Neuromechanics of Knee Extensor

Mechanisms in Patellofemoral Pain Patients with Patellar Malalignment

This project seeks to quantify the mechanical and neuromuscular changes in the knee extensor mechanism of patellofemoral pain patients with patellar malalignment and with/without patellar taping. An innovative method has been developed to determine in vivo the knee extension moment distribution among the quadriceps components. Beside differences in torque amplitude of individual muscles, the contraction delay (timing) associated with individual quadriceps components in knee extension is also studied in vivo for each individual muscle. Changes in load sharing, contraction delay and patellar tracking (measured noninvasively with a patellar clamp or dynamic imaging) induced by patellar malalignment and correction induced by patellar taping are quantified.

Fig. 1. Experimental setup for studying the knee extensor mechanism. The seat is adjusted in four DOF to align the knee flexion axis with the motor shaft. For this study, the motor is locked at a chosen knee flexion angle. A six-axis force sensor is mounted between the motor shaft and the aluminum beam. The knee and hips are fixed relative to the seat. Force sensitive resistors (FSRs) can be used to monitor the forces between the body and the fixture at the epicondyles, anterior knee and the greater trochanters. A short-leg cast is fixed to the aluminum beam through two half-rings, and it can be adjusted and locked in four DOF to achieve appropriate alignment.

Fig. 2. Experimental setup (medial view) for in vivo and noninvasive measurement of patellar and tibial movement produced by contraction of anindividual or all quadriceps components. The (right) knee is clamped at the lateral and medial epicondyles and supported from beneath. Thecushion underneath the thigh can be adjusted for different knee flexion angles near full extension. A small and lightweight frame is clampedonto the patella tightly with three markers on it. Markers 1 to 3, 4 to 6 and 7 to 9 are attachedto the femur, patella and tibia, respectively. Markers 1, 3 and 7 are on the lateral side of the lower limb and the remaining markers are on the anterior side of the limb. The nsert gives the anterior, axial (from distal to proximal) and medial views of the frame clamped onto the patella of a right knee joint.