Infection in orthopaedic implants.

The infection rate in hip prostheses should be less than 1.0% but in other joints is higher probably because of proximity to the skin surface and less experience in joint design. The organisms causing hip implant infection are Staphylococcus aureus 35%, S. epidermidis 15%, coliforms 25%, and anaerobes and others 25%; in other joints there may be a higher incidence of staphylococci. Clinical diagnosis is difficult since symptoms, X-rays and scans do not distinguish infection from loosening, but the erythrocyte sedimentation rate (ESR) moderately rises in infection. Treatment of deep infection by antibiotics alone is unlikely to succeed, but suppression of infection in patients unsuited to operation is possible. Surgeons should be encouraged to aspirate from the affected joint to obtain a bacteriological diagnosis; in the absence of this procedure broad spectrum antibiotics with good activity against S. aureus and S. epidermidis are required. Antibiotics must penetrate the membrane which forms in many patients at the implant or cement/bone interface but there is no evidence as to which antibiotics do so best. For prophylaxis there are three areas of uncertainty: (1) does antibiotic-impregnated cement provide additional effect to systemic antibiotics, since antibiotics can be found in the wound fluid after operation and gentamicin remains at the interface for many months?; (2) what proportion of late infections are haematogenous and do they demand prophylaxis for dental and surgical procedures?; (3) should greater protection from spread of staphylococci for the patient's skin and carrier sites be considered?