Delayed gastrocnemius muscle response to sudden perturbation in rehabilitated patients with anterior cruciate ligament reconstruction.

This nonrandomized, posttest-only comparison between two experimental groups and a control group compared the lower extremity muscle activation latencies of patients following rehabilitated unilateral anterior cruciate ligament (ACL) reconstruction (allograft or autograft bone-patellar tendon-bone tissue) and normal control subjects. Twenty-three subjects (seven allograft, eight autograft, eight normal control) of similar age, height, weight, isokinetic knee extensor, and flexor peak torque/bodyweight, functional capability (single leg broad jump and single leg vertical jump) and recreational activity level participated in this study. Experimental group subjects were 21.3+/-5 months (allograft) and 27.6+/-10 months (autograft) after surgery. Kinematic and electromyographic data were sampled during ten randomly timed unilateral perturbations. Experimental group gastrocnemius latencies were delayed (allograft 59.5+/-25 ms, autograft 69+/-20 ms) compared to the control group (31.8+/-11 ms). The allograft (r=0.80) and autograft (r=0.40) unilateral ACL reconstruction groups displayed moderate and weak positive relationships between anterior knee laxity and knee angular displacements following perturbation, respectively. Control group subjects did not display significant relationships between these variables (r=-0.07). In the allograft group there was also a moderate inverse relationship between gastrocnemius latency and knee angular displacement following perturbation (r=-72). The autograft (r=-0.06) and control (r=-0.21) groups did not show similar relationships between these variables. Delayed gastrocnemius latencies for the experimental groups suggested prolonged neuromuscular deficits during weight-bearing dynamic knee stabilization. Knee angular displacement magnitude following sudden perturbation was related more strongly to knee laxity and gastrocnemius latency among subjects who had undergone ACL reconstruction using allograft bone-patellar tendon-bone tissue.