The Pectoral Reflex

The pectoral reflex is also a muscle stretch reflex that occurs with normal neural function. The outer pectoral insertion, just medial to the shoulder and inferior to the clavicle, is struck with the hospital percussion hammer. A normal response is anterior and medial movement of the shoulder as the pectorals contract.

A normal response is little, if any, contraction of the pectoralis muscle. If there is hyperreflexia when compared to the opposite side, it is indicative of a corticospinal tract lesion above the level of the fifth cervical segment.

The pectoral muscles are innervated by the medial and lateral pectoral nerves innervated by C5.

Altered neurology at C5 nerve root level or further along its distal trunks and branches in the brachial plexus may diminish the pectoral reflex. A secondary possible cause of absent pectoral reflex is  subluxation of the A/C or glenohumeral joints

In the event that a scapulohumeral reflex (C5) is intact but the pectoral reflex (also C5) is not, the subluxation must be at a point distal to the spine where there is no longer a common denominator.

Weakened muscles and local pain findings at the A/C joint and shoulder will assist the differentiation.