ABSTRACT
The skeleton is a complex, metabolically active tissue that serves multiple physiologic functions. However, its most important purpose is to maintain normal posture and locomotion by virtue of its hardness. This quality is conferred by a unique arrangement of plates of a calcium/phosphorus-containing mineral called hydroxyapatite [Ca
(PO
)
(OH)
] interspaced within the interstices of a protein matrix composed predominately of type 1 collagen (90+%). The matrix also contains a large number of noncollagenous proteins, some of which are unique to bone (Table 61.1). This structure confers extreme hardness, but also sufficient flexibility during strain to minimize brittleness.
