Unilateral Incomplete Coalition of the Capitate, Trapezoid, and Trapezium with Trapezoid Fracture.

Carpal coalition, the union of at least two carpals, is a rare and often incidental finding. Although typically asymptomatic, symptoms may arise from altered biomechanics, degenerative arthritis, or increased fracture risk. Nearly all combinations of carpal coalitions have been reported, with lunate-triquetrum coalitions being the most common. We present the case of a 62-year-old woman with left radial wrist pain after a ground-level fall whose initial radiographs were negative for fracture; however, careful review of the radiographs revealed an unusual articulation between the capitate, trapezoid, and trapezium. Magnetic resonance imaging confirmed an incomplete capitate-trapezoid-trapezium coalition, and an isolated nondisplaced trapezoid fracture with edema. She was treated conservatively with splinting and fully recovered within 2 months. An incomplete capitate-trapezoid-trapezium coalition has not been previously documented and given the rarity of isolated trapezoid fractures, this case highlights a unique presentation in which abnormal carpal kinematics likely predisposed the trapezoid to fracture.