| Anterior cruciate ligament rupture is common, often requiring surgical reconstruction to allow people to return to high level sports. Although most people experience substantial knee instability after ACL rupture (non-copers) not all people have difficulty with hard cutting and pivoting motions. A group of individuals has been identified who are ACL deficient and continue to participate in high level sports without knee giving way (copers). Inclusion of coper subjects in studies on the movement and muscle activity patterns has likely contributed substantially to the contradictory findings reported in the literature. The purpose of this study was to prospectively classify ACL deficient individuals by functional ability and study their kinematics, kinetics and electromyographic activity during walking, jogging, single leg hopping and ascending/descending a 26 cm high step.;Ten non-copers, 11 copers and 10 uninjured subjects were tested in the Motion Analysis Laboratory of the Department of Physical Therapy, University of Delaware. Hip, knee and ankle kinematics and kinetics, and muscle activity (timing and magnitude) from the vastus lateralis, lateral hamstrings, medial gastrocnemius, soleus and gluteus maximus were analyzed. The results indicate that when subjects are appropriately classified by knee stability consistent differences in movement patterns do emerge. The non-copers appear to stiffen their knee joints through a strategy of generalized co-contraction whereas coper subjects use unique stabilization strategies to suit the demands of the task. The stabilization strategies in the non-copers appears to be related to quadriceps strength and could lead to accelerated joint degeneration over time. The results suggest that rehabilitation strategies for people following ACL rupture should include on neuromuscular retraining to restore rapid muscle activation in response to a variety of external demands on the knee. |
