Purpose: To study how well an anterior cruciate ligament (ACL) graft fixed at the 10 and 11 o'clock positions can restore knee function in response to both externally applied anterior tibial and combined rotatory loads by comparing the biomechanical results with each other and with the intact knee.
Type of study: Biomechanical experiment using human cadaveric specimens.
Methods: Ten human cadaveric knees (age, 41+/-13 years) were reconstructed by placing a bone-patellar tendon-bone graft at the 10 and 11 o'clock positions, in a randomized order, and then tested using a robotic/universal force-moment sensor testing system. Two external loading conditions were applied: (1) 134 N anterior tibial load with the knee at full extension, 15 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion, and (2) a combined rotatory load of 10 N-m valgus and 5 N-m internal tibial torque with the knee at 15 degrees and 30 degrees of flexion. The resulting kinematics of the reconstructed knee and in situ forces in the ACL graft were determined for each femoral tunnel position.
Results: In response to a 134-N anterior tibial load, anterior tibial translation (ATT) for both femoral tunnel positions was not significantly different from the intact knee except at 90 degrees of knee flexion as well as at 60 degrees of knee flexion for the 10 o'clock position. There was no significant difference in the ATT between the 10 and 11 o'clock positions, except at 90 degrees of knee flexion. Under a combined rotatory load, however, the coupled ATT for the 11 o'clock position was approximately 130% of that for the intact knee at 15 degrees and 30 degrees of flexion. For the 10 o'clock position, the coupled ATT was not significantly different from the intact knee at 15 degrees of flexion and approximately 120% of that for the intact knee at 30 degrees of flexion. Coupled ATT for the 10 o'clock position was significantly smaller than for the 11 o'clock position at 15 degrees and 30 degrees of flexion. The in situ force in the ACL graft was also significantly higher for the 10 o'clock position than the 11 o'clock position at 30 degrees of flexion in response to the same loading condition (70 +/- 18 N v 60 +/- 15 N, respectively).
Conclusions: The 10 o'clock position more effectively resists rotatory loads when compared with the 11 o'clock position as evidenced by smaller ATT and higher in situ force in the graft. Despite the fact that ACL grafts placed at the 10 or 11 o'clock positions are equally effective under an anterior tibial load, neither femoral tunnel position was able to fully restore knee stability to the level of the intact knee.