The effect of hamstring muscle compensation for anterior laxity in the ACL-deficient knee during gait

The hamstring muscles have been recognized as an important element in compe nsating for the loss of stability in the ACL-deficient knee, but it is stil l not clear whether the hamstring muscle force can completely compensate fo r the loss of ACL, and the consequences of increased hamstring muscle force . A two-dimensional anatomical knee model in the sagittal plane was develop ed to examine the effect of various levels of hamstring muscle activation o n restraining anterior tibial translation in the ACL-deficient knee during level walking. The model included the tibiofemoral and patellofemoral joint s, four major ligaments, the medial capsule, and five muscle units surround ing the knee. Simulations were conducted to determine anterior tibial trans lation and internal joint loading at a single selected position when the kn ee was under a peak external flexion moment during early stance phase of ga it. Incremental hamstring muscle forces were applied to the modeled normal and the ACL-deficient knees. Results of simulations showed that the ACL inj ury increased the anterior tibial translation by 11.8 mm, while 56% of the maximal hamstring muscle force could reduce the anterior translation of the tibia to a normal level during the stance phase of gait. The consequences of increased hamstring muscle force included increased quadriceps muscle fo rce and joint contact force. (C) 2000 Elsevier Science Ltd. All rights rese rved.