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The humerus is the longest bone in the upper extremity, and it plays a crucial role in the movement and stability of the upper limb. The humerus serves as an attachment point for several muscles that contribute to the hand and elbow movements. The shoulder's main motions are flexion, extension, abduction, adduction, internal rotation, and external rotation. Adduction is the motion of lowering the arm towards the body, and several muscles are involved in this movement.
| Characteristics | Values |
|---|---|
| Muscles that adduct the humerus | Pectoralis major, anterior deltoid |
| Other functions of the pectoralis major | Flexes the humerus, medially rotates the humerus |
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What You'll Learn
The pectoralis major muscle
Injuries to the pectoralis major muscle are uncommon but have become more prevalent in recent years due to increased participation in weight lifting. Patients with pectoralis major injuries often present with localized swelling, muscular deformity, thinning of the anterior axillary fold, and weakness in adduction and internal rotation of the arm. Diagnosis and management of pectoralis major injuries involve the use of imaging techniques such as magnetic resonance imaging (MRI) to identify tears or ruptures and determine the extent of the damage.
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Shoulder adduction and abduction
The shoulder is a complex ball-and-socket joint formed by the head of the humerus, the clavicle (collarbone), and the scapula. The shoulder's main motions are flexion, extension, abduction, adduction, internal rotation, and external rotation.
Adduction and abduction of the shoulder serve to lower the arm towards and lift the arm away from the body, respectively. Adduction is accomplished primarily by the pectoralis major, latissimus dorsi, teres major, triceps, and coracobrachialis. The deltoid and the supraspinatus are the two main abductors of the shoulder. The supraspinatus muscle is responsible for the initiation of arm abduction by stabilising the humeral head in the glenoid fossa. It controls movement up to the first 15 degrees of abduction, after which the deltoid takes over to assist with abduction up to 90 degrees.
The coracobrachialis, which originates from the coracoid process and inserts at the medial aspect of the middle of the humerus, is involved in the flexion and abduction of the arm and helps to stabilise the shoulder joint. The biceps brachialis muscle, which originates with its long head from the supraglenoid tubercle of the scapula and with its short head from the coracoid process of the scapula, facilitates adduction on a horizontal plane. The triceps also help with extension and adduction of the arm.
The ability to abduct the arm is crucial to the full range of motion of the arm. External rotation of the shoulder, such as in a tennis backhand stroke, is attributed primarily to the deltoid, the teres minor in the armpit area, and the infraspinatus muscle, which covers the scapula. Internal rotation of the shoulder is the opposite of external rotation, such as the shoulder movement that occurs when reaching into a back pocket. This movement is achieved through the coordinated action of the pectoralis major, latissimus dorsi, deltoid, teres major, and subscapularis muscles.
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The deltoid muscle
The primary function of the anterior deltoid is flexion, internal rotation, and horizontal adduction. The primary function of the posterior deltoid is extension, external rotation, and horizontal abduction.
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The supraspinatus muscle
Additionally, the supraspinatus muscle assists in the abduction of the arm, which involves moving the arm away from the body. It also contributes weakly to the lateral rotation of the humerus, which is the movement of the arm away from the body's midline.
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The coracobrachialis muscle
The coracobrachialis is innervated by the musculocutaneous nerve and receives its blood supply from a branch of the brachial artery. It is perforated by the musculocutaneous nerve, which arises from the anterior division of the upper trunk. The nutrient foramina of the humerus are located in the region of insertion of the coracobrachialis muscle.
Injuries to the coracobrachialis muscle can cause weakness, soreness, or instability when using the arm for various activities, such as lifting and carrying weight close to the body, pushing a heavy door open, performing push-ups, or swimming with a breaststroke. It can be challenging to isolate the coracobrachialis for testing or therapy due to its location beneath the short head of the biceps brachii and the involvement of other muscles during movement.
In summary, the coracobrachialis muscle is a small, deep muscle that supports upper arm movement and shoulder stability. While it is not a prime mover, it can be susceptible to overuse and injury, particularly in athletes and individuals with repetitive tasks.
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Frequently asked questions
The pectoralis major, latissimus dorsi, teres major, triceps, and coracobrachialis are the primary muscles responsible for adducting the humerus.
Adduction is the motion of a limb or appendage toward the midline of the body. In the case of the arm, it is the movement of the arm towards the body.
The humerus is the longest bone in the upper extremity, forming the upper arm. It is a long bone consisting of a shaft (diaphysis) and two extremities (epiphysis).
The humerus serves as an attachment point for 13 muscles, which contribute to the movements of the hand and elbow, and the overall movement and stability of the upper limb.
Reaching into a back pocket is an example of adduction. This movement is achieved through the coordinated action of the pectoralis major, latissimus dorsi, deltoid, teres major, and subscapularis muscles.
