To keep this next group of Marion Clark posts more in line with Osteopathic scholarship I will generally refer to thoracic vertebrae as dorsal vertebrae (we have to keep the language of Osteopathy alive!). That being said, it is now time to take a look at the twelfth dorsal segment.
The first thing to note about the twelfth dorsal segment is that it is a transitional segment – meaning that it exists at a point where movement characteristics are changing from being flexion and rotation biased in the dorsal spine to being flexion/extension biased in the lumbar spine. The eleventh dorsal, twelfth dorsal, and first lumbar segments are often collectively referred to as the thoraco-lumbar junction. The general characteristics of the twelfth dorsal segment suggest this with the presence of a shorter and thicker spinous process that points almost directly posterior as well as inferior facets that almost directly inwards to articulate with the facets of the first lumbar segment. Also, it is important to note that the twelfth rib articulates directly with the twelfth dorsal vertebrae and does not attach to the sternum thus allowing for much greater mobility of the segment.
For a little bit more anatomy it is time to outline some of the areas that receive nervous tone from the twelfth dorsal segment: the renal plexus (which includes the least splanchic nerve, the spermatic plexus in men and the ovarian plexus in women), the skin from the area of the twelfth dorsal segment on the posterior aspect of the body following around the lateral wall of the abdomen down to above the iliac crest, and the intestines as low as the rectum. If you are interested in the circulatory structures associated with the twelfth dorsal vertebrae please check out my previous entry on the twelfth rib.
On to the slightly juicier stuff! Considering the nervous connections it is important to understand that a lesion of the twelfth dorsal segment will have influence over: the intestines, the uterus, the ovaries, the urinary bladder, the ureters, the testicles, the kidneys, and all of the fluid flow in and out of these areas through vasomotor influence.
It is important to consider what Marion Clark says about a lesion of the twelfth thoracic vertebrae (I am paraphrasing here): the mobility of the twelfth dorsal segment is very marked and often turns in to hypermobility as it is the site of compensation for other lesions. In terms of propulsion/locomotion, the thoraco-lumbar junction is the meeting point for transmission of force between the upper girdle and lower girdle. As a brief example – when humans run they use contralateral coordination (right arm and left leg do the same thing) and this is often seen as an issue of balance…the other important factor is summation of force where flexion/extension, side bending, and rotation are all able to effectively meet at the thoraco-lumbar junction to enhance the force produced for locomotion.
Now that I am done with that idea, I will re-iterate that Marion Clark suggests hypermobility of the twelfth dorsal segment is reflexive, as are many lesions of this segment.
I would like to make special mention of the quadratus lumborum as it receives motor tone from the twelfth dorsal segment as well as articulating with the twelfth rib. The quardatus lumborum has a unique ability to effect the twelfth dorsal segment via the twelfth rib and should be corrected from the pelvis first. If there is an innominate lesion there will be a reflexive lesion through the twelfth rib to the twelfth dorsal segment. Again, another reason that the principle of Osteopathic treatment begins at the pelvis! The spinal curves are related and should be treated as such!