Laboratory analysis in the assessment of painful total knee arthroplasty

Abstract

Careful use of laboratory investigations is an essential component in the workup of the painful total knee replacement (TKR). For the most part, these tests will be used to diagnose or exclude infection. In all cases, the C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) should be obtained. Aspiration of synovial fluid should be obtained when the CRP or ESR is abnormal or when there is high clinical suspicion for infection, although some advocate routine aspiration. Aspirated fluid is assessed for white blood cell count (WBC) and polymorphonuclear (PMN) neutrophil differential. Higher levels of synovial WBC and PMN differential should be expected following recent TKR. Aspiration is the first opportunity to obtain culture, essential to direct antibiotic therapy. Surgeons should be familiar with the relative sensitivity and specificity of all tests especially in combination, as well as the cutoff levels appropriate to the presenting patient.