Height gain measurement

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Just adding some thoughts.
Measuring the fracture gap shows 4 cm on tibia x-ray
 
Trying to measure it in "real life" shows more something like 3 cm.

Measurement of leg length x-ray (measured from femur head to medial malleolus of same leg) shows 2.7cm.

All of this makes me wonder, if there's really a gap between measured gain in x-ray compared to actual gain, perhaps it's because the bone is lengthened, but the surrounding tissues kinda resist the lengthening and is not lengthened the exact same amount.

Other than that I can't see an explanation or a way of measuring the actual height gain.
Except measuring height with a tape or those standing machines with laser... I guess one day I'll get to that.

Edit Post

Pure external.
It's possible to measure the gap of the fracture with the imaging program. I know it is said that with tibia the amount measured is precise because the tibia is straight, but I don't find it exactly true, at least in my case. Perhaps there's some kind of an error of measurement.