I have purchased a screen protractor and was wondering if it can be used to measure a cobb angle? For example, I am trying to measure the angle formed by a line bisecting the thigh bone and one bisecting (both in the long axis) the tibia (lower leg). Sometimes these lines do not intersect close to the center of the knee, therefore, it is useful if the protractor can disarticulate- one arm on the center of the thighbone's long axis and the other arm on the lower leg. The protractor extends the lines in space and measures the angle even if the center point is off the page so to speak.

Yes you should be able to measure the Cobb Angle quite easily with the Screen Protractor. If you look at this image of measuring the Cobb Angle:
http://upload.wikimedia.o...s_cobb.gif

Now place the Protractor so that it's center is on the left where the two lines intersect, in the picture that's at 89 degrees.

I too, need the arms to "disarticulate"

I measure x-rays, where sometimes the intersection cannot be on the screen even if you extend the lines out....the angles are usually less than 10 deg and at the spine are a couple inches apart...the intersection point may be a few feet away! I would need a 60" monitor!! :-)

is there a way to separate the arms???

I'm sorry but we really don't have any way to do that. The best suggestion I have would be to zoom out on the image until it's all visible.

Hi, this is the method to "dissarticulate" the arms of the Screen Protractor to measure the angle of such small degrees. The trick is using two protrators. Place the first one with the top arm along the verterbral end plate. Place the other arm at 90 degrees to it. Then, take the second protractor, the bottom arm along the vertebral end plate and the other arm at 90 degrees to it. Then, align the two 90 degree arms on top of each other (the arms form a square-bottomed U). The numbers that shows up on the protractors are the angles, add them together. Wha-la! The COBB angle.

How do you get a measurement? The Numbers that show up on the protractors are  awlays 90 degrees and 90 degrees?

What the other chap means is that you align the 90 degree arms (use one protractor or the other) - then once you have done that - that protractor that you have adjusted will give you the reading for the Cobb angle.  A clever method because there are v few software programs available that will give you the Cobb angle.