Observer variability in measurements of carpal bone angles on lateral wrist radiographs.

Determinations of carpal bone angles are used in the clinical evaluation of carpal malalignment. Eleven frequently referred radiological measures in lateral projection of the wrists in 23 wrists were assessed using different definitions of axes. Interobserver- and intraobserver variations were calculated. The standard deviation of the interobserver variation ranged from 2.60 degrees to 18.15 degrees, and the intraobserver variation from 1.89 degrees to 4.66 degrees depending on the angles measured. The use of three angles for the least observer variability in assessment of carpal alignment is recommended. These angles were defined from the following carpal bone axes: radius, the line through the center of the medullary canal at 2 cm and 5 cm proximal to the radiocarpal joint; lunate, the line perpendicular to the tangent of the two distal poles; scaphoid, the tangent of the palmar proximal and distal margins, and capitate, the tangent of the dorsal margin of the diaphysis of the third metacarpal bone (substitute axis).