Biomedical Engineering Reference
In-Depth Information
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Compact bone.
Compact bone is also known as cortical bone. It is the
hard material that makes up the shaft of long bones and the outside
surfaces of other bones. Compact bone consists of cylindrical units
called osteons (see Figure 1.1). Each osteon contains concentric
lamellae (layers) of hard, calcified matrix with osteocytes (bone cells)
lodged in lacunae (spaces) between the lamellae. Smaller canals, or
canaliculi, radiate outward from a central canal, which contains
blood vessels and nerve fibers. Osteocytes within an osteon are con-
nected to each other and to the central canal by fine cellular exten-
sions. Through these cellular extensions, nutrients and wastes are
exchanged between the osteocytes and the blood vessels. Perforating
canals (Volkmann's canals) provide channels that allow the blood
vessels running through the central canals to connect to the blood
vessels in the periosteum that surrounds the bone. In general the
Young's modulus of compact bone is about 18 GPa and its porosity
ranges from 5% to 30%.
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Spongy bone.
Spongy bone, also called cancellous or trabecular
bone, is an interior meshwork of trabeculae. Trabeculae consist of
thin, irregularly shaped plates arranged in a latticework network
(see Figure 1.1). They are similar to osteons in that both have
Lamellae
Osteon
Compact
bone
Spongy
bone
Periosteum
Central canal
Blood vessels
Perforating canals
Nerve
Trabeculae
Canaliculi
Osteocyte
Lacunae
FIGURE 1.1
Illustration of compact and spongy bone.
