Dalley, 10th Edition

95

Vertebrae

Abnormal Fusion of Vertebrae

convex and their diameter increases (Fig. B2.9B, D) (Bogduk, 2012). The bone loss and consequent change in shape of the vertebral bodies may account in part for the slight loss in height that occurs with aging. The develop ment of these concavities may cause an apparent narrow ing of the intervertebral “space” on radiographs based on the distance between the margins of the vertebral bodies; however, this should not be interpreted as a loss of IV disc thickness. Aging of the IV discs combined with the changing shape of the vertebrae results in an increase in compressive forces at the periphery of the vertebral bodies, where the discs at tach. In response, osteophytes (bony spurs) commonly de velop around the margins of the vertebral body (along the attachments of the bers of the outer part of the disc), es pecially anteriorly and posteriorly (Fig. B2.9). Similarly, as altered mechanics place greater stresses on the zygapophy sial joints, osteophytes develop along the attachments of the joint capsules and accessory ligaments, especially those of the superior articular process (Fig. B2.9A), whereas exten sions of the articular cartilage develop around the articular facets of the inferior processes.

In approximately 5% of people, L5 is partly or completely incorporated into the sacrum. These conditions are known as hemisacralization and sa cralization of the L5 vertebra, respectively (Fig. B2.8A). In others, S1 is more or less separated from the sacrum and is partly or completely fused with L5 vertebra, which is called lumbarization of the S1 vertebra (Fig. B2.8B). When L5 is sacralized, the L5–S1 level is strong and the L4– L5 level degenerates, often producing painful symptoms.

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L5

L5

S1

S1

Pelvic surface

Dorsal surface

(A)

Sacralization of L5 vertebra

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B

SP

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S2

B

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(A) Anterosuperior oblique view, lumbar vertebra

(B) Anteroposterior radiograph

Pelvic surface

Dorsal surface

(B)

Lumbarization of S1 vertebra (S1 is not part of sacrum in this case)

Lumbar spine A–D Vertebral body Spinal cord Spinous process B S SP

FIGURE B2.8. Abnormal fusion of vertebrae.

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B

Effect of Aging on Vertebrae

VP V (C) Median section, lumbar vertebra Copyright © 2027 Wolters Kluwer. Unauthorized reproduction of the article is prohibited.

Vacuum phenomenon (gas in degenerated IV disc and body of vertebra) Vertebral arch Osteophytes Vertebral body compression Erosion

Between birth and age 5, the body of a typical lum bar vertebra increases in height threefold (from 5–6 mm to 15–18 mm), and between ages 5 and 13, it increases another 45–50%. Longitudinal growth continues throughout adolescence, but the rate decreases and is completed between ages 18 and 25. During middle and older age, there is an overall de crease in bone density and strength, particularly centrally within the vertebral body. Consequently, the articular sur faces gradually bow inward so that both the superior and inferior surfaces of the vertebrae become increasingly con cave (Fig. B2.9A, C), and the IV discs become increasingly

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B

VP

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(D) Sagittal CT

FIGURE B2.9. Effects of aging on vertebrae.