The influence of asymmetric quadriceps loading on patellar tracking--an in vitro study.

Background: In patients with anterior knee pain and patellar instability, a specific training of the quadriceps muscle - especially the vastus medialis - is often recommended, although the practicability is discussed controversially and the proof of a measurable clinical effect is difficult. Therefore, this in vitro study investigates the influence of asymmetric muscle loading on the motion of the human patella. Methods: Seven human knee specimens were tested in a specially developed knee simulator. During simulated weight-bearing knee flexion, the kinematics of tibia, femur and patella were measured using an ultrasound motion capture system. The quadriceps forces were controlled to achieve a constant ankle force over the whole flexion range which is assumed to represent almost physiological loading. Three different force distributions of the quadriceps were tested - a central, equally distributed load as well as mainly lateral and medial loads. Results: A significant influence of different quadriceps force distributions was found for patellar tilt around a proximodistal axis (up to 1.7 degrees) and patellar rotation around an anteroposterior axis (up to 3.8) with respect to the femur. Interestingly, the patellar mediolateral shift was influenced only marginally (<1.5 mm). Conclusions: Specific muscle training might help patients with patellofemoral pain and cartilage damage by a slight modification of the kinematics, but we could show that even highly asymmetric quadriceps loads only led to a small alteration of the mediolateral shift in case of a physiologic anatomy of the trochlear groove. (C) 2012 Elsevier B.V. All rights reserved.