Acromioclavicular joint
Updates to Article Attributes
The acromioclavicular joint (ACJ) is a plane planar diarthrodial synovial joint (diarthrodial joint) of the pectoral girdle.
Gross anatomy
The acromioclavicular joint is between the small facet of the convex distal clavicle and flat medialanteromedial acromion. The articular surfaces are lined with fibrocartilage (like the sternoclavicular joint, it is an atypical synovial joint).
A fibrocartilaginous wedge-shaped articular disc, measuring between 1.5-4.0 mm 8, separates the two articular surfaces, but its function is unknown 2,6. There are three types of disc 8-11:
- complete disc (rare)
- meniscoid-like disc
- superior and inferior wedge-shaped meniscoid disc
A weak, synovium-lined joint capsule is attached to the articular margins and is reinforced superiorly by blending fibres of the trapezius muscle 6.
The acromioclavicular joint space measures 1-6 mm (females) and 1-7 mm (males), decreasing with age 12.
Movements
No muscles act directly on this joint. In turn, it permits passive movements only. Instead, the basic scapular movements of protraction/retraction, rotation and elevation/depression transmit to corresponding movements to AC joint.
Ligaments
Static stabilisation is provided by:
- coracoclavicular ligament: main stabiliser 2,5
- coracoacromial ligament
- superior and inferior acromioclavicular ligaments: reinforce the relatively weak joint capsule 5
Dynamic stabilisation is also provided by the deltoid and trapezius muscles, with the superior acromioclavicular ligament blending with these muscles' aponeuroses.
Forces transmitted from the upper limb to the glenoid are transmitted to the clavicle via the trapezoid ligament, largely bypassing the acromioclavicular joint. This means that a fall onto an outstretched hand or elbow can spare the ACJ (but fracture the mid-shaft of the clavicle) while falls onto the shoulder itself may dislocate the ACJ by forcing the acromion to sublux under the clavicle and tear the coracoclavicular ligament. 7
Arterial supply
Innervation
- axillary, suprascapular and lateral pectoral nerves 2,6
Variant anatomy
Related pathology
-<p>The <strong>acromioclavicular joint (ACJ) </strong>is a plane synovial joint (diarthrodial joint) of the <a href="/articles/pectoral-girdle">pectoral girdle</a>.</p><h4>Gross anatomy</h4><p>The acromioclavicular joint is between the small facet of the convex distal <a href="/articles/clavicle">clavicle</a> and flat medial <a href="/articles/acromion">acromion</a>. The articular surfaces are lined with fibrocartilage (like the sternoclavicular joint, it is an atypical synovial joint). </p><p>A fibrocartilaginous wedge-shaped articular disc, measuring between 1.5-4.0 mm <sup>8</sup>, separates the two articular surfaces, but its function is unknown <sup>2,6</sup>. There are three types of disc <sup>8-11</sup>:</p><ul>- +<p>The <strong>acromioclavicular joint (ACJ) </strong>is a planar diarthrodial <a href="/articles/synovial-joints">synovial joint</a> of the <a href="/articles/pectoral-girdle">pectoral girdle</a>.</p><h4>Gross anatomy</h4><p>The acromioclavicular joint is between the small facet of the convex distal <a href="/articles/clavicle">clavicle</a> and flat anteromedial <a href="/articles/acromion">acromion</a>. The articular surfaces are lined with fibrocartilage (like the sternoclavicular joint, it is an atypical synovial joint). </p><p>A fibrocartilaginous wedge-shaped articular disc, measuring between 1.5-4.0 mm <sup>8</sup>, separates the two articular surfaces, but its function is unknown <sup>2,6</sup>. There are three types of disc <sup>8-11</sup>:</p><ul>
-</ul><p>A weak, synovium-lined joint capsule is attached to the articular margins and is reinforced superiorly by blending fibres of the <a href="/articles/trapezius-muscle">trapezius muscle</a> <sup>6</sup>.</p><h5>Movements</h5><p>No muscles act directly on this joint. In turn, it permits passive movements only. Instead, the basic scapular movements of protraction/retraction, rotation and elevation/depression transmit to corresponding movements to AC joint. </p><h5>Ligaments</h5><p>Static stabilisation is provided by: </p><ul>- +</ul><p>A weak, synovium-lined joint capsule is attached to the articular margins and is reinforced superiorly by blending fibres of the <a href="/articles/trapezius-muscle">trapezius muscle</a> <sup>6</sup>.</p><p>The acromioclavicular joint space measures 1-6 mm (females) and 1-7 mm (males), decreasing with age <sup>12</sup>. </p><h5>Movements</h5><p>No muscles act directly on this joint. In turn, it permits passive movements only. Instead, the basic scapular movements of protraction/retraction, rotation and elevation/depression transmit to corresponding movements to AC joint. </p><h5>Ligaments</h5><p>Static stabilisation is provided by: </p><ul>
References changed:
- 12. Flores D, Goes P, Gómez C, Umpire D, Pathria M. Imaging of the Acromioclavicular Joint: Anatomy, Function, Pathologic Features, and Treatment. Radiographics. 2020;40(5):1355-82. <a href="https://doi.org/10.1148/rg.2020200039">doi:10.1148/rg.2020200039</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/32762593">Pubmed</a>
Tags changed:
- rg_40_5_edit