Measuring cup angle

[Dannywayoflife]

Hi everyone,
                im a little bored at home and as a little interest thing id like to measure my cup angle. Im in no way concerned that its miss placed or anything as about 5 different orthos have viewed my xrays and all have said placement is perfect.
I would just like to measure it just out of interest. The thing im struggling with is how do you ensure that line along the bottom that you measure off is horizontal? Are there any refference points that you use?
Thanks Danny

[John C]

There are two different sets of landmarks that I have seen used.
1. Draw a line across the bottom of the two ischial tuberosities. (the curved bones at the bottom of the pelvis, sometimes called the sitz bones.)
2. Draw a line across the top of the two iliac crests. (The bones that are on top at the side of the pelvis, just below your rib cage.)

[Dannywayoflife]

Thanks John I'll give that a go

[ScubaDuck]

I agree with John.  I found identifiable matching landmarks and made the lines.  I used multiple measurements to get an approximation.  I come up with about 39 degrees for mine.

Dan

[horse doc]

hi dan, is there a larger image of your replacement?  post it up so we can do our own measurements.  who ever guesses the closest to actual wins a beer or something

was your xray taken while standing?  that would give a "functional angle".  If you stand with a tilted pelvis, your functional angle might not be the same as the surgical angle

This just gave me an idea.  If a cup isn't placed in an ideal angle, could you change your gait or stance to ameliorate "edge loading"?  I guess your back or knees would start to complain though.

[ScubaDuck]

@horse doc - That is a great idea for future hippies.  Post your x-ray and people can guess the angle.

I had x-rays both standing up and laying down.  I assumed that because we are taking the angle of a reference line between identifiable matching points on the two hips it wouldn't matter.  But you may be right.

That is an interesting thought about adjusting your gait.  We all changed how we moved when we had OA to avoid/lessen the pain.  I suppose you could do a little big to affect edge loading using the same idea.  But as you pointed out we all suffered through pain in other joints from the adjustment.

Best wishes.

Dan

[Tin Soldier]

Interesting discussion.  I simply assumed that the pelvis was symmetrical and found 2 matching landmarks to make the horizontal ref line.  Keep in mind that there is still the forward-facing (anterversion) angle, which is not easilly measured with standard frontal x-rays.  The point about the funcitonal angle is interesting.  I was super crooked with regards to the x-ray frame, when I go my 2 week x-rays.  I think it has a lot to do with how tendor and swollen things are early on.  So obviously using the x-ray frame is not a good reference line. 

Horse - I think you'd have to make some significant changes in the gait to modify the functional angle to get away from a high angle.  I think you'd get a lot of complaints from vairous body parts.  I think you'd have to be constantly bent over, like the old man on the cover of Zeppelin 4.  Actually, that would be anteversion, no you'd have to have your arse sticking out to one side all the time.  That wouldn't work for bi-lats.  I suppose you could swing your hips back and forth at each step, sexy!