Coracoid Apophysis: Structure, Function, Clinical Significance, United Muscles and Fractures

It is a small, hook-shaped structure on the lateral border of the upper anterior portion of the scapula.

Pointing laterally forward, together with the acromion , serves to stabilize the shoulder joint. It is palpable in the deltopectoral sulcus between the deltoid and pectoralis major muscles.

Structure

The coracoid process is a curved and thick bony protrusion, joined by a broad base to the upper part of the neck of the scapula, at first projected upwards and inwards; then, smaller and smaller, it changes its direction and projects forward and to the sides.

The ascending portion, flattened backward, presents a smooth concave surface at the front, through which the subscapular passes .

The horizontal portion is flattened from the top down, its upper surface is convex and irregular, and gives fixation to the pectoralis minor. Its lower surface is smooth, its medial and lateral edges are rough.

In the medial part of the root of the coracoid process there is an approximation to the union of the conoid ligament, and it extends obliquely forward and laterally, and it is an elevated edge for the union of the trapezoid ligament.

Function

It is the link site for several structures:

  • The pectoralis minor to the 3rd, 4th and 5th rib.
  • The short head of the biceps brachii muscle to the radial tuberosity.
  • The coracobrachial muscle to the medial humerus.
  • The coracoclavicular ligament to the clavicle. (It is formed by the conoid ligament and the trapezoid ligament).
  • The coracoacromial ligament to the acromion.
  • The coracohumeral ligament to the humerus.
  • The superior transverse scapular ligament, from the base of the coracoid portion to the medial portion of the suprascapular notch.

Clinical significance

The coracoid process is palpable just below the lateral end of the clavicle. It is also known as the “surgeon’s lighthouse” because it serves as a reference point to prevent neurovascular damage.

The main neurovascular structures enter the medial upper limb to the coracoid process, so that surgical approaches in the shoulder region should always take place laterally to the coracoid process.

Other animals

Reptiles, birds and frogs (not salamanders) also have a bone with this name, but it is not homologous to the coracoid process of mammals.

Analyzes of the size and shape of the process of the coracoid process in Australopithecus africanus (fossil hominid species from South Africa), have shown that in this species had a prominent dorsolateral tuber located more laterally than in modern humans.

This reflects, according to one interpretation, a scapula placed on the top of a funnel-shaped thorax and a clavicle placed obliquely as in the existing great apes.

Muscles attached to the coracoid process

Pectoralis minor:  It is a small muscle deep to the pectoralis major, the largest muscle of the thorax. It originates in the 3-5 ribs near the sternum and is then inserted into the coracoid process.

Your job is to rotate the scapula down, as well as lift the ribs.

Coracobrachial muscle:  It is on the medial side of the upper arm. It is inserted into the medial medial surface of the humerus. The coracobrachial muscle flexes and adducts the arm in the shoulder.

Brachial biceps:  also attaches to the coracoid process. It is inserted into the radial tuberosity, the bicipital aponeurosis and the forearm fascia. This muscle weakly flexes the arm in the shoulder and bends to help supinate the forearm at the elbow.

Fractures of the coracoid process

Fractures of the coracoid process are uncommon, comprising approximately 13% of all scapular fractures and 5% of all shoulder fractures.

Fractures of the coracoids are usually seen with other fractures of the scapula or shoulder region. Isolated coracoid fractures are rare and are due to direct impact or avulsion.

Fractures of the base are most commonly due to the direct impact of an external object or the head of the humerus .

Tip fractures are more common due to avulsion injuries associated with the coracoclavicular ligament during acromioclavicular dislocation, or sudden contraction of the short head of the biceps and coracobrachial muscles.

It has been reported that stress fractures of the coracoid are secondary to repetitive trauma due to recoil when firing a rifle, also known as the trapeze artist’s shoulder.