The lumbar spine is typically comprised of five vertebrae that lie between the pelvis and the ribcage. A study by Hanson et al (2010) reported that 20% of people do not have five lumbar vertebrae: 14.5% have six; 5.3% have four; and 0.13% have the rare finding of three lumbar vertebrae.

The lumbar spine supports much of our body weight and the vertebrae are large with thick intervertebral discs to compensate for this. This section of the spine is concave posteriorly because of wedge shaped intervertebral discs, creating a natural lumbar lordosis. Humans are the only vertebrates to have a lordotic lumbar spine, allowing us to stand on two limbs for prolonged periods.

The lumbar facets are generally oriented in the sagittal plane, favouring the movements of flexion and extension. Kapandji (2010) stated that the shape and the orientation of the superior and inferior facets typically allow for 20° of lateral flexion and 5° of rotation in the lumbar spine. For extension and flexion, the author grouped the thoracic and lumbar spine together and stated that 60° and 105° are the typical ranges of movement respectively. In reality there is a huge amount of human variation here in the range of movement available.

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References:

Hanson, E., Mishra, R., Chang, D., Perkins, T. et al. (2010) ‘Sagittal whole-spine magnetic resonance imaging in 750 consecutive outpatients: Accurate determination of the number of lumbar vertebral bodies - Clinical article. Journal of neurosurgery.’ Spine 12, 47-55.

Kapandji, I. (2010) The Physiology of the Joints. 6 th ed. London: Churchill Livingstone.