Impact of aberrant beam paths on antero-posterior shoulder radiographs in proximal humeral fractures.

Abstract

Accurate radiographic assessment of proximal humeral fractures (PHF) is important as it influences clinical decision-making and predicts clinical outcome. Since aberrant radiographic views might influence the assessment of fracture displacement, it was the goal of this study to investigate the impact of aberrant beam paths on radiographic assessment of PHF. Ten consecutive patients with a displaced PHF, bilateral computed tomography (CT) scan, and a true clinical AP radiograph were included. Digitally reconstructed radiographs (DRRs) were generated and aberrant beam paths were simulated by rotation of ± 30° around the horizontal (flexion and extension) and vertical axis (internal and external rotation) by increments of 10°. Measurement of the neck-shaft-angle (NSA) and eccentric head index (EHI) addressed humeral angulation and offset, respectively. Paired comparisons determined the influence of aberrant beam paths on both measurements between incremental altered views, and between clinical and digital true AP views. Descriptive statistics assessed the change in Neer classification and recommended treatment. True AP DRRs approximated the clinical true AP view by a mean difference of 2° for NSA, and a mean difference of 0.12 for EHI. NSA in injured shoulders was most susceptible to malrotation around the vertical axis (p < 0.03), with largest differences seen for internal rotation. Aberrant projections in extension had no influence on NSA (p > 0.70), whereas flexion of ≥ 20° and 30° demonstrated differences in injured and uninjured shoulders, respectively (p < 0.05). EHI was only influenced by malrotation in internal rotation in uninjured shoulders (p < 0.03). Alterations in Neer type occurred at 30° of malrotation in 5 cases, with a change in recommended treatment in 2. Humeral angulation and offset measurements on AP radiographs are more susceptible to aberrant beam paths in fractured humeri. Altered radiographic beam paths around the vertical axis showed the most substantial influence on the assessment of PHF, with angular measurements demonstrating larger differences then offset measurements. Beam path alterations of 30° can influence the Neer classification, and might influence fracture displacement-based decisions.