WHAT IS A SHOULDER IMPINGEMENT AND WHY IT'S IMPORTANT TO ADDRESS IT BEFORE IT AFFECTS THE ROTATOR CUFF OR LABRUM (CAUSES A SLAP TEAR)Read Now
SHOULDER IMPINGEMENT SYMPTOMS
"Neer first introduced the concept of rotator cuff impingement in 1972. He believed the etiology to be impingement of the rotator cuff tendons under the acromion and the rigid coracoacromial arch [see pic above], eventually leading to degeneration and tearing of the rotator cuff tendon, which are more common in older populations. The increased forces and repetitive overhead motions can cause attritional changes in the distal part of the supraspinatus tendon, which is most at risk due to its poor blood supply." Cherry-picked from a 2004 issue of Physical Medicine and Rehabilitation Clinics of North America (Shoulder Impingement Syndrome)
"Shoulder pain is the third most common musculoskeletal complaint in orthopedic practice, and impingement syndrome is one of the more common underlying diagnoses. Shoulder impingement is a clinical syndrome in which soft tissues become painfully entrapped in the area of the shoulder joint." From the November 2017 issue of Deutsches Arzteblatt International (Impingement Syndrome of the Shoulder)
As you can see from the quote above, shoulder problems of all kinds are common (HERE). Dog common. There are DISLOCATIONS & SEPARATIONS. There are numerous TENDINOPATHIES, including that of the ROTATOR CUFF and BICEPS TENDON. And there is the dreaded SLAP lesion --- the torn labrum (Superior Labrum, Anterior to Posterior). Remember this, however. It was the distinguished orthopedic sports surgeon, DR. JAMES ANDREWS, who famously said, "if you need an excuse to do shoulder surgery, just do an MRI". Which brings me to shoulder impingement.
The most common muscle of the rotator cuff group-of-four to be injured --- the supraspinatus, seen in red in the pics --- takes a path that runs underneath the AC joint (the acromio-clavicular joint, where the collar bone attaches to the knob of bone coming over the top of the shoulder blade), attaching it's distal or 'distant' tendon (the one with the poor blood supply mentioned above) to the upper outside part of the shoulder (again, see pictures). This is why most cases of shoulder impingement hurt at --- you guessed it --- the upper, outer part of the shoulder; frequently running to just above the elbow (BUT DO NOT CONFUSE THIS WITH CERVICAL RADICOLOPATHY). All of this begs the question, how common are shoulder impingements?
Largely a function of UPPER-CROSSED SYNDROME (a combination of POOR POSTURE and upper extremity muscle imbalance) and CHRONIC OVERUSE (work, sports, swimming, lifting weights, etc, etc) --- particularly in those who do lots of overhead activities --- shoulder impingement (often referred to as SAPS -- Sub-Acromial Pain Syndrome, or SIS -- Subacromial Impingement Syndrome) is the number one reason reason for shoulder pain, accounting for as much as 65% of it according to some studies, with those numbers getting larger as the birthdays pile up (the most common decade of life for this problem is the fifties). All great to know, but what is a shoulder impingement?
The first thing to remember is that you will often see shoulder impingements spoken of as either primary or secondary. The primary impingement occurs because of a compression by bone spurs at the AC joint or a congenital anomaly of the bony structure of the shoulder. Primary impingements are not as common and not really what we are talking about today (see first embedded YouTube video below). The subject of today's post is the secondary shoulder impingement.
If you simply look at the pictures (especially the overhead view below left) you will notice that the SUPRASPINATUS runs underneath the AC joint. Although INFLAMMATION leads to swelling, swelling is not the only reason for impingement; not by a long shot. Besides what we've already mentioned, the biggest factors in developing shoulder impingement syndrome include things like ARTHRITIS, THICKENING of the connective tissues in the area (including the FASCIA), which leads to tightness, SUBACROMIAL BURSITIS. However, one could argue that the number one reason for shoulder impingement is POOR BIOMECHANICS of the shoulder blade (aka scapular dyskinesis), which is fantastic because there are relatively simple ways to address it, which we'll get to shortly. How can you tell you may have a shoulder impingement?
Although you could opt for an MRI, just remember that significant numbers of musculoskeletal pathologies do not image well on MRI, with an equal number of people who have no pain showing, as Dr. Andrews insinuated earlier, an array of abnormalities (HERE), making imaging far from a sure thing as far as determining the source of one's shoulder pain is concerned. The best bet may be to look for the obvious by answering some simple questions.
It's not rocket science. The more of these questions you answered yes to, the greater the chance you have a shoulder impingement. Follow along as we dig a bit deeper.
SHOULDER IMPINGEMENT SYNDROME
"Instead of the roof of the subacromial space (the AC joint) coming down and pressing on the structures, I really think that most of it is that the floor (the glenoid ball of the shoulder) is coming up." This means that inferior glide of the humeral head is a must!
Watch as these same two physical therapists demonstrate four different orthopedic tests used to determine the likelihood that your shoulder problem is an impingement or something else (HERE).
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SHOULDER IMPINGEMENT SYNDROME
A VIEW OF BOTH SHOULDERS WITH CERTAIN PARTS REMOVED
THE LIGAMENTS THAT MAKE UP THE JOINT CAPSULE OF THE LEFT SHOULDER. THE ANATOMICAL STRUCTURE ON THE TOP FAR-RIGHT IS THE ACROMION PROCESS. THE AREA JUST BELOW IT IS CALLED THE SUB-ACROMIAL SPACE.
YOU CAN SEE THE BICEPS TENDON
THE TWO HEADS OF THE BICEPS TENDON (LEFT SHOULDER) THE LONG HEAD (LATERAL) & SHORT HEAD (MEDIAL). ALTHOUGH THEY ARE DIFFICULT TO SEE, NOTE THE TWO BURSAE JUST ABOVE AND TO EITHER SIDE OF THE TOP OF THE BICEPS TENDON (LONG HEAD).
THIS PICTURE OF A RIGHT SHOULDER SHOWS THE LONG HEAD OF THE BICEPS TENDON AS WELL AS ONE OF THE MANY BURSAE (BLUE). NOTE THAT THE COLLAR BONE AND ACROMIAN ARE REMOVED IN THIS PICTURE.
IN THIS PICTURE OF A RIGHT SHOULDER, YOU CAN SEE THE SUPRASPINATUS TENDON AND THE LONG, FLAT BURSA IN THE SUB-ACROMIAL SPACE. YOU CAN ALSO SEE THE PROXIMITY OF THE BURSA TO THE TOP OF THE BICEPS TENDON. PAY ATTENTION TO THE AC (ACROMIOCLAVICULAR) JOINT AS WELL.
THE ROTATOR CUFF MUSCLES OF THE BACK SIDE OF THE LEFT ARM (PARTICULARLY THE SUPRASPINATUS MUSCLE AT THE VERY TOP) WITH THE CLAVICLE / ACROMION REMOVED.
Bursa or Bursae (plural) are fluid filled sacs that whose purpose is to reduce friction / wear by providing a barrier cushion between bones and tendons. Healthy bursae create an almost frictionless gliding surface for tendons that makes normal movement painless. Enter BURSITIS. The word "itis" means INFLAMMATION. When inflammation is seen in a bursa, the problem is referred to as "bursitis". With bursitis, movement that occurs on the inflamed bursa becomes difficult and painful. This painful and restricted movement of muscle tendons over the inflamed bursa further aggravates the condition causing even more inflammation. Do you see a vicious cycle starting to spin?
Bursitis is usually caused by repetitive injury. In the case of the subacromial bursa (the bursa below the acromion), this is frequently due to repetitive micro-trauma to the SUPRASPINATUS TENDON. As the bursitis progresses, you see a proliferation of COLLAGEN FORMATION in the area. And unless specific steps are taken, this collagen will be laid down in a tangled, twisted, matted fashion (like a hairball) as opposed to a uniformly smooth fashion (well-combed hair). Furthermore, because Inflammation (a chemical problem) attracts fluid to it, you can often find increased fluid production and swelling inside the bursa, while seeing a decreased fluid production on the outside of the bursa. As you can imagine, this can dry out the joint.
The shoulder bursae allow for smooth motion of the Rotator Cuff underneath the arch made by the Acoromioclavicular (AC) joint (see second picture from the top). Any pressure on the anatomical structures under the arch (in the sub-acromial space) can lead to something called Shoulder Impingement Syndrome. Some of the causes of Shoulder Impingement Syndrome include.......
- Bone Spurs (DEGENERATION):
- Shoulder Instability (Previous Dislocations or Separations):
- Loss of Rotator Cuff Strength:
- RADICULITIS or Nerve Entrapment: (entrapment of the nerve, artery, or vein can also cause something called THORACIC OUTLET SYNDROME)
With both Shoulder Impingement Syndrome and BICEPS TENDINOSIS, the most common symptom is pain along the front of the shoulder. This pain is often associated with muscle weakness as well as lost range of motion in the shoulder. A Subacromial Bursitis causing Shoulder Impingement will often have lateral shoulder pain as well. The classic Orthopedic Test to determine whether or not someone has a subacromial bursitis is the Subacromial Push Button Sign. You simply push the area on the front of the arm / shoulder below the Acromion Process to see if a pain response can be elicited.
As you can imagine, this results of this test are fairly vague and do not provide a lot of valuable information. Neer's Sign (pain in the front of the shoulder when it is raised straight up, directly out in front of you) is not very specific either. These tests tell you something is wrong with the shoulder, they are not very specific as to what that problem really is. Be aware that people with Shoulder Impingement Syndrome will usually have difficulty with overhead activities (throwing, swimming, overhead work, etc) and may find that their problem is actually worse at night.
Make sure you come back tomorrow to learn about the differences between a separated shoulder and a dislocated shoulder ---- two totally different problems (HERE).
Dr. Schierling completed four years of Kansas State University's five-year Nutrition / Exercise Physiology Program before deciding on a career in Chiropractic. He graduated from Logan Chiropractic College in 1991, and has run a busy clinic in Mountain View, Missouri ever since. He and his wife Amy have four children (three daughters and a son).
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