Biomechanical characteristics of the anatomic rectangular tunnel anterior cruciate ligament reconstruction with a bone-patellar tendon-bone graft.

PURPOSE: To clarify 1) the force sharing between two portions of BTB graft in anatomic rectangular tunnel (ART) reconstruction and 2) the knee stability in ART technique under anterior tibial load.

METHODS: Eleven fresh cadaveric knees were used. First, anterior-posterior (A-P) laxity was measured with Knee Laxity Tester® in response to 134 N of A-P tibial load at 20° on the normal knees. Then ART ACL reconstruction was performed with a BTB graft. For graft, the patellar bone plug and tendon portion was longitudinally cut into half as AM and PL portions. After the tibial bone plug was fixed at femoral aperture, AM/PL portions were connected to the tension-adjustable force gauges at tibial tubercle, and were fixed with 10 N to each portion at 20°. Then the tension was measured 1) under anterior tibial load of 134 N at 0, 30, 60, and 90°, and 2) during passive knee extension from 120 to 0°. Next the graft tension was set at 0, 10, 20, 30, or 40 N at 20°, and the A-P laxity was measured by applying A-P load of 134 N. By comparing the laxity for the normal knee, the tension to restore the normal A-P laxity (LMP) was estimated.

RESULTS: The AM force was significantly smaller at 0° and larger at 90° than the PL force under anterior load, while the force sharing showed a reciprocal pattern. During knee extension motion, the tension of both portions gradually increased from around 5 N to 20-30 N with knee extended. And the LMP was 1.6 ± 1.0 N with a range from 0.3 to 3.5 N.

CONCLUSION: The pattern of force sharing was similar to that in the normal ACL in response to anterior tibial load and during passive knee extension motion. LMP in this procedure was close to the tension in the normal ACL.

LEVEL OF EVIDENCE: Level IV, a controlled-laboratory study.