Clavicle

Clavicula

Also known as: collarbone, collar bone

An S-shaped long bone lying horizontally at the root of the neck that acts as a strut holding the upper limb away from the trunk. It is the only bony link between the upper limb and the axial skeleton.

Overview

First bone to ossifyWeeks 5–6 of gestation

Last epiphysis to fuseMedial end, ≈22–30 years

Commonest fracture siteMiddle third (≈80%)

The clavicle is subcutaneous along its whole length. Its medial two-thirds are convex anteriorly and roughly cylindrical; its lateral third is flattened and concave anteriorly. The large sternal (medial) end articulates with the manubrium and 1st costal cartilage at the sternoclavicular joint; the flat acromial (lateral) end articulates with the acromion at the acromioclavicular joint.

On its inferior surface, the medial end bears an impression for the costoclavicular ligament; the middle third has a groove for subclavius and the nutrient foramen; the lateral third has the conoid tubercle and trapezoid line for the two parts of the coracoclavicular ligament, the principal suspensory ligament of the upper limb. Muscles attaching include sternocleidomastoid and trapezius (upper surface), pectoralis major and deltoid (anterior border) and subclavius (below).

Behind the medial clavicle lie the subclavian vessels and the brachial plexus, crossing the first rib — explaining the neurovascular risks of clavicular fractures. Transmitted forces from the hand pass up the limb to the clavicle and then to the axial skeleton.

Location

Horizontally across the root of the neck, between the manubrium and the acromion.

Parts & subdivisions

Sternal end

Large, articulates with the manubrium via an articular disc.

Acromial end

Flat facet for the acromion.

Conoid tubercle and trapezoid line

Attachments of the coracoclavicular ligament.

Subclavian groove

Insertion of subclavius, which cushions the subclavian vessels in fractures.

Shaft

S-shaped; weakest at the junction of the middle and lateral thirds.

Anatomy

Arterial supply

Suprascapular and thoracoacromial arteries.

Articulations

Manubrium and 1st costal cartilage (sternoclavicular joint), acromion of scapula (acromioclavicular joint).

Ligaments

Sternoclavicular, interclavicular, costoclavicular, acromioclavicular and coracoclavicular (conoid + trapezoid) ligaments.

Ossification

The first bone to ossify (weeks 5–6) — mostly intramembranous from two primary centres in the shaft; the ends form in cartilage. A secondary centre for the sternal end appears ≈18–20 years and is the last epiphysis to fuse (≈22–25, up to 30 years).

Clinical significance

Clavicle fracture

Among the commonest fractures — fall on the shoulder or outstretched hand; also birth injury. ≈80% occur in the middle third. The medial fragment is pulled upward by sternocleidomastoid; the lateral fragment drops under the weight of the arm (and trapezius cannot hold it) and is pulled medially by pectoralis major and adductors. Most heal with a sling; complications include malunion and, rarely, subclavian vessel or brachial plexus injury.

Cleidocranial dysplasia

RUNX2 mutation with absent or hypoplastic clavicles (patients can bring their shoulders together in front of the chest), delayed fontanelle closure and supernumerary teeth.

Test yourself

Fracture of the middle third of the clavicle typically shows which displacement?

Medial fragment pulled downward by pectoralis major; lateral fragment elevated by trapezius
Medial fragment elevated by sternocleidomastoid; lateral fragment depressed by the weight of the arm
Both fragments displaced posteriorly by subclavius
No displacement because of the coracoclavicular ligament

Answer: Medial fragment elevated by sternocleidomastoid; lateral fragment depressed by the weight of the arm

Sternocleidomastoid pulls the medial fragment upward, while the weight of the upper limb (and pull of pectoralis major) drags the lateral fragment downward and medially.

Which bone is the first in the body to begin ossifying, mainly by intramembranous ossification?

Femur
Clavicle
Mandible
Frontal bone

Answer: Clavicle

The clavicle starts ossifying in weeks 5–6 of gestation, largely by intramembranous ossification, and its medial epiphysis is the last to fuse (≈22–30 years).