A Slightly Dorsally Tilted Lunate on MRI can be Considered Normal.

Background: Abnormal angulation of the lunate can be an indication of intercarpal pathology. On magnetic resonance images (MRIs) the lunate often looks dorsally angulated, even in healthy wrists. The tilt on individual slices can also be different and might be misinterpreted as pathological, contributing to inaccurate diagnoses and unnecessary surgery. The primary aim of this study was to determine the average radiolunate angle on sagittal wrist MRI images as well as the radiolunate angle in the most radial, central and most ulnar part of the lunate; also the interobserver reliability was determined.

Methods: 140 MRIs from adult, non-pregnant patients presenting to the outpatient hand and upper extremity service between 2010 and 2013 with wrist pain were used for this retrospective study. One author measured the radiolunate and capitolunate angle (i.e., tangential and axial method) in all MRIs. Additionally, two authors measured the same angles independently in 46 MRIs to analyze interobserver reliability.

Results: The average radiolunate angle was 8.7 degrees dorsal. There were no significant differences in the radiolunate angles between the different parts of the lunate. A very good interrater agreement was measured considering the radiolunate angle and capitolunate angle (tangential and axial method).

Conclusions: Our study showed that the lunate appears slightly dorsally angulated on an MRI of a healthy wrist. Regarding the radiolunate angle, 10 to 15 degrees of dorsal tilt can be considered normal. This study provides reference information of normal anatomy for carpal axial alignment that may facilitate diagnoses of wrist pathology.