Facet inclinations and interfacet angle of the distal radius on posteroanterior radiographs

Abstract

Purpose: To determine the lunate facet inclination (LFI), scaphoid facet inclination (SFI), and interfacet angle (IFA) of the distal radius on posteroanterior (PA) radiographs; evaluate the reliability of the IFA measurements; and define normative reference values for all 3 parameters. Methods: The IFA was defined as the angle between the lines tangential to the scaphoid and the lunate facets. The reliability of the IFA measurements was investigated using 2 serial measurements made by 3 observers. Three parameters (the IFA, LFI, and SFI) were measured on PA wrist radiographs of 400 normal Caucasians. Between-side and -sex differences among the 3 parameters were analyzed statistically. Results: The inter- and intraobserver reliability of the IFA measurements was excellent. The mean values were as follows: IFA, 20 degrees; LFI, 14 degrees; and SFI, 34 degrees. Although no statistically significant difference was found between the right and the left wrists, sex-based analyses revealed significant differences between the wrists of women and men. Based on the standard distribution of IFAs, 3 groups of distal radii were defined as follows: slightly, moderately, and steeply angled. Conclusions: The LFI, SFI, and IFA are easily measured radiographic parameters of the distal radius. Although a moderate correlation was evident between the IFA and the LFI, the IFA is a novel parameter to evaluate the carpal articular shape of the distal radius. The IFA measurement on PA radiographs is reliable.