Hypothesis
Idiopathic osteoporosis: an evolutionary dys-adaptation?
C Alexander
Department of
Anatomy with Radiology, School of Medicine, University of Auckland, New
Zealand
Correspondence to: Professor C Alexander, School of Medicine, University of Auckland, Private Bag 92019, Auckland, New Zealand c.alex{at}xtra.co.nz
Accepted for publication 13 December
2000
Osteoporosis is characterised by simultaneous net bone growth
and net resorption on different surfaces, suggesting that systemic factors are not the sole explanation for the findings. The main clinical consequence is fracturing in the largely trabecular bones of
the spine, hip, and radius, and the key problem in these areas is
finding an explanation for the preferential loss of transverse trabeculae. In normal bone, local maintenance depends on a negative feedback response to intermittent compression strain, and it is concluded, from biomechanical analysis of the response required to
achieve negative feedback, that a preferential loss of transverse trabeculae is indicative of a selective deficiency of radial
compression loading. The only significant source of radial compression
in humans is the induced strain produced by axial tension. This is a
necessary component of the lifestyles of quadrupeds and arboreal primates, but in humans occurs only on the convex side when the bone is
offset loaded. The resulting strain is a function of the range of
movement. It is suggested that the asymmetrical pattern of bone loss in
cortical and trabecular osteoporosis reflects chronic underuse of
movement range, resulting from the adoption of a bipedal lifestyle.
Exercise regimens based on using the whole of the available movement
range should better prepare the skeleton to adjust to other factors
hostile to bone maintenance.
© 2001 by Annals of the Rheumatic Diseases
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