Nerve palsy after leg lengthening in total replacement arthroplasty for developmental dysplasia of the hip

We reviewed 508 consecutive total hip replacements in 370 patients with old developmental dysplasia of the hip, to relate the amount of leg lengthenin g to the incidence of nerve palsies after operation. There were eight nerve palsies (two femoral, six sciatic), two complete and six incomplete, We found no statistical correlation between the amount of lengthening and t he incidence of nerve damage (p = 0.47), but in seven of the eight hips, th e surgeon had rated the intervention as difficult because of previous surge ry, severe deformity, a defect of the acetabular roof, or considerable flex ion deformity. The correlation between difficulty and nerve palsy was signi ficant (p = 0.041), We conclude that nerve injury is most commonly caused b y direct or indirect mechanical trauma and not by limb lengthening on its o wn.