Biomechanical comparison of tibial inlay and tibial tunnel techniques for reconstruction of the posterior cruciate ligament - Analysis of graft forces

Background: The tibial inlay technique of reconstruction of the posterior cruciate ligament offers potential advantages over the conventional transtibial tunnel technique, particularly with regard to the graft force levels that develop over a functional range of knee flexion. Abnormally high graft forces generated during rehabilitation activities could lead to stretch-out of the graft during the critical early healing period. The purpose of this study was to compare graft forces between these two techniques and with forces in the native posterior cruciate ligament. Methods: A load cell was installed at the femoral origin of the posterior cruciate ligament in twelve fresh-frozen cadaveric knees to measure resultant forces in the ligament during a series of knee loading tests. The posterior cruciate ligament was then excised, and the femoral ends of 10-mm-wide bone-patellar tendon-bone grafts were attached to the load cell to measure resultant forces in the grafts. For the tunnel reconstruction, the distal bone block of the graft was placed into a tibial tunnel and thin stainless-steel cables interwoven into the bone block were gripped in a split clamp attached to the anterior tibial cortex. With the inlay technique, the distal bone block was fixed in a tibial trough with use of a cortical bone screw with a washer and nut. The proximal ends of all grafts were pretensioned to a level of force that restored intact knee laxity at 90degrees of flexion, and loading tests were repeated. Results: There were no significant differences in mean graft forces between the two techniques under tibial loads consisting of 100 N of posterior tibial force, 5 N-m of varus and valgus moment, and 5 N-m of internal and external tibial torque. Mean graft forces with the tibial tunnel technique were approximately 10 to 20 N higher than those with the inlay technique with passive knee flexion beyond 95degrees. Mean graft forces with both reconstruction techniques were significantly higher than forces in the native posterior cruciate ligament with the knee flexed beyond approximately 90degrees for all but one mode of loading. Conclusions: In this cadaveric testing model, neither technique for reconstruction of the posterior cruciate ligament had a substantial advantage over the other with respect to generation of graft forces. Clinical Relevance: The relatively high graft forces (compared with the forces in the native posterior cruciate ligament) observed beyond 90degrees of knee flexion after reconstruction of the posterior cruciate ligament with either the tunnel or the inlay technique suggest that rehabilitation activities that involve loading of the knee while it is flexed beyond 90degrees (such as kneeling, squatting, or climbing high stairs) should be avoided in the early postoperative period.