It’s entirely possible. When the injury is severe enough, not only does the AC joint separate, but other damage can occur in and around the joint, too. AC joint refers to the acromioclavicular junction. Sometimes this is referred to as a shoulder separation or AC joint dislocation.
The AC joint is located along the front of the shoulder where the clavicle (collar bone) meets the acromion (the bone that comes across the top of the shoulder from off the shoulder blade). AC joint separation or dislocation is the result of direct trauma (usually from a fall) on the shoulder or arm when it is next to the body. Falling on an outstretched hand or elbow can also cause the same injury. The mechanism is more indirect as force through the hand or elbow transfers to the shoulder. With enough force, the head of the humerus is pushed upward — right into the acromion.
The majority of injuries occur during activities such as bike accidents, skiing or snowboarding, and other types of falls. Other activities leading to AC joint dislocation include soccer, motorcycle accidents, ice hockey, judo accidents, or horseback riding injuries.
It’s not uncommon for the associated injuries to be missed at the time of the diagnosis for AC joint separation. The patient’s shoulder is painful and range-of-motion is limited. So clinical testing is also limited. Without a full arthroscopic exam, no one knows there are other problems. But once the AC joint has been treated, the patient with continued shoulder pain may need a second look.
Anyone with a high grade AC joint injury who continues to experience pain and loss of motion after surgical treatment should be further evaluated. The surgeon will look for the presence of other intra-articular injuries, especially labral tears, rotator cuff tears, and fractures. Post-operative MRIs using an intra-articular contrast dye give the best information.