KNEE KINEMATICS, QUADRICEPS TENSION, AND PATELLOFEMORAL FORCES IN TOTAL KNEE ARTHROPLASTY

Abstract

Quadriceps moment arm is one of the factors determining quadriceps force. Total knee arthroplasty designs with larger quadriceps moment arms should generate less quadriceps and patellofemoral forces. A study was conducted to measure knee kinematics, quadriceps and patellofemoral forces in two knee designs with differing centers of rotation. In addition, the effect of a central dome-shaped versus a medialized patella component was determined. Six human cadaver knees were tested before implantation and after sequential implantation with two posterior cruciate retaining designs: Scorpio and Control. The quadriceps moment arm of the Scorpio design was 1 cm longer than that of the Control design. Knee kinematics was measured with an eletromagnetic tracking device while the knee was put through dynamic simulated stair climbing under peak flexion moments of 40 N-m. Quadriceps tension and patellofemoral compressive and shear forces were measured for both conditions and for the central and medialized patella components. The normal unimplanted condition showed increasing rollback with flexion while both implanted conditions displayed relatively less rollback. Overall, quadriceps tension was highest in the unimplanted condition and lowest in the Scorpio condition. The Scorpio design showed a 10-20% reduction in quadriceps tension at angles greater than 40° when compared to the Control design. Patellofemoral forces were also significantly reduced in the Scorpio design when compared to Control. There were no differences noted between the central and medialized patella component. The Scorpio design, with its more posterior center of rotation, reduced quadriceps tension and patellofemoral forces. Reduced quadriceps forces may facilitate postoperative rehabilitation and activities such as stair climbing. Reduction in patellofemoral forces could reduce patellar complications such as anterior knee pain, component wear and loosening. These results are currently undergoing validation with a prospective clinical study.