The shoulder region is frequently called the shoulder complex because of its numerous muscles and joints which work together to allow for normal functional shoulder movements. The joints of the shoulder consist of the ball and socket joint (glenohumeral joint), the scapulothoracic joint (the shoulder blade and its relationship to the thoracic rib-cage), the sternoclavicular (SC) joint (the only connection of the shoulder to the axial skeleton), and the acromioclavicular (AC) joint. Decreased motion at any four of these joints affects the ability of the shoulder to properly move, which places more emphasis on other joints to compensate, and/or changes the movement patterns and muscle activations within the shoulder region, leading towards potential injury and pain. This blog briefly discusses the acromioclavicular (AC) joint, its importance to shoulder mobility, and the mechanisms of injury to the joint along with rehabilitation points of discussion.
The acromioclavicular (AC) joint is the joint between the acromion (tip of the shoulder blade) and the clavicle (collar bone). As the arm raises during functional activities, movement of the clavicle and the shoulder blade are important to allow for full shoulder mobility. If you place your opposite hand on your collar bone and raise up your arm, one can feel the amount of rotation which occurs within the clavicle during arm elevation. Likewise, if you look into the mirror sideways and raise your arm forward, you can see how your shoulder blade rotates up, retracts, and tilts back slightly as your arm reaches towards the ceiling. These movements are vital to allow the upper arm (and the ball in the socket) to freely move within the shoulder socket without impinging the rotator cuff or placing undue stress on the other shoulder structures. Ligaments spanning across the AC joint provide horizontal stability, while other ligaments attaching from the clavicle to the shoulder blade provide more supero-inferior stability of the region (see figure).
There are several ways to injure the AC joint. Commonly, injury occurs from a fall onto outstretched hands, a side-ways blow to the shoulder from a fall with your arm by your side, a motor vehicle accident where the across-chest seatbelt (which crosses over the collar bone) locks up, while lifting heavy weights on the butter fly machine at the gym, or from a football player blocking a tackle by hitting with the top of his shoulder. These injuries can result in the AC joint being stretched too far and creating minor ligamentous tears or, in more severe cases, a full thickness tear of the ligaments that hold this joint together. Depending on the grade of injury, there may be a visible step-deformity where the clavicle appears higher than the acromial attachment point.
There are various grades of injury to the AC joint, depending on the amount of injury to the ligamentous structures and the direction of trauma which occurs to the joint. An acute injury will usually present with local swelling and superior shoulder pain, along with moderate/severe pain with any shoulder movement. Chronic injuries of the AC joint, an injury which has never fully resolved, can manifest as pain radiating up the neck or upper trapezius region secondary to common nerve innervation of the AC joint and that region. The injury will also affect how the clavicle moves on the sternum at the SC joint, possibly causing pain in the center of the chest. Pain will occur with raising the arm up overhead, moving the arms into horizontal abduction (such as a fly), bringing the arm across the body, and sleeping on the affected shoulder.
Your physical therapist is trained at correctly evaluating the AC joint and determining the extent of injury to the surrounding ligamentous and muscular structures in the area. Early identification of AC joint injuries will allow your therapist to determine the best course of treatment (i.e. referral to an orthopedist for further consultation if severe injury is suspected, short-duration immobilization or taping, etc), and start you on an individualized treatment plan for improving your function and getting you back towards normal activities. Conservative treatment early-on includes treatment modalities to decrease the joint inflammation (ice, modalities, relative rest/immobilization, activity modification), cross-friction mobilization of the injured ligaments to promote appropriate healing of the ligamentous tears, progressive shoulder range of motion exercises, functional re-strengthening of the shoulder and scapular musculature, and postural re-training. As your motion, pain, ligamentous stability, and surrounding strength improves, further loading of the healing ligaments occurs through functional re-training, and physical therapy will focus on getting you back towards normal activities.
If you are experiencing pain in your shoulder, contact your physical therapist today. He/she will help determine the source of your symptoms, as well as any other underlying issues which may be contributing to your problem. They are highly skilled at not only getting you back towards your activities, but also help you prevent future problems through promotion of self-management and long-term general health. Shoulder pain is a common complaint in the general population, but does not have to become chronic, and your physical therapist will help you get on the right path of recovery.