Comparison of hypoallergenic knee arthroplasties in patients with metal hypersensitivity versus standard arthroplasties in non-hypersensitivity patients: A scoping review.

Background: Metal hypersensitivity in Total Knee Arthroplasty (TKA) continues to intrigue surgeons and researchers, with significant limitation of allergy tests due to the absence of clear cut-offs for a definitive diagnosis and their limited diffusion worldwide. We analyzed the literature to compare clinical outcomes in patients with metal hypersensitivity undergoing hypoallergenic knee arthroplasties and subjects without metal allergy undergoing standard knee arthroplasties.

Methods: This review adhered to PRISMA guidelines. A comprehensive search of MEDLINE, EMBASE, and Cochrane databases was conducted from inception to October 1st, 2023. Eligibility criteria included studies comparing clinical outcomes of hypoallergenic and standard knee arthroplasties in patients with and without metal hypersensitivity, respectively. Two independent reviewers screened studies, extracted data, and assessed risk of bias using the ROBINS-I tool. The primary outcome measure was the Knee Society Score (KSS). A random-effects model meta-analysis was performed to account for heterogeneity, with results expressed as standardized mean differences (SMD) with 95 % confidence intervals.

Results: From an initial 1846 studies identified, six met the inclusion criteria after rigorous screening. The quantitative included 409 knee replacements from three studies, comprising 95 hypersensitive patients who received hypoallergenic TKA and 314 non-allergic patients who underwent standard CoCr implant procedures. Risk of bias assessment revealedmoderate risk or lower across all included studies. Analysis of the KSS yielded an overall effect size (SMD) of -0.18 (95 % CI: -0.54 to 0.18), slightly favoring standard knee arthroplasties. Moderate heterogeneity was observed (I = 53 %, τ = 0.0526). The qualitative analysis included three studies. Significantly lower improvements were found in KSS, WOMAC, SF-12, and Euro-QoL-5D L-VAS among metal-sensitive patients. The third one reported no significant clinical differences between groups.

Conclusion: The scoping analysis showed similar clinical outcome after hypoallergenic TKA in patients with metal hypersensitivity compared to standard knee implants in patients without metal allergy.