The measurement of anterior cruciate ligament strain in vivo.

This article describes the use of the Hall Effect strain transducer (HEST) in a new arthroscopic technique to study the normal anterior cruciate ligament (ACL) in-vivo. Study participants were patient volunteers with normal ACLs undergoing diagnostic arthroscopic or meniscal surgery under local anaesthesia. The HEST was implanted into the Anterior Medial Band (AMB) of the ACL. Anterior shear loading of the tibia in relation to the fixed femur at 30 degrees of knee flexion (Lachman test), produced significantly greater strain values in comparison to anterior shear loading at 90 degrees (Anterior Drawer test). During isometric quadriceps contraction a significant increase in AMB strain was measured with the knee flexed to 30 degrees, while no significant change was measured at 90 degrees. For quadriceps contraction there were significantly higher values of AMB strain measured at 30 degrees of knee flexion in comparison to that observed at 90 degrees. For active range of motion (AROM) the AMB was strained between 10 degrees and 48 degrees, and unstrained between 48 degrees and 110 degrees. During passive range of motion (PROM) the AMB remained unstrained until the joint was brought into extension. There were significant differences in strain values found between AROM and PROM at the flexion angles 10 degrees, 20 degrees, 30 degrees and 40 degrees, while between 50 degrees and 110 degrees there were no significant differences. These results confirm previous studies that the Lachman test is a superior technique in comparison to the classic anterior drawer test for evaluating the AMB. They suggest that isometric quadriceps activity at 90 degrees of knee flexion can be prescribed for rehabilitation immediately after ACL reconstruction. These data indicate that AROM (between the limits of 50 degrees and 110 degrees) and PROM may also be performed with minimal risk of strain to a reconstructive replacement. The PROM data may also serve as an important standard for the reconstruction of the ACL.