Saved by the bell shoulder meme

The A.C. joint isn’t the big ball and socket joint we think of when we think of our shoulder, but a smaller joint where the collarbone (clavicle) meets the highest point of the shoulder blade (acromion).

What happened to Randall Cobb and what the heck is an AC joint sprain?

Last Saturday, Green Bay Packers wide receiver Randall Cobb went down with a suspected broken collarbone. After further testing, he was diagnosed with a “minor” AC joint sprain.

An AC joint sprain (a.k.a shoulder separation) refers to injury to the Acromio-clavicular joint in our shoulder. AC injuries represent 40-50% of shoulder injuries in athletes and represent approximately 9-12% of all shoulder girdle injuries.

The A.C. joint isn’t the big ball and socket joint we think of when we think of our shoulder, but a smaller joint where the collarbone (clavicle) meets the highest point of the shoulder blade (acromion). It allows us the ability to raise the arm above the head and functions as a pivot point, acting like a strut to help with movement of the shoulder blade (scapula) resulting in a greater degree of arm rotation.

Most often it is a direct injury, which results from a force to the acromion with the shoulder and arm tucked (adducted) into the side of ones body. This results in the acromion moving downward and medially while the SC joint ligaments stabilize the clavicle (the other side of the collarbone). Think of a hockey player hitting the boards with their shoulder, or a football player falling down directly onto their shoulder. I should also note that AC injuries could also result from an indirect force like a fall on the outstretched arm or elbow.

Before we get into the types of AC injuries, I want to talk about the ligament attachments at the AC joint, as these play into the different diagnoses. As you know from previous posts, sprain refers to ligament damage. Check out the Bob Marley picture below:

The acromioclavicular ligament predominantly provides horizontal stability to the AC joint. The coracoclavicular ligament, made up of the conoid and trapezoid ligaments also provide static stabilization and serve to restrain vertical translation of the clavicle. It is the strongest stabilizer of the AC joint. 

There are 6 types of AC joint injuries. These range from “minor” to “major league”.  I will brush on Type 1-3, as the rest are pretty gnarly and are in need of surgical repair. If you’re still curious about type 4-6…google image them, or just imagine the Type 3 with major displacement of the collarbone and possible fractures.

Type I (minor)- There is a sprain of the AC ligaments with the AC and coracoclavicular ligaments intact, and therefore the AC joint is intact. There is no visible deformity, with a normal x-ray.

Type II- There is a complete tear of the AC ligaments with the coracoclavicular ligaments intact. Distal clavicle is unstable and can be displaced. On an x-ray the AC joint is disrupted.

Type III- Involves a complete tear of the AC and coracoclavicular ligaments, the AC joint is completely dislocated. Distal clavicle is unstable vertically and horizontally. Acromion is displaced inferiorly relative to the clavicle.


Grade I and II require conservative treatment. Grade III treatment can go either way. The evidence is controversial, but health care practitioners are leaning towards conservative treatment. A big study done showed that of 1172 patients, 88% who were operatively treated and 87% who were non-operatively treated had satisfactory outcomes. I’d suggest giving the conservative route a go first. The crucial factor to prevent persistent pain and disability is to adhere to a rehab program focused on strengthening the shoulder and scapular stabilizers.

If you suspect that this is something that has happened to you, here are my suggestions on how to give yourself the best possible odds of healing.

  1. Get evaluated by a health care professional
  2. Look to control pain first with things like ice, analgesics, relative rest, and immobilization with a sling as necessary.  
  3. As pain decreases, range of motion and strengthening exercises should be progressed within tolerance. Again, consult your health care practitioner.
  4. Once painless range of motion is restored, activity-specific training can be introduced with a gradual return to sports.

Here are a few good shoulder rehab exercise videos that you can add to your arsenal for rehab purposes or for general shoulder health. 

  1. Shoulder packing-
  2. (Ensure you start each exercise with your shoulder packed)
  3. D2 Extension-
  4. Scaption-
  5. Prone Horizontal Abduction-

Oh, and in the case of Randall Cobb, he’ll be fine. I imagine he falls into the Grade 1 category. No major structural damage. It may be painful, but he will be back at for week 1 for sure.