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Suprascapular Nerve Block (Anterior Approach above the Clavicle)
The suprascapular nerve (SSN) arises from the superior trunk of the brachial plexus, containing contributions from the C5 and C6 ventral rami. The SSN provides the majority of the sensory innervation of the shoulder joint (approximately 70% on anatomic dissections). There also are articular fibers carried by the axillary nerve, lateral pectoral nerve, and the nerve to the subscapularis. Isolated SSN block may be indicated in patients with severe pulmonary and compromise undergoing shoulder surgery or rehabilitation of adhesive capsulitis (frozen shoulder syndrome).
Cutaneous innervation of the SSN is not common, being demonstrated in only about 10% to 15% of subjects. When present, the cutaneous distribution is similar to the typical distribution for the axillary nerve. The SSN has motor branches to the supraspinatus and infraspinatus muscles.
The SSN diverges distally 2 cm from the junction of C5 and C6 into the superior trunk (range, 0 to 2.5 cm). Recognition of the takeoff of the SSN from the brachial plexus is an important consideration for complete brachial plexus blocks when performed low in the neck. Selective SSN block should not only spare the remainder of the brachial plexus but also the phrenic nerve.
Limitations to Traditional Approach to Blocks at the Suprascapular Notch
Isolated SSN block is traditionally performed where the nerve crosses the suprascapular notch, because the nerve usually does not have major branches before this notch, and the bony landmark is useful. However, there are limitations to this traditional approach. The SSN lies deep to the trapezius and supraspinatus muscles within the suprascapular notch. While distal block of the SSN near the suprascapular notch is potentially more selective, the nerve and needle imaging for this procedure can be challenging.
The suprascapular notch, which is a landmark for the distal SSN block below the clavicle, is often absent (approximately 15% of scapulae). The SSN always runs under the suprascapular ligament, while the position of the suprascapular artery and vein with respect to the ligament is variable. The suprascapular ligament is frequently ossified, thereby reducing image quality. In approximately 50% of cases, sensory branches already separate from the main stem before the main stem enters the suprascapular notch. Injuries to the SSN after blocks performed near the suprascapular notch have been reported (blocks were performed near a site of nerve entrapment).
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