Infection of an orthopaedic implant: epidemiology and diagnosis

Infection of an orthopaedic implant is a source of considerable morbidity. Infection rates for primary total hip arthroplasties have been reported to be 1-2%. Major risk factors for deep infection are rheumatoid arthritis and diabetes mellitus. Other potential risk factors have also been described. From the majority of the patients with an infected hip arthroplasty, Gram-positive microorganisms can be isolated. Coagulase-negative staphylococci and Staphylococcus aureus are isolated in > 50% of cases, in almost equal numbers. Gram-negative bacilli are usually secondary invaders of open, draining wounds in patients with deep sepsis of a hip arthroplasty. Anaerobic microorganisms are isolated in 10% of such patients. To facilitate the management of the patients with an infected hip arthroplasty several classification systems have been described, but none of these is universally accepted. It can be difficult to make the correct diagnosis of infected joint arthroplasty with reasonable certainty: a diagnosis can be reached with an acceptable degree of certainty only by combining various investigations. In most cases, an infection can be diagnosed or excluded on the basis of a carefully obtained clinical history and the measurement of the sedimentation rate and/or the C-reactive protein level. Other preoperative investigations, such as radiography, arthrography, radio-nuclide imaging, aspiration of the joint and peroperative investigations, such as frozen sections, Gram stains and cultures, may provide additional evidence. Peroperative cultures provide the most accurate diagnostic information.