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Interscalene Brachial Plexus Block: Shoulder Paresthesia versus Deltoid Motor Response: Revisiting the Anatomy to Settle the Controversy

Sukhani, Radha, MD; Candido, Kenneth D., MD

doi: 10.1097/00000539-200212000-00067
LETTERS TO THE EDITOR: Letters & Announcements

Department of Anesthesiology

Northwestern University Medical School

Chicago, IL

To the Editor:

In the original description of the interscalene technique of brachial plexus block (ISB), Winnie emphasized that only a paresthesia distal to the shoulder was acceptable to ensure successful block (1). This recommendation was based on the anatomical fact that a paresthesia to the shoulder itself might result from stimulation of the suprascapular nerve (C5 and C6 nerve roots), which may be within or outside the fascial sheath enclosing the brachial plexus roots, and hence, offers no guarantee of effecting successful shoulder anesthesia.

By virtue of its objective evaluation of the nerves being stimulated, peripheral nerve stimulator (PNS) techniques have recently gained in popularity. Originally, Winnie’s recommendation of eliciting a distal paresthesia for ISB was extrapolated to include the PNS technique also, i.e., insisting on a motor response distal to the deltoid (biceps, triceps, or more distal musculature) (2–4). A study of Silverstein et al. (5) however, demonstrated that the deltoid motor response at the shoulder is equally efficacious. The apparent explanation is that the nerve supply to both the deltoid (axillary nerve) and biceps (musculocutaneous) originates from cervical nerve roots 5 and 6.

If one were to revisit the anatomy of a shoulder paresthesia and that of a deltoid motor response, it would become readily apparent that those two end-points are not equivalent, even though the nerve roots (C5 and C6) responsible for mediating the two responses are identical (6). A shoulder paresthesia results from stimulation of the suprascapular nerve, which may be within or outside the fascial sheath, while a deltoid motor response results from stimulation of axillary nerve roots which lie within the fascial sheath. The sensory and motor elements of shoulder innervation essential for successful brachial plexus block, therefore, are clearly distinct and separate.

Revisiting the anatomy supports Winnie’s original recommendation for seeking paresthesias distal to the shoulder when performing interscalene brachial plexus block by the paresthesia technique. On the other hand, when performing ISB using a PNS technique, a deltoid motor response is an appropriate end-point.

Radha Sukhani, MD

Kenneth D. Candido, MD

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1. Winnie AP. Interscalene brachial plexus block. Anesth Analg 1970; 49: 455–66.
2. Singelyn FJ, Seguy S, Gouverneur JM. Interscalene brachial plexus analgesia after open shoulder surgery: continuous versus patient controlled infusion. Anesth Analg 1999; 89: 1216–20.
3. Klein SM, Grant SA, Greengrass RA, et al. Interscalene brachial plexus block with a continuous catheter insertion system and a disposable infusion pump. Anesth Analg 2000; 91: 1473–8.
4. Borgeat A, Ekatodramis G, Kalberer F, et al. Acute and nonacute complication associated with interscalene block and shoulder surgery: a prospective study. Anesthesiology 2001; 95: 875–80.
5. Silverstein WB, Moin MD, Saiyed MY, et al. Interscalene block with a nerve stimulator: a deltoid motor response is a satisfactory end point to successful block Reg Anesth 2000; 25: 356–9.
6. Clemente CD. The peripheral nervous system: brachial plexus ( Chapter 12 ). Gray’s Anatomy. 30th ed. Baltimore: Williams & Wilkins, 1993: 1205–21.
© 2002 International Anesthesia Research Society