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News
Diagnosing periprosthetic joint infection (PJI) is notoriously tricky, and new evidence suggests widely used synovial fluid tests aren't reliable enough to stand alone. An audit of a 2025 meta-analysis found that synovial white blood cell count and polymorphonuclear percentage have poor positive predictive values, meaning roughly one in three positive results could be a false alarm — a serious concern when the diagnosis can trigger major surgery.
Diagnosing periprosthetic joint infection (PJI) — an infection around a prosthetic joint — has always been complex, and experts are now pushing back on proposals to simplify it too much. A recent audit reanalyzed the 2025 meta-analysis from the Unified PJI Definition Task Force and found that two commonly used synovial fluid tests — white blood cell (WBC) count and polymorphonuclear (PMN) percentage — are not reliable enough to diagnose PJI on their own.
The audit uncovered critical methodological flaws in the original meta-analysis, including switched data columns and a study-selection bias that artificially inflated the tests' apparent accuracy. After corrections, the numbers told a different story. Meanwhile, promising biomarkers like alpha defensin and leukocyte esterase show near-100% specificity in some studies, but follow-up research has tempered that initial optimism.
By the Numbers:
Why it matters: A false-positive PJI diagnosis can lead to unnecessary surgery and prolonged antibiotic therapy — serious harms for patients. Experts argue that PJI diagnosis must remain a multimodal process, weighing multiple tests together rather than relying on any single result.
