If you search for images of "human female rib cage" then you'll get results like
this one.
That is not a normal human female rib cage shape. It shows rib #7 as the widest point. In reality rib #9 is usually the widest point. This can be seen by searching instead for images of "human female chest x-ray" to get results like
this one.
Searching for images of "human female skeleton" will return diagrams like
this one in which the hip bones are significantly wider than the rib cage: almost 25% wider in that image.
That is not a normal ratio of rib cage width to hip bone width.
This is a replica of a real human female skeleton. The skeleton is at a slight angle so we cannot measure exactly, but the apparent width of the hip bones is slightly less than the apparent width of the rib cage: 3% less or so.
This is another one, in which the hip bones are around 4% wider than the rib cage.
We can also use
https://grayoasis.com/ANSUR/ to see this in the ANSUR 2 data. We want the "bicristal hip breadth" and "chest breadth" measurements. The
instructions specify to compress soft tissue for both, so we're getting as close as possible to the actual bony measurements. Switching the chart to "bell curve bar chart" we can see that the mean ratio is around 0.95 for males and 1.02 for females. SD is about 0.06 for both. Now, there is a caveat with the ANSUR 2 data: the dataset comes from US Army personnel, not the general population. However, for this post we're only looking at bony measurements, not soft tissue measurements, so I wouldn't expect it to be vastly different to the general population for our purposes.
If your bicristal width is below the female mean for your height then do not immediately despair. If its ratio with your biacromial and rib cage breadths is close to the female mean then you simply have a slender frame.
What can we conclude from this?
- Diagrams of the human skeleton are frequently unrealistic. You ought not to compare your own bony structure with them.
- Women's hip bones are not usually a lot wider than their rib cages. Hips are mostly soft tissue.
- Ratios between pairs of breadth measurements can be just as important as ratios between breadth measurements and height.
- Don't jam calipers into "top surgery" scars that are still sore. Ouch!
- It is more useful to consider bony measurements (e.g. bicristal breadth, biacromial breadth, rib cage breadth) than soft tissue measurements (e.g. bideltoid breadth, hip breadth at lateral buttock landmarks). Soft tissue can generally be changed through fat redistribution and muscle hypertrophy. Bone structure generally cannot. Bony measurements are a better indicator of passing potential.
- If you're considering iliac crest implants then don't simply go for the largest size available. If you have the average male rib cage breadth (around 29cm) and hip bone ratio (0.95) then your bicristal breadth will be roughly 27.5cm. If you instead had the average female rib cage breadth to hip bone ratio then your bicristal breadth would be roughly 29.5cm. That means you would need to gain 2cm overall or 1cm each side to reach the mean female ratio. The smallest iliac crest implant size is 1.5cm (each side) and would put you slightly over the female mean. Going for, say, 3cm implants would give you a rib cage breadth to hip bone ratio of 1.16, significantly beyond the mean female ratio. Coupled with the implants not moving your trochanters it could result in an awkward and unnatural appearance.
Why am I posting this here and not on asktransgender, mtf, or any of the other mainstream trans subs? I like this place. I don't like those other places. Y'all here are real, even more real than I am.
I love it.