The Ticklish Gene
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BONES-DESIGNED FOR MAXIMUM STRENGTH
the application of plates, screws, and nails does just the opposite and,
rather than helping nature, the treatment impedes healing.
From a researcher's point of view, the question here is: What activates
the cells of the periosteum and marrow? In the case of the marrow, we
can expect it to be the same factor that switches on the cells in a sala-
mander's amputated leg.
There's a third process of growth that's unique to bone. It follows
Wolff's law, which is named after the orthopedic surgeon J. Wolff, who
discovered it at the end of the nineteenth century. Basically, Wolff's law
states that a bone responds to stress by growing into whatever shape best
meets the demands its owner makes of it. When a bone is bent, one side
is compressed and the other is stretched. When it's bent consistently in
one direction, extra bone grows to shore up the compressed side, and
some is absorbed from the stretched side. It's as though a bridge could
sense that most of its traffic was in one lane and could put up extra
beams and cables on that side while dismantling them from the other.
As a result, a tennis player or baseball pitcher has heavier and differently
contoured bones in the racket arm or pitching arm than in the other
one. This ability is greatest in youth, so in childhood fractures it's often
best to put the bone ends together gently by manipulation without sur-
gery, settling for a less than perfect fit. Sometimes the hardest part is
convincing the parents that a modest bend will straighten itself out in a
few months in accordance with Wolff's law.