Bilateral Ultrasonographic Mapping and Morphometry of the Infraclavicular Brachial Plexus: A Prospective Multicenter Study

Background/Objectives: The infraclavicular region contains a complex arrangement of the brachial plexus cords and axillary vessels. Accurate ultrasonographic characterization of these relationships is important for anatomical image interpretation and has direct relevance to ultrasound-guided infraclavicular procedures. This study aimed to evaluate the bilateral topographic distribution and morphometric relationships of the lateral, medial, and posterior cords relative to the axillary artery and axillary vein. Methods: This prospective, multicenter, observational anatomical–ultrasonographic study included 50 adults (25 women and 25 men), each examined bilaterally, yielding 100 potential side-specific examinations. The lateral cord (LC), medial cord (MC), posterior cord (PC), and axillary vein (AV) were mapped using a 12-sector radial model centered on the axillary artery (AA). Center-to-center intercord, cord-to-AA, and cord-to-AV distances were measured. Topographic confidence intervals were estimated using participant-level cluster bootstrap resampling, and bilateral morphometric data were analyzed using linear mixed-effects models. Results: The LC was located in sectors 10–11 in 85/94 examinations (90.4%; 95% CI, 84.4–95.7%), the MC in sectors 2–4 in 84/89 (94.4%; 95% CI, 89.2–98.9%), the PC in sectors 6–7 in 78/83 (94.0%; 95% CI, 88.6–98.8%), and the AV in sectors 4–5 in 95/100 (95.0%; 95% CI, 90.0–99.0%). Mean intercord distances were 11.20 ± 1.18 mm for LC/MC, 7.30 ± 1.61 mm for LC/PC, and 5.70 ± 1.10 mm for MC/PC. Mean cord-to-AA distances were 7.60 ± 0.74, 4.60 ± 0.93, and 6.60 ± 0.91 mm for the LC, MC, and PC, respectively. Mean cord-to-AV distances were 15.50 ± 2.01, 6.60 ± 1.22, and 8.50 ± 1.10 mm, respectively. Mixed-effects models demonstrated significant differences among measurements within each distance family (all p < 0.001), without significant overall side or sex effects. Conclusions: The brachial plexus cords and AV demonstrated a consistent topographic organization around the AA during bilateral mid-infraclavicular ultrasonographic assessment. The MC showed the shortest center-to-center distance to both the AA and AV, and the three cords formed a non-equidistant spatial configuration.