NEUROMUSCULAR PERFORMANCE IN NORMAL AND ANTERIOR CRUCIATE LIGAMENT-DEFICIENT LOWER-EXTREMITIES

The neuromuscular function of the lower extremity in 40 normal and 100 anterior cruciate ligament-deficient volunteers was evaluated by phys ical examination, KT-1000 arthrometer measurements, isokinetic strengt h and endurance testing, subjective functional assessment, and an ante rior tibial translation stress test. A specially designed apparatus de livered an anteriorly directed step force to the posterior aspect of t he leg while anterior tibial translation was monitored and electromyog raphic signals were recorded at the medial and lateral quadriceps, med ial and lateral hamstrings, and gastrocnemius muscles. Testing was don e at 30 degrees of knee flexion with the foot tired to a scale to moni tor weightbearing, while the tibia remained unconstrained. Results ind icate that muscle timing and recruitment order in response to anterior tibial translation are affected by anterior cruciate ligament injury. These alterations in muscle performance change with time from injury, correlate with an individual's physical activity level, affect subjec tive functional parameters, and are directly related to the degree of dynamic anterior tibial laxity seen with stress testing.