Introduction: Revision hip surgery is likely to become more frequent with the continued use of cemented primary hip prostheses.

Primitive stem cells from bone marrow become osteocytes in the presence of hydroxyapatite ceramic (HAC). Consequently there is osseointegration of an HAC surface in bleeding cancellous bone/marrow.

However, damaged bone in the revision situation does not provide the necessary stem cells for osseointegration. Revision surgery using standard length (150mm) HA coated stems is not always satisfactory.

Using a 200 mm stem will extend the operating field into fresh, undamaged cancellous bone and marrow.

Method: Since 1988 more than 2600 HAC hips have been implanted for primary and revision hip cases. This includes 148 revisions. The continued use of primary HAC hips has reduced the necessity for revision hip surgery. There is a dwindling population of cemented, loosening hips requiring revision. Patients are assessed radiologically and using the Harris Hip Score (HHS) pre. and post-operatively on an annual basis.

Results: Since 1991 the longer 200mm stems have been used in 73 cases. The results have been rewarding.

The system works with improved HHS. Defects from debris disease fill in and stems are seen to bond to the host bone particularly at the tip. There have been no prosthetic fractures.

Only one case has needed re-revision when a stem remained un-bonded in the presence of a transverse femoral fracture. Two other stems are probably not bonded. This represents 4% failure.

Discussion: HA bonding is a successful system of fixation in primary hip arthroplasty. Using a 200mm stem in revision cases allows virgin bone marrow to provide the necessary stem cells for fixation. These longer HA coated stems should be used in revision surgery.

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.