maneuvers of abduction and external rotation, performed at 30% maximum voluntary contraction at 30°, 45°, and 90° arm elevation in sitting and standing. The raw data were analyzed in DataLITE® software, and the mean power frequency (MPF) was extracted to analyze the fatigue response of RC muscles. The Wilcoxon signed-rank test and Kruskal–Wallis test with Bonferroni corrections analyzed fatigue differences between postures and various activities. P < 0.05 was considered significant for the results. Results Supraspinatus muscle demonstrated significant fatigue at 90° of arm elevation in standing as compared to sitting (MPF −5.40: −5.41; P = 0.03) posture. Between the three elevation angles, all the RC muscles showed increased fatigue at 90° (MPF range −5.22 to −6.64). When compared between abduction and external rotation, only infraspinatus showed fatigue in external rotation (MPF range −5.42 to −6.08). Among all the three RC muscles, infraspinatus showed the maximum fatigue of MPF −6.64 when compared to supraspinatus −5.22 and teres minor −5.36. Conclusion The findings indicate that alterations in the body postures and different elevation angles affect the RC muscles’ fatigue response.
... The shoulder complex represents a perfect balance between mobility and stability [1][2][3][4], which is mainly provided by the combined action of the rotator cuff muscles and the superior capsule [3,[5][6][7][8][9][10]. In elderly and low-demand patients, the preferred treatment option for intractable shoulder pain and irreparable RCTs (IRCTs) is reverse total shoulder arthroplasty, which meets patients' functional demands and effectively reduces shoulder pain [11][12][13][14]. ...
Article
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In arthroscopic superior capsular reconstruction (ASCR) in irreparable rotator cuff tears (IRCTs), a graft is positioned and fixed between the superior rim of the glenoid and the humeral supraspinatus footprint. The fixation of the graft aims to restore the stability and improve the kinematics of the shoulder. The shoulder position during fixation of the graft may be a key factor impacting the outcome of ASCR; however, biomechanical evidence is lacking, as most studies addressing ASCR have been conducted in cadavers. In this study, graft strain and glenohumeral joint reaction force, estimated using a 3-D musculoskeletal model of the upper limb, were used to evaluate graft integrity and shoulder stability, respectively. The results suggest that ASCR significantly improved shoulder stability compared to the preoperative condition; however, the shoulder positions of fixation associated with the greatest improvements were also associated with the highest risk of compromising the integrity of the graft due to high strains. This study provides new and important information regarding the role of shoulder positioning during fixation of the graft.
... For decades, histology from tendinopathic human tendons has been well characterized, which has enabled benchmarks for load induced tendinopathy models in rodents. After high mechanical loading in rodent overuse models, cell number has been shown to increase in multiple tendons: the SS[55, 56, 103,114], AT [60,86,115,116], and FDL [110,117]. Additionally, with high loading a rounder cell morphology is reported in the SS[56, 57, 103], FDL [110], and AT [115,116]. ...
Article
Tendinopathy is a debilitating disease that causes as much as 30% of all musculoskeletal consultations. Existing treatments for tendinopathy have variable efficacy, possibly due to incomplete characterization of the underlying pathophysiology. Mechanical load can have both beneficial and detrimental effects on tendon, as the overall tendon response depends on the degree, frequency, timing, and magnitude of the load. The clinical continuum model of tendinopathy offers insight into the late stages of tendinopathy, but it does not capture the subclinical tendinopathic changes that begin before pain or loss of function. Small animal models that use high tendon loading to mimic human tendinopathy may be able to fill this knowledge gap. The goal of this review is to summarize the insights from in-vivo animal studies of mechanically-induced tendinopathy and higher loading regimens into the mechanical, microstructural, and biological features that help characterize the continuum between normal tendon and tendinopathy. Statement of Significance This review summarizes the insights gained from in-vivo animal studies of mechanically-induced tendinopathy by evaluating the effect high loading regimens have on the mechanical, structural, and biological features of tendinopathy. A better understanding of the interplay between these realms could lead to improved patient management, especially in the presence of painful tendon.
... A rotator cuff tendon provides dynamic stability to the glenohumeral joint (1,2). However, rotator cuff disease is a common musculoskeletal disorder with an incidence of 22.1% in the general population, and its prevalence increases with age (3). ...
Article
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Objective: This study aimed to investigate the anatomical relationship between the subscapularis tendon and glenosubscapularal ligament (GSL) that we accidentally identified from our previous study on a rabbit shoulder model and to determine whether this anatomical relationship has an impact on the rabbit shoulder model for studying the human chronic rotator cuff pathology. Methods: In this study, 15 male New Zealand rabbits aged 12 weeks and weighing 2.5 kg were used. Moreover, 3 rabbits were sacrificed for the anatomical and histological investigation of the relationship between the subscapularis tendon and GSL at baseline. The remaining 12 rabbits underwent the subscapularis tendon tenotomy from the lesser tuberosity using a standardized procedure. The GSL was cut on the left side and preserved on the right side. For histomorphometric analysis, 6 rabbits were first sacrificed at 6 weeks and then the remaining 6 rabbits at 12 weeks. Results: In all the rabbits, GSL was identified, connecting the upper portion of glenoid and subscapularis muscle-tendon junction. The mean thickness of the middle portion of GSL was 1.1±0.2 mm; the mean length of GSL was 8.4±2.3 mm. The mean widths of the proximal and distal attachments were 2.4±0.3 and 4.2±0.5 mm, respectively. The mean size of the native subscapularis muscle fibers was 122.6±4.3 μm2. The mean size of the muscle fibers in shoulders with tenotomy alone was 112.6±6.2 and 102.6±4.8 μm2 at 6 and 12 weeks, respectively. The mean size of the muscle fibers in shoulders with tenotomy plus GSL cut severing was 88.3±9.7 and 56.4±5.2 μm2 at 6 and 12 weeks, respectively. The significant muscle atrophy was observed both at 6 and 12 weeks in the shoulders with tenotomy plus GSL cut compared with those with tenotomy alone as well as those with the native subscapularis. However, the muscle atrophy was not significantly different in the shoulders with tenotomy alone at different time points. Conclusion: Because GSL may prevent the subscapularis retraction, the rabbit subscapularis tendon model may not be suitable for studying the human chronic rotator cuff pathology if GSL is neglected or preserved.
... In addition, the long head of biceps tendon showed at least in biomechanical studies a humeral head depressor function [27]. For example, when the long head of biceps tendon is ruptured, the humeral head is known to translate superiorly during abduction [28]. Biomechanical studies have also shown that tension in the long head of biceps reduces superior-inferior and anterior-posterior translation, with anterior and posterior stabilising function when the arm is internally and externally rotated, respectively [29]. ...
Chapter
The glenohumeral joint facilitates the large range of upper limb motion that is essential for undertaking most activities of daily living. The shallow concavity of the bony glenoid and fibrocartilaginous labrum, together with the humeral head, comprises an inherently unstable joint that is dependent on the integrity and morphology of the articular surfaces, as well as the simultaneous activity of the rotator cuff for glenohumeral joint compression and stability. The scapulothoracic joint provides an additional stabilization by increasing upper limb range of motion and providing a moving “seat” for the humeral head, while the bony glenoid concavity, joint capsule and ligaments generate passive support to the glenohumeral joint, particularly in the mid-range and end range of joint motion. Disease or trauma to any of these bony or soft-tissue stabilizers may result in glenohumeral instability.
... [7][8][9] The congruent articular surfaces provide stability through the negative intra-articular pressure and concavitycompression effect, which is particularly important during the midrange of glenohumeral movement when there is capsular and ligamentous laxity. 8,10 Labroligamentous complex The labral and ligamentous structures, specifically the inferior portions, are the main stabilizers of the glenohumeral joint with the arm at the end-range of movement that is abduction external rotation (ABER), and adduction internal rotation. 4,8,11,12 The glenoid labrum is a fibrocartilaginous structure that circumferentially covers the rim of the bony glenoid fossa, increasing the bony contact size by about one-third and improving joint surface congruity. ...
Anterior shoulder instability (ASI) is a common problem in the general population with incidence rates in the general US population estimated at 0.08 per 1000 person-years 1,2 ASI is characterized by the disruption of the dynamic and static stabilizers of the glenohumeral joint, resulting in dislocation, subluxation, and/or apprehension.1 It represents a continuum, from an acute traumatic event causing first-time dislocation followed by repeated dislocations requiring lesser degrees of provocation at one end of the spectrum, to glenohumeral hypermobility without antecedent trauma leading to progressive instability over time at the other end of the spectrum. 3 Imaging plays an important role in the evaluation of the ASI patient population, identifying and char- acterizing associated injuries for treatment planning. The purpose of this article is to review the role of various imaging modalities in the assessment of patients with ASI. Advances in 3D computed tomography (CT) and MR imaging, particularly for the quantification of bone loss is discussed, as well as concepts of engaging/non- engaging lesions and on-track/and off-track lesions.
... That kind of joint is described as a "ball and socket joint". As there is a limited interface between these two articulating bones, this is an inherently unstable connection [12][13][14][15][16] . There are different musculoskeletal components which provide stability and allow functional movement of that major joint: the rotator cuff as dynamic stabilizer, as well as the capsule, labrum complex, other connective tissue elements and glenohumeral ligaments as static stabilizers [15][16][17] . ...
... The SSC muscle is the major internal rotator of the shoulder and contributes more to shoulder elevation strength than the supraspinatus or infraspinatus tendons [5,6]. It is important in passive and active stabilization of the glenohumeral joint [7]. The SSC is inserted between the scapula and the humerus. ...
... Glenohumeral instability is generally accompanied by injury to the labrum, capsule, and glenohumeral ligaments [1,5,6,9,10,28,29,[42][43][44]. Shoulder instability is thought to involve injury to primary and secondary stabilizers of the capsule and capsular ligaments on both sides of the joint, like in the "circle stability concept" reported by Bowen and Warren [7,9]. ...
Article
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Background: Surgical treatment for shoulder instability generally involves labral repair with a capsular plication or imbrication. Good results are reported in both open and arthroscopic procedures, but there is no consensus on the amount or location of capsular plication that is needed to achieve stability and anatomic anterior, posterior, and inferior translation of the joint. Questions/purposes: (1) What are the separate and combined effects of increasing plication magnitude and sequential additive plications in the anterior, posterior, and inferior locations of the joint capsule on glenohumeral joint translation in the anterior, posterior, and inferior directions? (2) What plication location and magnitude restores anterior, posterior, and inferior translation to a baseline level? Methods: Fourteen cadaveric shoulders were dissected down to the glenohumeral capsule and underwent instrumented biomechanical testing. Each shoulder was loaded with 22 N in anterior, posterior, and inferior directions at 60° abduction and neutral rotation and flexion and the resulting translation were recorded. Testing was done over baseline (native), stretched (mechanically stretched capsule to imitate a lax capsule), and 5-mm, 10-mm, and 15-mm plication conditions. Individually, for each of the 5-, 10-, and 15-mm increments, plications were done in a fixed sequential order starting with anterior plication at the 3 o'clock position (Sequence I), then adding posterior plication at the 9 o'clock position (Sequence II), and then adding inferior plication at the 6 o'clock position (Sequence III). Each individual sequence was tested by placing 44 N (10 pounds) of manual force on the humerus directed in an anterior, posterior, and inferior direction to simulate clinical load and shift testing. The effect of plication magnitude and sequence on translation was tested with generalized estimating equation models. Translational differences between conditions were tested with paired t-tests. Results: Translational laxity was highest with creation of the lax condition, as expected. Increasing plication magnitude had a significant effect on all three directions of translation. Plication location sequence had a significant effect on anterior and posterior translation. An interaction effect between plication magnitude and sequence was significant in anterior and posterior translation. Laxity in all directions was most restricted with 15-mm plication in anterior, posterior, and inferior locations. For anterior translational laxity, at 10-mm and 15-mm plication, there was a progressive decrease in translation magnitude (10-mm plication anterior only: 0.46 mm, plus posterior: 0.29 mm, plus inferior, -0.12 mm; and for 15-mm anterior only: -0.53 mm, plus posterior: -1.00 mm, plus inferior: -1.66 mm). For posterior translational laxity, 10-mm and 15-mm plication also showed progressive decrease in magnitude (10-mm plication anterior only: 0.46 mm, plus posterior: -0.25 mm, plus inferior: -1.94; and for 15-mm anterior only: 0.14 mm, plus posterior: -1.54 mm, plus inferior: -3.66). For inferior translational laxity, tightening was observed only with magnitude of plication (anterior only at 5 mm: 0.31 mm, at 10 mm: -1.39, at 15 mm: -3.61) but not with additional plication points (adding posterior and inferior sequences). To restore laxity closest to baseline, 10-mm AP/inferior plication best restored anterior translation, 15-mm anterior plication best restored posterior translation, and 5 mm posterior with or without inferior plication best restored inferior translation. Conclusions: Our results suggest that (1) a 10-mm plication in the anterior and posterior or anterior, posterior, and inferior positions may restore anterior translation closest to baseline; (2) 10-mm anterior and posterior or 15-mm anterior plications may restore posterior translation closest to baseline; and (3) 5-mm anterior and posterior or anterior, posterior, and inferior plications may restore inferior translation closest to baseline. Future studies using arthroscopic techniques for plication or open techniques via a true surgical approach might further characterize the effect of plication on glenohumeral translation. Clinical relevance: This study found that specific combinations of plication magnitude and location can be used to restore glenohumeral translation from a lax capsular state to a native state. This information can be used to guide surgical technique based on an individual patient's degree and direction of capsular laxity. In vivo testing of glenohumeral translation before and after capsular plication will be needed to validate these cadaveric results.
... The subscapularis (SSC) is the largest of the rotator cuff muscles. It is important in passive and active stabilization of the glenohumeral joint (1)(2)(3). Isolated SSC tendon tears are very rare and most occur in the setting of chronic supraspinatus tendon tears (4)(5)(6)(7). Early studies of rotator cuff tendon tears focused on the supraspinatus tendon. ...
Article
Full-text available
Objective To compare the T1-weighted spectral presaturation with inversion-recovery sequences (T1 SPIR) with T2-weighted turbo spin-echo sequences (T2 TSE) on 3T magnetic resonance arthrography (MRA) in the evaluation of the subscapularis (SSC) tendon tear with arthroscopic findings as the reference standard. Materials and Methods This retrospective study included 120 consecutive patients who had undergone MRA within 3 months between April and December 2015. Two musculoskeletal radiologists blinded to the arthroscopic results evaluated T1 SPIR and T2 TSE images in separate sessions for the integrity of the SSC tendon, examining normal/articular-surface partial-thickness tear (PTTa)/full-thickness tear (FTT). Diagnostic performance of T1 SPIR and T2 TSE was calculated with arthroscopic results as the reference standard, and sensitivity, specificity, and accuracy were compared using the McNemar test. Interobserver agreement was measured with kappa (κ) statistics. Results There were 74 SSC tendon tears (36 PTTa and 38 FTT) confirmed by arthroscopy. Significant differences were found in the sensitivity and accuracy between T1 SPIR and T2 TSE using the McNemar test, with respective rates of 95.9–94.6% vs. 71.6–75.7% and 90.8–91.7% vs. 79.2–83.3% for detecting tear; 55.3% vs. 31.6–34.2% and 85.8% vs. 78.3–79.2%, respectively, for FTT; and 91.7–97.2% vs. 58.3–61.1% and 89% vs. 78–79.3%, respectively, for PTTa. Interobserver agreement for T1 SPIR was almost perfect for T1 SPIR (κ = 0.839) and substantial for T2 TSE (κ = 0.769). Conclusion T1-weighted spectral presaturation with inversion-recovery sequences is more sensitive and accurate compared to T2 TSE in detecting SSC tendon tear on 3T MRA.
... The glenohumeral joint stability relies on a complex combination of static and dynamic stabilizers [4] and compromise of these structures can lead to dislocation and often, recurrent instability. ...
Article
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Background The glenohumeral joint is a ball-and-socket joint that is inherently unstable and thus, susceptible to dislocation. The traditional and most common anatomic finding is the Bankart lesion (anterior-inferior capsule labral complex avulsion), but there is a wide variety of anatomic alterations that can cause shoulder instability or may be present as a concomitant injury or in combination, including bone loss (glenoid or humeral head), complex capsule-labral tears, rotator cuff tears, Kim´s lesions (injuries to the posterior-inferior labrum) and rotator interval pathology. Methods A review of articles related to shoulder anatomy and soft tissue procedures that are performed during shoulder instability arthroscopic management was conducted by querying the Pubmed database and conclusions and controversies regarding this injury were exposed. Results Due to the complex anatomy of the shoulder and the large range of movement of this joint, a wide variety of anatomic injuries and conditions can lead to shoulder instability, specially present in young population. Recognizing and treating all of them including Bankart repair, capsule-labral plicatures, SLAP repair, circumferential approach to pan-labral lesions, rotator interval closure, rotator cuff injuries and HAGL lesion repair is crucial to achieve the goal of a stable, full range of movement and not painful joint. Conclusion Physicians must be familiarized with all the lesions involved in shoulder instability, and should be able to recognize and subsequently treat them to achieve the goal of a stable non-painful shoulder. Unrecognized or not treated lesions may result in recurrence of instability episodes and pain while overuse of some of the techniques previously described can lead to stiffness, thus the importance of an accurate diagnosis and treatment when facing a shoulder instability.
... 17 The precise pathophysiology and natural history of joint degeneration in CTA remains poorly understood. RC tendons play a crucial role in maintaining the dynamic stability of the inherently unstable GH joint, 18,19 so it stands to reason that mechanical forces are the primary cause of articular cartilage degeneration in the setting of a massive RCT. 20,21 However, loss of mechanical properties does not fully explain the development of CTA, as degeneration and destruction of articular cartilage occurs in <10% of patients with a massive RCT. ...
Article
Untreated rotator cuff tears can progress to a distinct form of shoulder arthritis, and the mechanism of this progression is poorly understood. Biomechanical, molecular and genetic factors may be at play, and a reliable animal model is needed to enable further research. The purpose of this study was to create a reproducible model of posttraumatic shoulder arthritis in the mouse, and to develop a scoring system for this model to enable future research on interventions, the role of various gene products, and the development of therapies to alter the natural course of the disease. Forty-five mice underwent operative ligation of the rotator cuff tendons and were followed for 45 weeks following surgery, with free cage activity post-operatively. Mice were sacrificed at various intervals from 2-45 weeks post-injury and histopathologic scoring was developed and tested by blinded reviewers using both quantitative computational analysis of coronal sections of the shoulder joint and semi-quantitative grading. The scoring system revealed a progressive, time-dependent set of tissue changes in the shoulder joint with features similar to human cuff tear arthropathy including acetabularization of the acromion and femoralization of the humeral head. This model establishes that osteoarthritis of the shoulder is distinct from osteoarthritis of the knee or hip, with different stages of degeneration and unique histopathologic features. Using the novel grading procedure and quantitative assessments presented here, future research using this model will enable investigators to test established and novel therapies and evaluate the role of inflammatory factors and gene products in shoulder arthritis. This article is protected by copyright. All rights reserved
... The forces acting on it may be divided into static (capsule-ligamentous complex, glenoid morphology) and dynamic (rotator cuff muscles, long head of the biceps) constraints [1]. ...
Article
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In the anterior shoulder instability with glenoid bone loss among 25 % or more of the inferior glenoid diameter (inverted-pear glenoid), the consensus of recent authors is that glenoid bone grafting (Latarjet procedure) should be performed. The engaging Hill-Sachs lesion has been recognized as a risk factor for recurrent anterior shoulder instability. We have developed a method using radiographic and arthroscopic studies and the concept of the glenoid track to determine whether a Hill-Sachs lesion will engage the anterior glenoid rim, whether or not there is concomitant anterior glenoid bone loss. If the Hill-Sachs lesion engages, it is called an "off-track" Hill-Sachs lesion; if it does not engage, it is an "on-track" lesion. On the basis of our quantitative method, we have developed a treatment paradigm with specific surgical criteria for all patients with anterior shoulder instability (first dislocation or recurrent dislocation), both with and without bipolar bone loss.
... When shoulder instability exist, the central nervous system activates atypical or substitution muscle patterns to maintain both stability and mobility [29]. However, these atypical muscle substitution patterns are not optimal for efficient motion at the end of range of arm elevation [31,74,77]. The following muscle substitution patterns highlight some of these features after shoulder dysfunction: ...
Article
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This review of the glenohumeral joint provides the reader with an understanding of the dynamic stability alliances that exist between the active, passive and neuromotor control systems at during overhead arm elevation. Electromyography studies of patients with anterior shoulder instability performing overhead arm elevation into the apprehension arm position identified substitution muscle actions that concurrently regulate dynamic glenohumeral stability and retain shoulder joint mobility. Yet the temporal component of these substitution muscle actions has not been quantified. Quantifying the temporal features of glenohumeral muscle activation is important for a better understanding of the neuromotor control and more accurate estimation of joint reaction forces that occurs at the unstable shoulder joint during overhead arm elevation.
... Muscles are thought to help stabilize the shoulder joint by fi ve mechanisms: passive muscle tension; joint motion that secondarily tightens the passive ligamentous constraints; activation causing compression of the humeral head into the glenoid concavity (i.e. concavity compression); barrier effect of contracted muscles; and coordinated activation to redirect the joint force through the center of the glenoid surface [ 110 ]. Depending on joint position and the direction of injurious loading, different shoulder muscles affect joint stability to different degrees [ 111 ]. ...
Article
Skeletal muscle is the most abundant tissue in the human body and can play various roles in the context of accidental injuries. First, muscles make up 38 ± 5 % of male total body mass and 31 ± 6 % of female total body mass (Janssen et al., J Appl Physiol 89(1):81–88, 2000), and thus represent a considerable proportion of the body’s inertia. Second, muscles provide padding to many bones and other tissues, and thus can attenuate impacts to the body. Third, muscles generate forces within the body that alter the load state of other tissues during an impact. And finally, muscles themselves can be injured by impacts to the body. Despite these varied roles, muscles are often ignored in the study of accidental injury. For some types of accidental injury, muscles indeed contribute little or nothing to the injury mechanism. For other types of injury, however, muscle forces can exacerbate, mitigate and sometimes even cause specific injuries. The goal of this chapter is to review our current understanding of how skeletal muscles affect accidental injury. Our focus is on traumatic injuries, but we address chronic or overuse injuries where they contribute to the understanding of traumatic injuries. We begin with a brief overview of muscle mechanics and then examine the role of muscles on injuries to various anatomic regions, including the head, spine, upper extremity and lower extremity. We close with a consideration of how muscle activation affects whole body motion and traumatic injury patterns in general.
... Miyashita et al.37 estimated that for the maximum shoulder external rotation of 144.2° during baseball pitching, glenohumeral external rotation accounted for 105.7°, or 73.3%. At the end ROM of external rotation, the inferior glenohumeral ligament and inferior capsule rotate anteriorly and are stretched to limit further external rotation and humeral head anterior shift.199 With repetitive stretching, microtrauma can accumulate and lengthen these structures, reducing their capacity of limiting external rotation. ...
Article
A wide spectrum of shoulder injuries has been identified in baseball players. Scapular kinematics during pace-controlled scaption, glenohumeral joint range of motion, and shoulder muscle strength have been associated with shoulder injuries in baseball players. The purpose of this study was to investigate scapular kinematics during maximum effort baseball throwing and to identify the potential association among these measures and scapular kinematics during pace-controlled scaption, glenohumeral range of motion, shoulder muscle strength, and shoulder kinetics during maximum effort baseball throwing. Thirty-five subjects (age 23.3±5.8yrs, height 180.1±7.8cm, weight 83.3±13.8kg) with previous experience in organized baseball (15.2±5.8yrs) were recruited. Passive video-based motion analysis was used for capturing maximum effort throwing and pace-controlled scaption. Glenohumeral range of motion and shoulder muscle strength were measured. Pearson’s product-moment correlation coefficient was used to evaluate the correlation among the measured variables. Positive correlations were observed between scapular kinematics during scaption and throwing at the same arm elevation angle at stride foot contact and the occurrence of maximum shoulder compression force, indicating that kinematic patterns that appeared during scaption also appeared during throwing. Maximum shoulder inferior force was negatively correlated to decreased posterior shoulder tightness and increased supraspinatus strength. Subjects with tighter posterior shoulder and stronger supraspinatus tended to have greater shoulder inferior force. Scapular retraction and posterior tilt were both positively correlated to maximum shoulder compression force. Subjects with a more retracted and posteriorly tilted scapula generated greater shoulder compression force. Evidential support for using a scaption test as a tool to evaluate baseball players’ shoulder function was established. Examination of posterior shoulder tightness and supraspinatus strength may be appropriate for screening for high shoulder forces during throwing. The current findings also presented a potential approach to reduce shoulder force by adjusting scapular kinematics, although future research is needed to confirm the existence of causality.
Chapter
The glenohumeral (GH) joint is a complex and unstable articulation. The interaction between various structures of the shoulder caused by mechanical stimuli and motion provides multiple degrees of shoulder motion. The static stability of the shoulder is supported by the articulation of the humeral head and the glenoid with additional GH ligaments, capsule, and labrum. The rotator cuff muscles surrounding the shoulder joint provide dynamic stability. The combination of these factors forms the biomechanical system that can respond in accordance with the arm movement. Different pathological processes and injuries may result in similar clinical manifestations. It is crucial to know the etiology of these different pathological factors from the viewpoint of the shoulder joint biomechanics to provide the most effective and curable treatments for patients suffering from shoulder diseases and disorders.
Article
Purpose: To investigate the effectiveness of two home-based exercise programs for treating multidirectional shoulder instability (MDI) in patients diagnosed with Hypermobile Ehlers-Danlos syndrome (hEDS) or Hypermobility Spectrum Disorders (HSD). Methods: Twenty-one hEDS/HSD patients with MDI were recruited from the Center for Medical Genetics of the Ghent University Hospital. Patients were randomly assigned to either the experimental or the control group. Both groups received a 6-month home-based exercise program. The primary outcome measure was the Western Ontario Shoulder Index (WOSI). Secondary outcomes included the Disabilities of the Arm, Shoulder and Hand (DASH), Tampa Scale for Kinesiophobia (TSK), Patient-Specific Functional Scale (PSFS), Global Rating of Change (GROC), and pain pressure thresholds. Outcomes were assessed at baseline, after 6 weeks, 12 weeks, and 24 weeks. Results: Significant main effects for time were observed for all questionnaires, except for the TSK (p = 0.12). Patients improved 240 and 325 points on the WOSI after 12 (p = 0.02) and 24 weeks (p = 0.001), respectively. Additionally, patients improved 8.6 points on the DASH (p = 0.002), 4.3 points on the PSFS (p = 0.01), and 1.02 points on the GROC (p = 0.001) after 24 weeks. Conclusion: No significant differences were found between group A and B. Both home-based exercise programs led to significant improvements in shoulder function. IMPLICATIONS FOR REHABILITATIONHome-based exercise therapy may be effective for treating MDI in the hEDS/HSD population.Home-based training is beneficial for improving shoulder function, but a multidisciplinary, supervised approach might be more effective for altering kinesiophobia in this patient population.
Chapter
The glenohumeral joint is one of the most mobile joints in the body with surrounding soft tissue restraints such as the labrum, ligaments, and musculature support. With that said, the tradeoff for this freedom of movement is the lack of stability which makes this joint susceptible to injury. In addition, fractures of the proximal upper extremity are also in the differential of shoulder pain that can have profound implications to an athlete if not treated appropriately. In this chapter, we will discuss shoulder dislocations and fractures.KeywordsShoulder dislocationGlenohumeral joint instabilityProximal humerus fractureClavicle fractureScapula fracture
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Objective: To summarize the relationship between shoulder instability and superior labrum anterior posterior (SLAP) lesion. Methods: The characteristics of shoulder instability and SLAP lesion were analyzed, and the relationship between them in pathogenesis, clinical symptoms, and biomechanics was discussed by referring to relevant domestic and foreign literature. Results: Shoulder instability and SLAP lesion can occur both spontaneously and respectively. SLAP lesion destroys the superior labrum integrity and the long head of biceps tendon (LHBT) insertion, causing excessive humeral head displacement against glenoid, and leading to shoulder instability. While chronic repetitive or acute high-energy traumatic shoulder instability can in turn aggravate SLAP lesion, resulting in expansion and increased degree of the original lesion. Conclusion: SLAP lesion destroys mechanisms of shoulder stability, while shoulder instability causes tears of the upper labrum and the LHBT, showing a connection between shoulder instability and SLAP lesion. However, the existing evidence can only demonstrate that shoulder instability and SLAP lesion induce and promote the development of each other, instead of a necessary and sufficient condition. Therefore, the specific causal relationship between the two remains unknown and needs to be further studied.
Article
»: Shoulder instability is a complex problem with a high rate of recurrence in athletes. Treatment of a first-time subluxation or dislocation event is controversial and depends on patient-specific factors as well as the identified pathology. »: Athletic trainers and physical therapists are an integral part of the treatment team of an in-season athlete who has experienced a shoulder instability event. Through comprehensive physiological assessments, these providers can effectively suggest modifications to the patient's training regimen as well as an appropriate rehabilitation program. »: Surgical intervention for shoulder stabilization should use an individualized approach for technique and timing. »: A team-based approach is necessary to optimize the care of this high-demand, high-risk population.
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Pain in the upper extremities can be severely functionally limiting with activities of daily living. The shoulder girdle is comprised of multiple joints, ligaments, tendons, muscles, and nerves which may contribute to shoulder pain. An appropriate workup should include but not be limited to history, physical exam, and imaging studies. Radiofrequency of the suprascapular n., axillary n., and/or lateral pectoral n. may provide a minimally invasive long-term treatment for chronic shoulder pain.
Article
Background The three glenohumeral ligaments (superior, middle and inferior) are discrete thickenings of the glenohumeral joint capsule and are critical to shoulder stability and function. Injuries to this area are a cause of significant musculoskeletal morbidity. Methods A literature search was performed by a review of PubMed, Google Scholar and OVID for all relevant articles published up until 2020. Results This study highlights the anatomy, biomechanical function and injury patterns of the glenohumeral ligaments, which may be relevant to clinical presentation and diagnosis. Conclusion A detailed understanding of the normal anatomy and biomechanics is a necessary prerequisite to understanding the injury patterns and clinical presentations of disorders involving the glenohumeral ligaments of the shoulder.
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Musculoskeletal disorders of the upper limb are common and can involve structures such as bone, joint, ligament, tendon, and muscle. This chapter begins with a description of physical examination maneuvers that can be used to assist with the identification of upper limb pathology. This is followed by a description of the rehabilitation principles that can be used to treat these disorders. The remainder of the chapter discusses the identification and management of upper limb conditions frequently encountered by physiatrists. This information can be applied to accurately diagnose and appropriately treat upper limb conditions, thus maximizing the patient’s functional outcome.
Article
Objectives: This study aims to compare the clinical results of patients with traumatic isolated Bankart lesions and type V superior labrum anterior to posterior (SLAP) lesions after arthroscopic repair. Patients and methods: Patients who underwent arthroscopic repair for traumatic anterior glenohumeral instability were evaluated retrospectively between December 2014 and January 2019. Fifty-one patients (49 males, 2 females; mean age 25 years; range, 18 to 36 years) without bone defects affecting >20% of the glenoid fossa, off-track engaging Hills-Sachs lesions, multidirectional instability, or ligamentous laxity were included in the study. Group 1 had 31 patients with isolated Bankart lesions and group 2 had 20 patients with type V SLAP lesions. There were only two female patients in group 1 and all patients were male in group 2. The mean age was 25 years (range, 18 to 36 years) in group 1 and 25 years (range, 19 to 35 years) in group 2. Rowe, Constant, and Western Ontario Shoulder Instability (WOSI) scoring systems were used to evaluate the clinical outcomes of the patients preoperatively and at the last follow-up. Results: The mean follow-up time was 32 months (range, 12 to 48 months) in group 1 and 28.5 months (range, 12 to 42 months) in group 2. There were no statistically significant differences between the two groups in terms of the number of shoulder dislocations before the surgery, mean age at the time of surgery, and the mean time from the first dislocation to surgical treatment. When the Rowe, Constant, and WOSI scores were evaluated preoperatively and at the last follow-up, there were statistically significant changes within, but not between, the two groups. Conclusion: In type V SLAP lesions, the affected and repaired labrum surface area is larger than isolated Bankart lesions. However, as a result of appropriate surgical treatment, the affected surface area does not have a negative effect on clinical outcomes, and similar clinical results can be obtained in patients with type V SLAP lesions compared to patients with isolated Bankart lesions.
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The ideal graft should have a high rate of integration, a low resorption rate, and a low risk of hardware fixation complications, and it should prevent the progression of osteoarthritis secondary to instability. Glenoid bone grafting techniques are necessary for restoring glenoid width and for preventing instability recurrence, while humeral grafting is used in order to treat symptomatic engaging Hill-Sachs lesions. Coracoid transfer procedures are described along with the more recent autograft techniques by means of the corticocancellous iliac crest bone, the distal clavicle, and the allografts from fresh-frozen femoral or humeral head and from the talus. The complications related to graft resorption are a current limitation of grafting technologies. New perspectives in bone grafting technologies come from the field of the basic science in the form of growth factor-infused bioscaffolds and of engineered functional bio-scaffold ricapitulating endochondral ossification.
Chapter
In this chapter, the bones, joints, and the muscles of the shoulder complex and their role in the shoulder function are discussed in detail. The specific aims of this chapter are to; describe the structures of the bones and joints of the shoulder complex, discuss the stability and instability, and normal and abnormal motion at each joint and the role of the individual yet interdependent joints to the overall motion of the shoulder complex, describe the characteristics of the shoulder muscles, and discuss their role and the effects of their impairments in the shoulder complex.
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Recurrent anterior dislocation of shoulder is a rarely encountered condition characterized by shoulder pain and movement restriction. In patients in whom conservative measures have failed, more invasive interventions such as arthroscopic repair can be very effective in relieving symptoms and improving range of movement. Radiological imaging plays an important role in these conditions. We present four cases referred to our institution where the diagnosis of recurrent anterior shoulder made, confirmed and managed by arthroscopic surgery. ese cases highlight the importance of careful review of the radiology and the need for reconsideration of the diagnosis in case of recurrent shoulder dislocation. Introduction :
Chapter
To prevent abnormal translation of the humeral head on the glenoid, the shoulder is stabilised by both static and dynamic mechanisms. The static mechanisms include the bony configurations of the glenoid and humerus, the glenoid labrum, the joint capsule and the glenohumeral ligaments. Although the avulsion of the capsulolabral complex (Bankart lesion) accounts for more than 80% of instability cases, the humeral avulsion of the glenohumeral ligaments (HAGL) has only been reported in 1–9% of patients but may be even higher when looking at specific subgroups. The mechanism of injury is commonly traumatic but with accurate diagnosis and early surgical repair predictable good outcomes can be obtained.
Article
Im Sport findet sich häufig die Problematik der Schulterinstabilität, besonders bei Überkopf- und Hochrasanzsportarten. Die höchste Inzidenz zeigt mit 95% die anteriore-inferiore Schulterluxation. Neben der Luxationsrichtung sind Mechanismus und Ereignishäufigkeit für die Klassifizierung der Verletzung bedeutend. Zu den wichtigsten Begleitverletzungen Gehören neben Kapsel-/Labrum-, Knorpel- und ossären Läsionen auch die seltenen Nerven- und Gefäßverletzungen. Zur Schulterreposition etablieren sich zunehmend schonende Manöver. Standard in der primären Bildgebung ist das konventionelle Röntgen. Eine Schnittbildgebung des Gelenkes sollte erfolgen. Bildgebung und Verletzungsmusters entsprechend erfolgt die Therapie konservativ oder operativ. Die Notwendigkeit zur operativen Versorgung hängt vor allem vom Reluxationrisiko ab. Ein individuell abgestimmtes Rehabilitationsprogramm ermöglicht ein sicheres Wiederaufnehmen der sportlichen Aktivität.
Chapter
The rotator cuff has two main functions: to allow the humerus to change position with respect to the scapula and stabilize the humeral head in the glenoid fossa. These two functions cooperate; in fact, when a rotator cuff muscle is working, at the same time the antagonist must remain immobile/still. Any alteration of this mechanism will lead to a reduction in the range of motion and in the stability of the shoulder [1]. Beyond these two functions, cuff tendons have complex and partially unknown biomechanical tensile and compressing properties. Tension is the consequence of muscle contraction; compression is caused by the pull of the cuff, which is constricted between the humeral head and the coracoacromial arch. In the light of recent studies that have considered the movement, stability, and biomechanical properties of the cuff, it is possible to understand how a small rotator cuff tear will lead to an alteration of the factors reported above and a redistribution of the load to the remaining tendons, thus determining the progression of the tear in the tendon [2].
Chapter
Treatment of patients with glenohumeral joint instability is a complex process and involves a complete understanding of the functions and role of both the static and dynamic stabilizers of the glenohumeral joint. Additionally, a thorough knowledge of the surgical concepts and procedures outlined throughout this fine text to address the compromised anatomical structures in the patient with glenohumeral instability is of critical importance as well. The purpose of this chapter is to review the rehabilitative concepts and protocol for the treatment of the patient following arthroscopic Bankart reconstruction.
Article
The biomechanics of the glenohumeral joint depend on the interaction of both static and dynamic stabilizing structures. The combined effect of these stabilizers is to support the multiple degrees of motion within the glenohumeral joint. Total shoulder arthroplasty requires release of contracted tissues, repair of rotator cuff defects, reconstruction of normal skeletal anatomy with proper sizing, and positioning of components. Arthroplasty of the shoulder is unlike arthroplasty of the hinge joints when the collateral ligaments afford a high degree of stability and is even distinct from the hip when bony conformity is large and range of motion is less. The goal of this paper is biomechanical analyses of normal, injured and implanted shoulder joint.
Physiotherapists lack confidence in managing patients with shoulder problems, partly as a result of the complexity of presentation and lack of clear understanding of the pathology. Recently, tendon pathology has been proposed to occur in a continuum, with pathologic, imaging, and clinical evidence to support the hypothesis. Rotator cuff pathology in the older population has been demonstrated to relate to a primary degenerative tendinopathy, similar histologically and clinically to degenerative tendinopathies elsewhere in the body. Evidence to support degenerative tendinopathy as the primary pathology within the subacromial space is growing. Building on this evidence and hypothesis, a model of rotator cuff tendinopathy is presented, with suggestions for conservative management of each stage within the tendinopathy continuum based on tendinopathy management elsewhere in the body. Attention to contributing biomechanical, motor control, muscular strength and endurance, external pain referral, metabolic and psychosocial factors by physiotherapists is discussed within the context of the evidence in support of physiotherapy management of rotator cuff disorders. The current lack of research evidence in support of the proposed treatment protocol is acknowledged.
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The purpose of this article are to review scapular anatomy and function, describe imaging features of traumatic scapular injury, and discuss the role of diagnostic imaging in clinical decision making after shoulder trauma. Knowledge of scapular anatomy, function, injury patterns, imaging appearance, and clinical management is important for the radiologist to the care of patients who present with acute shoulder trauma.
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This study was performed to evaluate the relationship of the humeral head to the scapula in the horizontal plane of motion and to describe in detail a method of obtaining and interpreting modified axillary roentgenograms. Twenty normal subjects and twelve patients who had anterior instability of the shoulder were evaluated with this technique. In the control group, the humeral head was centered in the glenoid cavity throughout the horizontal plane of motion except when the arm was in maximum extension and external rotation. In this position, the cocked stage of the throwing motion, the center of the humeral head rested approximately four millimeters posterior to the center of the glenoid cavity. When the arm was flexed or rotated from this cocked position, the humeral head glided anteriorly, producing a shearing stress on the articular surface of the glenoid and labrum. In seven of the twelve patients who had anterior instability, abnormal mechanics were observed: anterior translation of the humeral head occurred. This indicates a significant disruption of the structures responsible for containing the humeral head within the glenoid fossa.
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Experimental work has shown that dislocation of the shoulder may involve disruption of the capsule from its lateral humeral attachment. We report two patients with recurrent dislocation due to this injury. Lateral repair gave good results. It is suggested that this injury be considered and looked for when glenoid labral injury is minimal or absent.
Article
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We investigated the stabilizing mechanism of the glenohumeral joint that prevents anterior dislocation by anatomical dissections of the subscapularis, the shoulder capsule, and the superior, middle, and inferior glenohumeral ligaments in thirty-six shoulders of embalmed cadavera. We also performed roentgenographic studies of ten unembalmed cadaver shoulders in which radiopaque markers were used to demonstrate the position, tightness, and laxity of the subscapularis muscle and of the middle and inferior glenohumeral ligaments during external rotation of the shoulder at zero, 45, and 90 degrees of abduction. The subscapularis muscle and the three glenohumeral ligaments were cut in different sequences to determine their relative contributions to stability (limitation of external rotation). The conclusions from these experiments were that at zero degrees of abduction, the subscapularis muscle stabilizes the joint to a large extent; at 45 degrees of abduction, the subscapularis, middle glenohumeral ligament, and anterosuperior fibers of the inferior glenohumeral ligament provide the stability; and as the shoulder approaches 90 degrees of abduction, the inferior glenohumeral ligament prevents dislocation during external rotation.
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A principle of organization of spinal circuitry which emerges from the studies reviewed here is that the structure of the distributed network of pathways in the spinal cord contains a detailed representation of the corresponding three dimensional architecture of the musculoskeletal system. The pertinent architectural features for a given muscle include (1) the number and identity of spanned joints, and (2) the line of action at a joint with respect to the torque directions of other muscles and to the gravity vector. In accordance with established ideas, muscles with common primary actions (synergists) at the ankle are linked by excitatory, length-dependent pathways. Those muscles which have opposite actions are linked by reciprocal inhibition, although muscles which are not principally involved in postural control are not connected in this way. Among antigravity and stabilizing muscles, force-dependent, inhibitory pathways link (1) muscles crossing different joints, and (2) members of different synergistic groups which exert torques in different directions. Therefore, each muscle has a unique set of actions in terms of joints spanned and line of action, and each muscle receives a unique combination of reflex inputs. The cross-joint coordination resulting from actions of force-dependent pathways becomes stronger at higher forces with a consequent reduction in degrees of freedom of the musculoskeletal system. Length-dependent pathways link muscles which share some, but not all, mechanical actions at a joint and may have different patterns of activation during locomotion. Length-dependent pathways appear to coordinate muscle responses to postural disturbances and enhance joint stiffness.
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The stabilising effects on the glenohumeral joint of each of the rotator-cuff muscles and of the biceps were studied with the arm in abduction and external rotation in 13 cadaver shoulders. The muscles were loaded one at a time with forces proportional to their cross-sectional areas. We recorded the positions of the humeral head before and after the application to the humerus of an anterior force of 1.5 kg. When the capsule was intact, the anterior displacement with the subscapularis loaded was significantly larger than with the other muscles loaded (p = 0.0009). With the capsule vented, the displacement with the biceps loaded was significantly smaller than that with the subscapularis loaded (p = 0.0052). After creating an imitation Bankart lesion, the displacement with the biceps loaded was significantly less than with any of the rotator-cuff muscles loaded (p = 0.0132). We conclude that in the intact shoulder, the subscapularis is the least important anterior stabiliser, and that the biceps becomes more important than the rotator-cuff muscles as stability from the capsuloligamentous structure decreases. Strengthening of the biceps as well as the rotator-cuff muscles should be part of the rehabilitation programme for anterior shoulder instability.
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Ten cadaveric shoulders were tested to evaluate the effect of simulated contraction of the long head of the biceps brachii on glenohumeral translation. The shoulders were mounted on a special apparatus attached to a servo-controlled hydraulic testing device. Sequential 50 N anterior, posterior, superior, and inferior forces and a 22 N joint compressive load were applied to the shoulders. An air cylinder applied a constant force to the tendon of the long head of the biceps brachii. The shoulders were tested in seven positions of glenohumeral elevation and rotation. Application of a force to the long head of the biceps brachii resulted in statistically significant decreases in humeral head translation. The influence of the long head of the biceps was more pronounced at middle and lower elevation angles. When the shoulder was placed in 45 degrees of elevation and neutral rotation, application of a 55 N force to the biceps tendon reduced anterior translation by 10.4 mm (p = 0.001), inferior translation by 5.3 mm (p = 0.01), and superior translation by 1.2 mm (p = 0.004).
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Surgical treatment for traumatic, anterior glenohumeral instability requires repair of the anterior band of the inferior glenohumeral ligament, usually at the site of glenoid insertion, often combined with capsuloligamentous plication. In this study, we determined the mechanical properties of this ligament and the precise anatomy of its insertion into the glenoid in fresh-frozen glenohumeral joints of cadavers. Strength was measured by tensile testing of the glenoid-soft-tissue-humerus (G-ST-H) complex. Two other specimens of the complex were frozen in the position of apprehension, serially sectioned perpendicular to the plane containing the anterior and posterior rims of the glenoid, and stained with Toluidine Blue. On tensile testing, eight G-ST-H complexes failed at the site of the glenoid insertion, representing a Bankart lesion, two at the insertion into the humerus, and two at the midsubstance. For those which failed at the glenoid attachment the mean yield load was 491.0 N and the mean ultimate load, 585.0 N. At the glenoid region, stress at yield was 7.8 ± 1.3 MPa and stress at failure, 9.2 ± 1.5 MPa. The permanent deformation, defined as the difference between yield and ultimate deformation, was only 2.3 ± 0.8 mm. The strain at yield was 13.0 ± 0.7% and at failure, 15.4 ± 1.2%; therefore permanent strain was only 2.4 ± 1.1%. Histological examination showed that there were two attachments of the anterior band of the inferior glenohumeral ligament at the site of the glenoid insertion. In one, poorly organised collagen fibres inserted into the labrum. In the other, dense collagen fibres were attached to the front of the neck of the glenoid.
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The antero-inferior capsule (AIC) is the primary restraint to antero-inferior glenohumeral dislocation. This study utilizes a biomechanical model to determine the total strain field of the AIC in a subluxed shoulder. Strains were calculated from two capsule states: a nominal strain state set by inflation and a strained state set by subluxation. Marker coordinates on the AIC were reconstructed from stereoradiographs and strain fields calculated. Peak strain on the glenoid side of the AIC was significantly greater than the humeral side and strain fields were highly variable. This study reports an accurate method for measuring planar strains in a three-dimensional membrane.
Article
The purpose of this study was to quantify in a biomechanical model the contributions to shoulder joint stability that are made by tensions in the four tendons of the rotator cuff and by static resistance of defined portions of the capsular ligaments. A materials testing machine was used to directly determine anterior joint laxity by measurement of the force required to produce a standard anterior subluxation. Shoulders were tested in external or neutral humeral rotation. Data were analyzed by multiway analysis of variance with regression analysis. This model simulated tensions in the rotator cuff musculature by applying static loads at the tendon insertion sites acting along the anatomic lines of action. A load in any of the cuff tendons resulted in a measurable and statistically significant contribution to anterior joint stability. The contributions between different tendons were not significantly different and did not depend on the humeral rotation (neutral or external). In neutral humeral rotation the superior and middle glenohumeral ligaments together function equally with the inferior glenohumeral ligament as primary stabilizers against anterior humeral translation. The posterior capsule is a secondary stabilizer. The external rotation of the abducted humerus increases anterior stability by more than doubling the stability contribution from the inferior glenohumeral ligament. The stability contribution from the posterior capsule is larger in external rotation than in neutral rotation but is still of secondary magnitude. In external rotation the stability contribution of the anterior capsule, including the superior glenohumeral ligament and the middle glenohumeral ligament, becomes insignificant. The model presented here simulates the combined effect of two major sources of shoulder stability. This versatile model permits the direct measurement of the contributions to anterior shoulder stability that are made by tensions in the rotator cuff tendons and by static resistance of defined capsular zones. The use of multiple regression analysis-a standard statistical technique but one relatively new to the orthopaedic literature-permits quantitative determination of the contribution of each independent variable to the dependent variable, shoulder stability.
Article
The contribution of the long head of the biceps (LHB) to shoulder stability was studied. Nine fresh-frozen cadaveric shoulders were tested in the hanging arm position. The muscle belly of the long head of the biceps was removed and replaced with a spring device to apply load to the long head of the biceps. An electromagnetic tracking device was used to record the positions of the humeral head (1) without load and with loads of 1.5 kg and 3 kg on the long head of the biceps, (2) with 1.5 kg of force to the proximal humerus in three different directions, and (3) in three different rotations of the arm. Displacement in the anterior and posterior directions was significantly decreased by long head of the biceps loading and was less significant in internal rotation. Inferior displacement in external rotation was significantly decreased by long head of the biceps loading. It is concluded that in the hanging arm position, the long head of the biceps could, if contracted, provide some stabilizing function to the humeral head in all directions, and more importantly, in anterior/posterior directions. Furthermore, the stabilizing function of the LHB is influenced by rotation of the arm.
Article
The macroscopic anatomy and the architecture of the collagen fiber bundles were studied in the joint capsules of 43 cadaver shoulders. All the specimens were transilluminoted by polarized light after preparation by Spalteholz' technique. Areas of high-fiber density and complex structure were examined histologically. The macroscopically recognizable ligaments are composed of collagen fiber bundles in several layers of differing thickness and orientation. A simple pattern of radial and circular fibers is found only in the relatively thin posterior capsule. A complex pattern of cross-linking was visible in the superior capsule, and a system of fiber bundles spirally crossing each other was present in the anterior/inferior capsule. The examination under polarized light revealed a continuous transition between the ligamentous reinforcements at the anterior inferior capsule, which radiated obliquely from the glenoid rim and varied greatly in form and orientation. The complicated structure of the joint capsule would suggest that the capsular cylinder has to be regarded as a functional entity and that the current biomechanical concepts must be modified if we want to understand its stabilizing effect. The structural features of the superior capsule present new insight about the pathogenesis of rotator cuff tearing, which can develop as a result of shearing stress between the capsular and tendinous layers.
Article
The purpose of this research was to determine the degree to which compression of the humeral head into the glenoid concavity stabilizes it against translating forces. Ten normal fresh-frozen cadaver glenohumeral joints in which the labrum was preserved were used. A compressive load of 50 N was applied to the humeral head in a direction perpendicular to the glenoid surface. Increasing tangential forces were then applied until the head dislocated over the glenoid lip. The tangential force at dislocation was examined for eight different directions, 45° apart around the glenoid. Concavity-compression stability was then examined for an increased compressive load of 100 N. Finally, the protocol with 50 and 100 N of compressive load was repeated after the glenoid labrum was excised. Concavity-compression of the humeral head into the glenoid is a most efficient stabilizing mechanism. With the labrum intact the humeral head resisted tangential forces of up to 60% of the compressive load. The degree of compression stabilization varied around the circumference of the glenoid with the greatest magnitude superiorly and inferiorly. This may be attributed to the greater glenoid depth in these directions. Resection of the glenoid labrum reduced the effectiveness of compression stabilization by approximately 20%. These results indicate that concavity-compression may be an important mechanism for providing stability in the mid-range of glenohumeral motion where the capsule and ligaments are lax. The effectiveness is enhanced by the presence of an intact glenoid labrum.
Article
The inferior glenohumeral ligament (IGHL) is an important structure for maintaining shoulder stability. This study was aimed at determining the geometric and anatomic characteristics of the IGHL and its tensile properties at a higher strain rate than previously tested. Eight fresh-forzen human cadaver shoulders (average age 69 years, age range 62 to 73 years) from four female and four male cadavers were used to harvest bone-ligament-bone specimens from the three regions of the IGHL (superior band, anterior axillary pouch, and posterior axillary pouch). Uniaxial tensile tests were performed at the moderately high strain rate of approximately 10% per second with a servo-hydraulic testing machine. This represented a strain rate that was approximately 100 to 1000 times faster than that previously reported. During tensile testing, bone-ligament-bone strains were calculated from grip-to-grip motion on the testing machine, and mid-substance strains were determined by a video dimensional analyzer. Although all regions of the IGHL had similar lengths (averaging 43.4 mm), their thickness varied by region and by proximal-to-distal location. The superior band was the thickest (2.23±0.38 mm) of the three regions. Of the remaining two regions the anterior axillary pouch (1.94±0.38 mm) was thicker than the posterior axillary pouch (1.59±0.64 mm). By proximal-to-distal location the IGHL was thicker for all three regions near the glenoid (2.30±0.57 mm) than near the humerus (1.61±0.52 mm). The superior band had a greater stiffness (62.63±9.78 MPa) than either the anterior axillary pouch (47.75±17.89 MPa) or the posterior axillary pouch (39.97±13.29 MPa). Tensile stress at failure was greater in the superior band (8.4±2.2 MPa) and the anterior axillary pouch (7.8±3.1 MPa) than the posterior axillary pouch (5.9±1.7 MPa). The anterior axillary pouch demonstrated greater bone-to-bone and mid-substance strains (30.4%±4.3% and 10.8%±2.4%, respectively) before failure than the other two regions (superior band: 20.8%±3.8% and 9.1%±2.8%, respectively; posterior axillary pouch: 25.2%±5.8% and 7.8%±2.6%, respectively). Bone-to-bone strain was always greater than mid-substance strain, indicating that when the IGHL is stretched, the tissue near the insertion sites will experience much greater strain than the tissue in the mid-substance. Insertion failures were more likely at slower strain rates, and ligamentous failures were predominant at the fast strain rate. When compared with other tensile studies of the IGHL at slower strain rates (0.01% per second and 0.1% per second), the superior band and the anterior axillary pouch demonstrated the viscoelastic effects of increased stiffness and failure stress. This superior band and anterior axillary pouch viscoelastic stiffening effect suggests that these two regions may function to restrain the humeral head from rapid abnormal anterior displacement in the clinically vulnerable position of abduction and external rotation.
Article
The mechanical response of the inferior glenohumeral ligament to varying subfailure cyclic strains was studied in 33 fresh frozen human cadaver shoulders. The specimens were tested as bone-ligament-bone preparations representing the 3 regions of the inferior glenohumeral ligament (superior band and anterior and posterior axillary pouches) through use of uniaxial tensile cycles. After mechanical preconditioning, each specimen was subjected to 7 test segments, consisting of a baseline strain level L1 (400 cycles) alternating with either 1 (group A, 10 shoulders), 10 (group B, 13 shoulders), or 100 (group C, 10 shoulders) cycles at increasing levels (L2, L3, L4) of subfailure strain. Cycling to higher levels of subfailure strain (L2, L3, L4) produced dramatic declines in the peak load response of the inferior glenohumeral ligament for all specimens. The group of ligaments subjected to 100 cycles of higher subfailure strains demonstrated a significantly greater decrease in load response than the other 2 groups. Ligament elongation occurred with cyclic testing at subfailure strains for all 3 groups, averaging 4.6% ± 2.0% for group A 6.5% ± 2.6% for group B, and 7.1% ± 3.2% for group C. Recovery of length after an additional time of nearly 1 hour was minimal. The results from this study demonstrate that repetitive loading of the inferior glenohumeral ligament induces laxity in the ligament, as manifested in the peak load response and measured elongations. The mechanical response of the ligament is affected by both the magnitude of the cyclic strain and the frequency of loading at the higher strain levels. The residual length increase was observed in all of the specimens and appeared to be largely unrecoverable. This length increase may result from accumulated microdamage within the ligament substance, caused by the repetitively applied subfailure strains. The clinical relevance of the study is that this mechanism may contribute to the development of acquired glenohumeral instability, which is commonly seen in the shoulders of young athletes who participate in repetitive overhead sports activities.
Article
Stability of the glenohumeral joint with an anterior, posterior, and inferior displacement force of 50 N was measured in a dynamic shoulder model. Controlled hydrodynamic actuator forces were applied to the deltoid muscle and to the rotator cuff in seven anatomic specimens. During elevation of the arm the position of the humerus was measured with a six-degree-of-freedom ultrasonic sensor device. The rotational center of the humeral head was used as a reference point for translation. A displacement force of 50 N led to significant humeral head displacement anteriorly and posteriorly but not inferiorly. A 50% reduction of rotator cuff forces increased anterior displacement by 46% and posterior displacement by 31%. Venting of the glenohumeral joint space and of the subacromial bursa resulted in a 50% increase of anterior displacement, a 19% increase of posterior displacement, and significant inferior displacement. This study demonstrates that in addition to passive stabilizers and negative intraarticular pressure, rotator cuff force significantly contributes to stabilization of the glenohumeral joint during arm motion. Muscle strength and coordination should gain more emphasis in the diagnosis and treatment of shoulder instability.
Article
We studied the gross, histological, and vascular anatomy of the glenoid labrum in twenty-three fresh-frozen shoulders from cadavera to demonstrate its cross-sectional anatomy, its microvascularity, and its attachments. The superior and anterosuperior portions of the labrum are loosely attached to the glenoid, and the macro-anatomy of those portions is similar to that of the meniscus of the knee. The superior portion of the labrum also consistently inserts directly into the biceps tendon, while its inferior portion is firmly attached to the glenoid rim and appears as a fibrous, immobile extension of the articular cartilage. The arteries supplying the periphery of the glenoid labrum come from the suprascapular, circumflex scapular, and posterior circumflex humeral arteries. In general, the superior and anterosuperior parts of the labrum have less vascularity than do the posterosuperior and inferior parts, and the vascularity is limited to the periphery of the labrum. Vessels supplying the labrum originate from either capsular or periosteal vessels and not from the underlying bone.
Article
The tensile properties of the inferior glenohumeral ligament have been determined in 16 freshly frozen cadaver shoulders. The inferior glenohumeral ligament was divided into three anatomical regions: a superior band, an anterior axillary pouch, and a posterior axillary pouch. This yielded 48 bone-ligament-bone specimens, which were tested to failure in uniaxial tension. The superior band was consistently the thickest region, averaging 2.79 mm. The thickness of the inferior glenohumeral ligament decreased from antero-superiorly to postero-inferiorly. The resting length of all three anatomical regions was not statistically different. Total specimen strain to failure for all bone-ligament-bone specimens averaged 27%. Variations occurred between the three regions, with the anterior pouch specimens failing at a higher strain (34%) than those from the superior band (24%) or the posterior pouch (23%). Strain to failure for the ligament midsubstance (11%) was found to be significantly less than that for the entire specimen (27%). Thus, larger strain must occur near the insertion sites of the inferior glenohumeral ligament. Stress at failure was found to be nearly identical for the three regions of the ligament, averaging 5.5 MPa. These values are lower than those reported for other soft tissues, such as the anterior cruciate ligament and patellar tendon. The anterior pouch was found to be less stiff than the other two regions, perhaps suggesting that it is composed of more highly crimped collagen fibers. Three failure sites were seen for the inferior glenohumeral ligament: the glenoid insertion (40%), the ligament substance (35%), and the humeral insertion (25%). In addition, significant capsular stretching occurred before failure, regardless of the failure mode.
Article
The gross and histologic anatomy of the inferior glenohumeral ligament was studied in 11 fresh frozen cadaver shoulders. Arthroscopic observations of the joint capsule through the normal range of motion re vealed that the inferior glenohumeral ligament is actually a complex of structures consisting of an anterior band, a posterior band, and an interposed axillary pouch. While these components of the inferior glenohumeral ligament complex were present in all 11 specimens, they were best demonstrated in some shoulders by placing the humeral head in internal or external rotation in varying degrees of abduction. Histologic examination of the joint capsule revealed that the anterior and posterior bands of the inferior glenohumeral ligament complex were readily identifiable as distinct structures comprised of thickened bands of well-organized colla gen bundles. Although slight variations were noted in the attach ment sites of the anterior and posterior bands to the glenoid, the inferior glenohumeral ligament complex was observed to attach to the humeral neck in one of two distinct configurations. A collar-like attachment, in which the entire inferior glenohumeral ligament complex attaches just inferior to the articular edge of the humeral head, was observed in six specimens. In the remaining five specimens, the attachment was in the shape of a "V," with the anterior and posterior bands attaching adjacent to the articular edge of the humeral head and the axillary pouch attaching at the apex of the "V" distal to the articular edge. The orientation and design of the inferior glenohu meral ligament complex supports the functional con cept of this single structure as an important anterior and posterior stabilizer of the shoulder joint.
Article
The purpose of this study was to investigate the liga mentous stabilizing mechanisms preventing anterior instability in the glenohumeral joint. Six freshly thawed, unembalmed cadaveric shoulders were dissected, preserving the joint capsule and gle nohumeral ligaments, the coracohumeral ligament, and the subscapularis tendon. Hall-effect strain transducers were placed on the superior, middle, and inferior gle nohumeral ligaments. The humerus and scapula were fixed in a specifically designed mounting apparatus that allowed the glenohumeral joint to be placed in 0°, 45°, or 90° of abduction. The mounting apparatus was placed in a model TTC Instron Universal Testing Instru ment, which applied an external rotation torque to the humerus. Strain produced in the three glenohumeral ligaments was recorded on a three-channel X-Y chart recorder. At 0° of abduction, the superior and middle gleno humeral ligaments developed the most strain. At 45° of abduction, the inferior and middle glenohumeral lig aments developed the most strain, with considerable strain also being developed in the superior glenohu meral ligament. At 90° of abduction, the inferior gleno humeral ligament developed the most strain, with strain also seen in the middle glenohumeral ligament.
Article
Fifteen male athletes who were skilled in throwing and who had chronic anterior instability of the shoulder (Group 1) were evaluated by dynamic intramuscular electromyography while pitching a baseball. Indwelling wire electrodes recorded the levels of activity in the biceps, middle deltoid, supraspinatus, infraspinatus, pectoralis major, subscapularis, latissimus dorsi, and serratus anterior throughout the entire pitching sequence. These signals were synchronized electronically with records of the pitch that were made using high-speed photography. The pitch was divided into five phases: wind-up, early cocking, late cocking, acceleration, and follow-through. The results were compared with previous identical studies of twelve healthy, uninjured male athletes who were skilled in throwing (Group 2). Activity increased mildly in the biceps and supraspinatus in Group 1 as compared with Group 2. Similar patterns of activity were demonstrated in the deltoid. In Group 1 the infraspinatus had increased activity during early cocking and follow-through but had decreased activity during late cocking. The pectoralis major, subscapularis, latissimus dorsi, and serratus anterior in Group 1 all were shown to have markedly decreased activity. The study revealed a difference between Groups 1 and 2 in all of the muscles of the shoulder that were tested with the exception of the deltoid. The mildly increased activity levels of the biceps and supraspinatus that were found in Group 1 may compensate for anterior laxity. The marked reduction in activity in the pectoralis major, subscapularis, and latissimus dorsi added to the anterior instability by decreasing the normal internal-rotation force that is needed during the phases of late cocking and acceleration.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Dynamic, fine-wire, intramuscular electromyography (EMG) was performed on 12 different shoulder muscles in 13 normal male subjects as they pitched a baseball. Seven were major league baseball pitchers and six were amateur pitchers. The act of pitching a fast ball was filmed at 450 frames per second with the EMG signals recorded synchronously. The subscapularis, su praspinatus, and infraspinatus muscles were tested in 13 subjects, the biceps brachii muscle was tested in 12, and other shoulder muscles were tested variously among the subjects. Two groups of muscles were identified. Group I mus cles, the supraspinatus, infraspinatus, teres minor, del toid, trapezius, and biceps brachii, served primarily to position the shoulder and elbow for the delivery of the pitch. These muscles were found to have greater activ ity during the early and late cocking stages, with less activity during acceleration. Group II muscles acceler ated the arm and baseball forward in space. These muscles, the pectoralis major, serratus anterior, sub scapularis, and latissimus dorsi, had stronger activity during the propulsive phase of the pitch. The professional pitchers were able to use the mus cles about the shoulder in an efficient manner to achieve greater pitching velocities. The subscapularis and latis simus dorsi muscles of Group II had stronger activity among the professionals, whereas the supraspinatus, teres minor, and biceps brachii muscles of Group I had only minimal activity. The amateurs, on the other hand, continued to use all of the rotator cuff muscles and the biceps brachii muscle of Group I through the accelera tion stage of the pitch. These data may provide a basis for understanding improved performance and an ad junct for sport-specific rehabilitation programs.
Article
A tear of the rotator cuff often accompanies primary acute anterior dislocations of the shoulder in older patients. These structures, weakened by wear or degeneration, tear when the shoulder dislocates, permitting the humerus to hinge on intact anterior structures. Three typical cases illustrate the posterior structural reactions to acute anterior dislocation.
Article
In thirty-six patients (forty shoulders) with involuntary inferior and multidirectional subluxation and dislocation, there had been failure of standard operations or uncertainty regarding diagnosis or treatment. Clinical evaluation of these patients stressed meticulous psychiatric appraisal, conservative treatment, and repeated examination of the shoulder. All patients were treated by an inferior capsular shift, a procedure in which a flap of the capsule reinforced by overlying tendon is shifted to reduce capsular and ligamentous redundancy on all three sides. This technique offers the advantage of correcting multidirectional instability through one incision without damage to the articular surface. One shoulder began subluxating again within seven months after operation, but there have been no other unsatisfactory results to date. Seventeen shoulders were followed for more than two years.
Article
A dynamic shoulder testing apparatus has been developed to examine unconstrained glenohumeral joint motion in human cadaveric full upper extremities. Six computer-controlled hydraulic cylinders are used to simulate muscle action, while the corresponding tendon excursions and six-degree of freedom joint motion are measured. Trials showed that the testing apparatus creates highly reproducible glenohumeral joint motion in the scapular plane. The apparatus can be used to examine the function of the shoulder musculature and capsuloligamentous structures during normal and pathologic motion at the glenohumeral joint.
Article
The purpose of this study was to determine the effect of sectioning of the anterior part of the inferior glenohumeral ligament (a simulated Bankart lesion) on load-induced multidirectional glenohumeral motion. Nine fresh, intact cadaveric shoulders were tested on a special apparatus that constrained three rotations but allowed simultaneous measurement of anterior-posterior, superior-inferior, and medial-lateral translation. Coupled anterior-posterior and superior-posterior translations were recorded while anterior, posterior, superior, and inferior forces of fifty newtons were applied sequentially. Testing was done in three positions of humeral elevation in the scapular plane, in three positions of humeral rotation, and with an externally applied joint-compression load of twenty-two newtons. A liquid-metal strain-gauge was placed on the posterior band of the inferior glenohumeral ligament to assess concomitant posterior capsular strain during the various test conditions. All shoulders were tested intact and again after the inferior glenohumeral ligament and the labrum had been detached from the glenoid from just superior to the anterior band of the inferior glenohumeral ligament to a point just posterior to the infraglenoid tubercle. The simulated Bankart lesion resulted in selected increases in anterior translation at all positions of elevation, in posterior translation at 90 degrees of elevation, and in inferior translation at all positions of elevation. However, these increases were very small; the maximum mean increase in translation seen over-all was only 3.4 millimeters, which occurred during inferior translation at 45 degrees of elevation.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
The authors conducted a study to determine if the long head of the biceps muscle and its attachment at the superior glenoid labrum play a role in stability of the shoulder in an overhead position. Their study used a dynamic cadaveric shoulder model that simulated the forces of the rotator cuff and long head of biceps muscles as the glenohumeral joint was abducted and externally rotated. Their data suggest that the long head of the biceps muscle contributes to anterior stability of the glenohumeral joint by increasing the shoulder's resistance to torsional forces in the vulnerable abducted and externally rotated position. The biceps muscle also helps to diminish the stress placed on the inferior glenohumeral ligament. Detachment of the superior glenoid labrum is detrimental to anterior shoulder stability as it decreases the shoulder's resistance to torsion and places a greater magnitude of strain on the inferior glenohumeral ligament.
Article
The avulsion of the glenohumeral ligament labral complex at the glenoid (Bankart lesion), as well as ligamentous laxity are well known causes of anterior shoulder instability. A lesser known entity, the humeral avulsion of glenohumeral ligaments (HAGL), was studied to determine its incidence and its role in anterior glenohumeral instability. Sixty-four shoulders with the diagnosis of anterior instability were prospectively evaluated by arthroscopy for intraarticular pathology, including Bankart, capsular laxity, and HAGL lesions. Six shoulders were found to have HAGL lesions (9.3%), 11 shoulders with generalized capsular laxity (17.2%), and 47 shoulders with Bankart lesions (73.5%). In patients with documented anterior instability without a demonstratable "primary" Bankart lesion, a HAGL lesion should be ruled out. This lesion is readily recognized arthroscopically, and an appropriate repair of this lesion can restore anterior stability to the patient. The pathological anatomy of the HAGL lesion and our treatment of this lesion is discussed.
Article
Twenty-three fresh-frozen cadaver shoulders free of degenerative arthritis or rotator cuff disease were tested biomechanically to quantitate the contribution of specific capsular structures to restricting anterior-posterior translation of the abducted shoulder. With the glenohumeral joint in 90 degrees of abduction on a servohydraulic control testing system, translation was measured in 30 degrees of forward flexion (with regard to the coronal plane of the scapula), 0 degree, and 30 degrees of extension while a 25 N anterior-posterior load was applied. Measurements were taken both in the intact (vented) shoulder and after selective cutting of different capsuloligamentous structures was performed. In the intact shoulder the largest anterior-posterior translation occurred in 0 degree of horizontal flexion and extension with regard to the scapular plane, with equal amounts of anterior and posterior translation noted. The primary anterior-posterior stabilizer of the abducted shoulder is the inferior glenohumeral ligament complex. The anterior band is the primary stabilizer in 30 degrees of horizontal extension and at 0 degree (neutral). The posterior band is the primary stabilizer in 30 degrees of horizontal flexion. This study quantifies for the first time the normal amount of anterior-posterior translation in the intact cadaveric shoulder model. In addition, it demonstrates the relative role of the anterior and posterior band of the inferior glenohumeral ligament complex in stabilizing the glenohumeral joint at 90 degrees of abduction, where most clinical instability of the shoulder occurs.
Article
One of the primary stabilizing mechanisms of the glenohumeral joint is concavity-compression, the maintenance of the humeral head in the concave glenoid fossa by the compressive force generated by the surrounding muscles. This mechanism is active in all glenohumeral positions but it is particularly important in the functional mid-range, in which the capsule and ligaments are slack. The effectiveness of concavity-compression in the stabilization of a joint can be characterized in terms of the ratio between the maximum dislocating force that can be stabilized in a given direction and the load compressing the head into the glenoid (the stability ratio). Glenoid concavity can be described by the lateral humeral displacement during translation across the glenoid. The purpose of the present investigation was to characterize the concavity and stability ratios of normal cadaveric glenoids, to measure the effect of an anteroinferior chondral-labral defect on these parameters, and to measure the effectiveness of a simulated operative reconstruction on the restoration of glenoid concavity and the stability ratio. The chondral-labral defect created in this study reduced the height of the glenoid by approximately 80 per cent and the stability ratio by approximately 65 per cent for translation in the direction of the defect. Reconstruction of the anteroinferior aspect of the glenoid concavity with use of an autogenous biceps-tendon graft restored normal values for these variables.
Article
The aim of this study was to evaluate the anterior stabilizing factors of the glenohumeral joint over a range of translations. The stabilizers examined included the capsular ligaments, the coracohumeral ligament, the rotator cuff muscles, and the long head of the biceps. Simulated muscle forces were applied to eight shoulder specimens to produce 90 degrees of total elevation of the arm in the scapular plane. Stability, defined as the force required to reach a specified subluxation, then was evaluated under varying configurations of capsule cuts, humeral rotation, and muscular loads. The overall force-displacement relationship of the subluxation was found to increase exponentially in external rotation to 239 N at 10 mm of displacement and to level off in neutral rotation to 172 N at 10 mm of displacement. Among the muscles, the biceps was the most important stabilizer in neutral rotation, providing more than 30 N of stabilization; the subscapularis provided the greatest degree of stabilization in external rotation, increasing to approximately 20 N. The subscapularis and supraspinatus were the most consistently important stabilizers in both types of rotation. In external rotation, the superior, middle, and inferior glenohumeral ligaments were the most effective ligamentous stabilizers, and all provided progressively more stabilization as higher displacements were reached. The stability provided by some of the ligaments reached nearly 50 N at 10 mm of displacement.
Article
We conducted this cadaveric study to define a biomechanical rationale for rotator cuff function in several deficiency states. A dynamic shoulder testing apparatus was used to examine change in middle deltoid muscle force and humeral translation associated with simulated rotator cuff tendon paralyses and various sizes of rotator cuff tears. Supraspinatus paralysis resulted in a significant increase (101%) in the middle deltoid force required to initiate abduction. This increase diminished to only 12% for full glenohumeral abduction. The glenohumeral joint maintained ball-and-socket kinematics during glenohumeral abduction in the scapular plane with an intact rotator cuff. No significant alterations in humeral translation occurred with a simulated supraspinatus paralysis, nor with 1-, 3-, and 5-cm rotator cuff tears, provided the infraspinatus tendon was functional. Global tears resulted in an inability to elevate beyond 25 degrees of glenohumeral abduction despite a threefold increase in middle deltoid force. These results validated the importance of the supraspinatus tendon during the initiation of abduction. Glenohumeral joint motion was not affected when the "transverse force couple" (subscapularis, infraspinatus, and teres minor tendons) remained intact. Significant changes in glenohumeral joint motion occurred only if paralysis or anatomic deficiency violated this force couple. Finally, this model confirmed that rotator cuff disease treatment must address function in addition to anatomy.
Article
The glenohumeral joint relies on static and dynamic contributions of the local soft tissues to maintain joint stability. Dynamic stabilizers consist of the local musculature (the rotator cuff and periscapular muscles), whereas static stabilizers include the glenoid labrum and associated capsuloligamentous components. The functional interaction of static and dynamic components is complex and not completely understood. Selective cutting studies have been done to define the effect of sectioning various static components on resultant glenohumeral translation. These studies have played a pivotal role in the understanding of static factors controlling shoulder stability: the anatomic variability in capsuloligamentous anatomy has been recognized, and the complex interaction among various regions of the shoulder capsule and their labral attachment sites has been shown. Additionally, it has been recognized that the function of the capsuloligamentous restraints is highly dependent on arm position.
Article
The shoulder is characterized foremost by its mobility and large range of motion. The glenohumeral joint is notable for its relative lack of bony constraint, relying heavily on the congruent articulating surfaces and surrounding soft tissue envelope for static and dynamic stability. Effective function in the articulation is achieved by a complex interaction between the various articular and soft tissue restraints. The rotator cuff muscles center the humeral head in the congruent glenoid fossa through the midrange of motion, when the capsuloligamentous structures are lax. However, incongruent joints, especially in positions of loading asymmetry (in external rotation), have larger translations that occur at the extremes of motion. Excessive translations are then effectively restricted by the mechanical properties of the inferior glenohumeral ligament. When the capsule is tightened anteriorly it results in an anterior tether and causes an associated posterior shift in contact on the glenoid. The posterior migration of the humeral head center and glenohumeral contact are again more pronounced in shoulders with reduced congruence. Additional studies of normal motion in different planes, the effects of rotator cuff pathology and dysfunction on the kinematics of the joint, proprioception of the capsule, and biomechanical tests of the inferior glenohumeral ligament and other components of the joint capsule at strain rates associated with injury, need to be conducted to understand the specifics of normal shoulder function and the pathophysiologic processes that occur during shoulder degeneration.
Article
This study evaluates the role of the glenoid labrum and capsule in the prevention of shoulder dislocation. Fifteen shoulder joints from nine fresh cadavers were used. The labrum and capsule were cut into sections 5 mm wide, and the strength of each slice to rupture was measured. The rupture site was observed microscopically. The anterior-inferior portion was the weakest, with a mean force necessary to cause rupture of 3.84 +/- 1.00 kg/5 mm. The rupture site was the portion of the labrum close to the cartilage of the glenoid. Histologic structure and degenerative changes of the labrum did not differ in the anterior to posterior portions. These results show that the anterior-inferior portion of the labrum is relatively weak. This finding may explain the lesion commonly identified in anterior shoulder dislocation.
Article
Efficacious surgical treatment of glenohumeral instability requires a combination of anterior band origin repair and capsuloligamentous plication. The purpose of this article was to determine anterior band of the inferior glenohumeral ligament stretching at the time of glenohumeral failure. Thirteen fresh-frozen cadaver glenohumeral joints were thawed and dissected of soft tissue except for the capsuloligamentous structures. Testing was performed with a material testing system device, simulating the anterior instability apprehension position of the shoulder with 90 degrees of shoulder abduction and the humerus externally rotated until the bicipital groove was aligned with the supraglenoid tubercle. The length of each anterior band of the inferior glenohumeral ligament was obtained, and a variable reluctance transducer was applied to the anterior band midsubstance. Tensile testing at a strain rate of 100%/sec ensued until complete capsular failure occurred. Mid-substance strain of the anterior band of the inferior glenohumeral ligament at the time of capsular failure averaged 7.23% +/- 2.25% (mean +/- SD) with a range of 3.68% to 10.68%. Load to failure was 712.9 +/- 238.2 N (range 363.6 to 1136.9 N). All of the glenohumeral capsules failed at the glenoid origin, simulating a Bankart lesion, except for one that failed at the humeral insertion. When the intact capsuloligamentous tissue of the glenohumeral joint is tensile-tested in the apprehension position, there is only slight anterior band strain and failure occurring, predominantly at the glenoid insertion site. This has implications for the success of surgical procedures designed for acute repair of Bankart lesions.
Article
This study hypothesizes that full-thickness tearing of the rotator cuff can lead to joint instability and that the degree of instability depends on the size and location of the tear. Twelve cadaveric shoulder specimens were divided into two groups: group 1 had a circular tear centered at the critical area, and group 2 had a circular tear centered at the rotator interval. Each group was tested at 2.5 cm and 5 cm tear sizes. Unloaded, and with the arm in 90 degrees flexion and full internal rotation, the humeral head shifted posteriorly. With loading, a large and more anteriorly located defect had the most influence on stability. The tear size had the greatest effect on stability in the inferior direction for group 1 and on the anterior direction for group 2. The tear location had the most significant effect on stability in the inferior and anterior directions for the smaller tear and on the anterior direction for a larger tear.
Article
A Bankart repair is performed to reduce abnormal translations of the humeral head on the glenoid due to a Bankart lesion, a separation of the capsulolabral complex from the glenoid rim. However, this is often accompanied by a loss of rotational range of motion that may lead to decreased function and osteoarthritis. This loss of rotation, coupled to the goal of reducing humeral translations, may be a result of the amount of imbrication of the capsule during repair. To determine the effects of capsular imbrication, we investigated how two Bankart repairs (2.5 and 5.0 mm of capsular imbrication) and a Bankart lesion altered the translations and rotations of the human glenohumeral joint in vitro. Coupled moments were applied to the unconstrained humerus in abduction-adduction, in flexion- extension, and to simulate the cocked phase of throwing. Motion was measured with an electromagnetic system. There were no differences in the kinematics between the intact specimens and those with a Bankart lesion or between normal specimens and the first (2.5 mm) Bankart repair. The first repair significantly reduced external rotation for the cocked phase of throwing compared with the Bankart lesion: from 46.8 ± 23.6°to 32.4 ± 14.2°(±SD). The second (5.0 mm) Bankart repair produced significantly different posterior translation (-4.7 ± 3.9 mm) of the humeral head relative to the glenoid compared with normal (5.1 ± 4.7 mm anterior) and the first repair (6.1 ± 8.3 mm anterior), as the humerus moved from full flexion to full extension. Differences were also found for all rotations in the cocked phase of throwing. For the second repair, the humerus extended 24.3°and externally rotated 18.6°less than normal and was abducted 15.4°more. These results indicate that both Bankart repairs do little to affect humeral translations with unconstrained moment loading but that rotations are affected during the cocked phase of throwing, with significant losses of external and extension rotations.
Article
The shoulder is the most commonly dislocated joint in the body. The primary restraint to anterior instability is the anterior band of the inferior glenohumeral ligament, where lesions are found after dislocation. The amount of surgical plication required to eliminate instability and maintain full range of shoulder motion remains unclear. We performed tensile testing with the shoulder in abduction and external rotation in 11 human, fresh-frozen, cadaveric glenohumeral joints to improve understanding of the glenoid origin of the anterior band of the inferior glenohumeral ligament and to quantify midsubstance irrecoverable elongation. After measuring the length, width, and thickness of the anterior bands with digital micrometry, biomechanical properties were obtained on bone-ligament-labrum-bone (b-l-l-b) complexes. The complexes were aligned for tensile testing with the humerus abducted 60 degrees and externally rotated. The b-l-l-b complexes were then loaded to failure at a strain rate of 100%/sec. Seven of the complexes failed at the glenoid insertion site (representing the Bankart lesion), 2 at the humeral insertion site, and 2 at the anterior band midsubstance. The ultimate load for the b-l-l-b complexes was 353+/-32 N (mean+/-SE), and tensile stress at failure of the glenoid insertion site averaged 9.6+/-2.1 MPa. When the complex failed at the glenoid insertion site, total elongation of the b-l-l-b complex was 9.1+/-0.5 mm, and the ligament midsubstance strain was 13.0%+/-1.8%. Irrecoverable elongation was only 0.8 mm when failure occurred at the glenoid insertion site. Our results indicate patients with initial anterior glenohumeral instability have small irrecoverable capsuloligamentous elongation so that meaningful plication in addition to repair of the Bankart lesion may be unnecessary.
Article
Our objective was to examine the function of the glenohumeral capsule and ligaments during application of an anterior-posterior load by directly measuring the in situ force distribution in these structures as well as the compliance of the joint. We hypothesized that interaction between different regions of the capsule due to its continuous nature results in a complex force distribution throughout the glenohumeral joint capsule. A robotic/universal force-moment sensor testing system was utilized to determine the force distribution in the glenohumeral capsule and ligaments of intact shoulder specimens and the joint kinematics resulting from the application of external loads at four abduction angles. Our results suggest that the glenohumeral capsule carries no force when the humeral head is centered in the glenoid with the humerus in anatomic rotation. However, once an anterior-posterior load is applied to the joint, the glenohumeral ligaments carry force (during anterior loading, the superior glenohumeral-coracohumeral ligaments carried 26+/-16 N at 0 degrees and the anterior band of the inferior glenohumeral ligament carried 30+/-21 N at 90 degrees). Therefore, the patient's ability to use the arm with the humerus in anatomic rotation should not be limited following repair procedures for shoulder instability because the repaired capsuloligamentous structures should not carry force during this motion. Separation of the capsule into its components revealed that forces are being transmitted between each region and that the glenohumeral ligaments do not act as traditional ligaments that carry a pure tensile force along their length. The interrelationship of the glenohumeral ligaments forms the biomechanical basis for the capsular shift procedure. The compliance of the joint under our loading conditions indicates that the passive properties of the capsule provide little resistance to motion of the humerus during 10 mm of anterior or posterior translation with anatomic humeral rotation. Finally, this knowledge also enhances the understanding of arm positioning relative to the portion of the glenohumeral capsule that limits translation during examination under anesthesia.
Article
An osseous defect of the glenoid rim is sometimes caused by multiple recurrent dislocations of the shoulder. It is generally thought that a large defect should be treated with bone-grafting, but there is a lack of consensus with regard to how large a defect must be in order to necessitate this procedure. Some investigators have proposed that a defect must involve at least one-third of the glenoid surface in order to necessitate bone-grafting. However, it is difficult to determine (1) whether a defect involves one-third of the glenoid surface and (2) whether a defect of this size is critical to the stability of the shoulder after a Bankart repair. The purposes of the present study were (1) to create and quantify various sizes of osseous defects of the glenoid and (2) to determine the effect of such defects on the stability and motion of the shoulder after Bankart repair. The glenoids from sixteen dried scapulae were photographed, and the images were scanned into a computer. The average shape of the glenoid was determined on the basis of the scans, and this information was used to design custom templates for the purpose of creating various sizes of osseous defects. Ten fresh-frozen cadaveric shoulders then were obtained from individuals who had been an average of seventy-nine years old at the time of death, and all muscles were removed to expose the joint capsule. With use of a custom multiaxis electromechanical testing machine with a six-degrees-of-freedom load-cell, the humeral head was translated ten millimeters in the anteroinferior direction with the arm in abduction and external rotation as well as in abduction and internal rotation. With a fifty-newton axial force constantly applied to the humerus in order to keep the humeral head centered in the glenoid fossa, the peak force that was needed to translate the humeral head a normalized distance was determined under eleven sequential conditions: (1) with the capsule intact, (2) after the creation of a simulated Bankart lesion, (3) after the capsule was repaired, (4) after the creation of an anteroinferior osseous defect with a width that was 9 percent of the glenoid length (average width, 2.8 millimeters), (5) after the capsule was repaired, (6) after the creation of an osseous defect with a width that was 21 percent of the glenoid length (average width, 6.8 millimeters), (7) after the capsule was repaired, (8) after the creation of an osseous defect with a width that was 34 percent of the glenoid length (average width, 10.8 millimeters), (9) after the capsule was repaired, (10) after the creation of an osseous defect with a width that was 46 percent of the glenoid length (average width, 14.8 millimeters), and (11) after the capsule was repaired. With the arm in abduction and external rotation, the stability of the shoulder after Bankart repair did not change significantly regardless of the size of the osseous defect (p = 0.106). With the arm in abduction and internal rotation, the stability decreased significantly as the size of the osseous defect increased (p<0.0001): the translation force in shoulders in which the width of the osseous defect was at least 21 percent of the glenoid length (average width, 6.8 millimeters) was significantly smaller than the force in shoulders without an osseous defect. The range of external rotation in shoulders in which the width of the osseous defect was at least 21 percent of the glenoid length was significantly less than that in shoulders without a defect (p<0.0001) because of the pretensioning of the capsule caused by closing the gap between the detached capsule and the glenoid rim. The average loss of external rotation was 25 degrees per centimeter of defect. An osseous defect with a width that is at least 21 percent of the glenoid length may cause instability and limit the range of motion of the shoulder after Bankart repair.
Article
Both static and dynamic factors are responsible for glenohumeral joint stability. We hypothesized that dynamic factors could potentially operate throughout the entire range of glenohumeral motion, although capsuloligamentous restraints (a static factor) have been thought to be primarily responsible for stability in the end-range of motion. The purpose of this study was to quantitatively compare the dynamic glenohumeral joint stability in the end-range of motion (the position of anterior instability) with that in the mid-range by investigating the force components generated by the rotator cuff muscles. Ten fresh-frozen shoulders from human cadavera were obtained, and all soft tissues except the rotator cuff were removed. The glenohumeral capsule was resected after the rotator cuff muscles had been released from the scapula. A specially designed frame positioned the humerus in 60 degrees of abduction and 45 degrees of extension with respect to the scapula. The compressive and shear components on the glenoid were measured before and after a constant force was applied individually to each muscle with the humerus in five different positions (from neutral to 90 degrees of external rotation). The dynamic stability index, a new biomechanical parameter reflecting these force components and the concavity-compression mechanism, was calculated. The higher the dynamic stability index, the greater the dynamic glenohumeral stability. In the mid-range of motion, the supraspinatus and subscapularis provided higher dynamic stability indices than did the other muscles (p < 0.05). On the other hand, when the position of anterior instability was simulated in the end-range of motion, the subscapularis, infraspinatus, and teres minor provided significantly higher dynamic stability indices than did the supraspinatus (p < 0.005). The rotator cuff provided substantial anterior dynamic stability to the glenohumeral joint in the end-range of motion as well as in the mid-range. A glenohumeral joint with a lax capsule and ligaments might be stabilized dynamically in the end-range of motion if the glenoid concavity is maintained and the function of the external and internal rotators, which are efficient stabilizers in this position, is enhanced.