Material Properties of Fiber Bundles of the Superficial Medial Collateral Ligament of the Knee Joint.

The superficial medial collateral ligament (sMCL) of the human knee joint has functionally separate anterior and posterior fiber bundles. The two bundles are alternatively loaded as the knee flexion angle changes during walking. To date, the two bundles are usually not distinguished in knee ligament simulations because there has been little information about their material properties. In this study, we conducted quasi-static tensile tests on the sMCL of matured porcine stifle joints and obtained the material properties of the anterior bundle (AB), posterior bundle (PB), and whole ligament (WL). AB and PB have similar failure stress but different threshold strain, modulus, and failure strain. As a result, we recommend assigning different material properties (i.e., modulus and failure strain) to the two fiber bundles to realize biofidelic ligament responses in human body models. However, it is often inconvenient to perform tensile tests on AB and PB. Hence, we proposed a microstructural model-based approach to predict the material properties of AB and PB from the test results of WL. Such obtained modulus values of AB and PB had an error of 2% and 0.3%, respectively, compared with those measured from the tests. This approach can reduce the experimental cost for acquiring the needed mechanical property data for simulations.

Knee Ligament Anatomy and Biomechanics.

An understanding of knee ligament anatomy and biomechanics is foundational for physicians treating knee injuries, especially the more rare and morbid multiligamentous knee injuries. This chapter examines the roles that the cruciate and collateral anatomy and morphology play in their kinematics. Additionally, the biomechanics of the ACL, PCL, MCL, and LCL are discussed as they have surgical and reconstructive implications.

Fluorescence recovery after photobleaching: direct measurement of diffusion anisotropy.

Fluorescence recovery after photobleaching (FRAP) is a widely used technique for studying diffusion in biological tissues. Most of the existing approaches for the analysis of FRAP experiments assume isotropic diffusion, while only a few account for anisotropic diffusion. In fibrous tissues, such as articular cartilage, tendons and ligaments, diffusion, the main mechanism for molecular transport, is anisotropic and depends on the fibre alignment. In this work, we solve the general diffusion equation governing a FRAP test, assuming an anisotropic diffusivity tensor and using a general initial condition for the case of an elliptical (thereby including the case of a circular) bleaching profile. We introduce a closed-form solution in the spatial coordinates, which can be applied directly to FRAP tests to extract the diffusivity tensor. We validate the approach by measuring the diffusivity tensor of [Formula: see text] FITC-Dextran in porcine medial collateral ligaments. The measured diffusion anisotropy was [Formula: see text] (SE), which is in agreement with that reported in the literature. The limitations of the approach, such as the size of the bleached region and the intensity of the bleaching, are studied using COMSOL simulations.

The Medial Collateral Ligament in Primary Total Knee Arthroplasty: Anatomy, Biomechanics, and Injury.

Understanding the anatomy and biomechanics of the medial collateral ligament (MCL) is crucial in producing good outcomes after total knee arthroplasty. A solid grasp of the surgical techniques that address the MCL are necessary to ensure good coronal plane ligament balance. Furthermore, intraoperative injury to the MCL in total knee arthroplasty is an uncommon yet serious complication which often goes unrecognized. Loss of the integrity of the MCL can lead to instability, loosening, and accelerated polyethylene wear. There is still controversy regarding the ideal method of treatment of intraoperative MCL injuries with suggested treatment modalities ranging from conservative management to use of varus-valgus constrained implants.

Release of the medial collateral ligament is mandatory in medial open-wedge high tibial osteotomy.

PURPOSE: The purpose of this study was to quantify the effect of clinically relevant open-wedge high tibial osteotomies on medial collateral ligament (MCL) strain and the resultant tibiofemoral contact mechanics during knee extension and 30° knee flexion. METHODS: Six human cadaveric knee joints were axially loaded (1 kN) in knee extension and 30° knee flexion. Strains at the anterior and posterior regions of the MCL were determined using strain gauges. Tibiofemoral contact mechanics (contact area, mean and maximum contact pressure) were investigated using pressure-sensitive sensors. Open-wedge osteotomy was performed using biplanar cuts and osteotomy angles of 5° and 10° were maintained using an external fixator. Tests were performed first with intact and then with dissected MCL. RESULTS: Nonparametric statistical analyses indicated a significant strain increase (p < 0.01) in the anterior and posterior fibres of the MCL with increasing osteotomy angle of up to 8.3% and 6.0%, respectively. Only after releasing the MCL the desired lateralisation of the mechanical axis was achieved, indicating a significant decrease in the maximum contact pressure in knee extension of - 25% (p = 0.028) and 30° knee flexion of - 21% (p = 0.027). CONCLUSIONS: The results of the present biomechanical study suggest, that an open-wedge high tibial osteotomy is most effective in reducing the medial contact pressure when spreading the osteotomy to 10° and concomitantly releasing the MCL. To transfer the results of this biomechanical study to the clinical day-to-day practice, it is necessary to factor in the individual ligamentous laxity of each patient into the treatment options e.g. particularly for patients with distinct knee ligament laxity or medial ligamentary instability, the release of the MCL should be performed with care. LEVEL OF EVIDENCE: Controlled laboratory study.

A biomechanical analysis of triangular medial knee reconstruction.

BACKGROUND: The purpose of this study was to evaluate and compare knee kinematics and stability following either triangular or anatomical reconstruction of the superficial medial collateral ligament (sMCL) and posterior oblique ligament (POL). METHODS: In a cadaveric model (12 knees), the stability and kinematics following two experimental sMCL and POL reconstructions were compared in sMCL- and POL-deficient knees versus normal knees. The first reconstruction was a triangular reconstruction of the sMCL and POL, while the second involved an anatomical reconstruction of the sMCL and POL. All knees were tested through four different states. The changes in valgus angles, external rotation, and internal rotation were measured in the normal and sMCL- and POL-deficient knees, as well as in the knees that had undergone the two different forms (triangular and anatomical) of reconstruction. RESULTS: After initial sectioning of the sMCL and POL, we observed significantly increased valgus rotation, external rotation, and internal rotation at all knee flexion angles (0°, 20°, 30°, 60°, 90°). Additionally, passive stability testing demonstrated a significant increase in tibial internal rotation following triangular reconstruction compared with anatomical reconstruction at knee flexion angles of 20° and 30°. A significant increase in internal rotation was present following triangular reconstruction compared with anatomical reconstruction at 20° (mean difference = 2.77) (P = 0.008) and 30° (mean difference = 0.99) (P < 0.001) of knee flexion. CONCLUSION: This study suggests that anatomical sMCL and POL reconstruction produces slightly better biomechanical stability than triangular reconstruction. However, triangular reconstruction may restore a near-normal knee joint is both less invasive and more practical.

New parameters describing how knee ligaments carry force in situ predict interspecimen variations in laxity during simulated clinical exams.

Knee laxity, defined as the net translation or rotation of the tibia relative to the femur in a given direction in response to an applied load, is highly variable from person to person. High levels of knee laxity as assessed during routine clinical exams are associated with first-time ligament injury and graft reinjury following reconstruction. During laxity exams, ligaments carry force to resist the applied load; however, relationships between intersubject variations in knee laxity and variations in how ligaments carry force as the knee moves through its passive envelope of motion, which we refer to as ligament engagement, are not well established. Thus, the objectives of this study were, first, to define parameters describing ligament engagement and, then, to link variations in ligament engagement and variations in laxity across a group of knees. We used a robotic manipulator in a cadaveric knee model (n=20) to quantify how important knee stabilizers, namely the anterior and posterior cruciate ligaments (ACL and PCL, respectively), as well as the medial collateral ligament (MCL) engage during respective tests of anterior, posterior, and valgus laxity. Ligament engagement was quantified using three parameters: (1) in situ slack, defined as the relative tibiofemoral motion from the neutral position of the joint to the position where the ligament began to carry force; (2) in situ stiffness, defined as the slope of the linear portion of the ligament force-tibial motion response; and (3) ligament force at the peak applied load. Knee laxity was related to parameters of ligament engagement using univariate and multivariate regression models. Variations in the in situ slack of the ACL and PCL predicted anterior and posterior laxity, while variations in both in situ slack and in situ stiffness of the MCL predicted valgus laxity. Parameters of ligament engagement may be useful to further characterize the in situ biomechanical function of ligaments and ligament grafts.

The challenges of measuring in vivo knee collateral ligament strains using ultrasound.

Ultrasound-based methods have shown promise in their ability to characterize non-uniform deformations in large energy-storing tendons such as the Achilles and patellar tendons, yet applications to other areas of the body have been largely unexplored. The noninvasive quantification of collateral ligament strain could provide an important clinical metric of knee frontal plane stability, which is relevant in ligament injury and for measuring outcomes following total knee arthroplasty. In this pilot cadaveric experiment, we investigated the possibility of measuring collateral ligament strain with our previously validated speckle-tracking approach, but encountered a number of challenges during both data acquisition and processing. Given the clinical interest in this type of tool, and the fact that this is a developing area of research, the goal of this article is to transparently describe this pilot study, both in terms of methods and results, while also identifying specific challenges to this work and areas for future study. Some challenges faced relate generally to speckle-tracking of soft tissues (e.g. the limitations of using a 2D imaging modality to characterize 3D motion), while others are specific to this application (e.g. the small size and complex anatomy of the collateral ligaments). This work illustrates a clear need for additional studies, particularly relating to the collection of ground-truth data and more thorough validation work. These steps will be critical prior to the translation of ultrasound-based measures of collateral ligament strains into the clinic.

The evaluation of the role of medial collateral ligament maintaining knee stability by a finite element analysis.

BACKGROUND: A three-dimensional finite element model (FEM) of the knee joint was established to analyze the biomechanical functions of the superficial and deep medial collateral ligaments (MCLs) of knee joints and to investigate the treatment of the knee medial collateral ligament injury. METHODS: The right knee joint of a healthy male volunteer was subjected to CT and MRI scans in the extended position. The scanned data were imported into MIMICS, Geomagic, and ANSYS software to establish a three-dimensional FEM of the human knee joint. The anterior-posterior translation, valgus-varus rotation, and internal-external rotation of knee joints were simulated to observe tibial displacement or valgus angle. In addition, the magnitude and distribution of valgus stress in the superficial and deep layers of the intact MCL as well as the superficial, deep, and overall deficiencies of the MCL were investigated. RESULTS: In the extended position, the superficial medial collateral ligament (SMCL) would withstand maximum stresses of 48.63, 16.08, 17.23, and 16.08 MPa in resisting the valgus of knee joints, tibial forward displacement, internal rotation, and external rotation, respectively. Meanwhile, the maximum stress tolerated by the SMCL in various ranges of motion mainly focused on the femoral end point, which was located at the anterior and posterior parts of the femur in resisting valgus motion and external rotation, respectively. However, the deep medial collateral ligament could tolerate only minimum stress, which was mainly focused at the femoral start and end points. CONCLUSIONS: This model can effectively analyze the biomechanical functions of the superficial and deep layers of the MCLs of knee joints. The results show that the knee MCL II° injury is the indication of surgical repair.

Evaluation of the Morphology and Function of Medial Collateral Ligament afterTotal Knee Arthroplasty with High-frequency Ultrasound.

Objective To explore the feasibility and clinical value of ultrasonography in evaluating the morphology and function of medial collateral ligaments (MCL) after total knee arthroplasty (TKA). Methods Totally 38 patients undergoing routine KTA (group A) and 22 patients undergoing constrained condylar knee arthroplasty KTA with MCL injury (group B) were included. Long axis views of MCL were taken and the MCL thickness was measured on femur side and tibial side 1 cm away from the joint line, respectively. The thicknesses were compared between the two groups. Subsequently, the gap between the metal part of the femoral prosthesis and the spacer after dynamic valgus stress was measured. The distribution and composition of the gap between the two groups were compared. Results High-frequency ultrasound clearly showed the prosthesis and MCL after TKA. MCL fiber structures of both groups were intact. The MCL thickness on the tibial side in group B was (0.25±0.06)cm, which was significantly thinner than group A [(0.32±0.14)cm] (t=2.12, P=0.040).For the femur side, there was no significant difference (t=1.65, P=0.110) between these two groups [(0.37±0.09) cm in group B versus (0.42±0.12)cm in group A]. Under the condition of valgus stress, the gaps between the metal part of the femoral prosthesis and the spacer could be found in 11 cases in group B but only in 1 case in group A. The proportion of gaps in group B was significantly higher than that in group A (Fisher's exact test, P=0.000). Conclusions High-frequency ultrasound can clearly show the prosthesis and MCL after TKA. The injured MCL can be well joined but the thickness is thinner. Under the condition of valgus stress of the knee, the stability of the TKA can be evaluated according to the gap between the prosthesis and the spacer.

High strains near femoral insertion site of the superficial medial collateral ligament of the Knee can explain the clinical failure pattern.

The three dimensional (3D) deformation of the superficial medial collateral ligament (sMCL) of the knee might play an important role in the understanding of the biomechanics of sMCL lesions. Therefore, the strain and deformation pattern of the sMCL during the range of motion were recorded in five cadaveric knees with digital image correlation. During knee flexion, the sMCL was found to deform in the three planes. In the sagittal plane, a rotation of the proximal part of the sMCL relative to the distal part occurred with the center of this rotation being the proximal tibial insertion site of the sMCL. This deformation generated high strains near the femoral insertion site of the sMCL. These strains were significantly higher than in the other parts and were maximal at 90° with on average +3.7% of strain and can explain why most lesions in clinical practice are seen in this proximal region. The deformation also has important implications for sMCL reconstruction techniques. Only a perfect anatomic restoration of the insertion sites of the sMCL on both the proximal and distal tibial insertion sites will be able to reproduce the isometry of the sMCL and thus provide the adequate stability throughout the range of motion. The fact that knee motion between 15° and 90° caused minimal strain in the sMCL might suggest that early passive range of motion in physical therapy postoperatively should have little risk of stretching a graft out in the case of an anatomical reconstruction. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2016-2024, 2016.

Distribution of Force in the Medial Collateral Ligament Complex During Simulated Clinical Tests of Knee Stability.

BACKGROUND: Pivot-shift injury commonly results in combined anterior cruciate ligament (ACL)/medial collateral ligament (MCL) injury, yet the contribution of the components of the MCL complex to restraining multiplanar rotatory loads forming critical subcomponents of the pivot shift is not well understood. PURPOSE: To quantify the role of the MCL complex in restraining multiplanar rotatory loads. STUDY DESIGN: Controlled laboratory study. METHODS: A robotic manipulator was used to apply combined valgus and internal rotation torques in a simplified model of the pivot-shift examination in 12 cadaveric knees (49 ± 11 years). Tibiofemoral kinematics were recorded with the ACL intact. Loads borne by the superficial MCL (sMCL), posterior oblique ligament (POL), deep MCL (dMCL), and ACL were determined via the principle of superposition. RESULTS: The POL bore about 50% of the load carried by the ACL in response to the combined torques at 5° and 15° of flexion. The POL bore load during the internal rotation component of the combined torques, while the sMCL carried load during the valgus and internal rotation phases of the simulated pivot. Load in the dMCL was always <10% of the ACL in response to combined valgus and internal rotation torques. CONCLUSION: The POL provides complementary load bearing to the ACL near extension in response to combined torques, which capture key components of the pivot-shift examination. The sMCL resists the valgus component of the maneuver alone, a loading pattern unique from those of the POL and ACL. The dMCL is not loaded during clinical tests of rotational knee stability in the ACL-competent knee. CLINICAL RELEVANCE: Both the sMCL and POL work together with the ACL to resist combined moments, which form key components of the pivot-shift examination.

Influence of the Medial Knee Structures on Valgus and Rotatory Stability in Total Knee Arthroplasty.

BACKGROUND: Precise biomechanical knowledge of individual components of the MCL is critical for proper MCL release during TKA. This study was to define the influences of the deep MCL and the POL on valgus and rotatory stability in TKA using cadaveric knees. METHODS: This study used six fresh-frozen cadaveric knees. All TKA procedures were performed using a cruciate-retaining TKA with a CT-free navigation system. We did a sequential sectioning on each knee, S1; femoral arthroplasty only, S2; medial half tibial resection with spacer, S3; anterior cruciate ligament cut, S4; tibial arthroplasty, S5; release of the dMCL, S6; release of the POL. The navigation system monitored motion after application of 10 N-m valgus loads and 5 N-m internal and external rotation torques to the tibia at 0°, 20°, 30°, 60°, and 90° of knee flexion for each sequence. RESULTS: There were no significant differences in medial gaps. Internal rotation angles significantly increased after S2 at 0°, 20°, and 30°, and after S6 at 90° compared with those after S1. External rotation angles significantly increased after S3 at 0°, S4 at 60°, S5 at 0°, 30° and 90°, and after S6 at 30°, 60° compared with those after S1. CONCLUSION: Significant increases of rotatory instability were seen on release of the dMCL, and then further increased after release of the POL. Surgical approach of retaining the dMCL and POL has a possibility to improve the outcome after primary TKA.

[The effect of the biopolymer chondroitin sulfate on reparative regeneration of connective tissue].

The research objective is a study of an intra-articular method of introduction of the preparation "mukosat" for stimulation of reparative regeneration of connective tissue of knee joints in rabbits with an experimental arthritis. It is ascertained that intra-articular maintenance of chondroitin sulfate (the preparation "mukosat") acts as a stimulus for reparative regeneration of connective tissue thus showing up positive changes in the status of connective tissue elements of joints: decrease in glycosaminoglycan content in blood serum and normalization of the composition of glycosaminoglycan carbohydrate component. It probably depends on stimulation of biosynthesis of autologous normal glycosaminoglycans in tissues of animal knee joints.

Aging affects mechanical properties and lubricin/PRG4 gene expression in normal ligaments.

Age-related changes in ligament properties may have clinical implications for injuries in the mature athlete. Previous preclinical models documented mechanical and biochemical changes in ligaments with aging. The purpose of this study was to investigate the effect of aging on ligament properties (mechanical, molecular, biochemical) by comparing medial collateral ligaments (MCLs) from 1-year-old and 3-year-old rabbits. The MCLs underwent mechanical (n=7, 1-year-old; n=7, 3-year-old), molecular (n=8, 1-year-old; n=6, 3-year-old), collagen and glycosaminoglycan (GAG) content (n=8, 1-year-old; n=6, 3-year-old) and water content (n=8, 1-year-old; n=5, 3-year-old) assessments. Mechanical assessments evaluated total creep strain, failure strain, ultimate tensile strength and modulus. Molecular assessments using RT-qPCR evaluated gene expression for collagens, proteoglycans, hormone receptors, and matrix metalloproteinases and their inhibitors. While total creep strain and ultimate tensile strength were not affected by aging, failure strain was increased and modulus was decreased comparing MCLs from 3-year-old rabbits to those from 1-year-old rabbits. The mRNA expression levels for lubricin/proteoglycan 4 (PRG4) and tissue inhibitor of metalloproteinase-3 increased with aging; whereas, the mRNA expression levels for estrogen receptor and matrix metalloproteinase-1 decreased with aging. Collagen and GAG content assays and water content assessments did not demonstrate any age-related changes. The increased failure strain and decreased modulus with aging may have implications for increased susceptibility to ligament damage/injury with aging. Lubricin/PRG4 gene expression was affected by aging and its speculated role in ligament function may be related to interfascicular lubrication, which in turn may lead to altered mechanical function with aging and increases in potential for injury.

Relative strain in the anterior cruciate ligament and medial collateral ligament during simulated jump landing and sidestep cutting tasks: implications for injury risk.

BACKGROUND: The medial collateral (MCL) and anterior cruciate ligaments (ACL) are, respectively, the primary and secondary ligamentous restraints against knee abduction, which is a component of the valgus collapse often associated with ACL rupture during athletic tasks. Despite this correlation in function, MCL ruptures occur concomitantly in only 20% to 40% of ACL injuries. HYPOTHESIS/PURPOSE: The purpose of this investigation was to determine how athletic tasks load the knee joint in a manner that could lead to ACL failure without concomitant MCL failure. It was hypothesized that (1) the ACL would provide greater overall contribution to intact knee forces than the MCL during simulated motion tasks and (2) the ACL would show greater relative peak strain compared with the MCL during simulated motion tasks. STUDY DESIGN: Controlled laboratory study. METHODS: A 6-degrees-of-freedom robotic manipulator articulated 18 cadaveric knees through simulations of kinematics recorded from in vivo drop vertical jump and sidestep cutting tasks. Specimens were articulated in the intact-knee and isolated-ligament conditions. After simulation, each ACL and MCL was failed in uniaxial tension along its fiber orientations. RESULTS: During a drop vertical jump simulation, the ACL experienced greater peak strain than the MCL (6.1% vs 0.4%; P < .01). The isolated ACL expressed greater peak anterior force (4.8% vs 0.3% body weight; P < .01), medial force (1.6% vs 0.4% body weight; P < .01), flexion torque (8.4 vs 0.4 N·m; P < .01), abduction torque (2.6 vs 0.3 N·m; P < .01), and adduction torque (0.5 vs 0.0 N·m; P = .03) than the isolated MCL. During failure testing, ACL specimens preferentially loaded in the anteromedial bundle failed at 637 N, while MCL failure occurred at 776 N. CONCLUSION: During controlled physiologic athletic tasks, the ACL provides greater contributions to knee restraint than the MCL, which is generally unstrained and minimally loaded. CLINICAL RELEVANCE: Current findings support that multiplanar loading during athletic tasks preferentially loads the ACL over the MCL, leaving the ACL more susceptible to injury. An enhanced understanding of joint loading during in vivo tasks may provide insight that enhances the efficacy of injury prevention protocols.

Elastin governs the mechanical response of medial collateral ligament under shear and transverse tensile loading.

Elastin is a highly extensible structural protein network that provides near-elastic resistance to deformation in biological tissues. In ligament, elastin is localized between and along the collagen fibers and fascicles. When ligament is stretched along the primary collagen axis, elastin supports a relatively high percentage of load. We hypothesized that elastin may also provide significant load support under elongation transverse to the primary collagen axis and shear along the collagen axis. Quasi-static transverse tensile and shear material tests were performed to quantify the mechanical contributions of elastin during deformation of porcine medial collateral ligament. Dose response studies were conducted to determine the level of elastase enzymatic degradation required to produce a maximal change in the mechanical response. Maximal changes in peak stress occurred after 3h of treatment with 2U/ml porcine pancreatic elastase. Elastin degradation resulted in a 60-70% reduction in peak stress and a 2-3× reduction in modulus for both test protocols. These results demonstrate that elastin provides significant resistance to elongation transverse to the collagen axis and shear along the collagen axis while only constituting 4% of the tissue dry weight. The magnitudes of the elastin contribution to peak transverse and shear stress were approximately 0.03 MPa, as compared to 2 MPa for axial tensile tests, suggesting that elastin provides a highly anisotropic contribution to the mechanical response of ligament and is the dominant structural protein resisting transverse and shear deformation of the tissue.

Mapping of contributions from collateral ligaments to overall knee joint constraint: an experimental cadaveric study.

Understanding the contribution of the soft-tissues to total joint constraint (TJC) is important for predicting joint kinematics, developing surgical procedures, and increasing accuracy of computational models. Previous studies on the collateral ligaments have focused on quantifying strain and tension properties under discrete loads or kinematic paths; however, there has been little work to quantify collateral ligament contribution over a broad range of applied loads and range of motion (ROM) in passive constraint. To accomplish this, passive envelopes were collected from nine cadaveric knees instrumented with implantable pressure transducers (IPT) in the collateral ligaments. The contributions from medial and lateral collateral ligaments (LCL) were quantified by the relative contribution of each structure at various flexion angles (0-120 deg) and compound external loads (±10 N m valgus, ±8 N m external, and ±40 N anterior). Average medial collateral ligament (MCL) contributions were highest under external and valgus torques from 60 deg to 120 deg flexion. The MCL showed significant contributions to TJC under external torques throughout the flexion range. Average LCL contributions were highest from 0 deg to 60 deg flexion under external and varus torques, as well as internal torques from 60 deg to 110 deg flexion. Similarly, these regions were found to have statistically significant LCL contributions. Anterior and posterior loads generally reduced collateral contribution to TJC; however, posterior loads further reduced MCL contribution, while anterior loads further reduced LCL contribution. These results provide insight to the functional role of the collaterals over a broad range of passive constraint. Developing a map of collateral ligament contribution to TJC may be used to identify the effects of injury or surgical intervention on soft-tissue, and how collateral ligament contributions to constraint correlate with activities of daily living.

Malrotated tibial component increases medial collateral ligament tension in total knee arthroplasty.

Malrotation of the tibial component can lead to complications after total knee arthroplasty (TKA). Despite reports of internal rotation being associated with more severe pain or stiffness than external rotation, the biomechanical reasons remain largely unknown. We used a computer simulation model and evaluated traction forces in the lateral collateral ligament (LCL) and medial collateral ligament (MCL) with a malrotated tibial component during squatting. We also examined tibiofemoral and patellofemoral contact forces and stresses under similar conditions. A dynamic musculoskeletal knee model was simulated in three different constrained tibial geometries with a prototype component. The testing conditions were changed between 15° external and 15° internal rotation of the tibial component. With internal rotation of the tibial component, the MCL force increased progressively; the LCL force also increased, but only up to less than half of the MCL force values. A higher degree of constraint of the tibial component was associated with greater femoral rotational movement and higher MCL forces. The tibiofemoral and patellofemoral contact forces were not influenced by malrotation of the tibial component, but the contact stresses increased because of decreased contact area. This altered loading condition could cause patient complaints and polyethylene problems after TKA.