Clavicle

The clavicle, commonly known as the collarbone, is a long, slender bone that serves as a key structural component of the shoulder girdle. It acts as a strut between the sternum and scapula, facilitating upper limb movement while protecting underlying neurovascular structures. Understanding its anatomy and physiology is essential for evaluating clavicular injuries and disorders.

Anatomy

Gross Anatomy

The clavicle consists of a medial (sternal) end, a lateral (acromial) end, and a curved shaft connecting the two. The medial end articulates with the manubrium of the sternum at the sternoclavicular joint, while the lateral end forms the acromioclavicular joint with the acromion of the scapula. The shaft exhibits a medial convexity and a lateral concavity, which provides strength and resilience against forces transmitted through the upper limb.

Surface Features

• Conoid Tubercle: Located on the inferior surface near the lateral end, serving as the attachment site for the conoid ligament.
• Trapezoid Line: Extends from the conoid tubercle for attachment of the trapezoid ligament.
• Subclavian Groove: Runs along the inferior surface of the medial shaft for attachment of the subclavius muscle.

Relations

The clavicle provides attachment points for several muscles, including the sternocleidomastoid, pectoralis major, deltoid, and trapezius. Ligamentous attachments include the conoid, trapezoid, costoclavicular, and interclavicular ligaments. Neurovascular structures, such as the subclavian artery, subclavian vein, and brachial plexus, lie just inferior to the clavicle, making them vulnerable during fractures or trauma.

Physiology

Role in Shoulder Mechanics

The clavicle acts as a strut that maintains the lateral position of the scapula, allowing a wide range of upper limb motion. It transmits mechanical forces from the arm to the axial skeleton, contributing to shoulder stability and facilitating overhead and rotational movements.

Protection of Neurovascular Structures

By spanning the superior thoracic aperture, the clavicle shields underlying vital structures, including the subclavian vessels and brachial plexus. Its curvature and rigid structure help absorb and distribute external forces, reducing the risk of injury to these critical components.

Development and Embryology

Ossification Centers

The clavicle is unique in being the first bone to ossify during fetal development and exhibits both intramembranous and endochondral ossification. Primary ossification begins in the shaft around the fifth to sixth week of gestation, while secondary ossification centers appear at the sternal end around puberty.

Timeline of Clavicular Ossification

Ossification of the clavicle progresses from medial to lateral. The medial epiphysis fuses with the shaft between ages 22 and 25, completing the bone’s growth. The lateral epiphysis may fuse slightly earlier or later depending on individual variation.

Growth and Fusion

During childhood and adolescence, the clavicle grows in length and thickness, adapting to biomechanical demands. Fusion of the secondary ossification centers ensures structural integrity and allows the clavicle to fulfill its role in shoulder mechanics and force transmission.

Biomechanics

Movements Allowed at the Sternoclavicular and Acromioclavicular Joints

The clavicle allows complex movements of the shoulder by articulating with the sternum and scapula. At the sternoclavicular joint, it permits elevation, depression, protraction, retraction, and limited rotation. At the acromioclavicular joint, it enables scapular rotation and tilting, which are essential for overhead arm motion.

Force Transmission During Upper Limb Activity

The clavicle transmits forces from the upper limb to the axial skeleton, distributing loads during lifting, pushing, or impact activities. This function prevents excessive stress on the scapula and sternum, maintaining joint congruency and stability.

Role in Shock Absorption

The curvature and elasticity of the clavicle allow it to act as a shock absorber, mitigating forces transmitted during falls or blunt trauma. This protective function reduces the risk of injury to the shoulder girdle and underlying neurovascular structures.

Common Injuries and Pathologies

Fractures

Clavicular fractures are common, particularly in young, active individuals. They are classified based on location:

• Medial Fractures: Rare and often associated with high-energy trauma.
• Midshaft Fractures: Most frequent type due to the thin midportion and minimal muscular coverage.
• Lateral Fractures: Occur near the acromial end and may involve the acromioclavicular joint.

Dislocations

Dislocations involve the sternoclavicular or acromioclavicular joints:

• Sternoclavicular Joint Dislocation: Rare but potentially serious due to proximity to major vessels and the trachea.
• Acromioclavicular Joint Dislocation: Often results from direct trauma to the shoulder and is classified by the Rockwood system based on severity.

Congenital Anomalies

• Cleidocranial Dysplasia: Genetic disorder causing clavicular hypoplasia or aplasia, often resulting in hypermobility of the shoulders.
• Hypoplasia or Aplasia of the Clavicle: Rare congenital variations affecting clavicular development and shoulder mechanics.

Degenerative and Inflammatory Conditions

• Osteoarthritis of AC or SC Joints: Degeneration of articular cartilage leading to pain and reduced range of motion.
• Osteolysis of the Distal Clavicle: Seen in weightlifters and manual laborers, resulting in pain and structural changes at the acromial end.

Clinical Features

Symptoms

Patients with clavicular injuries or pathologies commonly present with:

• Pain localized to the fracture or joint site, often exacerbated by arm movement
• Swelling and bruising over the affected area
• Deformity or prominence in cases of fracture or dislocation
• Limited range of motion of the shoulder

Signs

• Palpable tenderness along the clavicle or joint line
• Visible or palpable step-off deformity in fractures
• Joint instability in AC or SC dislocations
• Crepitus or abnormal movement on palpation

Special Tests

• Cross-body adduction test for AC joint injury
• Sternoclavicular compression test for SC joint instability
• Observation of shoulder droop or winging for clavicular malalignment

Diagnosis

History and Physical Examination

Diagnosis begins with a detailed history, including mechanism of injury, onset of symptoms, previous shoulder injuries, and activity level. Physical examination assesses pain, swelling, deformity, range of motion, and stability of the AC and SC joints, as well as neurovascular status of the upper limb.

Imaging

Imaging is essential to confirm diagnosis, classify injuries, and guide management.

• X-ray: First-line imaging to detect fractures, dislocations, and alignment abnormalities.
• CT Scan: Useful for complex or medial clavicle fractures and detailed joint evaluation.
• MRI: Provides assessment of soft tissue structures, including ligaments and associated muscle injuries.

Differential Diagnosis

• Shoulder girdle fractures (scapula, proximal humerus)
• Acromioclavicular or sternoclavicular joint sprains
• Brachial plexus or neurovascular injury
• Soft tissue contusions and muscle injuries

Management

Conservative Treatment

Non-surgical management is appropriate for most midshaft fractures, minor dislocations, and non-displaced injuries.

• Immobilization using a sling or figure-of-eight bandage
• Pain control with analgesics or NSAIDs
• Gradual physiotherapy focusing on range of motion and strengthening once pain subsides

Surgical Management

Surgical intervention is indicated for displaced fractures, severe AC or SC joint dislocations, or injuries involving neurovascular compromise.

• Open reduction and internal fixation for midshaft or distal fractures
• Reconstruction or stabilization of AC or SC ligaments in joint dislocations
• Postoperative rehabilitation to restore function and prevent stiffness

Rehabilitation Protocols

Rehabilitation involves progressive mobilization, strengthening of shoulder girdle muscles, and functional training to restore full range of motion and prevent long-term deficits.

Complications

Malunion or Nonunion

Improper healing of clavicular fractures can result in malalignment, shortening, or nonunion, leading to functional impairment and cosmetic deformity. Surgical intervention may be required to correct significant malunion.

Neurovascular Compromise

Fractures or dislocations of the clavicle can injure nearby structures, including the brachial plexus, subclavian artery, and vein. Symptoms may include numbness, weakness, or vascular insufficiency in the upper limb, necessitating prompt evaluation and management.

Post-Traumatic Arthritis

Chronic instability or joint incongruity, particularly at the acromioclavicular or sternoclavicular joints, can lead to degenerative changes and osteoarthritis, resulting in pain and restricted shoulder motion.

Prognosis

Recovery Timeline

The prognosis of clavicular injuries varies based on the location and severity. Midshaft fractures and minor dislocations treated conservatively generally heal within 6 to 12 weeks. Surgical cases may require longer rehabilitation but often achieve excellent functional outcomes with proper management.

Long-Term Functional Outcomes

Most patients regain full shoulder function, especially when early mobilization and physiotherapy are implemented. Persistent pain, limited range of motion, or cosmetic deformity may occur in cases of severe displacement, malunion, or associated ligamentous injury.

Prevention

Protective Measures in Sports and High-Risk Activities

Preventing clavicular injuries involves minimizing trauma during sports and high-risk activities. Use of protective gear, such as shoulder pads in contact sports, and avoiding high-impact falls can reduce the risk of fractures and dislocations.

Ergonomic Considerations

Proper techniques for lifting, carrying, and overhead activities help prevent excessive stress on the clavicle. Strengthening shoulder and chest muscles also supports the clavicle and shoulder girdle, enhancing stability and reducing injury risk.

References

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