Key points
LISB
PNEUMOTHORAX

We proposed the middle interscalene brachial plexus block (MISB) for the first time and assessed its efficacy for the sensory and motor block.MISB provides a non-inferior anesthesia effect to low interscalene brachial plexus block (LISB) for surgery at or below the elbow.MISB may be considered a valuable alternative for LISB, especially for patients with poor ultrasound images or a high risk of pneumothorax.Both MISB and LISB improved the success rate of the inferior trunk compared to the classical interscalene brachial plexus block.We observed the diffusion of the local anesthetics with MRI 3D STIR SPACE images.