An in vivo comparison of anterior tibial translation and strain in the anteromedial band of the anterior cruciate ligament.

The objective of this in vivo study was to determine if strain in the anteromedial band (AMB) of the anterior cruciate ligament (ACL) may be predicted by an external measurement of anterior tibial-femoral translation. A Hall effect strain transducer was implanted on the AMB of five human subjects with normal intact ACLs. AMB strain was then measured during anterior shear loading of the tibia relative to the femur, with the knee flexed to 30 and 90 degrees, simulating the loads applied in the Lachman and anterior drawer tests, respectively. The Knee Signature System, a commercially available arthrometer, was used to simultaneously measure anterior tibial translation relative to the femur. The resulting AMB strains and translations during anterior shear loading of the tibia with respect to the femur at 30 and 90 degrees were compared using a regression analysis to determine if AMB strain could be predicted from a measure of anterior tibiofemoral translation at either flexion angle. AMB strain at 150 N anterior shear load at 30 degrees flexion (3.0%) was significantly greater than that at 150 N anterior shear load at 90 degrees flexion (0.9%). During anterior shear loading at 30 degrees flexion, AMB strain correlated with anterior tibial translation (r2 = 0.59). However, there was no significant correlation between AMB strain and anterior tibial translation for anterior shear loading at 90 degrees flexion (r2 = 0.002). Therefore, AMB strain was not accurately predicted from an external measurement of tibial displacement at 90 degrees in this experiment.