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The clavicle, also known as the collarbone, is an S-shaped bone that connects the axial skeleton to the pectoral girdle, allowing for functional movement and weight transfer from the upper limbs to the body. The clavicle is essential for the optimal function of the upper extremity, providing significant range of motion and protecting the upper extremity by dispersing force transmission. The bone has multiple attachment sites for muscles, including the deltoid, trapezius, sternocleidomastoid, pectoralis major, subclavius, and sternohyoid muscles. These muscles are distributed along the lateral third or medial two-thirds of the bone, with specific attachment sites on the anterior, posterior, superior, and inferior surfaces of the clavicle.
| Characteristics | Values |
|---|---|
| Number of muscles attached to the clavicle | 5 or 6 |
| Muscles attached to the lateral third of the clavicle | Trapezius, Deltoid |
| Muscles attached to the medial third of the clavicle | Sternocleidomastoid, Pectoralis Major, Subclavius, Sternohyoid |
| Clavicle's role | Connection between the axial skeleton and the pectoral girdle, allowing weight transfer from the upper limbs to the axial skeleton |
| Clavicle shape | Double curved, S-shaped, sigmoid-shaped, elongated |
| Clavicle surface | Superior surface is smooth, inferior surface is rough |
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What You'll Learn
The trapezius muscle
The upper trapezius is frequently involved in neck injuries and can refer pain to the head. Tearing or straining the trapezius is uncommon, usually only occurring in bodybuilders lifting too heavy a weight or in high-velocity accidents. Overuse, injuries, and nerve damage are the most common causes of trapezius muscle pain. The muscle receives its innervation from the spinal accessory nerve (CN XI) and the C3 and C4 spinal nerves.
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The deltoid muscle
Deltoid strengthening exercises can be performed to improve muscle strength. These include standing next to a wall with a straight back and elbow and pushing the arm against the wall without causing pain. Dumbbell weight, arm raises, and resistance band exercises are also effective in strengthening the deltoid muscle.
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The sternocleidomastoid muscle
The sternocleidomastoid (SCM) muscle is a powerful neck muscle that allows you to bend your neck and turn or tilt your head. It is the largest muscle in the front of your neck and is located just below your skin on both the right and left sides of your neck. The SCM is one of over 20 pairs of muscles acting on the neck.
The SCM is a two-headed neck muscle, which bears attachments to the manubrium of the sternum, the clavicle, and the mastoid process of the temporal bone. The sternal head originates from the manubrium of the sternum, while the clavicular head originates from the medial third of the clavicle. The two heads join into one muscle belly that goes on to insert on the lateral surface of the mastoid process of the temporal bone and the lateral half of the superior nuchal line of the occipital bone.
The SCM plays an important role in the posture of the neck and the body. It helps stabilize the neck even when one is not moving. It also works with other neck muscles to lift the breastbone and collarbone when inhaling. This movement creates space for the lungs to take air.
Injuries, tension, sprains, strains, atrophy, and tumors can damage the SCM muscle. Sternocleidomastoid syndrome is an acute or chronic condition involving neck stiffness, pain, and other symptoms. It occurs when the SCM muscle develops tightened, sensitive areas, or trigger points. Treatment options for SCM issues include stretching, physical therapy, osteopathic manipulation, massage, and surgery in severe cases.
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The pectoralis major muscle
The pectoralis major is a thick, fan-shaped or triangular convergent muscle of the human chest. It is the largest and most superficial muscle in the chest area, lying under the breast. The pectoralis major arises from the anterior surface of the sternal half of the clavicle, as well as the sternum, costal cartilages of the true ribs, and the aponeurosis of the abdominal external oblique muscle. It is innervated by the medial pectoral nerve and the lateral pectoral nerve, which originate from the medial and lateral cords, respectively. The medial pectoral nerve innervates the lateral sternocostal head and the pectoralis minor muscle, while the lateral pectoral nerve innervates the clavicular head and medial sternocostal head. The pectoralis major receives blood supply from the pectoral branch of the thoracoacromial artery.
The primary functions of the pectoralis major are flexion, adduction, and internal rotation of the humerus. It is also capable of humeral flexion when the arm is in a position of extension posterior to the coronal plane of the thorax. The pectoralis major is targeted by exercises that include horizontal adduction and elbow extensions, such as the barbell bench press, dumbbell bench press, and machine bench press. These exercises induce high activation of the pectoralis major in the sternocostal region.
Injuries to the pectoralis major are uncommon but have become more prevalent in the past 20 years due to increased participation in weight lifting. Tears typically affect healthy individuals and are often seen in high-impact contact sports such as powerlifting. The classic patient is a muscular male between the ages of 20 and 40 years old, who experiences a tearing sensation, an audible pop, and immediate pain, localized swelling, weakness, and ecchymosis in the axilla and upper arm. Strength testing demonstrates weakness with adduction and internal rotation of the affected arm.
Poland syndrome is a rare congenital condition in which the pectoralis major muscle is completely missing, usually on one side of the body. This condition may be accompanied by the absence of the breast in females.
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The subclavius muscle
The main function of the subclavius is to actively stabilize the clavicle at the sternoclavicular joint during movements of the shoulder and arm. It also helps prevent dislocation of the clavicle at the sternoclavicular joint. Additionally, the subclavius is important in preventing injuries to the adjacent neurovascular structures, such as the brachial plexus and subclavian vessels, in the event of a clavicular fracture.
The subclavius is innervated by the subclavian nerve (C5-6), a small branch arising from the superior trunk of the brachial plexus. It receives arterial blood from the clavicular branch of the thoracoacromial artery, with contributions from the suprascapular artery.
The subclavius may also contribute to controlling the position of the scapula in relation to the thorax through its lateral aponeurotic extension and fascial connections. This regulation of the scapula's position may influence the kinetic energy output of the upper extremity's movement.
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Frequently asked questions
Five or six muscles attach to the clavicle, depending on the source.
The trapezius and deltoid muscles attach to the lateral third of the clavicle.
The sternocleidomastoid, pectoralis major, subclavius, and sternohyoid muscles attach to the medial third of the clavicle.
The subclavius muscle, which attaches to a groove in the middle of the clavicle, draws the clavicle downwards and forward. It also functions to depress the shoulder and pull the clavicle anteroinferiorly.
