Kinematics of the capitolunate joint in the sagittal plane. A new method based on reference points and triangulation.

A new method of assessing capitolunate alignment is presented. Three anatomical carpal reference points were evaluated on lateral radiographs using triangulation. Connecting these three points forms a triangle with dorsal, palmar and somewhat vertical sides. One hundred normal lateral wrist radiographs were measured. The overall dorsal limb (DL) to palmar limb (PL) ratio was found to be 0.74 (SD 0.07) over a range of 40 degrees extension to 42 degrees flexion. As the DL to PL ratio approached 1.0, a dorsal intercalated segment instability (DISI) deformity developed. Conversely, as the DL to PL ratio approached 0.5, a palmar intercalated segment instability (PISI) occurred. This method appears useful for evaluating static lateral radiographs for intercalary carpal alignment and possibly instability.