Ultrasound-guided spinal accessory nerve block is useful in the diagnosis and management of the acute pain and spasm involving the sternocleidomastoid and/or trapezius muscle. This technique may also be utilized as a diagnostic maneuver to help identify the exact location and course of the spinal accessory nerve when surgical procedures in the posterior triangle of the neck are being contemplated or if spinal accessory nerve to suprascapular nerve transfer is being contemplated to improve external rotation of the shoulder following brachial plexus injury. If destruction or sacrifice of the spinal accessory nerve is being considered, this technique is useful as a prognostic indicator of the degree of motor impairment that the patient may experience. Compromise of the spinal accessory nerve will result in pain, stiffness, and ptosis of the ipsilateral shoulder with associated loss of full abduction and winging of the scapula. Patients with isolated spinal accessory nerve palsy will demonstrate a positive scapular flip sign, which is the finding of the scapular “flipping” or winging off the posterior thoracic wall with active resisted external rotation of the humerus (Fig. 18.1). The scapular flip sign occurs when the pull of the contracting infraspinatus and deltoid muscles is unopposed by the paralyzed or weakened trapezius muscle during resisted external rotation of the humerus. To differentiate spinal accessory nerve palsy from long thoracic nerve of Bell palsy, first the patient puts the affected upper extremity at the side of the body and then elevates it in front of the body and observes for any scapular abnormality. If no scapular abnormality occurs, spinal accessory nerve function is intact (Fig. 18.2).

The fibers that comprise the spinal accessory nerve (cranial nerve XI) arise from lower motor neurons of the spinal accessory nucleus, which are located in the lateral horn of the spinal cord. The fibers coalesce to form the spinal accessory nerve, which ascends through the foramen magnum and travels along the inner skull to exit the cranium via the jugular foramen along with the glossopharyngeal and vagus nerves. The spinal accessory nerve has two branches: a small cranial root and a larger spinal root. The fibers of the larger spinal root pass inferiorly and posteriorly to exit beneath the posterior border of the sternocleidomastoid muscle at the junction of the upper and middle third of the muscle to lie on top of the levator scapulae and middle scalene muscles ventral as it passes in an inferocaudal course toward the anterior border of the trapezius muscle (Fig. 18.3). The spinal accessory nerve provides motor innervation to the sternocleidomastoid and trapezius muscles while providing minimal sensory innervation.

To perform ultrasound-guided injection technique for spinal accessory nerve block, place the patient in supine position with the head turned away from the side to be blocked. The posterior border of the sternocleidomastoid muscle is identified by having the patient raise his or her head against the resistance of the clinician’s hand (Fig. 18.4). The junction of the upper and middle third of the posterior margin of the muscle is identified, which is the approximate point at which the spinal accessory nerve emerges from behind the sternocleidomastoid muscle and is most easily identified on ultrasound imaging. After preliminary identification of the approximate location of the nerve utilizing surface landmarks, the skin is prepped with antiseptic solution, and 2 mL of local anesthetic is drawn up in a 10-mL sterile syringe, with 40 to 80 mg of depot steroid added if the condition being treated is thought to have an inflammatory component. A linear ultrasound transducer is then placed over the previously identified approximate location of the nerve in the transverse plane (Fig. 18.5). The spinal accessory nerve should appear as a 2- to 3-mm hypoechoic oval structure with a hyperechoic perineurium lying on top of the levator scapula muscle as it exits beneath the posterior margin of the sternocleidomastoid muscle (Fig. 18.6). Its course can be traced in a posterior and caudad direction toward the anterior margin of the trapezius muscle. When the nerve is identified, a 22-gauge, 2-inch stimulating needle is advanced under real-time ultrasound guidance using an in-plane approach (Fig. 18.7). When the needle tip is in proximity to the nerve, stimulation is carried out with isolated contraction of trapezius muscle indicating satisfactory needle placement. After careful



aspiration reveals no blood or cerebrospinal fluid, 2 mL of solution should be slowly injected. The needle is removed and pressure is placed on the injection site to avoid bleeding complications. Subsequent daily nerve blocks are carried out in a similar manner.