Dominic Stone
The clavicle, or collarbone, is an S-shaped bone that connects the arm to the trunk, joining the axial skeleton to the pectoral girdle. This bone is essential for functional movement, acting as a brace for the shoulder and allowing weight transfer from the upper limbs to the axial skeleton. The clavicle has several attachment sites for muscles, ligaments, and neurovascular structures. The specific muscles that attach to the clavicle include the trapezius, deltoid, sternocleidomastoid, pectoralis major, subclavius, and sternohyoid muscles. These muscles are distributed along the lateral third and medial two-thirds of the clavicle, with some attaching to the anterior, posterior, superior, or inferior surfaces.
| 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 it to act as a brace for the shoulder |
| Ligaments attached | Coracoclavicular ligament (trapezoid and conoid ligaments), Costoclavicular ligament |
| Arteries supplying blood | Suprascapular, Thoracoacromial, Internal thoracic |
| Nerves supplying clavicle and clavicular joints | Subclavian, Lateral pectoral, Supraclavicular |
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What You'll Learn
Trapezius muscle
The trapezius muscle is a large, paired trapezoid-shaped muscle that starts at the base of the neck and extends across the shoulders and down to the middle of the back. It gets its name from its shape, resembling a trapezium, also known as a trapezoid or diamond-shaped quadrilateral. The trapezius muscle is made up of long muscle fibres that span a large width of the upper back.
The trapezius muscle has three sections: upper, middle, and lower. The upper section connects to the skull and neck (cervical spine), while the middle and lower sections attach to bones in the thoracic spine. The muscle is also connected to the lateral sides of the shoulder blade (scapula) and collarbone (clavicle). The trapezius muscle is one of the commonly affected muscles in facioscapulohumeral muscular dystrophy (FSHD), with the lower and middle fibres typically affected first.
The trapezius muscle plays a crucial role in maintaining posture and moving the upper back, neck, and head. It helps with various motions, including turning the head from side to side, adjusting posture (such as standing up straight or bending the upper back forward), twisting the torso, shrugging the shoulders, and moving the shoulders when lifting the arm or throwing something. The trapezius muscle works in conjunction with other muscles to produce coordinated movements, particularly involving the scapula. For example, it works with the rhomboids to retract and stabilise the scapula, contributing to shoulder movement and posture.
In terms of motor function, the trapezius muscle is supplied by the accessory nerve. Its contraction can result in two effects: movement of the scapulae when the spinal origins are stable, and movement of the spine when the scapulae are stable. The upper fibres of the trapezius elevate the scapulae, the middle fibres retract them, and the lower fibres depress them. Additionally, the trapezius induces scapular rotation, with the upper and lower fibres rotating the scapula around the sternoclavicular articulation.
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Deltoid muscle
The deltoid muscle, also known as the common shoulder muscle, forms the rounded contour of the human shoulder. It is made up of three distinct sets of muscle fibres: the anterior or clavicular part (commonly known as the front delt), the posterior or scapular part (or rear delt), and the intermediate or acromial part (or side delt). The deltoid muscle is responsible for elevating the arm in the scapular plane, and its contraction elevates the humeral head. It also helps to lift the arm to the front, side, and back.
The deltoid muscle is one of six muscles attached to the clavicle, with the anterior portion of the muscle attached to the periosteum at the anterior surface of the bone. The deltoid's anterior or clavicular fibres arise from most of the anterior border and upper surface of the lateral third of the clavicle. The anterior origin lies adjacent to the lateral fibres of the pectoralis major muscle, as do the end tendons of both muscles. These muscle fibres are closely related and only a small chiasmatic space, through which the cephalic vein passes, prevents the two muscles from forming a continuous muscle mass.
The deltoid muscle works alongside other shoulder muscles, such as the rotator cuff muscles, to help perform a variety of movements. Deltoid muscle functions include arm abduction, flexion (moving the arm forward and towards an overhead position), and extension (moving the arm backward and behind the body). It also helps to stabilise the shoulder joint to prevent dislocations when lifting the arm or carrying weight.
The deltoid muscle is susceptible to various issues and abnormalities, including tears, fatty atrophy, enthesopathy, deltoid fibrosis, and rotator cuff tears. Deltoid muscle pain can affect swimmers, pitchers, or anyone who performs repetitive overhead arm movements.
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Sternocleidomastoid muscle
The sternocleidomastoid muscle (SCM) is a large, superficial cervical muscle that divides the neck into anterior and posterior triangles. It is a paired muscle, with one side of the neck having one SCM that binds the skull to the sternum and clavicle. The SCM has multiple functions, including rotating the head to the opposite side, flexing the neck, and acting as an accessory muscle of inspiration.
The SCM is innervated by the accessory nerve, which supplies only motor fibres. The cervical plexus provides proprioception and other sensory information. The SCM is a unique muscle in that it has a variable origin and variable innervation arrangements. In some cases, the clavicular head may be narrow, while in others it may be much broader. When the clavicular origin is broad, it is sometimes subdivided into several slips separated by narrow intervals.
The SCM has two heads that originate at two locations: the manubrium of the sternum and the clavicle. As the SCM ascends, it spirals behind the other head and blends with its deep surface below the middle of the neck, forming a thick, rounded muscle. The two heads are separated by a triangular surface depression called the lesser supraclavicular fossa.
The SCM is an important landmark in the neck and plays a protective role for the vertical neurovascular bundle of the neck, branches of the cervical plexus, deep cervical lymph nodes, and soft tissues of the neck. It is also involved in complex physiological movements as part of the muscular group of the cervicofacial region.
The SCM is involved in the range of motion of the neck and head. When contracting alone, the SCM causes the head to rotate to the opposite side and laterally bend on the same side. When both SCMs contract together, this results in head flexion.
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Pectoralis major muscle
The pectoralis major muscle is a thick, fan-shaped or triangular convergent muscle that makes up the bulk of the chest muscles. It is located on the anterior surface of the thoracic cage, underneath the breast in women and a deep layer of fascia, subcutaneous tissue, and skin in men. It is also referred to as the ""pecs"" or "chest muscle". The pectoralis major has three parts: the clavicular part, the sternocostal part, and the abdominal part. All three parts converge laterally and insert onto the greater tubercle of the humerus. The pectoralis major is innervated by the lateral and medial pectoral nerves, which stem from the brachial plexus. It is vascularized by the pectoral branches of the thoracoacromial artery and the perforating branches of the internal thoracic artery.
The primary functions of the pectoralis major are flexion, adduction, and internal rotation of the humerus. When the arm is in the anatomical position, the pectoralis major acts as a strong adductor and internal rotator of the humerus at the shoulder joint. The clavicular portion of the muscle flexes the humerus up to 90 degrees in a horizontal plane. The sternocostal portion of the muscle can produce the antagonistic movement and extend the humerus back to the anatomical position. Acting together with the latissimus dorsi muscle, the pectoralis major pulls the trunk forwards or upwards when its humeral attachment is fixed, which is important in activities such as climbing.
The pectoralis major is also responsible for keeping the arm attached to the trunk of the body. The clavicular part is close to the deltoid muscle and contributes to flexion, horizontal adduction, and inward rotation of the humerus. At an approximately 110-degree angle, it contributes to adduction of the humerus. The sternocostal part contributes to the downward and forward movement of the arm and inward rotation when accompanied by adduction.
The pectoralis major can be targeted through various exercises, such as the barbell bench press, dumbbell bench press, and machine bench press, which induce high activation of the pectoralis major in the sternocostal region. Heavy loads are strongly correlated with pectoralis major activation. Tears of the pectoralis major are rare and typically affect healthy individuals in high-impact contact sports such as powerlifting.
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Subclavius muscle
The subclavius muscle is a small, triangular muscle in the anterior thorax located between the clavicle and the first rib. It originates from the first rib and courses laterally to insert on the undersurface of the middle third of the clavicle. The subclavius is enclosed by the clavipectoral fascia, a fibrous connective tissue that spans the interval between the clavicle and pectoralis minor muscle. The pectoralis major muscle courses superficial to the subclavius and clavipectoral fascia.
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 subclavian blood vessels and the superior trunk of the brachial plexus, in the event of a fractured clavicle.
The subclavius is innervated by the subclavian nerve (C5-6), a small branch that arises 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 brachial plexus, suprascapular artery, subclavian artery, and subclavian vein pass deep to the subclavius muscle.
Myofascial pain or muscle strain of the subclavius may 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, using a heavy backpack or strap across the clavicle, or sleeping with the upper extremity positioned overhead.
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Frequently asked questions
Five or six muscles attach to the clavicle.
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 depresses the shoulder and pulls the clavicle anteroinferiorly.
