Ultrasound-guided trans-quadrangular space (TQS) approach to axillary nerve block: evaluation of dye spread after simulated cadaveric injections

INTRODUCTION: Axillary nerve blockade contributes to selective shoulder analgesia while minimizing phrenic nerve involvement. However, reliable ultrasound-guided approaches remain undefined. We evaluated dye spread following a novel ultrasound-guided trans-quadrangular space approach targeting the axillary nerve in a cadaveric simulation study. METHODS: 12 ultrasound-guided trans-quadrangular space injections using 7 mL of methylene blue were performed in six fresh, unembalmed cadavers positioned laterally. The needles were inserted into the quadrangular space with a posterior approach. Dissections were conducted 15 min after injection using a standardized protocol. The primary outcome was the frequency and degree of staining of the axillary nerve trunk and its anterior and posterior divisions. Secondary outcomes included staining of the radial nerve, musculocutaneous nerve, and posterior cord. RESULTS: The main axillary nerve trunk demonstrated consistent staining in 100% (12/12) of injections. At the branching point, the anterior and posterior divisions were stained in 83% (10/12) and 90% (11/12) of injections, respectively. The radial nerve was lightly stained in 25% (3/12) of injections. No staining of the musculocutaneous nerve or posterior cord was observed. In all injections, dye tracking extended longitudinally within the quadrangular space and slightly beyond the nerve's entrance at anterior quadrangular space. CONCLUSION: The ultrasound-guided trans-quadrangular space approach consistently stained the axillary nerve trunk and divisions with minimal unintended spread. This posterior technique, performed in the lateral position without shoulder abduction, demonstrates anatomical feasibility and may support further clinical investigation of selective axillary nerve blockade.