Single Radius TKA implants better than multi radii knee implants


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

David F. Hamilton*, A. Hamish R.W. Simpson, Richard Burnett, James T. Patton, Matthew Moran, Nicholas D. Clement, Colin R. Howie, Paul Gaston Article first published online: 20 MAR 2013DOI: 10.1002/jor.22344


Journal of Orthopaedic Research

Volume 31, Issue 8, pages 1201–1207, August 2013

Quality of Evidence: Therapy Level 2 Randomised control trial

Aim of the study

  • The postulated biomechanical advantage conferred to the extensor mechanism by a change in knee implant design was investigated as to whether it could be detected in patients by direct physical testing.
  • Recent studies showed that flexion-extension of the knee occured in a single flexion- extension axis and thereby a single radius implant has been developed
  • These single radii implants have been postulated to increase the quadriceps lever arm and thereby an increased quadriceps power
  • Single-axis designs promote normal ligament function with isometric stability throughout the full arc of motion.This results in more femoral rollback,increased patellofemoral moment arm, improved quadriceps muscle efficiency,and lower patellofemoral joint forces

Materials and Methods

  • The traditional implant and the one which incorporated the new single radius design features were given to 212 TKA patients who were enrolled in a double blind randomised controlled  trial.
  • Population:  212 patients undergoing unilateral  TKA
  • Intervention: Single radius group, 97 patients
  • Control: Multiradius group, 107 patients
  • Outcome: power output using leg extensor power rig


  • Pre-operatively and also at 6, 26, and 52 weeks post-operatively,the extensor mechanism power output and the physical perfomance on a battery of  timed functional activities were assesed.
  • Post arthroplasty,significantly enhanced power output was observed in both groups .
  • The new design implant group however demonstrated a greater change in power output than the traditional implant group.
  • 116% of the power output of the contralateral limb was  achieved in patients receiving the implant with the postulated biomedical advantage at  52 weeks.
  • Whereas 90% was achieved by the patients with the traditional multiradii design .


  • Thus,it was found that significantly greater extensor power was generated by the patients receiving a knee implant of single radius design



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