Final answer:
In an interscalene block, primarily the C8 and T1 nerve roots may be missed, which can lead to an incomplete block for procedures involving the ulnar aspect of the forearm and hand. The accessory nerve, which controls the sternocleidomastoid and trapezius muscles, may not be directly affected by this block.
Step-by-step explanation:
What nerve roots may be missed with interscalene block? Interscalene block is a procedure commonly used to provide anesthesia or analgesia for surgical procedures on the shoulder and upper arm. This block targets the brachial plexus at the level of the scalene muscles, affecting the ventral rami of the cervical spinal nerves. However, in an interscalene block, there can be variability in nerve root anesthesia. Specifically, the lower roots of the brachial plexus, which include C8 and T1, may not be adequately anesthetized. These roots contribute to the innervation of the ulnar aspect of the forearm and hand, manifesting in an incomplete block for procedures involving these areas.
Additionally, it is important to acknowledge that during an interscalene block, motor nerves such as the accessory nerve, which innervates the sternocleidomastoid and trapezius muscles, may not be directly targeted. These muscles receive motor input from other cervical spinal nerves, which may or may not be affected depending on the spread of the local anesthetic. The accessory nerve itself contributes to the movement of the head and shoulders, but since this is not primarily a region targeted in an interscalene block, it is typically not a matter of concern.