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Pectoralis Minor – Functional Anatomy

Pectoralis minor is a fan-shaped muscle in the front of the shoulder that secures the lateral angle of the scapula to the rib cage. Superficially, it is covered by the pectoralis major.

Brief Anatomy Overview

Origin

  • ribs 3-5

Insertion

  • coracoid process of the scapula

Function

  • protracts scapula
  • depresses scapula
  • Assists in labored breathing

Innervation

  • medial pectoral nerve (C8-T1)

Anomalies are clinically significant on attachments and innervation. See the section below.

Attachment Details

The upper attachment runs along the medial aspect of the coracoid process of the scapula. This is usually a separate tendon from the coracobrachialis and biceps femoris.

The lower attachments have clinically significant variations in the number of rib attachments and their proximity to the pectoralis major. The lower attachments along the ribs in a fan-like configuration. The underside of the attachment weaves with the intercostal aponeurosis. The superficial edge attaches to the fascia of the intercostal muscles.

Functional Considerations

The pectoralis minor has notable correlations with the vertebral bellies of the serratus anterior. The serratus anterior typically has 3 heads that attach along the edge of the vertebral border. (Other heads attach at the superior or inferior angle.) These 3 heads at different in shape and are often associated with elevating the scapula whereas the lower heads depress the scapula.

When the ribs are stabilized, pectoralis minor protracts and depresses the scapula. It stabilizes the pectoral girdle during downward movements like chopping wood or walking with a crutch. It synergizes with the pectoralis major, subclavius, and latissimus dorsi in depressing the pectoral girdle.

When the pectoral girdle is stabilized, the pectoralis minor lifts the ribs for inhalation, especially during labored breathing. It synergizes with scalenes, serratus posterior superior, and serratus anterior to lift the upper ribs and increase lung capacity. You can read more about that in the collection on Pain with Breathing.

Anomalies, Etc.

Noted anomalies include a common tendon with the biceps and coracobrachialis. One study showed that the upper attachment extends to the glenohumeral capsule in about 23% of cases.

The space between the attachment of the pectoralis minor and major has been studied for breast implants that are placed under the pectoralis major. Unexpectedly, there were 49 women and 53 men in this study. The distance between attachments varies a great deal. 24% were less than 1cm. 41% were between 1-3cm. 70% were over 3cm.

Frequently a head attaches to the second rib. In fact, it is frequent enough that some sites and studies list ribs 2-5 as the attachment. This study mentions that cadavers showed attachments to the fourth rib in 100% of cases. But, attachments to the 5th ribs occurred 78% of the time and the 6th rib 3% of the time.

Most texts name the medial pectoral nerve for innervation. The lateral pectoral nerve weaves into the brachial plexus and is involved as well making the nerve roots C5-T1.

Thoracic Outlet Syndrome

Pectoralis minor is invested in the costocoracoid membrane. This fascial structure forms a sheet that extends across the upper chest to also invest the subclavius. This membrane ties together the upper ribs, subclavius, pectoralis minor, clavicle, and coracoid process.

This membrane also covers the neurovascular bundle that feeds the upper extremity, making it an important part of Thoracic Outlet structures. you can read more about these structures in this post about Anatomy of Thoracic Outlet Syndrome.

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Tony Preston has a practice in Atlanta, Georgia, where he sees clients. He has written and taught about anatomy, trigger points, and cranial therapies since the mid-90s.

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