Failure to diagnose injury to the posterolateral structures has been found to increase the forces experienced by the anterior cruciate ligament (ACL) and ACL grafts which may cause their subsequent failure. An isolated injury to the popliteus complex (PC) consisting of the popliteus tendon and popliteofibular ligament is not uncommon. Therefore, the purpose of this study was to discover if an isolated injury to the PC can significantly affect the forces experienced by the ACL graft under external loading conditions. We hypothesised that, under external tibial torque, the ACL graft will experience a significant increase in force, in knees with PC injury compared to the intact PC condition. Under varus tibial torque (10 N m), we observed minimal changes in the varus tibial rotation due to isolated sectioning of the PC in an ACL reconstructed knee (P> 0.05). Consequently, no significant increase in the ACL graft force was observed under varus tibial torque. In contrast, sectioning the PC resulted in a significant increase in the external tibial rotation compared to the intact PC knee condition under the external rotational tibial torque (5 N m) at all flexion angles (P<0.05). These changes in kinematics under external tibial torque were manifested as elevated ACL graft forces at all selected flexion angles (P<0.05). Prompt diagnosis of isolated PC injury and its treatment are warranted to prevent potential failure of ACL reconstruction.
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