Abstract
Sciatic nerve palsy after total hip replacement (THR) may result from direct injury of the nerve. Occasionally, a palsy may occur without an obvious cause.
The case we now report is the basis for an hypothesis to account for some idiopathic palsies. Case report: A right THR was performed on a 56-year-old woman at another hospital.
Immediately after the procedure, a sciatic palsy developed. Four weeks later, the patient fell and loosening of the acetabular component was diagnosed.
She was referred to our care at four months. Neurophysiological tests were performed and a palsy affecting both the medial and the lateral components of the sciatic nerve was identified.
Neither was complete although the lateral component was more severely affected than the medial. At revision of the acetabular component, a variant of the relationship between the sciatic nerve and the piriformis muscle was found.
The lateral part of the nerve penetrated the muscle and the medial half passed distal to it. The piriformis had retracted after an external rotator tenotomy performed at the primary surgery.
The nerve was stretched, adherent to the muscle and embedded in immature scar tissue. Part of the piriformis was resected to release that part of the nerve passing through the muscle while the remainder of the nerve was dissected from scar tissue.
After the operation, sciatic nerve function started to improve and gradually progressed to full recovery. Nerve conduction one year after the revision procedure showed normal function.