The AAHKS Surgical Techniques and Technologies Award: Synovial Fluid Metal Ion Levels as a Biomarker for Aseptic Loosening Following Cemented Total Knee Arthroplasty: A Prospective Study.

BACKGROUND

Implant loosening following primary total knee arthroplasty (TKA) remains the most common aseptic indication for revision. Aseptic loosening can be difficult to diagnose, as radiographic findings may be absent or difficult to detect or interpret. Commercially available bone cement contains either barium or zirconium to allow for radiographic detection. We hypothesized that implant loosening leads to abrasion-related release of detectable amounts of metal ions from the implant or bone cement, which may serve as biomarkers of aseptic loosening.

METHODS

We prospectively enrolled 50 patients (mean age: 65 years, 52% were women) undergoing revision of a cemented TKA requiring component explantation. Synovial fluid was obtained prior to arthrotomy during revision surgery and analyzed for concentrations of barium, zirconium, titanium, cobalt, and chromium in parts per billion (ppb). The diagnostic utility of each ion for detecting loosening was assessed. The operative surgeon determined whether the femoral and tibial components were well-fixed or loose at the time of removal.

RESULTS

There were 25 (50%) patients who had intraoperatively confirmed component loosening. Patients who had confirmed component loosening had elevated levels of zirconium (median levels: 27 versus 6 ppb, P = 0.016) and cobalt (median levels: 16 versus 1.5 ppb, P = 0.002) compared to patients who did not have loosening. The most accurate synovial metal ion levels for diagnosing aseptic loosening were cobalt (area under the curve: 0.76 (95% confidence interval = 0.611 to 0.92); P = 0.001) and zirconium (area under the curve: 0.79 (95% confidence interval = 0.6 to 0.99); P = 0.003). In this series, barium, titanium, and chromium levels were not predictive of component loosening.

CONCLUSIONS

Aseptic loosening remains a challenging diagnosis without an available confirmatory test. Although the current sample size is limited, our results indicate that synovial fluid cobalt and zirconium levels are valuable indicators of component loosening. In the absence of definitive X-ray findings, synovial fluid analysis offers a promising diagnostic modality. This test can potentially improve patient outcomes by enabling earlier and more accurate detection of aseptic loosening following primary cemented TKA.