Measurements on Plain Radiographs to Define Distinctive Morphological Patterns of the Wrist

Objective: To understand wrist biomechanics, anatomical variation should be delineated. We further described two structural wrist types based on the morphology of the midcarpal joint, using multiple measurements performed on plain wrist radiographs.

Methods: One-hundred-seventy-two normal adult wrist radiographs were evaluated for: lunate and capitate shape, ulnar variance, radial inclination and height, volar tilt, distance and angle between two lines of reference, and percent of lunate and capitate radial to these lines, percentage of capitate circumference articulating with the lunate, scaphoid and trapezoid. Wrists type 1 included a lunate type -1 and spherical proximal capitate articulation. Wrists type 2 included a lunate type 2 and flat proximal capitate articulation.

Results: We had 49 wrist types -1 and 49 wrists type- 2. Wrists type-1 included a longer contact area between the lunate and capitate and between the capitate and base of middle metacarpal (p=0.001) and hamate (p=0.004). There was a significant association between capitate circumference and the distance of the capitate (ulnar most border) to the line of reference 3 (line that was drawn perpendicular to the horizontal line used for ulnar variance and radial height that passes through the volar anterior ulnar corner of the radius on a PA view) (p=0.03) and to lines 1 and 2-the anatomical axis of the radius and the index metacarpal- p=0.000.

Conclusions: We further delineated the two wrist patterns using differences in the CMC joints and the facets between the capitate, hamate, and scaphoid bones. Further study should translate these measurements into 3- dimensional structures to evaluate true contact areas. Finite element analysis can be used to estimate the transfer of forces in different wrist patterns