Introduction and Aims: Recently, concerns have emerged regarding the high stiffness of acetabular components inserted with alumina ceramic liners, which might potentially cause early migration and loosening. This study was designed to investigate in-vivo the migration pattern of these constructs

Method: Fifty patients (50 hips) operated on using the same surgical technique and the same prosthesis were randomised in two groups. The study group of hips was treated with an alumina ceramic liner, the control group of hips received a polyethylene liner. An alumina femoral head with a diameter of 28mm was used in all hips. Radiostereometric analysis (RSA) was performed to assess migration using serial follow-up radiographs.

Results: The median pre-operative Harris hip score (HHS) was rated 48.9 points in the alumina group, and 47.7 points in the polyethylene group. At the two-year follow-up, the median HHS of the alumina group was rated 94.1 points, and was rated 93.7 points in the polyethylene group. There were no clinical or radiological signs of aseptic loosening. RSA of the alumina group of cups showed a median axial displacement of 0.026 mm (SD 0.35mm). The median axial displacement of the polyethylene group was 0.047 mm (SD 0.26 mm) (p=0.9). The median tilting of the cup was 0.21 degrees (SD 0.54 degrees) in the alumina group, and 0.35 degrees (SD 0.71 degrees) in the polyethylene group (p=0.12).

Conclusion: At an average of two years post-operatively, the cups inserted with an alumina ceramic liner appeared stable, RSA showed low rates of non-progressive migration. Results did not differ from those observed using the same cup inserted with a polyethylene liner.

In severe hip dysplasia the fixation of the cup becomes a technical hazard, and the augmentation of the acetabulum with an autologous bone graft is helpful when the bone stock is deficient.

Twenty-four patients (25 hips) were operated on between 1993 and 1994; the mean age at operation was 49 years (range, 28 to 71 years). The mean Sharp acetabular angle was 55degrees (range, 45 to 63degrees). The dislocation of the femoral head was graded Crowe 1 in 4 hips, grade II in 5 hips, Grade III in 10 hips, and grade IV in 6 hips. Autologus bone was harvested from the femoral head and from the proximal metaphysis of the femur. The fixation of the graft to the anterior wall and to the roof of the acetabulum was achieved using impaction using the reinforcement ring with hook of Ganz. A separate cohort of 25 patients (25 hips) operated on between 1998 and 1999 was investigated using radiostereometry (RSA).

The clinical outcome of the hips was prospectively reviewed using the Harris hip score at an average of 8.3 years (range 8 to 9 years) postoperatively. Twenty-four hips were pain-free, and had a range of motion of 210 degrees or more except 3. A positive Trendelenburg sign disappeared in 88% of the hips. One cup (4%) showed radiological loosening with migration and required revision surgery. No signs of migration or progressive radiolucent lines were present in the remaining hips. The graft appeared united without resorption in 24 hips. The results of micromotion analysis using RSA confirm the stable fixation of the reinforcement ring in dysplasia.

Satisfactory middle term results of total hip replacement for severe dysplasia can be achieved using appropriate surgery and specific components. The use of reinforcement ring is important to obtain adequate primary stability, and to protect the graft during healing.