Home Baseball Content AC Joint Impingement vs. “Regular” Shoulder Impingement

AC Joint Impingement vs. “Regular” Shoulder Impingement

Written on July 7, 2010 at 5:32 am, by Eric Cressey

I’ve seen a few acromioclavicular (AC) joint impingement cases at our facility in the last couple of weeks and thought it’d be good to do a quick blog to talk about how different they are from “regular” (external) shoulder impingement cases.  And, it is a very important differentiation to make.

I’ve already written at length about AC joint issues in Getting Geeky with AC Joint Injuries: Part 1 and Part 2.  And, I kicked out a two-part series called The Truth About Shoulder Impingement; here are Part 1 and Part 2.

While I talk a lot about the symptoms for both, several provocative tests for these issues, and training modifications to avoid exacerbating pain under these conditions, there was one important “differential assessment that I missed.”  Mike Reinold actually taught me it as we were planning the Optimal Shoulder Performance DVD set.


Just paying close attention to (and asking about) where folks have their pain during overhead motion can tell you quite a bit.  In an external impingement – where we’re talking about the rotator cuff tendons and bursa rubbing up against the undersurface of the acromion – you’ll usually get pain as folks approach 90 degrees of abduction (arm directly out to the side).  That pain will persist as they go further overhead, and in my experience, start to die off as they get to the top.


Conversely, for those with AC joint impingement – what is essentially bone rubbing up against bone – you see a “painful arc” only at the last portion of abduction:


You can usually confirm your suspicions on this front with direct palpation of the AC joint and checking to see if folks have pain when reaching across the chest.

Much of the training modifications will be the same for these two conditions, but there are also going to be several key things that should be managed completely differently.  For instance, front squatting someone with an AC joint issue would not be a good idea due to the direct pressure of the bar on the AC joint; it would, however, be just fine for most cases of external shoulder impingement.  In another example, some serious AC joint issues are exacerbated even by just doing the end-range of a rowing motion (to much shoulder extension/horizontal abduction) – whereas even folks with full-blown rotator cuff tears can generally do rows pain-free.

Assess, don’t assume!

For more information – including loads more assessments like these – check out the Optimal Shoulder Performance DVD set.


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7 Responses to “AC Joint Impingement vs. “Regular” Shoulder Impingement”

  1. James Says:


    I’ve been diagnosed with AC joint hypermobility in both shoulders — I get a popping feeling right in the AC joint with certain motions or ranges of motion, sometimes even just the bottom end of a bench press. I’ve been proscribed from doing any vertical plane exercises (with an exception for pulldowns, as they’re more stable than pull-ups/chin-ups), and I’m very cautious about benching — floor pressing and dumbbells are my very good friends. Obviously, doing buttloads of rows is always a high priority.

    So do some of the other restrictions you mention for those who suffer from AC joint impingement apply to me as well, e.g. front squatting? I front squatted just the other day for the first time in a while and had no pain, despite having floor pressed just before that. But no pain doesn’t always mean no problem, as you’ve written many times. Same goes for the end range of the many rows I do — no pain, feels good. Any thoughts?


  2. Eric Cressey Says:

    James, I think you should be okay. Just let symptoms be your guide, and start tinkering with things if it begins to act up on you.

  3. Goi Says:

    I have pain when reaching my right hand across the chest, as well as when I put it behind my back, yet front squats cause no pain at all. Ultrasound also shows a minor supraspinatus tear. Would this be in line with an AC joint impingement?

  4. John G Says:

    Goi supraspinatus is one of the rotator cuff muscles–you’ve got yourself a minor rotator cuff tear. If you perform the supraspinatus muscle test (see here: http://ahn.mnsu.edu/athletictraining/spata/shouldermodule/supraspinatusmmt.wmv) it should be painful. Where are you getting the pain? Back of the shoulder? Top? Front?

  5. Ryan Says:

    After doing front squats one day I came out with AC joint pain. That was in March. I still feel mild point tenderness but more concerning, when I shrug my right shoulder, rotate it back, bring it down and then forward and up to normal position something “snaps” in the joint. It has been snapping less severely recently but this is July and it’s still snapping!

  6. Goi Says:

    Ryan, I tried doing that muscle test with a band instead of someone applying pressure down – no pain. When I reach my right hand across to the top of my chest and behind(eg scratching my back) I would say the pain is at the front/side of the shoulder, though it’s hard to pinpoint. Same thing when I put my right hand behind my back from underneath. Both movements are internal rotation, right? Seems like I have a problem with that.

  7. Chris Says:

    Hi eric read your articles on shoulder savers on t nation, recently done my AC joint with a grade 2 tear. Was really looking forward to a good rugby off season, unfortunately can only do leg presses (depressingly) and swiss ball ham string curls. Is there any exercises i should be doing for not only my shoulder but perhaps my posterior chain or trapezius etc that can speed recovery and strengthen my shoulder so it doesn’t happen again and my shoulder comes out stronger?

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