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Abstract
spinal stenosis is defined as the narrowing of the central lumbar canal, the lateral recess, or the intervertebral foramen. Although there are many causes of spinal stenosis, this study focussed on the degenerative process. Degenerative changes and narrowing can occur (1) centrally; (2) in the lateral recess, leading to nerve – root impingement from an overhanging hypertrophic facet joint; (3) within the nerve-root canal (foraminal stenosis); or (4) extraforaminally, frequently because of entrapment by osteophytes, discs, transverse processes or the sacroiliac articulation for the fifth lumbar nerve root.
The clinical features of the disease are often subjective, vague, ill-described and lack substantiation on examination; therefore the history, rather than the objective findings, is the clue to reach a proper diagnosis. The typical symptoms of spinal stenosis include neurogenic claudication, back and leg pain, and mixed symptoms. Physical signs may include positive back signs, motor and sensory deficits, reflex changes and positive stretch signs. In many instances, the clinical examination may be completely normal. The pathophysiology of the symptoms is still controversial, but recent observations suggest that a two-level stenosing pathology plays a significant role. Two-level venous compression, with venous pooling of one or several nerve roots, would explain some of the pathophysiology of neurogenic claudication.
Plain radiographs always show degenerative disease. They are essential to exclude other pathologies. The anatomical level of stenosis can not be determined from the history and examination alone. We have found that CT and MRI are satisfactory and can show central canal and lateral recess stenosis and nerve-root entrapment.
Conservative treatment consists of anti-inflammatory analgesic drugs, back exercises, elastic back support and local injection (in the posterior joints or epidural space). Failure to respond to medical treatment necessitates surgical intervention.
Surgical treatment consisted of a decompressive lumbar laminectomy of stenotic levels. The surgical technique consisted of standard midline spinal exposure, central decompression via removal of the spinous process and lamina staying medial to the articular facets and pars interarticularis, followed by appropriate lateral recess decompression, being careful to undercut the articular facets. The decompression should be as limited as possible to avoid post-operative iatrogenic stenosis and instability. The extent of decompression should be guided by the clinical features, the radiological studies and the operative findings.
Our study included twenty-five patients with degenerative stenosis of the lumbar spinal canal. The mean age of this group of patients was 44.3 years and the highest incidence lied in the 5th. decade of life. Fifteen patients (60%) were hard workers and farmers and ten patients (40%) were light workers including office workers and housewives.
The history reveals an insidious onset of low back pain which was present in 100% of our patients for a mean period of 5 years before surgery. Other symptoms consisted of leg pain, weakness and paraesthesia which may present as continuous or intermittent symptoms. Leg pain was the commonest symptom presenting in 100% of our cases with continuous or intermittent symptoms. Sphincteric troubles in the form of urine incontinence were present in 20% of cases. Physical examination revealed the following abnormalities: positive straight-leg raising test in 80% of cases, sensory hyposthesia in 72% of cases, reduced knee and ankle reflexes in 72% of cases and motor weakness mainly affecting the extensor hallucis longus muscle in 68% of cases. This means that sensory deficit in our series was more frequent than motor weakness. We found no difference in the symptoms between cases of degenerative spondylolisthesis and those of the degenerative stenosis; both presented with similar proportion of neurogeric claudication and sciatica.
All the patients were subjected to plain X-ray lumbosacral spine, 32% to CT scanning, 48% to MRI examination and 4 % to myelography. Magnetic resonance imaging has rapidly become the imaging study of choice for the diagnosis of spinal stenosis and for the planning of the operation. Narrow central canal was evident radiologically in 100% of cases, narrow lateral recess in 64% of cases, foraminal encroachment in 16% of cases. Hypertrophy of ligamentum flavum was evident in 48% of cases and facet joint degeneration and hypertrophy was evident in 24% of cases. Degenerative spondylolisthesis was present in 16% of cases. Radiological evidence of disc prolapse demonstrated the presence of 32 disc herniations in the 25 patients, and that L4-5 was the commonest level of prolapse.
The major indications for surgery were: intolerable pain in activities of daily living, inspite of adequate non-operative treatment; progressively limited walking distance and progressive neurological deficits. The surgical strategy was bases on the patient’s symptoms and roentgenographic findings. The commonest operative findings were narrowing of the central and the lateral canals. The number of disc prolapse revealed surgically was 18 soft disc herniations, and L4-5 level was the commonest level of discectomy. One level laminectomy was performed in 32% of cases. Also two-level and three level laminectomy were performed in 32% of cases for each, where four-level laminectomy was performed in only 4% of cases. The decision on how far cranial to proceed with decompression was dependant on the neurological examination, the roentgenographic and operative findings for every case. Comparison between the level of stenosis and the laminectomy performed showed that, stenosis at the level L4-5 was decompressed in 100% of case, L5-S1 level was decompressed in 80% of cases and lastly L3-4 level was decompressed in only 54.5% of cases. Fusion was done in 20% of cases and pedicle screws were used to augment fusion.
JOA scoring system was used for grading the outcome of
surgery. Improvement after surgery was calculated after one year and at the
final follow-up period (The mean duration was 4.8 years). The mean improvement rate was 85.3% after one year and was 86% after 4.8 years. This means that the improvement rate in our series either did not change or become improved slightly.
The preoperative factors that have often been cited as influencing the results are: age, period between the onset of symptoms referable to the spine and the time of operation, type of stenosis, number of decompressed levels and the presence or absence of fusion. The sex of the patients as well as the preoperative walking distance were found to have no influence on the outcome of surgery.
We drew the following conclusions about the results of surgical treatment of lumbar spinal stenosis:
• The history, rather than the objective findings, is the clue to reach a proper diagnosis.
• Magnetic resonance imaging has rapidly become the imaging study of choice for the diagnosis of spinal stenosis and for the planning of the operation.
• The extent of decompression should be tailored according to clinical, radiological and operative findings. It should be as limited as possible.
• Exploration of the lateral recesses should never be missed during operation.
• Unless a disc protrusion is compromising the nerve roots, the intervertebral disc should be left alone, its removal will increase the potential for spinal instability.
• The facet joints should be preserved by using an undercutting technique in combination .