Treatment Outcome of Distal Ulnar Fracture Complicated by Distal Radius Fracture According to the Size of Ulnar styloid Process Fracture.

[Background] There is no consensus on the treatment of distal ulnar fractures associated with distal radius fractures. In our institution, the Acu-Loc VDU system is commonly used in surgery, but we have observed numerous cases of malunion and nonunion in fractures of the ulnar styloid process.

[Objective] This study aimed to evaluate postoperative outcomes in fractures of the ulnar styloid process associated with distal radius and ulna fractures, classified by fragment size. [Subjects] We included 21 cases (21 wrists) of patients with Biyani type 3 and 4 distal ulnar fractures, excluding open fractures classified as Gustilo type 3 and patients under 15 years old, who were treated with plate fixation between 2012 and 2020. The cohort included 6 men and 15 women with a mean age of 71 years; 7 cases involved open fractures. Nine cases underwent one-stage external fixation with an average waiting period of 0.5 days. All cases of distal radius fractures were treated with plate fixation, with an average waiting period of 10.3 days. [Study Design] Cross-sectional retrospective cohort study.

[Statistical Analysis] JMP17 was used for statistical analysis. [Intervention] Ulnar styloid fractures were classified according to the Nakamura classification (tip, middle, base horizontal, oblique).

[Outcomes] (1) Range of motion, (2) X-ray evaluation, (3) grip strength, and (4) X-ray assessment were evaluated.

[Results] (1) The oblique type of ulnar styloid fracture showed a significant decrease in final range of motion in palmar flexion, dorsiflexion, pronation, and supination. (2) Radiographic evaluation showed no significant differences in volar tilt, radial inclination, or volar tilt between groups, with values being maintained across all groups. (3) The grip strength ratio showed a significant decrease in the oblique type compared to the base horizontal type.

[Conclusion]In our institution, almost all cases of distal ulnar fractures were surgically treated with the Acu-Loc VDU system. However, the oblique type exhibited significantly poorer postoperative outcomes. One potential cause is that large fracture fragments often involve damage to the TFCC attachment at the fovea. In cases with large fracture fragments, it may be necessary to select implants, such as hook plates, that also allow for fixation of the styloid process.