Dalley, 10th Edition

89

Vertebrae

hiatus can be palpated at the inferior end of the sacrum lo cated in the superior part of the intergluteal cleft. The transverse processes of thoracic and lumbar verte brae are covered with thick muscles and may or may not be palpable. The coccyx can be palpated in the intergluteal cleft, inferior to the apex of the sacral triangle. The apex of the coccyx can be palpated approximately 2.5 cm postero superior to the anus. Clinically, the coccyx is examined with a gloved nger in the anal canal. Variations in Vertebrae Most people have 33 vertebrae, but developmental errors may result in 32 or 34 vertebrae (Fig. 2.14). Estimates of the frequency of abnormal numbers of vertebrae superior to the sacrum (the normal number is 24) range between 5% and 12%. Variations in vertebrae are affected by race, gender, and developmental factors (genetic and environmental). An increased number of vertebrae occur more often in males and a reduced number occurs more frequently in females. Some races show more variation in the number of vertebrae. Variations in the number of vertebrae may be clinically im portant. An increased length of the presacral region of the vertebral column increases the strain on the inferior part of the lumbar region of the column owing to the increased leverage. However, most numerical variations are detected incidentally during diagnostic medical imaging studies being performed for other reasons and during dissections and au topsies of persons with no history of back problems. Caution is necessary when describing an injury (e.g., when reporting the site of a vertebral fracture). When count ing the vertebrae, begin at the base of the neck. The number of cervical vertebrae (seven) is remarkably constant (and not just in humans, but among vertebrates—even giraffes and snakes have seven cervical vertebrae). When considering a numerical variation, the thoracic and lumbar regions must be considered together because people having more than ve lumbar vertebrae often have a compensatory decrease in the number of thoracic vertebrae (Chiu et al., 2024). Variations in vertebrae also involve the relationship be tween the vertebrae and ribs, and the number of vertebrae that fuse to form the sacrum (Fig. 2.14). The relationship of presacral vertebrae to ribs and/or sacrum may occur higher

Cranial shift

Normal

Caudal shift

Cervical rib

C7

C7

2

T12

T12

Lumbar rib

L5

L5

Sacralized L5

Lumbarized S1

Anterior views

(A)

(B)

(C)

( cranial shift ) or lower ( caudal shift ) than normal. Note, however, that a C7 vertebra articulating with a rudimentary cervical rib(s) is still considered a cervical vertebra. The same is true for lumbar vertebrae and lumbar ribs. Likewise, an L5 vertebra fused to the sacrum is referred to as a “sacral ized 5th lumbar vertebra” (see the Clinical Box “Abnormal Fusion of Vertebrae” in this chapter). FIGURE 2.14. Variations in vertebrae and their relationship to ribs. A. “Cranial shift.” In this case, there are 13 ribs, including a cervical rib articulating with vertebra C7 and a diminished 12th rib articulating with vertebra T12. Vertebra L5 is shown partially incorporated into the sacrum, but such “sacralization” can also be complete. The lowest sacral segment (S5) is partially segmented. B. Common arrangement of vertebrae and position of 1st and 12th ribs. C. “Caudal shift.” Here the 12th rib is increased in size, and there is a small lumbar rib. The transverse process of vertebra L4 is increased in size, whereas that of vertebra L5 is greatly reduced. The rst sacral segment is shown partially separated from the rest of the sacrum, but such “lumbarization” can also be complete. The 1st coccygeal segment is incorporated into the sacrum—that is, it is “sacralized.”

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CLINICAL BOX

VERTEBRAE Vertebral Body Osteoporosis

a disruption of the normal balance of calcium deposition and resorption. As a result, the quality of bone is reduced and atrophy of skeletal tissue occurs. Although osteoporosis af fects the entire skeleton, the most affected areas are the neck of the femur, the bodies of vertebrae, the metacarpals (bones of the hand), and the radius. These bones become weakened and brittle and are subject to fracture.

Vertebral body osteoporosis is a common meta bolic bone disease that is often detected during routine radiographic studies. Osteoporosis results from a net demineralization of the bones caused by