Spondylolisthesis
From Wikipedia, the free encyclopedia
| ICD-10 | M43.1 |
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Spondylolisthesis (not to be confused with spondylosis or spondylolysis) is an anteroposterior translatory movement of two spinal vertebrae in relationship to each other caused by instability between the two involved vertebrae. The instability can be caused by degenerative changes of the facet joints, or by congenital or traumatic disruption of the pars interarticularis of the upper of the two vertebrae. It occurs most commonly in the lumbar spine.
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[edit] Developmental anatomy
In the very early stages of fetal development, all bones are initially represented as cartilaginous precursors; as in utero tissue differentiation progresses bone comes to form within this cartilage; a process called ossification. This occurs in specific and consistent sites within the forming bones, and the areas in which it takes place are called ossification centres.
A fully formed vertebra consists of the centrum, the main weight-bearing part of the bone, and the dorsal arch, which surrounds the spinal cord and the posterior part of which can be felt externally. There are also lateral processes to which spinal muscles are attached, and superior and inferior articular processes which form joints with the vertebrae above and below.
In the fetus, three ossification cenres form in each vertebra; one in what will become the centrum, and one in each side of the dorsal arch. During development these centres normally ossify and fuse together to form a normal vertebra. Occasionally, however, for reasons which are presently unknown, the ossification centres fail to fuse. When the dorsal arch fails to fuse with the centrum the condition created is called spondylolysis. If the two dorsal arch centres fail to fuse the condition resulting is called spina bifida.
Spondylolysis also runs in families and is more prevalent in some populations, suggesting a hereditary component such as a tendency toward thin vertebral bone.
Spondylolysis is the most common cause of spondylolisthesis. The hereditary factor mentioned above is quite notable, since the frequency of spondylolisthesis in Eskimos is 30–50%.
Trauma can also cause spondylolysis. It is more common in gymnasts, particularly where the spine is often loaded in extreme extension, such as when landing on the feet. This places extreme stress on the dorsal arches, acting like a nutcracker.
[edit] Pathology
Simple spondylolysis is an asymptomatic condition detectable only by specialized X-ray or Magnetic Resonance Imaging (MRI) techniques. As the centrum of the affected vertebra is connected to the dorsal arch only by fibrous tissue, however, there is a weakness present. There is a potential for this fibrous union to become stretched, either by major or by minor injury or indeed just by the ongoing strain involved in supporting the weight of the body while standing upright.
When this disruption occurs the anatomy of the intervertebral joints dictates that the centrum of the defective vertebra moves forward in relation to the vertebra below it, while the dorsal arch remains correctly located. This condition is now a true spondylolisthesis.
A spondylolisthesis can be stable or unstable, depending on posture and loading. It can be symptomatic or asymptomatic.
[edit] Symptomatology
The condition will almost invariably cause back pain, which will be worse during activity, which may feel like a muscle strain. The distortion of the anatomy of the back makes compression of one or more lumbar nerve roots likely, which will cause sciatica and possibly disturb bladder control or bowel function. In extreme cases, particularly in an upper lumbar lesion, pressure on the whole nerve bundle within the spinal canal may lead to paralysis of the lower limbs. This condition is known as cauda equina syndrome, and acute treatment is imperative, as delay can result in lifelong handicaps.
Typical physical changes that occur in an individual with spondylolisthesis will be a general stiffening of the back and a tightening of the hamstrings, with a resulting change in both posture and gait. The posture will typically give the appearance that the individual leans forward slightly and/or that they are suffering from lordosis. The gait of the individual may change to give the appearance of more of a "waddle" than a walk, where the individual rotates the pelvis more due to the decreased mobility in the hamstrings. A result of the change in gait is often a noticeable atrophy in the gluteal muscles due to lack of use.
[edit] Treatment
Bed-rest will relieve the symptoms to some extent, but will not be effective in terms of the production of a cure. Similarly, pain killing or anti-inflammatory medication or physiotherapy have only a temporary palliative effect. The only effective long-term curative treatment, if symptoms are sufficiently severe to warrant it, is by reconstructive surgery and fusion of the affected vertebra to its lower neighbour. As the development of a spondylolisthesis will commonly destroy the intervertebral disc, this will usually also need to be removed during the same surgical procedure.
