LOAD AND LENGTH CHANGES IN AN ARTIFICIAL LIGAMENT SUBSTITUTE - 10 CASES OF ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

In 10 patients who had reconstruction of the anterior cruciate ligamen t, the load and length changes in an artificial ligament substitute we re measured during passive knee motion. Using a special drill guide, t he ligament was placed within +/-2 mm of the normal anatomic center on the femur. With the femoral end fixed with a bicortical screw the lig ament was preloaded to 40 N at the flexion angle with the shortest int raarticular ligament length, usually 45-degrees. The change in load wa s then registered from 90-degrees of flexion to full extension. In 2/1 0 cases loads of > 200 N were registered in full extension, but the me an load was 160 N. There was a higher loss of load during the first ex tension/flexion cycle than during the 4th cycle. The load change corre lated to the length change, but the degree of length change could not predict the maximum load level. There was a large variation in load le vels between different knees, even with similar ligament placements, b ut the least change in load and length was obtained by an anatomic pla cement. Isometer readings did not predict the load level in the ligame nt substitute, but could indicate the angle of flexion with minimum lo ad. Therefore, the isometer can be used to control the placement of th e attachment points for the substitute. After fixation, fiber settling and stretching the ligament, as well as adaptation of the tissues, wi ll tend to reduce the load levels.