The acromioclavicular (AC) joint — along with ligaments — connects your collarbone and shoulder blade.

An injury to to the AC joint is a shoulder separation.

Types of AC joint injuries

The type of shoulder separation depends on how much you tear the AC joint or coracoclavicular (CC) ligaments that hold the joint in place.

• Type I = the AC ligament is slightly torn, but there’s no damage to the CC ligament is unharmed.
• Type II = the AC ligament is completely torn, and there’s little or no tear to the CC ligament.
• Type III = both the AC and CC ligaments are completely torn. In this case, the collarbone separates from the end of the shoulder blade.

Three more types of AC joint injury are also possible, but rare. These involve tearing of the ligaments and surrounding muscle tissue.

Shoulder separation or AC joint injury causes

Shoulder separation often happens because of a hit to:

• The tip of your shoulder.
• The top part of your shoulder.
• Your outstretched arm.

You may damage the AC joint or rotator cuff from a fall or tackle during a game.