ABSTRACT

Interest in biomechanics of the spine developed in the latter half of the twentieth century. Sir Frank Holdsworth proposed the two-column model of the spine in 1963. The functional spinal unit is the smallest physiological unit of the spine that exhibits biomechanical properties similar to that of the entire spine. White and Panjabi defined spinal stability as the ability of the spine under physiological loads to limit patterns of displacement that can damage or irritate the spinal cord or nerve roots and, in addition, to prevent incapacitating deformity or pain caused by structural changes. A complete free-body diagram of the lumbar spine should include the individual weights of the head, trunk, upper limb and the weight lifted, along with their respective distances from the centre of spinal motion. The thoracic spine is unique in being the least mobile segment of the spine and having additional stability and stiffness as a result of its articulation with the rib cage.