“NICKEL-FREE” OXINIUM HYPOALLERGENIC VERSUS STANDARD COBALT-CHROME CONTAINING TOTAL KNEE ARTHROPLASTY: IS THERE A DIFFERENCE IN SYNOVIAL METAL IONS AT MINIMUM TWO-YEAR FOLLOW-UP?

Background Metal allergy and adverse local tissue reaction (ALTR) to metal debris may both be modes of failure in total knee replacement (TKA). Yet, the intraarticular synovial fluid metal ion levels in well-fixed implants beyond the first postoperative day remain unknown. The aim of this study was to compare intraarticular synovial fluid levels of metal ions in patients with a hypoallergenic TKA implant versus a matched cohort with a standard cobalt-chromium (Co-Cr) containing TKA implant at minimum 2-year follow-up. Methods A retrospective, matched, case-control study was performed using prospectively collected data from a single institution. A total of 22 cases (metal allergy/sensitivity with Oxinium hypoallergenic TKA implants) and 18 controls (standard Co-Cr TKA implants) were enrolled, with a median follow-up of 4.9 (IQR 4.0 to 5.2) years. Cases and controls were matched for age, sex, BMI, ASA, indication for primary TKA, femoral component design, patellar resurfacing, and time from TKA surgery ( P >0.05). Synovial fluid from sterile aspirations of the study knees were analyzed for metal ion levels of cobalt (Co), chromium (Cr), nickel (Ni), and titanium (Ti). Well-fixed implants were confirmed radiographically and functional outcomes were analyzed. Results The median Ni ion level in the synovial fluid of the hypoallergenic cases was 3.6 times higher than standard Co-Cr containing implant controls (1.0 vs. 0.28 ug/L, P <0.001). Co ion levels in the hypoallergenic cases were 17.7 times lower compared to the controls (0.07 vs. 1.24 ug/L, P <0.001). Similarly, the Cr ion levels in synovial fluid of the hypoallergenic case knees was 3.2 times lower compared to control knees (0.39 vs. 1.26, P <0.001). The OHS ( P =0.577) and FJS ( P =0.675) were similar between cohorts. Conclusion Patients with hypoallergenic implants had intraarticular synovial Ni ion levels 3.6 times higher versus standard implant controls. Our results do not support the use of this Oxinium hypoallergenic implant performed using manual instrumentation for patients with Ni allergy/hypersensitivity. However, if ALTR metal debris such as Co does become a bigger issue in TKA, our data support the use of the hypoallergenic implant. Further definitive study on the subject matter is necessary and warranted