Sunday, September 25, 2011

ROM rant

Well it's been a while since I ranted about anything, so this goes out to the anatomists or physiotherapists or anyone else that follows the nonsensical pattern of rotational axis naming.

First off, there are a few planes that the body can get divided by:
Frontal plane or coronal plane, which is like cutting you down from top to bottom so your face falls off, or rather divides you into a front and a back.
Next up is a transverse or horizontal plane, which, for example, could cut horizontally so you have a top and a bottom half. Incidentally, guillotines do this.
And finally there is a sagittal plane, which cuts to divide left from right, like if you straddled and then fell and sat on a running chainsaw (that's never almost happened to anybody I know *cough*).

If you're still unclear:

So that's all fine, I buy that, it's helpful and reasonable.

Now, someone got it into their head that since some body joints allow motion, we need to describe the motion of the bones and joints in terms of the axes that they rotate around. That's fine too, a shaking head indicating "no" is one example. A straight leg kicking a ball rotates around another axis, and bringing your arm straight out from your side to the left is the third axis. And these axes need names apparently and THIS is where all mathematical reason is discarded.

I'll just say what they are named and then I'll explain why it is just wrong. The frontal axis passes through the body from left to right (like a pencil passed through your ear holes - apologies for the graphic examples, but it's hard to describe planes and axes without describing things passing through the body). The sagittal axis passes through the body from front to back (like when someone pokes you in the chest with their index finger - there, nice and harmless). The final axis comes up with a new word and calls it the longitudinal axis, which when you shake your head "no" is what the head is rotating around (an axis passing from top to bottom). And movement examples of the frontal axis and the sagittal axis would be kicking a ball and lifting your arm out from your side, respectively. Confused? Yeah, and it's totally not my fault. What were they thinking?

Okay, I'll start with the most basic and logical argument against this nonsense naming. An axis exists in ONE dimension. A plane exists in TWO dimensions. ERGO, there are TWO axes that run parallel to a plane, and ONE axis that runs perpendicular to a plane. So, it is NOT possible to unambiguously name an axis after a plane UNLESS that axis runs perpendicular to the plane and NOT parallel to it, which is the case here. According to these preposterous naming conventions, the sagittal axis actually runs parallel to BOTH the sagittal plane AND the transverse plane. The frontal axis runs parallel to the frontal plane AND the transverse plane. The longitudinal axis runs parallel to both the sagittal and frontal planes. Okay, so there's no transverse axis, so theoretically you can't get confused, IF you remember which one the longitudinal axis is, but it still doesn't make sense and it does my head in.

I am forced to think in this manner: Abduction of the arm is rotating around an axis. It is not the longitudinal axis, so it must be either the sagittal or frontal axis. The axis runs parallel to both the coronal and transverse planes. There is neither a coronal nor transverse plane, but the coronal is also known as the frontal, so it must be rotating around the frontal axis. Was I right? Not 100% sure. No, I looked at it again and I'm wrong. Abduction of the arm is rotating around an axis parallel to the transverse and sagittal planes. Ergo sagittal.

I will defer to a mathematical example. If you have a cube that sits in XYZ space, you can take that cube and move it in the XY plane. You can move it in the YZ plane, and also the XZ plane. You can also rotate the cube around each of the X, Y, and Z axes. NOTICE that if you are rotating.... ah never mind. I'm too tired for this.


"/rant" is an internet typing to signify the end of a rant. It's derived from XML as far as I can work out, where any element is terminated by a forward slash followed by the name of the element (in this case the rant) and enclosed in , but I guess were deemed unnecessary for the /rant version.

Have a good week!


P.S. ROM stands for Range of Movement, which is apparently what this stuff is used for.

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