[Transtrochanteric rotation osteotomies for osteonecrosis of the femoral head. Apropos of 20 cases].

PURPOSE OF THE STUDY

Twenty consecutive rotation osteotomies for idiopatic necrosis of the femoral head were reviewed with an average follow-up of 6,5 years, in order to evaluate an original technique (which uses a nail plate for rotation and fixation of the fragments), and to determine the middle term results (and therefore indications) of anterior and posterior rotation osteotomies.

TECHNIQUE

rotations were achieved by rotating the femoral head with the nail of the nail plate, and without dissection of the posterior vascular bundle. We performed 16 anterior rotation osteotomies (according to Sugioka, with an average rotation of 52 degrees) and 4 posterior rotation osteotomies (described by Kempf, with an average rotation of 77 degrees). Only two patients were lost after 2 years follow-up (with good result), and the radio-clinical outcome of 18 operations at 5 years was known.

RESULTS

Global results were : 7 failures, 3 fair and 10 very good or good. In the 4 posterior rotations (Kempf) we achieved 4 very good results, even in Ficats stage 3. In the 16 anterior rotations we could in all cases obtain, on the hip in extension, an almost complete discharge of the necrotic zone, as after osteotomy it was no more in front of the acetabular major bearing zone (defined as an angle of 40 degrees around the apex of the femoral head on the lateral Lequesne view). We obtained 6 good and very good results, 3 fair, and 7 failures requiring a THR. There were 2 factors of poor prognosis : Stage of the necrosis, as we observed 4 failures in the 4 Ficat's stage 3, and only 3 failures in the 12 stage 2. Depth of the necrosis, as we achieved 6 very good and good results and 1 poor in the 7 cases when it was no more than 1/3 of the head diameter. But in the 9 cases where depth was over one third there were 3 fair and 6 poor results.

DISCUSSION

Our technique proved to be reliable as it achieved the rotation planned before operation (only one hypo-correction of 15 degrees) and bone fusion, allowing full weight bearing at 3 months in all cases. No extension of the necrotic area was observed. Posterior rotation osteotomy was followed by long term favorable results, may be because it achieves an anatomic discharge of the necrotic zone not only when the hip is in extension, but also when the hip is flexed. Anterior rotation is only recommended when : a rotation not exceeding 60 degrees (therefore without risks for the posterior bundle) allows a discharge of the necrotic zone when the hip is in extension. The necrosis is stage 2. In Stage 3 a progressive arthritis may occur as, in hip flexion, the necrotic sector of the non spherical head comes in front of the acetabular major bearing zone. The depth of the necrosis does not exceed 1/3 of the femoral head, such as in cases of a very large necrosis, mechanical degradation of the non necrotic part of the head may occur, even if discharge of the necrosis is achieved.

CONCLUSION

Transtrochanteric rotation osteotomy may delay of a decade or more the occurring of osteoarthritis, if its indications are restricted to patients under 40, suffering from idiopatic necrosis. In our series Sugioka osteotomy gave good results in stage 2 when necrosis depth was no more than 1/3 of the head diameter. Posterior osteotomy allows a better discharge of the necrotic zone and thus may be proposed in less restricted conditions.