Biomechanics of the lumbar spine.

The magnitude of low back pain in terms of its occurrence and cost is reviewed. The biomechanics of the lumbar spine are related to the functional anatomy. The disparate functional mechanical requirements of the spine, support, mobility, housing, protection and control are reviewed. Typical forces one applies to the spine in activities of daily living as well as in mechanical overloads are discussed. The loads are broken down into tensile, compressive, shear and torsional loads. The posterior elements, the vertebral body and the intervertebral disc are reviewed separately and some implication in terms of the aetiology of low back pain is given. Finally, the behavior of the unit (the functional spinal unit) is discussed.