title: 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.
authors.affiliation: Department of Orthopaedics and Trauma, Royal Infirmary of Edinburgh and University of Edinburgh, 49 Little France Crescent, Edinburgh EH16 4SB, United Kingdom. d.f.hamilton@ed.ac.uk
authors.forename: David F
authors.initials: DF
authors.lastname: Hamilton
authors.forename: A Hamish R W
authors.initials: AH
authors.lastname: Simpson
authors.forename: Richard
authors.initials: R
authors.lastname: Burnett
authors.forename: James T
authors.initials: JT
authors.lastname: Patton
authors.forename: Matthew
authors.initials: M
authors.lastname: Moran
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Clement
authors.forename: Colin R
authors.initials: CR
authors.lastname: Howie
authors.forename: Paul
authors.initials: P
authors.lastname: Gaston
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000379:methods* / Q000534:rehabilitation; D004311:Double-Blind Method; D006801:Humans; D007719:Knee Joint / Q000502:physiology* / Q000601:surgery; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology*; D010329:Patella / Q000601:surgery*; D011474:Prosthesis Design; D016059:Range of Motion, Articular / Q000502:physiology*; D020127:Recovery of Function