Hey everyone, Dr. Lell here. Today’s topic is shoulder impingement syndrome; a pretty common condition that isn’t typically investigated to the fullest extent. There are four classifications of this condition but I’ll just cover the most common one – primary mechanical impingement. Let’s go over some of the simple anatomy first.
Basic Anatomy Of Shoulder Impingement
The important players are the scapula (shoulder-blade), supraspinatus muscle (posterior rotator cuff), and a tunnel called the subacromial space. The space is what’s really important. Take a look at the diagram. That unlabeled space above the glenoid fossa and below the acromion and clavicle is the subacromial space (let’s just call it the space). What isn’t pictured is the supraspinatus muscle which is inside the space and attaches to the upper arm.
That’s about as technical as we’ll get.
Causes of Impingement Syndrome
What causes impingement syndrome? -Anything that causes that area in the space to get smaller. The big three things that cause this are:
- The content in the space gets bigger. There’s stuff in that tunnel. Most notably, the supraspinatus muscle and a bursa. If a person has been using that arm a lot (swimming, working overhead, throwing), then the contents can get irritated/swollen. I usually see this in the younger athletic population.
- The walls of the tunnel get bigger causing the space to get smaller. Years of wear and tear or a single large injury can cause changes in the joints and bones making the amount of free area in the space smaller. Alternatively, some people can be born with a misshapen bone; this will have the same effect. I usually see this in the older populations.
- The scapula is unstable during movement. The roof of the space is the scapula. The scapula isn’t strongly locked into place like other bones of its size but it’s held down by many muscles coming from many different directions. If those muscles are unbalanced, the scapula can have too much free motion which consequently changes and decreased the area in the subacromial space. This scapular instability or scapular dyskenesis is what I see the most of in non-athletic patients under 60; especially in people who sit at computers a lot. Sometimes this can cause irritation of the space’s contents and then you end up with what was described in scenario 1.
How you treat impingement syndrome relies on what’s causing it.
I generally approach this condition functionally. Once any inflammation or pain is decreased, I like to give the patients ergonomic advice along with stretches and exercises that they can do at home to prevent future flare-ups.
Research Update!! Feb 27, 2020
Since writing this post, more information about shoulder impingement has come available. Before, the common element of all scenarios resulting in impingement had to deal with the tendon being aggravated and damaged by the bone on top. But someone took a look at the tendons of people with various stages of impingement and they found that the initial damage occurs on the underside of the tendon, not the top (where the bony roof is) suggesting that a weakness / reconditioning of the tendon itself precedes the swelling and other mechanical factors more commonly associated with the pain shoulder impingement syndrome.
How does this change things clinically?
We still want to make sure things are moving the best they can but it’s also important to make sure that old shoulder injuries heal properly and to make sure shoulders are strong and mobile after injuries to help avoid any deconditioning. It also means that tendon rehab should be a large part of any shoulder impingement treatment protocol.