Many diseases, conditions, and injuries are described using grades, stages, or types. Usually these classifications or groups represent a range from mild to severe. They are often numbered 1, 2, 3, 4 or I, II, III, IV. Sometimes one problem is even classified using more than one method.
Acromioclavicular (AC) separation was first classified as I, II, and III in the early 1960s. Three additional grades (IV, V, VI) were added in 1984. Type I is a sprain of the AC ligaments. The ligament isn’t torn and repair isn’t needed. Nothing else around the joint is damaged.
The AC ligament is torn with a Type II injury. The muscles around the joint aren’t injured. Type III occurs as a result of a severe trauma to the joint. Type III is equal to a dislocation of the joint. An X-ray of this type will show one clavicle (collar bone) lifted up above the other clavicle. The clavicle is no longer level with the acromion bone on the other side of the joint.
Types IV, V, and VI are all grades of Type III. Each type is a little more serious than the number before it. Type IV is also a dislocation of the AC joint. Instead of being displaced (pushed) up, the clavicle is moved backward or pushed into the trapezius muscle. Type V is the worst form of Type III injury.