Optimization of knee ligament position for lateral extraarticular reconstruction.

A kinematic study of five adult cadaver knees was performed to determine the behavior of the separation distances connecting all combinations of a network of points on the lateral side of the knee. Measurements were obtained between each pair of points at the level of the capsule for seven different angles of flexion ranging from 0 to 125 degrees. The data obtained allow further analysis of tendinous reconstructions attached to each pair of points as regards stretching and laxity throughout a normally occurring range of motion. The Rowe-Zarins combined intra- and extraarticular reconstruction, the Sling-and-Reef procedure, and other extraarticular methods were analyzed in light of these data. Attachment of a reconstruction at the proximal anterolateral tibia, in front of Gerdy's tubercle paired with femoral attachment high and proximal to the origin of the lateral collateral ligament on the femur, was observed to demonstrate favorable behavior for several reasons. First, such a check reign represents an obvious, major restraint to anterior translation as it is positioned well posteriorly on the femur and anteriorly on the tibia. Second, the attachment points were seen to demonstrate maximum separation between 15 and 45 degrees of flexion, thereby not being forced into any undesirable stretching if the knee were to move normally throughout the other portions of the motion cycle. Consequently, obligate stretch with full flexion or full extension would appear unlikely. Separation distances between attachment points were highly dependent upon changes in the femoral fixation point and much less variable as a result of tibial attachment position. Placing the knee through a flexion-extension range of motion with the tibia held unnaturally in external rotation, which is frequently done in the operating room, violates the normal kinematic pattern of knee motion. As a result, unsuitable attachment points may erroneously appear well behaved. This observation may offer one important explanation for long-term stretching of a ligament reconstruction which appeared satisfactorily tight and strong at the time of surgery. The data obtained allow proper positioning of anterolateral reconstructions so that this mode of stretching will not be encountered as a result of normal knee motion.