Kinematics of the Sternoclavicular (SC) Joint

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Kinematics of the Sternoclavicular (SC) Joint

The kinematics of the clavicle exhibit three-dimensional motion with full degrees of freedom, making it an essential component in upper limb movement. Each degree of freedom aligns with one of the three cardinal planes:

  • Sagittal plane
  • Frontal plane
  • Transverse plane

The primary function of these movements is to optimally position the scapula, ensuring proper alignment of the glenohumeral (GH) joint. Notably, every functional movement of the GH joint necessitates concurrent motion at the SC joint.

When lifting the arm above the head, the clavicle undergoes a complex combination of rotational movements across all three degrees of freedom to facilitate efficient shoulder function.

Elevation and Depression

  • Clavicular elevation and depression occur along an anteroposterior axis, primarily within the frontal plane.
  • The clavicle can elevate up to ~45° and depress up to ~10°.
  • These vertical movements are closely linked to scapular motion, forming a coordinated movement pattern.

Arthrokinematics of Elevation and Depression

  • Elevation: The convex medial clavicle rolls superiorly while gliding inferiorly along the concave sternal facet.
  • Depression: The convex medial clavicle rolls inferiorly while gliding superiorly.

During clavicular elevation, the costoclavicular ligament (CCL) becomes taut, preventing excessive upward displacement and stabilizing the SC joint. Conversely, during depression, the interclavicular ligament and superior portion of the joint capsule become stretched, limiting downward motion.

Protraction and Retraction

  • Clavicular protraction and retraction occur around a vertical axis, primarily within the transverse plane.
  • The clavicle can protract and retract up to ~15–30°.
  • These motions are functionally linked to scapular protraction and retraction.

Arthrokinematics of Protraction and Retraction

  • Retraction: The concave medial clavicle rolls and glides posteriorly along the convex sternal facet.
    • The anterior costoclavicular ligament and anterior joint capsule fibers limit excessive retraction.
  • Protraction: The concave medial clavicle rolls and glides anteriorly along the convex sternal facet.
    • The posterior costoclavicular ligament, posterior capsule, and scapular retractors (e.g., trapezius, rhomboids) limit excessive protraction.

Maximal protraction occurs when reaching forward, such as in pushing or throwing motions.

Overall Functional Importance

The SC joint’s mobility allows optimal scapular positioning, ensuring efficient upper limb mechanics. Dysfunction in SC joint mobility may impair shoulder motion, affecting arm elevation, protraction, and retraction.

Understanding SC joint kinematics is essential for diagnosing movement disorders, preventing clavicular injuries, and optimizing rehabilitation strategies for shoulder dysfunctions.