[C-reactive protein. An independent risk factor for the development of infection after primary arthroplasty]

Infection is a severe complication after primary arthroplasty of the hip (THA) or knee joint (TKA). Based on its high sensitivity, the C-reactive protein (CRP) concentration has become a valuable tool in the diagnosis of infection, although it has only moderate specificity. Because of this, it remains unclear whether a preoperative increased CRP without clinical symptoms is a risk factor for infection after primary arthroplasty.

In a retrospective analysis, we investigated individuals with infection after primary THA or TKA and matched them with patients without infection after similar operations. Matching criteria were age, gender, and present diseases. The average age of the 50 included individuals was 67.4 (range 48-81) years, with eight men and 17 women in each group. In addition to preoperative CRP, specific patient and surgery data and microbiological and histopathologic findings were obtained.

The average preoperative CRP concentration in the infected patient group was 1.3+/-2.5 mg/dl, in contrast to 0.4+/-0.7 mg/dl in the noninfected group. A threshold of 0.5 mg/dl was appropriate for discriminating between the two groups [13/25 (52%) in the infection group vs. 3/25 (12%) in the control group, p=0.003]. Independent from the patient group, CRP concentrations were significantly increased in individuals with diabetes mellitus (1.2+/-1.5 vs. 0.7+/-2.0 mg/dl, p=0.03).

An increased preoperative CRP concentration without clinical findings of infection is a risk factor for prosthetic infection after primary THA or TKA with a threshold concentration of 0.5 mg/dl. Latent local or systemic infections or aseptic inflammation with subsequent local immune suppression seem to be responsible. We recommend evaluating CRP before every THA and TKA. For values beyond 0.5 mg/dl, an exploration for infection should be done. Otherwise, the patient should be informed about the increased risk of infection.