Dalley, 10th Edition

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Muscles of Back

This abnormal extension deformity is often associated with weakened trunk musculature, especially the anterolat eral abdominal muscles. To compensate for alterations to their normal line of gravity, women develop a temporary ex cessive lumbar lordosis during late pregnancy. This lordotic curvature may cause lower back pain, but the discomfort normally disappears soon after childbirth. Obesity in both sexes can also cause excessive lumbar lor dosis and lower back pain because of the increased weight of the abdominal contents (e.g., “potbelly”) anterior to the normal line of gravity. Loss of weight and exercise of the anterolateral abdominal muscles facilitate correction of this type of excessive lordosis. Scoliosis (G., crookedness or curved back) is character ized by an abnormal lateral curvature that is accompanied by rotation of the vertebrae (Fig. B2.21D, E, G). The spi nous processes turn toward the cavity of the abnormal cur vature, and when the individual bends over, the ribs rotate posteriorly (protrude) on the side of the increased convexity. Deformities of the vertebral column, such as failure of half of a vertebra to develop ( hemivertebra ), are causes of Joints of vertebral column: Vertebrae are joined to form a semirigid column by IV discs and zygapophysial joints. ■ The relative thickness of the discs determines the degree of mobility. ■ The disposition of the zygapophysial joints controls the type of movement between adjacent vertebrae. ■ The anterior longitudinal ligament resists hyperextension; all other ligaments resist forms of exion. ■ The atlantooccipital joints enable the “yes” (nodding) movement of the head. ■ The atlantoaxial joints enable the “no” (rotational) movement of the head. Alar ligaments limit rotation. Movements of vertebral column: The cervical and lumbar regions are most mobile (and consequently most vulnerable to injury). ■ Flexion and extension occur primarily in the cervical and lumbar regions. ■ Rotation occurs in the cervical and thoracic regions. Curvatures of vertebral column: Primary curvatures (thoracic and sacral kyphoses) are developmental; secondary The Bottom Line: Vertebral Column

structural scoliosis . Sometimes a structural scolioses is com bined with excessive thoracic kyphosis— kyphoscoliosis —in which an abnormal AP diameter produces a severe restric tion of the thorax and lung expansion (Culham et al., 1994). Approximately 80% of all structural scolioses are idiopathic (a disease of unknown cause), occurring without other asso ciated health conditions or an identi able cause. Idiopathic scoliosis rst develops in females between the ages of 10 and 14 and in males between the ages of 12 and 15. It is most common and severe among females. Problems extrinsic to a structurally normal vertebral column, such as asymmetrical weakness of the intrinsic back muscles ( myopathic scoliosis ), or a difference in the length of the lower limbs with a compensatory pelvic tilt, may lead to a functional scoliosis . When a person is standing, an obvious inclination or listing to one side may be a sign of scoliosis that is secondary to a herniated IV disc. Habit scoliosis is supposedly caused by habitual standing or sitting in an improper position. When the scoliosis is entirely postural, it disappears during maximum ex ion of the vertebral column. Functional scolioses do not persist once the underlying problem has been effectively treated. curvatures (cervical and lumbar lordoses) are acquired in relation to the erect human posture. ■ The curvatures provide shock-absorbing resilience and exibility to the axial skeleton. ■ Extensors of the back and abdominal exors provide dynamic support to maintain the curvatures. Vasculatures of vertebral column: Spinal branches of the major cervical and segmental arteries supply the vertebral column. ■ Internal and external vertebral venous plexuses collect blood from the vertebrae and drain, in turn, into the vertebral veins of the neck and the segmental veins of the trunk. Nerves of vertebral column: Zygapophysial joints are innervated by medial branches of adjacent posterior rami; (recurrent) meningeal branches of spinal nerves supply most bone (periosteum), IV discs, and ligaments as well as the meninges (coverings) of the spinal cord. ■ These two (groups of) nerves convey all localized pain from the vertebral column.

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MUSCLES OF BACK

There are two major groups of muscles in the back. The extrinsic back muscles include super cial and intermedi ate muscles that produce and control limb and respiratory movements, respectively. The intrinsic ( deep ) back muscles include muscles that speci cally act on the vertebral col umn, producing its movements and maintaining posture.

Most body weight lies anterior to the vertebral column, especially in obese people; consequently, the many strong muscles attached to the spinous and transverse processes of the vertebrae are necessary to support and move the column.