Objectives: Because the co-contraction of the gastrocnemius and hamstring muscles strains the anterior cruciate ligament, the role of the gastrocnemius muscle is of particular importance after semitendinosus and gracilis tendon autografts for anterior cruciate ligament reconstruction. This study aimed to examine the neuromuscular mechanisms underlying postsurgical torque deficits during knee flexion by using surface electromyography.
Design: A total of 14 volunteer patients (eight men, six women; age, 32.5 +/- 9.3 yrs; height, 172.7 +/- 6 cm; weight, 69.6 +/- 10.2 kg) were enrolled in the study; all had undergone anterior cruciate ligament reconstruction performed by the same surgeon. The neuromuscular mechanisms were assessed using isometric tests and surface electromyographic recordings at 19 mos post-reconstruction. The torque deficits in the injured knee were compared with the uninjured knee, which served as control values.
Results: Significant differences in torque production were observed between the two limbs at specific angular positions during the extension and flexion tests (P < 0.05). The difference in the root mean square myoelectrical activity between the limbs was computed at each tested position, revealing that the gastrocnemius muscle had greater activity at 75 degrees than at 45 degrees (P < 0.05).
Conclusions: In deep flexion (>70 degrees), the gastrocnemius muscle may compensate for the weakened hamstrings and thereby strain the anterior cruciate ligament graft after anterior cruciate ligament semitendinosus and gracilis tendon reconstruction.