A sixty-three-year-old woman who had osteoarthrosis of the left hip joint was managed with total hip replacement with use of an acetabular reinforcement ring that was made of titanium. Postoperatively, mobilization of the patient was hampered by pain in the medial aspect of the thigh and weakness of the adductors of the hip; these symptoms had not been present preoperatively, and transient disturbance of the obturator nerve was suspected. One year after the operation, a neurological examination revealed atrophy and paresis of the adductor muscles (strength, grade 2 of 5), absence of the adductor reflex, and hypoesthesia in the medial aspect of the distal part of the left thigh. Electromyography demonstrated normal findings in the rectus femoris and iliopsoas muscles but partial denervation of the adductor magnus muscle; these results were consistent with a lesion of the obturator nerve. The patient was first seen in our clinic fourteen months after the operation, at which time the neurological symptoms were identical to those that had been noted at one year; the patient still used crutches for walking outdoors. Radiographs made at that time showed that two of the four screws that had been used for fixation of the acetabular reinforcement ring had perforated the medial pelvic wall; a lesion of the obturator nerve was suspected at this site (Fig. 1).
Operative exploration was performed with use of an extraperitoneal approach, which involved a curvilinear skin incision in the left lower quadrant of the abdomen, division of the aponeurosis of the external oblique muscle superior to the inguinal ligament, and splitting of the internal oblique and transverse abdominis muscles. After blunt dissection, the peritoneum was retracted upward and the urinary bladder was retracted medially. This approach permitted the surgeon to explore the intrapelvic course of the obturator nerve without exposing the patient to the risks associated with a transperitoneal approach. The nerve was dissected from the surrounding scar tissue and was found to contain a neuroma-in-continuity that was located approximately three millimeters away from the tip of the inferior perforating screw, on an extrapolated line along the axis of that screw. Intraoperative electrical stimulation both central and peripheral to the lesion failed to produce any contraction of the adductor muscles. Examination of an unstained section of the neuroma with use of loupe magnification showed what appeared to be fibrous tissue. Additional resection of both nerve ends was necessary to demonstrate a normal-appearing fascicular structure; to obtain this finding on the distal side, it was necessary for the nerve to be dissected distal to the obturator foramen after lengthening of the incision to the anterior part of the thigh. The defect was bridged with two twelve-centimeter-long sural-nerve grafts with use of the operating microscope and 9-0 epi-perineural sutures. The grafts did not follow the anatomical course of the obturator nerve through the obturator foramen, but they descended underneath the inguinal ligament. This course was chosen because it facilitated the distal sutures and allowed the grafts to be directed away from the tips of the screws, which were not removed.
Four months later, a positive Tinel sign was present distal to the inguinal ligament; this finding subsequently progressed distally. Two years after the reconstruction of the obturator nerve, the pain in the medial aspect of the thigh had resolved, the hypoesthesia in the distal third of the medial aspect of the thigh was less severe than it had been before grafting, the patient was able to walk without any assistive devices for as long as one hour, the circumference of the thigh had increased by 1.5 centimeters, and the strength of the adductor muscles had improved from grade 2 to grade 4.