Abstract
Introduction:
While survivorship of total knee arthroplasty (TKA) is excellent, up to 25% of patients remain dissatisfied with their outcome [1, 2]. Knee instability, which is common during high demand activities, contributes to patient dissatisfaction [3]. As younger patients undergo TKA, longevity requirements and functional demands will rise [4]. Design factors influence the functional outcome of the procedure [5, 6], although in clinical studies it can be difficult to distinguish joint mechanics differences between designs due to confounding variability in patient-related factors. The objective of the current study was to assess the stability and mechanics of several current TKA designs during high-demand dynamic activities using a computational model of the lower limb.
Methods:
Three high-demand dynamic activities (gait, stepdown, squat) were simulated in a previously described lower limb model (Fig. 1) [7]. The model included calibrated tibiofemoral (TF) soft-tissue structures, patellofemoral (PF) ligaments and extensor mechanism [8]. Loading conditions for the simulations were derived from telemetric patient data in order to evaluate TKA designs under physiological kinematic and loading conditions [7, 9]. Four fixed-bearing TKA designs (both cruciate-retaining (CR) and posterior-stabilizing (PS) versions) were virtually implanted into the lower limb model and joint motion, contact mechanics and interface loads were evaluated during simulation of each dynamic activity.
Results:
The range of anterior-posterior (A-P) and internal-external (I-E) motion for the least stable design was twice that of the most stable design during dynamic activity (Fig. 2). The increased anterior stability on some components did not translate directly to the largest bone-implant interface shear loading, which was dependent on coronal plane conformity and I-E torque, as component ranking varied throughout activity (Fig. 2, 3). Current designs varied substantially in conformity, resulting in reduced contact area and increased contact pressures with low-conformity articulation (Fig. 2).
Discussion:
While contemporary TKA designs all have good survivorship, there exists significant design differences related to the inherent stability of the articulating surfaces which result in kinematic differences during simulated high demand activities. The dynamic activity simulations developed in this study are representative of activities of daily living and provide a useful platform for design-phase iteration and pre-clinical testing of prospective TKA components.
