Pectoralis minor muscle
The pectoralis minor is a fan-shaped muscle of the shoulder girdle.
Anatomy and innervation
It is innervated by the medial and lateral pectoral nerves (C6-Th1), branches of the brachial plexus. The pectoralis minor is located under the pectoralis major, and both form the anterior wall of the axilla. The contracted muscle can be easily palpated there. It is also located close in relation to the brachial plexus and both the subclavian artery and vein, which all run between the muscle and the ribcage.
The pectoralis minor has two main functions. On one hand, it pulls the scapula anteriorly and inferiorly toward the ribs (abduction and depression respectively). This leads to a dorsomedial movement of the inferior angle of the scapula. This movement is both helpful when retracting the elevated arm and as well as moving the arm posteriorly behind the back. On the other hand, the pectoralis minor elevates the third to fifth ribs (given a fixed scapula) and expands the ribcage. By those means, it can also serve as an accessory muscle during inspiration.
Both the axillary artery and vein, as well as some nerves of the brachial plexus run between the pectoralis minor and the coracoid process (coracopectoral space). In cases of hypertrophy or stiffening (e.g. when permanently leaning your upper body over the table while sitting) a compression of the neurovascular bundle can often occur. This is referred to as pectoralis minor syndrome (PMS), one form of thoracic outlet syndrome (TOS). Common complaints are
- numbness up to pain in the affected arm (especially in the ring and small finger)
- a stiff shoulder
In plastic surgery, the pectoralis minor is regarded as one of the best choices for reanimation of a paralyzed face. That is true due to the fact that this muscle is flat, triangular shaped and has double innervation. Those characteristics enable one transplant to replace two or more paralyzed facial muscles at the same time.