The effect of ulnar shortening on lunate and triquetrum motion—a cadaveric study

Background. Ulnar shortening osteotomy is a widely used procedure for a number of pathologic conditions. However, there is little biomechanical data on its effect on the surrounding soft tissue structures. Therefore, the objective of this study was to determine the effects of progressive ulnar shortening on the distal radioulnar joint and the proximal carpal bones. Methods. The kinematics and strain between the ulnar styloid, lunate, and triquetrum were evaluated with varying supination and pronation forces. Six fresh-frozen cadaveric upper extremity specimens were tested after progressive ulnar shortening using a custom jig. Biomechanical measurements including strain and translation were made by evaluating the change in position of the digitizing markers on the carpal bones, radius and ulna. Findings. There were significant changes in marker positions with respect to intact specimens for each amount of shortening at the ulnar styloid (P < 0.001), the lunate (P < 0.001), and triquetrum (P < 0.001). With progressive ulnar shortening, the strain data demonstrated that there was no significant change in lunato-triquetral strain, but demonstrated a significant increase in both ulno-triquetral and ulno-lunato strain (P < 0.04). Interpretation. Progressive ulnar shortening increases ulno-triquetral and ulno-lunato strains with an ensuing reduction in motion between the carpal bones.