Aims: To ascertain whether or not Hydroxyapatite Ceramic coated implants (HAC) will survive more than ten years after implantation. Method: Since May 1988 HAC hip prostheses have been used in more than 1900 operations. The patients are assessed using the Harris Hip Score (HHS) pre- and postoperatively and then annually. Post mortem specimens are sectioned to study bone integration to the HAC. Initial X-rays are reviewed and followed by annual X-ray after þve years. Results: HHS indicates that the system works with only 7% scoring less than 90. Only seven hips had a deterioration in HHS associated with the implant including three with aseptic loosening. One had catastrophic third body wear in a plastic acetabular liner. Histology shows early bony bonding (six weeks) to HAC particularly in cancellous bone. The HAC coating behaves biologically and is ultimately replaced with bone with no intervening þbrous layer: a Perfect Fit (seen at variable times after six years)Conclusions: HAC hip prostheses provide a ten year, pain free arthroplasty. There is one case of polyethylene debris/granuloma disease. Maximum follow-up is þfteen years. Longer term results will be awaited with interest.

Hydroxyapatite Ceramic Coated Hips (HAC) were first used in Sunderland, U.K. in May 1988. More than 1725 HAC hips have been inserted. There are 264 hips in 237 patients with ceramic/ceramic (alumina) bearings.

These hips are inserted into patients with a 20+ year life expectancy. Their mean age is 50.5 years.

All patients are assessed using the Harris Hip Score pre. and postoperatively. There are 14 patients with Harris Hip Scores of less than 80, but only 8 patients have problems attributable to HAC hip surgery. These include 1 patient with infection, 3 fractured ceramic acetabular liners, one broken ceramic head, 2 with aseptic loosening and 1 patient who chronically dislocated her hip.

Amongst the indications were osteoarthritis 136, hip dysplasia 44, and ankylosing spondylitis 13. Twenty six had had previous childhood hip disorders, and 16 had rheumatoid arthritis. The series also includes 4 revisions from cemented hip replacement.

The results have been rewarding. There are 1700+ HAC hips in the whole series. This sub group of 264 ceramic/ceramic HAC hips is small and follow up is relatively short. There have been few failures which could be attributed to the HA coated device. However, there are 4 broken ceramic components.

Conclusion: Hydroxy Apatite bony bonding secures the implants. No polyethylene is used which can contribute to debris disease.

Wear in ceramic bearings will be negligible. Third body inclusions must be avoided.

The femoral spigot must not impinge on the acetabular margin. The ceramic material has to be supported to prevent fracture.

Isolated wear of the polyethylene tibial component led to failure in five of a series of 108 uncemented porous-coated knee replacements. The clinical features included pain, effusion and instability with progressive varus deformity. In all cases there was extensive wear on the medial side of the polyethylene surface of the prosthesis. The mechanism of such wear is complex, being due in part to the unconstrained nature of the joint and the incongruity of its surfaces. Other design characteristics may have contributed.