Synovial Fluid Metal Ion Levels are Superior to Blood Metal Ion Levels in Predicting an Adverse Local Tissue Reaction in Failed Total Hip Arthroplasty.

BACKGROUND

Adverse local tissue reactions (ALTR) are associated with total hip arthroplasty (THA) failure in patients with metal-on-metal bearings and/or taper corrosion, which can also occur in metal-on-polyethylene 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. 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.

METHODS

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.

RESULTS

The ratio of synovial fluid to whole blood Co concentration in ALTR and non-ALTR hips was 120:1 and 18:1 (P = .006). The mean ratio of synovial fluid to whole blood Cr concentration in ALTR and non-ALTR hips was 414:1 and 24:1 (P = .01). The mean synovial fluid Co/Cr concentrations were elevated in patients with ALTR compared with those without (2007.3 vs. 12.4 ppb, P = .007) and (3188.2 vs. 10.3 ppb, P = .02). The synovial fluid Co concentration was the most accurate test for detecting ALTR (cut off: 19.75 PPB, AUC 0.973).

CONCLUSION

In patients with ALTR, synovial fluid Co and Cr levels were 120 times higher and 414 times higher than whole blood Co and Cr levels. Synovial fluid Co ion concentration was the most accurate in predicting ALTR.

LEVEL OF EVIDENCE

Diagnostic level II.