Formed by 33 vertebral segments and divided into four distinct portions, the spinal column and its associated muscles provide postural control to the torso and skull, while also protecting the spinal cord. The conflicting needs for range of motion (ROM) versus protection of the spinal cord are met in varying degrees throughout the spine (Fig. 13-1).
The three segments of the mobile spinal column with their normal curvature noted.
The cervical spine provides the greatest ROM, but here the spinal cord is the most vulnerable. The thoracic spine provides the greatest protection of the spinal cord but does so at the expense of ROM. The lumbar spine provides a more equal balance between protection of the spinal cord and available ROM. The sacrum and coccyx are composed of fused bones. The sacrum affixes the spinal column to the pelvis and serves as a site for muscle attachment. At this level, the spinal cord has exited the column.
Spine-related pain is a prevalent condition. During any given year, up to 36% of adults will experience low back pain for the first time, with recurrence of symptoms a common phenomenon.1 The prevalence of back pain in adolescents mimics that in adults, with reports of up to 70% to 80% of the population affected.2,3 The high prevalence, the significant association of back pain to mental illnesses such as depression, and the resulting demands on the healthcare system make the cost of back pain exorbitant. Acute injury to the spine during athletic competition accounts for an estimated 10% to 15% of all spinal injuries, and each injury carries the risk of traumatizing the spinal cord or spinal nerve.4 This chapter discusses conditions affecting the lumbar and sacral regions. Conditions affecting the cervical and thoracic regions are presented in Chapter 14. Traumatic (emergent) spinal injuries are discussed in Chapter 20.
Figure 13-2 compares the relative sizes of the cervical (n = 7), thoracic (n = 12), and lumbar (n = 5) vertebrae and identifies the bony landmarks. The body's weight is transmitted primarily along the spinal column via the vertebral body, whose size is related to the amount of force it transmits. Carrying only the weight of the head, the vertebral bodies of the cervical vertebrae are much smaller than those of the lumbar vertebrae, which are required to transmit and absorb the weight of the entire torso. A segment, comprised of two adjacent vertebral bodies, the intervening disc, and the soft tissue that holds the vertebrae together, represents the smallest functional unit of the spine. The vertebrae of the cervical spine are included in this section for a basis of comparison. Refer to Chapter 14 for further description of the cervical spine.