Dalley, 10th Edition

Chapter 2 ■ Back

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W

P

B

FIGURE B2.1. Effects of osteoporosis on vertebral column. A. Early to moderate osteoporosis. This phase is characterized by vertical striation in the vertebral bodies. B. Later osteoporosis. Now the striated pattern is lost as the continued loss of trabecular bone produces uniform radiolucency (less white, more “transparent”). In contrast, the cortical bone, while thinned, appears relatively prominent. C. Late osteoporosis in thoracic region of vertebral column. There is excessive thoracic kyphosis, a result of the collapse of the vertebral bodies, which have become wedge shaped ( W ), planar ( P ), and biconcave ( B ). (C) Left lateral radiograph (A) Right lateral radiograph (B) Left lateral radiograph

Fracture and Dislocation of Atlas The atlas (vertebra C1) is a bony ring, with two wedge-shaped lateral masses, connected by rela tively thin anterior and posterior arches and a trans verse ligament (see Fig. 2.8B). Because the taller side of the lateral mass is directed laterally, vertical forces (e.g., striking the bottom of a pool in a diving accident)

Radiographs taken during early to moderate osteopo rosis demonstrate demineralization, which is evident as diminished radiodensity of the trabecular (spongy) bone of the vertebral bodies, causing the thinned cortical bone to appear relatively prominent (Fig. B2.1B). Osteoporo sis especially affects the horizontal trabeculae of the tra becular bone of the vertebral body (compare Figs. 2.4 and B2.9C). Consequently, vertical striping may become ap parent, re ecting the loss of the horizontal supporting tra beculae and thickening of the vertical struts (Fig. B2.1A). Radiographs in later stages may reveal vertebral collapse (compression fractures) and increased thoracic kyphosis (Fig. B2.1C; see Fig. B2.21B, F). Vertebral body osteo porosis occurs in all vertebrae but is most common in thoracic vertebrae and is an especially common nding in postmenopausal females. Laminectomy The surgical excision of one or more spinous pro cesses and the adjacent supporting vertebral lami nae in a particular region of the vertebral column is called a laminectomy ( 1 in Fig. B2.2A). The term is also commonly used to denote removal of most of the verte bral arch by transecting the pedicles ( 2 in Fig. B2.2A). Laminectomies are performed surgically (or anatomi cally in the dissection laboratory) to gain access to the ver tebral canal, providing posterior exposure of the spinal cord (if performed above the L2 level) and/or the roots of speci c spinal nerves. Surgical laminectomy is often performed to relieve pressure on the spinal cord or nerve roots caused by a tumor, herniated IV disc, or bony hypertrophy (excess growth).

Vertebral body

Vertebral foramen (vertebral canal in the articulated vertebral column)

Pedicle

Vertebral arch

2 1

Lamina

Spinous process

(A) Posterosuperior view

L3 L4

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Laminectomy of L4 vertebra L5

Dural sheath enclosing spinal cord

Extradural space

(B) Posterior view

FIGURE B2.2. Laminectomy. A. Sites at which laminectomies are performed. B. Postlaminectomy.