3+ 4/2002 - Společnost pro pojivové tkáně

unit of LM than controls in proportion with
the reduction observed in LM, reaching
very low BMC or FA-BMC values in the
extreme cases.
Results suggest that l. dialysed men and
pre-MP women show a normal control of
bone mass by muscle mass; 2. however, the
metabolic interference from CAPD/HD
reduces the BMC/LM proportionality regardless
of the patient's fat mass, and 3. this situation
is further affected by menopause, after
which the BMC control seems to be
impaired in proportion with the reduction
in mechanical usage (muscle mass reduction).
This would confirm that dialysisinduced
systemic factors affected the bone
mechanostat setpoint over the natural
endocrine influences in these patients.
BIOCHEMICAL PROCESSES IN THE
CORTICAL BONE DURING THE
STRESS/STRAIN CHANGES
M. Petrtýl, and J. Danešová
Laboratory of Biomechanics and Biomaterial Engineering,
Department of Structural Mechanics, Faculty of
Civ. Eng., Czech Technical University,Thákurova 7,
Prague 6, 160 00, Czech Republic
E-mail: petrtyl@fsv.cvut.cz
Aim of the study: The bone tissue
remodelling is controlled in a dominant
way by biomechanical remodelling initiators
(i.e. by spherical strain tensors) and by
biomechanical speed regulators of metabolic
remodelling processes (i.e. by deviators
of the stress/strain tensors).
The bone tissue remodelling is relatively
avery slow process. In physiologically
„normal“ conditions, it tends towards the
state of remodelling equilibrium in which
the coincidence of the first dominant principal
stress/strain direction, and the direction
of the first principaI axis of anisotropy,
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LOCOMOTOR SYSTEM vol. 9, 2002, No. 3+4
and the principal directions of the structure
(longitudinal axes of osteons) is
reached at the point of macrostructure.The
presented theory is concerned to the exact
formulations of the mechanical (i.e.
stress/strain fields) effects on the biochemical
metabolic processes.
Materials and methods: On the basis
of the up-to-now recognized and available
knowledge of biochemical processes related
to the creation of a new bone, the kinetics
of chemical substances (molecular mixtures)
can be expressed by five global
stoichiometric equations of bone remodelling.
In regard to the stoichiometric equations,
it is necessary to point out that they
express global metabolic processes which
.are initiated by mechanical loading effects
in the cases of dominant biomechanical
activities.The biochemical reactions related
to the cortical bone remodeling and
expressed by stoichiometric equations proceed
at certain speeds that depend on the
speed constants and on the concentrations
of individual substrates Di.
Results: The fundamental kinetic equations
of bone remodelling present the relations
between the time change and the concentrations
of molar substances. The speed
remodelling constants with speed remodelling
functions depend on the mechanical
stress, resp. on the spheric stress tenzor.
Conclusions: the biochemical reactions
are initiated by the deviator of the
stress/strain tensor. Shear stresses (the components
of stress tensor deviator) deform
the microelements of bone tissue and the
flow of extracelular liquid mechanochemically
(with the direct activity of integrins a,
b) starting the production of prostaglandin
E which initiates bone compartment
resorption (Klein-Nulend, E. H. Burger).