The effect of weightbearing and external loading on anterior cruciate ligament strain

A force balance between the ligaments, articular contact, muscles and body weight maintains knee joint stability. Thus, it is important to study anter ior cruciate ligament (ACL) biomechanics, in vivo, under weightbearing cond itions. Our objective was to compare the ACL strain response under weightbe aring and non-weightbearing conditions and in combination with three extern ally applied loadings: (1) anterior-posterior shear forces, (2) internal-ex ternal torques, and (3) varus-valgus moments. A strain transducer was impla nted on the ACL of 11 subjects. All joint loadings were performed with the knee at 20 degrees of flexion. A significant increase in ACL strain was obs erved as the knee made the transition from non-weightbearing to weightbeari ng. During anterior shear loading, the strain values produced during weight bearing were greater than those of the non-weightbearing knee (shear loads < 40 N). At higher shear loads, the strain values became equal. During axia l torsion, an internal torque of 10 Nm strained the ACL when the knee was n on-weightbearing while an equivalent external torque did not. Weightbearing significantly increased ACL strain values in comparison to non-weightbeari ng with the application of external torques and low internal torques ( < 3 Nm). The strains became equal for higher internal torques. For V-V loading, the ACL was not strained in the non-weightbearing knee. However, weightbea ring increased the ACL strain values over the range of moments tested. Thes e data have important clinical ramifications in the development of rehabili tation protocols following ACL reconstruction since weightbearing has been previously thought to provide a protective mechanism to the healing graft. (C) 2001 Elsevier Science Ltd. All rights reserved.