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The clavicle, also known as the collar bone, is a long bone that sits between the shoulder blade and the sternum. There are two clavicles in a person, one on the right and one on the left. The bone receives its name from the Latin clavicula, meaning 'little key', due to its ability to rotate along its axis when the shoulder is abducted. The clavicle is connected to several muscles, including the trapezius, deltoid, sternocleidomastoid, pectoralis major, and subclavius. These muscles play a crucial role in the movement and stability of the shoulder joint. In this text, we will focus specifically on the muscle that elevates the clavicle and its associated functions and clinical significance.
| Characteristics | Values |
|---|---|
| Clavicle definition | A slender, S-shaped or sigmoid-shaped long bone, approximately 6 inches (15 cm) long, that serves as a strut between the shoulder blade and the sternum (breastbone). |
| Number of clavicles in a person | Two, one on each side of the body |
| Clavicle orientation | A broad, flat acromial end (lateral third) and a round pyramidal-like sternal end (medial two-thirds) |
| Clavicle function | Plays an essential role in functional movement, serving as the connection between the axial skeleton and the pectoral girdle, allowing it to act as a brace for the shoulder and transfer weight from the upper limbs to the axial skeleton |
| Clavicle protection | Protects neurovascular structures entering the thorax, such as the brachiocephalic arterial trunk, internal jugular vein, common carotid artery, vagus and phrenic nerves, along with the sternum |
| Clavicle joints | Acromioclavicular joint (between the clavicle and the scapula) and sternoclavicular joint (between the clavicle and the manubrium) |
| Clavicle arteries | Suprascapular, thoracoacromial, and internal thoracic (mammalian) arteries provide arterial supply to the clavicle |
| Clavicle nerves | Innervated by the subclavian, lateral pectoral, and supraclavicular nerves; the sternoclavicular joint is directly innervated by the medial supraclavicular nerve (C3-C4) and the subclavius nerve (C5-C6) |
| Number of muscles attached to the clavicle | Five or six, found distributed at either the lateral third or medial two-thirds of the bone |
| Muscles attached to the lateral third of the clavicle | Trapezius muscle and deltoid muscle |
| Muscles attached to the medial third of the clavicle | Sternocleidomastoid muscle, pectoralis major muscle, sternohyoid muscle, and subclavius muscle |
| Clavicle fractures | Common, usually resulting from injury or trauma, such as falling on the shoulder or with an outstretched hand, or a direct hit to the collarbone |
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What You'll Learn
The trapezius muscle
Injuries to the trapezius muscle are less common than with other muscles, but they can occur, especially in bodybuilders lifting heavy weights or in high-velocity accidents such as car crashes. Symptoms of trapezius injuries include upper back pain, muscle spasms or cramps, pain between the shoulder blades, limited mobility, neck and shoulder stiffness, and swelling, bruising, or tenderness in the shoulders, neck, or back.
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The deltoid muscle
The anterior deltoid is responsible for flexion, internal rotation, and horizontal adduction. To stretch this muscle, the action is reversed by extension, external rotation, and horizontal abduction. The posterior deltoid, on the other hand, is responsible for extension, external rotation, and horizontal abduction. Its stretching is achieved by performing flexion, internal rotation, and horizontal adduction.
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The sternocleidomastoid muscle
The SCM has multiple functions. It helps you maintain your posture and stabilize your neck. It also works with other neck muscles to lift your breastbone and collarbone when you inhale, creating space for your lungs to take in air. Additionally, the SCM supports the temporomandibular joint (TMJ), which is the joint that connects your jaw to your skull and allows you to open and close your mouth.
The SCM is susceptible to injuries, tension, and strain, which can lead to pain, stiffness, and neck disorders. Treatments for SCM issues include massage, osteopathic manipulation, physical therapy, and surgery in severe cases. Proper care for the SCM includes managing stress, maintaining good posture, and getting adequate sleep.
The SCM is a two-headed neck muscle, with one head originating from the manubrium of the sternum (sternal head) and the other from the medial third of the clavicle (clavicular head). These two heads join into one muscle belly that inserts 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 is innervated by the accessory nerve (cranial nerve XI) and direct branches of the cervical plexus (C2-C3). Blood supply to the SCM is through the superior thyroid artery, a branch of the external carotid artery.
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The pectoralis major muscle
The pectoralis major has four actions which are primarily responsible for the movement of the shoulder joint. The first action is flexion of the humerus, as in throwing a ball underhand, and in lifting a child. The second action is horizontal adduction, which is the movement of the arm towards the body. The third action is internal rotation, which is the movement of the arm towards the body's midline. The fourth action is humeral flexion, which is the movement of the arm forward and upwards.
The pectoralis major is innervated by the medial (C8-T1) and lateral (C5-C7) pectoral nerves, which originate from the medial and lateral cords, respectively. The medial pectoral nerve innervates the lateral sternocostal head as well as the pectoralis minor muscle, and the lateral pectoral nerve innervates the clavicular head and medial sternocostal head. The pectoralis major maintains its blood supply via the pectoral branch of the thoracoacromial artery.
Injuries to the pectoralis major are uncommon but have become more prevalent over the past 20 years due to increased participation in weight lifting. Tears of the pectoralis major typically affect otherwise healthy individuals and are known to affect athletes, especially in high-impact contact sports such as powerlifting.
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The subclavius muscle
The main function of the subclavius muscle is to actively stabilize the clavicle, or collarbone, during movements of the shoulder and arm. Specifically, it helps to prevent dislocation of the clavicle at the sternoclavicular joint. Additionally, the subclavius plays a protective role by safeguarding the neurovascular structures beneath it, such as the brachial plexus and subclavian vessels, in the event of a clavicular fracture.
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. While contraction of the subclavius does not appear to shorten the distance between the sternoclavicular and acromioclavicular joints, it is hypothesized that it increases tension at the tendinous border and the aponeurosis. This suggests that the subclavius may regulate the output of kinetic energy during the movement of the upper extremity rather than solely acting as a stabilizer.
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Frequently asked questions
The trapezius muscle is attached to the clavicle and helps to lift and lower the shoulder.
The trapezius is a large triangular muscle at the back of the shoulder. It helps with the backward movement of the arm.
Yes, five or six muscles are attached to the clavicle, depending on the source. The deltoid muscle, the sternocleidomastoid muscle, the pectoralis major muscle, the subclavius muscle, and the sternohyoid muscle are all attached to the clavicle.
