Counting Scalenes (Because Functional Anatomy Says So)

scaleneThere are 3 scalenes – anterior, middle, and posterior. Simple enough. Why should you care? We are going to take a walk through some positional anatomy to figure out why really knowing about the scalenes is important.

First we will look at the connections of each scalene. Anterior scalene runs from the anterior tubercle of the transverse processes of C3-C6 to the scalene tubercle of the inner border the first rib. Middle scalene runs from the posterior tubercle of the transverse processes of C2-C7 to the upper surface of the first rib between the tubercle and the subclavian groove. Posterior scalene runs from the posterior tubercles of the transverse processes of C5-C7 to the outer surface of rib 2. That is the dry stuff which doesn’t help us understand why the scalenes are important.

subclaviansTo start getting a bigger picture we need to look at the structures that are related to the scalenes. Running between the anterior and middle scalene is the subcalvian artery and the brachial plexus. Another very important structure related to the anterior scalene is the subclavian vein which passes in front of the anterior scalene and posterior to the SCM. Now we have a picture that shows us neural communication from the cord to portions of the anterior and posterior thorax (dorsal scapular nerve, suprascapular nerve, medial and lateral pectoral nerves, long thoracic nerve, nerve to subclavius, upper and lower subscapular nerves, thoracodorsal nerve…) as well as to the arm (axillary nerve, musculocutaneous nerve, median nerve, radial nerve, ulnar nerve…). This communication is a two way street that can easily be altered by the anterior and middle scalenes. We can also see that the subclavian artery will be affected as it passes between the anterior and middle scalene. The other part of this picture starts to come in to focus when we see the subclavian vein between the SCM and anterior scalene which means that the position of the clavicle and mastoid process (both are attachments of the SCM) are extremely important to the subclavian vein which is also important as it receives systemic fluid flow via the right lymphatic duct and the thoracic duct (to the left subclavian vein).

3D thoraxThis is where the Osteopathic lens becomes VERY important. Through direct connections the scalenes are related to the cervical vertebrae and the first two ribs. The relationship between the subclavian vein and the anterior scalene open up the relationship between the clavicle, the SCM, and the mastoid process. The relationship between the clavicle and the SCM means that anything else that attaches to the clavicle (pectoralis major, subclavius) begin affecting the subclavian vein. The SCM having an attachment to the mastoid process then creates a relationship between the trapezius and all of the attachments it shows (scapular spine, acromion process, and the lateral 1/3 of the clavicle as well as the spinous processes of C7-T12). The scapula and all of the muscles that attach to it become related to the scalenes via connection to the trapezius and SCM. Going back to the ribs, there needs to be a recognition of the connection to the sternum (which also then connects back to the SCM and the pectoralis major as it connects to the clavicle as well). The movement of the sternum now shows possible affects to the brachial plexus as well as the subclavian artery and vein.The position of the hyoid also becomes important as the sternohyoid runs from the sternum to the hyoid while the omohyoid runs from the hyoid to the scapula (this is one way your scapula might affect your hyoid and then the mandible as the suprahyoid muscles join the hyoid and the mandible).

Now that I read all of that it looks like a bit of a whirlwind! I need to try to make that more cohesive…so here goes nothing. Based on the positional anatomy and structural relationships of the anterior/middle/posterior scalene, the movement characteristics of the dorsal and cervical spine, the scapula, the sternum, the clavicle, the first two ribs, the hyoid, and the mastoid process should all be inspected if there are notable functional alterations with active (arterial) fluid dynamics, passive (venous/lymphatic) fluid dynamics, or neurological alterations that may be related to the scalenes. The whole idea is that the pathways of the fluid vessels and the brachial plexus weave through the scalenes and SCM which means that those spaces need to be maintained for appropriate function in the thorax as well as the arm. Hopefully some of this makes it more understandable as to why it is necessary to look at the many connections between structures to improve the function of the structure you are attempting to affect as the solution may not be in the local area.


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