Coracoacromial Ligament

1. Overview

The coracoacromial ligament is a strong, triangular band of connective tissue located in the shoulder. It connects the coracoid process to the acromion, both of which are projections of the scapula. This ligament forms part of the coracoacromial arch, a protective arch over the head of the humerus, preventing its upward displacement. Although it does not directly stabilize the glenohumeral joint, it plays a crucial role in maintaining the structural integrity of the shoulder and preventing impingement.

2. Location

The coracoacromial ligament is found in the superior aspect of the shoulder, forming a roof over the glenohumeral joint:

• Proximally: Attaches to the lateral border of the coracoid process.

• Distally: Inserts onto the medial border of the acromion process.

• Orientation: Extends obliquely over the head of the humerus, forming a protective arch along with the acromion and coracoid process.

3. Structure

The coracoacromial ligament is composed of dense regular connective tissue and has the following structural characteristics:

• Shape: Flat and triangular, with a broad base at the acromion and an apex at the coracoid process.

• Fibers: Run obliquely, blending with the deep fascia of the shoulder and sometimes with the deltoid or trapezius muscle fascia.

• Coracoacromial arch: Along with the acromion and coracoid process, it forms a bony-ligamentous arch over the humeral head.

4. Function

The coracoacromial ligament serves important mechanical and protective functions:

• Prevents superior dislocation: Acts as a barrier to upward displacement of the humeral head during shoulder movements.

• Supports the coracoacromial arch: Maintains the integrity of the arch, which protects the rotator cuff and glenohumeral joint from direct trauma.

• Limits excessive motion: Assists in restricting superior translation of the humerus.

5. Physiological role(s)

Though not a dynamic stabilizer, the coracoacromial ligament has several physiological roles:

• Passive restraint: Provides a static check-rein to upward movement of the humeral head, especially during deltoid contraction.

• Force redirection: Helps distribute forces exerted by surrounding muscles and tendons over the superior shoulder.

• Anatomical roof: Forms a part of the shoulder's subacromial space, influencing the biomechanics of the rotator cuff tendons and bursa.

6. Clinical Significance

The coracoacromial ligament is implicated in various shoulder pathologies, particularly in impingement syndromes:

• Subacromial impingement syndrome:

  • The coracoacromial arch can impinge on the supraspinatus tendon or subacromial bursa during arm elevation, causing pain and reduced mobility.

  • Thickening or ossification of the ligament may contribute to narrowing of the subacromial space.

• Rotator cuff tears:

  • Chronic impingement against the ligament can cause wear and eventual tearing of the supraspinatus tendon.

• Coracoacromial ligament release:

  • In severe or recurrent impingement cases, partial resection of the ligament may be performed surgically to decompress the subacromial space.

• Shoulder instability evaluation:

  • Though it does not directly stabilize the glenohumeral joint, an intact coracoacromial arch is a secondary restraint to superior translation in the event of rotator cuff failure.