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High-frequency, 38-mm broadband linear array transducer is preferred for this block.
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For catheter insertion, the Tuohy needle is usually used. The catheter is placed beneath the transverse scapular ligament around the suprascapular nerve (SSN). The correct position of the catheter can be confirmed under ultrasound by injecting either local anesthetic or 1 mL of air via the catheter and observing its distribution in relation to the SSN and the transverse scapular ligament.
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The incidence of pneumothorax associated with SSN block is reported as less than 1%. The use of ultrasound and the in-plane approach will decrease this risk markedly.
Sonoanatomy
The SSN arises from the C5 and C6 nerve roots, emerges from the superior trunk of the brachial plexus, and then enters the supraspinatus fossa via the suprascapular notch underneath the superior transverse scapular ligament. With application of color Doppler, the SSN can be visualized medial to the pulsation of the suprascapular artery as an oval or round, slightly hyperechoic structure. In the supraspinous fossa, the nerve is in direct contact with bone and exits the suprascapular fossa lateral to the infrascapular fossa and lateral to the spinoglenoid notch ( Fig. 7.1 ).
Indications
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Shoulder arthroscopic surgeries that approach the joint from its posterior aspect. The SSN innervates up to 70% of the superior and posterior part of the shoulder. The superior articular branch from the SSN supplies the coracohumeral ligament, subacromial bursa, and posterior aspect of the acromioclavicular joint capsule, whereas the inferior articular branch from the SSN supplies the posterior joint capsule. The SSN has no innervation to the anterior and inferior shoulder regions.
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Frozen shoulder, dislocated shoulder, rotator cuff syndrome, and scapular fracture.
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Supplementation to the supraclavicular block for shoulder replacement surgeries if the patient has pain on the posterior part of the shoulder joint postoperatively.
Technique
The patient ideally should be placed in a sitting position, and the operator should be behind the patient with the ultrasound machine in front of the patient and facing the operator. This will allow an uninterrupted field of view of the ultrasound screen. The ultrasound transducer should be placed parallel to the scapular spine. A transverse plane of imaging is optimum for the ultrasound-guided SSN block. By moving the transducer cephalad, the suprascapular fossa can be identified. While imaging the supraspinatus muscle and the bony fossa underneath, the ultrasound transducer should be slowly moved laterally to locate the suprascapular notch. The SSN should be seen as a round, hyperechoic structure beneath the transverse scapular ligament in the scapular notch. Also, with application of color Doppler, the SSN can be visualized medial to the pulsation of the suprascapular artery as an oval or round, slightly hyperechoic structure. We prefer to use the in-plane approach for this technique. The echoic needle should be advanced using the in-plane approach medial to lateral to visualize the whole length of the needle ( Fig. 7.2 ). The endpoint for injection is an ultrasound image demonstrating the needle tip in proximity to the SSN in the suprascapular notch below the transverse scapular ligament and the spread of the local anesthetic confirmed as a separation between the supraspinatus muscle and the spine of the scapula ( Figs. 7.3 and 7.4 ).
