Acromioclavicular joints or AC joints are easily injured and susceptible to secondary issues such as arthritis, laxity and shoulder pain. Often referred to as a “separated shoulder”, an AC separation takes place when the ligaments that stabilize the collar bone (clavicle) and the shoulder blade (scapula) become damaged.
The acromioclavicular joint is the connection between the lateral end of the clavicle (collar bone) and the lateral end of the scapula (shoulder blade). This bony section of the scapula is referred to as the acromion. The AC joint creates a stabilizing union between the front and back of the shoulder girdle. It’s important to note that when healthy this joint has ample mobility, which allows for significant motion of the shoulder. The AC joint forms an important archway that protects the rotator cuff and shoulder joint below.
Stabilized by a joint capsule, the acromioclavicular joint encompasses the ends of the clavicle and acromion along with several ligaments. Because ligaments attach bones to bones, when the AC joint ligaments, located under the clavicle, are damaged with a separated shoulder they create a downward pull to the clavicle and AC joint.
What Causes a Sprained AC Joint?
Falls are often the cause of separated shoulder injuries. The AC joint is not overly stable and its location makes it quite vulnerable to injury.
The two most common reasons for injury are:
- Landing on the lateral part of the shoulder forcing the shoulder downward.
- Landing on an outstretched arm or elbow, which forces the shoulder joint upward in into the undersurface of the acromioclavicular joint.
With either of these, the AC joint capsule is disrupted and the stabilizing ligaments are compromised. The grade or degree of separation depends upon the level of damage to both the ligaments and capsule.
Grades of Separation
Shoulder Separation, Grade I
A mild disruption of the AC joint capsule resulting in minimal instability of the joint.
Shoulder Separation, Grade II
A moderate disruption of both the AC joint capsule and stabilizing ligaments resulting in moderate instability of the AC joint. Partial tears of both the AC joint capsule and the stabilizing ligaments are present. You’ll notice moderate laxity of the AC joint with a visible elevation of the outer clavicle when holding a weighted object with the injured arm at your side. The amount of elevation with a Grade II AC sprain is typically ½ to 1 inch when compared bilaterally.
Shoulder Separation, Grade III
A significant disruption of both the AC joint capsule and stabilizing ligaments resulting in significant instability of the AC joint. Complete tears of the AC joint capsule and possibly complete tears of at least some of the stabilizing ligaments are present. There is visible laxity of your acromioclavicular joint with a visible elevation of the outer clavicle with the injured arm resting at the side of your body. When your arm is reached across your body towards the back of the other shoulder, the abnormal lateral clavicle elevation increases.
AC Sprain Grade IV to VI’s are much more severe and are based on the hyper-mobility of the acromioclavicular joint.
Signs & Symptoms You Have an AC Joint Sprain
- Pain and localized swelling on the top of the shoulder at the acromioclavicular joint.
- Swelling and or bruising may be present on the top of the shoulder.
- An obvious bony lump on the top of the shoulder, which is the end of the displaced collarbone. The higher the grade of shoulder separation, the larger the elevation of the outer tip of the clavicle.
- Limited range of motion (ROM) and pain with any lifting of the arm.
- With a grade II and grade III AC joint sprains, a “clicking” or shifting can be felt in the AC joint with shoulder motion.
- With active motion (when you move your arm) or passive motion (when someone else moves your arm) of the injured arm horizontally across the body towards the back of the other shoulder, significant AC pain will occur.
Treating a Separated Shoulder
- Ice the top and front of your shoulder with the elbow flexed to approximately 90 degrees and supported.
- Using an arm sling is helpful if having pain or clicking with walking. This helps to support the weight of your arm while restricting motion.
- Once a fracture is ruled out, early motion is started to reduce stiffness and pain. No horizontal adduction motion (horizontal movement of the arm across the midline of the body) is allowed until you have full pain-free motion.
- Easy pendulum swings to help regain motion of the shoulder.
- A shoulder strengthening program can be started early with a Grade I & II sprain as tolerable. Starting with rotational motions and progressing with overhead lifts as tolerable. Continue to avoid horizontal adduction as long as possible.
Questions a Pro Athlete Would Ask To Heal Quickly and Safely
As always, my goal is to help you get back in the game as quickly as possible while ensuring you can return safely. Ask the following questions—the same ones a smart professional athlete with a Separated Shoulder would ask his sports medicine specialist, so you too can recover quickly and safely:
- What grade is my shoulder separation?
- Do you think I can manage this AC joint sprain with rehab without needing surgery?
- Do I need any special padding, taping or altering of my sports equipment to minimize the chances to reinjuring this acromioclavicular joint?
- What specific lifts, activities and motions do I need to avoid to allow my AC joint separation to heal quickly?
Sports Medicine Tips For an AC Joint Separation
- Little Need for a Knife – AC joint surgeries are not overly common unless the instability is severe or the limitations are complex.
- Sleep Well? – Don’t plan on sleeping on the injured shoulder for a while. I severely separated my right AC joint in a winter mountain bike race on a ski slalom course (I know, it’s not the smartest thing that I’ve ever done but it sure was a lot of fun…until I crashed!) in Vermont in 1994 and I still can’t sleep on that side!
- Posture is a Factor – Any position, any movement or any activity that rounds your shoulders will worsen your pain. It’s that simple.
- Ice, Motion, Ice – Ice it, move it in pain-free directions and then ice it again. Simple formula with fast results.
- Upper Back Squeezes – While sitting or standing tall, relax your arms while you squeeze your shoulder blades (scapula) together while exhaling hard. Hold for 2 seconds and repeat 10 times. Do this drill as much as possible to stretch out your chest muscles, strengthen your shoulder stabilizing muscle and, very importantly, decompress your AC joint.