Background

Several factors are involved in patellofemoral (PF) stability. In severe cases of PF instability characterized by tibial tubercle-trochlear groove (TT-TG) distances greater than 20 mm, tibial tuberosity transfer (TTT) – a procedure wherein the tibial tubercle is medialized - may be considered to alter patellar tracking kinematics otherwise be primed for lateral patellar dislocation. TTT may also accompany lateral release and/or medial patellofemoral ligament (MPFL) reconstruction to correct alignment in lateral tracking to decrease the propensity of future dislocation, and post-traumatic chondral wear. The biomechanical consequences of lateral release in association with TTT, though, are not well described.

AIMS

The primary aim of this study is to develop and validate a finite element (FE) model of the patellofemoral joint. In using this model, the effect of lateral release in combination with tibial tuberosity transfer with respect to contact pressures, contact area and kinematics during knee flexion are investigated. The hypothesis is that lateral release performed with tibial tuberosity transfer would result in decreased contact pressures and contact areas and increased lateral patellar displacement producing lateral instability of the patella.

Methods

A finite element model of the PFJ is developed and validated. The model is modified to simulate patellar instability, tibial tuberosity transfer (medialization), and lateral release in combination with tibial tuberosity transfer. Patella contact pressure, contact area and lateral displacement are analysed.

Results

FE model reliably simulates contact pressures contact area and patellofemoral kinematics within one standard deviation of uncomplicated cadaveric specimens in a controlled laboratory setting without underlying pathology. Tibial tuberosity transfer in combination with lateral retinacular release markedly decreases patellofemoral contact pressures and contact areas and increases lateral displacement.

Discussion

This model is the first FE model of the PFJ that analyses the effect of lateral release in association with tibial tubercle medialization on patellofemoral contact pressures, contact area as well as patellar kinematics during knee flexion. The results of this study demonstrate that the FE model described reliably simulates patellofemoral kinematics and contact pressures within 1 standard deviation of uncomplicated cadaveric specimens in a controlled laboratory setting without underlying pathology. As such, the FE model described is well-suited to investigate the role of lateral release with concomitant TTT under various degrees of knee flexion with respect to PF contact pressures and patellar tracking kinematics – two biomechanical measurements that may clinically correspond to stages of post-traumatic arthritis, chondrosis and predictors of future patellar dislocation.