In an upright position, the spine is submitted to axial load, which probably leads to the premature disc degeneration from which humans are apt to suffer. However, during development from quadruped to biped, the function of the spine had to alter completely ( Table 31.1) this has serious consequences. Comparative anatomical evidence suggests that the spine has evolved as a hanging structure between the anterior and the posterior parts of the body. The development of the erect posture is recent and it seems that, apart from the compensatory lordosis, not much in the way of structural adaptation has taken place. Maintaining normal physiological lordosis is therefore important in the prophylaxis of low back syndromes. Indeed, these very sensitive structures lie at the weakest and most unprotected part of the column, and it is good posture, rather than any ligamentous device, that protects them against a posterior or posterolateral shift of the disc.
A backward shift of the disc is a very undesirable event because nerve roots and dura mater emerge at the posterior aspect of the vertebral column. It is clear that axial pressure exerted on the disc in a lordotic spine will result in a forward strain on the disc, whereas increased axial pressure during trunk flexion will force the disc backwards.
4įig 31.1 Development of the lumbar lordosis.Īs a result of the lumbar lordosis, the intervertebral space is larger in front than behind, which has some consequences for the intervertebral disc. At 13 months the lumbar spine is straight, at 3 years some lumbar lordosis is present, and by 8 years the lumbar spine has attained its normal adult posture ( Fig. In intrauterine life and during the first 5 months after birth, the spinal curves are absent and there is only one slight kyphosis of the whole spine. The phylogenetic evolution from the large thoracolumbar kyphotic spine of a quadruped into two kyphotic and lordotic curves is also reflected in the spine’s ontogeny. This S form seems to be a compromise between the static and the dynamic qualities of the spine 2 theoretical considerations suggest that the S form is the shape an elastic bar adopts when it is subjected to axial compression. 1 The four curves resulted: cervical lordosis, thoracic kyphosis, lumbar lordosis and sacrococcygeal kyphosis. After a further 1.5 million years, the definitive erect posture had been adopted – Homo erectus. This began in Africa 3 million years ago with Homo australo-pithecus, which had a pelvis strong enough to support an erect posture. Erect, there are four sagittal curves, which are the result of man’s evolution from quadruped to biped. The human spine is a self-supporting construction of skeleton, cartilage, ligaments and muscles.
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