The (ProteUS) Anisotropy Effect in Deep Fascia Ultrasonography: The Impact of Probe Angulation on Echogenicity and Thickness Assessments

This study investigates the influence of probe angulation on echogenicity and thickness measurements of the deep fascia, addressing methodological challenges in musculoskeletal ultrasound examination. The anisotropic nature of connective tissues can lead to distortions, affecting US imaging accuracy and diagnostic reliability. Echogenicity and thickness variations were analyzed across different probe inclinations in both transverse and longitudinal orientations. Measurements at 0° were compared with −5° and +5° angles to assess their impact on imaging consistency due to 3D-printed support. Echogenicity differed significantly with probe angulation, in particular in transverse scan at 0°, which showed substantial variation at −5° (mean diff. = 55.14, <i>p</i> < 0.0001) and +5° (mean diff. = 43.75, <i>p</i> = 0.0024). Thickness measurements also varied, reinforcing that non-perpendicular probe angulation introduces distortions. The same results were reported for longitudinal scans. These findings highlight the need for the use of standardized scanning protocols to improve reliability. The protean nature of deep fascia anisotropy, highly sensitive to minimal changes in probe orientation, necessitates precise and consistent imaging to accurately reveal its structural organization. Optimizing probe orientation is essential for advancing fascial US diagnostics.