Metal Hypersensitivity in Total Knee Arthroplasty: Innovation Disproportionate to Clinical Necessity

Metal hypersensitivity in patients undergoing total knee arthroplasty (TKA) remains a poorly defined clinical entity. This study aimed to characterize the clinical burden of metal hypersensitivity in a national database. The primary objective was to evaluate trends in metal hypersensitivity diagnosis in the general and TKA populations, as well as the TKA revision rate in patients with and without metal hypersensitivity. Secondary objectives were to identify trends in the release of "metal-sensitive" joint replacement alternatives. A retrospective analysis was conducted using the Merative MarketScan Commercial and Medicare Supplemental databases from January 2018 to December 2023. Patients with a diagnosis of metal hypersensitivity were identified using International Classification of Diseases, 10th Edition (ICD-10) codes. Annual incidence was calculated for the general population and for patients undergoing TKA. TKA revision rates were calculated for patients with and without metal hypersensitivity. Secondary analyses assessed the incidence of novel TKA implants that are specifically advertised as "metal sensitive." The overall incidence of metal hypersensitivity in the general database population ranged from 0.019 to 0.025%. Patients undergoing TKA demonstrated significantly higher rates of metal allergy diagnosis (p < 0.001, annually), with the overall incidence ranging from 0.133 to 0.165%. Nonsignificant downward trends in the incidence of metal hypersensitivity were noted in both the general and TKA populations. Patients with metal hypersensitivity had TKA revisions at a rate that was significantly higher than those who did not (14.03% vs. 3.15%; p < 0.001). Patients with a diagnosis of metal allergy represented 0.68% of all revision cases. Seven novel orthopedic implants with explicit "metal sensitive" marketing were released between 2018 and 2025. This national database study demonstrates low and stable rates of metal hypersensitivity among both the general and TKA patients. There was no change in the incidence of metal hypersensitivity in either population over time. Patients with metal hypersensitivity represented less than 1% of TKA revisions. These findings challenge the value of medical device development for niche markets.