Shoulder Impingement: Are You getting Trapped by Your Trap?
POSTED ON 11/13/2012 IN Research BY Christopher Centeno
Should you be looking for a shoulder surgery alternative? For the last several decades, many of the patients who have been told that they have shoulder impingement have had surgery to "release" the shoulder. In many ways it's this phenomenon which led to our current hip impingement surgery craze. So what is shoulder impingement? The concept is that when the patient lifts the arm, the humerus arm bone "impinges" (read pinches) the rotator cuff muscles under the "coracoarcromial arch" (read top of shoulder where the collar bone and shoulder blade come together). This can cause small tears in the rotator cuff. What's never made sense to me (either in the shoulder or the hip), is why surgery is a good answer for this problem. Basically, the surgeon destabilizes the shoulder complex by removing very important structures at the top of the shoulder (that coracoacromial arch-see the red ligament that I have outlined above). So you have a shoulder that no longer impinges, but is now unstable as this ligament holds the top of the shoulder bones together. This then sets up a new problem that also beats up the rotator cuff. Well a new study may shed some light on why all of this impingement happens in the first place. The study looked at muscle activation patterns and found that in patients with shoulder impingement, their upper trapezius muscle contracts too early and too much and the scapular muscles give way too easily, which causes the impingement. See the diagram I created below. The upper trap is outlined in red and goes from the top of the shoulder to the head. The red arrow shows what would happen if your upper trapezius contracted too much. The lower highlighted muscles at the back of the shoulder are the scapular muscles discussed in the paper. Notice that as you lift your arm, they're in a perfect spot to help pull the shoulder down (green arrow). So if these muscles are too weak, the shoulder will drift up and impinge. Could it be even more complex? We frequently see the upper trap muscle kick in excessively when the neck stabilizing muscles are weak, so the upper trap problem may also be caused by this secondary problem. What are the neck stabilizing muscles? They are deep cervical muscles that keep the neck bones perfectly aligned. They can go off line due to neck joint or nerve irritation, so the upper trap kicks in to help stabilize. In this case, while it may be helping neck stability (by making it very tight and stiff), it also seems to cause issues in the shoulder. All of this is discussed in much more detail in our e-book, Orthopedics 2.0. What can you do if you have shoulder impingement? A tried and true method is rotator cuff strengthening exercises. If these fail, rather than impingement surgery, consider getting your neck checked out!
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