Quadriceps moment arm and quadriceps forces after total knee arthroplasty

Knee prosthetic designs that increase quadriceps moment arm can reduce quad riceps tension and patellofemoral compressive forces. Six knees from cadave rs were tested on the Oxford knee rig, which simulates closed chain knee ex tension under load. Three conditions were tested sequentially for each knee : Normal, Control (implanted with the Osteonics 7000 knee design), and Scor pio (implanted with the Osteonics Scorpio design). The center of flexion-ex tension of the Scorpio design was 10 mm posterior to that of Control that s erved to lengthen the quadriceps moment arm. An electromagnetic tracking sy stem measured dynamic knee kinematics, and a uniaxial load cell measured qu adriceps tension. The Scorpio design reduced quadriceps tension when compar ed with the Normal or Control knee ranging from 5% to 20%. This was statist ically significant at flexion angles greater than 50 degrees. In three knee s, the patellar component was instrumented with a triaxial load cell that m easured patellofemoral forces. Patellofemoral forces were lower with the Sc orpio design compared with the Control. Increasing quadriceps lever arm red uces quadriceps forces and can facilitate activities of daily living and en hance patient rehabilitation. Reduced quadriceps forces may result in reduc ed patellofemoral forces that can have a beneficial effect on anterior knee pain, patellar component wear, and loosening.