Biomechanics and function of spine

Two adjacent vertebrae with the intervening intervertebral discs form a basic unit called “motion segment”. The movement between the vertebrae take place in front at the intervertebral discs and behind at facet joints. Superior and inferior articular facets of adjacent vertebra form the facet joints. All the three joints, the intervertebral disc and the two facet joints can be source of pain if they undergo degeneration i.e wear and tear.

On loading 80% of the weight is transmitted through the anterior column comprising of vertebral bodies and intervertebral disc. The pressures in intervertebral disc are highest in bending forwards and lifting weights (Fig1). Remaining 20% is transmitted through posterior column formed by the vertebral arches, facet joints and intervening ligaments. The posterior paraspinal muscles play an important role in supporting the spine.

The basic function of vertebral column is

  • Protect spinal cord, which carries nerves supplying different parts of body
  • Provides basic structure for posture and locomotion.