Type

It is a plane kind of the synovial joint between the lateral end of the clavicle and acromion process of the scapula. The acromioclavicular joint is situated about 2.5 cm medial to the point of the shoulder.

Articular Surfaces

These are small facets found on the lateral end of clavicle and the medial margin of the acromion process of the scapula. The articular surfaces are covered with fibrocartilage. The joint cavity is separated by an incomplete wedge- shaped articular disc.

Joint Capsule

It is thin, lax fibrous sac connected to the margins of articular surfaces.

Ligaments

These are acromioclavicular and coracoclavicular ligaments.

  • Acromioclavicular ligament: It is a fibrous band that prolongs from acromion to the clavicle. It strengthens the acromioclavicular joint superiorly.
  • Coracoclavicular ligament: It lies a little away from the joint itself but play an essential role in sustaining the integrity of the joint.
  • The coracoclavicular ligament comprises of two parts: (a) conoid and (b) trapezoid, which are united posteriorly and frequently separated by a bursa.
  • The conoid ligament is an upside down cone-shaped fibrous band. The apex is attached to the root of the coracoid procedure just lateral to the scapular notch and base is attached to the conoid tubercle on the inferior surface of the clavicle.
  • The trapezoid ligament is a horizontal fibrous band that extends from upper surface of the coracoid process to the trapezoid line on the inferior surface of lateral end of the clavicle.
  • The coracoclavicular ligament is largely responsible for suspending the weight of the scapula and upper limb from clavicle.
  • The coracoclavicular ligament is the strongest ligament of the upper limb.

Movements

The acromioclavicular joint permits the turning of acromion of scapula at the acromial end of the clavicle. These motions are associated with motions of scapula at the scapulothoracic joint/linkage.

Clinical Relevance

  • Dislocation of the acromioclavicular joint: It may take place following a severe blow on the superolateral part of the shoulder. In severe form, both acromioclavicular and coracoclavicular ligaments are torn. Consequently the shoulder separates from the clavicle and falls due to the weight of the limb. The acromioclavicular joint dislocation is frequently termed shoulder separation.