Overview
The clavicle is a sigmoid-shaped long bone extending between the manubrium of the sternum and the acromion process of the scapula, connecting the appendicular and axial skeleton. It primarily functions to:
- Attaches the upper limb to the trunk as part of the ‘shoulder girdle’.
- Protects the underlying neurovascular structures supplying the upper limb.
- Transmits force from the upper limb to the axial skeleton.
Structure
Sternal end (medial)
- A rounded pyramidal-shaped end featuring a large facet for articulation with the manubrium of the sternum at the sternoclavicular joint.
- The inferior surface of the sternal end is marked by a rough oval depression, the costal tuberosity, for the costoclavicular ligament (a ligament of the SC joint).
Shaft
The shaft of the clavicle acts a point of origin and attachment for several muscles – deltoid, trapezius, subclavius, pectoralis major, sternocleidomastoid and sternohyoid
Acromial end (lateral)
The acromial end is a flattened oval-shaped, featuring a small facet for articulation with the acromion of the scapula at the acromioclavicular joint. It also serves as an attachment point for two ligaments:
- Conoid tubercle – attachment point of the conoid ligament, the medial part of the coracoclavicular ligament.
- Trapezoid line – attachment point of the trapezoid ligament, the lateral part of the coracoclavicular ligament.
The coracoclavicular ligament is a very strong structure, effectively suspending the weight of the upper limb from the clavicle.
Articulations
- Acromioclavicular joint (laterally) – has incomplete disc
- Sternoclavicular joint (medially) – has a complete disc
- Both are atypical synovial joints
Muscular Attachments
Lateral attachments
- Deltoid – Anterolateral half of the superior surface.
- Trapezius – Posterolateral third of the superior surface
Medial attachments
- Pectoralis major – Anteromedial half of the superior surface
- Sternocleidomastoid (clavicular head) – Posteromedial third of the superior surface
- Subclavius – Resides in the subclavian groove, middle third of inferior surface
- Sternohyoid – Medial end of the clavicle
Ligamentous Attachments
Lateral Attachments
- Acromioclavicular ligaments
- Coracoclavicular ligaments
- Trapezoid
- Conoid
Medial Attachments
- Costoclavicular ligaments
- Sternoclavicular ligaments
- Anterior and posterior
- Interclavicular ligaments
Relations
- The cephalic vein courses in the deltopectoral groove
Posterior
- Subclavian vein, phrenic nerve, anterior scalene, subclavian artery
Development
- The first bone to begin ossification – derivative of the lateral mesoderm
- Medial end undergoes endochondral ossification (bony structure is preceded by a cartilaginous model constructed by chondrocytes before mineralization and ossification)
- Lateral end undergoes intramembranous ossification (intramembranous ossification which constitutes woven bone formed directly without cartilage)
- Growth plates may not close until 20 – 25 years of age
Anatomical Variants
- Forked clavicle
- Supraclavicular foramen Clavicle pierced by branch of supraclavicular nerve
- Coracoclavicular joint Between conoid tubercle of clavicle and coracoid process of scapula