After a knee injury, exercise is very important. This is especially true when there's a torn or damaged anterior cruciate ligament (ACL). Knowing which muscles to work on is a major part of a successful rehabilitation process.

Rehab specialists are teaming up with engineers to study muscle actions after injury. New technology makes it possible to measure joint movement and muscle strength. The dynamometer measures muscle strength in various positions and at different speeds.

The arthrometer is used to measure joint laxity, a gauge of how "loose" a joint is. Joint laxity occurs when one bone slides too far over another. In the case of a torn ACL, laxity increases and can result in an unstable knee joint. Using measures of strength and laxity, researchers can compare people with normal knees to patients with ACL damage. These studies are ongoing.

Patients with ACL deficiency have less strength in the quadriceps muscle on the front of the thigh. The hamstrings behind the thigh aren't usually affected. It is thought that the loss of quadriceps strength leads to a loss of muscle and knee function. The loss of strength is most obvious during strenuous activities.

In this study, joint laxity, didn't seem to cause a change in muscle function. This was true whether the patient was walking, jogging, or going up and down stairs. According to this study, restoring quadriceps muscle strength and function after ACL injury seems to be the most important goal for rehab.

Reference:

Rohita R. Patel, MS, et al. Comparison of Clinical and Dynamic Knee Function in Patients with Anterior Cruciate Ligament Deficiency. In The American Journal of Sports Medicine. January/February 2003. Vol. 31. No. 1. Pp. 68-74.'