Radiographic overall linearity of the forearm

This study aimed to describe a radiographic parameter for assessing forearm alignment based on the angular relationship between three anatomical axes on standard radiographs. We aimed to quantify the angular deviation between the radial neck axis, the ulnar diaphyseal axis, and the forearm rotation axis in healthy adults.

A single-center observational study included 50 adults with no history of upper limb trauma or forearm pathology. Standardized bilateral anteroposterior radiographs were obtained in neutral position and full supination. Three axes were defined: the forearm rotation axis (AB axis), the ulnar axis (U axis), and the radial neck axis (R axis). Two angles (α and β) were measured, and their sum defined the Overall Linearity of the Forearm (OLF). Measurements were performed by two independent observers. Reproducibility was assessed using intraclass correlation coefficients and agreement using Bland-Altman analysis.

In neutral position, the median OLF was 2.9°, with an interquartile range of 1.02-4.47. In full supination, the median OLF was 3.2°, with an interquartile range of 1.92-4.7. Right-left correlation within the same volunteer was r = 0.75 in neutral position and r = 0.61 in supination. Inter-observer reliability was good, with ICC values of 0.805 in neutral position and 0.821 in supination. Bland-Altman analysis showed a mean bias of 0.37°, with limits of agreement ranging from - 0.34° to 1.07°.

The Overall Linearity of the Forearm provides a reproducible radiographic parameter describing the angular alignment of three forearm axes on standard anteroposterior views. Further studies are required to determine its relevance in pathological conditions.

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