Acromioclavicular Sprain Anatomy
To better understand AC separation, it helps to understand the anatomy of the shoulder joint.
The shoulder joint allows motion between two major bones: the humerus and the scapula. The shoulder joint is a ball and socket joint. A depression in the scapula, called the glenoid, provides the socket for the head of the humerus. Ligaments and muscles hold the joint together as the bones move.
The clavicle, or collar bone, connects to the scapula at the acromion, which is a bony projection off the scapula. The acromioclavicular ligaments normally surround and secure this joint.
There are two main ligaments supporting the AC joint. One or more can be sprained (torn) during this injury.
The two main ligaments supporting the AC joint include:
- Acromioclavicular ligament
- Fastens the acromion, a portion of the scapula, to the clavicle
- Coracoclavicular ligament:
- Fastens the coracoid process, a portion of the scapula, to the clavicle
- Composed of the conoid ligament and the trapezoid ligament
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- Jerosch J, Filler T, Peuker E, Greig M, Siewering U. Which stabilization technique corrects anatomy best in patients with AC-separation? An experimental study. Knee Surg Sports Traumatol Arthrosc. 1999;7(6):365-72. 
- Rolla PR, Surace MF, Murena L. Arthroscopic treatment of acute acromioclavicular joint dislocation. Arthroscopy. 2004 Jul;20(6):662-8.