Three-Dimensional Morphometric Analysis of the Volar Cortical Shape of the Lunate Facet of the Distal Radius

Abstract

In cases of distal radius fractures, the fixation of the volar lunate facet fragment is crucial for preventing volar subluxation of the carpal bones. This study aims to clarify the sex differences in the volar morphology of the lunate facet of the distal radius and its relationship with the transverse diameter of the distal radius. Sixty-four CT scans of healthy wrists (30 males and 34 females) were evaluated. Three-dimensional (3D) images of the distal radius were reconstructed from the CT data. We defined reference point 1 as the starting point of the inclination toward the distal volar edge, reference point 2 as the volar edge of the joint on the bone axis, and reference point 3 as the volar edge of the distal radius lunate facet. From the 3D coordinates of reference points 1 to 3, the bone axis distance, volar-dorsal distance, radial-ulnar distance, 3D straight-line distance, and inclination angle were measured. The transverse diameter of the radius was measured, and its correlations with the parameters were evaluated. It was found that in males, compared to females, the transverse diameter of the radius is larger and the protrusion of the volar lunate facet is greater. This suggests that the inclination of the volar surface is steeper in males and that the volar locking plate may not fit properly with the volar cortical bone of the lunate facet, necessitating additional fixation.

Keywords: computer analysis; distal radius fracture; lunate facet; volar locking plate.

Figure 1

Measured reference points and the measurement parameters. The starting point of the inclination towards the volar margin of the distal end was defined as reference point 1; the volar edge of the joint on the bone axis was defined as reference point 2; and the volar edge of the lunate facet at the distal end of the radius was defined as reference point 3.

Figure 2

Measurement parameters. (a) Bone-axis distance, (b) Volar−dorsal distance, (c) Radial−ulnar distance, (d) 3D straight-line distance (e) Inclination angle A: the angle formed between the line connecting reference points 1 and 2 and the line connecting reference points 1 and 3 in the sagittal plane, (f) Inclination angle B: the angle formed between the line connecting reference points 2−3 and the z-axis in the axial plane.