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The acromioclavicular joint is a plane type synovial joint. It is located where the
lateral end of the clavicle articulates with the acromion of the scapula. The joint can be
palpated during a shoulder examination; 2-3cm medially from the ‘tip’ of the shoulder
(formed by the end of the acromion).
In this article, we shall look at the anatomy of the acromioclavicular joint its
articulation, ligaments, neurovascular supply, and any clinical correlations.
Structures of the Acromioclavicular Joint
Articulating Surfaces
© 2015-2016 TeachMeAnatomy.com
Fig 1.0 Articulating surfaces of the AC joint.
The acromioclavicular joint consists of an articulation between the lateral end of the
clavicle and the acromion of the scapula. It has two atypical features:
The articular surfaces of the joint are lined with fibrocartilage (as opposed to hyaline
cartilage).
The joint cavity is partially divided by an articular disc a wedge of fibrocartilage
suspended from the upper part of the capsule.
Joint Capsule
The joint capsule consists of a loose fibrous layer which encloses the two articular
surfaces. It also gives rise to the articular disc. The posterior aspect of the joint
capsule is reinforced by fibres from the trapezius muscle.
As would be expected of a synovial joint, joint capsule is lined internally by a synovial
membrane. This secretes synovial fluid into the cavity of the joint.
Ligaments
There are three major ligaments present in the acromioclavicular joint:
Acromioclavicular runs horizontally from the acromion to the lateral clavicle. It
covers the joint capsule, reinforcing its superior aspect.
Conoid runs vertically from the coracoid process of the scapula to the conoid
tubercle of the clavicle.
Trapezoid runs from the coracoid process of the scapula to the trapezoid line of
the clavicle.
Collectively, the conoid and trapezoid ligaments are known as the coracoclavicular
ligament. It is a very strong structure, effectively suspending the weight of the upper
limb from the clavicle.
By Jay F. Cox (2006) [CC-BY-2.5], via Wikimedia Commons
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