The Elongation Behavior of the Anterior Cruciate Ligament Graft In Vivo

Abstract

The relationship between the elongation values of an autogenous bone-patellar tendon-bone graft immediately after fixation and the anterior-posterior laxity of the knee 5 years later was studied in vivo. Immediately after fixation, the change in the graft midsubstance length during passive knee flexion-extension was measured using a Hall-effect transducer, and anterior-posterior knee laxity was measured with the KT-1000 arthrometer. Subjects were divided into group 1 (N 6), with graft elongation values bounded by the 95% confidence intervals of the normal anterior cruciate ligament elongation values, and group 2 (N 7), subjects with values outside these intervals. Immediately after reconstruction, the side-to-side difference in anterior-posterior laxity between the reconstructed and uninjured knees was not different between group 1 ( 2.6 0.7 mm, mean SEM) and group 2 ( 1.7 1.0 mm) (P 0.49). At 5-year follow-up, the difference was 1.2 0.7 mm for group 1, while for group 2 it was significantly greater at 4.7 0.6 mm (P 0.004). At surgery, graft elongation values produced by flexion of the knee that are outside the limits of the anterior cruciate ligament result in significant increases in anterior knee laxity at long-term follow-up, while grafts with elongation values similar to the normal anterior cruciate ligament do not. Not only is restoration of anterior-posterior laxity values to within normal limits important, but the biomechanical behavior of the graft produced by flexion-extension of the knee should be appreciated.