It's easy to "miss" something when doing a block for shoulder surgery. These days many of us, myself included, will settle for a less than a perfect "stoplight sign" and do a high, modified, supraclavicular block. That said, I believe an ISB (classic C5-C6 location with local) is the BEST spot for shoulder surgery:
The shoulder area is innervated by nerves of both cervical and brachial plexuses.
The shoulder joint is supplied by the anterior primary divisions of cervical nerve roots C5-C6 (with a small contribution of C7), while the cutaneous innervation of the shoulder is predominantly derived from C4-C3 (superficial cervical plexus). An interscalene block will consistentely block C4 and C3 as well as C5, C6, and C7. Cervical nerve roots C8 and T1 are blocked approximately 40 to 60 % of patients. The commonly used superior and deltopectoral surgical approaches are within the dermatomes anesthetized by an ISB. The lower anterior aspect of the shoulder, and the dorsal aspect as well, are innervated by thoracic nerve roots T2 and T3. These areas can be blocked combining an ISB with a subcutaneous infiltration of local anesthetic to cover a larger surgical incision (
3). The acromioclavicular joint is largely supplied by the suprascapular nerve, which also provides some innervations to the capsule and glenohumeral joint. The inferior aspect of the capsule and glenohumeral joint are supplied by the axillary nerve, with a small variable contribution from the muscolocutaneous and subscapular nerves. To summarize, it is mandatory to block supraclavicular, suprascapular and axillary nerves for the arthroscopic surgery. For open shoulder surgery, knowledge of the surgical approach is useful because the surgical incision may also involve other territories (
10).
The interscalene approach to the brachial plexus is best suited to surgery of the shoulder where a block of the lower cervical plexus is also desirable.
Anesthesiological Considerations in Shoulder Surgery
