The Fate of the Inconclusive Periprosthetic Joint Infection Workup and Reliability of Data Points.

In 2018, periprosthetic joint infection (PJI) criteria were revised to include a new category labeled "inconclusive." The purpose of this study was to characterize and describe the fate of the inconclusive PJI workup and to analyze preoperative factors associated with outcomes. We reviewed all PJI workups at our institution during a 3-year period (426 patients). Patients were labeled "infected," "not infected," or "inconclusive" according to 2018 PJI preoperative criteria. In addition to standard diagnostic variables, the presence or absence of clinical elements that increase the pretest probability of infection were collected. Patients with any missing preoperative diagnostic test results and those with clinical follow-up less than 30 days were excluded. Logistic regression was used to identify the factors associated with infection. Two hundred ninety-six workups remained after exclusion criteria were applied, consisting of 66 (22.2%) with a preoperative score of 6 or greater defined as infected, 52 (17.6%) inconclusive (score 2-5), and 178 (60.1%) not infected (score 0-1). Postoperative re-scoring of the inconclusive group based on intraoperative findings as per the 2018 criteria identified 6 of 52 (11.5%) as infected, 12 (23.1%) inconclusive, and 34 (65.4%) not infected. Among those preoperatively scored as inconclusive, variables statistically correlated with the presence of infection included history of PJI, factors that increase skin barrier penetration (eg, psoriasis and venous stasis), and presence of comorbidities predisposing to infection. For patients labeled inconclusive, clinical elements of the pretest probability for infection (eg, history of prior PJI) were as reliable as any diagnostic test, including alpha-defensin, in the diagnosis of PJI. [Orthopedics. 202x;4x(x):xx-xx.].