Overview
A shoulder separation is not truly an injury to the shoulder joint. The injury actually involves the acromioclavicular joint (also called the AC joint). The AC joint is where the collarbone (clavicle) meets the highest point of the shoulder blade (acromion). If the force is severe enough, the ligaments attaching to the underside of the clavicle are torn. This causes the “separation” of the collarbone and wingbone. The wingbone actually moves downward from the weight of the arm.
Causes
Injury (most commonly, a fall directly onto the shoulder
Symptoms
Bump or bulge above the shoulder
Pain at the end of the collar bone
Swelling
Pain when moving the shoulder, especially when trying to raise the arms above shoulder height
Diagnosis
Physical examination
X-rays
Treatment
Rest
Application of ice
Immobilization
Anti-inflammatory medications
Physical therapy
Ultrasound therapy
Surgery
Source: http://orthoinfo.aaos.org/topic.cfm?topic=a00033 http://www.sportsinjuryclinic.net/sport-injuries/shoulder-pain/ac-joint-sprain