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Pectoralis Minor

Key Points:
• With loss of function (or use of the nerve as donor material), arm extension strength may be decreased and may increase respiratory difficulty in patients with pre-existing respiratory compromise. However, due to the redundancy of the nerve branches, clinical deficit is rarely observed and we don not consider it functionally important.
Nerve Transfers: Nerves to the pectoralis minor (and major) are often a useful source for donor nerve material (for use in nerve transfer procedures) in brachial plexus injury and this muscle should be examined with the pectoralis major muscle.
Muscle Function:
• Test is completed by resisting against forward thrust of the shoulder while the subject is in supine.
• Origin Fixed: Tilts the scapula anteriorly.
• Insertion Fixed: With the scapula stabilized, assists in forced inspiration.
Strength Testing: Position – the subject is in supine with arms by their side. Stabilize – None unless abdominal muscles are weak, in which case the rib cage on the same side being tested should be held down firmly. Resist – against forward thrust of the shoulder with the arm at the side. The subject must exert no downward pressure from the head to force the shoulder forward. If necessary, elevate the subject’s hand and elbow off the table.  
Palpation: Can not be palpated as is deep to the pectoralis major.
Possible Substitutions: Pectoralis major.
Relevant Anatomy: 
• Roots: (C6), C7, C8, T1
• Nerve: Medial pectoral nerve.
• Innervation Route: (C6), C7, C8, T1 → medial pectoral nerve → pectoralis minor.
• Note that pectoralis minor heads could be cross innervated by the lateral and medial pectoral nerve, hence the variation and range of root origins for these nerves.
• Note that there are often multiple branches innervating this muscle.
Origin: Superior margins and outer surfaces of the third, fourth, and fifth ribs near the cartilages and fascia over the corresponding intercostals muscles.
Insertion: Medial border and superior surface of the coracoids process of the scapula.