The Coracobrachialis Muscle is a relatively small but functionally important skeletal muscle located on the medial (inner) side of the upper arm. It extends from the coracoid process of the scapula to the mid-portion of the humerus and is located in the forearm compartment. This muscle is one of the muscle groups that increase stability around the shoulder joint and facilitate certain movements of the upper extremity. It plays a particularly active role in shoulder flexion and adduction (movement of the arm forward and toward the trunk). Due to its deep location, the coracobrachialis, which lies beneath the superficial muscles, is a noteworthy muscle due to its anatomical adjacencies and clinical associations.

Anatomy

Morphology and Connection Points

This muscle originates from the coracoid process of the scapula and shares this point with the short head of the biceps brachii. In some individuals, fibers may also be observed from the proximal portion of the biceps tendon. The muscle's insertion point is in the middle of the medial surface of the humeral shaft. This insertion is located between the medial head of the triceps brachii and the brachialis muscle. The short head of the biceps brachii lies above and the brachialis muscle below as adjacent structures. A musculocutaneous nerve passes through the muscle, and this anatomical relationship is of clinical importance.

Embryological Origin and Classification

This muscle is located in the anterior region of the upper extremity and is anatomically classified as a flexor muscle group. It plays a role in motor control of the upper extremity by contributing to flexion and adduction movements at the shoulder joint. Embryologically, it develops from the ventral (anterior) mesodermal muscle mass, and this developmental origin determines the muscle's functional properties.

Nerve Innervation and Vascular Supply

The muscle's neural innervation is provided by the musculocutaneous nerve (C5–C7). This nerve passes through the muscle fibers, providing direct innervation. Blood circulation is provided by branches of the brachial artery. This vascular structure enables the muscle to maintain its function by meeting its metabolic needs.

Function and Clinical Relationships

The muscle contributes to shoulder flexion; it is a weak aid in raising the arm forward. It also plays a role in adduction, which is pulling the arm toward the body. Furthermore, it provides frontal stabilization, particularly during abduction, helping the shoulder move in a controlled manner. Clinically, this muscle is associated with various conditions. It can cause stiffness and pain due to overuse, particularly during intense activities such as gymnastics and weightlifting. In these cases, symptoms such as shoulder and arm pain, and sometimes even pain radiating to the back of the hand, can be observed. Compression of the musculocutaneous nerve can cause loss of sensation on the lateral surface of the forearm and weakness in elbow flexion. Tears of this muscle are quite rare and usually result from direct trauma. Diagnostic testing involves assessing pain during shoulder movement during a physical examination and performing resistance tests. MRI or ultrasonography are preferred imaging modalities. Treatment generally involves a conservative approach: rest, nonsteroidal anti-inflammatory drugs (NSAIDs), and physical therapy are the first steps. However, in severe cases of nerve compression, surgical decompression may be necessary.