Comparison in Joint-Position Sense and Muscle Coactivation Between Anterior Cruciate Ligament-Deficient and Healthy Individuals.

CONTEXT: Tearing of the anterior cruciate ligament (ACL) may disrupt the ability to recognize the knee position in space during limb-repositioning tasks, which is referred to as joint-position sense (JPS). Impairments in JPS have been shown to be lower during active than passive repositioning tasks, thus suggesting that coactivation patterns of the muscles surrounding the knee might compensate for the disrupted JPS and ensure accurate limb repositioning in ACL-deficient individuals. OBJECTIVE: To investigate muscle coactivation patterns during JPS repositioning tasks in ACL-deficient and healthy individuals. DESIGN: Prospective observational study. SETTING: Functional assessment laboratory. PARTICIPANTS: 8 men age 25 ± 8 y with isolated ACL rupture and 10 men age 30 ± 4 y with no history of knee injury. INTERVENTION: JPS was evaluated by means of an electrogoniometer in a sitting position during either passive or active joint-positioning and -repositioning tasks with a 40° target knee angle. MAIN OUTCOME MEASURES: Root mean square (RMS) of the surface electromyogram from the vastus lateralis and biceps femoris muscles was measured during active joint positioning and repositioning. RESULTS: Healthy participants showed a significant decrease in vastus lateralis RMS (-19%) and an increase in biceps femoris RMS (+26%) during joint repositioning compared with positioning. In contrast, ACL-deficient patients showed no modulation in muscle coactivation between joint positioning and repositioning, although they exhibited significantly lower RMS of the vastus lateralis (injured limb, -28%; uninjured limb, -21%) and higher RMS of the biceps femoris (injured limb, +19%; uninjured limb, +30%) than the healthy participants during joint positioning. CONCLUSIONS: The lack of modulation in muscle coactivation patterns between joint positioning and repositioning in ACL-deficient patients might be attributed to disrupted neural control after the injury-related loss of proprioceptive information. These results should be taken into account in the design of rehabilitation protocols with emphasis on muscle coactivation and JPS.