Questioning the Clinical Relevance of Positive Post-implantation Allergy Testing for Metal Hypersensitivity in Total Knee Arthroplasty: A Didactic Case Report

Allergy Testing Has No Correlation with Intraoperative Histopathology from Revision Total Knee Arthroplasty for Implant-Related Metal Allergy

Lymphocyte transformation testing (LTT) is often used in the workup for possible metal allergy after total knee arthroplasty (TKA) but the correlation of this test with other diagnostic metal-allergy findings in patients undergoing revision TKA for suspected metal allergy has not been established. A single-center, single-surgeon cohort of 19 TKAs in which both components were revised for presumed implant-related metal allergy based on history, physical, and LTT testing, to nonnickel-containing implants were retrospectively identified. Histopathologic samples obtained intraoperatively were semiquantitatively analyzed using both the Hospital for Special Surgery (HSS) synovial pathology score and the Campbell aseptic lymphocyte-dominant vasculitis-associated lesion (ALVAL) score. As histopathology control group, we included in the study an additional cohort of 17 patients who received aseptic revision TKA and had no history of reported or tested metal sensitivity. All preoperative LTT results were highly reactive to nickel. However, this did not correlate with local periarticular tissue response in 18 of 19 cases which demonstrated a low HSS synovial score (mean: 3.8 ± 2.8, of a maximum score of 28) and the low Campbell ALVAL scores (mean: 2.5/10 ± 1.3, of a maximum score of 10). There were not any significant differences between the study group (suspected implant-related metal allergy) and the control group (nonsuspected implant-related metal allergy) in regard to (1) the Campbell score and (2) the HSS synovial inflammatory score. Knee Society Clinical Rating System (KSCRS) function score improved significantly after revision (mean postoperative increase: 34.0 ± 17. 2; p < 0.001), as well as mean visual analog scale (VAS) pain (mean postoperative decrease: 33.3 ± 26.4; p < 0.01) score. The short-term survival rate (at mean follow-up of 26.1 months) of this patient cohort was 100%. In this cohort of revised TKA patients with suspected nickel allergy based on clinical presentation and LTT positive results, intraoperative histopathology was essentially normal. However, all patients with suspected nickel allergy showed a significant clinical and functional improvement with excellent short-term survival rates. The clinical significance of a positive LTT needs further study.