Radiographic Determination of the Distal Ulnar Diaphyseal Angle

Characterizing the distal ulnar diaphyseal angle (DUDA) may be important for anatomic recreation of the distal ulna during ulnar shortening osteotomy procedures using conventional straight plates. This study characterized the DUDA and determined side-to-side, age, and sex effects on DUDA magnitudes and locations.

Retrospective analyses of bilateral wrist radiographs were performed on 60 patients. The DUDA was defined as the angle of intersection between a line passing through the center of the distal ulnar metadiaphyseal region, in line with the landmarked long axis of the ulna, on a lateral radiograph. This inflection point was measured from the most distal aspect of the ulnar head and recorded as the DUDA tip-to-apex distance (TAD). Rater reliability was determined using the intraclass correlation coefficient.

We found DUDAs in 94% of radiographs. The mean DUDA angle was 5.6° ± 2.6° and the mean TAD was 45.3 ± 9.5 mm. The Pearson correlation coefficients for side-to-side comparisons were 0.47 for the DUDA angle and 0.69 for the TAD. For male and female patients, the mean DUDAs were 5.4° ± 2.3° and 5.9° ± 2.9°, respectively, and the mean TADs were 47.8 ± 9.7 mm and 41.7 ± 7.9 mm, respectively. The DUDA angle and TAD had negligible associations with age (r = -0.15 and -0.08, respectively). At 0.74 (95% CI, 0.58-0.85), interrater reliability was good. At 0.93 (95% CI, 0.88-0.96), intrarater reliability was excellent.

We demonstrated DUDAs, representing valgus deviations from the center axis and anteroposterior views of the ulna. Contralateral lateral wrist radiographs are moderate to strongly reliable in determining a DUDA. Rater reliability was good to excellent.

Re-creation of the DUDA may benefit procedures such as ulnar shortening osteotomy, fractures, or malunion by contributing to knowledge of distal radioulnar joint biomechanics.