Inter Scalene Triangle

Keywords; inter scalene triangle, thoracic outlet.



Five large trunks of nerves known as the brachial plexus emerge from the lower neck; together with the large subclavian artery that supplies the arm with blood, they pass from the chest cavity via this narrow passageway to the upper limb.

Inter because it lies between two small muscles in the neck called the anterior and medial scalenes; and the word triangle is used because it is bounded beneath on the third side by the first rib.

Clinically, this space is of vital importance being the underlying cause of many of the debilitating upper limb syndromes.

Vital structures pass through this passage on their way to the limb. In a small percentage of cases the subclavian vein passes through the space bringing venous blood back from the arm. Then swelling is a possibility; a clot is not common, but must be first differentially diagnosed, obviously.

Spasm of the scalene muscles, a subluxated first rib or a cervical rib are often at the root of conditions like carpal tunnel syndrome; tingling in the fingers always excludes the pinkie.

A thoracic outlet syndrome, as it is known, very frequently does affect the pinkie as the lowermost trunk of the brachial plexus lies directly on the first rib.



Remember, the classic carpal tunnel syndrome where the median nerve is pinched in the wrist, never affects the pinkie.



Inter Scalene Triangle

Through this triangle pass the artery and nerves to the arms.


Anterior Scalene muscle

The anterior border of this triangle is the anterior scalene muscle which laterally flexes the neck to the same side, and raises the first rib.

It originates from the transverse processes of the middle cervical vertebrae and inserts into the first rib.

The nerve supply is from the C4 to C6 spinal nerves.

The posterior border of the triangle is the medial scalene muscle. It too originates from the transverse processes of the cervical vertebrae and inserts further posteriorally on the first rib; behind the subclavian groove in the rib for the artery.

It too laterally flexes the neck and raises the first rib.

The nerve supply is the cervical spine nerves, C3 to C6.

Incidently, if you have swelling in the lower arm it's not likely to be a classic case of thoracic outlet syndrome.


The venous blood return from the arm is via the subclavian vein which does not pass usually through the inter scalene triangle. Can you spot the groove in the first rib where it usually goes?

In my book, if your lower arm is swollen, think first of seeing your medical doctor, not your chiropractor. True, it could be a strain or sprain in the lower arm, but first we should rule out a clot in the vein, or more serious, a mass, from the lung, for example, pressing on the vein.

There are many conditions that can affect the scalene muscles including an interference of one of the cervical spine nerves, C3 to C6. Subluxations of the mid to lower vertebrae are common, caused by

  • poor posture, for example long hours at the computer.
  • falling asleep in the car or plane or in front of the TV.
  • sleeping on the abdomen.
  • injuries to the neck such as whiplash, falls from a horse or whilst skiing; diving into shallow water.
  • talking for an extended period with someone sitting to the side; for example, at the dinner table.
  • holding the telephone between neck and shoulder; Pinched nerve in neck ...
  • many others.

A careful, thorough examination is called for obviously when faced with the patient suffering from neck pain, with or without swelling and tingling in the arms and hands.


Medial Scalene muscle


Vertebral subluxation complex

In chiropractic nomenclature this is described as the vertebral subluxation complex; you'll find the link lower down.



Again notice how the subclavian vein does not usually pass through the inter scalene triangle, but it does pass throught the thoracic outlet and under the clavicle. Sub-clavian meaning under the clavicle.


Cervical ribs and Thoracic Outlet syndrome

In the normal spine only the twelve thoracic vertebrae have ribs however anomalies do occur. Fairly commonly the first lumbar vertebra may have a small rudimentary rib, mostly usually associated with another anomaly at the lumbosacral junction; see the sacralization of L5 casefile page.

Less commonly, the last cervical vertebra, C7, may also have a rudimentary rib. Mostly they are quite small and of no clinical significance. But very occasionally the cervical rib may be quite large and, because it also passes through this narrow space, taking up room, it may impinge on either the subclavian artery or the brachial plexus producing a bizarre mixture of vascular and neurological signs in the arm. 

Here is a simple test that you can do. Raise your arm above your head as you would do, say, as in hanging the washing. Does it increase the tingling in your arm or does it relieve it?

The whole is complicated by the close approximation of the collar bone; these structures, after leaving the inter scalene triangle must pass through the so called thoracic outlet. Raising the arms closes down this space; if the impingement is in this region then you will get increased symptoms.



It's well recognised that casefiles have no scientific status, but they do give us insight into how others perceive their problems, and howthey cope, or don't cope. And whether chiropractic has a contribution to make or not. Do keep in mind that very large cervical ribs like this one are relatively rare. Not every tingle in the arm is caused by a cervical rib! 


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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've left alone. After seven treatments his pain and stiffness is 50 percent better, and he's 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's doing well.

3. Mrs T looked like the leaning tower of Pisa; she had a slipped disc at L5 making her lean towards the opposite side. It's called the postero lateral disc hernia; she's much better after two weeks of treatment and will go back to work next week, part time. Lateral discs are more difficult; both take a minimum of six weeks to heal. In my opinion, antalgic patients need what I call exercising bed rest. Sit and it won't get better.

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 groin pain, and a degenerative facet causing the sciatica. Both are responding well to chiropractic and he's well pleased; sixty five percent better after three treatments.

5. Mr T is a wise man; he's 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 walk 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.

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 lower back is just as important as the pain.

7. My own granddaughter, only 7 is hypermobile giving her hip, knee and ankle issues. Xrays show a mildly dysplastic hip. Years ago we would have called it growing pains. She too regularly needs chiropractic care and luckily responds well. Hypermobility is more difficult that too stiff in my opinion. Chiropractic 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 year 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's a non complicated upper cervical facet syndrome, and she's doing well.

12. Mr D is a 38 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 couldn't 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 shouldn't be treating the elderly most medical sites state but that's so much bunkum.



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