[Bone grafts in hip prosthesis revisions].

PURPOSE OF THE STUDY: We describe the collection, storage and examination of allogenic bone grafts and their use in revision hip arthroplasty, indicated because of acetabular loosening, that involved either an uncemented cup or an augmentation device with a cemented cup according to the extent and nature of acetabular defects.

MATERIAL: Allogenic bone grafts, usually long bones, were collected from deceased humans within 12 hours of death. They were processed according to the standards of US tissue banks. Using ELISA, the blood of each donor was serologically examined for antibodies against selected antigens (HIV I, HIV II, syphilis, HbsAg, HCV, and p24HIV I, HTLV I and II, and HbcAg, if required). Microbiological examination of each bone sample was also included. The samples were kept in a quarantine box until the examination results were known. When these were negative, the bones were cut, under aseptic conditions, to obtain parts (condyle, metaphysis, diaphysis, patella, etc.) weighing from 80 to 150 gr. Subsequently, another quality check, involving microbiological and histological examination, was performed. The allografts were stored at -80 degrees C.

METHODS: Between October 1999 and October 2000, 67 revision total hip replacements were performed. Of these, allogenic bone grafting was used for acetabular reconstruction in 30 cases (45%). The average amount of graft tissue per operation was 107 gr (range, 43 to 163 gr). Eleven grafts had been harvested from the tibial condyle, nine from the trochanters, eight from the femoral condyle and two from the patella. The graft bone, ground into coarse chips, was washed with an antibiotic solution. Two techniques were used in graft implantation. 1) Impaction grafting, under pressure, of the acetabulum whose surface was free from any granulation tissue and scratched to make the bone bleed, and implantation of a cemented cup (LOR or Spotorno CLS). 2) Filling of large defects with a bulk of allograft bone chips, using an augmentation ring, mesh or Burch-Schneider cage, and implantation of a cemented polyethylene acetabular component. Uncemented implants were used in 17 and cemented cups with an augmentation device in 13 cases. The hips were checked by X-ray at 3, 6 and 12 months and then at yearly intervals.

RESULTS: In the postoperative period of 26 to 38 months, an early recurrent infection led to temporary removal of the implant in one case, one hip showed superficial infection that responded to therapy and there was one case of aseptic acetabular loosening. A recurrent dislocation led to femoral stem exchange for a modular component with a longer neck in one case. The remaining 28 cases showed good incorporation of the graft without any signs of implant migration.

DISCUSSION: Segmental defects of the acetabulum can be treated by implantation of specific types of acetabular cups or by massive bone grafting. Cavitary defects can be filled with cancellous allograft bone or bioactive, artificial materials. We prefer morselized allograft bone from the tissue bank and this was used in 45% of repeat surgeries for failure of the acetabular component. An uncemented cup is more convenient, supposing sufficient primary stability can be ensured. When defects are extensive, augmentation devices and filling with graft bone are necessary. Cadaver allografts offer advantages over autologous bone because they are available at any amount and thus enable us to avoid extensive damage to the iliac crest by autologous tissue harvesting. Cadaver grafts are bones of good quality, free from degenerative or dystrophic changes because they are usually taken from young subjects. The size of 7 to 10 mm is optimal because it permits the grafts to maintain both structure and strength. The strict procedure of sample collection and examination minimizes the risk of infection transfer. The progress of graft bone ingrowth was evaluated on radiographs that showed incorporation of allograft into the surrounding bone during 3 to 6 months and no radiolucent areas at host bone-implant contact.

CONCLUSIONS: Our patients showed good allogenic bone ingrowth in relation to the acetabular bed and good bone restructuring and incorporation in relation to the implant. Neither mechanical failure of implants nor graft rejection were recorded. The risk of infection transfer was low and comparable with routine blood transfusion. The necessary prerequisite for revision hip arthroplasty is a well-operating bone tissue bank.