The interscalene nerve block using ultrasound guidance can be useful to anesthetize the shoulder and upper arm, and is particularly useful for emergency physicians dealing with shoulder dislocations.
The interscalene block, although helpful, does have some important complications that should be considered. Multiple studies have demonstrated that the ipsilateral phrenic nerve may be affected during these blocks, causing unilateral diaphragmatic paralysis. This paralysis is typically temporary and does not manifest clinically in many cases, but it is important to watch for this complication. Patients with underlying lung disease or other chronic medical conditions may not tolerate this paralysis and may become symptomatic.
Other blocks have been touted as possible alternative methods for achieving adequate analgesia for reduction of shoulder dislocations. The suprascapular nerve arises from the upper trunk of the brachial plexus (C5 and C6) before passing posteriorly to come to lie on the posterior aspect of the scapula. The suprascapular nerve innervates the supraspinatus muscle, the subacromial bursa, the AC joint, the shoulder joint, and the infraspinatus muscle, which is why it is thought to be an alternative block for conditions of the shoulder.
A recent article in the American Journal of Emergency Medicine compared the ultrasound-guided suprascapular nerve block with procedural sedation in managing patients with shoulder dislocations. (2014;32:549.) Tezel et al. found no significant difference in reduction success or patient-physician satisfaction. A significantly longer ED stay was seen in the patients receiving procedural sedation, however.
To perform the suprascapular block, the patient should be sitting upright and slightly forward, so that the area can be accessed. A high-frequency transducer is placed along the scapular spine in the slightly oblique plane, so that it lies atop the spine. (Image 1.) The transducer is then moved cephalad until the scapular notch is visualized. (Image 2.) This is an important landmark because the suprascapular artery and nerve will be seen at this point lying deep to the overlying trapezius and supraspinatus muscles. (Image 3.)
Color Doppler can be helpful to identify and avoid the artery. It will also frequently be seen to pulsate. The needle can be inserted under direct ultrasound guidance from the medial aspect of the transducer once the artery and nerve have been identified. Using an in-plane approach will allow the needle tip to be visualized at all times. The nerve is fairly deep, and a longer needle (such as a spinal needle) may be needed to approach the nerve. Local anesthetic can be injected once the needle tip is seen adjacent to the nerve. Typically 10-15 ml is sufficient for adequate analgesia.