Anterior positioning of tibia during motion after anterior cruciate ligament injury

Purpose: The purpose of this study was to describe the sagittal tibial tran slation and EMG activity of muscles v. medialis and lateralis, gastrocnemiu s, and hamstrings, during common locomotion, in patients with an anterior c ruciate ligament deficiency (ACL-def) and uninjured controls. Methods: In 1 2 ACL-def patients and 17 controls, sagittal tibial translation was registe red with the CA-4000 electrogoniometer during level walking, cutting, and s tair walking. Tibial position at each flexion angle was expressed relative to the femuro-tibial position at passive knee extension. EMG activity, meas ured with ME-4000, was normalized to the individual maximum isometric volun tary contraction for each muscle. Results: During the weight-bearing phase of motion, the tibia was anteriorly positioned in all legs. In the injured leg, the tibia translated more rapidly to an anterior position that was mai ntained for a longer time during the gait cycle. In the noninjured knees, m otions with increased load lead to an increased anterior tibial translation in contrast to the injured knees, where the maximum displacement was alrea dy reached during level walking. The quadriceps and gastrocnemius muscles w ere simultaneously active during stance phase. Hamstrings were mainly activ e when the knee was close to extension and translation increased in spite o f this activity. Conclusions: The mechanism of the anterior positioning of tibia is qualitatively similar in the normal and the injured knee, but that position is obtained much further forward in the ACL deficient knee. Quadr iceps and gastrocnemius muscles seem to work synergistically to stabilize t he knee by maintaining the anterior position of tibia during weight-bearing motion. The role of hamstrings to restrict anterior translation is questio ned.