Acromioclavicular Joint

Acromioclavicular Joint / 3D image and Description

Acromioclavicular Joint / 3D image and Description

Acromioclavicular Joint / Motion

The acromioclavicular joint is classified as a multiaxial synovial plane joint but it is more helpful to think of it as a pivot point. As the name suggests it is the articulation of the acromion of the scapula with the clavicle. It allows you to raise your arms above your head i.e. scapular elevation as well as scapular depression, protraction, retraction, upward and downward rotation.

Stability

The fibrous capsule of the acromioclavicular joint contributes to the joints stability.

The three key ligaments which are important in stabilizing the acromioclavicular joint include:

  • Acromioclavicular ligament (superiorly)
  • Coracoclavicular ligament (composed of anterior trapezoid and posterior conoid ligaments)
  • Coracoacromial ligament

The muscles crossing the joint are also involved in stabilizing the acromioclavicular joint.

Muscles

Elevation:

  • Trapezius
  • Levator scapulae

Depression:

  • Trapezius
  • Pectoralis minor

Retraction (towards midline):

  • Trapezius
  • Rhomboids

Protraction (away from midline):

  • Pectoralis minor
  • Serratus anterior

 

Upward rotation (abduction 90-degree)

  • Trapezius
  • Serratus anterior

Downward rotation:

  • Pectoralis minor
Clinical

Separated shoulder. A dislocation injury distinct from shoulder dislocation which refers to dislocation at the glenohumeral joint. Common in persons who participate in collision sports such as rugby, ice hockey etc.

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