There is considerable variation in the mobility of the lumbar spine among people. People with acute and chronic low-back pain have reduced mobility, but in prospective studies mobility has not predicted the incidence of low-back pain.
Low-back pain is related to frequent or heavy lifting, carrying, pulling and pushing. High tensile forces are directed to the muscles and ligaments, and high compression to the bones and joint surfaces. These forces can cause mechanical injuries to the vertebral bodies, intervertebral discs, ligaments and the posterior parts of the vertebrae. The injuries may be caused by sudden overloads or fatigue due to repetitive loading. Repeated microtrauma, which may even occur without being noticed, have been proposed as a cause for degeneration of the lumbar spine.
Most patients with spondylolysis or pars stress reactions respond favorably to non-operative treatment. Usually this treatment includes a period of rest or immobilization followed by physical therapy. The role and best type of bracing continue to be debated. In selective cases, epidural steroid injections or selective nerve root blocks help in controlling symptoms. Most authors agree that patients may return to normal activities when they are pain-free, regardless of whether there is radiographic evidence of pars healing.9
After failure of nonoperative management, surgical intervention can be considered. Surgical treatment is more likely in patients with neurologic deficits or spondylolisthesis of Grade III or greater. Various surgical techniques have been utilized, including decompressive laminectomy, posterolateral fusion, interbody fusion, and direct pars repair.10 The patient can usually return to activities once they are pain-free and any fusion has healed.
(11a) A T2-weighted axial image at the L4-5 level reveals severe bilateral facet hypertrophic changes (arrows). This feature is typical of a degenerative etiology of spondylolisthesis, and is rarely found in patients with spondylolysis.
The main function of the disc is mechanical. The disc transmits load along the spinal column and also allows the spine to bend and twist. The loads on the disc arise from body weight and muscular activity, and change with posture (see ). During daily activities the disc is subject to complex loads. Extending or flexing the spine produces mainly tensile and compressive stresses on the disc, which increase in magnitude going down the spine, due to differences in body weight and geometry. Rotating the spine produces crosswise (shear) stresses.
There are 24 intervertebral discs in the human spine, interspersed between the vertebral bodies. Together these make up the anterior (front) component of the spinal column, with the articulating facet joints and the transverse and spinous processes making up the posterior (rear) elements. The discs increase in size down the spine, to approximately 45mm antero-posteriorly, 64mm laterally and 11mm height in the lower back region.
The intervertebral discs occupy about one-third of the spine. Since they not only provide the spinal column with flexibility but also transmit load, their mechanical behaviour has a great influence on the mechanics of the whole spine. A high proportion of cases of low-back pain are associated with the disc, either directly through disc herniation, or indirectly, because degenerated discs place other spinal structures under abnormal stress. In this article, we review the structure and composition of the disc in relation to its mechanical function and discuss changes to the disc in disease.
11 Rosenberg NJ, Bargar WL, Friedman B. The incidence of spondylolysis and spondylolisthesis in nonambulatory patients. Spine. 6:35, 1981.
8 Ulmer JL, Mathews VP, Elster AD, Mark LP, Daniels DL, Mueller W. MR imaging of lumbar spondylolysis: the importance of ancillary observations. Am J Roentgen. 169:233, 1997.
7 Ulmer JL, Elster AD, Mathews VP, Allen AM. Lumbar spondylolysis: reactive marrow changes seen in adjacent pedicles on MR images. Am J Roentgen. 164:429, 1995.
Spondylolisthesis: Spondylolisthesis is a forward, horizontal slip of one vertebra in relation to another. It may result from a fracture in the bridge of bone connecting the front to the posterior of the vertebra. Obviously the intervertebral disc between two such vertebrae is stretched and subjected to abnormal loads. The matrix of this disc, and to a lesser extent, adjacent discs, shows changes in composition typical of degeneration-loss of water and proteoglycan. This condition can be diagnosed by x ray.
6 Ulmer JL, Mathews VP, Elster AD, King JC. Lumbar spondylolysis without spondylolisthesis: recognition of isolated posterior element subluxation on sagital MR. Am J Neuroradiology. 7:1393, 1995.
4 Amato M, Totty WG, Gilula LA. Spondylolysis of the lumbar spine: demonstration of defects and laminal fragmentation. Radiology.1984; 153:627 -9.