Interscalene

Interscalene refers to the region between the anterior and middle scalene muscles in the lower neck. The term is used in anatomy and in regional anesthesia to describe approaches to the brachial plexus where the nerve trunks pass through the interscalene groove. This area is most commonly exploited for shoulder and upper arm anesthesia and analgesia.

Anatomically, the interscalene space contains the upper, middle, and occasionally partial lower trunks of the brachial plexus, formed from the C5 to T1 nerve roots. The phrenic nerve runs in close proximity to the anterior scalene muscle, so injections in this vicinity can affect diaphragmatic function. Nearby structures include the apex of the lung, making accurate technique important to minimize complications.

Clinically, the interscalene region is used to perform brachial plexus blocks, particularly the interscalene brachial plexus block. This technique provides anesthesia for most shoulder surgeries and is also used for analgesia of the shoulder and proximal arm. Blocks may be performed as a single-shot injection or via a continuous catheter for extended analgesia. Ultrasound guidance is commonly used to improve accuracy and safety, with nerve stimulation as an alternative method in some settings.

Potential risks and complications include diaphragmatic paresis from phrenic nerve involvement, Horner’s syndrome, nerve injury or intravascular injection, infection, hematoma, and, rarely, pneumothorax. The choice of technique, local anesthetic volume, and patient anatomy influence both efficacy and risk. Interscalene blocks are one of several regional anesthesia options for the shoulder, with alternatives including supraclavicular, infraclavicular, and axillary approaches.