I think the they're two different sets of terms:
"structural" vs "functional"
so, if you can do something simple, like sit up straight, and the curve goes away, then it's functional instead of structural
and then, within the structural curve, there is
"rigid" vs. "flexible"
both of these are counted in the overall curve measurement, but one part of it disappears when you do something not simple (like the bending xray or bracing). The part of the structural curve which reduces during these procedures is considered "flexible" and the part that stays is considered "rigid"
"structural" vs "functional"
so, if you can do something simple, like sit up straight, and the curve goes away, then it's functional instead of structural
and then, within the structural curve, there is
"rigid" vs. "flexible"
both of these are counted in the overall curve measurement, but one part of it disappears when you do something not simple (like the bending xray or bracing). The part of the structural curve which reduces during these procedures is considered "flexible" and the part that stays is considered "rigid"
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