The Distal Radius Ulnar and Volar Cortices Are a Reliable Radiographic Marker of the Normal Wrist Centre of Rotation

Assessment of the microstructure of the distal radius demonstrates that the ulnar and volar cortices are the load-bearing components of the radius. We hypothesize that the center of rotation (COR) for the wrist lies directly distal to these cortices. The aim of this study was to define the radiographic relationship between the distal radius and the COR.

In total, 200 consecutive normal wrist radiographs were identified. The COR of the wrist, defined by Youm as the center of the proximal pole of the capitate on the posteroanterior (PA) view and the lunocapitate articulation on the lateral view, was identified. We drew circles of best fit over the capitate (PA view) and the lunocapitate joint (lateral view). These circles were portioned into thirds. Lines were drawn through the ulnar and volar cortices of the radial shaft parallel to the long axis of the radius on PA and lateral radiographs. We defined the offset as the distance from this line to the COR. The offset and the third of the COR through which the line passed was recorded.

In total, 200 (90 left/110 right) wrists were identified in 195 patients (74 males and 121 females) with a mean age 40 years. On the PA radiographs the mean COR offset was ulnar 0.07 mm (±1.1 mm). The ulnar cortical line passed through the central third of the COR in 94% of wrists. On lateral radiographs the mean COR offset was dorsal 0.09 mm (±1.4 mm). The volar cortical line passed through the central third of the COR in 97% of wrists. If both PA and lateral radiographs are considered, the ulnar cortical line and volar cortical line pass through the central third of the COR in 91% of wrists.

The COR lies directly above the ulnar-volar cortex of the radius in over 90% of normal wrists. We believe that this radiographic relationship may be of considerable clinical use when assessing normal and abnormal wrist radiographs.

Diagnostic IV.