The Effects of Capitate Height Alteration on Dorsal Intercalated Segment Instability.

 Carpal kinematics may be influenced by the manipulation of carpal dimensions. This may provide a surgical alternative to unpredictable soft tissue reconstruction for scapholunate dissociation. The purpose of this study was to determine if altering capitate height can correct dorsal intercalated segment instability (DISI).  Five cadaveric wrists had baseline radiolunate (RL) angles and scapholunate (SL) intervals measured fluoroscopically, confirming no baseline DISI. We simulated open- and clenched-fist testing via a constant load of the wrist extensors and sequential loading of the digital flexors. We confirmed no baseline static/dynamic DISI. The SL ligament and secondary stabilizers (scapho-trapezio-trapezoid [STT] and dorsal intercarpal ligaments) were transected. Repeat loading and fluoroscopic measurements confirmed creation of static DISI. Capitate height was altered in three interventions: 2 mm shortening osteotomy of capitate waist, 7 mm shortening osteotomy of capitate waist, and 2 mm lengthening of original capitate height by insertion of a spacer at capitate waist. The osteotomized capitate was stabilized with a Kirschner wire; RL angles and SL intervals were measured via fluoroscopy during open- and clenched-fist testing. Primary and secondary outcomes were change in RL angle and SL interval, from the DISI stage to each capitate shortening and lengthening stage.  SL ligament and secondary stabilizers sectioning created a DISI pattern, with abnormal RL angles (>15°) and widened SL intervals. Neither capitate shortening nor overexpansion corrected RL angles or SL intervals in any DISI-induced wrists.  Under the conditions studied, isolated capitate shortening or lengthening did not correct radiographic DISI posturing of the lunate following sectioning of the SL and STT interosseous ligaments. Further study of carpal kinematics with more substantial bone changes and loading of adjacent joints may be beneficial.  Surgeons performing capitate shortening osteotomy in isolation should not expect to improve DISI.