ONE-STAGE NON-CEMENTED REVISION OF SEPTIC HIP PROSTHESIS USING ANTIBIOTIC LOADED BONE GRAFT

Abstract

Infection of total hip replacement still is considered a devastating complication. One-stage revision, meaning complete removal of the implant and thorough debridement of the site together with the insertion of a new prosthesis during the same operation, is desirable because of improved rehabilitation of the patient and reduced costs. Although this method is known since more than 30 years it is not used widely yet because of several related risks: known methods rely on the use of antibiotic-loaded cement, which often has shown insufficient release of the added antibiotic. The carrier may even act as a bed for colonisation with selected bacteria. Osseous conditions presented during revisions prevent interconnection of the cement with the sclerotic bone. The toxic monomers of PMMA and heating during polymerisation causes necroses which may be origin of repeated loosening and new growth of bacteria. Filling the defects with cement provides unfavourable conditions in case of another revision, which has to be expected at a high percentage. To overcome these disadvantages uncemented techniques seem to be favourable.

After removal of the implants debridement is performed as in conventional septic surgery. After thorough cleaning and rinsing, bone voids are filled with bone graft using an impaction technique. We use allograft or xenograft bone that is free from antigenic material but intact structures of bone concerning collagen and mineral content. The bone is impregnated with high loads of antibiotic, using a specific incubation technique. There are two options of antibiotic impregnation: vancomycin (“V”) or tobramycin (“T”), the choice being dependent on the causative pathogen isolated. Combinations are possible in cases of mixed infections. The impregnation procedure guarantees high levels of antibiotics at the grafting site for several weeks during which the antibiotic is released into the surroundings. Systemic drug levels are usually undetectable. At the acetabular site we take care that the ground be sufficiently filled with antibiotic graft. Preferably an uncemented cup of hemispherical design is inserted. At the femoral site we prefer implants with a rectangular diameter. This design enables stable press fit contact with the shaft medially and laterally and leaves enough space for graft impaction at the posterior and anterior aspect of the endoprosthesis. Wounds are drained and closed immediately; rehabilitation is performed as after non-septic surgery.

Between 1998 and 2004 thirty-seven patients have been revised because of culture-proven infection of hip endoprosthesis. Causative pathogens were Coag.neg. staph (18x), S.aureus (11x), MRSA (4x), enterococci (9x) and other gram-positive pathogens (3x). In 6 hips gram-negative germs were found additionally. All hips could be followed up with a minimum of 2 years and a maximum of 8 years (mean: 4.1 years).

Wound healing was uneventful in all cases. Mean hospital stay was 16 days (10–32 days). Rehabilitation was in the range of uncomplicated primary THR in cases with short history of infection (up to 3 months) and prolonged in relation to duration of infection and amount of preceding surgery. In three hips there was recurrence of the infection, diagnosed between 6 and 12 weeks after surgery. In one of them the well-fixed stem had not been exchanged, in another one a technical error had occurred during impregnation of the bone graft. This one could be successfully re-operated using the same technique with appropriately impregnated bone graft, the other two were converted to a girdlestone situation. All other 32 hips showed no sign of infection until the last follow-up.

Bone processed in an adequate way represents an excellent carrier for vancomycin and tobramycin. With antibiotic graft compound eradication of pathogens, grafting of bony defects and re-insertion of an uncemented prosthesis may be accomplished in a single operation, making it an ideal tool in one stage non-cemented revision for infected total hip replacement. However, principles of septic surgery need to be observed. We now recommend removing even well-fixed prostheses and taking care, that we implant at least 50cc of well impregnated bone graft. Since the graft gradually is replaced by healthy own bone, improved conditions may be expected even in the case of another revision.