NERVE TRACTION DURING CORRECTION OF KNEE FLEXION DEFORMITY - A CASE-REPORT AND CALCULATION

We report the case of a child with cerebral palsy and spastic diplegia treated for bilateral fixed flexion of the knee by bilateral hamstrin g lengthening. An attempt to straighten the legs from 90 degrees to 20 degrees flexion damaged the sciatic nerve. There are no objective mea ns of estimating how much deformity can be reduced safely. We present a method of calculating the extra strain in the sciatic nerve produced by reducing a flexion deformity. The result, combined with clinical j udgement, provides guidelines for safe corrective surgery.