Attachments
Muscles attach to the upper, front and back surfaces of the clavicle, and ligaments to its ends and under-surface.
| Structure | Site on the clavicle | Other attachment |
|---|---|---|
| Sternocleidomastoid (clavicular head) | Upper surface of the medial third | Mastoid process and superior nuchal line |
| Pectoralis major (clavicular head) | Anterior surface of the medial half | Lateral lip of the intertubercular sulcus |
| Sternohyoid | Posterior surface of the medial end | Hyoid bone |
| Subclavius | Subclavian groove, under-surface of the middle third | First rib at its junction with the costal cartilage |
| Deltoid | Anterior border of the lateral third | Deltoid tuberosity of the humerus |
| Trapezius (upper fibres) | Posterior border of the lateral third | Occiput, ligamentum nuchae |
| Costoclavicular ligament | Impression on the under-surface of the medial end | First rib and costal cartilage |
| Interclavicular ligament | Upper part of the sternal end | Opposite clavicle, across the jugular notch |
| Conoid ligament | Conoid tubercle | Base of the coracoid process |
| Trapezoid ligament | Trapezoid line | Upper surface of the coracoid process |
Deltoid and trapezius arise and insert on the same continuous line: the lateral third of the clavicle, the acromion and the spine of the scapula. The clavipectoral fascia attaches to the edges of the subclavian groove and encloses subclavius.
Articular surfaces and ligaments
The clavicle has an articular surface at each end, and each joint depends more on a ligament away from the joint than on its capsule.
Sternal end
The sternal articular surface is saddle-shaped and meets the clavicular notch of the manubrium and the first costal cartilage. An articular disc divides the joint into two cavities. The costoclavicular ligament, running from the under-surface of the medial clavicle down to the first rib, is its strongest stabiliser and the pivot for elevation and depression of the clavicle.
Acromial end
The acromial articular surface is a small flat oval facet for the acromion. The acromioclavicular ligament resists horizontal displacement. Vertical stability comes from the coracoclavicular ligament in two parts: the conoid ligament, a cone rising almost vertically from the base of the coracoid to the conoid tubercle, and the trapezoid ligament, a flatter quadrilateral sheet passing from the upper coracoid to the trapezoid line in front and lateral to it.
Relations: the first rib and costoclavicular space
The clavicle and the first rib form the costoclavicular space, one of the three narrow points of the thoracic outlet.
The first rib is short, broad and flat, with upper and lower surfaces and a single facet on its head for T1. On its upper surface the scalene tubercle takes scalenus anterior. In front of the tubercle a groove lodges the subclavian vein; behind it a groove carries the subclavian artery and the lower trunk of the brachial plexus, with scalenus medius attached behind that. Subclavius arises from the rib at the costochondral junction and runs up to the clavicle.
The subclavian vein, subclavian artery and brachial plexus pass through the costoclavicular space between the middle third of the clavicle and the first rib, with subclavius and the clavipectoral fascia cushioning them from the bone. The space narrows when the shoulder is braced back and down. The other two outlet sites are the interscalene triangle, between scalenus anterior, scalenus medius and the first rib, and the space behind pectoralis minor.
Clinical relevance
The attachments of the clavicle decide how its fractures displace and how acromioclavicular injuries are graded.
- Midshaft fracture: sternocleidomastoid lifts the medial fragment; the weight of the arm drags the lateral fragment down, and pectoralis major pulls it medially, shortening the shoulder.
- Lateral fracture: if the break lies medial to the coracoclavicular ligament, the medial fragment loses its tether and rides up, and the fracture is prone to non-union.
- Acromioclavicular dislocation: tearing of the acromioclavicular ligament alone gives a sprain; tearing of the conoid and trapezoid ligaments as well lets the clavicle ride up above the acromion, the basis of the Rockwood grades.
- Thoracic outlet syndrome: compression in the costoclavicular space, or by a cervical rib or band in the interscalene triangle, gives pain and paraesthesia in the ulnar border of the forearm and hand, and sometimes arm swelling or a positional loss of the radial pulse.
- Subclavian vein thrombosis: repetitive overhead work can compress the vein between the clavicle, subclavius and the first rib (effort thrombosis).
On the specimen
On this station the attachments are painted or pinned on a dry clavicle, so each mark is identified by surface and by third.
- Medial third, upper surface: sternocleidomastoid (labelled sternomastoid on older specimens).
- Medial half, front: pectoralis major; do not confuse it with deltoid, which lies on the lateral third of the same border.
- Lateral third, front: deltoid. Lateral third, back: trapezius.
- Middle third, under-surface groove: subclavius.
- Under-surface, medial end: costoclavicular ligament. Top of the sternal end: interclavicular ligament.
- Under-surface, lateral third: conoid ligament on the tubercle near the posterior border; trapezoid ligament on the line running laterally and forwards from it.
- Articular surfaces: the large saddle surface for the sternum and the small flat surface for the acromion.
The ends, borders, shaft and conoid tubercle themselves are also pinned; the clavicle station covers them as bony features.