Curvature of the spine can be from an abnormal formation of spinal components. Portions may be missing or formed too small, perhaps even from the wrong stuff. Extra parts, complete or partial may be present. Almost any mix-up you can think of happens. Oddly enough, you can have many malformed parts with extras here and there and yet have no abnormal curvature. It gets down to the growth characteristics of those pieces. Do they follow the big picture or their own?

To the right we see a front view of an extra half of vertebral body with an extra transverse process nesting within a nearly normal spinal contour. Interesting ... but ... OK.

Yet here on the left we see a side view MRI of a vertebra missing it’s front half. It collapses the anterior line of growth and causes the remaining normal portion to jut backward. This is flat out dangerous. The “normal” portion can skewer the spinal cord - and it WILL - if left alone.

So you see, it’s the behavior or expected behavior that gets our attention.

But does it get this way? Well, when you see how things form you might wonder that it ever is right. Let’s take a look. We’ll make it a bit more simple by showing things logically in parts rather in exact sequence as there isn’t a real divided sequence - many things are going on all at once.

Early in the embryo’s formation, a polarity appears. Running the length of the blob of cells a stripe called the notocord appears.

 This rod of cells orchestrates the linearity that follows. Segmentation follows along its length. The early embryo is somewhat like a loaf of sliced bread - repeating units - one after the next. (to cut = ‘TOME’ or slice).

The repeating units are precursors of future tissues. The sclerotome (sclero = hard) is to become the skeleton. Between and connecting these sclerotome units are softer fluffy tissue (called soft fluffy stuff - just kidding).

On the surface of the embryo a stripe of cells overlying this, begins to dive deep and migrate along the boundaries. These are the neural cells. The sclerotome will sink deeper and engulf the central neural cells (the vertebrae surrounding the spinal cord) and the nerve cells that wandered off but leaving a trail of nerve cells along the way become the peripheral nerves.

The nerves dive into the myotomes (myo = muscle, tome = hunks or slices). Hey, wanna see myotomes? Look at some muscley guy’s “six-pack”, the segmentation persists there. Ohhhh, and the vertebrae? Like you can SEE that? Ahh, but things get way more complicated, and it turns out that that last guess is wrong.

Gotcha. So pay attention! You.

Whereas the neural stuff begins everything from the surface, the vessels do a similar segmentation deep to the notocord.. The vessels shoot out branches between the muscle segments (myotomes) whereas the nerves dove right into them.

Now you are just thinking... there =>

Right there are the vertebrae! Right?

Nope. Not yet.

The notocord which organized the linearity of all this is breaking up into islands, one centered in each TOME or segment.

Right about now that changes the rules. Or does it? The notocord had a head end and a tail end which everything followed. By breaking up, it now has many head ends and tail ends.

So those blocks that looked so uniform now suddenly have head and tail ends. Guess what? Opposites attract. At least, here they do.

<= This used to be the plan, but it’s way too easy for any complex organization.

The sclerotome heads join with adjacent tails
        =>
and in so doing create a new segmentation plan offset by 1/2.

Confusing? You bet. And it can and does get mixed up. To recap, the notocord went the length, but broke into islands now represented by the jelly stuff in the disc spaces. The original segmentation is centered on the discs and so the bottom of one vertebra, the disc below, and below that, the top of the next vertebra represent the original segmentation.

What if subtle chemical interactions get off by just a wee bit? Then things divide too many times, or not enough. It isn’t just vertebrae, ribs can be stuck together (actually failing to form separately).

The real issue to us, is what makes for trouble? Some of this is interesting. But, when is it bad?

In general there has to be the ability to GROW. If defective parts that do not have a sense of linear growth bracket other tissue, then the other tissues restrained may fail to grow or bubble out in some lopsided escape from capture.

Close to mid-line you get a sense of how bad it MIGHT be by simply counting up one edge of the spinal structure for how many growth plates (intact vertebral surfaces adjacent disc space) there are. If on the left in a given interval there are 5 but on the right 8, then there are 3 additional sources of linear growth on the right. That smacks of trouble. But normal tissue growth on the less represented side can hold back that run away growth. geometry matters.

The very bad ones are thos with a growth focus missing on one side and a free growth center within this constraint on the opposite.

If you compare this spine to the one at the top of this page, we see three signs of trouble. Very subtle here (as it often is on x-ray as well) there are “fused” (undivided) ribs.

There isn’t just an extra half vertebra (which add two growth surfaces) but that extra growth has been pinched by a “bar” on the opposite side. The bar not only firmly constrains that side’s growth in this zone, it removes two growth surfaces from that side’s tally.

Worse, a bar opposite extra growth has just got to tilt and do so badly.

Also note that the transverse processes look suspiciously intimate?

Test your own eyes. Here are some examples (sparing you the very nasty stuff).

Position can alter the angulation seen.

CT scan makes the details easier to sort.