Adaptation to upright walking
leaves humans susceptible;
© panthermedia.net/K. Pargeter
Osteoporosis is blamed for backbone fractures. The real culprit could well be our own vertebrae, which evolved to absorb the pounding of upright walking, researchers at Case Western Reserve University say.
Compared to apes, humans have larger, more porous vertebrae encased in a much thinner shell of bone. The design works well until men and women age and suffer bone loss, leaving them vulnerable to cracks and breaks, the scientists say. Apes, on the other hand, can suffer comparable bone loss as they age, but have much thicker vertebral shells to begin with so that their vertebrae remain intact.
"In evolution we have great adaptation, but there is sometimes a trade off," said Meghan Cotter of Case Western Reserve University School of Medicine. "The structure is great for walking around, but not good when you have osteoporosis," she said.
Researchers took measurements and used computer tomography (CT) scans, Micro CT scans and computer modelling to compare the size, shape, structure, microstructure, biomechanics and strength of the 8th thoracic vertebra from skeletons of humans, gorillas, chimpanzees and orang-utans. The 8th thoracic vertebra is the one of the bones most often fractured in humans with osteoporosis.
They found that just like the broad heel bone and broad ends of the leg bones in humans, the large, porous bone of the vertebra dissipates impact. The architecture is useful for mitigating the forces of walking on two feet, protecting cartilage in joints and the discs between vertebrae.
In apes, the vertebra is shorter and wider and has a thick ring of shell around a centre of porous tissue – a design well-suited to providing stability needed to climb in trees and for knuckle-walking.
Much recent research has suggested that our sedentary lifestyle and modern diet are to blame for the susceptibility to bone loss and damage.
"We're now living about twice as long as when the adaptation evolved and that results in major problems," Cotter said. "It highlights we are not perfectly evolved specimens."
REHACARE.de; Source: Case Western Reserve University