An Isolated Long Thoracic Nerve Injury in a Navy Airman

Military Medicine, Sep 2004 by Oakes, Michael J, Sherwood, Daniel L

Discussion

The long thoracic nerve is a purely motor nerve originating from the ventral rami of the fifth, sixth, and seventh cervical roots. It, alone, innervates the serratus anterior muscle. The fifth and sixth cervical roots pass through the body of the scalenus medius muscle along with the dorsal scapular nerve. The seventh cervical root passes anterior to the scalenus medius. The nerve then courses beneath the brachial plexus and clavicle where it passes over the first rib and descends along the lateral aspect of the thorax, where it innervates the serratus anterior. The nerve extends as far inferior as the eighth or ninth rib. This long, relatively superficial course makes it susceptible to injujy 5,6,8,11

The main function of the serratus anterior is to protract and upwardly rotate the scapula.6,12-14 As one of the major scapular stabilizers, normal function of the serratus anterior is critical in maintaining the proper scapulohumeral position during glenohumeral movement, particularly arm elevation.13 The serratus anterior is more active in forward flexion than pure abduction, as abduction requires some retraction of the scapula.15 Without upward rotation and protraction of the scapula by the serratus anterior, full glenohumeral elevation is not possible, resulting in scapular winging. Scapular winging is an uncommon but potentially disabling condition. Dysfunction of the serratus anterior muscle from the long thoracic nerve is the most common cause of scapular winging.16

The pathophysiology of long thoracic nerve palsy may be caused by direct pressure, stretching, or ischemia of the nerve. In most cases, acute nerve lesions are caused by excess force on the shoulder generating direct pressure on the nerve. In chronic overexertion ischemia is the cause of damage to the nerve.2

Long thoracic nerve palsy resulting from a single, violent force has been described following sudden stretching of the arm, work with arms extended above the head, cervical chiropractic manipulation, lifting a heavy weight, involvement in an automobile accident, and following an electrical shock.17"22 cases described demonstrating a sustained compression of the long thoracic nerve include soldiers carrying a rucksack and during sleep or when lying in bed with abducted arms, such as while reading a book.17'23,24 Recurrent traction force on the long thoracic nerve may cause a palsy in occupations such as carpentry, operation of certain machines, and in sports.12

Nontraumatic insult of the long thoracic nerve include: viral illness, immunizations, Parsonage-Turner syndrome, and isolated long thoracic neuritis.4'25"27 Compression of the C7 nerve root at the neural foramen can lead to weakness of the serratus anterior and scapular winging.28 A tight fascial band of tissue found to arise from the inferior aspect of the brachial plexus was proposed to cause a bow-stringing injury to the long thoracic nerve with abduction and external rotation of the upper extremity.29 Compression of the long thoracic nerve by a cervical rib was reported.30