What role does metal allergy sensitization play in total knee arthroplasty revision?

Background: Clinicians are often faced with the decision whether to revise a painful total knee replacement in patients who have chronic vague pain with no apparent explanation. A sensitive metal testing assay called the lymphocyte stimulation test has been used to detect nickel sensitization in patients with orthopedic implants. We hypothesize that nickel sensitization plays a role in the pathology of failed joint arthroplasty in patients with unexplained dissatisfaction. Methods: 32 patients with symptomatic total knee arthroplasty without obvious mechanical findings were tested prior to revision surgery. 19 nickel-sensitized and 13 non-sensitized patients were compared by cell counts of synovium surgical specimens for CD4⁺ and CD8⁺ cell lines. Patients were then revised with ceramic-coated implants. Secondary evaluation of functional outcomes, range of motion, and pain relief were assessed. Results: Nickel-sensitive patients showed a statistical increase in CD4⁺ reactivity compared to CD8⁺ reactivity. The ratio of CD4⁺/CD8⁺ T lymphocytes was 1.28 in nickel-sensitive patients versus 0.76 in the control (p = 0.009). There was no difference in functional scores, clinical scores, or range of motion after revision. Conclusions: This study provides objective data via histological analysis in support of a nickel allergic sensitization in failed arthroplasties where clinical and/or radiographic abnormalities may not be apparent. Biopsy for CD4⁺/CD8⁺ cell counts may provide further proof of the existence of nickel sensitization in lymphocyte stimulation test positive patients, and more importantly, may implore the surgeon to consider low nickel implant design in these patients.