Acromioclavicular joint
Updates to Article Attributes
The acromioclavicular (AC) joint (ACJ) is a plane synovial joint of the pectoral girdle.
Gross anatomy
The acromioclavicular joint is between the small facet of the convex distal clavicle and flat medial acromion. The articular surfaces are lined with fibrocartilage (like the sternoclavicular joint, it is an atypical synovial joint). A fibrocartilaginous wedge-shaped articular disc separates the two articular surfaces, but its function is unknown 2,6.
A weak, synovium-lined joint capsule is attached to the articular margins and is reinforced superiorly by blending fibres of the trapezius muscle 6.
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
stabliserstabiliser 2,5 - 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 ACacromioclavicular joint. This means that a fall onto an outstretched hand or elbow can spare the AC jointACJ (but fracture the mid-shaft of the clavicle) while falls onto the shoulder itself may dislocate the AC jointACJ by forcing the acromion to sublux under the clavicle and tear the coracoclavicular ligament 7.
BloodArterial supply
-
arterial supply:thoraco-acromialthoracoacromial arteries 6
Innervation
- axillary, suprascapular and lateral pectoral nerves 2,6
Variant anatomy
Related pathology
-<p>The <strong>acromioclavicular (AC) joint </strong>is a plane synovial 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). A fibrocartilaginous wedge-shaped articular disc separates the two articular surfaces, but its function is unknown <sup>2,6</sup>. </p><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>- +<p>The <strong>acromioclavicular joint (ACJ) </strong>is a plane synovial 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). A fibrocartilaginous wedge-shaped articular disc separates the two articular surfaces, but its function is unknown <sup>2,6</sup>. </p><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>
-<a href="/articles/coracoclavicular-ligament">coracoclavicular ligament</a>: main stabliser <sup>2,5</sup>- +<a href="/articles/coracoclavicular-ligament">coracoclavicular ligament</a>: main stabiliser <sup>2,5</sup>
-</ul><p>Dynamic stabilisation is also provided by the <a href="/articles/deltoid-muscle">deltoid</a> and <a href="/articles/trapezius-muscle">trapezius muscles</a>, with the superior acromioclavicular ligament blending with these muscles' aponeuroses. </p><p>Forces transmitted from the upper limb to the glenoid are transmitted to the clavicle via the trapezoid ligament, largely bypassing the AC joint. This means that a fall onto an outstretched hand or elbow can spare the AC joint (but fracture the mid-shaft of the clavicle) while falls onto the shoulder itself may dislocate the AC joint by forcing the acromion to sublux under the clavicle and tear the coracoclavicular ligament <sup>7</sup>.</p><h4>Blood supply</h4><ul><li>-<strong>arterial supply:</strong> <a href="/articles/suprascapular-artery">suprascapular</a> and <a href="/articles/thoraco-acromial-artery">thoraco-acromial arteries</a> <sup>6</sup>- +</ul><p>Dynamic stabilisation is also provided by the <a href="/articles/deltoid-muscle">deltoid</a> and <a href="/articles/trapezius-muscle">trapezius muscles</a>, with the superior acromioclavicular ligament blending with these muscles' aponeuroses. </p><p>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 <sup>7</sup>.</p><h4>Arterial supply</h4><ul><li>
- +<a href="/articles/suprascapular-artery">suprascapular</a> and <a href="/articles/thoraco-acromial-artery">thoracoacromial arteries</a> <sup>6</sup>
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