Range of motion after total knee arthroplasty (TKA) is increasingly an issue of critical concern in the performance of knee replacements and their ability to meet the functional demands of diverse patient populations. The goal of this study was to measure maximum weight bearing flexion in patients with one knee replaced using a posterior cruciate retaining (CR) device and the other a cruciate substituting (PS) device on a prospective basis.

Sixteen patients (32 knees) with bilateral TKA and excellent clinical/functional outcomes at least one year after surgery participated in this study. Eight patients received knee replacements from one surgeon, and eight patients received knee replacements of another design from a second surgeon. Their knees were imaged using fluoroscopy as the patients were asked to bend to maximum flexion with their foot on a 25 cm step. CAD model based shape matching techniques were used to measure knee flexion, axial rotation, and the anterior/ posterior (AP) location of tibio-femoral contact relative to the AP centre of the tibial insert. Paired t-tests were used to evaluate differences in means (p = 0.05).

PS knees had larger average flexion angles (121±8 deg vs. 114±5 deg, p=0.01) and greater femoral rollback (14±3 mm vs. 12±3 mm, p=0.02) than the CR knees. There was no difference in axial rotation (6±4 deg vs. 5±6 deg). The same trends were observed within the single design subgroups.

In patients with heterogeneous bilateral TKA, greater femoral rollback and weight-bearing flexion is exhibited by the knee with a posterior stabilised TKA.