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Saturday, March 14, 2015

What Is Shoulder Impingement Syndrome?

As a physical therapist this is a complicated question and the fix can also be complex.  The shoulder by far is one of the most complicated joints in the body.  It has the greatest amount of movement than any other joint in our bodies.  And do you really have shoulder impingement syndrome?  As a practitioner, if someone comes to me with a prescription or request to treat shoulder impingement syndrome, I'm not going to just look at the shoulder.  I'm going to do an evaluation and assessment on the neck or cervical spine as well.  As I stated, shoulders are complex joints requiring a very skilled practitioner to correctly diagnose impingement syndrome.  Obviously something is impinged.  It's either the shoulder or something coming from the cervical spine.  But for this article, I'm going to just stick with the shoulder joint.  I'm making a firm diagnoses for this article that a person does have  "shoulder" impingement syndrome.

So What Is Shoulder Impingement Syndrome?

From my point of view, this is simply answered.  It is when the tissue underneath the roof of the shoulder gets pinched when the arm is moved in a specific manner.  So now, what's the next question?  

How Do You Resolve Impingement Syndrome?

This is the hard part.  Sometimes it's easy but most of the time it takes some work by the physical therapist and especially by the patient.  Before we go into answering how you get rid of it, we have to look at the anatomy of the shoulder to understand its' mechanics so that the right treatment application can be applied.

The Rotator Cuff Muscles & Shoulder Anatomy
On the left side of the diagram, you'll see the four muscles of the rotator cuff (RTC).  On the right side of the picture you can see that the RTC muscles are what steer the humeral head in that very tiny socket on the shoulder blade or scapula that's called the glenoid fossa.  So, when looking at the size of the humeral head and then looking at the size of the socket that the humeral head sits in, it's quite remarkable what the RTC has to do.  The RTC is responsible for making sure the humeral head sits in that tiny socket.  The attachments of the four RTC muscles are all within the red circle.  The space between the acromium process and the top of the humeral head are where shoulder impingement occurs.  The muscles of the RTC elevate the hummers to a certain point and rotate the humerus inward and outward. 

So why do some people acquire shoulder impingement syndrome and some don't?

Again, we have to look at some more anatomy of the shoulder.  Below are three different types of shoulders.  
Type I Acromium Process

Type I acromium process (AC) is where the bony structure at the edge of the scapula or shoulder blade turns slightly upwards.  Unless there is severe weakness or trauma to this type of shoulder, impingement syndrome does not occur often in a type I acromium process.  These are the people that usually do not have to worry about shoulder impingement syndrome.

Type II Acromium Process
With a type II AC process, the bony structure on the end of the scapula protrudes out laterally or just slightly downwards.  A type II AC process is the most common type.  With a type II process, acquiring impingement syndrome is more likely than a type I.  With a type II AC process, there is usually an aggravating factor that brings about impingement syndrome vs. the type of AC process listed next.

Type III Acromium Process
With a type III AC process, the end of the bony protrusion of the scapula orients itself in a hooked or downward position.  This type of process as you may have already surmised is very common with acquiring impingement syndrome.  Typically if a person has a type III AC process, then some point in their life they will have to tend to resolving shoulder impingement syndrome.

As previously stated, impingement syndrome is when the soft tissue becomes compressed between the head of the humerus and the AC process.  The next question is:

What Role Do The RTC Muscles Have With Regards To Impingement Syndrome?

The RTC muscles are what steer the head of the humerus in that tiny little socket.  So, if one of the RTC muscles becomes weakened then this means that this particular RTC muscle is not doing its job and the humerus is not staying centered in the socket.  When the humerus doesn't stay centered it then begins to "bang" against structures adjacent to the humerus.  This means structures above it as well.  These include the RTC tendons and the lubricating sack called the bursa.  When this occurs, it causes an inflammatory response.  When an inflammatory response occurs this means swelling.  Given the way the shoulder is already built, there isn't much room for any type of inflammation to occupy this space.  There's also no room for extra movement of the humerus outside of the socket or glenoid fossa.  When the humerus moves too much with impingement syndrome, it can also aggravate the bursa that lies on top of the humeral head and just under the AC process.  This bursa is a lubricating  sack that allows the tissues such as the RTC muscles to glide smoothly and evenly under the AC process.  But if the humeral head is not being steered properly by the RTC muscles, this bursa too can become aggravated and inflamed.  When the bursa becomes inflamed, it too swells and takes up space between the humerus and AC process.  So, let's take a look at what's happening now.

  1. RTC muscles become weak and do not properly steer the head of the humerus in it's socket.
  2. Because of this extra movement of the humerus, it bangs against tissues that it's not supposed to bang against on a continual basis
  3. Inflammation begins to occur in the RTC muscle tendons.  This again occupies precious space between the humeral head and the AC process.
  4. If the initial impingement syndrome is not addressed, the lubricating sack called the bursa then becomes irritated and swollen.  When this happens you now are dealing with shoulder bursitis (inflammation of the bursa) and impingement syndrome.  By now there is significant pain present even when the arm and shoulder are at rest
In summation:  RTC muscle weakness + Type of AC process + extra humeral head movement + onset of bursitis = A severe case of Shoulder Impingement Syndrome.
Symptoms Felt With Shoulder Impingement Syndrome

The initial symptoms felt with impingement syndrome are a pinching sensation on the front or lateral edge of the shoulder when reaching out away from your body, behind you, across your body, or when reaching overhead.  As the impingement syndrome worsens, the pinching pain can become very strong and begin to refer pain down the arm through one or all of the following muscles; the biceps, the triceps or posterior arm, or along the lateral aspect of the arm.  Typically symptoms of impingement syndrome do not refer past the elbow.  However this is not always the case.  This is why an evaluation of the cervical spine is performed as well.  The therapist wants to make sure that the referred pain into the upper arm and forearm are coming from the shoulder and not coming from the cervical spine.

What Causes Shoulder Impingement Syndrome?

This is not an easy question to answer.  Shoulder impingement syndrome can simply be caused by the type of AC process one has.  However, most shoulder impingement syndrome is caused simply through weakening of the RTC muscles.  The weakening then allows for improper movement of the humeral head in the socket.  Repetitive use is another way.  One might say though that they are used to working all day long lifting items of weight overhead or in front of oneself.  This thought of being strong through normal daily activity is usually the cause of impingement syndrome.  The most common cause of impingement syndrome is through overuse or repetitive use syndrome.  Just because you are using your arms in a physical manner doesn't mean that this is keeping the RTC muscles strong.  What is happening is that a person will think that they have strong shoulders because of the daily physical use.  Here's the downfall with this thinking.  "Daily use" is a normal daily activity.  And if this normal daily activity is performed in high repetition then the "daily" wear and tear on the shoulder will eventually become "too much daily activity".  The RTC muscles and tendons weaken and then the process of impingement syndrome sets in.

Other causes of impingement syndrome can be:

  • Trauma
  • Habitual posturing such as the position you might sleep in or sitting in your chair reading a book.  Habitual and prolonged posturing can cause decreased blood and oxygen supply to the RTC which causes weakness and allows impingement syndrome to set in
  • Weakness of the shoulder itself such as the deltoids, triceps, and biceps muscles
  • A compromised nerve in the cervical spine causing decreased motor signal impulses to reach the muscles of the shoulder and RTC
  • Type of AC process
  • And again of note, repetitive use or over use syndrome leading to shoulder girdle and RTC muscle weakness
  • Specific sports that require a lot of overhead reaching such as tennis, swimming, or being a baseball pitcher.  These sports are very demanding on the shoulder.  If a proper strength regiment is not performed in addition to just playing these sports, then the likely hood of impingement syndrome setting in becomes high
  • Age.  Getting older and loosing the elasticity in the soft tissues of the shoulder can cause excess joint play of the humeral head causing impingement syndrome
There are physical therapists that specialize in the treatment of shoulder injuries.  As previously stated, the shoulder is a very complex structure.  In this article, I have just glazed over in the simplest manner about the anatomy of the shoulder and the basics of shoulder impingement.  There are many primary nerves, arteries, and other vessels that are adjacent to the shoulder complex.  In order to isolate the cause of shoulder impingement, the therapist has to rule out pathologies of these adjacent tissues as well as the cervical spine.  It takes patience and compliancy with physical therapy to permanently overcome shoulder impingement syndrome.

In the meantime, enjoy reaching across the table for that last favorite delight!

Always In Good Health!

Brad Senska, PT, DPT, BS, ASTYM


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