Shoulder Impingement: Part 3 – The Shoulder Blade’s Role in Impingement

Understanding what is happening inside of the shoulder joint is a very important part of understanding impingement.  If you haven’t checked out part 1 and part 2I’d recommend starting there before reading about the shoulder blade. To make matters a bit more complex, the musculature that surrounds and controls the shoulder blade (scapula) plays a large role in this condition as well.  I wanted to leave no stone unturned in fully understanding impingement so next we’ll discuss how the scapular musculature can affect impingement.

Patients with impingement have changes in shoulder blade kinematics that differs from healthy patients.  Basically this means that the shoulder blade is not moving normally as it should in normal patients.  In the world of shoulder pain and pathology, this is often referred to as scapular dyskinesia.

Why is this happening?  Part of the problem lies in what is happening to the musculature that attaches to the shoulder blade.  Similar to issues with the rotator cuff in impingement, we’re having these problems in scapular musculature.  These dysfunctions can present as:

• Muscle timing issues (Muscles don’t fire as fast or reflexively as they are meant to)
• Force couple imbalances
• Weakness
• Length issues (short and overpowering vs. long and weak)

The problems associated with the scapular musculature is thought to alter the orientation of the humeral head in its socket and decrease the subacromial space.  As discussed earlier, a decreased subacromial space can compress the rotator cuff tendons, bursa and the biceps tendon.  If we want healthy shoulders we’ve got to address this area.

Here’s what we typically see out of whack in this population:

1. Dominance of the upper trapezius
2. Weakness or delayed activation of the middle, lower trapezius and serratus anterior
3. Scapular Winging and Anterior Tilt of the Scapula
4. Poor Posture
5. Scapular Dyskinesis

1. Patients with Impingement had on average greater recruitment of the upper trapezius and less recruitment of the lower trapezius when raising their arms overhead in the scapular plane.  This upper trapezius dominance can cause hiking or shrugging of the shoulder during overhead movement and decrease the ability of the scapula to rotate normally.

Taking a look at where the trapezius originates and inserts (attachment points to bone)  you can see that the upper trapezius will be responsible for elevating the scapula and rotating it upward as you elevate them arms overhead.  The lower trapezius will be responsible for keeping the shoulder blade stable and keeping it from excessively elevating.  The lower trapezius counterbalances the upper trapezius and allows the scapula to rotate normally.  Lastly, if the lower trapezius is not doing its job correctly then the upper trapezius will do more hiking/shrugging as opposed to rotating the scapula normally as you raise your arms overhead.

2. Those with impingement typically have either a weakness or delayed activation of the middle/lower trapezius as well as the serratus anterior.  These muscles play a large role in stabilizing the scapula flat against the ribcage with movement.

3.  Patients with impingement often present with scapular winging or anterior tilt of the scapula at rest and with movement.  Scapular winging and anterior tilt of the scapula are two terms for the same condition.  Scapular winging can either be caused by weakness in the mid/lower trapezius and serratus anterior or by tightness in the Pectoralis Minor.

As you can see if the pec minor is tight it will pull the shoulder blade forward, tilting the shoulder blade, protracting the shoulder (bringing the shoulder forward) and decreasing the subacromial space.  (bad news bears)

Here’s how it might look from behind.  Notice how prominent the inferior (bottom) and medial (inside) borders of the scapula become compared to the normal right side.  This individual is definitely getting some compression of the subacromial space.

4. Posture is also normally implicated in shoulder pain.  We know that a protracted shoulder can decrease the subacromial space, decreasing the amount of blood supply and nutrition the damaged tendons of the rotator cuff receive at rest.  Unfortunately the area where we usually acquire supraspinatus tendon tears is also an area of hypovascularity known as “the critical zone”.  Hypovascularity means that the area has poor blood supply.  If we want these damages tissues to heal and remain healthy then it makes sense to open the subacromial space and get more blood supply to the area at rest.  This is where the role of posture comes into play.  Posture will be a critical component to allowing our rotator cuff to heal and we’ll have to address this all throughout the day and when we sleep and not just at the gym.

One very common postural problem that is often associated with shoulder impingement is upper cross syndrome popularized by the late Dr. Janda.

Janda’s upper crossed syndrome demonstrates common postural problems in the upper body.  In his model, addressing protracted shoulders will not only take strengthening the lower trapezius, rhomboids and serratus anterior, but stretching tight pectorals.  Weak deep cervical flexors, tight/overactive traps and levator scapulae and poor thoracic spine extension range of motion are also probably culprits.  Even the position of your lower body impacts the upper body position as well.  (We may have a total body problem on our hands here but that is beyond the scope of this article.  It’s already long enough!)

5. Scapular dyskinesis is basically abnormal position of the scapula with movement.  Normally the scapula should slide flat on the ribcage and rotate normally as your bring your arms overhead.  This helps keep the shoulder centered in its socket and minimizes stress on the subacromial space.  In those with impingement the shoulder blade can be anteriorly tilted, elevated and may not upwardly rotate as much as it should.  This becomes evidence when you watch these patients raise their arms overhead or do pushups.

Notice how this woman’s shoulders are shrugged up while attempting a pushup against the wall.  Also notice her left shoulder blade looks as if it is lifting off the ribcage.  This is known as scapular winging and that’s the anterior scapular tilt we were discussing earlier that is associated with impingement.

Next we’ll talk a bit about the thoracic spine and rib cage and how it effects the shoulder in impingement.  I’m pumped!

My brain is tired after all of that science.  Please let me know if you enjoyed this article by posting in the comments below.  If you enjoyed the content please sign up for my newsletter in the top right hand of the page.

Is scapular dyskinesis a real word or did you just make it up?

Dan Pope

References:

1. Behnke, R. S. (2006). Kinetic anatomy. (2 ed., pp. 35-56). Champaigne, IL: Human Kinetics.
2. Bigliani LU, Morrison DS, April EW: The morphology of the acromion and its relationship to rotator cuff tears. Orthop Trans 10:228, 1986.
3. Morrison DS, Bigliani LU: The clinical significance of variations in acromial morphology. Orthop Trans 11:234, 1987.
4. Page, P., Frank, C. C., & Lardner, R. (2010). Assessment and treatment of muscle imbalances the janda approach. (pp. 195-207). Champaigne, IL: Human Kinetics.
5. Sahrmann, S. A. (2002). Diagnosis and treatment of movement impairment syndromes. (1 ed., pp. 193-261). St. Louis, MO: Mosby.
6. Smith, M., Sparkes, V., Busse, M., & Enright, S. (2009). Upper and lower trapezius muscle activity in subjects with subacromial impingement symptoms: Is there imbalance and can taping change it? Physical Therapy in Sport, 10 (2), 45-50 DOI: 10.1016/j.ptsp.2008.12.002
7. Wilk, K. E., Reinold, M. M., & Andrews, J. R. (2009). The Athlete’s Shoulder . (2 ed.). Philadelphia, PA: Churchhill Livingstone.