Which Part Of The Clavicle Articulates With The Manubrium

The clavicle, also known as the collarbone, is a long, slender bone that serves as a crucial link between the upper limb and the axial skeleton. Its unique S-shape and subcutaneous position make it easily palpable and visible. Understanding the clavicle's anatomy, particularly its articulations, is essential in fields such as orthopedics, sports medicine, and physical therapy. This article will delve into the specific part of the clavicle that articulates with the manubrium, providing a comprehensive overview of this important joint.

Introduction to the Clavicle and its Articulations

The clavicle is a bone of dual curvature, acting as a strut that suspends the upper limb, keeping it away from the thorax and allowing for maximum range of motion. It is the first bone to begin ossification during fetal development and the last to complete ossification, usually around the age of 25. The clavicle articulates with two bones:

• The manubrium of the sternum medially, forming the sternoclavicular (SC) joint.
• The acromion of the scapula laterally, forming the acromioclavicular (AC) joint.

These articulations are vital for upper limb function and stability. The sternoclavicular joint, in particular, is the only bony attachment of the upper limb to the axial skeleton, making it a critical point for force transmission and movement.

The Medial End of the Clavicle: The Articular Surface

The part of the clavicle that articulates with the manubrium is the medial end, also known as the sternal end. This end is significantly expanded and has a triangular or quadrilateral shape. The articular surface on the medial end is covered with fibrocartilage, which is essential for shock absorption and reducing friction during movement.

Anatomical Features of the Medial End

• Shape: The medial end of the clavicle is noticeably larger than the lateral end. Its shape allows for a broad area of contact with the manubrium.
• Articular Facet: The articular facet is the specific area on the medial end that directly articulates with the manubrium. It is covered with hyaline cartilage in young individuals, which transitions to fibrocartilage with age.
• Ligament Attachments: The medial end of the clavicle serves as an attachment site for several important ligaments, which provide stability to the sternoclavicular joint.

The Sternoclavicular (SC) Joint: Anatomy and Function

The sternoclavicular joint is a synovial joint, specifically a saddle joint, although it functions more like a ball-and-socket joint due to its wide range of motion. It is formed by the articulation of the medial end of the clavicle with the manubrium of the sternum and the first costal cartilage.

Components of the SC Joint

• Medial Clavicle: As discussed, the medial end of the clavicle provides the articular surface.
• Manubrium: The manubrium is the superior portion of the sternum. It articulates with the clavicle via a concave facet on its superior-lateral aspect.
• First Costal Cartilage: The superior aspect of the first costal cartilage also contributes to the SC joint, adding to its stability.
• Articular Disc: The SC joint contains an articular disc made of fibrocartilage. This disc lies between the clavicle and the sternum, improving the congruity of the articular surfaces and acting as a shock absorber.
• Joint Capsule: A fibrous capsule surrounds the joint, providing additional support.
• Ligaments: Several ligaments reinforce the joint capsule, providing significant stability.

Ligaments of the SC Joint

The stability of the SC joint is primarily provided by its ligaments. These ligaments are crucial for maintaining the joint's integrity and preventing dislocation. The primary ligaments include:

• Anterior Sternoclavicular Ligament: This ligament reinforces the anterior aspect of the joint capsule, preventing anterior displacement of the clavicle.
• Posterior Sternoclavicular Ligament: Located on the posterior aspect, it prevents posterior displacement of the clavicle.
• Interclavicular Ligament: This ligament connects the medial ends of the two clavicles, running across the jugular notch of the manubrium. It limits excessive downward movement of the clavicles.
• Costoclavicular Ligament: This strong ligament connects the inferior surface of the clavicle to the first rib and its costal cartilage. It is the primary stabilizer of the SC joint, resisting upward displacement of the clavicle.

Function of the SC Joint

The sternoclavicular joint allows for a wide range of movements of the upper limb, including:

• Elevation and Depression: Movement of the clavicle upwards and downwards.
• Protraction and Retraction: Movement of the clavicle forward and backward.
• Rotation: Rotation of the clavicle along its longitudinal axis.

These movements are essential for activities such as reaching, lifting, and throwing. The SC joint acts as a pivot point, allowing the scapula to move freely across the thorax, thereby maximizing upper limb range of motion.

Clinical Significance of the SC Joint

The sternoclavicular joint is relatively stable due to its strong ligamentous support. However, it is still susceptible to injuries, particularly dislocations, which can be classified as anterior or posterior.

SC Joint Dislocation

• Anterior Dislocation: This is the more common type of SC joint dislocation. It typically occurs due to a direct blow to the anterior aspect of the clavicle or an indirect force applied through the shoulder. The clavicle displaces anteriorly, resulting in a visible prominence.
• Posterior Dislocation: This is a less common but more serious injury. Posterior dislocation can occur due to a direct blow to the anterior clavicle or a high-energy impact. The clavicle displaces posteriorly, potentially compressing structures in the mediastinum, such as the trachea, esophagus, and major blood vessels. This can lead to life-threatening complications.

Symptoms of SC Joint Dislocation

Common symptoms of SC joint dislocation include:

• Pain: Localized pain around the sternoclavicular joint.
• Swelling: Swelling and tenderness over the joint.
• Deformity: Visible or palpable deformity, depending on the direction of the dislocation.
• Limited Range of Motion: Difficulty moving the affected arm.
• Dyspnea or Dysphagia: In cases of posterior dislocation, difficulty breathing (dyspnea) or swallowing (dysphagia) may occur due to compression of mediastinal structures.

Diagnosis and Treatment

Diagnosis of SC joint dislocation typically involves a physical examination and imaging studies.

• Physical Examination: A thorough examination can reveal the presence of deformity, tenderness, and limited range of motion.
• Radiographs: X-rays are often the initial imaging modality used. However, they can be difficult to interpret due to the overlapping bony structures.
• CT Scan: Computed tomography (CT) scans are the preferred imaging modality for evaluating SC joint dislocations, especially posterior dislocations. CT scans provide detailed cross-sectional images, allowing for accurate assessment of the joint and surrounding structures.

Treatment for SC joint dislocation depends on the severity and direction of the dislocation.

• Conservative Treatment: Minor anterior dislocations may be treated conservatively with pain medication, ice, and immobilization with a sling.
• Closed Reduction: This involves manually manipulating the clavicle back into its normal position. It is typically performed under anesthesia.
• Open Reduction and Internal Fixation (ORIF): This surgical procedure is indicated for irreducible dislocations, dislocations associated with ligamentous injuries, or posterior dislocations with mediastinal compression. It involves surgically exposing the joint, reducing the dislocation, and stabilizing the joint with plates, screws, or sutures.

SC Joint Arthritis

The SC joint can also be affected by arthritis, either osteoarthritis or rheumatoid arthritis. Arthritis can cause pain, stiffness, and decreased range of motion in the joint.

• Osteoarthritis: This is a degenerative joint disease that results from the breakdown of cartilage. It is more common in older individuals.
• Rheumatoid Arthritis: This is an autoimmune disease that causes inflammation of the joint lining. It can affect multiple joints, including the SC joint.

Treatment for SC Joint Arthritis

Treatment for SC joint arthritis may include:

• Pain Medication: Over-the-counter or prescription pain relievers can help manage pain.
• Physical Therapy: Exercises to improve range of motion and strength.
• Corticosteroid Injections: Injections into the joint to reduce inflammation.
• Surgery: In severe cases, surgery may be necessary to remove damaged cartilage or fuse the joint.

Biomechanical Considerations

The sternoclavicular joint is a complex joint that plays a crucial role in upper limb biomechanics. Understanding the biomechanics of the SC joint is essential for understanding its function and the mechanisms of injury.

Force Transmission

The SC joint is the primary point of force transmission from the upper limb to the axial skeleton. Forces generated during activities such as lifting, pushing, and throwing are transmitted through the clavicle to the sternum and then to the rest of the body.

Range of Motion

The SC joint allows for a wide range of motion, including elevation, depression, protraction, retraction, and rotation. The amount of motion at the SC joint is coordinated with movements at the acromioclavicular (AC) joint and the scapulothoracic joint (the articulation between the scapula and the rib cage).

Stability

The stability of the SC joint is provided by its ligaments and the articular disc. The costoclavicular ligament is the primary stabilizer, resisting upward displacement of the clavicle. The anterior and posterior sternoclavicular ligaments prevent anterior and posterior displacement, respectively.

Development of the Clavicle and SC Joint

The clavicle is unique in that it is the first bone to begin ossification during fetal development. It ossifies via intramembranous ossification, meaning it forms directly from mesenchymal tissue without a cartilage intermediate.

Ossification

• Primary Ossification Center: The primary ossification center appears in the middle of the clavicle around the fifth week of gestation.
• Secondary Ossification Centers: Secondary ossification centers develop at the sternal end and the acromial end of the clavicle. The sternal end secondary ossification center appears around the age of 18-25 years and fuses with the rest of the clavicle around the age of 25-30 years.

Development of the SC Joint

The sternoclavicular joint develops from the same mesenchymal tissue that forms the clavicle and the sternum. The articular disc forms from the interzonal mesenchyme between the developing bones.

Variations in Clavicle Anatomy

There can be variations in clavicle anatomy, including variations in length, curvature, and the shape of the articular surfaces. These variations can affect the biomechanics of the SC joint and may predispose individuals to certain injuries.

Clavicle Length and Curvature

• Length: Clavicle length can vary between individuals. Longer clavicles may be more prone to fracture, while shorter clavicles may limit range of motion.
• Curvature: The curvature of the clavicle can also vary. A more pronounced curvature may provide greater stability, while a straighter clavicle may be more susceptible to dislocation.

Shape of Articular Surfaces

The shape of the articular surfaces on the medial end of the clavicle and the manubrium can vary. Variations in the shape of these surfaces can affect the congruity of the joint and may predispose individuals to arthritis.

Frequently Asked Questions (FAQ)

Q: What is the most common type of SC joint dislocation?

A: The most common type of SC joint dislocation is anterior dislocation, where the clavicle displaces forward.

Q: Is a posterior SC joint dislocation serious?

A: Yes, posterior SC joint dislocations are considered more serious because the clavicle can compress vital structures in the mediastinum, such as the trachea and major blood vessels.

Q: How is an SC joint dislocation diagnosed?

A: An SC joint dislocation is typically diagnosed through a physical examination and imaging studies, such as X-rays and CT scans.

Q: What is the primary stabilizer of the SC joint?

A: The costoclavicular ligament is the primary stabilizer of the SC joint.

Q: Can arthritis affect the SC joint?

A: Yes, both osteoarthritis and rheumatoid arthritis can affect the SC joint, causing pain and stiffness.

Q: What movements does the SC joint allow?

A: The SC joint allows for elevation, depression, protraction, retraction, and rotation of the clavicle.

Q: How is an SC joint dislocation treated?

A: Treatment depends on the severity and direction of the dislocation. Minor dislocations may be treated conservatively, while more severe dislocations may require closed reduction or surgery.

Q: What is the role of the articular disc in the SC joint?

A: The articular disc improves the congruity of the articular surfaces and acts as a shock absorber.

Q: How does the clavicle develop?

A: The clavicle is the first bone to begin ossification during fetal development. It ossifies via intramembranous ossification.

Q: What are the ligaments that support the SC joint?

A: The ligaments that support the SC joint include the anterior sternoclavicular ligament, posterior sternoclavicular ligament, interclavicular ligament, and costoclavicular ligament.

Conclusion

In summary, the medial end of the clavicle articulates with the manubrium of the sternum to form the sternoclavicular (SC) joint. This joint is a crucial link between the upper limb and the axial skeleton, allowing for a wide range of movements and force transmission. The SC joint is stabilized by a complex network of ligaments and an articular disc. While relatively stable, the SC joint is susceptible to injuries, such as dislocations and arthritis. Understanding the anatomy, biomechanics, and clinical significance of the SC joint is essential for healthcare professionals involved in the diagnosis and treatment of upper limb injuries. The unique structure and function of the clavicle and its articulations highlight its importance in overall musculoskeletal health.