Lateral Decubitus Positioning Increases Pleura–Plexus Distance in Ultrasound-Guided Supraclavicular Brachial Plexus Targeting

To evaluate whether lateral decubitus positioning increases the pleura–plexus distance at the supraclavicular level and to characterize its role as a modifiable anatomical factor relevant to ultrasound-guided interventions. This prospective observational ultrasound study included 90 adults comprising individuals with complex regional pain syndrome, cervical spine stenosis, and healthy controls. Pleura–plexus distance was measured at end expiration in three standardized positions: semi-reclined supine, 45° lateral tilt, and lateral decubitus. Positional effects were assessed using mixed repeated-measures analysis of variance, and associations with demographic variables were examined using correlation and multivariable linear regression. Pleura–plexus distance increased progressively across positions in all groups. Compared with the semi-reclined position (0.37–0.46 cm), lateral decubitus positioning more than doubled the distance (0.82–1.04 cm; p < 0.001), with a significant group interaction. Body mass index independently predicted pleura–plexus distance in the lateral position (+0.028 cm per kg/m2, p < 0.001), whereas age was not significantly associated. Lateral decubitus positioning was consistently associated with increased pleura–plexus distance at the supraclavicular level across all study groups. These findings suggest that patient positioning represents a measurable and potentially modifiable anatomical factor that may influence anatomical conditions relevant to ultrasound-guided supraclavicular procedures. Ultrasound-guided procedures near the brachial plexus can be technically challenging because the plexus lies close to the pleura, creating limited anatomical separation between neural and pleural structures. This study showed that changing patient position from semi-reclined to lateral decubitus significantly increased the distance between the brachial plexus and pleura. The effect was consistent across clinical populations, and higher body mass index was associated with greater positional widening. These findings suggest that patient positioning may represent a simple and noninvasive strategy to optimize anatomical conditions relevant to ultrasound-guided supraclavicular procedures without requiring additional equipment or procedural modification.