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Acromioclavicular joint

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A shoulder joint that connects the clavicle to the scapula.

Shoulder joint
Shoulder joint

Anatomy

Acromioclavicular joint is located between the acromion and clavicle

Acromioclavicular joint
Acromioclavicular joint

Type of joint

This is a gliding type of joint.

Ligaments

The ligaments that serve to support and strengthen this joint are called the capsular;

  • superior and inferior acromioclavicular;
  • articular capsule
  • articular disk; and
  • coracoclavicular (trapezoid and conoid) ligaments.
  • synovial membrane

The Articular Capsule (capsula articularis; capsular ligament)

  • The articular capsule completely surrounds the articular margins, and is strengthened above and below by the superior and inferior acromioclavicular ligaments.

The Superior Acromioclavicular Ligament (ligamentum acromioclaviculare)

  • This ligament is a quadrilateral band, covering the superior part of the articulation, and extending between the upper part of the acromial end of the clavicle and the adjoining part of the upper surface of the acromion.
  • It is composed of parallel fibers, which interlace with the aponeuroses of the Trapezius and Deltoideus; below, it is in contact with the articular disk when this is present.

The Inferior Acromioclavicular Ligament

  • This ligament is somewhat thinner than the preceding; it covers the under part of the articulation, and is attached to the adjoining surfaces of the two bones.
  • It is in relation, above, in rare cases with the articular disk; below, with the tendon of the Supraspinatus.

The Articular Disk (discus articularis)

  • The articular disk is frequently absent in this articulation.
  • When present, it generally only partially separates the articular surfaces, and occupies the upper part of the articulation.
  • More rarely, it completely divides the joint into two cavities.

The Synovial Membrane There is usually only one synovial membrane in this articulation, but when a complete articular disk is present, there are two.

Glenoid fossa of right side.
Glenoid fossa of right side.

The Coracoclavicular Ligament (ligamentum coracoclaviculare)

  • This ligament serves to connect the clavicle with the coracoid process of the scapula.
  • It does not properly belong to this articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion.
  • It consists of two fasciculi, called the trapezoid and conoid ligaments.

The Trapezoid Ligament (ligamentum trapezoideum)

  • The anterior and lateral fasciculus, is broad, thin, and quadrilateral: it is placed obliquely between the coracoid process and the clavicle.
  • It is attached, below, to the upper surface of the coracoid process; above, to the oblique ridge on the under surface of the clavicle. Its anterior border is free; its posterior border is joined with the conoid ligament, the two forming, by their junction, an angle projecting backward.

The Conoid Ligament (ligamentum conoideum)

  • The posterior and medial fasciculus, is a dense band of fibers, conical in form, with its base directed upward.
  • It is attached by its apex to a rough impression at the base of the coracoid process, medial to the trapezoid ligament; above, by its expanded base, to the coracoid tuberosity on the under surface of the clavicle, and to a line proceeding medialward from it for 1.25 cm.
  • These ligaments are in relation, in front, with the Subclavius and Deltoideus; behind, with the Trapezius.

Movements

The movements of this articulation are of two kinds:

  1. a gliding motion of the articular end of the clavicle on the acromion;
  2. rotation of the scapula forward and backward upon the clavicle. The extent of this rotation is limited by the two portions of the coracoclavicular ligament, the trapezoid limiting rotation forward, and the conoid backward.

Function

The acromioclavicular joint has important functions in the movements of the upper extremity.

Muscles

Common problems

  • A common injury to the AC joint is dislocation, often called AC separation or shoulder separation as opposed to shoulder dislocation which refers to a dislocation of the other joint in shoulder complex called glenohumeral joint.
  • Shoulder injuries are very common in contact sports.

See also


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