Collarbone
Clavicula
location_on Anterior superior thorax, connecting the sternum to the scapula
The clavicle is an S-shaped bone that acts as a strut connecting the upper limb to the axial skeleton. It is the first bone to begin ossification (during the 5th fetal week) and the last to complete it (medial epiphysis fuses around age 25). The clavicle is the most commonly fractured bone in the body, typically at the junction of its middle and lateral thirds.
Key Anatomical Features
- S-shaped double curve: medially convex anteriorly, laterally concave anteriorly
- Sternal end is rounded and articulates with the manubrium
- Acromial end is flat and articulates with the acromion of the scapula
- Conoid tubercle on the inferior surface is the attachment for the conoid ligament
- Subclavian groove on the inferior surface marks where the subclavius muscle attaches
- It is the only long bone that ossifies intramembranously (not endochondrally)
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Deltoid | Anterior border of lateral third | Abducts the arm |
| Trapezius | Posterior border of lateral third | Elevates and retracts the scapula |
| Pectoralis major (clavicular head) | Medial half of anterior surface | Flexes and adducts the arm |
| Sternocleidomastoid (clavicular head) | Superior medial third | Rotates and flexes the head |
| Subclavius | Subclavian groove on inferior surface | Depresses and stabilizes the clavicle, protects subclavian vessels |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| Sternoclavicular joint | Synovial saddle with articular disc | Sternum |
| Acromioclavicular joint | Synovial plane with articular disc | Acromion of scapula |
Common Pathologies
Clavicle fracture
The most commonly fractured bone in the body, accounting for 5% of all fractures. Middle third fractures (80%) result from falls on an outstretched hand or direct shoulder impact.
Acromioclavicular separation
Injury to the AC joint ligaments from a fall directly onto the point of the shoulder. Classified by Rockwood into six types based on severity of ligament disruption.
Distal clavicle osteolysis
Stress resorption of the distal clavicle seen in weightlifters and overhead athletes, causing pain at the AC joint.
Sternoclavicular dislocation
Rare but potentially dangerous injury. Posterior dislocations can compress the great vessels, trachea, or esophagus and may constitute a surgical emergency.
Clinical Relevance
Clavicle fractures in the middle third cause the lateral fragment to drop inferiorly (from the weight of the arm) and the medial fragment to elevate (from sternocleidomastoid pull). The subclavian vessels and brachial plexus pass directly behind the middle third of the clavicle and can be injured in displaced fractures. The clavicle is also the most common site of birth fracture in neonates.
Development and Ossification
The clavicle is the first bone to begin ossification in the body, starting intramembranously during the 5th fetal week. It later develops secondary cartilaginous centers at each end. The medial epiphysis is one of the last in the body to fuse, around age 23-25, making it useful for forensic age estimation.
Did You Know?
- The clavicle is the first bone to begin ossification in the embryo
- Clavicula means little key in Latin, as the bone was thought to resemble an ancient Roman key
- The clavicle is the most commonly broken bone in the human body, and also the most common fracture sustained during birth
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