Abstract
Introduction
Persistent patellofemoral (PF) pain is a common postoperative complication after total knee arthroplasty (TKA). In the USA, patella resurfacing is conducted in more than 80% of primary TKAs [1], and is, therefore, an important factor during surgery. Studies have revealed that the position of the patellar component is still controversially discussed [2–4]. However, only a limited number of studies address the biomechanical impact of patellar component malalignment on PF dynamics [2]. Hence, the purpose of our present study was to analyze the effect of patellar component positioning on PF dynamics by means of musculoskeletal multibody simulation in which a detailed knee joint model resembled the loading of an unconstrained cruciate-retaining (CR) total knee replacement (TKR) with dome patella button.
Material and Methods
Our musculoskeletal multibody model simulation of a dynamic squat motion bases on the SimTK data set (male, 88 years, 66.7 kg) [5] and was implemented in the multibody dynamics software SIMPACK (V9.7, Dassault Systèmes Deutschland GmbH, Gilching, Germany). The model served as a reference for our parameter analyses on the impact on the patellar surfacing, as it resembles an unconstrained CR-TKR (P.F.C. Sigma, DePuy Synthes, Warsaw, IN) while offering the opportunity for experimental validation on the basis of instrumented implant components [5]. Relevant ligaments and muscle structures were considered within the model. Muscle forces were calculated using a variant of the computed muscle control algorithm. PF and tibiofemoral (TF) joints were modeled with six degrees of freedom by implementing a polygon-contact model, enabling roll-glide kinematics. Relative to the reference model, we analyzed six patellar component alignments: superior-inferior position, mediolateral position, patella spin, patella tilt, flexion-extension and thickness. The effect of each configuration was evaluated by taking the root-mean-square error (RMSE) of the PF contact force, patellar shift and patellar tilt with respect to the reference model along knee flexion angle.
Results
The analysis showed that the PF contact force was mostly affected by patellar component thickness (RMSE=440 N) as well as superior-inferior (RMSE=199 N), and mediolateral (RMSE=98 N) positioning.. PF kinematics was mostly affected by mediolateral positioning, patellar component thickness, and superior-inferior positioning. Medialization of the patellar component reduced the peak PF contact force and caused a lateral patellar shift.
Discussion
Based on our findings, we conclude that malalignment in mediolateral and superior-inferior direction, tilt and thickness of patellar resurfacing are the most important intraoperative parameters to affect PF dynamics. It could be shown that the translational positioning is more critical than rotational positioning regarding PF contact force. Reported findings are in good agreement with previous experimental and clinical studies [2–4]. Our data reveal that patellar component positioning has to be aligned precisely during total knee arthroplasty to prevent postoperative complications.
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