Chapter 14: The Spine: Structure, Function, and Posture

Introduction

Posture is alignment of the body parts whether upright, sitting, or recumbent. It is described by the positions of the joints and body segments and also in terms of the balance between the muscles crossing the joints.⁴¹ Impairments in the joints, muscles, or connective tissues may lead to faulty postures, or, conversely, faulty postures may lead to impairments in the joints, muscles, and connective tissues as well as symptoms of discomfort and pain. Many musculoskeletal complaints can be attributed to stresses that occur from repetitive or sustained activities when in a habitually faulty postural alignment. This chapter reviews the structural relationships of the spine and extremities to normal and abnormal posture and describes the mechanisms that control posture. Common postural impairments and general guidelines for their management are described. Specific exercises for the upper and lower extremities that affect posture are highlighted in this chapter and are described in detail in the succeeding chapters in Part IV of the text. Chapter 15 describes the common pathologies associated with the spine and details management guidelines, and Chapter 16 describes spinal exercises and manual interventions in detail.

Structure and Function of the Spine

Joints of the Spine

The spinal column consists of 33 vertebrae (7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 3 or 4 coccygeal) and their respective intervertebral discs. Articulating with the spine are the 12 pair of ribs in the thoracic region, the cranium at the top of the spine at the occipital-atlas joint, and the pelvis at the sacroiliac joints (Fig. 14.1).¹³

Functional Components of the Spine

Functionally, the spinal column is divided into anterior and posterior pillars (Fig. 14.2).

• The anterior pillar is made up of the vertebral bodies and intervertebral discs and is the hydraulic, weight-bearing, shock-absorbing portion of the spinal column. The size of the disc influences the amount of motion available between two vertebrae.

• The posterior pillar (articular pillar), or neural arch, is made up of the articular processes and facet joints, which provide the gliding mechanism for movement. The orientation of the facets influences the direction of motion. Also part of the posterior unit are the bony levers, the two transverse processes, and the spinous process to which the muscles attach and function to cause and control motions and provide spinal stability.