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No abstract

Thta form of t.he vertebral column is definitely related to its function as a supporting rod, :i hme for attarhment of body and limb muscles, and a protection of the spinal cord and nerves. Priniitivdy composed of a series of simple undifferentiated blocks, it progressively beconies ctrrnplioat,ed through development of articular processes giving added strength and greater mobility. Simultaneously, the c,entrum and the neural arch become adapted to withstand tension and compression stresses which r m y with the movements possible in different regions of the column. These movements a r e partially determined by t.he plane of the zygapophyws and the nature of the intercentral articulation, together with the action of the axial muscles and ligaments.

Tensile breaking load, strength, strain, modulus of elasticity and density plus the histological structure at the fracture site, were determined for 207 standardized specimens of cortical bone from the embalmed femur, tibia, and fibula of 17 men from 36 to 75 years of age. The men were divided into a younger group (41.5 years old-avg)) and an older group (71 years old-avg). Specimens from younger men had a greater average breaking load, strength, strain, modulus and density than those from older men. The percentage of spaces in the break area was greater in specimens from older men, but specimens from younger men had a slightly greater percentage of osteons, osteon fragments, and interstitial lamellae. The number of osteons/mm2 and of osteon fragments/mm2 was greater in specimens from older men but the average area/osteon and area/osteon fragment was greater in specimens from younger men. Thus, there are quantitative and qualitative differences in the histological structure of bone from younger and older men. Differences in the tensile properties of bone from younger and older men can be explained by histological differences in the bone.