Apparent Proximal Ulna Dorsal Angulation Variation Due to Ulnar Rotation
Journal of orthopaedic trauma
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OBJECTIVE: To investigate the effect of ulna rotation on the apparent proximal ulna dorsal angulation (PUDA). METHODS: Computed tomography images of 59 ulnas were included in this study, 48 being bilateral specimens and the remaining 11 were unilateral. Three-dimensional models of the entire ulna were obtained, and the ulnas were rotated in 5-degree increments in internal rotation or external rotation from neutral. PUDA, PUDA apex, varus angulation, and varus apex were measured on each ulna. RESULTS: With the ulna in neutral rotation, the mean (95% CI) PUDA was 3.7 (2.9-4.5) degrees, whereas the mean varus angle was 10.5 (9.8-11.1) degrees. The varus angle apex and PUDA apex were 28.9 (27.5-30.2)% and 19.6 (18.7-20.6)% along the total length of the ulna, respectively. As the ulna was rotated externally by 5, 10, and 15 degrees, the PUDA increased by 0.7 (0.5-0.9) degrees, 1.2 (0.9-1.4) degrees, and 1.4 (1.1-1.8) degrees, respectively. Conversely, with internal rotation of 5, 10, and 15 degrees, the PUDA decreased by 0.9 (0.8-1.1) degrees, 2.0 (1.8-2.3) degrees, and 3.3 (2.7-3.9) degrees, respectively. CONCLUSIONS: This study demonstrates that small degrees of ulna rotation result in a statistically significant change in the apparent PUDA; however, this may not represent a clinically significant difference. Because of the anatomic variation between patients, it is important to obtain a contralateral film to determine the PUDA for anatomic reduction of the ulna in complex cases. When using a contralateral image, it is important to obtain a true lateral film or consider using 3-dimensional imaging for preoperative planning.