Do surgical patellar interventions restore patellar kinematics in fixed-bearing, cruciate-retaining total knee arthroplasty?: An in vitro study

[Patellar tracking in knee arthroplasty]

Knee arthroplasty is a demanding procedure that, when carried out appropriately, results in significant pain relief and patient satisfaction. The success of the operation is influenced by many factors. The most important ones describe the implant design, the orientation of the components and the ligament tension. The patellofemoral joint is often neglected as an important part of the operation. Initially, complications in the area of the patellofemoral joint do not appear to be devastating, but in many cases, they lead to significant consequences for the patient, along with severe pain and limited mobility. The most common complications arise from patellar maltracking. This often occurs due to misplacement of the tibial and femoral components and the altered shape of the patella. If the placement of the components with regard to patellar tracking is considered, bony and/or soft tissue addressing measures remain to further optimize the movement of the patella. The following manuscript is dedicated to discussing causes to avoid patellar maltracking and improve clinical outcomes.

Medial Open Wedge High tibial Osteotomy (MOWHTO) does not relevantly alter patellar kinematics: a cadaveric study

PURPOSE

The purpose of this study was to quantify the influence of medial open wedge high tibial osteotomy on patellar kinematics using optical computer navigation, as anterior knee pain infrequently occurs postoperatively and the reason is still being unknown.

METHODS

Ten medial open wedge high tibial osteotomies at supratuberosity level in 5 full body specimens were performed. The effect of the surgical procedure on patellar kinematics, measured at 5 and 10 degrees of leg alignment correction angle, was analyzed and compared to native patellar kinematics during passive motion-regarding patella shift, tilt, epicondylar distance and rotation. Linear mixed models were used for statistical analysis, a two-sided p value of ≤ 0.05 was considered statistically significant.

RESULTS

Tilt behavior, medial shift and epicondylar distance did not show a significant difference regarding natural patellar kinematics at both osteotomy levels. Both osteotomy correction angles showed a significant less external rotation of the patella (p < 0.001, respectively) compared to natural kinematics.

CONCLUSIONS

Except less external rotation of the patella, medial open wedge high tibial osteotomy does not seem to relevantly alter patellar alignment during passive motion. Future clinical studies have to prove the effect of MOWHTO on patellar kinematics measured in this experimental setup, especially regarding its influence on anterior knee pain.

The influence of varus and valgus deviation on patellar kinematics in healthy knees: An exploratory cadaver study

BACKGROUND

Patellofemoral instability may lead to osteoarthritis, anterior knee pain, and patellar luxation. The purpose of this study was to conduct an exploratory investigation into the difference of patellar kinematics of healthy knees during extension/flexion cycles in neutral, varus and valgus alignment.

METHODS

The three-dimensional patellar kinematics of 10 lower extremities of whole body cadavers were examined during passive motion, in neutral position, and under valgus and varus stress. Kinematics was recorded by means of an optical computer navigation system.

RESULTS

The study samples did not significantly differ with regard to mediolateral patellar shift and epicondylar distance. Varus stress led to significantly higher external rotation than valgus stress (P=0.04) and to a significantly higher lateral patellar tilt than neutral position (P=0.016) and valgus stress (P=0.016). No difference was found between valgus stress and neutral position.

CONCLUSION

Analysis of tibiofemoral alignment alone is insufficient for predicting patellar kinematics.

The Evolution of Implant Design Decreases the Incidence of Lateral Release in Primary Total Knee Arthroplasty

BACKGROUND

Appropriate balancing of the patellofemoral joint (PFJ) using a lateral release can help to prevent patellar instability in total knee arthroplasty (TKA). Contemporary total knee implant designs are characterized by enhanced trochlear geometry more similar to native knee anatomy to minimize instability and reduce utilization of a lateral release.

METHODS

We retrospectively reviewed consecutive TKA cases from a single senior surgeon's practice with 3 successive total knee designs: the Press-Fit Condylar (PFC), the Sigma, and the ATTUNE (DePuy, Warsaw, IN). We evaluated the use of lateral release with each implant type to determine if design changes have improved patellar stability, reducing the need for lateral release. We used multivariate analysis to determine the association between implant type and lateral release, adjusting for age, sex, preoperative alignment, and bearing type.

RESULTS

We evaluated 1991 records of primary TKAs performed from 1980-2015. As compared with the ATTUNE, the adjusted odds of lateral release were greater for patients receiving PFC implants (Odds ratio [OR] 6.35, 95% confidence interval [CI] 3.85,10.49) and Sigma implants (OR 2.02, 95% CI 1.26, 3.23). In addition, fixed bearing implants were associated with greater adjusted odds of lateral release (OR 1.80, 95% CI 1.24, 2.62).

CONCLUSION

We found that older knee implants were associated with higher use of lateral release, with successive designs the need for lateral release to balance the PFJ decreased. Continued design improvements to match the native knee anatomy may further improve the stability of the PFJ in future designs.

Stress distribution of the patellofemoral joint in the anatomic V-shape and curved dome-shape femoral component: a comparison of resurfaced and unresurfaced patellae

PURPOSE

Whether to resurface the patella in knee replacement remains a controversial issue. The geometrical design of the trochlear groove in the femoral component could play an important role in determining the stress distribution on the patellofemoral joint, but this has not been sufficiently reported on. This study attempted to determine the effect of implant design on contact mechanics by means of a finite element method.

METHODS

Two designs, an anatomical V-shape design (VSD) and a dome-shape design (DSD), for the anterior trochlear surface in a contemporary femoral component were chosen for examining the contact characteristics. The use and absence of patella resurfacing was simulated. The stress and strain distribution on the patellar bone and the polyethylene component were calculated for comparison.

RESULTS

Without patellar resurfacing, the maximal compressive strain in the patellar bone in the VSD model was about 20 % lower than the DSD model. On the other hand, with resurfacing, the maximal strain for the VSD model was 13.3 % greater than for DSD. Uneven stress distribution at the bone-implant interface was also noted for the two designs.

CONCLUSION

The femoral component with a V-shape trochlear groove reduced the compressive strain on the unresurfaced patella. If resurfacing the patella, the femoral component with a curved domed-shape design might reduce the strain in the remaining patellar bone. Uneven stress could occur at the bone-implant interface, so design modifications for improving fixation strength and medialization of the patellar button would be helpful in reducing the risk of peg fracture or loosening.

LEVEL OF EVIDENCE

III.

[Patella navigation in computer-assisted TKA : Intraoperative measurement of patellar kinematics. Video article]

INTRODUCTION

Patellofemoral maltracking is a relevant problem after total knee arthroplasty (TKA). Patella navigation is a tool that allows real time monitoring of patella tracking.

MATERIAL

This video contribution demonstrates the technique of patellofemoral navigation and a possible consequence of intraoperative monitoring. A higher postoperative lateral tilt is addressed with a widening of the lateral retinaculum in a particular manner.

CONCLUSION

In selected cases of patellofemoral problems, patella navigation is a helpful tool to evaluate patellofemoral tracking intraoperatively. Modifications of implant position and soft tissue measurements can then prevent postoperative patellofemoral maltracking.

An Open-Source Toolbox for Surrogate Modeling of Joint Contact Mechanics

GOAL

Incorporation of elastic joint contact models into simulations of human movement could facilitate studying the interactions between muscles, ligaments, and bones. Unfortunately, elastic joint contact models are often too expensive computationally to be used within iterative simulation frameworks. This limitation can be overcome by using fast and accurate surrogate contact models that fit or interpolate input-output data sampled from existing elastic contact models. However, construction of surrogate contact models remains an arduous task. The aim of this paper is to introduce an open-source program called Surrogate Contact Modeling Toolbox (SCMT) that facilitates surrogate contact model creation, evaluation, and use.

METHODS

SCMT interacts with the third-party software FEBio to perform elastic contact analyses of finite-element models and uses MATLAB to train neural networks that fit the input-output contact data. SCMT features sample point generation for multiple domains, automated sampling, sample point filtering, and surrogate model training and testing.

RESULTS

An overview of the software is presented along with two example applications. The first example demonstrates creation of surrogate contact models of artificial tibiofemoral and patellofemoral joints and evaluates their computational speed and accuracy, while the second demonstrates the use of surrogate contact models in a forward dynamic simulation of an open-chain leg extension-flexion motion.

CONCLUSION

SCMT facilitates the creation of computationally fast and accurate surrogate contact models. Additionally, it serves as a bridge between FEBio and OpenSim musculoskeletal modeling software.

SIGNIFICANCE

Researchers may now create and deploy surrogate models of elastic joint contact with minimal effort.