Verification of the reliability of sagittal MR images in assessment of segmental instability of the wrist

To determine the reliability of carpal angle measurement using sagittal wrist MR images for the diagnosis of dorsal intercalated segmental instability (DISI) or ventral intercalated segmental instability(VISI). In ten asymptomatic adult volunteers, capitolunate, scapholunate, and radiolunate angles were measured on lateral radiographs and five different series of sagittal MR images, and compared and statistically analysed. The four MR series, obtained in a prone position, with the wrists over the head, were as follows: A, sagittal images parallel to the third metacarpal bone axis, in a neutral position; B, oblique sagittal images parallel to the fourth metacarpal axis, in a neutral position; C and D, sagittal images parallel to the third metacarpal bone axis, with the wrist at 15 deg radially and ulnarly deviated positions, respectively. The fifth true sagittal MR image(E) was obtained in a supine position with the wrists located beside the trunk, in a neutral position. In the MR series performed in the prone position, the capitolunate and radiolunate angles measured in the series A, B, and D were significantly larger than those seen on lateral radiographs. The scapholunate angle showed a statistically significant difference (p=3D.014) in series D, where one case showed DISI configuration at a scapholunate angle of 81 deg. In other series, the angles were not significantly different from those seen on lateral radiographs. The lunate appears more dorsally tilted on sagittal MR images obtained in the prone position with the wrists above the head than on lateral radiographs, and a DISI configuration can be mimicked. If diagnosing wrist segmental instability by interpreting sagittal MR images without lateral radiographs, there is potential risk of misdiagnosis. It is believed that wrist positioning is crucial for the correct measurement of angles.=20