No Increased Risk of Knee Arthroplasty Failure in Patients With Positive Skin Patch Testing for Metal Hypersensitivity: A Matched Cohort Study

Background: It is unclear whether a positive skin patch test for metal allergy in patients with skin hypersensitivity to metals is associated with an increased risk of total knee arthroplasty (TKA) failure. Our aim was to determine whether patients with a history of metal allergy who had a positive skin patch test (SPT+) had worse outcomes after primary TKA compared with those with a negative skin patch test and compared with controls. Methods: Over 12 years, 127 patients underwent 161 TKA after skin patch testing (SPT; 56 were positive). Cases were matched by age, gender, body mass index, American Society of Anesthesiologists score, implant type, and implant manufacturer to 161 control knee arthroplasties without any prior history of metal allergy and no SPT. Median follow-up was 5.3 years. Differences in outcome measures were assessed between groups. Results: Patients with a SPT+ to metal did not have a higher complication, reoperation, or revision rates compared with patients with a SPT- and matched controls. Survivorship free of revision at 5 years was 98.1% for SPT+; 100% for SPT-; 97.6% for SPT+ controls, 99.0% for SPT- controls. There was no statistically significant difference in postoperative pain between SPT+ and SPT- patients and matched controls. Conclusion: This study was designed to evaluate the effect of metal hypersensitivity on TKA outcomes and the role of SPT in patients before TKA. In this study, a SPT+ for metals was of little practical value in predicting the midterm outcome after TKA and cannot be strongly recommended as a method to guide the selection of implant type.