Background/Purpose: Medical imaging is commonly obtained in evaluating patients with suspected prosthetic joint septic arthritis (PJSA); it may be helpful to detect other pathology in the joint (e.g., chondrocalcinosis), to establish a baseline, or to detect the presence of synovial fluid. Imaging may even help diagnose PJSA, but there is little data available to evaluate the value of various imaging modalities for the diagnosis of PJSA.

Objectives: To examine how the use of medical imaging for PJSA has changed over the 17 years of this study and to assess the value of different imaging modalities in differentiating patients with culture-positive PJSA from patients with culture-negative PJSA.

Methods: We conducted a retrospective study that included all patients ages 18 years and older who were diagnosed with monoarticular  PJSA and underwent surgical intervention at a single, tertiary-care hospital between 1997 and 2014.

Results: Of the 280 patients with diagnosed PJSA, 214 (76.4%) had at least one imaging study during the index admission. Radiographs were performed in 167 patients (59.6%). The second most common imaging modality was CT scan (17 patients; 6.1%). The most common imaging findings were joint effusion in 91 (32.5%) patients and soft tissue swelling in 41 (14.6%) patients.  Of the 280 patients assigned a diagnosis of PJSA, 190 (69.3%) were culture-positive. Patients with culture-positive PJSA were less likely to have normal findings in their plain radiographs (3.7 vs. 13.1%, p=0.007), more likely to have gas/free air (7.4 vs. 1.2%, p=0.043), but no more likely to have joint effusions (28.9 vs. 25.0%, p=0.56) or soft tissue swelling (13.2 vs. 8.3%, p=0.31). The percentage of patients receiving each imaging modality remained relatively constant over the course of the study (Figure 1).

Conclusion: Imaging studies—especially radiographs—are commonly ordered to evaluate patients with suspected PJSA. Our study demonstrates that patients with culture negative PJSA are more likely to have normal findings on imaging, including radiographs. Patients with culture-positive PJSA were significantly more likely to have radiographic findings of gas or free air. Imaging studies in general and radiographs in particular demonstrated joint effusions in patients at similar rates among PJSA patients with and without positive cultures. This study demonstrates that in most cases imaging studies have limited utility among patients with suspected PJSA and cannot be relied upon to demonstrate specific findings to suggest the diagnosis.

Figure 1: Trend over time for the percentage of patients receiving different modalities of imaging studies. The line labeled “Overall” indicates the percentage of patients receiving any form of imaging study.