In-vivo sagittal plane knee kinematics: ACL intact, deficient and reconstructed knees

Sagittal plane video fluoroscopy was used to analyse the bilateral knee kinematics of patients with unilateral ACL deficiency (ACLD) before, and 4 months after, hamstrings graft ACL reconstruction. Kinematics were studied during weight resisted knee extension, passive knee extension, and a step up. Thigh EMG records were also obtained from five subjects. In addition, six uninjured control subjects were analysed to establish normal kinematics. Kinematics were analysed by calculating the angle between the long axis of the tibia and the patella tendon through the range of knee flexion. Shear forces were calculated using a model of knee extension and force plate data. A maximum anterior TT of 7.3 (S.D. 2.1) mm was recorded in ACL intact (ACLI) knees during the weightbearing activity. Hamstrings activity was able to control ATT in the ACLD tibia to within the normal range of translation of the ACLI knee. Despite clinical improvements, ATT increased postoperatively in the reconstructed knees to 11.6 (S.D. 3.8) mm (P<0.048). The findings suggest that the ACL has only a minor role in the control of ATT during activity, and that the extent of ATT is more closely related to the level of quadriceps-generated shear force. A reduction in hamstrings force is proposed as the most likely cause for increased ATT post reconstruction. These findings have implications for the development of ACL rehabilitation regimes, and also may modify graft choice and the surgical aims of the procedure.