Osteoarthritis of the facet joints can lead to instability of a vertebral segment. As continued degeneration weakens the facet joints, the L4 vertebral body slips forward on the L5 vertebral body. The L4-L5 is most likely to slip. The next most likely level is L3-L4, and rarely L5-S1. As the body tries to capture the unstable segment, the facet joints get bigger and place pressure on the nerve root (lumbar spinal stenosis). In considering surgery for potential treatment, both the lumbar spinal stenosis and the instability need to be addressed. A lumbar laminectomy (open decompression—taking pressure off the nerve root) is done along with a posterolateral gutter fusion (eliminating the motion at a painful motion segment). There are some surgeons who recommend only doing the laminectomy/decompression, but literature on the subject seems to favor doing both the fusion and laminectomy/decompression at the same time. Ironically, even though this represents more surgery, results for a fusion and decompression for a degenerative spondylolisthesis are better than for a decompression alone for spinal stenosis, with a 90-95% expected success rate. Additionally, the results of the combined surgery tend to last because the fusion provides the following advantages: It stops the progression of the stenosis. It stops motion in the joint and therefore stops the arthritic pain.
Four syndromes of degenerative spondylolisthesis:
1. Syndrome associated with segmental instability and manifested by low back pain with ambulation (standing or walking), with relief of pain almost immediately after sitting or lying down.
2. Syndrome of lumbar or neurogenic claudication associated with central spinal stenosis at the level of DS. Central stenosis is a result of not only subluxation, but also hypertrophy of the facet joints and the yellow ligament and at times development of synovial cyst or synovial chondroma. Symptoms of lumbar claudication include progressively increasing difficulties walking due to feeling of profound numbness and weakness and, at times, diffuse pain in the legs. Again, sitting down or, better, lying down eliminates the symptoms. Bowel and bladder dysfunction fortunately are seen very rarely in DS, and are associated with an extremely sever degree of spinal stenosis.
3. Syndrome of subarticular or recess stenosis caused by compression of the traversing nerve root (L5 nerve root in cases of DS at L4-L5 level). Impingement of the nerve root most commonly is occurring at a very short segment of the root and is caused by the most medical part of the superior articular process of the lower vertebra at the level of the disc just above the pedicle. Less frequently the nerve root is compromised by a synovial cyst originating from the facet joint and quite commonly seen in cases of DS. Acute accumulation of synovial fluid or hemorrhage into the cyst may produce the clinical picture of a very acute radiculitis or radiculopathy.
4. Syndrome of lateral stenosis caused by compression of the exiting nerve root within the foramen (L4 nerve root in case of DS at L4-L5 level). The nerve root is being trapped by the bony structures of the foramen and buckling annulus of the disc. Frank lateral herniation or extrusion of the disc into the foramen are seen very infrequently.
Spondylolisthesis is a Latin term for "slipped vertebral body". For approximately 5% of the population, a stress fracture occurs (usually between the ages of five and seven) in the lowest lumbar vertebral segment (L5). As a result, the L5 vertebral body slips forward on the S1 (sacral 1) vertebral body. This process is almost never due to trauma. This occurrence often results in no noticeable symptoms, and probably 80% of people never even know they have the problem. In the 20% who do develop low back pain, their pain is usually due to disc degeneration in young adulthood. Without the stabilizing effect of the bony arch, the disc is forced to work harder to resist shear forces (forward subluxation). The disc is designed to function very effectively in compression, but tends to break down when shear forces are applied to it. Pain can also come from the fracture itself, and the reparative tissue within may become irritated and generate pain. Although low back pain is usually the predominant symptom, some patients experience leg pain due to nerve pinching. The leg pain will generally be worse when the patient stands or walks, and it is almost always the L5 nerve that is pinched.