The Cobb angle measures the lateral curvature of the spine, which is to say the sideways curve. A virtual line is drawn from the top of the first vertebrae that goes off piste and another line is drawn just below the last vertebrae that tilts at an angle. Two more lines are drawn between them and the intersecting angle is - oh blow it, it's too confusing. Time for a helpful diagram I think don't you?
The thing is, even though this is the one and only measurement that is used for noting the severity and the change of scoliosis, it's not all that useful.
For one thing, the standard range of error is 5 degrees.
This was a particularly startling and slightly discouraging piece of information to me. I had been thrilled to find that my Cobb angle had gone from 41 degrees last September to 38 degrees this February. I put it down to all the hard work and exercise I had done over the intervening months and now you tell me my Cobb angle might not have changed at all?
Apparently errors can be made when it is calculated by different people, on different machines, or even at different times of the day. One person might have measured it from the x-ray itself and another from a computer screen. I may have carried myself a teeny bit differently each scan, my body may have slouched a bit or showed the effects of the gravity at the end of a day instead of in the morning. In other words, unless you can ensure that x-rays are taken at exactly the same time of day, by the same person at the same place, and measured by the same person in the same way, you can't possbily know if your Cobb angle has changed much at all.
And for another thing, scoliosis is a 3 dimensional condition and the Cobb angle is a 2 dimensional measurement.
I guess that should have really been the first thing because it makes the whole Cobb angle thing pretty much dead in the water.
So if the Cobb angle is a useless form of measurement, how on earth does one know how and if the condition has changed or worsened, and whether surgery is needed or not?
The Scoliosis SOS clinic staff were clear that the best form of measurement is a subjective one, based on the following:
- Quality of Life
- Cosmetic Appearance
- Trunk Rotation (measured by a little device called the Scoliometre*)
- Lung Function
- Back Surface (measured with a Formetric Scan**)
**A radiation-free method whereby a 3D image is produced by the topography of a patient's back
So the real assessment derives from answering questions such as "Is your breathing better?" "are you happier with your posture?" "Has your pain been reduced?"
Surgery might be necessary for those who do not have the motivation to complete a daily exercise programme, or for those in imminent danger of having their heart squeezed or their lung punctured by a rotated rib for example, but even those with a Cobb angle measuring 90 degrees can avoid surgery and improve their condition purely with targeted, diligent exercise.
So rather than relying on a semi-annual round of x-rays as advised by the spine surgeon as a way to monitor my progress, it looks like I'm really better off becoming my own spine specialist and answering my own quality of life questions.