No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Anterior referencing of tibial slope in total knee arthroplasty considerably influences knee kinematics: a musculoskeletal simulation study
Abstract
Purpose:
In total knee arthroplasty (TKA), the posterior tibial slope is not always reconstructed correctly, and the knee ligaments may become too tight in flexion. To release a tight flexion gap, surgeons can increase the posterior tibial slope using two surgical resection techniques: the anterior tibial cortex (ACR) or the centre of tibial plateau (CPR) referencing. It is not known how this choice affects the knee laxity and function during activities of daily living. The aim of this study was to investigate the effect of tibial slope on knee laxity, kinematics and forces during a squatting activity using computer simulation techniques. We hypothesised that the effects depend on the referencing technique utilised.
Methods:
A validated musculoskeletal model of TKA was used. Knee laxity tests were simulated in flexion and extension. Then, a squat motion was simulated to calculate: movement of the tibiofemoral joint (TFJ) contact points and patello-femoral joint (PFJ) contact force. All analyses were repeated with more anterior (-3°), neutral (0°), and more posterior tibial slope (+3°, +6°, +9°), and with two referencing techniques (ACR, CPR).
Results:
Knee laxities increased dramatically with more posterior slope with the ACR technique (up to 400%), both in flexion and in extension. The CPR technique, instead, had much smaller effects (up to 42% variations). During squatting, more slope with the ACR technique resulted in larger movements of the TFJ contact point. The PFJ contact force decreased considerably with more slope with the CPR technique (12% body weight reduction every 3° more posterior slope), thanks to the preservation of the patellar height and quadriceps-femur load sharing.
Conclusion:
ACR technique alters considerably the knee laxity, both in flexion and extensions, and surgeons should be cautious about its use. More slope with CPR technique induces more favourable TFJ kinematics and loading of the knee extensor apparatus and does not substantially alter knee laxity. Preferably, the tibial slope resection should be pre-planned thoroughly and performed using CPR technique as accurately as possible. Surgeons can directly translate the results of this study into the clinical practice.
Supplementary resources (2)
... Such in-vivo measurements are ethically not possible. On the other hand, computational studies 18,25,36,38 lack the capability to effectively simulate realistic contact properties. ...
... In line with reported findings 17,18,24,38,64 , an increased tibial slope prevents an excessive load on the implant components during flexion. The relaxing of the collateral ligaments and PCL due to the increased tibial slope is due to the decrease in the distance between the ligament attachments during flexion 64 . ...
... The relaxing of the collateral ligaments and PCL due to the increased tibial slope is due to the decrease in the distance between the ligament attachments during flexion 64 . Our results show that soft tissue structures are unloaded due to increased tibial slopes, which are also in accordance with reported findings 17,18,24,38 . Increasing tibial slope leads to a higher posterior translation of the femoral component in the early-to mid-flexion range (10°-70°), while slightly higher anterior femoral translation was found at higher flexion angles, thus reducing the amount of anterior-posterior translation, which is in excellent agreement with the cadaver study of Dai et al. 22 for the same load case. ...
The complicated interplay of total knee replacement (TKR) positioning and patient-specific soft tissue conditions still causes a considerable number of unsatisfactory outcomes. Therefore, we deployed a robot-assisted test method, in which a six-axis robot moved and loaded a bicondylar cruciate-retaining (CR)-TKR in a virtual lower extremity emulated by a musculoskeletal multibody model. This enabled us to systematically analyse the impact of the posterior cruciate ligament (PCL), tibial slope, and tibial component rotation on TKR function while considering the physical implant components and physiological-like conditions during dynamic motions. The PCL resection yielded a decrease of femoral rollback by 4.5 mm and a reduction of tibiofemoral contact force by 50 N. A reduced tibial slope led to an increase of tibiofemoral contact force by about 170 N and a decrease of femoral rollback up to 1.7 mm. Although a higher tibial slope reduced the contact force, excessive tibial slopes should be avoided to prevent joint instability. Contrary to an external rotation of the tibial component, an internal rotation clearly increased the contact force and lateral femoral rollback. Our data contribute to improved understanding the biomechanics of TKRs and show the capabilities of the robot-assisted test method based on a musculoskeletal multibody model as a preoperative planning tool.
... Many studies on misalignment of components have also used a rigid body bone model (Fig. 7). Such studies have been performed in both FE and MBD models (Essner et al., 2011;Kang et al., 2018a;Kang et al., 2016;Kang et al., 2017f;Kang et al., 2018b;Kang et al., 2018c;Kang et al., 2018e;Kang et al., 2019b;Kang et al., 2018g;Kuriyama et al., 2014;Marra et al., 2018;Suh et al., 2017;Thompson et al., 2011). Investigations have included pre-or post-clinical evaluation for translation and rotation in coronal and sagittal planes. ...
... The surgeon should therefore take care in choosing the PTS in CR-TKAs. Marra et al. investigated the effect of tibial slope on knee laxity, kinematics and forces in squatting activity using computer simulation (Marra, Strzelczak, Heesterbeek, van de Groes, Janssen, Koopman, Wymenga and Verdonschot, 2018). They hypothesized that the effects depend on the referencing technique. ...
Computational models have been widely used for more than four decades to evaluate the mechanical behavior of knee joint arthroplasty. Validated computational models provide a virtual platform to develop optimal articular surfaces which achieve desired implant characteristics. This review paper provides a comprehensive overview of the computational models available to represent knee joint arthroplasty. A brief overview of knee joint anatomy and arthroplasty is provided, followed by computational model development techniques. Use of the computational models in development of knee joint arthroplasty and pre- or post-clinical evaluation is summarized. This review paper presents current modeling capabilities for implant design and stability, with further suggestions for studying the performance of implants on a population level. However, simulations must include closely corroborated multi-domain analysis in order to account for real-life variability.
... These simplified generic and subject-specific models allow for computational convenience; but do not capture the elasticity of the joint. At the other end of the spectrum exists computationally complex, 11-12 DOF multibody contact tibiofemoral models (Guess et al., 2014;Hast and Piazza, 2013;Marra et al., 2017Marra et al., , 2015Smith et al., 2016;Thelen et al., 2014) and finite element models (Adouni et al., 2012;Halonen et al., 2017;Kiapour et al., 2013;Mootanah et al., 2014). ...
... Specifically, the kinematics will remain the same independent of external load, which for some applications may play a role. Complex multibody contact models (Guess et al., 2014;Marra et al., 2017Marra et al., , 2015Smith et al., 2017;Thelen et al., 2014) were established to avoid these limitations; these models are much more computationally expensive and therefore applied on smaller cohorts. Although large improvements were achieved by modeling the TF joint as a moving-axis, creating a linear relationship between EFC and FFC axes may not capture the entire trend. ...
The aims of this study were to introduce and validate a novel computationally-efficient subject-specific tibiofemoral joint model. Subjects performed a quasi-static lunge while micro-dose radiation bi-planar X-rays (EOS Imaging, Paris, France) were captured at roughly 0°, 20°, 45°, 60°, and 90° of tibiofemoral flexion. Joint translations and rotations were extracted from this experimental data through 2D-to-3D bone reconstructions, using an iterative closest point optimization technique, and employed during model calibration and validation. Subject-specific moving-axis and hinge models for comparisons were constructed in the AnyBody Modeling System (AMS) from Magnetic Resonance Imaging (MRI)-extracted anatomical surfaces and compared against the experimental data. The tibiofemoral axis of the hinge model was defined between the epicondyles while the moving-axis model was defined based on two tibiofemoral flexion angles (0° and 90°) and the articulation modeled such that the tibiofemoral joint axis moved linearly between these two positions as a function of the tibiofemoral flexion. Outside this range, the joint axis was assumed to remain stationary. Overall, the secondary joint kinematics (ML: medial-lateral, AP: anterior-posterior, SI: superior-inferior, IE: internal-external, AA: adduction-abduction) were better approximated by the moving-axis model with mean differences and standard errors of (ML: -1.98 ± 0.37 mm, AP: 6.50 ± 0.82 mm, SI: 0.05 ± 0.20 mm, IE: 0.59 ± 0.36°, AA: 1.90 ± 0.79°) and higher coefficients of determination (R2) for each clinical measure. While the hinge model achieved mean differences and standard errors of (ML: -0.84 ± 0.45 mm, AP: 10.11 ± 0.88 mm, SI: 0.66 ± 0.62 mm, IE: -3.17 ± 0.86°, AA: 11.60 ± 1.51°).
... Typically, multibody human models are composed of rigid bodies connected with mechanical joints, representing the passive locomotor apparatus, as well as muscle-tendon models, representing the active locomotor apparatus (Damsgaard et al. 2006). Using force-dependent kinematics (Andersen et al. 2009(Andersen et al. , 2010, these multibody models can be supplemented with detailed artificial joint models to compute joint kinematics as well as muscle, ligament and contact forces (Marra et al. 2018(Marra et al. , 2015. Moissenet et al. (2017) and recently Tomasi et al. (2022) systematically reviewed the state-of-the-art for estimating hip and knee joint loads through musculoskeletal modeling. ...
Fundamental knowledge about in vivo kinematics and contact conditions at the articulating interfaces of total knee replacements are essential for predicting and optimizing their behavior and durability. However, the prevailing motions and contact stresses in total knee replacements cannot be precisely determined using conventional in vivo measurement methods. In silico modeling, in turn, allows for a prediction of the loads, velocities, deformations, stress, and lubrication conditions across the scales during gait. Within the scope of this paper, we therefore combine musculoskeletal modeling with tribo-contact modeling. In the first step, we compute contact forces and sliding velocities by means of inverse dynamics approach and force-dependent kinematic solver based upon experimental gait data, revealing contact forces during healthy/physiological gait of young subjects. In a second step, the derived data are employed as input data for an elastohydrodynamic model based upon the finite element method full-system approach taking into account elastic deformation, the synovial fluid's hydrodynamics as well as mixed lubrication to predict and discuss the subject-specific pressure and lubrication conditions.
... Of all the parameters that define the spatial positioning of the implant, the slope of the tibial component had the greatest effect. Marra et al. [48] demonstrated that increasing the posterior tibial slope up to 9° from neutral, referenced from the center of the tibial plateau, is not detrimental to the post-operative knee function. Surgeons should, however, carefully consider the native tibial slope of the patient when deciding on the appropriate level of slope correction, as excessive slope increase may affect the overall stability of the knee. ...
Robotic-assisted total knee arthroplasty can attain highly accurate implantation. However, the target for optimal positioning of the components remains debatable. One of the proposed targets is to recreate the functional status of the pre-diseased knee. The aim of this study was to demonstrate the feasibility of reproducing the pre-diseased kinematics and strains of the ligaments and, subsequently, use that information to optimize the position of the femoral and tibial components. For this purpose, we segmented the pre-operative computed tomography of one patient with knee osteoarthritis using an image-based statistical shape model and built a patient-specific musculoskeletal model of the pre-diseased knee. This model was initially implanted with a cruciate-retaining total knee system according to mechanical alignment principles; and an optimization algorithm was then configured seeking the optimal position of the components that minimized the root-mean-square deviation between the pre-diseased and post-operative kinematics and/or ligament strains. With concurrent optimization for kinematics and ligament strains, we managed to reduce the deviations from 2.4 ± 1.4 mm (translations) and 2.7 ± 0.7° (rotations) with mechanical alignment to 1.1 ± 0.5 mm and 1.1 ± 0.6°, and the strains from 6.5% to lower than 3.2% over all the ligaments. These findings confirm that adjusting the implant position from the initial plan allows for a closer match with the pre-diseased biomechanical situation, which can be utilized to optimize the pre-planning of robotic-assisted surgery.
... (PGY1 fellow). Knee joint movements in relation to other joints like hip, ankle and foot could in uence TKA surgery outcomes (24). Therefore, TKA simulator should contain mentioned parts. ...
Objective
Surgery simulators have gained popularity in medical education during recent decades especially following COVID-19 pandemics. This study was designed to find the most effective and applicable model for development of total knee arthroplasty surgery simulator.
Method
The protocol of this study is evaluated and confirmed by Tehran university of Medical Sciences research committee (No: 52841-101-1-1400) in March 2021. This is a qualitative study using focus group discussion (FGD) for data gathering. Three FGDs were performed through online platform. Eligible five orthopedics residents, four fellowship trainees, and seven university professors from 3 different university hospitals were interviewed.
Results
The main domains of discussion were the necessity of a TKA simulator, virtual vs. physical model, bone and soft tissue characteristics, and the feedback system. 12% of participants (2 senior residents) said a virtual model has more advantages than a physical one while the other two thought physical model is more applicable. 12% of them (One senior resident and a fellowship trainee) suggested a mixed model would be more useful. The essential parts of the TKA simulator were mainly addressed by fellowship trainees focusing on presence of foot, ankle and hip in the model and inclusion of vital soft tissue elements and ligaments and tendons (especially collateral ligaments). Gap balancing was noticed as a crucial part by 40% of participants (senior residents and fellowships). To improve the simulator, participants suggested that it should have a modular design with sensors to alarm any damage to vital elements and feedbacks given during the procedures.
Conclusion
Through this study, the participants highlighted the most important parts of hard and soft tissues in the model, as well as the fundamental points in designing the TKA simulator.
... The correct direction and thickness of the tibia bone cutting are associated with the success of the operation [1,2]. Proper posterior slope angle (PSA) can achieve the femoral condyle rollback motion [3,4]. The thickness of the medial and lateral tibia bone cutting affects the balance of soft tissue. ...
Background The tibial bone cutting can affect the postoperative mechanical axis (MA), joint function and prosthesis life in total knee arthroplasty (TKA). Traditional intramedullary or extramedullary positioning systems have the possibility of embolization, difficulty in positioning and prolonged operation time. A bone cutting guide block with a fixed posterior slope angle (PSA) also may change the original physiological PSA.
Methods We describe a tibial bone cutting technique with the help of a new tibial bone cutting guide block without a positioning rod. The positioning plate and metal probe were used to determine the PSA and thickness of bone cutting by preoperative X-ray measurement according to the preoperative measurement.
Results The tibial bone cutting block without guide rod can keep the physiological PSA, reduce the error and operating time of the traditional positioning method in surgery.
Conclusion This technique may be a good option for TKA patients, especially those with tibial deformities.
Trial registration: retrospectively registered
... Contrary to our expectations, the PF compressive force slightly decreased with 2 mm and 4 mm greater PE insert thickness, compared to the reference case, and this change was more perceivable from mid-flexion to 90 • . This is in agreement with the findings of a previous study [32] and might be explained by quadriceps-femur load sharing as the quadriceps wraps around the distal femur in a flexed knee position. This mechanism is also reflected in the PF kinematics. ...
The thickness of the tibial polyethylene (PE) insert is a critical parameter to ensure optimal soft-tissue balancing in the intraoperative decision-making procedure of total knee arthroplasty (TKA). However, there is a paucity of information about the kinetic response to PE insert thickness variations in the tibiofemoral (TF) joint, and subsequently, the secondary effects on the patellofemoral (PF) biomechanics. Therefore, the purpose of this study was to investigate the influence of varying PE insert thickness on the ligament and TF compressive forces, as well as on the PF forces and kinematics, after a cruciate-retaining TKA. A previous patient-specific musculoskeletal model of TKA was adapted to simulate a chair-rising motion in which PE insert thickness was varied with 2 mm increments or decrements compared to the reference case (9 mm), from 5 mm up to 13 mm. Greater PE insert thickness resulted in higher ligament forces and concurrently increased the TF compressive force by 21% (13 mm), but slightly unloaded the PF joint with 7% (13 mm) while shifting the patella distally in the trochlear groove, compared to the reference case. Thinner PE inserts showed an opposite trend. Our findings suggest that the optimal PE insert thickness selection is a trade-off between the kinetic outcomes of the TF and PF joints.
... In terms of implementation, they have differences that affect performance and how easy it is to extend with new mechanical elements, etc., but this discussion is beyond scope of this chapter. Both FDK and COMAK have been applied for several recent studies Marra et al., 2015Marra et al., , 2018Smith et al., 2019;Brandon et al., 2017;Halonen et al., 2017) that have clearly demonstrated the advantages of being able to include these rather advanced joint models within the simulations of musculoskeletal models. ...
In this chapter, we introduce musculoskeletal modelling and how such models can be applied to estimate internal quantities that are difficult or impossible to measure experimentally such as muscle, joint, and ligament forces. We briefly introduce the different simulation approaches available before we go through an inverse dynamics approach in detail, describing how to perform kinematic and kinetic analysis and the underlying models of bones, joints, and muscles. For kinetic analysis, we cover the topic of muscle recruitment, which is required to handle the so-called underdeterminacy problem within the model. We also briefly introduce the Force-dependent Kinematics (FDK) simulation approach as an extension to inverse dynamics and describe how it enables advanced models of joints.
After the theoretical framework has been established, we describe how cadaver-based template models are created and how they are made subject-specific depending on the available data. Finally, we introduce a few model applications to show the diverse possibilities these models offer.
... Imbalance of the soft tissues has been acknowledged as an important factor affecting the clinical outcomes [15,22]. Precise bony resection and correct implant positioning have been investigated to improve the gap balancing [19,20]. Recent studies have reported that contemporary TKAs could not maintain gap balance in the full range flexion of the knee [6,22]. ...
Purpose:
It is a challenge to evaluate the maintenance of medial and lateral soft tissue balance in total knee arthroplasty (TKA). This study aimed to determine the "isoheight" points and the "isoheight" axis (IHA) that can measure constant medial/lateral condyle heights during flexion of the knee, and compare the IHA with two major anatomical axes, the transepicondylar axis (TEA) and the geometric center axis (GCA).
Methods:
Twenty-two healthy human knees were imaged using a combined MRI and dual fluoroscopic imaging system while performing a single-legged lunge (0°-120°). The isoheight points of the medial and lateral femoral condyles were defined as the locations with the least amount of changes in heights during the knee flexion; an IHA is the line connecting the medial and lateral isoheight points. The measured changes of the condyle heights using the IHA were compared with those measured using the TEA and GCA.
Results:
Overall, the IHA was posterior and distal to the TEA, and anterior to the GCA. The isoheight points measured condyle height changes within 1.2 ± 2.3 mm at the medial and 0.7 ± 3.3 mm at the lateral sides during the knee flexion. Between 0° and 45°, the condyle height changes measured using the GCA (medial: 3.0 ± 1.8 mm, lateral: 2.3 ± 2.0 mm) were significantly larger than those of the IHA and the TEA (p < 0.05). Between 90° and 120°, the changes of the condyle heights measured using the TEA (medial: 5.3 ± 1.8 mm, lateral: 3.3 ± 1.8 mm) were significantly larger than those of the IHA and GCA (p < 0.05).
Conclusion:
There are isoheight points in the medial and lateral femoral condyles that can measure constant heights along the full range of knee flexion and could be used to formulate an "isoheight" axis (IHA) of the femur. The condyle height changes measured by the TEA and GCA were greater than the IHA measurements along the flexion path. These data could be used as a valuable reference to evaluate the condyle height changes after TKA surgeries and help achieve soft tissue balance and optimal knee kinematics along the flexion path.
Level of evidence:
IV.
... However, this study showed that a more femoral component flexion loosens the TF joint in flexion. Interestingly, an increase [56]. Such a trend can also be found in increased posterior tibial slope in which a contact point can be positioned posteriorly [42,54]. ...
Background:
Recently, there has been increasing interest in mobile-bearing total knee arthroplasty (TKA). However, changes in biomechanics with respect to femoral component alignment in mobile-bearing TKA have not been explored in depth. This study aims to evaluate the biomechanical effect of sagittal alignment of the femoral component in mobile-bearing TKA.
Methods:
We developed femoral sagittal alignment models with - 3°, 0°, 3°, 5°, and 7°. We also examined the kinematics of the tibiofemoral (TF) joint, contact point on the TF joint, contact stress on the patellofemoral (PF) joint, collateral ligament force, and quadriceps force using a validated computational model under a deep-knee-bend condition.
Results:
Posterior kinematics of the TF joint increased as the femoral component flexed. In addition, contact stress on the PF joint, collateral ligament force, and quadriceps force decreased as the femoral component flexed. The results of this study can assist surgeons in assessing risk factors associated with femoral component sagittal alignment for mobile-bearing TKA.
Conclusions:
Our results showed that slight flexion implantation may be an effective alternative technique because of its advantageous biomechanical effect. However, excessive flexion should be avoided because of potential loosening of the TF joint.
... Posterior tibial slope (PTS) was another essential characteristic in prostheses design and posterior angle of tibial osteotomy in TKA. [15,[21][22][23][24][25][26][27] Inadequate posterior angle of osteotomy would lead to narrow posterior gap and limited postoperative ROM. Although there was no widely accepted angle of tibial osteotomy, angle between 0°and 7°was generally recommended in worldwide. ...
Tibial component of total knee arthroplasty (TKA) is designed according to morphology of proximal tibia to a large extent. Owing to racial difference, current design of tibial component based on Caucasian may not be suitable for Chinese patients. Meanwhile, data of proximal tibial morphology in Chinese population is lacking. The objective of this research was to investigate proximal tibial morphology of northeast Chinese population.
Computer tomography (CT) image of 164 northeast Chinese participants was collected. After three-dimensional (3D) reconstruction, size of tibia plateau and TKA resected surface were gauged to guide the design of TKA tibia prothesis in northeast Chinese population. Measurement of tibial size mainly includes tibial mediolateral length (tML), tibial medial/lateral anteroposterior length (tMAP and tLAP). Afterwards, tML/tAP ratio of tibia plateau and TKA resected surface were calculated as feature point of tibia prothesis. tMAP/tLAP ratio of TKA resected surface was calculated to represent tibial asymmetry degree. Medial and lateral posterior tibial slope (MPTS and LPTS) were also measured to give reference to posterior angle of tibia prothesis and angle of tibia osteotomy in TKA. Independent sample t test was performed to conduct statistical analysis, P < .05 was regarded as statistically significance.
Northeast Chinese male has larger knee size than female. Significant difference of tML/tAP ratio was also observed between male and female on tibia plateau (1.71 ± 0.07 vs 1.77 ± 0.09) but not on TKA resected surface (1.60 ± 0.05 versus 1.61 ± 0.06). Significant difference of tMAP/tLAP ratio between male and female was also found and they were 1.31 ± 1.03 and 1.11 ± 0.05 respectively. Northeast Chinese female has higher PTS than male (MPTS: 9.56 ± 2.96° vs 8.81 ± 2.87° and LPTS: 8.57 ± 3.19° vs 8.44 ± 2.76°).
Significant gender-difference of tibial size and asymmetry degree of tibial resected surface were found between northeast Chinese male and female. Meanwhile, northeast Chinese population has smaller knee size, larger PTS and tML/tAP ratio than that of Caucasian population. Therefore, Chinese-specific and gender-specific tibial prostheses were strongly recommended to be designed.
... The patellofemoral joint is often excluded from pure kinematic models [13] ; however when it is included, it is frequently modeled as a 1 degree-of-freedom hinge joint with an additional rigid patella tendon [14][15][16][17][18][19][20][21][22] which may not provide realistic joint kinematics. In hopes of achieving more realistic joint kinematics, researchers have included a 6 degrees-of-freedom patellofemoral joint utilizing multi-body contact models [17,[23][24][25][26][27][28][29][30][31] . The main advantage of these models is that they can capture contact and ligaments forces; however, they may be too computationally slow for clinical applications. ...
The main objectives of this study were to expand the moving-axis joint model concept to the patellofemoral joint and evaluate the patellar motion against experimental patellofemoral kinematics. The experimental data was obtained through 2D-to-3D bone reconstruction of EOS images and segmented MRI data utilizing an iterative closest point optimization technique. Six knee model variations were developed using the AnyBody Modeling System and subject-specific bone geometries. These models consisted of various combinations of tibiofemoral (hinge, moving-axis, and interpolated) and patellofemoral (hinge and moving-axis) joint types. The newly introduced interpolated tibiofemoral joint is calibrated from the five EOS quasi-static lunge positions. The patellofemoral axis of the hinge model was defined by performing surface fits to the patellofemoral contact area; and the moving-axis model was defined based upon the position of the patellofemoral joint at 0° and 90° tibiofemoral-flexion. In between these angles, the patellofemoral axis moved linearly as a function of tibiofemoral-flexion, while outside these angles, the axis remained fixed. When using a moving-axis tibiofemoral joint, a hinge patellofemoral joint offers (-5.12 ± 1.23 mm, 5.81 ± 0.97 mm, 14.98 ± 2.30°, -4.35 ± 1.95°) mean differences (compared to EOS) while a moving-axis patellofemoral model provides (-2.69 ± 1.04 mm, 1.13 ± 0.80 mm, 12.63 ± 2.03°, 1.74 ± 1.46°) in terms of lateral-shift, superior translation, patellofemoral-flexion, and patellar-rotation, respectively. Furthermore, the model predictive capabilities increased as a direct result of adding more calibrated positions to the tibiofemoral model (hinge-1, moving-axis-2, and interpolated-5). Overall, a novel subject-specific moving-axis patellofemoral model has been established; that produces realistic patellar motion and is computationally fast enough for clinical applications.
... Given the results of the present study, delta angles of~88°(TKA/SPR) equal an actual slope of 5°whereas~93°(TKA) equal an actual slope of 0°. Biomechanical and kinematic results by Marra et al. [36] indicate a gradual significant reduction in patellofemoral contact forces with a slope increase from − 3°t o 9°. This leads to the assumption that insufficient patellar tracking (and thus tilting) may contribute more to the development of anterior knee pain and subsequent SPR than does sheer peak contact force. ...
Purpose Patellar resurfacing (PR) in total knee arthroplasty (TKA) is still one of the major controversies in orthopaedic surgery today. The aim of the present retrospective case-control study was to identify predictors for secondary patellar resurfacing (SPR) after initial TKA to create a rationale for surgeons to decide which patients to resurface primarily. It was hypothesized that proper TKA implantation and component positioning as well as a maintained physiological patellar geometry will lead to a reduced risk of SPR. Overmore, it was hypothesized that intrinsic factors like overweight might also have an influence on the need for SPR. Methods After identification of suitable patients and age/sex matching in a 1:2 fashion, 29 cases (TKA/SPR) and 58 controls (TKA) were included and screened for available clinical and epidemiological data as well as for radiographic data after primary TKA. Pearson’s correlation analysis as well as logistic regression modeling was performed to identify possible predictors for SPR following TKA.
Results Binary logistic regression was able to correctly classify 88.5% of patients into case or control groups. It indicated that patella tilt, patella height, and thickness as well as the delta angle were significant predictors of a need for SPR following primary TKA. An increase in patellar width by 1 mm will increase the risk of SPR, while an increase in patellar thickness by 1 mm will reduce it. An increase in patellar tilt by 1° will also increase the risk of SPR. Finally, an increase in delta angle by 1° will again reduce the risk of SPR.
Conclusions Easy and accessible radiographic measurements have been identified as possible predictors of SPR following primary TKA. Although indication for primary PR may still remain a controversial topic, a rationale has been proposed in this study to support surgeons in objectively estimating an individual patient’s risk for SPR prior to primary TKA measuring the patella tilt, width, and thickness. Overmore, regarding surgical aspects of TKA, tibial component positioning has also been shown to be of importance to reduce the risk of SPR.
A small posterior tibial slope (PTS) is generally recommended in posterior stabilized (PS) total knee arthroplasty (TKA). An unwanted anterior tibial slope (ATS), which can affect postoperative results, may be created in PS TKA because of the inaccuracy of surgical instruments and techniques, as well as high inter-patient variability. We compared mid-term clinical and radiographic results of PS TKAs with ATS and PTS performed on paired knees using the same prosthesis. One-hundred-twenty-four patients who underwent TKAs with ATS and PTS on paired knees using ATTUNE® posterior-stabilized prostheses were retrospectively reviewed after a minimum follow-up period of 5 years. The mean follow-up period was 5.4 years. The Knee Society Knee and Function scores, Western Ontario and McMaster Universities Osteoarthritis Index, Feller and Kujalar scores, and range of motion (ROM) were evaluated. The preferred TKA out of ATS and PTS was also investigated. The hip-knee-ankle angle (HKA), component positions, tibial slope, posterior femoral offset (PFO), Insall–Salvati ratio (ISR), and knee sagittal angle were measured by radiography. There were no significant differences in the clinical results, including ROM, between TKAs with ATS and PTS preoperatively and at the last follow-up. Regarding patient preference, 58 patients (46.8%) were satisfied with bilateral knees, 30 (24.2%) preferred knees with ATS, and 36 (29%) preferred knees with PTS. There was no significant difference in the rate of preference between TKAs with ATS and PTS (p=0.539). Except for the postoperative tibial slope (-1.8° vs. 2.5°, p<0.001), there were also no significant differences in the radiographic results, including the knee sagittal angle, preoperatively and at the last follow-up. The mid-term outcomes were similar between PS TKAs with ATS and PTS performed on paired knees at a minimum of 5 years of follow-up. Non-severe ATS did not affect mid-term outcomes in PS TKA with proper soft tissue balancing and the current prosthesis of improved design. However, a long-term follow-up study is required to confirm the safety of non-severe ATS in PS TKA.
Background:
Recently, there has been an increasing interest in mobile-bearing total knee arthroplasty (TKA). However, changes in biomechanics for femoral component alignment in mobile-bearing TKA have not been explored in depth.
Objective:
This study aims to evaluate the biomechanical effect of sagittal alignment of the femoral component in mobile-bearing TKA.
Methods:
We developed femoral sagittal alignment models with -3°, 0°, 3°, 5°, and 7° flexion. We also examine the kinematics of the tibiofemoral (TF) joint, contact point on the TF joint, contact stress on the patellofemoral (PF) joint, collateral ligament force, and quadriceps force using a validated computational model under a deep-knee-bend condition.
Results:
Posterior kinematics of the TF joint increases as the femoral component flexes. The contact stress on the PF joint, collateral ligament force, and the quadriceps force decreases as the femoral component flexes.
Conclusions:
Our results show that a slight, approximately 0°∼3°, flexion of the implantation could be an effective substitute technique. However, excessive flexion should be avoided because of the potential loosening of the TF joint.
The purposes of this study were to develop a cruciate-retaining total knee arthroplasty musculoskeletal model, which enables the adjustment of ligament length and implant alignment; validate the model; and evaluate the effects of varus/valgus alignment adjustment and unbalanced medial/lateral ligament laxity during gait. A cruciate-retaining total knee arthroplasty musculoskeletal model was constructed and validated against the in vivo contact forces. This model was transformed to 2° varus/valgus alignment of femoral or tibial replacement models and 2° medial/lateral laxity models. The contact forces and ligament tensions of the adjusted models were calculated. The contact forces in the model showed good agreement with the in vivo contact forces. Valgus replacement alignment with balanced ligament models showed a lower contact force at the medial compartment than at the neutral alignment model, whereas the varus replacement alignment with balanced ligament models showed a greater contact force at the medial compartment and medial/posterior cruciate ligament tension. The medial laxity with neutral alignment model showed a similar contact force with decreased medial ligament tension compared to the balanced neutral alignment model, whereas the lateral laxity with the neutral alignment model showed a greater contact force and decreased lateral ligament tension. The cruciate-retaining total knee arthroplasty model was validated using in vivo contact forces ( r = 0.939) Two degrees of valgus alignment adjustment with balanced ligament or neutral alignment with 2° of medial laxity can be safe without increasing contact force or ligament tension compared to neutral alignment with a balanced extension gap. However, 2° of varus alignment adjustment with balanced ligament or neutral alignment with 2° of lateral laxity may be unfavorable due to the overloading of the joints and knee ligaments.
PurposeTo investigate factors contributing to the de novo hyperextension after posterior cruciate ligament substituting (PS) total knee arthroplasty (TKA).Methods
Through a retrospective case–control study, de novo hyperextension patients were compared with patients without hyperextension after primary PS TKA. Eighty-five hyperextension patients were compared with 85 patients in a control group matched by age, sex, surgeon and implant. The clinical and radiographic parameters, including the mechanical axis (MA), joint line convergence angle (JLCA), posterior tibial slope angle (PTSA), posterior condylar offset (PCO), and the gamma angle, were evaluated preoperatively and immediate postoperatively. Comparisons between the two groups and logistic regression analysis were performed to investigate factors contributing to de novo hyperextension.ResultsAmong the clinical factors, preoperative flexion contracture was less (5° ± 6° vs. 11° ± 6°, p < 0.001) and the range of motion was greater (125° ± 12° vs. 118° ± 5°, p = 0.041) in the de novo hyperextension group than in the control group. Among the radiographic parameters, preoperative and postoperative JLCA were greater (8.1° ± 4.4° vs. 6.1° ± 3.5°, p < 0.001, 1.0° ± 1.3° vs. 0.2° ± 0.8°, p = 0.002, respectively), postoperative PTSA was greater (3.7° ± 2.0° vs. 3.3° ± 1.6°, p < 0.001) and preoperative and postoperative PCO were less in the hyperextension group than in the control group (26.3 mm ± 3.3 mm vs. 29.1 mm ± 3.2 mm, p < 0.001, 26.4 mm ± 3.2 mm vs. 29.1 mm ± 3.0 mm, p < 0.001, respectively), whereas, change in PCO was greater in the hyperextension group (1.1 mm ± 7.7 mm vs. − 0.1 mm ± 3.3 mm, p < 0.001). In multivariate analysis, the degree of medial soft tissue release [odds ratio (OR) 2.83, p = 0.003], flexion contracture [OR 0.86, p = 0.028], postoperative JLCA [OR 2.45, p = 0.004], preoperative PCO and a change in PCO [OR 0.74, p = 0.002, OR 1.89, p = 0.001, respectively] were the factors associated with de novo hyperextension.Conclusions
An increased degree of medial soft tissue release, small preoperative flexion contracture, increased postoperative JLCA, decreased preoperative PCO and increased change in PCO were risk factors of de novo hyperextension.Level of evidenceIII.
Das funktionelle Zusammenspiel von knöchernen und ligamentären Strukturen ist für die postoperative Biomechanik und Standzeit von Kniegelenkendoprothesen von herausragender Bedeutung. Trotz aller technischen Fortschritte und wissenschaftlichen Bemühungen ist aktuell unzureichend geklärt, welche Bedeutung der komplexen Anatomie des Tibiaplateaus und insbesondere ihrer dorsalen Inklination (tibialer Slope) in der Knieendoprothetik zugeschrieben werden soll. Vor diesem Hintergrund erfolgte die Auswertung, kritische Auseinandersetzung und Darstellung der gegenwärtigen wissenschaftlichen Datenlage. Der tibiale Slope nimmt Einfluss auf den postoperativen Bewegungsumfang, die Funktion des Streckapparat sowie Abrieb, Lockerung und Instabilität der Kniegelenkendoprothese. Die Literaturlage ist jedoch äußerst heterogen und Empfehlungen für einen optimalen tibialen Slope reichen von 0° bis 10°. Allerdings gibt es in den letzten Jahren zunehmend Bestrebungen, den präoperativen tibialen Slope zu rekonstruieren. Allen Studien ist gemein, dass bereits eine präoperative Auseinandersetzung mit dem tibialen Slope empfohlen wird.
Background
The effect of the changes in the femoral posterior condylar offset (PCO) on anterior–posterior (AP) translation and internal–external (IE) rotation in cruciate-retaining (CR) and posterior-stabilized (PS) total knee arthroplasty (TKA) remains unknown. The purpose of this study was to compare the kinematics in CR and PS TKA with respect to the difference in prosthetic design and PCO change through a computational simulation.
Methods
We developed three-dimensional finite element models with the different PCOs of ± 1, ± 2 and ± 3 mm in the posterior direction using CR and PS TKA. We performed the simulation with different PCOs under a deep knee bend condition and evaluated the kinematics for the AP and IE in CR and PS TKA.
Results
The more tibiofemoral (TF) translation in the posterior direction was found as PCO translated in posterior direction for both CR and PS TKA compared to the neutral position. However, the change of the AP translation with respect to the PCO change in CR TKA was greater than PS TKA. The more TF external rotation was found as PCO translated in the anterior direction for both CR and PS TKA compared to the neutral position. However, unlike the TF translation, the TF rotation was not influenced by the PCO change in both CR and PS TKA.
Conclusion
The PCO magnitude was influenced by a postoperative change in the kinematics in CR TKA although a relatively smaller effect was observed in PS TKA. Hence, surgeons should be aware of the PCO change, especially for CR TKA.
Background:
Postoperative changes of the femoral posterior condylar offset (PCO) and posterior tibial slope (PTS) affect the biomechanics of the knee joint after fixed-bearing total knee arthroplasty (TKA). However, the biomechanics of mobile-bearing is not well known. Therefore, the aim of this study was to investigate whether alterations to the PCO and PTS affect the biomechanics for mobile-bearing TKA.
Methods:
We used a computational model for a knee joint that was validated using in vivo experiment data to evaluate the effects of the PCO and PTS on the tibiofemoral (TF) joint kinematics, patellofemoral (PF) contact stress, collateral ligament force and quadriceps force, for mobile-bearing TKA. The computational model was developed using ±1-, ±2- and ±3-mm PCO models in the posterior direction and -3°, 0°, +3°, and +6° PTS models based on each of the PCO models.
Results:
The maximum PF contact stress, collateral ligament force and quadriceps force decreased as the PTS increased. In addition, the maximum PF contact stress and quadriceps force decreased, and the collateral ligament force increased as PCO translated in the posterior direction. This trend is consistent with that observed in any PCO and PTS.
Conclusions:
Our findings show the various effects of postoperative alterations in the PCO and PTS on the biomechanical results of mobile-bearing TKA. Based on the computational simulation, we suggest that orthopaedic surgeons intraoperatively conserve the patient's own anatomical PCO and PTS in mobile-bearing TKA.
Purpose:
This study aims to clarify the influence of the posterior tibial slope (PTS) on knee joint biomechanics after posterior-stabilized (PS) total knee arthroplasty (TKA) using a computer simulation.
Methods:
A validated TKA computational model was used to evaluate and quantify the effects of an increased PTS. In order to conduct a squat simulation, models with a - 3° to 15° PTS using increments of 3° were developed. Forces on the quadriceps and collateral ligament, a tibial posterior translation, contact point on a polyethylene (PE) insert, and contact stress on the patellofemoral (PF) joint and post in a PE insert were compared.
Results:
The maximum force on the quadriceps and the PF contact stress decreased with increases in the PTS. The kinematics on the tibiofemoral (TF) joint translated in an increasingly posterior manner, and the medial and lateral contact points on a PE insert were located in posterior regions with increases in the PTS. Additionally, increases in the PTS decreased the force on the collateral ligament and increased the contact stress on the post in a PE insert. A higher force on the quadriceps is required when the PTS decreases with an equivalent flexion angle.
Conclusions:
A surgeon should be prudent in terms of determining the PTS because an excessive increase in the PTS may lead to the progressive loosening of the TF joint due to a reduction in collateral ligament tension and failure of the post in a PE insert. Thus, we support a more individualized approach of optimal PTS determination given the findings of the study.
PurposePosterior tibial slope (PTS) for cruciate-retaining (CR) total knee arthroplasty (TKA) is usually pre-determined by the surgeon. Limited information is available comparing different choices of PTS on the kinematics of the CR TKA, independent of the balancing of the extension gap. This study hypothesized that with the same balanced extension gap, the choice of PTS significantly impacts the intraoperatively measured kinematics of CR TKA. Methods
Navigated CR TKAs were performed on seven fresh-frozen cadavers with healthy knees and intact posterior cruciate ligament (PCL). A custom designed tibial baseplate was implanted to allow in situ modification of the PTS, which altered the flexion gap but maintained the extension gap. Knee kinematics were measured by performing passive range of motion (ROM) tests from full extension to 120° of flexion on the intact knee and CR TKAs with four different PTSs (1°, 4°, 7°, and 10°). The measured kinematics were compared across test conditions to assess the impact of PTS. ResultsWith a consistent extension gap, the change of PTS had significant impact on the anteroposterior (AP) kinematics of the CR TKA knees in mid-flexion range (45°–90°), but not so much for the high-flexion range (90°–120°). No considerable impacts were found on internal/external (I/E) rotation and hip–knee–ankle (HKA) angle. However, the findings on the individual basis suggested the impact of PTS on I/E rotation and HKA angle may be patient-specific. Conclusions
The data suggested that the choice of PTS had the greatest impact on the mid-flexion AP translation among the intraoperatively measured kinematics. This impact may be considered while making surgical decisions in the context of AP kinematics. When using a tibial component designed with “center” pivoting PTS, a surgeon may be able to fine tune the PTS to achieve proper mid-flexion AP stability.
Background:
The reconstructed posterior tibial slope (PTS) plays a significant role in restoring knee kinematics in cruciate-retaining-total knee arthroplasty (TKA). A few studies have reported the effect of the PTS on biomechanics.
Methods:
This study investigates the effect of the PTS on tibiofemoral (TF) kinematics, patellofemoral (PF) contact stress, and forces at the quadriceps, posterior cruciate ligament (PCL) and collateral ligament after cruciate-retaining-TKA using computer simulations. The simulation for the validated TKA finite element model was performed under deep knee bend condition. All analyses were repeated from -3° to 15° PTS in increments of 3°.
Results:
The kinematics on the TF joint translated increasingly posteriorly when the PTS increased. Medial and lateral contact points translated in posterior direction in extension and flexion as PTS increased. The maximum contact stress on the PF joint and quadriceps, and collateral ligament force decreased when the PTS increased. An implantation of the tibial plate with increased PTS reduced the PCL load. Physiologic insert movement led to an increasingly posterior position of the femur and reduced quadriceps force especially for knee flexion angles above high flexion (120°) when compared to TKA with a decreased slope of the tibial base plate.
Conclusion:
An increase in the PTS increased medial and lateral movements without paradoxical motion. However, an excessive PTS indicated progressive loosening of the TF joint gap due to a reduction in collateral ligament tension during flexion.
When analyzing complex biomechanical problems such as predicting the effects of orthopedic surgery, subject-specific musculoskeletal models are essential to achieve reliable predictions. The aim of this paper is to present the Twente Lower Extremity Model 2.0, a new comprehensive dataset of the musculoskeletal geometry of the lower extremity, which is based on medical imaging data and dissection performed on the right lower extremity of a fresh male cadaver. Bone, muscle and subcutaneous fat (including skin) volumes were segmented from computed tomography and magnetic resonance images scans. Inertial parameters were estimated from the image-based segmented volumes. A complete cadaver dissection was performed, in which bony landmarks, attachments sites and lines-of-action of 55 muscle actuators and 12 ligaments, bony wrapping surfaces, and joint geometry were measured. The obtained musculoskeletal geometry dataset was finally implemented in the AnyBody Modeling System™ (AnyBody Technology A/S, Aalborg, Denmark), resulting in a model consisting of 12 segments, 11 joints and 21 degrees of freedom, and including 166 muscle-tendon elements for each leg. The new TLEM 2.0 dataset was purposely built to be easily combined with novel image-based scaling techniques, such as bone surface morphing, muscle volume registration and muscle-tendon path identification, in order to obtain subject-specific musculoskeletal models in a quick and accurate way. The complete dataset, including CT and MRI scans and segmented volume and surfaces, is made available at http://www.utwente.nl/ctw/bw/research/projects/TLEMsafe for the biomechanical community, in order to accelerate the development and adoption of subject-specific models on large scale. TLEM 2.0 is freely shared for non-commercial use only, under acceptance of the TLEMsafe Research License Agreement.
Copyright © 2014 Elsevier Ltd. All rights reserved.
Background
Adjusting the joint gap length to be equal in both extension and flexion is an important issue in total knee arthroplasty (TKA). It is generally known that posterior tibial slope would affect the flexion gap, however, the extent to which changes in the tibial slope angle directly affect the flexion gap remains unclear. This study aimed to clarify the influence of tibial slope changes on the flexion gap in cruciate-retaining (CR) or posterior stabilizing (PS) TKA.
Methods
The flexion gap was measured using a tensor device with the femoral trail component in 20 cases each of CR- and PS-TKA. A wedge plate with a 5° inclination was placed on the tibial cut surface by switching its front–back direction to increase or decrease the tibial slope by 5°. The flexion gap in changing the tibial slope was compared to that of the neutral slope measured with a flat plate that had the same thickness of the wedge plate center.
Results
When the tibial slope decreased or increased by 5°, the flexion gap decreased or increased by 1.9 ± 0.6 mm or 1.8 ± 0.4 mm, respectively, with CR-TKA and 1.2 ± 0.4 mm or 1.1 ± 0.3 mm, respectively, with PS-TKA.
Conclusions
The influence of changing the tibial slope by 5° on the flexion gap was approximately 2 mm with CR-TKA and 1 mm with PS-TKA.
Clinical relevance
This information is useful to consider the effect of manipulating the tibial slope on the flexion gap when performing CR- or PS-TKA.
Level of Evidence: Level III
The quadriceps mechanism consists of the patellar ligament distally and the quadriceps tendon proximally. The quadriceps tendon is the confluence of the tendinous portions of the vastus medialis, vastus lateralis, vastus intermedius, and rectus femoris. Lieb and Perry (J. Bone Joint Surg. 50A:1535–1547, 1968) have described the vastus medialis obliquus (VMO) and Hallisey et al. (J. Bone Joint Surg. 69A:545–549, 1987) have described the vastus lateralis obliquus (VLO). These muscles are the terminal medial and lateral insertions of the vastus medialis and vastus lateralis. This study delineates and quantifies anatomic sex differences for the medial and lateral angular terminal insertions of the vastus lateralis obliquus and vastus medialis obliquus in relationship to the longitudinal axis of the patella in 40 embalmed cadaver knees. A mathematical model is developed and discussed using least steps regression equations y = Ax + B, where y = the VLO insertion angle, x = the VMO insertion angle, A = the coefficients, and B = the y intercept. These equations are different in males and females, with males having more horizontally oriented VLO fibers than females. The vastus lateralis obliquus (VLO) insertion angle can be predicted based upon measurement of the vastus medialis obliquus insertion angle and sex: Log VLO = 1.36 + .00531 VNIO − 0.000166 (S × VMO), where S = 1 for females and S = 0 for males. In embalmed cadaver knees, the angular terminal insertion of the vastus lateralis obliquus related to the longitudinal axis of the patella is more horizontally oriented in males than in females. The angular terminal insertion of the vastus medialis obliquus of males and females does not increase equally with increases in the angular terminal insertion of the vastus lateralis obliquus. © 1993 Wiley-Liss, Inc.
Impairment of the human neuromusculoskeletal system can lead to significant mobility limitations and decreased quality of life. Computational models that accurately represent the musculoskeletal systems of individual patients could be used to explore different treatment options and optimize clinical outcome. The most significant barrier to model-based treatment design is validation of model-based estimates of in vivo contact and muscle forces. This paper introduces an annual ‘‘Grand Challenge Competition to Predict In Vivo Knee Loads’’ based on a series of comprehensive publicly available in vivo data sets for evaluating musculoskeletal model predictions of contact and muscle forces in the knee. The data sets come from patients implanted with force-measuring tibial prostheses. Following a historical review of musculoskeletal modeling methods used for estimating knee muscle and contact forces, we describe the first two data sets used for the first two competitions and summarize four subsequent data sets to be used for future competitions. These data sets include tibial contact force, video motion, ground reaction, muscle EMG, muscle strength, static and dynamic imaging, and implant geometry data. Competition participants create musculoskeletal models to predict tibial contact forces without having access to the corresponding in vivo measurements. These blinded predictions provide an unbiased evaluation of the capabilities and limitations of musculoskeletal modeling methods. The paper concludes with a discussion of how these unique data sets can be used by the musculoskeletal modeling research community to improve the estimation of in vivo muscle and contact forces and ultimately to help make musculoskeletal models clinically useful.
There are two different techniques for retaining the posterior cruciate ligament (PCL) in total knee arthroplasty. The attachment of the PCL can be spared during resection of the tibial plateau, so that a small posterior bone block remains. In contrast to this, many surgeons resect the tibial plateau completely and detach a part of the tibial PCL attachment from the resected material. The objective of this study was to determine how big this part is in an anatomical resection of the tibial plateau with 0° and 7° slope and whether it is gender-dependent.
Two hundred consecutive patients who had undergone MRI of a knee joint were included. Patients were excluded if they were younger than 18 years or had dysplasia of the knee joint or injuries of the posterior cruciate ligament. The MRIs of 182 knees that fulfilled the inclusion criteria were analysed. For each knee, an anatomical tibial resection with 0° and 7° posterior slope was simulated, and the parts of the tibial PCL attachment that were resected and retained were determined.
Given a measured tibial resection with 0° slope, 45 ± 28% of the tibial PCL attachment was removed in the men, compared with 46 ± 30% in the women (n.s.). Given a resection with 7° slope, 69 ± 24% of the tibial PCL attachment was removed in the men and 67 ± 25% in the women. This corresponded to a complete resection in 19 men (20%) and 16 women (24%).
Independently of gender, the anatomical resection of the tibia leads to the removal of a considerable part of the tibial PCL attachment, if this is not spared in the form of a bone block during resection. This becomes increasingly relevant with higher posterior slope of the resection plane. In the case of a cruciate-retaining surgical technique, the retention of the posterior tibial cortical bone in the area of attachment of the PCL is therefore strongly recommended.
II.
We hypothesized changes in rotations and translations after TKA with a fixed-bearing anterior cruciate ligament (ACL)-sacrificing but posterior cruciate ligament (PCL)-retaining design with equal-sized, circular femoral condyles would reflect the changes of articular geometry. Using 8 cadaveric knees, we compared the kinematics of normal knees and TKA in a standardized navigated position with defined loads. The quadriceps was tensed and moments and drawer forces applied during knee flexion-extension while recording the kinematics with the navigation system. TKA caused loss of the screw-home; the flexed tibia remained at the externally rotated position of normal full knee extension with considerably increased external rotation from 63 degrees to 11 degrees extension. The range of internal-external rotation was shifted externally from 30 degrees to 20 degrees extension. There was a small tibial posterior translation from 40 degrees to 90 degrees flexion. The varus-valgus alignment and laxity did not change after TKA. Thus, navigated TKA provided good coronal plane alignment but still lost some aspects of physiologic motion. The loss of tibial screw-home was related to the symmetric femoral condyles, but the posterior translation in flexion was opposite the expected change after TKA with the PCL intact and the ACL excised. Thus, the data confirmed our hypothesis for rotations but not for translations. It is not known whether the standard navigated position provides the best match to physiologic kinematics.
The experimental study of joint kinematics in three dimensions requires the description and measurement of six motion components. An important aspect of any method of description is the ease with which it is communicated to those who use the data. This paper presents a joint coordinate system that provides a simple geometric description of the three-dimensional rotational and translational motion between two rigid bodies. The coordinate system is applied to the knee and related to the commonly used clinical terms for knee joint motion. A convenient characteristic of the coordinate system shared by spatial linkages is that large joint displacements are independent of the order in which the component translations and rotations occur.
Musculoskeletal (MS) models should be able to integrate the patient-specific MS architecture and undergo thorough validation prior to their introduction into the clinical practice. We present a streamlined methodology to develop subject-specific models able to simultaneously predict body-level dynamics, muscle forces, ligament forces, knee joint contact forces and secondary knee kinematics. The MS architecture of a generic cadaver-based model was scaled using an advanced morphing technique to the subject-specific morphology of a patient implanted with an instrumented total knee arthroplasty available in the fifth "Grand Challenge Competition to Predict in Vivo Knee Loads" dataset. Inverse dynamics-like analyses of a hinge-like knee model and an 11-degree-of-freedom force-dependent kinematics (FDK) knee model were simulated for one gait, one right-turn and one unloaded leg-swing trial. Predicted tibiofemoral (TF) forces and secondary knee kinematics were evaluated using experimental data available in the Grand Challenge dataset. Total TF contact forces were predicted with a root-mean-square error (RMSE) and a coefficient of determination (R^2) smaller than 0.3 BW and higher than 0.9, respectively, for both gait and right-turn trials. Secondary knee kinematics from the leg-swing trial were overall better approximated using the FDK model (average Sprague and Geers' combined error C = 0.06) than when using a hinged knee model (C = 0.34). The proposed modeling approach allows detailed subject-specific scaling and personalization, and does not contain any non-physiological parameters. This modeling framework has potential applications in aiding the clinical decision-making in orthopedics procedures, and as a tool for virtual implant design.
Purpose:
The tibial insertion of the posterior cruciate ligament (PCL) frequently becomes damaged when performing a tibial cut in a PCL-retaining total knee replacement (TKA). The aim of this study was to quantify the functional effect of this structural damage on the tensile strength and failure load.
Methods:
Six paired knees from fresh-frozen cadaver specimens were used. All soft tissues but the PCL were removed. In the left-sided specimens, a classic tibial cut at a depth of 9 mm with 3° of posterior slope was made, while in the right-sided specimens, a bone block was left in front of the tibial PCL insertion. After cementing a tibial tray, the specimens were mounted in a loading frame in 60° of flexion. The femur was translated anteriorly at a constant velocity rate of 0.5 mm/s. Tensions in the PCL were measured continuously until failure occurred.
Results:
In one specimen, the tibial PCL insertion was completely removed by the tibial cut. In the other five paired specimens, the mean tensile strength of the PCL was 380.6 ± 154.7 N in the left-sided knees. In the right-sided knees, the mean tensile strength was 738.4 ± 166.7. The average right-to-left ratio was 2.2 ± 0.7 (p = 0.006).
Conclusion:
The results of this study indicate that the conventional technique for tibial preparation in cruciate-retaining total knee arthroplasty can result in a significant decrease in tensile strength of the PCL, rendering it susceptible to failure and subsequent midflexion instability. Therefore, we recommend leaving the posterior tibial cortex anterior to the PCL insertion intact when performing a cruciate-retaining TKA.
There is thought to be a link between vastus medialis oblique (VMO) architecture and patellofemoral pain syndrome (PFPS). Historical data are largely derived from older populations, whereas PFPS commonly affects younger populations. The aim of this study was to gather data on VMO architecture in young asymptomatic adults, to provide baseline values for comparison with symptomatic sufferers. VMO maximum fiber angle and insertion ratio were measured with ultrasound. The insertion ratio represents the proportion (%) of the patella which has the muscle fibers attaching to its medial border. Eighty knees from 40 healthy young subjects (18 males, 22 females, and age 20–30) were assessed. Individual Tegner scores were recorded to assess participants' level of physical activity. Results were compared with data in the literature for PFPS sufferers and normal older individuals. Mean fiber angle and insertion ratio were 56.6° and 57.8%, respectively. There was no significant difference between age groups. The insertion ratio was higher among females (61.2% F:53.6% M). There was some evidence of increased fiber angle and decreased insertion ratio with increased Tegner score. There was some overlap in fiber angle between healthy knees in this study and values reported elsewhere for pathological knees. VMO fiber angle and insertion ratio are not age-related. The overlap in fiber angle values between healthy and pathological knees suggests that the cause of PFPS is multifactorial. An individual's VMO architecture may be affected by their physical activity level, which could have important implications for PFPS. Clin. Anat., 2014. © 2014 Wiley Periodicals, Inc.
The purpose of the present study was to compare weight bearing (WB) and non-WB conditions, and to evaluate the effect of the posterior tibial slope (PTS) on the in vivo kinematics of 21 knees after posterior cruciate ligament-retaining total knee arthroplasty during midflexion using 2-dimensional/3-dimensional registration. During WB, medial pivot and bicondylar rollback were observed. During non-WB, both the medial and lateral condyles moved significantly more anteriorly as compared to the WB state. These patients were divided into 2 groups according to their PTS. The large PTS group showed a significant posterior displacement of the medial femoral condyle as compared with the small PTS group, but no significant difference was observed at the lateral femoral condyle during both WB and non-WB. The PTS influenced knee kinematics through gravity (124/125).
Purpose:
This study aims to make clear the influence of the tibial slope on intra-operative soft tissue balance measurements using a tensor in cruciate-retaining and posterior-stabilized total knee arthroplasty (TKA).
Methods:
Forty patients with osteoarthritis of the knee received TKAs (20 cruciate-retaining TKAs and 20 posterior-stabilized TKA). Soft tissue balance was measured using an offset type tensor at 0, 10, 45, 90, 135 degrees of knee flexion. The tibial slopes were measured by post-operative lateral radiograph. The correlation between the tibial slope and values of soft tissue balance were assessed.
Results:
Joint component gap at 90° (R = 0.537, p < 0.01) and 135° (R = 0.463, p < 0.05) of flexion and joint component gap change value of 90-0° (R = 0.433, p < 0.05) showed positive correlations with tibial slope in posterior-stabilized TKA. There was no relationship between the tibial slope and the value of soft tissue balances in cruciate-retaining TKA.
Conclusions:
In the present study, we confirmed that increasing the tibial slope resulted in a larger flexion gap compared to extension gap in posterior-stabilized TKA. Surgeons should be aware that increasing the tibial slope is one factor responsible for widening the flexion-extension gap difference in posterior-stabilized TKA.
Impairment of the human neuromusculoskeletal system can lead to significant mobility limitations and decreased quality of life. Computational models that accurately represent the musculoskeletal systems of individual patients could be used to explore different treatment options and optimize clinical outcome. The most significant barrier to model-based treatment design is validation of model-based estimates of in vivo contact and muscle forces. This paper introduces an annual "Grand Challenge Competition to Predict In Vivo Knee Loads" based on a series of comprehensive publicly available in vivo data sets for evaluating musculoskeletal model predictions of contact and muscle forces in the knee. The data sets come from patients implanted with force-measuring tibial prostheses. Following a historical review of musculoskeletal modeling methods used for estimating knee muscle and contact forces, we describe the first two data sets used for the first two competitions and summarize four subsequent data sets to be used for future competitions. These data sets include tibial contact force, video motion, ground reaction, muscle EMG, muscle strength, static and dynamic imaging, and implant geometry data. Competition participants create musculoskeletal models to predict tibial contact forces without having access to the corresponding in vivo measurements. These blinded predictions provide an unbiased evaluation of the capabilities and limitations of musculoskeletal modeling methods. The paper concludes with a discussion of how these unique data sets can be used by the musculoskeletal modeling research community to improve the estimation of in vivo muscle and contact forces and ultimately to help make musculoskeletal models clinically useful.
Total knee arthroplasty (TKA) is a widely used and successful orthopaedic procedure. During TKA, the posterior cruciate ligament (PCL) can either be retained or substituted by a post-cam mechanism. One of the main functions of the PCL is to facilitate femoral rollback during knee flexion. For adequate PCL functioning, the PCL should be balanced correctly after TKA. A tight PCL leads to more femoral rollback at the expense of a higher joint compression and potential polyethylene wear. Frequently used surgical techniques to balance a tight PCL are PCL release and increasing the posterior tibial slope. The objective of this study was to evaluate the effects of variations in PCL properties and balancing techniques on the mechanical outcome of a total knee replacement during a weight-bearing squatting movement (flexion range=45-150 degrees). For this purpose, a prosthetic finite element knee model was developed including a PCL having adjustable properties. Varying the PCL stiffness and PCL steepness (elevation angle) with respect to the tibial plateau considerably affected the TKA loading characteristics. Both a relatively high PCL stiffness and a low elevation angle at the start of the flexion cycle led to a high PCL force (1400-1500 N) and a high peak polyethylene contact stress of roughly 52 MPa during deeper knee flexion (120 degrees). Releasing the PCL with roughly 4 mm or increasing the posterior tibial slope to 7 degrees reduced the PCL force to 300-400 N and the polyethylene peak contact stress to 35-42 MPa at 120 degrees of flexion. The femoral rollback patterns during deep knee flexion were only marginally affected when extra posterior tibial slope was added, whereas additional PCL release resulted in paradoxical anterior movement of the femur.
The posterior tibial slope of the knee is an issue in total knee arthroplasty. It has also been suggested to be a determinant for the difference in the incidence of anterior cruciate ligament rupture between males and females. The current literature features discrepancies in inter-individual variation in posterior slope and the effect of gender. This in vitro study was aimed at quantifying the inter-individual variations of the posterior tibial slope and the gender difference.
The slope of the medial tibial plateau of 61 male and 44 female, bare human tibias was measured in three sagittal planes, separated by 5mm, with the use of a custom-made device. The effect of measurement location, gender and ethnicity was determined with analysis of variance.
The difference between the measurement locations was statistically significant but smaller than the variation between specimens. The mean posterior slope was 8.4 degrees (SD 3.7 degrees ), 95% confidence interval was 1.0-5.8 degrees . Ethnicity did affect posterior slope (p=0.001), but gender did not reach significance (p=0.091).
The results support the existence of a substantial inter-individual variation in posterior slope. For total knee arthroplasty, the pre-operative posterior slope is apparently not compatible with the suggestion not to cut a slope greater than 8 degrees , as more than half of the tibias had a greater slope. Secondly, part of the variance over subjects is related to ethnicity and possibly also to gender, which might have implications for the risk of sustaining an anterior cruciate ligament rupture and for the success of total knee arthroplasty.
With the exception of flexion gap tightness, which is common in cruciate-retaining (CR) total knee arthroplasty (TKA), the risk factors of flexion gap tightness have not been described. This retrospective study characterized factors that are associated with flexion gap tightness in CR TKA. Data on 203 consecutive knees that underwent CR TKA were reviewed. The prevalence rate of flexion gap tightness was 21.1%. By logistic regression analysis after adjusting for age, preoperative flexion contracture, and referencing method used for femoral sizing, insufficient tibial slope remained a significant independent risk factor of flexion gap tightness. Although excessive tibial slope should be avoided, the findings of the present study demonstrate that the risk of flexion gap tightness can be reduced by increasing the tibial slope in CR TKA.
In this paper, we introduce a new general method for kinematic analysis of rigid multi body systems subject to holonomic constraints. The method extends the standard analysis of kinematically determinate rigid multi body systems to the over-determinate case. This is accomplished by introducing a constrained optimisation problem with the objective function given as a function of the set of system equations that are allowed to be violated while the remaining equations define the feasible set. We show that exact velocity and acceleration analysis can also be performed by solving linear sets of equations, originating from differentiation of the Karush-Kuhn-Tucker optimality conditions. The method is applied to the analysis of an 18 degrees-of-freedom gait model where the kinematical drivers are prescribed with data from a motion capture experiment. The results show that significant differences are obtained between applying standard kinematic analysis or minimising the least-square errors on the two fully equivalent 3D gait models with only the way the experimental data is processed being different.
The effect of posterior tibial slope was evaluated in a rotationally unconstrained anterior cruciate ligament-sacrificing total knee replacement (Ortholoc, Dow Corning Wright, Arlington, TN). Sloping the surface 7 degree posteriorly loosened the knee to varus-valgus and anterior-posterior stress in flexion. Eliminating posterior slope improved varus-valgus stability in flexion but slightly increased anterior-posterior laxity in extension. Values for the 3 degree posterior slope knee were between the values for 0 degree and 7 degree sloped surfaces, but not significantly different statistically from either. Total knee replacement designs with a posterior tibial slope are likely to promote anterior-posterior and varus-valgus laxity in flexion, and those with no posterior slope or 3 degree posterior slope are most likely to achieve normal stability in flexion and extension.
Fifty-five unconstrained polyethylene tibial inserts were retrieved at revision total knee arthroplasty and examined for evidence of wear after a mean implantation time of 34.2 months (2.5-80 months). Twenty inserts were ultra-high molecular weight polyethylene (UHMWPE) and 35 were carbon-reinforced polyethylene. Topographic maps of the articular and metal-backed surfaces of each component were constructed to characterize the extent and location of polyethylene degradation, identified visually by mode. In 32 of the retrieved inserts, pre- and postarthroplasty or prerevision radiographs were analyzed for component positioning, sizing, and extremity alignment. These factors then were compared with the patterns and severity of polyethylene wear on the inserts to establish correlations. Severe generalized articular wear was seen in inserts with third body wear from patellar metal-backed failure and cement debris. Severe localized delamination wear was seen in inserts with rotational-subluxation patterns of wear (p = 0.05). The external rotation subluxation wear pattern was strongly associated with knees that had lateral subluxation of the patella (p = 0.0002). Articular wear and cold flow into screw holes tended to be greater in the tightest prearthroplasty compartment (medial in the varus knee [p = 0.0157]; lateral in the valgus knees [p = 0.0226]). Fourteen of 16 knees with a preoperative varus deformities--even when corrected to a normal postarthroplasty anatomic axis--still had greater medial compartment articular wear (p = 0.001). Twelve of these knees did not have a medial release at the time of initial arthroplasty. Preoperative varus also was found to be related to the occurrence of posteromedial cold flow of polyethylene into tibial tray screw holes (p = 0.007). Increasing tibial insert posterior slope was associated with increasingly posterior articular wear track location (p = 0.03). This study indicates that unconstrained tibial component wear patterns and severity may be associated with clinical and mechanical factors under the surgeon's control, including component size and position, and knee alignment and ligament balance.
The purpose of this study was to measure the strain in the posterior cruciate ligament as a function of knee flexion angle and posterior tibial slope following total knee arthroplasty with a posterior cruciate ligament-retaining design. Posterior cruciate ligament strain was measured in seven fresh-frozen cadavers for posterior tibial slopes of 10 degrees, 8 degrees, and 5 degrees. For all three levels of tibial slope tested, strain in the posterior cruciate ligament increased with increasing flexion angle to approximately 100 degrees and then decreased with increasing flexion. The strain measured at 8 degrees posterior tibial slope was greater than that measured at 10 degrees, but the difference was not significant. The strain measured at 5 degrees posterior slope was significantly greater than strain measured at both 8 degrees and 10 degrees. This increased strain may result in altered knee kinematics and reduced range of motion at higher flexion angles.
Increasing femoral rollback in flexion is thought to reduce patellofemoral contact load in total knee arthroplasty (TKA). The objectives of this study were to quantify the dependence of patellar load on rollback and to assess the effectiveness of posterior cruciate ligament (PCL)-retaining, PCL-sacrificing, and PCL-substituting TKA types in generating rollback. Nine cadaver knees were tested in simulated squatting. Six TKAs that were expected to produce varying amounts of femoral rollback were evaluated: PCL-retaining TKA, PCL-sacrificing TKA, a commercially available PCL-substituting TKA, and 3 modified PCL-substituting TKAs in which the anteroposterior position of the tibial post was varied. Kinematics, quadriceps loads, and patellofemoral contact loads were recorded. Significant differences in rollback were observed in the 30 degrees to 90 degrees flexion range. PCL-sacrificing TKAs generated the least rollback. PCL-retaining TKAs produced greater rollback but had the most variability. PCL-substituting TKAs produced the greatest and most reproducible rollback. Moving the tibial post posteriorly further increased rollback. Increased rollback correlated with reduced patellar load (-2.2%/mm). Reductions in patellar load of 17.6% were observed. Quadriceps loads were reduced by increasing rollback but to a smaller degree (-0.9%/mm). Rollback primarily affects patellar load rather than quadriceps load or efficiency.
An experimental study using fresh human cadaver knees was designed to evaluate the effect of partial posterior cruciate ligament release or posterior tibial slope on knee kinematics after total knee arthroplasty. Varus and valgus laxity, rotational laxity, anteroposterior laxity, femoral rollback, and maximum flexion angle were evaluated in a normal knee, an ideal total knee arthroplasty, and a total knee arthroplasty in which the ligaments were made to be too tight in flexion. The total knee arthroplasty specimens then were subjected to either partial posterior cruciate ligament release or increased posterior tibial slope, and the tests were repeated. Posterior tibial slope increased varus and valgus laxity, anteroposterior laxity, and rotational laxity in the knee that had flexion tightness. Posterior cruciate ligament release corrected only anteroposterior tightness, and had no effect on the abnormal collateral ligament tightness. Increased posterior tibial slope significantly improved varus and valgus laxity and rotational laxity in the knee that was tight in flexion more than with release of the posterior cruciate ligament. Therefore increasing posterior tibial slope is preferable for a knee that is tight in flexion during total knee arthroplasty.
Total knee arthroplasty implant designs with larger extensor moment arms theoretically should generate lower extensor forces for the same externally applied loads. This study measured knee kinematics, quadriceps forces, and patellofemoral forces under conditions of dynamic knee extension under load in two knee designs with differing quadriceps moment arms. Six human cadaver knees were tested both before implantation and after sequential implantation with two posterior cruciate retaining designs. The extensor moment arm of the LMA (long extensor moment arm design, Scorpio, Howmedica Osteonics, Rutherford, NJ) was approximately 1 cm longer than that of the Control design (7000, Howmedica Osteonics). Quadriceps tension was measured during dynamic closed kinetic chain knee extension. Patellar compressive and shear forces were also recorded using a patellar component instrumented with a custom triaxial load transducer. Knee kinematics were monitored using a three-dimensional electromagnetic tracking device. Both designs produced similar patterns of femoral rollback and tibial rotation. Quadriceps tension was lower in the LMA design compared with the Control design. Patellofemoral compressive forces were also significantly reduced in the LMA design when compared with Control (8-18% lower at angles greater than 50 degrees flexion). The design with the longer extensor moment arm required less quadriceps force to extend the knee under load and reduced patellofemoral compressive forces. Reduced quadriceps forces may facilitate postoperative rehabilitation and activities such as stair climbing. Reduction in patellofemoral forces could reduce patellar complications such as anterior knee pain, component wear, and loosening.
The relation between prosthesis component kinematics and posterior slope of the tibial component in total knee arthroplasty is much debated. Three-dimensional kinematics of the replaced knee was obtained by video fluoroscopy in 23 knees treated by cruciate-retaining or cruciate-substituting arthroplasty. Relative position and orientation of the metal components were calculated in stair ascending, getting up from and sitting down on a chair, and single step up-and-down. Significant correlations were found between tibial component posterior slope and anteroposterior position of tibiofemoral lateral contact and between this slope and maximum knee flexion. These correlations were task and design specific. However, the average of the tibiofemoral contact positions over all three motor tasks was slightly posterior to the midline of the tibial base plate, reaching at most 84% of its anteroposterior dimension. Performing a posterior slope of the tibial cut does not put total knee arthroplasty with high conforming designs at higher risk of failure, even when large posterior inclinations need to be achieved.
The purpose of this study was to investigate the influence of tibial base plate angulation on knee kinematics and kinetics during knee arthroplasty. The amount of quadriceps force required to extend the knee and the anteroposterior displacement of a mobile bearing insert as well as tibiofemoral position were measured during an in vitro simulation of an isokinetic knee extension cycle. Human knee specimens (n = 7, mean age 62, range 52-75 years, all male) were tested in a kinematic knee simulating machine after total knee arthroplasty (TKA) with a mobile bearing insert prosthesis (Interax), Stryker/Howmedica). During simulation, a hydraulic cylinder applied sufficient force to the quadriceps tendon to produce an extension moment of 31 N m about the knee. The quadriceps load was measured using a load cell attached to the quadriceps tendon, the anteroposterior displacement of the mobile bearing insert as well as the relative tibiofemoral position was measured using an ultrasound base motion analysis system (CMS 100, Zebris). Quadriceps load, insert and tibial displacement were first investigated with the tibial base plate implanted with a neutral tibial base plate orientation, and subsequently after 10 degrees posterior angulation. The quadriceps forces needed to produce a 31 N m knee extension moment after TKA with neutral slope reached levels as high as 1,391 N (SD 82 N). After applying a posterior slope of 10 degrees , maximum quadriceps force was measured to be up to 1,303 N (SD 34 N, P = 0.04). The mobile bearing insert was observed to move up to 0.1 mm (SD 4.2 mm) anteriorly relative to the tibial base plate with neutral tibial slope, and up to 1.0 mm (SD 4.5 mm, P = 0.47) with tibial slope. Femoral position relative to the tibia moved from a posterior position of 13.1 mm (SD 4.0 mm) anteriorly up to 0.5 mm (SD 6.3 mm), and from 16.0 mm (SD 6.4 mm, P = 0.67) to 9.5 mm (SD 9.9 mm, P = 0.33) with a 10 degrees tibial slope. Posterior slope of the tibial base plate resulted in a more physiologic insert movement with a more posterior position of the femur and reduced quadriceps force especially in knee flexion angles above 60 degrees compared to TKA with a neutral slope of the tibial base plate. Thus, the data suggest that the quadriceps lever arm was improved, which might have positive effect in mobilization of patients after TKA.
Restoration of the physiological flexor/extensor mechanism at the knee in terms of appropriate muscular lever arms, proper required quadriceps force, and suitable patellofemoral compressive force, is fundamental for the success of total knee replacement. Therefore, measurements of anteroposterior translation of the femoral component over the tibial base-plate against joint flexion during daily living activities are essential for the assessment of the in vivo performance of current prosthesis designs. Patients treated with posterior stabilized and cruciate retaining prostheses with excellent clinical scores were evaluated during stair climbing, sitting and rising from a chair, and step up and down, using a three-dimensional pose reconstruction technique based on videofluoroscopy. The posterior stabilized patients experienced a fairly consistent and physiological rollback specific of each motor task, demonstrating proper function of the spine-cam mechanism. Rollback was somehow inconsistent among subjects in the cruciate retaining group, accompanied with a smaller range of knee flexion. In this group, more posterior locations of the condyles correlated significantly with higher clinical and functional scores. Articular surface conformity restores physiological rollback in the presence of a spine-cam mechanism, but not coherently in the presence of the posterior cruciate ligament.
In order to determine how "tight" a total knee prosthesis should be implanted, it is important to know the amount of laxity in a healthy knee. The objective of this study was to determine knee laxity in extension and flexion in healthy, non-arthritic knees of subjects similar in age to patients undergoing a total knee arthroplasty and to provide guidelines for the orthopaedic surgeon in his attempt to restore the stability of an osteoarthritic knee to normal. Thirty healthy subjects (15 male, 15 female), mean age 62 (SD 6.4) years, were included in the study. For each subject one, randomly selected, knee was stressed in extension and in 70 degrees flexion (15 Nm). Varus and valgus laxity were measured on radiographs. The passive range of motion and active flexion was assessed. Mean valgus laxity in extension was 2.3 degrees (SD 0.9, range 0.2 degrees -4.1 degrees ). In extension mean varus laxity was 2.8 degrees (SD 1.3, range 0.6 degrees -5.4 degrees ). In flexion, mean valgus laxity was 2.5 degrees (SD 1.5, range 0.0 degrees -6.0 degrees ) and mean varus laxity was 3.1 degrees (SD 2.0, range 0.1 degrees -7.0 degrees ). Varus and valgus knee laxity in extension and in flexion were comparable. This study shows that the normal knee in this age group has an inherent degree of varus-valgus laxity. Whether the results of the present study can be used to optimise the total knee arthroplasty implantation technique requires further investigation.
Changes in knee kinematics reflect the articular geometry after arthroplasty
- Amj Bull
- O Kessler
- M Alam
- A A Amis
Bull AMJ, Kessler O, Alam M, Amis AA (2008) Changes in
knee kinematics reflect the articular geometry after arthroplasty.
Clin Orthop Relat Res 466:2491-2499