Clavicle Movement: Articulations, Functions, and Clinical Relevance

How does the clavicle move?

The clavicle, or collarbone, is a unique long bone that acts as a crucial strut for the shoulder girdle, enabling a wide range of upper limb movements through its articulations with the sternum and scapula, undergoing elevation, depression, protraction, retraction, and rotation.

Introduction to the Clavicle's Role

The clavicle is the only bony attachment between the upper limb and the axial skeleton. Its distinctive S-shape provides both strength and flexibility, acting as a critical spacer that keeps the scapula and humerus positioned laterally, away from the trunk. This anatomical positioning is fundamental for maximizing the range of motion of the arm and shoulder. Far from being a static bone, the clavicle is highly dynamic, undergoing complex movements that are integral to the proper function of the entire shoulder complex.

Key Articulations of the Clavicle

The clavicle participates in two primary synovial joints, each contributing uniquely to its mobility:

• Sternoclavicular (SC) Joint: This is the articulation between the medial end of the clavicle and the manubrium of the sternum, along with the first costal cartilage.

  • Type: Classified as a saddle joint, it allows for significant movement in multiple planes, making it the most mobile joint of the shoulder girdle.
  • Stability: Despite its mobility, it is remarkably stable due to strong ligaments (anterior and posterior sternoclavicular, interclavicular, and costoclavicular ligaments) and an intra-articular disc that acts as a shock absorber.
  • Movements: It permits elevation/depression, protraction/retraction, and rotation of the clavicle.

• Acromioclavicular (AC) Joint: This is the articulation between the lateral end of the clavicle and the acromion process of the scapula.

  • Type: Classified as a plane (gliding) joint, it allows for more subtle movements.
  • Stability: Its stability is primarily provided by the acromioclavicular ligaments and, more importantly, the very strong coracoclavicular ligaments (conoid and trapezoid ligaments), which connect the clavicle to the coracoid process of the scapula. These ligaments are crucial for preventing superior displacement of the clavicle relative to the acromion.
  • Movements: It allows for gliding and rotational movements of the scapula on the clavicle, which are critical for maintaining the scapula's position relative to the thoracic cage during arm movements.

Primary Movements of the Clavicle

The movements of the clavicle are always coupled with, and facilitate, the movements of the scapula. They are often described in relation to the SC joint:

• Elevation: The clavicle moves superiorly (upwards) at the sternoclavicular joint. This motion accompanies scapular elevation (e.g., shrugging the shoulders). The medial end of the clavicle glides inferiorly, while the lateral end moves superiorly.
• Depression: The clavicle moves inferiorly (downwards) at the sternoclavicular joint. This accompanies scapular depression (e.g., pressing shoulders down). The medial end glides superiorly, and the lateral end moves inferiorly.
• Protraction: The clavicle moves anteriorly (forwards) at the sternoclavicular joint. This accompanies scapular protraction (e.g., reaching forward). The medial end glides anteriorly, and the lateral end moves anteriorly.
• Retraction: The clavicle moves posteriorly (backwards) at the sternoclavicular joint. This accompanies scapular retraction (e.g., pulling the shoulder blades together). The medial end glides posteriorly, and the lateral end moves posteriorly.
• Rotation: This is a crucial, often overlooked, movement. The clavicle rotates along its longitudinal axis.
  • Posterior Rotation: Occurs as the arm elevates above 90 degrees of abduction or flexion. The anterior surface of the clavicle rotates posteriorly (upwards), allowing the conoid tubercle to clear the first rib. This motion significantly contributes to achieving full overhead range of motion.
  • Anterior Rotation: Occurs as the arm returns from an elevated position. The anterior surface of the clavicle rotates anteriorly (downwards).

Muscles Influencing Clavicular Movement

While no muscles insert exclusively on the clavicle to produce its movements, several muscles directly or indirectly influence its motion by acting on the sternum, scapula, or humerus:

• Sternocleidomastoid: Its clavicular head can elevate the clavicle.
• Subclavius: Depresses the clavicle and stabilizes the SC joint.
• Pectoralis Major (Clavicular Head): Can depress and protract the clavicle.
• Trapezius (Upper Fibers): Elevates the clavicle and scapula.
• Trapezius (Middle Fibers): Retracts the clavicle and scapula.
• Trapezius (Lower Fibers): Depresses and rotates the scapula, indirectly influencing clavicular position.
• Serratus Anterior: Protracts and upwardly rotates the scapula, which translates to clavicular protraction and rotation.
• Levator Scapulae: Elevates the scapula, leading to clavicular elevation.
• Rhomboids: Retract and downwardly rotate the scapula, influencing clavicular retraction.

Functional Significance of Clavicular Movement

The intricate movements of the clavicle are not merely incidental; they are fundamental for optimal upper limb function:

• Maximizing Range of Motion: Clavicular movements, particularly posterior rotation, are essential for achieving full overhead elevation of the arm (flexion and abduction). Without this motion, overhead reach would be severely limited.
• Stability and Force Transmission: The clavicle acts as a rigid strut, keeping the scapula and humerus away from the trunk, allowing for greater freedom of movement. It also efficiently transmits forces from the upper limb to the axial skeleton, such as during pushing or pulling activities.
• Protection: It provides a bony protection for the neurovascular bundle (brachial plexus and subclavian vessels) passing beneath it.
• Scapulohumeral Rhythm: Clavicular motion is a key component of scapulohumeral rhythm, the coordinated movement of the scapula and humerus during arm elevation. Proper clavicular movement ensures that the glenoid fossa (shoulder socket) is optimally positioned to receive the humeral head, preventing impingement and maximizing leverage for the rotator cuff muscles.

Clinical Relevance and Common Issues

Given its exposed position and critical role, the clavicle is susceptible to injury and dysfunction:

• Clavicle Fractures: These are among the most common fractures, often resulting from falls onto the shoulder or outstretched arm.
• AC Joint Separations: Injuries to the ligaments supporting the AC joint (especially the coracoclavicular ligaments) can lead to a "separated shoulder," where the clavicle appears prominent.
• SC Joint Dislocations: While less common due to strong ligamentous support, these can occur, often requiring significant force.
• Dysfunctional Movement Patterns: Restricted clavicular mobility due to injury, posture, or muscle imbalances can significantly impair overall shoulder function, leading to pain, reduced range of motion, and compensatory movements.

Conclusion

The clavicle, often perceived as a simple collarbone, is a highly dynamic and indispensable component of the shoulder girdle. Its complex movements at the sternoclavicular and acromioclavicular joints—elevation, depression, protraction, retraction, and crucial rotation—are meticulously coordinated to facilitate the vast range of motion of the upper limb, transmit forces, and provide structural integrity. Understanding how the clavicle moves is essential for comprehending shoulder biomechanics, optimizing athletic performance, and effectively rehabilitating shoulder injuries.