Friday, February 12, 2010

Off Topic: Brittle Bones?

Off Topic: Brittle Bones?

How often we hear of elderly individuals with broken hips, or fractured bones. And for most the believe is this is attributable to a byproduct of increased brittleness in ones bones. This though is only partially true.

We are all aware of the amazing ability of children to “bounce back” from seemingly horrendous falls or bumps. This is due to the nature of children’s bones. Early on in the bones of children the calcification and formation of osseous tissue, or Calcium tissue, is incomplete and does not reach full tensile strength of roughly 20,000 MN/m2 (20GPa – compare this with steel at 200 GPa) until adulthood. Interestingly though, between the ages of twenty-five and seventy-five the tensile strength of bones only decreases roughly 22%. Although a portion of the increased incidence of fractures may be attributable to this embrittlement, it can by no means account for the disproportionate number of fractures in the elderly. So what then may be the cause?

Interestingly the source of a large number of fractures in seniors may not be structural but rather neurological. It appears that on occasion senior’s diminished command of their nervous responses may by the culprit. The sudden response to being startled or trying to correct a potential fall may cause the misfire and contraction of the iliopsoas and gluteus medium muscles, producing sufficient force to shear the neck of the femur. This results in the individual falling to the ground, possibly on an object, that is then erroneously blamed for the broken hip. Apparently a similar type of situation has been observed in certain African deer that experience a similar fracture when startled by a lion.

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