Internal Rotation and Transthoracic Lateral Radiographs Frequently Disagree on Sagittal Angulation in Humeral Shaft Fractures (AO/OTA 12)

OBJECTIVES: To compare humeral shaft fracture sagittal angulation between transthoracic and internal rotation radiographs at the time of injury, and to identify fracture patterns associated with discrepancies between views. METHODS: Design: Retrospective cohort study. SETTING: Single Level 1 academic trauma center. PATIENT SELECTION CRITERIA: Adult patients presenting with closed humeral shaft fractures (AO/OTA 12A-C) between May 2018 and December 2024 were screened for inclusion. Patients with radiographs that included both internal rotation and transthoracic lateral views at the time of injury prior to bracing or splinting were included. OUTCOME MEASURES AND COMPARISON: Demographic variables, injury mechanism, AO/OTA classification, and fracture location were collected. Sagittal angulation was measured on both views, and differences of greater or less than 10 degrees between views were noted. Acceptable humeral shaft fracture alignment was defined as <20 degrees of sagittal angulation. A paired sample t-test was used to compare angulation between the two views. Fisher's Exact Test was used to compare fracture characteristics between patients with ≤10 degrees and >10 degrees of difference. RESULTS: Thirty-one patients were included. The cohort was 54.8% female, with a mean age of 42.4±20.4 years. The two views disagreed on acceptable alignment in 11 patients (35%). The mean sagittal angulation on transthoracic views (19.3±13.2 degrees) was significantly greater than on internal rotation views (12.8±11.7 degrees, p=0.02). The difference between the two views was greater than 10 degrees in 17 patients (54%). There were no differences in fracture type or location between patients with >10 degrees or those with ≤10 degrees of difference. CONCLUSIONS: The internal rotation view often provided conflicting sagittal alignment when compared to a transthoracic view in patients with humeral shaft fractures, which should be considered in treatment decisions. LEVEL OF EVIDENCE: Level III.