Anterior-posterior and rotational displacement of the tibia elicited by quadriceps contraction

The anterior-posterior displacement and rotation of the tibia elicited by isolated loading of the quadriceps mus cle was determined as a function of joint angle and muscle load using a computerized radiographic tech nique. Data collected from 12 fresh-frozen cadaveric knees demonstrated that quadriceps contraction can result in significant (<7 mm) anterior displacement of the tibia in the range of 0° to 80° of flexion, and a mild (<2 mm) posterior displacement in the range of 80° to 120° of flexion. Peak anterior displacement of 6.3 mm was observed at 30° of flexion under a 12 kg load in the quadriceps, while a constant 1.5 mm posterior displacement was observed throughout flexion angles exceeding 80°. It was further shown that the magnitude of the anterior displacement increased nonlinearly as the quadriceps force increased. Loading of the quadri ceps also resulted in internal rotation of the tibia in the range of 0° to 90° of flexion, and in external rotation of the tibia in the range of 90° to 120°. Peak internal rotation of 7° was observed at 15° of flexion and a peak external rotation of 1 ° was detected at 120° of flexion. Larger quadriceps load resulted in larger rota tion. We concluded that quadriceps contraction during knee extension has direct impact on anterior displace ment and rotation of the tibia and therefore on anterior cruciate ligament stress, increasing it as the muscle's force is increased during knee extension. It is sug gested that partial quadriceps atrophy in knees with anterior cruciate ligament deficiency may be explained as a protective response. This would bring into question the practice of quadriceps exercise after ligament inju ries and repair, as well as current orthotics concepts.