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Getting Geeky with AC Joint Injuries

Written on September 2, 2009 at 6:39 am, by Eric Cressey

Getting Geeky with AC Joint Injuries

Lately, I’ve gotten quite a few in-person evaluations and emails relating to acromioclavicular (AC) joint issues.  As such, I figured I’d devote a newsletter to talking about why these injuries are such a pain in the butt, what to do to train around them, and how to prevent them in the first place (or address the issue once it’s in place).

First off, there is a little bit about the joint that you ought to know.  While the glenohumeral joint (ball-and-socket) is stabilized by a combination of ligamentous and muscular (rotator cuff) restraints, the AC joint doesn’t really have the benefit of muscles directly crossing the joint to stabilize it.  As such, it has to rely on ligaments almost exclusively to prevent against “shifting.”


As you can imagine, then, a traumatic injury or a significant dysfunction that affects clavicle positioning can easily make that joint chronically hypermobile.  This is why many significant traumatic injuries may require surgery.  While almost all Grade 4-6 separations are treated surgically, Grades 1-2 separations are generally left alone to heal – with Grade 3 surgeries going in either direction.

In many cases, you’ll actually see a “piano key sign,” which occurs when the separation allows the clavicle to ride up higher relative to the acromion.  Here’s one I saw last year that was completely asymptomatic after conservative treatment.  It won’t win him any beauty contests, and it may become arthritic way down the road, but for now, it’s no problem.


Now that I’ve grossed you out, let’s talk about how an AC joint gets injured.  First, we’ve got traumatic (contact) injuries, and we can also see it in people who bench like this:

Actually, that’s probably a fractured sternum, but you can probably get the takeaway point: don’t bounce the bar off your chest, you weenie.  But I digress…

Insidious (gradual) onset injuries occur just as frequently, and even moreso in a lifting population.  Most of the insidious onset AC joint problems I’ve encountered have been individuals with glaring scapular instability.  With lower trapezius and serratus anterior weakness in combination with shortness of pec minor, the scapula anteriorly tilts and abducts (wings out) – and you’ll see that this leads to a more inferior (lower) resting posture.


In the process, the interaction between the acromion (part of the scapula) and clavicle can go a little haywire.  The acromion and clavicle can get pulled apart slightly, or the entire complex can get pulled downward a bit.  In this latter situation, you can also see thoracic outlet syndrome (several important nerves track under the clavicle) and sternoclavicular joint issues in addition to the AC joint problems we’re discussing.

As such, regardless of whether we’re dealing with a chronic or insidious onset AC joint issue, it’s imperative to implement a good scapular stabilization program focusing on lower trapezius and serratus anterior to get the acromion “back in line” with the clavicle.  Likewise, soft tissue and flexibility work for the pec minor can also help the cause tremendously.

Anecdotally, a good chunk of the insidious onset AC joint problems I’ve seen have been individuals with significant glenohumeral internal rotation deficits (GIRD).  The images below demonstrate a 34-degree GIRD on the right side.


It isn’t hard to understand why, either; if you lack internal rotation, you’ll substitute scapular anterior tilt and abduction as a compensation pattern – whether you’re lifting heavy stuff or just reaching for something.  And, as I discussed in the paragraph above, a scapular dyskinesis can definitely have a negative effect on the AC joint.

Lastly, you can’t ever overlook the role of thoracic spine mobility.  If your thoracic spine doesn’t move, you’ll get hypermobile at the scapulae as a compensation – and we already know that’s not good.  And, as Bill Hartman discussed previously, simply mobilizing the thoracic spine can actually improve glenohumeral rotation range-of-motion, particularly in internal rotation.  Inside-Out is a fantastic resource in this regard – and is on sale this week, conveniently!

So, as you can see, everything is interconnected!  In part 2 of this series, I’ll discuss training modifications to work around acromioclavicular joint problems and progress back to more “normal” training programs.

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10 Responses to “Getting Geeky with AC Joint Injuries”

  1. BD Says:

    Can you give any info on a sternoclavicular joint problem? I’m a high school strength/conditioning coach and I have an athlete who has developed some sc joint instability. It pops sometimes when doing backward shrug rotations, and at random times with arm movements generally when extending/externally rotating. He says there is mostly constant pain (low-grade, ache) but not severe and there is noticeable inflammation on the right sc joint. What would you suggest for treatment?
    PS – I have both Inside/Out and MM and am looking forward to the new product!
    Thank you, much appreciated!

  2. Hale Says:

    I can attest to the fact that increasing internal rotation works wonders. Great article.

  3. Bob Parr Says:

    About 10 years ago, I remember meeting my nephew’s friend from school, about 12 or 13 years old. The front of this kid’s right shoulder had a this huge bulge that looked like he had had a baseball surgically implanted under the skin! (Much worse your photo.) He said it had gradually developed since he’d started playing baseball – and it didn’t really hurt. Now, years later, I know what it was!

  4. Eric Beard Says:

    Love the post Eric. I have sprained my AC ligament on each shoulder. Not fun. If anyone is looking for a good free video on rotater cuff training, I have one on http://athleticshoulder.com . Simple approach can increase rotater cuff activation 20-30%.

    Thank you again for the content Eric. You area great resource.

    Eric Beard

  5. Jeff Says:

    Do have any insight . My operating physician and 2nd opinion just give me the give it time and it should improve. I went in for a decompression surgery and mumford(although I did not know I was getting mumford) I came out with a big bump on my shoulder.(can see through my tshirts easily). I inquired about it and had to do extensive research to figure out why. I have not been able to find anywhere as this being a common complication. The only think I could think is that the ac ligament must have been severed during surgery. Its been 8 weeks post op and I don’t think this thing is going away. What should I do? I feel like I am in the twilight zone with the physicians like they don’t see this big problem or assume responsibility or even explain why it is there. The lack of response is probably causing me as much depression and irritation as the deformity.

  6. Eric Cressey Says:


    Hard to say for sure without seeing it. I’d encourage you to get a second opinion from another doctor.

  7. Thomas Says:

    Hi Eric,
    Great information on AC problems and traing (part 2 about AC). I can relate a lot to the possible causes of problem, as I sit all days in front of a pc and also having an unflexible thoracic spine. Forward rotated shoulders can also give impingement problems which was the diagnosis from the fist physiotherapist I went to but the second one pointed at AC joint injuri which makes more sense (could be both). X-ray has shown some sign of AC arthrithis and my question is if your articles apply also when arthrites is diagnosed or is it only related to low grade separations? (Or is maybe a low grade separation a possible reason for the Arthritis?)


  8. Eric Cressey Says:


    The majority of this info would also apply to AC arthritis (distal clavicle osteolysis). Remember that the focus should be on how you move, not just what the imaging says. Clean that up and go from there!

  9. Andrew Says:

    Hi Eric.

    Thank you for writing these articles. It helps to get all the information you can. I live in the Canadian Arctic where we dont have a full time physio (also takes about a year to get an appointment) and we have a terrible chiro. He wouldnt give me exercises to help with ac problems bc I canacelled my last ultrasound session (which was $100).

    Anywho. I am hoping you will be able to help me out. I hurt my ac pushing out one too many dips. I have taken nearly six weeks off and can finally do pushups again. But when I try dips (a favorite exercise that I used to pair with pullups) it still hurts, alot.

    I want to keep training and am wondering if you have ac specific rehab exercises?

    I hope to hear form you!

    Thank you!!


  10. Eric Cressey Says:


    Everyone is a bit different in this regard.  Feel free to email me if you’re interested in online consulting and we’ll see what we can do.

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