Posterior cruciate ligament reconstruction. An in vitro study of femoral and tibial graft placement.

We studied posterior cruciate ligament reconstruction in a cadaveric model using two substitutes: a 1-mm diameter flexible cable and an 11-mm diameter Achilles tendon autograft. The thin cable allowed us to study five femoral and five tibial attachments in each knee. A nearly isometric attachment was located after cutting the posterior cruciate ligament while the tibia was reduced with a 100 N anterior force. The five femoral locations studied were the isometric location and four locations centered around this isometric point. The Achilles tendon reconstruction was used with both an isometric and a nonisometric femoral site, allowing us to confirm the results with the wire cable. Posterior motion limits were measured under a 100 N posterior force in the intact, posterior cruciate ligament-deficient, and posterior cruciate ligament-reconstructed knees. We found that the restoration of knee stability in flexion depended strongly on the femoral attachment location. A femoral attachment that was nonisometric by intraoperative measurement, but within the posterior cruciate ligament anatomic footprint, most closely reproduced the intact knee's posterior motion limits. Variations in the tibial attachment site produced only minor changes in the posterior motion limits. We concluded that the proximal-distal location selected for the femoral attachment of a posterior cruciate ligament substitute was particularly important in the restoration of normal posterior motion limits.