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.


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.

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.


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.


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

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Interesting challenges of the day

1. Mrs B has had one of the nastiest of conditions; vertigo caused by a disturbance in the inner ear. Falling repeatedly and vomiting she consulted her doctor but medication didn't help. After two sessions of the Epley manoeuvres she was 50 percent better. After two weeks she was 75 percent improved; no longer vomiting or falling. She's not enjoying the Brandt Daroff home exercises.

2. Mr S, a 48 year old man, has right low back pain, groin pain and a numb feeling in his lower leg when he sports. For six months he's been off football. He too has two problems; a very treatable lumbar facet syndrome and a very serious blocked artery in the groin; it's called intermittent claudication. Smokers beware.  

3. Mr S looks like the leaning tower of Pisa; he has a slipped disc at L5 making him lean towards the opposite side. It's called the postero lateral disc hernia; we'll fix it, but he has to stop for a week or two. Antalgias are serious so take them seriously. 

4. Mrs V too has two conditions; a chronic low grade sciatica giving her an ache in the right leg, and a threatening Morton's neuroma. She's glad I'm back in Holland; chiropractic fixed it before, and we'll fix it again. 

5. Mrs W is one of the lucky ones, says her doctor. I agree. He says only 40% of patients with lumbar stenosis have a successful operation. We fixed a nasty slipped disc three years ago, but it came back two years later; the surgeon did a fine job but she has a weak ankle now giving her subtalar joint pain; it's routine stuff. 

6. I myself had an acute exacerbation of a femoral nerve lesion last year. One immediate treatment of the new strain by my colleague has fixed the pain in the lower back, but there's some residual numbness in the lower leg; no soaring tomorrow alas.

7. This lady is a 86 year old woman with a 63 scoliosis. Chronic lower back has been her lot in life but she's well pleased with chiropractic and comes for chiropractic help once a month; some conditions you can never cure.

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. A 61 year old man with upper cervical pain yesterday; it's not severe but also not getting better of its own accord. He's afraid it may turn very acute as when I treated him three years ago. Since then it's been fine. 

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. Mrs 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. Mr D, a 71 year old man, has a severe ache in the shoulder and midback since working above his head. Trapped nerve tests are negative but he has advanced degenerative joints of Luschka; after just two treatments he is 50 percent better. Can we reach 90?

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