Role of Synovial Fluid Metal Ion Levels in Failed Total Hip
The purpose of this study was to determine how the blood and prosthetic hip synovial fluid levels of Co and Cr correlate with one another, and determine which concentration is more predictive of ALTR. Adverse local tissue reactions (ALTR) are associated with total hip arthroplasty (THA) failure in patients with metal-on-metal (MoM) bearings and/or taper corrosion, which can also occur in metal-on-polyethylene (MoP) articulations. Patients are monitored with blood cobalt (Co) and chromium (Cr) concentrations which do not always correlate with the degree of soft-tissue reaction at revision THA.

Synovial fluid and blood samples were collected at the time of revision THA in patients with (n=26) and without ALTR (n=27). Whole blood, serum and synovial fluid metal ion concentrations were correlated with one another and clinical findings.

--The ratio of synovial fluid to whole blood Co concentration in ALTR and non-ALTR hips was 120:1 and 18:1.

--The mean ratio of synovial fluid to whole blood Cr concentration in ALTR and non-ALTR hips was 414:1 and 24:.

--The mean synovial fluid Co/Cr concentrations were elevated in patients with ALTR compared to those without (2,007.3 vs. 12.4 ppb), and (3,188.2 vs. 10.3 ppb).

--The synovial fluid Co concentration was the most accurate test for detecting ALTR (Cut off: 19.75 PPB, AUC 0.973).

Finally, synovial fluid Co and Cr levels were 120 times higher and 414 times higher than whole blood Co and Cr levels in ALTR patients. The concentration of Co ions in synovial fluid was the most accurate predictor of ALTR.