As part of a search for better articulation in total hip prostheses, the decrease in the thickness of the socket in different total hip prostheses was measured in vivo. The wear rates of (1) RCH 1000 (molecular weight, 106) socket gammairradiated with 100 Mrad articulating with a crude COP (stainless steel containing 20% cobalt and 0.01% phosphorous) metal femoral head; (2) RCH 1000 socket nonirradiated articulating with a crude COP femoral head; (3) RCH 1000 socket irradiated with 100 Mrad articulating with an alumina femoral head; (4) ultra high molecular weight polyethylene (molecular weight, 5–6 × 106) socket articulating with an alumina femoral head; and (5) ultrahigh molecular weight polyethylene socket articulating with a stainless steel femoral head (T-28) were 0.06, 0.30, 0.06, 0.10 and 0.25 mm/year, respectively, in the authors’ clinical cases. Alumina femoral heads were effective in decreasing wear of the polyethylene socket. However, the wear rates of gamma-irradiated sockets articulating with alumina and with metal femoral heads wear very low and were not different from each other. Regarding the relationship between wear rate and the thickness of the ultra high molecular weight polyethylene socket articulating with a 28 mm alumina femoral head, on radiographs, average wear rates of socket thicknesses of 7, 8, 9, 10 and 11 mm were 0.14, 0.15, 0.12, 0.06, and 0.08 mm/year, respectively. On measuring retrieved prostheses, average wear rates of 7, 8, 9 and 11 mm thickness sockets were 0.2, 0.19, 0.14, and 0.1 mm/year, respectively. The wear of sockets has been proven to be minimal in alumina femoral heads articulating with ultrahigh molecular weight polyethylene sockets thicker than 10 mm.

To avoid the consequences of polyethylene wear in a high-risk population, 128 alumina-onalumina total hip arthroplasties have been done in 104 consecutive patients. The maximum age of patients was 40 years. The main preoperative diagnoses were osteonecrosis and sequellae of congenital hip dislocation (71% of the hips). The same titanium alloy cemented stem was implanted in all of the hips. Four types of alumina acetabular component fixations were used: a cemented plain alumina socket (41 hips), a screw-in ring with an alumina insert (22 hips), a press-fit plain alumina socket (32 hips), and a press-fit titanium metal back with an alumina insert (33 hips). Eight patients (11 hips) died during the followup period. Sixteen revisions have been documented, 12 for acetabular aseptic loosening, three for bipolar loosening (two of which were septic), and one for unexplained pain. Eighty-eight hips in 74 patients have been followed up radiologically for 2 to 22 years. Wear was unmeasurable. Four additional sockets showed definite migration. The respective survival rates after 7 years were 94.1% for the cemented cup, 88.8% for the screw-in ring, 95.1% for cementless press-fit plain alumina socket and 94.3% for the metal-back press-fit component. The 10-year survival rate was 90.4% for the cemented socket and 88.8% for the screw-in ring. The 15-year survival rate was 78.9% for the cemented socket. Grafting was the only prognostic factor, with a survival rate of 62.6% after 10 years for the hips with a bone graft and of 90.1% for hips without a graft.

The alumina-on-alumina bearing surfaces seem to be a valuable alternative to the standard metal-on-polyethylene system for young patients. However, an improvement in socket fixation is required to lengthen the life span of the prosthesis to match the life expectancy of this demanding population.