Shoulder anatomy

Shoulder anatomy is actually four joints wrapped up in one arm.

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).

Dem dry bones...

The four shoulder joints.

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...

Rotator cuff muscles

Shoulder anatomy.

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".

Rotator cuff tears.

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.

Supraspinatus muscle.


Infraspinatus muscle.

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.

See Ultrasound of the shoulder: Rotator cuff and non-rotator cuff disorders

Frozen shoulder

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

Read more about FROZEN SHOULDER …

Teres Minor muscle

Teres Minor muscle.

Strains and tears can occur in all muscles in the body; the teres minor muscle is often affected. 

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.
  • Rotator cuff strengthening

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.

Anatomy lab.

Blood supply

Thoracic Outlet syndrome

The thoracic outlet syndrome 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; the blood supply is via the subclavian artery. 

Thoracic outlet syndrome.

Cervical rib

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

Cervical rib.

Adson's test

A difficult and subjective examination is commonly used to test for an impingement on the artery in the Thoracic Outlet syndrome and Cervical rib syndromes; Adson's test. Classically the symptom that you may feel is that your arm tires very quickly when working above your head, as in hanging the washing, or changing a light bulb.


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

Useful links

› Shoulder anatomy

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Interesting challenges of the day

1. Mr S is a 76 year old man with neck pain of some 9 months duration. Luckily, most of the discomfort is upper cervical which is only rarely arthritic; his lower cervical spine is a degenerative mess that I have left alone. After seven treatments his pain and stiffness is 50 percent better, and he is happy in the circumstances. He can sleep through the night now and that makes a huge difference.

2. Mr P is 32 year old man with very severe lower back pain radiating to the big toe which is 30 percent numb. He had an episode three weeks ago, took anti-inflammatories and was soon better as is typical of the medial disc herniation. But before it healed, after a trivia it came roaring back, much worse. The characteristic crossed sign was evident; sitting in a chair, straightening the right leg provoked severe left back pain and tingling in the leg. He is doing well.

3. Severe lower back pain is scary; just ask Mrs P. Just watching her get out of the car I she was in trouble; she had a slipped disc at L4 making her lean towards the opposite side; luckily she had no pain in the leg. Despite family pressure that this was far too severe for a chiropractor, she persevered. Within five days she was standing upright, and after two weeks almost pain-free. 

Despite a hectic job, she wisely took my advice and stayed home for what I call exercising bed rest.

4. Mr S has had lower back, groin and back of thigh and calf pain for fourth months.

He has a pincer deformity in the hip causing the stabs in the groin, and a degenerative facet causing the sciatica. Both are responding well to chiropractic and he is well pleased; sixty-five percent better after three treatments.

5. Mr T is a wise man; he has taken a warning TIA seriously and has lost 15 pounds, and has at least as much again to lose. A change to a low starch diet and half hour daily stroll has made the difference; but the walking is making his foot and back miserable. The expensive orthotic is hopeless; luckily his hips and back are fine, but he needs a simple heel lift; he has a short leg.

6. I too have had serious lower back issues, luckily fixed by my own chiropractor; so I too have to do my exercises, take care when lifting supers full of honey, gardening and using the chainsaw. Regaining the function of your spine is just as important as the pain.

7. My own granddaughter, only 7 is hypermobile giving her pelvic, knee and ankle issues. X-rays show a mildly dysplastic hip. Years ago we would have called it growing pains. She too regularly needs chiropractic care and luckily responds well. Increased range of motion is more difficult than too stiff in my opinion. Our care is for kids too.

8. This 65-year old lady is a serious gardener; every day she is bending, lifting and digging for 2 to 3 hours a day. It regularly catches her in the sacroiliac joint, so she has a treatment once a month that sorts it out. She does her lower back exercises faithfully.

9. This 88-year old lady is an inspiration; every day she is busy in the community. With a nasty scoliosis she manages very well with a chiropractic adjustment every six weeks and exercises faithfully done. 

10. Mr X is a 71-year old retired man who wants to continue with maintenance care every six to eight weeks; he had suffered from two years of lower back pain when he first came a few months ago. He has no discomfort now after 8 chiropractic treatments, but is aware that danger lurks.

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

12. Mr D is a 38-year old year man with chronic shoulder pain after a rotator cuff tear playing cricket. It responded well to treatment, but he knows he must do his exercises every day; for two years he could not sleep on that shoulder.

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 should not be treating the elderly most medical sites state but that is so much bunkum.

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Interesting questions from visitors

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Two common syndromes

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

Frozen shoulder exercises

Equipment to exercise the shoulder.
  • Shoulder arm exerciser ... easy to make.