summary THA Sciatic Nerve Palsy is an uncommon, but potentially devastating complication following THA that may lead to persistent foot drop. Diagnosis can be made clinically with post-operative complaints of numbness and paresthesias along the sciatic nerve distribution and weakness of the dorsiflexors of the foot. Treatment is placing the hip in extension and knee in flexion immediately post-operatively. Observation and AFO in the presence of foot drop are recommended to monitor for recovery of the nerve. epidemiology Incidence uncommon (0-3%) most common cause for medical malpractice litigation following THA Anatomic location peroneal division of sciatic nerve most commonly affected (80%) sciatic nerve travels closest to acetabulum at level of ischium exercise care with posterior acetabular retraction when hip in flexed position less commonly affected nerves include femoral obturator superior gluteal Etiology Causes direct trauma stretch compression due to hematoma heat from polymethylmethacralate polymerization unrecognized lumbar lateral recess stenosis unknown (40%) Risk factors for motor nerve palsies include developmental dysplasia of the hip revision surgery female gender limb lengthening posttraumatic arthritis surgeon self-rated procedure as difficult pre-existing lumbar stenosis operative time Presentation Post-operative complaints of numbness, paresthesias, or weakness Imaging Post-operative CT may be helpful if hematoma suspected Ultrasound may be helpful if hematoma suspected Studies EMGs may be used post-operatively to confirm level of injury and guide discussion with patient regarding prognosis Treatment Intraoperative adult hip dysplasia undergoing THA subtrochanteric osteotomy downsizing components Immediate postoperative place hip in extension and knee in flexion indications immediate post-operative palsy technique decreases tension along sciatic nerve immediate evacuation in operating room indications post-operative hematoma Persistent foot drop AFO orthosis indications first line of treatment for persistent foot drop Prognosis Only 35% to 40% recover full strength after complete palsy