A Novel Screening Technique for Ulnar-Sided Carpometacarpal Dislocations.

Diagnosing ulnar-sided carpometacarpal joint dislocation is difficult, and more than half of injuries are missed on initial examination. The authors hypothesized that measuring the angle between the capitate and the metacarpals (capitate-metacarpal angle) on a plain radiograph would provide a simple, reliable tool to aid in the diagnosis of ulnar-sided carpometacarpal dislocation. This study retrospectively reviewed patients who underwent surgery for ulnar-sided carpometacarpal dislocation (study group). Two authors identified the contour of the capitate and the second, fourth, and fifth metacarpals on plain radiographs. The control group consisted of patients who had radiographs and no bony carpal or metacarpal pathology. Information on the contour of each bone was entered into MATLAB, version 8.5, software (MathWorks, Natick, Massachusetts), which calculated the 2-dimensional angles. A 3-dimensional model based on computed tomography scan data was used to obtain a "true lateral" image to account for variable rotation on plain radiographs. With the use of conventional lateral hand radiographs, the average capitate-metacarpal angle in the control group was 10 degrees compared with 19 degrees in the study group. Using a screening value of 15 degrees on plain radiographs, the sensitivity of the capitate-metacarpal angle was 0.85 and the specificity was 0.79. Both 2-dimensional and 3-dimensional measurements showed that the angle between the capitate and the lesser metacarpals is a reliable screening tool for carpometacarpal dislocation. During evaluation of patients with posttraumatic hand pain, an increased capitate-metacarpal angle may indicate the need for advanced imaging studies to further evaluate the carpometacarpal joints.