Long Thoracic Nerve Block

Indications and Clinical Considerations

Long thoracic nerve entrapment syndrome is caused by compression or stretching of the long thoracic nerve as it passes beneath the subscapularis muscle to innervate the serratus anterior muscle ( Fig. 105.1 ). The most common causes of compression of the long thoracic nerve at this anatomic location include direct trauma to the nerve during surgical procedures, such as radical mastectomy and surgery for thoracic outlet syndrome. Direct blunt trauma from heavy items falling from shelves also can cause long thoracic nerve entrapment syndrome. Damage to the long thoracic nerve after first rib fracture also has been reported. Stretch injuries to the long thoracic nerve often occur from wearing improperly fitting heavy backpacks or doing prolonged heavy labor.

Clinically, the patient exhibits painless paralysis of the serratus anterior muscle, which results in the classic finding of winged scapula ( Fig. 105.2 ). The winging of the scapula is the result of the inability of the serratus anterior muscle to hold the scapula firmly against the posterior chest wall. The winged scapula can be identified by having the patient press both hands against the wall and press outward. The clinician, by observing the patient from behind, identifies the affected scapula projecting posteriorly or winging away from the posterior chest wall (see Fig. 105.1 ). The patient with long thoracic nerve syndrome also is unable to fully extend the upper extremity overhead on the affected side, and the last 25 to 30 degrees of extension is lost.

Electromyography helps diagnose long thoracic nerve entrapment syndrome. Plain radiographs are indicated for all patients with long thoracic nerve entrapment syndrome to rule out occult bony disease, including scapular and first rib fractures. Magnetic resonance imaging may help delineate the etiology of long thoracic nerve compromise ( Figs. 105.3 and 105.4 ).