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

This nonrandomized, posttest-only comparison between two experimental group s and a control group compared the lower extremity muscle activation latenc ies of patients following rehabilitated unilateral anterior cruciate ligame nt (ACL) reconstruction (allograft or autograft bone-patellar tendon-bone t issue) and normal control subjects. Twenty-three subjects (seven allograft, eight autograft, eight normal control) of similar age, height, weight, iso kinetic knee extensor, and flexor peak torque/bodyweight, functional capabi lity (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 tim ed unilateral perturbations. Experimental group gastrocnemius latencies wer e delayed (allograft 59.5+/-25 ms, autograft 69+/-20 ms) compared to the co ntrol group (31.8+/-11 ms). The allograft (r=0.80) and autograft (r=0.40) u nilateral ACL reconstruction groups displayed moderate and weak positive re lationships between anterior knee laxity and knee angular displacements fol lowing perturbation, respectively. Control group subjects did not display s ignificant relationships between these variables (r=-0.07). In the allograf t group there was also a moderate inverse relationship between gastrocnemiu s latency and knee angular displacement following perturbation (r=-72). The autograft (r=-0.06) and control (r= -0.21) groups did not show similar rel ationships between these variables. Delayed gastrocnemius latencies for the experimental groups suggested prolonged neuromuscular deficits during weig ht-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 u sing allograft bone-patellar tendon-bone tissue.