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Functional Fusion Angle for Thumb Interphalangeal Joint Arthrodesis

Background: A thumb interphalangeal (IP) joint arthrodesis is typically performed in 0° to 30° of flexion; most daily activities involve increased flexion at the IP joint to facilitate pinch and grip. This study evaluates the preferred thumb IP joint position with certain tasks of daily living to determine a more satisfactory angle. Methods: Twenty-eight healthy volunteers were splinted at various degrees (0°, 15°, 30°, 45°, bilaterally) with thumb orthotics, leaving the tip free, to mimic various angles of IP fusion. Participants underwent power tasks (pouring from a gallon jug, opening/closing a tight jar, lifting a heavy glass, and opening a door), timed precision tasks (writing, buttoning/unbuttoning a shirt, translating coins, zipping/unzipping a jacket, and opening/closing Velcro), as well as pinch and grip strength testing. All tasks were performed both at baseline (without any splinting) and with the thumb splinted in each angle. Participants used a 10-point Visual Analogue Scale (VAS) to rate the ease of each task as well as their overall satisfaction at baseline and at each of the various angles for their dominant and nondominant hand. Wilcoxon signed rank tests were conducted for outcomes, with P < .05 denoting statistical significance. Results: Power tasks were best accomplished at 0° for the nondominant hand and 0° to 30° for the dominant hand. Precision tasks were preferred at 15° for both dominant and nondominant hand. Grip strength was best at 15° and 0° for the nondominant and dominant hand, respectively. Pinch was equivocal between 0° and 30° for the nondominant hand and from 15° to 30° for the dominant hand. VAS ratings were most similar to baseline at a fusion angle of 15° followed by 30° for the dominant thumb and 30° followed by 15° for the nondominant thumb. Conclusions: A thumb IP fusion angle of 15° to 30° is a functional and preferred angle of thumb IP joint positioning for various activities of daily living.