Facet Inclinations and Interfacet Angle of the Distal Radius on Posteroanterior Radiographs.

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°; LFI, 14°; and SFI, 34°. 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.

CLINICAL RELEVANCE

The LFI has been accepted as a parameter for Madelung deformity and radiocarpal force transmission. The IFA may be considered as a parameter to evaluate radiocarpal coronal stability that could potentially be affected by changes in bifacet curvature.