Lengthening the moment arm of the patella confers enhanced extensor mechanism power following total knee arthroplasty

Abstract

We investigated whether a postulated biomechanical advantage conferred to the extensor mechanism by a change in knee implant design was detectable in patients by direct physical testing. 212 TKA patients were enrolled in a double blind randomized controlled trial to receive either a traditional implant or one which incorporated new design features. Extensor mechanism power output and physical performance on a battery of timed functional activities was assessed pre-operatively and then at 6, 26, and 52 weeks post-operatively. Significantly enhanced power output was observed in both groups post-arthroplasty; however, the new design implant group demonstrated a greater change in power output than the traditional implant group. Posthoc testing of between group differences highlighted greater improvement at all post-operative assessments. At 52 weeks, patients receiving the implant with the postulated biomechanical advantage achieved 116% of the power output of their contralateral limb, whereas patients with the traditional design achieved 90%. No between group difference was detected in the patient's time to complete functional tasks. Thus, patients receiving a knee implant of a modern design (theoretically able to confer a mechanical advantage to the extensor mechanism) were found to generate significantly greater extensor power than those receiving a traditional implant without the postulated mechanical advantage. © 2013 Orthopaedic Research Society.