BACKGROUND: Patients who have metal allergies frequently request hypoallergenic implants. In total knee arthroplasty (TKA), coating of standard implants is commonly used, with almost 10% of all primary TKAs in Germany in 2023. Registry data, however, have shown increased revision rates for coated implants. Whether this is due to the coating itself or the characteristics of allergy-prone patients remains unclear. The aim of this study was to compare revision rates, patient-reported outcomes (PROs), and serum metal levels in patients receiving coated versus standard TKA.

METHODS: In this randomized-controlled trial, patients undergoing primary, unconstrained TKA were enrolled. Exclusion criteria included other metal implants, the need for constrained prosthesis, or known implant material allergy. A total of 118 patients were randomized (59 per group) to receive a coated or standard TKA. Serum metal levels were assessed up to five years. At the 10-year follow-up, 20 patients had died, and two had undergone revision. Of the remaining 96, 79 were available for clinical evaluation. Outcomes included the Oxford Knee Score, Short Form-36 (SF-36), and patient satisfaction.

RESULTS: Overall, 10-year implant survival was 98% for both groups. A revision occurred in each group. After 10 years, both groups showed good functional outcomes, health-related quality of life, and patient satisfaction, with no significant differences. However, functional scores and the physical component summary of the SF-36 declined compared to the 5-year follow-up, likely due to aging. Serum metal levels after five years were mostly below detection limits and similar across groups.

CONCLUSION: Both coated and standard TKA implants demonstrated sustained improvement in function and health-related quality of life, as well as low revision rates. In comparable patient cohorts, the use of this coated implant system does not appear to be associated with inferior outcomes.