Radiologic measurement of the scapholunate joint: implications of biologic variation in scapholunate joint morphology

To determine the optimal location for measurement of the scapholunate (SL) joint intercortical width, normal biologic variation in SL joint morphology was evaluated in 40 normal, skeletally mature wrists (16 volunteers, 24 cadavers) using thin-section 1.5T magnetic resonance imaging performed in the axial and coronal planes. The integrity of the SL ligaments was confirmed by magnetic resonance imaging and verified with anatomic dissection of the cadaver wrists. Patterns of SL articular morphology were qualitatively determined using similarity grouping. Scapholunate interval measurements were made at 3 locations each on the mid-SL joint image from both the axial and coronal planes: the articular margins (dorsal-palmar and proximal-distal) and midjoint. Three patterns of midjoint space cortical conformation were observed: parallel congruent (78%), inverted Y (15%), and point-like (8%). The most consistent and narrowest distance between the scaphoid and lunate was found at midjoint: coronal 1.45 mm (44% coefficient of variation) and axial 1.00 mm (22% coefficient of variation). This study demonstrated that measurement of the apparent SL joint interval in an inappropriate site, as with extended or flexed clenched fist views, may provide inaccurate SL joint interval distance assessments. Regardless of SL joint configuration, the midportion of the SL joint shows only moderate biologic variation and the least absolute measurement variance in width and should be the most precise part of the joint to measure. On magnetic resonance imaging, the normal SL joint interval measures less than 2 mm.