Anterior tibial translation during different isokinetic quadriceps torque in anterior cruciate ligament deficient and nonimpaired individuals

Study Design: Factorial quasi-experimental design. Objectives: To quantify the effect of different levels of isokinetic concen tric and eccentric knee extensor torques on the anterior tibial translation in subjects with anterior cruciate ligament (ACL) deficiency Electromyogra m (EMC) activity of 4 leg muscles was recorded in order to detect any co-ac tivation of extensors and flexors. Background: The rehabilitation after an ACL injury is of importance for the functional outcome of the patient. In order to construct a rehabilitation program after that injury, it is important to understand the in vivo relati onships between muscle force and tibial translation. Methods and Measures: Twelve patients with unilateral ACL injury and 11 uni njured volunteers performed 36 repetitions of a quadriceps contraction at d ifferent isokinetic concentric and eccentric torque levels, on a KinCom mac hine (60 degrees .s(-1)), with simultaneous recordings of tibial translatio n (CA-4000) and EMG activity from quadriceps and hamstrings muscles. Tibial translations and EMC levels were normalized to the maximum of each subject . Results: The individual anterior tibial translation increased with increase d quadriceps torque in a similar manner in both quadriceps contraction mode s in all legs tested. During concentric mode, translation was similar in al l groups, but during eccentric mode, the mean translation was 38% larger in the ACL injured knees. No quadriceps-hamstrings co-activation occurred in any test or group. Conclusions: An ACL deficient knee can limit the translation within a norma l space during concentric muscle activity but not during eccentric activity . That limitation depends on other mechanisms than hamstrings co-activation .