Confirmation of Sexual Dimorphisms in Metal Hypersensitivity and Joint Pain Following Total Joint Arthroplasty: Commentary on an article by Marco S. Caicedo, PhD, et al.
In this Level-III study, Caicedo et al. completed a retrospective analysis of the rate of metal sensitization (i.e., metal allergy) to cobalt, chromium, and/or nickel among 1,038 male subjects and 1,575 female subjects with unexplained joint pain following TJA who were referred for metal-sensitivity testing. Joint pain was determined according to the patients’ self-assessed pain using an established visual analog scale (VAS), scored from 0 to 10. The rate and severity of metal sensitivity were determined with use of the metal-LTT blood test, in which the percentage of TJA subjects within each group with a stimulation index (SI) of ≥4 (reactive) or ≥8 (highly reactive) to nickel (as NiCl2), cobalt (CoCl2), and/or chromium (CrCl2) was quantified.
The retrospective analysis revealed that a similar majority of males (62%) and females (56%) with joint pain following TJA were referred for metal-sensitivity testing within 2 years of surgery and that >75% were referred within 5 years of TJA. This is consistent with a hypersensitive host response, as the painful symptoms occurred earlier than may be expected for aseptic loosening. The authors also confirmed several sex differences. In terms of self-reported pain by VAS, the average severity level at the time of metal-sensitivity testing was significantly greater for females than for males (6.8 compared with 6.1; p < 0.0001). However, the clinical importance of this difference is questionable, and the authors acknowledge that this result needs to be confirmed with the use of more sensitive instruments, for example, the WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index). In terms of metal sensitivity, the authors found that (1) females had a significantly greater rate of self-reported cutaneous metal allergy (e.g., to jewelry) prior to testing compared with males; (2) the overall rate of metal-LTT hypersensitivity was significantly greater among females (49% of females compared with only 38% of males); and (3) the degree of metal hypersensitivity was significantly higher among females than among males (median SI of 3.5 compared with 2.8).