Diagnosis of periprosthetic joint infection using alpha-defensin test or multiplex-PCR: ideal diagnostic test still not found.

PURPOSE: Diagnosing periprosthetic infection remains a challenge. Multiplex-PCR and biomarkers such as alpha-defensin are potentially useful and fast methods for detecting periprosthetic infection. This study compared these new methods with clinical assessment, conventional microbiological methods and histo-pathological examination.

METHODS: Twenty-eight consecutive patients with 30 joints and a mean age of 67.7 years (range 39 to 88) with removal of total hip arthroplasty (THA) or total knee replacement (TKR) were included in this study. Patients were classified according to the modified Musculoskeletal Infection Society score (MSIS) for infected joints. Punction fluid and tissue specimens were taken for conventional microbiological examination, alphadefensin test was performed, a synovial membrane specimen was used for multiplex-PCR and histopathological examination was carried out.

RESULTS: The alpha-defensin test and multiplex-PCR showed a sensitivity of 76.9 vs. 30.8% and a specificity of 82.4 vs. 100%, respectively. We found a significant difference between the positive and negative results (p = 0.0023). The conventional microbiological methods were not significantly different from the alpha-defensin test (p = 0.244) with a sensitivity of 84.6% and a specificity of 100% but did differ significantly from the multiplex PCR (p = 0.0030). There was a significant difference between modified MSIS classification and multiplex PCR (p = 0.0007).

CONCLUSIONS: Neither alpha-defensin test nor multiplex-PCR could detect periprosthetic infection immediately and reliably. Multiplex-PCR was suitable for detecting the non-infected but not the truly infected. Alpha-defensin test was helpful but showed no satisfactory results. Conventional microbiological methods remain the most reliable for periprosthetic infection diagnosis.