Interscalene approach to brachial plexus block does not provide optimal surgical anaesthesia in the area of distribution of which of the following nerve?

Ulnar nerve is usually spared when brachial plexus is blocked through interscalene approach. Interscalene Block. The interscalene block is the gold standard for shoulder anesthesia and the most commonly used block for shoulder procedures. This approach blocks the brachial plexus at the nerve root or trunk level. Local anesthetic is directed toward C5-C6 nerve roots or the superior trunk. Ref Robbins 9/e pg 256