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Ideal Fusion Angle For Thumb Interphalangeal Joint Arthrodesis
Danielle Cross, MD; Kristofer S. Matullo, MD
Orthopaedic Surgery, St. Luke's University Health Network, Bethlehem, PA

Introduction: While a thumb IP joint arthrodesis is typically performed in 0-10 degrees of flexion, most daily activities are completed with increased angles of flexion at the IP joint to facilitate pinch and grip. This study evaluated the preferred thumb IP joint position with certain tasks of daily living in an effort to determine if increased IP angles are more satisfactory.

Materials and Methods: 28 healthy volunteers (11 males, 17 females, average age of 33.5yrs) were splinted at various degrees (0°, 15°, 30°, 45° bilaterally) with thumb orthotics, leaving the tip free, to mimic various degrees of IP fusion angles. Subjects then underwent a series of 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, zippering/unzippering a jacket, and opening/closing Velcro), as well as pinch and grip strength testing, both at baseline (without any splinting to their thumb), and with the thumb splinted in each of the various angles. Subjects used a 10-point visual analogue scale (VAS) to rate the ease of completing each task, as well as their overall satisfaction with the splint, at baseline and at each of the various angles for their dominant and nondominant hand. Separate Wilcoxon signed rank tests were conducted for selected outcomes, with p < .05 denoting statistical significance.

Results: Significant decreases from baseline grip strength were found at 30° and 45° (p <0.05), while significant decreases in pinch strength were found at 0°(p>0.05). Across all categories and tasks, VAS ratings were most similar to baseline (thus, the most preferred splint) at a fusion angle of 15° for the dominant thumb, and at 30° for the nondominant thumb. The second most preferred angle of fusion for the dominant thumb was 30°, and for the nondominat thumb was 15°. The lowest scoring splint overall was at 45°, while a splint of 0° ranked third. Overall, the most difficult tasks to perform were precision tasks, such as translating coins or buttoning buttons, while the easiest tasks to perform were power tasks.

Conclusions: Our current study suggests that a thumb IP fusion angle of 15°- 30° is a functional and preferred angle of thumb IP joint positioning for various activities and should be considered when performing an IP joint arthrodesis.

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