Anterior Cruciate Ligament Strain Behavior During Rehabilitation Exercises In Vivo

Before studying the biomechanical effects of rehabili tation exercises on the reconstructed knee, it is impor tant to understand their effects on the normal anterior cruciate ligament. The objective of this investigation was to measure the strain behavior of this ligament dur ing rehabilitation activities in vivo. Participants were pa tient volunteers with normal anterior cruciate ligaments instrumented with the Hall effect transducer. At 10° and 20° of flexion, ligament strain values for active exten sion of the knee with a weight of 45 N applied to a sub ject's lower leg were significantly greater than active motion without the weight. Isometric quadriceps muscle contraction at 15° and 30° also produced a significant increase in ligament strain, while at 60° and 90° of knee flexion there was no change in ligament strain relative to relaxed muscle condition. Simultaneous quadriceps and hamstrings muscles contraction at 15° produced a significant increase in ligament strain compared with the relaxed state but did not strain the ligament at 30°, 60°, and 90° of flexion. Isometric contraction of hamstrings muscles did not produce change in ligament strain at any flexion angle. Exercises that produce low or un strained ligament values, and would not endanger a properly implanted graft, are either dominated by the hamstrings muscle (isometric hamstring), involve quad riceps muscle activity with the knee flexed at 60° or greater (isometric quadriceps, simultaneous quadri ceps and hamstrings contraction), or involve active knee motion between 35° and 90° of flexion.