Shoulder Anatomy

(Keywords: shoulder anatomy, rotator cuff syndrome, frozen shoulder, chiropractic help )

Shoulder anatomy is made up primarily of bones, muscles, ligaments, nerves and blood vessels. The arm bone (humerus), the shoulder blade (scapular), the collar bone (clavicle), and the rib cage (bony thorax) make up the relevant bones.

Note particularly the ACROMION (part of the shoulder blade) and the ACROMIOCLAVICULAR joint (AC joint).


1. Dem dry bones...


There are four important joints in the shoulder:

  1. The Gleno-Humeral joint (GH). The main shoulder joint where the arm joins the shoulder blade.
  2. The Acromio-Clavicular joint (AC). The joint between the collar bone and the shoulder blade.
  3. The Sterno-Clavicular joint (SC). The joint between the collar bone and the breast bone. 
  4. The Scapulo-Thoracic joint (STh). A muscular joint between the shoulder blade and the rib cage.

Working in harmony these four joints facillitate all the important movements of the shoulder enabling us to throw a ball, swing from a rope, lift a heavy basket, use a screwdriver, an axe...


2. Rotator cuff muscles


There are FOUR rotator cuff muscles to which we add a fifth for convenience because it's often involved.

  1. SUPRA-spinatus muscle. It lies above the spine of the scapula and is involved in raising the arm.
  2. INFRA-spinatus muscle. This muscle lies below the spine of the scapula, hence infra. It's involved in external rotation such as in winding down a car window.
  3. SUB-scapularis muscle. This muscle lies under the shoulder blade and is an internal rotator.
  4. Teres Minor muscle. Another external rotator. 
  5. The extra muscle: Biceps is really two muscles. Hence "bi".



This important muscle lies just below the neck, and just above the so-called "spine of the shoulder blade". You may find yourself rubbing it frequently as it may feel as though the pain is in the upper back. It travels through a tunnel in the shoulder and inserts into the upper arm. It is the primary lifter of the arm at 45 degrees with the thumb pointing down.



Infraspinatus


This large muscle is found "infra" or below the spine of the shoulder blade, and also inserts into the shoulder. It rotates the arm outwards.


Next time you carve the Sunday roast lamb shoulder, look out for the spine of the shoulder blade, with the Supraspinatus above it, and the large flat muscle, the Infraspinatus below it.

Sorry, anatomy is rather macabre. Chiropractors spend the best part of a year in the anatomy lab, so we become accustomed to such things ...




Biceps muscle


Scapula = Shoulder blade

The shoulder blade, seen below side-on, or what we call the lateral view. It is an important bone for the both the attachment of the arm - the head of the humerus fits in the 'glenoid fossa' - and for many shoulder muscles.


Here you can see the origin of the two heads of Biceps muscle - the short head starts from a bump of bone just in front of the shoulder called the Corocoid process (not important!), and the long head originates from deep inside the shoulder, from the Supraglenoid tubercle (just showing off! It's also not important!)

It's the long head that gives grief due to the long journey of its tendon through a groove in the humerus to its attachment just above the glenoid fossa (where the humerus sits). It ruptures sometimes, particularly in older men suddenly taking on a frenzy of heavy work such as shovelling snow. Also after cortisone injections.

See the two heads of the BI-ceps muscle? See if you can follow that long tendon of the biceps up to its origin at the Supraglenoid tubercle.

If flexes the forearm, and rotates it into what we call supination. Outwards.

If you prod with your thumb into your armpit, you'll feel the edge of the scapula, and between the scapula and the ribs is where you can feel the Subscapularis muscle - the very devil when it comes to a frozen shoulder.

Subscapularis muscle

This large flat muscle lies on the underside of the shoulder blade, between the scapula and the ribs. Opposite side to the Infraspinatus. It attaches to the arm at the Lesser Tuberosity (LT in the scan below). Have a good look for it too when carving the Sunday roast! The Subscapularis rotates the arm inwards.


The search this site function in the navigation bar on the left enables you to find stuff on this site.

Google has gone through an enormous shakeup in the last year, giving webmasters much grief.

Meantime, use that search function to find more information about subject material mentioned on the page where links have probably been removed.  There are over 360 pages at chiropractic help; it's become a veritable encyclopedia dedicated to better health.



In the author's experience the SUBSCAPULARIS MUSCLE (SSC in the scan below) is a much neglected muscle in shoulder anatomy conditions. It is best approached in the armpit with the arm flexed above the head. If it is involved, it may be exquisitely painful on palpation.

For interesting cases of shoulder pain (and other) at the Chiropractic Coalface, click here. Chiropractic Coalface ..

After serious soft tissue injury, a Doppler ultrasound scan often yields information that cannot be obtained from the clinical examination alone. It does however require specialised interpretation, and is best left to the specialist. This scan of the subscapular tendon (SSC) shows scar tissue (arrows) in the deltoid muscle (D). However that scar tissue can produce a confusing shadow (arrowheads) that mimics a tear.

See www.radiographics.rsna.org

Regular stretching in the healing phase is what prevents the ugly scar tissue in muscles that can turn a relatively minor shoulder injury into a frozen shoulder.

Read more about FROZEN SHOULDER …

Teres Minor muscle


Strains and tears can occur in all muscles in the body.

Usually these occur from:

  •  Injury eg. a fall especially on the outstretched arm.
  • Disturbed nerve innervation of the muscle eg. an irritated nerve in the neck weakens the muscle making it vulnerable to injury.
  • Overuse eg. repetitive action
  • Improper warmup in sport eg. Tennis players who do inadequate prematch preparation.



Shoulder Anatomy: The ANATOMY LAB

Yes, indeed, grotesque, but an important place where your chiropractor spent many long hours studying shoulder anatomy, preparing him or herself for a lifetime of helping you recover from your injury.



BLOOD SUPPLY

Thoracic Outlet syndrome

One of the syndromes that may commonly irritate the nerves that supply the shoulder affects both the artery and the brachial plexus as they pass through a narrow tunnel from the chest to the arm.


Cervical rib

Usually small and inconsequential, very occasionally a large neck rib may pass through the interscalene triangle dramatically affecting the artery and nerves.

Adson's test

A difficult and subjective test is commonly used to test for an impingement on the artery in the Thoracic Outlet syndrome and Cervical rib syndromes. Classically the sign that you may feel is that your arm tires very quickly when working above your head, as in hanging the washing.

Ligaments @ Shoulder anatomy

We'll write elsewhere of the ligaments affecting the shoulder.


Useful links


Did you find this page useful? Then perhaps forward it to a suffering friend. Better still, Tweet or Face Book it.


Interesting challenges of the day

1. Mr B  came initially for a painful and stiff neck and then asked whether chiropractic could help the cold numb feeling running down the side of his thigh for six months. Meralgia paresthetica is a double crush syndrome with the nerve affected in the back and groin. He's 80% improved after five treatments.

2. Mrs C has a long history of severe, disabling migraine headaches since having her wisdom teeth removed. She clenches her teeth at night. After six treatments she has no migraines but some jaw joint discomfort remains; a bite plate is in the offing.

3. Mrs U has the trophy for the worst back this year. After major surgery with plates and screws two years later she still had paresis in the lower leg and severe disabling back pain. She's doing far better than expected, in no little part due to a lift in her shoe for a very short leg.

4. Mr V is 86 years old and hurt his back helping his wife into the car. Just one treatment of the sacroiliac joint and he's eighty percent better. It's not always like that.

5. Mr W lay on his back knocking down a pillar. Turning his head causes severe vertigo. He needs the Epley exercises, not pills, research shows. Update, he's fine.

6. Mrs X, a young mother has severe lower back pain, with numbness down the posterior thigh, calf and side of her foot. It started after a long drive in the car. After six treatments she is 60 percent better, but it's slow and is going to take the full 6 weeks to heal.

And now a setback, after lifting her child she now has leg pain. It's going to the be difficult.

7. This lady is a 70 year old woman, is on maintenance care for a nasty lumbar stenosis despite having to do everything at home. Her husband has a hospital acquired infection after a total shoulder replacement. After four operations he is incapacitated.

8. She is an 78 year old woman, is doing remarkably well with a bad sciatica. But over 200 pounds she is not losing weight; in fact, gaining despite my suggestions. She's high risk for a stroke. I have referred her to a dietician to crack the whip.

9. This man is a 73 year old engineer, still working, is doing fine after a long episode of lower back pain. Some pain on the side of the hip remains after five treatments. I reassured him it's not hip arthritis.

10. A 64 year old woman has had scheuermanns disease; it's left her with a spinal kyphosis and chronic middorsal pain. She responds well to chiropractic treatment provides she come every six weeks or so for maintenance treatment.

11. Mr C has been having severe headaches, and taking a lot of analgesics. It's a non complicated upper cervical facet syndrome, and she's doing well.

12. Mrs D, a middle aged woman with hip pain of one year duration, despite other treatment. Xrays reveal an impingement syndrome and early hip arthritis. There's much to be done.

13. Both Mrs E and I can't believe how much better her lower back and leg pain are. Surgery for a scoliosis and spondylolysthesis three years ago helped greatly for one year. But then her leg went lame and weak. He was responded extremely well despite all expectations.

And so the day goes; chiropractors shouldn't be treating the elderly most medical sites state but that's so much bunkum.



Have a problem that's not getting better? Looking for a different slant on your pain? Want to pose a question?


Interesting questions from visitors

CLS writes:

Greetings, Dr B.
You helped me quite some time back with a soothing and professional response which turned out to be exactly correct. I now consult a local chiropractor. You write a superb newsletter, too.

Your own unresolved problem. Pose a question

Knowing that up to 70% of the time the correct diagnosis is made with no examination, no special tests, no xrays, but just from the history, there's a fair chance I can add some insight to your unresolved problem. But at least 30% of the time, I may be quite wrong! Give plenty of detail if you want a sensible reply.


You visited this chiropractic help site no doubt because you have a problem that is not resolving and want to know more about what chiropractors do.

The quickest and most interesting way is to read one of my ebooks of anecdotes. Described by a reader as gems, both funny and healthful, from the life and work of a chiropractor, you'll love them. Priced right at $2.99, though Kindle fiddles the price without telling me.


Two common syndromes

  1. Frozen shoulder ...
  2. Rotator cuff syndrome ...

Frozen shoulder exercises