Dominic Stone
The collarbone, also known as the clavicle, is an S-shaped bone that sits between the shoulder and sternum at the top of the ribcage. It is connected to five muscles: the subclavius, the trapezius, the anterior deltoid, the sternocleidomastoid, and the pectoralis major. The subclavius is the primary muscle that controls the clavicle, while the trapezius and deltoid muscles provide dynamic stability to the acromioclavicular joint. The pectoralis major and deltoid muscles are attached anteriorly, while the trapezius is attached posteriorly. The levator claviculae muscle, present in 2-3% of people, is also attached to the lateral half of the clavicle.
| Characteristics | Values |
|---|---|
| Number of muscles attached to the collarbone | 5 |
| Clavicle parts | Medial two-thirds, lateral third |
| Medial two-thirds attachment sites | Sternocleidomastoid (SCM) muscle, subclavius muscle, pectoralis major muscle, sternohyoid muscle |
| Lateral third attachment sites | Deltoid muscle, trapezius muscle |
| Clavicle function | Connects the shoulder to the rest of the skeleton, provides structural support, allows for increased range of motion of the shoulder away from the body |
| Collarbone length | Varies; generally longer in males than in females |
| Collarbone shape | Elongated, S-shaped; varies more than most other long bones |
| Collarbone composition | Medullary cavity (marrow cavity) in medial two-thirds, shell of compact bone |
| Collarbone conditions | Cleidocranial dysostosis (partial or complete absence of collarbones), clavicle fractures (broken collarbone) |
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What You'll Learn
The subclavius muscle
The main function of the subclavius is to stabilize the clavicle during movements of the shoulder girdle. It also helps to prevent dislocation of the clavicle at the sternoclavicular joint. In addition, the subclavius protects the neurovascular structures and subclavian blood vessels beneath it in the event of a clavicular fracture. The brachial plexus, suprascapular artery, subclavian artery, and subclavian vein all pass deep to the subclavius muscle.
The subclavius is innervated by the nerve to the subclavius, a branch of the brachial plexus. The nerve to the subclavius originates from the C5-C6 nerve roots. The muscle receives arterial blood from the clavicular branch of the thoracoacromial artery, with contributions from the suprascapular artery.
The subclavius may be associated with compression of the brachial plexus, a network of nerves that provide movement and sensation to the shoulder and arm. Myofascial pain or muscle strain of the subclavius can result in pain along the clavicle, sternoclavicular joint, shoulder, or radiate into the arm. This pain can be caused by heavy lifting, chronic forward shoulder positioning, or sleeping with the upper extremity positioned overhead.
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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. Pain in the trapezius muscle can also be caused by overuse and nerve damage, and symptoms of trapezius issues can include limited mobility, decreased range of motion, muscle weakness, neck and shoulder stiffness, and swelling, bruising, or tenderness in the shoulders, neck, or back.
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The deltoid muscle
The primary function of the anterior deltoid is flexion, internal rotation, and horizontal adduction. To stretch this muscle, perform the reverse action by extension, external rotation, and horizontal abduction. The primary function of the posterior deltoid is extension, external rotation, and horizontal abduction. To stretch this muscle, perform flexion, internal rotation, and horizontal adduction. The deltoid muscle also helps to stabilise the shoulder joint and prevent dislocations.
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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. You can feel it on both the right and left sides of your neck. The SCM muscle ends at the mastoid process, a section of bone at the base of your skull behind your ears.
The SCM muscle has multiple functions beyond its principal function as a lateral neck flexor. It helps stabilize your neck and helps you maintain your posture. 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, it supports the temporomandibular joint (TMJ), which connects your jaw to your skull and allows you to open and close your mouth.
The SCM muscle is closely related to neurovascular structures that pass through the neck towards the head or the periphery of the body. It is innervated by the accessory nerve (cranial nerve XI) and direct branches of the cervical plexus (C2-C3). The blood supply to the SCM muscle is through the superior thyroid artery, a branch of the external carotid artery.
Injuries, tension, sprains, strains, atrophy, and tumors can damage the SCM muscle. Sternocleidomastoid syndrome is a 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 massage, osteopathic manipulation, physical therapy, and surgery in severe cases. Maintaining good posture and managing stress can also help care for the SCM muscle.
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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 or lifting a child. The second action is horizontal adduction, the third is internal rotation of the humerus, and the fourth is keeping the arm attached to the trunk of the body. The pectoralis major 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 receives double motor innervation from the medial pectoral nerve and the lateral pectoral nerve. It 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. Both nerves enter the medial aspect of the pectoralis major deep into the muscle. The pectoralis major maintains its blood supply via the pectoral branch of the thoracoacromial artery.
Pectoralis major tears are uncommon injuries that have become more prevalent over the past 20 years due to increased participation in weight lifting. Tears typically affect otherwise healthy individuals and are known to affect athletes, namely in high-impact contact sports such as powerlifting.
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Frequently asked questions
The collarbone, or clavicle, is covered by the deltoid, trapezius, sternocleidomastoid, and pectoralis major muscles.
The deltoid muscle is responsible for helping you move your arm forward, backward, and to the side.
The trapezius muscle helps to lift and lower your shoulder.
The sternocleidomastoid muscle lifts the medial aspect of the collarbone superiorly.
The pectoralis major muscle originates from the medial clavicle and provides structural support to the shoulder joint.
