A CLINICAL AND RADIOGRAPHIC STUDY OF THE SAFE AREA USING THE DIRECT LATERAL APPROACH FOR TOTAL HIP-ARTHROPLASTY

The purpose of this clinical and radiographic study is to determine wh ether the surgeon can remain within the 5 cm ''safe zone'' while using the direct lateral approach during total hip arthroplasty (THA) witho ut endangering the superior gluteal nerve. The direct lateral approach was used in a prospective, consecutive series of 36 primary THAs in 3 1 patients performed by one surgeon. At the time of closure of the abd uctor muscle layer, a small metallic clip was placed at the superior e xtent of the incision into the gluteus medius. After surgery, the pati ents were mobilized on crutches with protected weight bearing for eith er a 6-week (hybrid THA) or 12-week (uncemented THA) period. Before su rgery, and at 3, 6, and 12 months after surgery, abductor strength and the Trendelenburg sign were measured by the same physical therapist. The vertical distance from the superior pole of the greater trochanter to the base of the clip was measured on all radiographs of the pelvis and corrected for magnification. Before surgery, only 25 of the 36 hi ps demonstrated abduction strength of 4/5 or greater. Three months aft er surgery, 34 hips had a grade of 4/5 or greater for abductor strengt h. The Trendelenburg sign was positive in 24 of 34 hips before surgery , in 5 hips at 3 months, in 1 hip at 6 months, but negative in all hip s by 12 months. The clip was located 3.2 +/- 1.3 cm (mean +/- SD) vert ically from the superior pole of the greater trochanter. In 34 of 36 h ips (95%), the 5 cm safe zone was respected. There was no correlation between abductor strength and the distance of the clip from the superi or pole of the greater trochanter. It would appear that, with careful surgical technique, the direct lateral approach can be safely performe d without compromising the superior gluteal nerve.