Tibia Tubercle Distalization Reduces Contact Pressures in Patella Alta and Instability

Abstract

Patella alta is associated with patellar instability and arthritis. Tibial tuberosity distalization is commonly performed to treat recurrent patellar instability related to patella alta. The current study was performed to characterize the influence of tuberosity distalization on patellar tracking and the pressure applied to patellofemoral cartilage. High resolution 3T MRI scans of eight patients (1 male, 7 female, mean age 17, range 13-21) being treated for patellar instability were used to create individual multibody dynamic computer simulation models with patella alta (Caton-Deschamps index ≥ 1.3). Dynamic knee squatting was simulated for 3 conditions: the native knee with patella alta; following distalization (Caton-Deschamps index = 1.0); and following distalization combined with patellar tendon tenodesis. Lateral patella tracking was measured by the bisect offset index (percentage of the patella lateral to the deepest part of the trochlear groove) and the patellofemoral contact pressures and distribution were based on discrete element analysis). Repeated measures comparisons were used to identify significant (p < 0.05) differences between the conditions. : Tibial tuberosity distalization significantly reduced lateral patellar maltracking at 10°, 15° and 25° of knee flexion. At 10°, the average bisect offset index decreased from 0.85 to 0.78. Tuberosity distalization significantly decreased the maximum pressure applied to cartilage at 15°, 20°, 30°, and 35° of flexion, with the decrease more than 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. Tibial tuberosity distalization improves patella tracking by decreasing lateral patellar maltracking at lower flexion angles. Additionally, this improved tracking is also associated with a reduction in peak patella contact pressure at low flexion angles.