Preoperative Diagnosis of Prosthetic Joint Infection

Making pre-operative diagnosis of intermediate and low-grade infections of prosthetic joint infection (PJI) is demanding and requires both clinical experience and good knowledge of diagnostic test performance. It is also necessary to know the rules of working with diagnostic tests based on the expected change in pre-test probability of PJI or the diagnostic odds ratio. This also requires a multi-modal approach with a rational combination of relevant tests because none of them can have both 100% sensitivity and 100% specificity. Suspicion of a developing PJI should be aroused by relevant information present in the patient s medical history and confirmed by clinical examination. Patients with an increased starting PJI probability, i.e. after taking the medical history and clinical examination, should be examined for the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels (screening tests). When both of these tests are positive and no other alternative explanation for their increase is plausible, then the post-test probability of PJI is significantly increased (up to 70%). Under such conditions the diagnosis is made definitive by positive results of synovial fluid analysis (leukocyte count, percentage of neutrophils and lymphocytes, IL-1, IL-6) or an increased IL-6 serum levels. On the other hand, when both ESR and CRP are negative, the post-test probability of PJI is significantly decreased and no further examination for the presence of infection is usually necessary. In case of inconsistent results of ESR and CRP or if there is a high suspicion of joint infection regardless of these test results, joint fluid aspiration (cytology, IL-1, IL-6) and IL-6 serum levels should be assessed. In this situation scintigraphy imaging (three-phase bone scan combined with labelled leukocytes or anti-granulocyte antibodies) can also support or exclude the diagnosis. In low-grade infections or after previous administration of antibiotics it is recommended to repeat the above-mentioned laboratory tests and joint aspiration after at least a two-week interval without antibiotics.