The influence of patellar height on patellofemoral contact force during total knee arthroplasty

Purpose

Residual anterior knee pain following total knee arthroplasty was reported to be related to high patellofemoral contact force. This study tried to show the relationship between patellar height and patellofemoral contact force in vivo, which has been demonstrated only in vitro thus far.

Methods

Fifty-five patients who had undergone a primary mobile-bearing posterior-stabilized total knee arthroplasty (28 cases using PFC Sigma and 27 cases using Attune) were included. After all the trial prostheses were placed, the patellar contact forces on the medial and lateral sides were measured using specially designed two uniaxial ultrathin force transducers at 0°–135° of knee flexion guided by the navigation system. Correlations between the pre-operative Insall-Salvati index and the medial or lateral patellar contact force in each flexion angle were analyzed using linear regression. Correlations between each patellar contact force and postoperative flexion angle were also assessed.

Result

There was a positive correlation between Insall-Salvati index and the lateral patellar contact force at 135° of flexion in all the patients, at 120° and 135° of flexion in patients with PFC Sigma and 135° of flexion in patients with Attune. The lateral patellar contact force at 120° and 135° of flexion in patients with PFC Sigma inversely correlated with postoperative flexion angle.

Conclusions

Patients with patella alta tended to demonstrate high lateral patellar contact force in deep knee flexion after total knee arthroplasty, which can affect the post operative flexion angle and should be treated to prevent residual anterior knee pain.