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, the 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. 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.



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