Purpose: To investigate sciatic nerve conduction during hamstring lengthening.

Conclusion: Sciatic nerve traction is caused during hamstring lengthening.

Summary of method, results, and discussion: Ten children with spastic cerebral palsy underwent distal hamstring lengthening, average popliteal angel before surgery was 80 degrees.

Methods: The tendon of the semitendinosus was elongated by sliding lengthening. The gracilis tendon was cut and the tendons of the biceps and semimembranosus were elongated by dividing the aponeurosis. Thereafter to elongate the hamstring the hip and knee were flexed to 90 degrees and the knee slowly extended with continuous evoked EMG monitoring. Bipolar nerve stimulation placed near the sciatic nerve consisted of the delivering of rectangular impulses of amplitude 0.8-1.2 ma for 100 US duration. The EMG recordings were performed from the tibialis anterior muscle.

Results: In all patients motor potential amplitude gradually decreased during extension of knee (hamstring lengthening). The average decrease of the amplitude at popliteal angle of 60 degrees was 37 percent (16-75) and at 30 degrees 83 percent (36-98). The elongation was stopped at 30° of popliteal angle. On extending the hip and knee motor potential amplitude returned to normal. Discussion: Elongation of hamstring muscle is associated with traction on the f sciatic nerve as appears by decrease in sciatic nerve motor potential amplitude. To avoid nerve injury no excessive hamstring lengthening should be done and no nerve traction should be allowed at postoperative immobilization.