ALUMINA ON ALUMINA BEARING WITH UNCEMENTED IMPLANT FOR DYSPLASTIC HIPS AGED SIXTY OR BELOW: A FIVE YEARS MINIMUM FOLLOW-UP STUDY TO ADVANTAGE THE BEARING PROPERTY, FROM A VIEWPOINT OF THE SURGEON

Abstract

Expecting the low wear property and the longevity, since October 1998, we have been using the alumina on alumina bearing for the hip arthroplasty. Until July 2008, for dysplastic 1078 hips we have implanted the bearing couple. Among them, we evaluated 86 hips in 79 patients (male 3, female 76) with the primary arthroplasty, Spongiosa Metal II Total Hip System (GHE: ESKA implants, Lübeck, Germany/Biolox Forte^®: Ceramtec AG, Plochingen, Germany), osteoarthritis secondary to developmental dysplasia, age 60 or below, and a minimum of five years follow-up. The preoperative diagnosis included the failed pelvic and/or femoral osteotomy, avascular necrosis after DDH, dislocation, and subdislocation. The average age at the surgery was 53 (27 to 60). The average of follow-up period was 6.3 (4.6 to 9.1) years. The implants have a macro-porous structure on the surface. To set the metal shell in the intended position, the sclerotic lesion was adequately resected by the chisels and then we used the acetabulum reamers. Otherwise the sclerotic lesion would prevent the reamer to go into the suitable direction. We reamed the acetabulum until the lamina interna to use the maximum size of the metal shell (i.e. to use the liner as thick as possible) and at the same time for the medialization of the hip center. To avoid impingement, the osteophyte was resected without hesitating. We added the adductor tenotomy for 19 hips, the extensive release of the flexor tendons (including the quadriceps origin, the sartroius origin, and the gluteus maximus insertion) for three hips, and the release of the extensor insertion (the gluteus maximus) for two hips, and the release of the flexor insertion (the iliopsoas) for two hips.

The hip score was improved in all patients. The average amount of the hip score was 59 before the surgery and was 90 at the final follow-up. A positive Trendelenburg sign was observed in 53 hips (62%) before the surgery and 12 hips (14%) at the final follow-up. We had no revision, no bearing failure (alumina fracture or excessive wear), no dislocation, and no squeaking in these patients. The average inclination angle of the cup was 41 (29 to 49) degrees. The average anteversion angle of the cup was 19 (13 to 27) degrees. No patient required the revision surgery. At the final follow-up, all implants were stable. In the acetabulum, the radio-lucent line was observed in two hips (2%) (zone I). In the femur the line was observed in 13 hips (15%). All lines existed in the proximal femur. There was no cystic osteolytic lesion. The prevalence of these periprosthetic reactions was less than those in the same type implant with the polyethylene on alumina bearing.

Some authors alerted that the alumina on alumina articulation should only be applied in when the optimized implant orientation is obtained so as to prevent the impingement and dislocation. Fortunately the alignment in this study was within the safe zone. However, we must always be very careful of the joint alignment, range of motion, and the muscle tension during the surgery to avoid the bearing failure, as setting an adequate alignment and obtaining a firm uncemented fixation of the cup is relatively difficult in dysplastic hips. From this view point, Spongiosa Metal II cup suits the use of the alumina on alumina bearing especially for dysplastic hips.