ISOLATED PARALYSIS OF THE SERRATUS ANTERIOR (MAGNUS) MUSCLE
M. THOMAS HORWITZ ; LEANDRO M. TOCANTINS

Abstract

1. Anatomical studies indicate that the coracoid process of the scapula, the second rib, and certain related scapular bursae, as well as morphological variations in the formation and course of the long thoracic nerve, play significant rôles in the pathogenesis of localized paralysis of the serratus anterior muscle. Postural compression of the long thoracic nerve must be allowed a part as an exciting or perpetuating factor.

2. The biceps brachii, as a strong antagonist of the serratus anterior, is a leading factor in the production of the classic "winged scapula". The shoulder drop seen in cases of serratus-anterior paralysis, is a result of stretching of the middle and lower portions of the trapezius muscle, while weakening of abduction power is due in part to stretching of the posterior portion of the deltoid muscle.

3. Relaxation of the paralyzed serratus anterior muscle and correction of the associated stretched and contracted muscles are secured by eliminating both the winging and the abnormal rotation of the scapula, and this is effectively performed by the brace illustrated. This apparatus is also recommended in the treatment of brachial-plexus neuritis, and has been successfully employed in cases with cervical-rib or scalenus-anterior syndromes.