My mom used to tell me that hips "spread" with age - particularly women's, particularly after childbirth. I'd chalked this up to an old wives' tale with a teeny bit of truth: during the last stage of pregnancy, the hormone relaxin is released that causes the cartilage at the pubic symphysis (the very front of the bony pelvis) to weaken, allowing women's pelvic inlets to widen so that we can give birth to giant-brained babies (whose heads are 102% the size of our pelves - yeah, that's a fun statistic). But after childbirth, the cartilage is strengthened again, and the pelvis returns to normal.
|20-year-old's pelvis in pink, |
79-year-old's pelvis in black
I'd initially thought that the growth would be restricted to women - after all, having a wider pelvic inlet should lead to much better outcomes in childbirth, and that makes evolutionary sense. But it's interesting that men's pelves also grow. I want to see a lot more of this kind of research - does it happen in other populations (that is, is this growth a result of our lifestyle of over-nutrition)? Does growth slow down at certain times (such as during menopause for women)? Very cool research - I can't wait to find out where researchers will go with it next.
Berger AA, May R, Renner JB, Viradia N, & Dahners LE (2011). Surprising evidence of pelvic growth (widening) after skeletal maturity. Journal of orthopaedic research : official publication of the Orthopaedic Research Society PMID: 21608025