Last Updated on March 10, 2025
The clavicle elongated, S-shaped bone that lies horizontally between the sternum and the acromial end of the scapula. It is an important connection between the axial skeleton and the pectoral girdle. The pectoral girdle or the shoulder girdle is the term used for bones in the appendicular skeleton which connects to the arm on each side. The clavicle and scapula constitute the pectoral girdle in humans.
The clavicle is a slender bone, wider medially at its sternal articulation and noticeably thinner at its lateral third. The clavicle assumes a gentle S-shape, the medial end convex forward and the lateral end concave forward.
The shape resembles the musical symbol clavicula. It is also known as the collarbone.
The female collarbone is shorter, lighter, thinner, smoother, and less curved than in males. In females, the lateral end is a little below the medial end, whereas in males, it is either at the same level or slightly higher than the medial end.
The clavicle unlike other long bones does not have a medullary cavity.
The clavicle serves as the connection between the axial skeleton and the pectoral girdle. It thus allows weight transfer from the upper limbs to the axial skeleton.
Bony Structure of Clavicle
The collarbone has the following parts
- Medial end
- Lateral ends
- A cylindrical shaft in between
- The lateral end is also called the acromial end and is flat from above downwards. It articulates with the acromion process of the scapula through a facet. The articular surface for the acromioclavicular joint gives attachment to the joint capsule.
- The medial end is called the sternal end, is quadrangular in shape. This part articulates with the clavicular notch of the manubrium sterni to form the sternoclavicular joint. It also articulates with first costal cartilage via an extension of the articular surface.
- The shaft of the collarbone can be divided into the lateral one-third and the medial two-thirds. The lateral one-third is flat from above downwards, concave anteriorly and convex posteriorly. The inferior surface has an elevation called the conoid tubercle and a ridge called the trapezoid ridge.
The medial two-thirds is rounded and has four surfaces- Convex anterior, thick posterior, superior, and inferior which harbors a longitudinal groove called subclavian groove in its lateral half. - Superior surface: It has a smooth appearance and one can visualize the acromial facet at the far posterior edge of the acromial end.
- Inferior Surface: The inferior surface of the clavicle is rough. The sternal facet is at the edge of the sternal end. It is triangular-shaped and forms the sternoclavicular joint. The costal tuberosity, a roughened area at the sternal end of the bone, serves as an attachment to the costoclavicular ligament.
The conoid tubercle is a rough eminence found towards the sternal end and is the site where the conoid ligament attaches. The trapezoid line, is nearby, running laterally from the conoid tubercle. It serves as an attachment site for the trapezoid ligament.
Determination of the Side of the Collarbone
- The lateral end is flat, and the medial end is large and quadrilateral.
- The shaft is slightly curved, so that it is convex forwards in its medial 2/3, and concave forwards in its lateral 1/3.
- The inferior surface is grooved longitudinally in its middle 1/3.
Joints
Acromioclavicular joint
The acromioclavicular joint, is formed by the acromial end of the clavicle and the acromion of the scapula. It only has slight gliding movement.
Sternoclavicular joint
It is formed by the sternal end and the sternum’s manubrium. It anchors the clavicle and scapula to the axial skeleton. This joint enables following movements of the limb-
- Protraction and retraction
- Depression and elevation
- Rotation (minimal)
Ligaments
Medial Ligaments
The bulbous medial clavicular end contributes to forming the sternoclavicular joint. Several ligaments support this joint.
- Capsular Ligaments: Capsular ligaments are thickenings of the sternoclavicular joint capsule referred to as the capsular ligaments on anterosuperior and posterior aspects of the capsule. These are responsible for limiting superior displacement of the medial clavicular or, through the clavicular moment arm, inferior displacement of the lateral end of an intact clavicle. The posterior part of the capsule resists both anterior and posterior translation at the sternoclavicular joint.
- Interclavicular Ligament: This ligament has strong bands that span the medial clavicle to the superior sternum to the contralateral clavicle. The ligament loosens with shoulder elevation and prevents downward displacement of the lateral end of the clavicle.
- Costoclavicular Ligament: These strong ligaments run from the upper aspect of the first rib and adjacent aspects of the sternum to the inferior clavicle. The costoclavicular ligament stabilizes the medial clavicle against upward and downward rotation.
Lateral Ligaments
- Coracoclavicular Ligaments: From the base of the coracoid process of the scapula to the inferior aspect of the lateral clavicle are two ligaments, called trapezoid and conoid ligaments. Trapezoid ligament is lateral and attaches on a specific osseous ridge, whereas the more medial conoid inserts at the conoid tubercle. These ligaments serve the important function of suspension of the shoulder girdle from the clavicle.
- Acromioclavicular Ligaments: The capsule of the acromioclavicular joint forms the acromioclavicular ligaments. Posterosuperiorly, the ligament serves to resist anteroposterior displacement of the distal clavicle.
Muscles
Six muscles are attached to the clavicle.
- Medially
- Anterior surface- origin clavicular head of the pectoralis major. It causes flexion, horizontal adduction, and inward rotation of the humerus.
- Posterior surface- origin of sternohyoid muscles. It causes hyoid bone depression
- Superomedial – origin of the sternocleidomastoid. It is the lateral flexor on the ipsilateral side and rotates the head to the opposite side, but when acts bilaterally, it flexes the neck and extends the head.
- The inferior surface in the middle- the subclavian groove- insertion of the subclavius muscle. It causes shoulder depression and pulls the clavicle anteroinferiorly.
- Laterally
- Anterior clavicle- origin for the anterior deltoid. It assists in the flexion of the shoulder.
- Posterosuperior clavicle- Accessory insertion for the trapezius. Trapezius stabilizes the scapula.
Blood Supply
The collarbone does not have a medullary cavity Therefore it lacks a nutrient artery. The is periosteal arterial blood supply is from suprascapular, thoracoacromial, and the internal thoracic arteries.
Functions
Strut Function
The collarbone is responsible for bracing the shoulder girdle and propping it away from the sternum and thoracic cage. This allows the shoulder to reach into cross-body and internal rotation positions without medial collapse. The clavicle increases the strength of shoulder girdle movements. The clavicle is so positioned as to keep the extremity far enough away from the thorax, allowing for the shoulder motion unimpeded.
Suspensory Function
The shoulder girdle is stabilized against inferior displacement by two mechanisms, one dynamic and one static. Posteriorly, the trapezius acts as a dynamic scapular elevator. Anteriorly, the shoulder girdle hangs from the clavicle by the coracoclavicular ligaments, similar to a sign hanging from a signpost.
Clinical Significance
- Midclavicular Line: It is an important clinical landmark. it is used to locate cardiac apex, liver size and gallbladder position. The gallbladder is located between the mid-clavicular line and transpyloric plane.
- Clavicle fractures: Fractures of clavicle constitute about 10% of all fractures and are often caused by falls on the shoulder. These can be managed nonoperatively in most of the cases.
- Aromioclavicular dislocations: These are common in sports and in most of them, the joint anatomy can be restored by surgical methods only but few can be managed by nonoperative methods.
- Sternoclavicular Dislocations: these are relatively rare but could pose an emergency because of posterior dislocation of the medial end causing impingement of thoracic structures. It can be reduced by closed methods but in case of failure of reduction, would need surgery.
- Clavicular Diseases: Many conditions like infection, tuberculosis, cysts, and tumors may affect the clavicle. Each condition would be treated according to the cause, severity and patient age.
- Acromioclavicular Osteoarthritis: Most commonly, it is caused as a sequel to acromioclavicular joint injury. Infection, degenerative and repetitive trauma are other causes. Rest, NSAIDs and local treatment are the mainstay of the treatment.
References
- Bernat A, Huysmans T, Van Glabbeek F, Sijbers J, Gielen J, Van Tongel A. The anatomy of the clavicle: a three-dimensional cadaveric study. Clin Anat. 2014 Jul;27(5):712-23. [PubMed]
