Force displacement characteristics of the posterior cruciate ligament

The percent force changes in the posterior cruciate ligament were calculated using a previously validated computerized knee model after the femoral insertion sites were varied 2.5 and 5.0 mm in an anterior, pos terior distal, anterior distal, and posterior distal direc tion. The tibial insertion sites were also varied 2.5 and 5.0 mm in the medial, lateral, proximal, and distal direc tions. Percent force changes were measured over a range of 0° to 90°. These insertion sites simulated potential surgical placement errors. Results of this study demonstrated that the greatest percent force changes in the posterior cruciate ligament were at full extension. The greatest absolute percent force change between 0° and 90° of flexion was with a femoral insertion of the posterior cruciate ligament placed 5 mm anterior to its normal attachment site, which resulted in a 39% change in the posterior cruciate ligament force. Distal femoral site attachment had the least effect (10% at 5.0 mm). Alterations at the tibial attachment site were less sensitive than on the femur; the greatest absolute percent force changes occurred with medial and lateral attachment sites (14% and 15%, respectively, at 5.0 mm). A minimal amount of percent force changes were seen between 45° and 75° of knee flexion in all positions tested for both tibial and femoral attachment sites. This model suggests that, like the anterior cruciate ligament, the force in the posterior cruciate ligament is also sensitive to attachment site position. As in anterior cruciate ligament studies, the femoral attachment site was found to be more sensitive. The greatest percent force changes for the posterior cruciate ligament were seen at the extremes of the knee motion tested (i.e., 0° and 90°). The posterior cruciate ligament sensitivity to graft placement lends credence to the importance of anatomic reconstruction. Results of this study can also be extrapolated to help in designing early continuous passive motion and rehabilitation programs, with the safest range of knee motion between 45° and 75°.