Clavicle Ligaments: Anatomy, Function, and Clinical Relevance

How many ligaments are attached to the clavicle?

The clavicle, or collarbone, is a crucial skeletal strut anchored by a complex network of approximately seven primary ligaments that stabilize its two main articulations: the sternoclavicular joint (with the sternum) and the acromioclavicular joint (with the scapula).

Introduction to the Clavicle

The clavicle is the only bony attachment between the axial skeleton (trunk) and the appendicular skeleton (upper limb). Serving as a strut, it transmits forces from the upper limb to the axial skeleton and provides attachment points for muscles and ligaments. Its unique S-shape allows for resilience and a wide range of shoulder movements. The stability of the clavicle is paramount for proper upper limb function, a role primarily maintained by its strong ligamentous attachments.

Key Ligaments of the Clavicle

The clavicle forms two significant joints, each reinforced by a specific set of ligaments:

Sternoclavicular Joint Ligaments

The sternoclavicular (SC) joint, where the medial end of the clavicle articulates with the manubrium of the sternum, is a highly mobile but remarkably stable joint. Its stability is largely due to its strong surrounding ligaments:

• Anterior Sternoclavicular Ligament: This broad, fibrous band covers the anterior aspect of the SC joint, connecting the anterior surface of the medial clavicle to the anterior surface of the manubrium. It resists anterior displacement of the clavicle.
• Posterior Sternoclavicular Ligament: Similar to its anterior counterpart, this ligament reinforces the posterior aspect of the SC joint, connecting the posterior surface of the medial clavicle to the posterior surface of the manubrium. It resists posterior displacement of the clavicle.
• Interclavicular Ligament: Spanning the jugular notch, this ligament connects the superior aspects of the medial ends of both clavicles. It strengthens the superior aspect of the SC joint capsule and helps prevent excessive superior displacement of the clavicle, particularly during shoulder depression.
• Costoclavicular Ligament: This exceptionally strong, short, and flat ligament connects the inferior surface of the medial clavicle to the superior surface of the first rib and its costal cartilage. It is a crucial extrinsic ligament, serving as the primary stabilizer of the SC joint, preventing superior displacement of the clavicle and limiting excessive medial and lateral movements.

Acromioclavicular Joint Ligaments

The acromioclavicular (AC) joint, where the lateral end of the clavicle articulates with the acromion process of the scapula, is less stable inherently than the SC joint and relies heavily on its ligaments for integrity.

• Acromioclavicular Ligament: This ligament reinforces the AC joint capsule, connecting the superior surface of the lateral clavicle to the superior surface of the acromion. It has both superior and inferior components, with the superior portion being stronger and more distinct, resisting anterior and posterior displacement of the clavicle relative to the acromion.
• Coracoclavicular Ligament: While not directly part of the AC joint capsule, this powerful extrinsic ligament is the primary stabilizer of the AC joint and critical for clavicular stability. It consists of two distinct parts:
  • Trapezoid Ligament: The more lateral and flatter part, originating from the superior surface of the coracoid process and inserting onto the trapezoid line on the inferior surface of the lateral clavicle. It primarily resists posterior displacement and medial rotation of the clavicle.
  • Conoid Ligament: The more medial and cone-shaped part, originating from the base of the coracoid process and inserting onto the conoid tubercle on the inferior surface of the clavicle. It primarily resists superior displacement and posterior rotation of the clavicle. Together, the trapezoid and conoid ligaments prevent superior dislocation of the clavicle from the acromion and transfer forces from the scapula to the clavicle.

Functional Significance of Clavicular Ligaments

The intricate arrangement of these seven primary ligaments ensures the clavicle's pivotal role in shoulder girdle mechanics:

• Stability and Support: They provide robust static stability to both the sternoclavicular and acromioclavicular joints, preventing excessive movement and dislocation.
• Force Transmission: They facilitate the efficient transmission of forces from the upper limb through the clavicle to the axial skeleton, crucial for activities like pushing, pulling, and lifting.
• Protection of Neurovascular Structures: By maintaining the clavicle's position, these ligaments indirectly help protect the underlying neurovascular bundle (brachial plexus and subclavian vessels) in the cervico-axillary canal.
• Optimizing Shoulder Girdle Kinematics: They guide and limit the complex movements of the clavicle, which are essential for the full range of motion of the scapula and, consequently, the entire upper limb.

Clinical Relevance and Injury

Given their critical roles, these clavicular ligaments are susceptible to injury, particularly from direct trauma or falls onto the shoulder.

• AC Joint Sprains: Often referred to as "separated shoulders," these injuries involve tearing of the acromioclavicular and/or coracoclavicular ligaments, leading to varying degrees of clavicular displacement relative to the acromion.
• SC Joint Dislocations: Though less common due to the joint's inherent stability and strong ligaments, these can occur from high-impact trauma and are classified as anterior or posterior, with posterior dislocations potentially posing a risk to vital mediastinal structures.

Conclusion

The clavicle, a seemingly simple bone, is a cornerstone of shoulder function, and its stability is inextricably linked to the integrity of its ligamentous attachments. Understanding the specific roles of the anterior and posterior sternoclavicular, interclavicular, costoclavicular, acromioclavicular, and the two parts of the coracoclavicular ligaments (trapezoid and conoid) is fundamental for appreciating shoulder biomechanics, diagnosing injuries, and guiding rehabilitation strategies. These seven primary ligaments collectively form a robust system that allows for both mobility and stability, vital for the dynamic demands placed upon the human upper limb.