Knee joint forces during isokinetic knee extensions: a case study

Objective. To describe the procedures to obtain knee joint forces during isokinetic knee extensions and evaluate the patellar ligament force, quadriceps tendon force, patellofemoral and tibiofemoral joint forces at different speeds measured from a female subject. Design. A technical note with a case study. Background. Two previous studies examined knee joint forces during isokinetic knee extension using different techniques reported inconsistent findings. Also, the highest speed used in these two studies (180° s−1) were much lower than the maximum speeds available in modern isokinetic dynamometers. Methods. The subject performed maximum effort isokinetic knee extensions at 16 different speeds ranged from 25 to 400° s−1. The gravitational and inertial effects were included in determining the resultant knee torque. Knee radiographs were used to determine the knee joint geometry. A combination of knee torque and geometric data was used to determine different knee joint forces. Results. All knee joint forces were found to decrease with increasing isokinetic speed. The tibiofemoral shears forces indicated that the anterior cruciate ligament was loaded throughout the range of motion. Conclusions. The magnitudes of knee joint forces are largely depending on the knee torque values.