A mechanical comparison of high-flexion and conventional total knee arthroplasty

Finite element analysis in the optimization of posterior-stabilized total knee arthroplasty

Posterior-stabilized total knee arthroplasty (PS-TKA) is associated with high rates of satisfaction and functional recovery. This is notably attributed to implant optimization in terms of design, choice of materials, positioning and understanding of biomechanics. Finite elements analysis (FEA) is an assessment technique that contributed to this optimization by ensuring mechanical results based on numerical simulation. By close teamwork between surgeons, researchers and engineers, FEA enabled testing of certain clinical impressions. However, the methodological features of the technique led to wide variations in the presentation and interpretation of results, requiring a certain understanding of numerical and biomechanical fields by the orthopedic community. The present study provides an up-to-date review, aiming to address the following questions: what are the principles of FEA? What is the role of FEA in studying PS design in TKA? What are the key elements in the literature for understanding the role of FEA in PS-TKA? What is the contribution of FEA for understanding of tibiofemoral and patellofemoral biomechanical behavior? What are the limitations and perspectives of digital simulation and FEA in routine practice, with a particular emphasis on the "digital twin" concept? LEVEL OF EVIDENCE: V, expert opinion.

Comparison of Modular Conventional and High-Flexion Posterior-Stabilized Total Knee Arthroplasties in the Same Patients at a Mean Follow-Up of 15 Years

BACKGROUND

As previous studies are limited to short-term clinical data on conventional and high-flexion total knee arthroplasties (TKAs), long-term clinical data on these TKAs remain unclear. Therefore, we evaluated long-term functional outcome, range of knee motion, revision rate, implant survival, and the prevalence of osteolysis after conventional and high-flexion TKAs in the same patients.

METHODS

The authors evaluated a cohort of 1206 patients with a mean age of 65.3 ± 7 years (range: 22-70) who underwent bilateral simultaneous sequential TKAs. One knee received a conventional TKA and the other received a high-flexion TKA. The mean duration of follow-up was 15.6 years (range: 14-17).

RESULTS

No significant differences were found between the 2 groups at the latest follow-up with respect to Knee Society score (93 vs 92 points, P = .765), pain score (45 vs 44 points, P = .641), range of knee motion (125° vs 126°, P = .712), and radiographic and computed tomography scan results. Furthermore, no significant revision rate differences were found between the 2 groups (1.3% for conventional TKA vs 1.6% for high-flexion TKA; P = .137). There was no osteolysis recorded in either group. The rate of survivorship free of implant revision or aseptic loosening was 98.7% (95% CI = 91-100) for conventional TKA and 98.4% (95% CI = 91-100) for high-flexion TKA at 17 years.

CONCLUSION

At the latest follow-up, we were not able to demonstrate any significant difference between conventional and high-flexion TKAs with respect to functional outcome scores, range of knee motion, revision rate, implant survival, and prevalence of osteolysis.

Weight Bearing Activities change the Pivot Position after Total Knee Arthroplasty

The knee joint center of rotation is altered in the absence of the anterior cruciate ligament, which leads to substantially higher variance in kinematic patterns. To overcome this, total knee arthroplasty (TKA) designs with a high congruency in the lateral compartment have been proposed. The purpose of this study was to analyze the influence of a lateral pivot TKA-design on in-vivo knee joint kinematics. Tibiofemoral motion was retrospectively addressed in 10 patients during unloaded flexion-extension and loaded lunge using single plane fluoroscopy. During the unloaded flexion-extension movement, the lateral condyle remained almost stationary with little rollback at maximum flexion. The medial condyle exhibited anterior translation during the whole flexion cycle. During the loaded lunge movement, a higher degree of rollback compared to the unloaded activity was observed on the lateral condyle, whereas the medial condyle remained almost stationary. The results showed a clear lateral pivot during the unloaded activity, reflective of the implant’s geometric characteristics, and a change to a medial pivot and a higher lateral rollback during the weight-bearing conditions, revealing the impact of load and muscle force. It remains unclear if the kinematics with a lateral TKA design could be considered as physiological, due to the limited knowledge available on native knee joint kinematics.

The Long-Term Results of Simultaneous High-Flexion Mobile-Bearing and Fixed-Bearing Total Knee Arthroplasties Performed in the Same Patients

BACKGROUND

Our study determined the long-term clinical, radiographic, and computed tomography scanning results of high-flexion mobile-bearing and fixed-bearing total knee arthroplasties (TKAs) in the same younger patients. In addition, the survivorship and complication rates of both groups were evaluated.

METHODS

Bilateral simultaneous sequential TKAs were performed in 164 patients (328 knees). There were 142 women and 22 men with a mean age of 63 ± 9 years (range 41-65), who received a high-flexion mobile-bearing prosthesis in one knee and a high-flexion fixed-bearing prosthesis in the other. The mean follow-up was 16.9 years (range 15-18).

RESULTS

At the latest follow-up, the mean Knee Society knee scores (94 ± 8 vs 95 ± 9 points, P = .7), Western Ontario and McMaster Universities Osteoarthritis Index (20 ± 11 vs 20 ± 11 points, P = 1.0), range of knee motion (125° ± 10° vs 127° ± 9°, P = .8), and University of California, Los Angeles activity scores (7.8 vs 7.8 points, P = 1.0) were below the level of clinical significance between the 2 groups. Survival rate of high-flexion mobile-bearing TKA was 98.2% and that of high-flexion fixed-bearing TKA was 97% at 16 years. No osteolysis was identified in either group.

CONCLUSION

After a minimum duration of follow-up of 13 years, we found no significant difference between these 2 groups with regard to functional outcome, knee motion, prevalence of osteolysis, or survivorship. This study does not clearly direct the surgeon toward either arm of treatment. Longer term follow-up is needed to prove the superiority of one type of implant over the other one.

Patients achieved greater range of movement when using high-flexion implants

PURPOSE

NexGen Legacy Posterior Stabilized high-flexion prostheses (LPS-Flex) have been popularized as an alternative to NexGen standard prostheses (LPS) in total knee arthroplasty (TKA). Advocates of this new generation prosthesis suggest improved postoperative knee flexion. The purpose of this study was to summarize the best evidence for comparing the range of motion (ROM) and functional outcomes of LPS-Flex prostheses and LPS in TKA.

METHODS

Electronic databases were systematically searched to identify relevant randomized controlled trials (RCTs). The last date for our research was July 2014. Our search strategy was followed the requirements of the Cochrane Library Handbook. The methodological quality was assessed, and the data were extracted independently by two authors.

RESULTS

Nine studies that included 978 knees met our inclusion criteria for review. The results showed that there was larger postoperative ROM (1.62, 95% CI 0.52-2.72) in the LPS-Flex group than in the LPS group. There was not a statistically significant difference in the clinical functional scores and complications between the LPS-Flex group and the LPS group in TKA. The pooled mean differences were as follows: total KSS, -0.64 (95% CI -1.41 to 0.13); functional KSS, -0.53 (95% CI -1.51 to 0.45); HSS, 0.23 (95% CI -0.87 to 1.33); complications, 0.49 (95% CI 0.20-1.24); and radiolucent lines, 1.56 (95% CI 0.68-3.55).

CONCLUSIONS

The preliminary results indicate that the NexGen LPS-Flex prosthesis provides an alternative to the NexGen LPS prosthesis, with greater range of motion and without severe complications or radiographic outcomes. The clinical advantages were not shown in the KSS or the HSS. Thus, the selection of a high-flexion prosthesis should depend on the characteristics of the patient, particularly high motivation and poor preoperative ROM. The potential benefits in the medium- and long-term outcomes require confirmation by larger, multicenter and well-conducted RCTs.

LEVEL OF EVIDENCE

Therapeutic study, Level I.

Design modifications of high-flexion TKA do not improve short term clinical and radiographic outcomes

BACKGROUND

The prosthesis of contemporary total knee arthroplasty (TKA) has been modified to provide a more familiar environment for higher flexion angle of the replaced knee. The design modifications continue based on evidence reported in the literature. However, whether these modifications of the prosthesis design lead to improvements in clinical results needs further investigation. We determined whether the prosthesis modifications based on recent evidence improve clinical and radiographic results following high flexion TKA.

METHODS

524 patients who underwent primary TKA using two different high flexion prostheses were divided to Group 1 (HF-1) using a high flexion prosthesis, group 2 (HF-2) using the more recently devised high flexion prosthesis, which claims to be adopted from evidence proposed in the literature. Clinical outcomes included ranges of motion (ROM), the Knee Society knee and function score (KSKS and KSFS), the Western Ontario and McMaster Universities Arthritis Index (WOMAC) score, radiologic evaluation, and complication related to surgery.

RESULTS

No differences in terms of clinical and radiographic results were observed between the groups at the 2 year follow-up. The mean ROM was 123°and 124° in the HF-1 and HF-2 groups, respectively. KSKS were 90 and 89.1, KSFS were 76.6 and 81.8, and total WOMAC scores were 23.1 and 24.9 in the HF-1 and HF- 2 groups. No differences of the incidences of radiolucency on radiographs (1.4% in HF-1, 2.1% in HF-2) and dislocation (1 case in HF-1 only) was observed.

CONCLUSIONS

Even if recent modifications in the design of high flexion TKA prosthesis were based on evidence in the literature, they did not provide meaningful improvements in short-term clinical and radiographic outcomes after TKA. Surgeons should consider our findings when choosing a prosthesis for their patients.

Total knee arthroplasty designed to accommodate the presence or absence of the posterior cruciate ligament

Evidence for selecting the same total knee arthroplasty prosthesis whether the posterior cruciate ligament (PCL) is retained or resected is rarely documented. This study reports prospective midterm clinical, radiographic, and functional outcomes of a fixed-bearing design implanted using two different surgical techniques. The PCL was completely retained in 116 knees and completely resected in 43 knees. For the entire cohort, clinical knee (96 ± 7) and function (92 ± 13) scores and radiographic outcomes were good to excellent for 84% of patients after 5–10 years in vivo. Range of motion averaged 124° ± 9°, with 126 knees exhibiting ≥120° flexion. Small differences in average knee flexion and function scores were noted, with the PCL-resected group exhibiting an average of 5° more flexion but an average function score that was 7 points lower compared to the PCL-retained group. Fluoroscopic analysis of 33 knees revealed stable tibiofemoral translations. This study demonstrates that a TKA articular design with progressive congruency in the lateral compartment can provide for femoral condyle rollback in maximal flexion activities and achieve good clinical and functional performance in patients with PCL-retained and PCL-resected TKA. This TKA design proved suitable for use with either surgical technique, providing surgeons with the choice of maintaining or sacrificing the PCL.

Femoral loosening of high-flexion total knee arthroplasty: the effect of posterior cruciate ligament retention and bone quality reduction

High-flexion total knee arthroplasty (TKA) may be more sensitive to femoral loosening than conventional TKA as the knee joint force increases during deep flexion. The objective of this study was to evaluate whether the probability of femoral loosening is equal in posterior cruciate ligament (PCL) retaining and substituting high-flexion knee implants and whether loosening is related to femoral bone quality. A three-dimensional finite element (FE) model of the knee was developed and a weight-bearing deep knee bend up to 155° was simulated. PCL conservation considerably increased the compressive tibio-femoral joint force as a maximal force of 4.7-6.0 × bodyweight (BW) was found, against a maximal force of 4.0 × BW for posterior-stabilized TKA. Roughly 14% of the fixation site beneath the anterior femoral flange was predicted to debond on the long-term in case of cruciate-retaining TKA compared to 20% in case of posterior-stabilized TKA. Reducing the femoral bone quality to 50% of its original bone mineral density increased the amount of potential anterior failure for cruciate-retaining TKA to 22% and posterior-stabilized TKA to 24%. We therefore conclude that the femoral fixation site has a similar failure potential for both cruciate-retaining and posterior-stabilized high-flexion TKA.

Comparable short-term results seen with standard and high-flexion knee arthroplasty designs in European patients

PURPOSE

In a prospective study we evaluated outcomes of total knee arthroplasty (TKA) procedures in 62 patients with a follow up of 12 months to test our hypothesis that high-flexion CR (cruciate retaining) TKA provides a better range of motion and better outcome than standard CR design in Central European patients with their special problems and demands.

METHODS

Patients were randomly divided into two groups (high flex vs. standard). The outcome was determined by measuring maximum knee flexion and using the KS-score and the SF-36 score.

RESULTS

After 12 months ability to flex the knee significantly improved in both groups to 115° (SD 11) in the high flex group versus 119° (SD 12) in the standard group. There was no difference between the designs regarding maximum flexion (p = 0.78). Overall clinical rating scores significantly improved in both groups, but there was no difference between groups at one year after surgery (p (KSS) = 0.7 and p (SF-36) = 0.63). KS-score values improved from 25 points to 89 points for standard TKAs and from 20 points to 90 points for high flex TKAs. SF-36-score "Physical Functioning" values improved from 33 points to 66 points for standard TKAs and from 27 points to 63 points for high flex TKAs.

CONCLUSION

Our results confirm known good results of the procedure and suggest that the benefit of high flex knee designs is similar to standard knee designs one year after index surgery. Further studies are required to evaluate long-term results of both designs.

Effect of implant design on knee flexion

From March 2006 to August 2008, 93 subjects (186 knees) underwent simultaneous bilateral total knee arthroplasty performed by eight surgeons at North American centers. This randomized study was conducted to determine whether non-weight-bearing passive flexion was superior for knees receiving a posterior stabilized high flexion device compared to a posterior stabilized standard device in the contra-lateral knee. Weight-bearing single leg active flexion was one secondary endpoint. Follow-up compliance was 92.5%. Results show small, but significant superiority in the motion metrics for the high flexion device compared to the standard device 12 months after surgery, especially for a subgroup of patients with pre-operative flexion less than 120° in both knees. Thus, the ideal candidate for the high flexion device may be one with lesser pre-operative flexion.

Does a mobile-bearing, high-flexion design increase knee flexion after total knee replacement?

This prospective randomised controlled double-blind trial compared two types of PFC Sigma total knee replacement (TKR), differing in three design features aimed at improving flexion. The outcome of a standard fixed-bearing posterior cruciate ligament-preserving design (FB-S) was compared with that of a high-flexion rotating-platform posterior-stabilised design (RP-F) at one year after TKR. The study group of 77 patients with osteoarthritis of the knee comprised 37 men and 40 women, with a mean age of 69 years (44.9 to 84.9). The patients were randomly allocated either to the FB-S or the RP-F group and assessed pre-operatively and at one year post-operatively. The mean post-operative non-weight-bearing flexion was 107° (95% confidence interval (CI) 104° to 110°)) for the FB-S group and 113° (95% CI 109° to 117°) for the RP-F group, and this difference was statistically significant (p = 0.032). However, weight-bearing range of movement during both level walking and ascending a slope as measured during flexible electrogoniometry was a mean of 4° lower in the RP-F group than in the FB-S group, with 58° (95% CI 56° to 60°) versus 54° (95% CI 51° to 57°) for level walking (p = 0.019) and 56° (95% CI 54° to 58°) versus 52° (95% CI 48° to 56°) for ascending a slope (p = 0.044). Further, the mean post-operative pain score of the Western Ontario and McMaster Universities Osteoarthritis Index was significantly higher in the RP-F group (2.5 (95% CI 1.5 to 3.5) versus 4.2 (95% CI 2.9 to 5.5), p = 0.043). Although the RP-F group achieved higher non-weight-bearing knee flexion, patients in this group did not use this during activities of daily living and reported more pain one year after surgery.

High-flexion total knee arthroplasty: survivorship and prevalence of osteolysis: results after a minimum of ten years of follow-up

BACKGROUND

We are aware of no information about the mid-term performance of the high-flexion total knee arthroplasty, although early results have been reported. The purpose of this study was to evaluate the mid-term results of high-flexion and conventional knee prostheses.

METHODS

We prospectively compared the results of 100 patients with osteoarthritis who had received a NexGen Legacy Posterior Stabilized (NexGen LPS) prosthesis in one knee and a NexGen Legacy Posterior Stabilized-Flex (NexGen LPS-Flex) prosthesis in the other. Seventy-five patients (150 knees) were women and twenty-five (fifty knees) were men. The mean age was sixty-five years (range, forty-eight to eighty-five years) at the time of the index procedure. The mean duration of follow-up was 10.3 years (range, ten to 10.6 years). The patients were assessed with radiographs, with the rating system of the Knee Society, and with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score at three months, one year, and annually thereafter.

RESULTS

Total knee scores, knee function scores, pain scores, WOMAC scores, knee motion, and activity scores did not differ significantly between the two designs of the implants, on the basis of the numbers studied, either preoperatively or at the time of final follow-up. One knee in the NexGen LPS-Flex group was revised because of recurrent infection. No knee in either group had aseptic loosening of the components. The Kaplan-Meier survivorship at ten years postoperatively, with revision defined as the end point, was 100% (95% confidence interval, 94 to 100) for the NexGen LPS prosthesis and 99% (95% confidence interval, 93 to 100) for the NexGen LPS-Flex prosthesis.

CONCLUSIONS

After a minimum duration of follow-up of ten years, there were no significant differences between the two groups with regard to implant survivorship, functional outcome, knee motion, or prevalence of osteolysis.

The effect of tibial posterior slope on contact force and ligaments stresses in posterior-stabilized total knee arthroplasty-explicit finite element analysis

Purpose

The purpose of this study is to evaluate the effect of change in tibial posterior slope on contact force and ligament stress using finite element analysis.

Materials and Methods

A 3-dimensional finite element model for total knee arthroplasty was developed by using a computed tomography scan. For validation, the tibial translations were compared with previous studies. The finite element analysis was conducted under the standard gait cycle, and contact force on ultra-high molecular weight polyethylene (UHMWPE) and stresses on lateral and medial collateral ligaments were evaluated.

Results

The tibial translations showed similarity with previous studies. As the tibial posterior slope angle increases, the contact stress area increased and was well distributed, and the contact force on UHMWPE decreased overall. However, the maximum contact force in the case for 10° case was greater than those for others. The stresses on ligaments were the greatest and smallest in 0° and 10° cases, respectively.

Conclusions

The higher tibial posterior slope angle leads to the lower contact stress and more extensive stress distribution overall in posterior-stabilized total knee arthroscopy. However, it does not absolutely mean the smallest contact force. The stresses on ligaments increased with respect to the smaller tibial posterior slope angle.

High-flexion vs conventional prostheses total knee arthroplasty: a meta-analysis

Whether high-flexion prostheses are superior to conventional prostheses after total knee arthroplasty (TKA) remains controversial. Therefore, this meta-analysis was conducted to evaluate the effects of these 2 different designs. After a comprehensive search, 11 trials with 1204 knees were eligible for data extraction and pooled analysis. The results demonstrated that there were no differences in range of motion of high-flexion posterior-stabilized vs standard posterior-stabilized TKA (weighted mean improvement, 0.93°; 95% confidence intervals, -0.75° to 2.60°; P = .28), range of motion of high-flexion cruciate-retaining vs cruciate-retaining TKA (2.06°; 0.06°-4.17°; P = .06), weight-bearing flexion (2.05°; 0.99°-5.08°; P = .19), Knee Society Scores (1.59 points; 0.42-3.60 points; P = .12), and Hospital for Special Surgery Scores (0.84 points; 0.37-2.04 points; P = .17) with at least 1-year follow-up. No infection, loosening, and osteolysis were found. The current evidences cannot confirm that high-flexion prostheses are superior to conventional prostheses.

In vivo knee kinematics in patients with bilateral total knee arthroplasty of 2 designs

Many younger and highly active patients desire to achieve high flexion after total knee arthroplasty. This study's purpose was to determine if a contemporary total knee arthroplasty design improved functional knee flexion compared with a traditional total knee arthroplasty in patients living a Western lifestyle. Ten patients with bilateral total knee arthroplasty of 2 types were studied during weight-bearing lunge, kneeling, and stair activities using fluoroscopic imaging. There were no differences in maximum knee flexion during lunging or kneeling. Statistically significant differences in tibial rotation and condylar translation were observed during the 3 activities. Although several joint kinematic differences were observed, no important functional differences were observed in clinically excellent, high performing subjects with bilateral total knee arthroplasty of 2 types.

Recent advances in designs, approaches and materials in total knee replacement: literature review and evidence today

Ever since Themistocles Gluck described the use of an ivory cup as a tibial hemiarthroplasty in 1894, knee arthoplasty has continued to evolve. Both human ingenuity and intensive clinical research has led to an improved understanding of biomaterials and knee kinematics, resulting in the modern total knee replacement which has enjoyed such a clinical and commercial success. As it increases in popularity, attempts to improve knee arthroplasty have been driven by demands for improved function and implant survival, particularly in younger, more demanding patients. Research continues to see if advances in implant instrumentation, materials and design will translate into improved clinical outcomes and longevity.

Does high-flexion total knee arthroplasty promote early loosening of the femoral component?

High-flexion knee replacements have been developed to accommodate a large range of motion (RoM > 120°). Knee implants that allow for higher flexion may be more sensitive to femoral loosening as the knee load is relatively high during deep knee flexion, which could result in an increased failure potential at the implant-cement interface of the femoral component. A 3D finite element knee model was developed including a posterior-stabilized high-flexion knee replacement to analyze the stress state at the femoral implant-cement interface during a full squatting movement (RoM ≤ 155°). During deep flexion (RoM > 120°), tensile and shear stress concentrations were found at the implant-cement interface beneath the proximal part of the anterior flange. Particularly, the shear stresses at this interface location increased during high flexion, from a peak stress of 4.03 MPa at 90° to 6.89 MPa at 140° of flexion. Tensile stresses were substantially lower, having a peak stress of 0.72 MPa at 100° of flexion. Using data from earlier interface strength experiments, none of the interface beneath the anterior flange was predicted to fail in the normal flexion range (RoM ≤ 120°), whereas the prediction increased to 2.2% of the interface during deeper knee flexion. Thigh-calf contact reduced the knee forces, interface load, and failure risk beyond 140-145° of flexion. Based on the more critical stresses at the femoral fixation site between 120° and 145° of flexion, we conclude that the femoral component has a higher risk of loosening at high-flexion angles.

Biomechanical analysis of posterior cruciate ligament retaining high-flexion total knee arthroplasty

BACKGROUND

High-flexion knee replacements have been developed to accommodate a large range of flexion (>120 degrees ) after total knee arthroplasty. Both posterior cruciate ligament retaining and sacrificing high-flexion knee designs have been marketed. The main objective of this study was to evaluate the biomechanical performance of a cruciate-retaining high-flexion knee replacement. Furthermore, the mechanical behaviour of this high-flexion knee replacement was compared to both a cruciate-retaining conventional and a posterior-stabilized high-flexion knee replacement.

METHODS

A finite element prosthetic knee model was developed to analyze the mechanical performance of the knee designs evaluated in this study. Polyethylene stresses and the amount of femoral rollback were studied during a squatting movement (flexion <or=150 degrees).

FINDINGS

During deep knee flexion, the cruciate-retaining high-flexion design demonstrated a lower peak tibio-femoral contact stress (74.7 MPa) than the cruciate-retaining conventional design (96.5 MPa). The posterior-stabilized high-flexion design showed the lowest peak tibio-femoral contact stress at the condylar articulation (54.2 MPa), although the post was loaded higher (77.4 MPa). The knee designs analyzed in this study produced a similar amount of femoral rollback during normal knee flexion (flexion > 120 degrees), whereas the cruciate-retaining designs showed a paradoxical anterior movement of the femoral condyles during high-flexion (flexion>120 degrees).

INTERPRETATION

The current study demonstrates a cruciate-retaining high-flexion knee replacement produces a lower prosthetic load than a conventional cruciate-retaining replacement during deep knee flexion. Compared to a posterior-stabilized high-flexion design, the cruciate-retaining high-flexion design demonstrated an equivalent prosthetic loading along with an inferior amount of femoral rollback in the high-flexion range. Posterior cruciate ligament balancing is an important surgical aim for high-flexion knee arthroplasty.

A Cadaverically Evaluated Dynamic FEM Model of Closed-Chain TKR Mechanics

Knowledge of the behavior and mechanics of a total knee replacement (TKR) in an in vivo environment is key to optimizing the functional outcomes of the implant procedure. Computational modeling has shown to be an important tool for investigating biomechanical variables that are difficult to address experimentally. To assist in examining TKR mechanics, a dynamic finite-element model of a TKR is presented. The objective of the study was to develop and evaluate a model that could simulate full knee motion using a physiologically consistent quadriceps action, without prescribed joint kinematics. The model included tibiofemoral (TFJs) and patellofemoral joints (PFJs), six major ligament bundles and was driven by a uni-axial representation of a quadricep muscle. An initial parameter screening analysis was performed to assess the relative importance of 31 different model parameters. This analysis showed that ligament insertion location and initial ligament strain were significant factors affecting simulated joint kinematics and loading, with the contact friction coefficient playing a lesser role and ligament stiffness having little effect. The model was then used to simulate in vitro experiments utilizing a flexed-knee-stance testing rig. General model performance was assessed by comparing simulation results with experimentally measured kinematics and tibial reaction forces collected from two implanted specimens. The simulations were able to reproduce experimental differences observed between the test specimens and were able to accurately predict trends seen in the tibial reaction loads. The simulated kinematics of the TFJ and PFJ were less consistent when compared with experimental data but still reproduced many trends.