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Assessment of Dorsal Subluxation in Thumb Carpometacarpal Osteoarthritis.

Background Although dorsal subluxation is a typical finding for osteoarthritis of the thumb carpometacarpal (CMC) joint, it is difficult to evaluate the subluxation after trapeziectomy and the significance of its surgical correction combined with trapeziectomy is still controversial. The purpose of this study was to develop a method to evaluate dorsal subluxation without using landmarks on the trapezium. Methods Thirty patients with thumb CMC arthritis and 13 normal patients were included in this study. Dorsal subluxation of the CMC joint was evaluated by measuring the distance between the volar tip of the thumb metacarpal base and dorsoradial border of the index metacarpal base (M1M2 overlap) on the X-ray true lateral view of the thumb as well as previously reported methods. Intraclass correlation coefficient (ICC) was used to assess inter- and intraobserver reliability for the measurement of M1M2 overlap by six examiners of different level of expertise. Dorsal subluxation was also evaluated after trapeziectomy with ligament reconstruction. Results There were almost perfect interobserver (ICC = 0.94) and intraobserver (ICC = 0.95 for an expert and 0.97 for a novice) reliabilities for the measurement of M1M2 overlap. There was a weak correlation between our method and previously reported methods. M1M2 overlap of the normal patients and the patients were 4.6 ± 1.2 mm and 2.3 ± 2.3 mm (mean ± SD), respectively. M1M2 overlap was corrected significantly after trapeziectomy with ligament reconstruction. Conclusion Dorsal subluxation of the thumb CMC joint could be evaluated by M1M2 overlap before and after trapeziectomy.