Diagnosis of periprosthetic joint infection after unicompartmental knee arthroplasty.

The purpose of this multicenter study is to determine the utility of the erythrocyte sedimentation rate, C-reactive protein, and synovial fluid white blood cell (WBC) count and differential for evaluating periprosthetic joint infection (PJI) in patients with a failed unicompartmental knee arthroplasty (UKA). A total of 259 patients undergoing revision of a failed UKA were reviewed; 28 (10.8%) met the study criteria for PJI. The optimal cutoff values were 27 mm/h for the erythrocyte sedimentation rate, 14 mg/L for the C-reactive protein, 6200/μL for the synovial fluid WBC count, and 60% for the differential. These tests are useful for diagnosing PJI after UKA with optimal cutoff values that are similar to those used for total knee arthroplasty; however, the optimal synovial WBC count was found to be somewhat higher, which may be related to the unresurfaced compartments. In addition, we found that nearly half of patients had suboptimal evaluation for PJI.