Thumb interphalangeal joint arthrodesis angles in patients with carpometacarpal osteoarthritis.

Purpose: Previous studies have shown that thumb interphalangeal (IP) joint arthrodesis is typically performed between 0 and 30° of flexion, with a recent study in healthy subjects having recommended a range of 15-30° to be an ideal functional IP joint fusion angle for various activities of daily living. The current study aimed to evaluate the ideal thumb IP fusion angle in patients with thumb carpometacarpal (CMC) osteoarthritis (OA).

Methods: Twenty-seven patients with thumb CMC OA were evaluated; five patients had bilateral pathology, for a total of thirty-two thumbs included. Hand dominance was noted and baseline unsplinted measurements were obtained for power tasks, precision tasks, pinch, and grip strength testing. Patients' thumbs were then splinted at 0, 15, 30, and 45° with repeat measurements taken and compared to baseline. Outcomes were measured by use of a 10-point Visual Analogue Scale, timing of tasks, and a dynamometer. Outcomes were analyzed by Wilcoxon sign ranked tests for each category of trials.

Results: For significant outcomes, the most favorable simulated thumb fusion angles were 15° in the dominant hand and 0°, 15° in the nondominant hand (precision tasks); the least favorable position was found to be 45° in the dominant hand (precision tasks, pinch strength). When combining all outcomes that both reached and approached significance, the most favorable position was found to be 15° and least favorable position, 45°.

Conclusions: In patients with thumb CMC OA, an IP fusion angle of 15° is preferable, while a fusion angle of 45° is to be avoided.

Type of study/level of evidence: Therapeutic Study, Level III.