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J Orthop Res. 2013 Aug;31(8):1201-7. doi: 10.1002/jor.22344. Epub 2013 Mar 20.

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

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Department of Orthopaedics and Trauma, Royal Infirmary of Edinburgh and University of Edinburgh, 49 Little France Crescent, Edinburgh EH16 4SB, United Kingdom.


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.

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