Summary

Tibial tubercle distalization decreased contact pressures and improved patella tracking in computational models of patients with patella alta and instability.

Abstract

Introduction

Tibial tuberosity distalization is commonly performed to treat recurrent patellar instability related to patella alta; however, it is unclear if this will result in an increase in articular cartilage contact pressure or improves tracking. We hypothesize that tibial tuberosity distalization will reduce lateral maltracking during knee flexion and will not elevate patellofemoral contact pressures.

Methods

Individual multibody dynamic simulation models were created from 3T MRI scans of seven patients (1 male, 6 female, mean age 17, range 13-21) with patella alta (Caton-Deschamps index = 1.3) being treated for patellar instability. The seven models chosen had the highest Caton-Deschamps index. Dynamic knee squatting was simulated for each knee in the pre-operative condition, following distalization of the attachment points for the patellar tendon on the tibia (Caton-Deschamps index = 1.0), and following distalization combined with patellar tendon tenodesis. The simulated motions were used to characterize the bisect offset index (percentage of the patella lateral to the deepest part of the trochlear groove) and the patellofemoral contact pressure distribution based on discrete element analysis. Repeated measures comparisons were used to identify significant (p < 0.05) differences between the pre-operative to post-operative data.

Results

Tibial tuberosity distalization significantly reduced lateral patellar maltracking at 10° and 15° of knee flexion. Tuberosity distalization significantly decreased the maximum pressure applied to cartilage at 15°, 30°, and 35° of flexion, with the decrease up to 20% of the pre-operative pressure. Distalization also significantly increased contact area from 15° to 40° of flexion. Tenodesis had a relatively small influence on the kinematics and pressure, compared to distalization.

Conclusions

The results indicate that in simulations derived from patients with patella alta, tibial tuberosity distalization pulls the patella into the trochlear groove at lower flexion angles to reduce lateral patellar maltracking. Improved tracking can also reduce the pressure applied to cartilage at low flexion angles. This suggests that clinically, patella alta patients treated with tuberosity distalization may benefit from improved stability and possibly decrease risk of cartilage overload and arthritis.