Biomedical Engineering Reference
In-Depth Information
4
Biomechanical aspects of bone repair
D. Lacroix, institute for Bioengineering of
catalonia (iBEc), Spain
Abstract
: in this chapter some biomechanical aspects of bone repair are
presented. The composition and structure of bone from a biomechanical
point of view are first presented to highlight physical differences between
cortical and trabecular bone. Then, the biomechanical properties of both
types of bone are presented and discussed. The concept of poroelasticity
is introduced to model bone and the effect of interstitial fluid flow on the
overall mechanical response of bone is indicated. Finally bone repair and
damage concepts are introduced. The remodelling of bone depending on
the type of bone and its age is discussed. The damage present in the form
of cracks in individual trabeculae and its effect on the overall mechanical
response of bone are discussed.
Key words
: biomechanics, bone, mechanical properties, remodelling, repair.
4.1 Bone composition and structure
4.1.1 Composition
Bone is a hard connective tissue that fulfils three main functions: (1) it gives
support to the body structure, (2) it serves as a protection shield against
external loadings and (3) it provides a framework that allows skeletal motion.
Bone is made up of a mineral or inorganic phase (60-70% of the tissue),
of water (5-8%) and of an organic matrix that makes up the remainder.
Approximately 90% of the organic matrix is collagen and 10% are non-
collagenous proteins. Bone strength is given mainly by its mineral phase
made of non-stochiometric hydroxyapatite crystals (Ca
10
(Po
4
)
6
(oH)
2
) with
carbonate ions (Hasegawa
et al
., 1994). The small crystals are in the shape
of needles, plates and rods located within and between collagen fibers. The
plate-like crystals have dimensions of 20-80 nm long and 2-5 nm thick.
Bone contains four types of cells: (1) osteoprogenitor cells, (2) osteoblasts,
(3) osteocytes and (4) osteoclasts, of which osteocytes are the most abundant.
Bone contains a small number of mesenchymal cells called osteoprogenitor
cells which have the ability to proliferate and differentiate into osteoblasts.
The bone matrix is produced by the osteoblasts which differentiate into
osteocytes when surrounded by bone matrix. Osteocytes are mature bone cells
with extensive cell processes that project through the canaliculi. Through a
network of cells, they establish contact and communication between adjacent
osteocytes and the central canals of osteons via gap junctions (Donahue,
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