The term shoulder separation refers to an injury of the acromioclavicular (AC) joint. This is where the collar bone meets the shoulder blade (scapula) above the shoulder joint.

Usually what happens is the collarbone is pulled up while the acromion, a bony projection on the scapula, is forced downward. The capsule of the AC joint is torn. If the ligaments around the joint are not torn, the AC joint is subluxed (partial dislocation). If the supporting structures are torn, the joint is dislocated.

A shoulder separation occurs when you tear the ligaments that hold your collarbone (clavicle) to the joint where it meets the shoulder blade. Your collarbone may move out of its normal place and push up the skin on the top of your shoulder. Other common terms for shoulder separation is AC separation or AC sprain.

Shoulder separations, or sprains, are graded I, II, or III, depending on how far the collarbone is separated from the shoulder. A grade I sprain has tenderness but no actual separation. A grade II sprain has slight separation of the clavicle from the shoulder, and grade III has a greater separation. With a grade III separation, the patient may have a bump caused by the separated joint. The bump may be seen or felt at the tip of the shoulder.