Spinal stenosis is defined as the focal, segmental or diffuse narrowing of the central canal or root canals by bony and/or soft tissue elements resulting in encroachment on the neural structures. Lumbar spinal stenosis was classified by Arnoldi as congenital, acquired (75%) or due to combination of both. However, it is impossible to determine if the narrow spinal canal in degenerative LSS is degenerative change due to age or genetics. If the narrow spinal canal in degenerative LSS is associated with aging, degenerative LSS is degenerative disease. However, if the narrow spinal canal in degenerative LSS is not associated with aging, it appears to be logical to change the definition of degenerative LSS which reflects the genetic cause. Degenerative LSS is uncommon in patient younger than 50 years in contrast to those with primary LSS due to a congenitally narrowed canal.
Degenerative LSS is a slowly progressive process that predominates at the three lower lumbar levels. The natural history of spinal stenosis remains poorly understood with studies reporting about a half of patients remain clinically stable, with a quarter worsening or improving. For any individual patient, the course can be unpredictable with flares and stable periods over time. Among older individuals, LSS can be a highly disabling condition and is the most common reason for spinal surgery.
Signs and symptoms are thought to result from vascular compromise to the vessels supplying the cauda equina (central stenosis) or from pressure on the nerve root complex (lateral or foraminal stenosis) by the degenerative changes. Clinically, the symptoms of LSS can be categorized into two groups: regional (low back pain, stiff back) or radicular mainly neurogenic intermittent claudication. Neurogenic claudication refers to leg symptoms encompassing the buttock, groin, and anterior thigh, as well as radiation down the posterior part of the leg to the feet. In addition to pain, leg symptoms can include fatigue, heaviness, weakness and/or paresthesia. Patients with LSS also can report nocturnal leg cramps and neurogenic bladder symptoms. A key feature of neurogenic claudication is its relationship to the patient’s posture where lumbar extension increases and flexion decreases pain. Symptoms progressively worsen when standing or walking and are relieved by sitting. Symptoms can be unilateral or more commonly bilateral and symmetrical.
In addition to neurogenic claudication, lumbar spinal stenosis can present with symptoms that are more radicular in nature. Unlike neurogenic claudication that is more commonly bilateral and associated with central canal stenosis, radicular symptoms due to spinal stenosis are more often unilateral and related to stenosis of the lateral recess or the foraminal canal.
LSS is a not uncommon finding in people who have no related signs or symptoms. When symptoms do occur, they often start gradually and worsen over years unless an additional pathology like a Lumbar Disc Herniation or neurogenic tumor develops.
They postulated that rotation and compression injuries led to degenerative changes of the three-joint complex. The results of these changes to the three joint complex create degenerative spondylolisthesis, retrolisthesis, degenerative scoliosis, and rotational deformities. The incidence of acquired lumbar stenosis is approximately 1 per 1000 in individuals older than 65 years.
Lumbar lordosis is a ventral orientated curve of the lumbar spine, which has been formed due to the wedge shape of intervertebral discs and the vertebral bodies. The form of the lumbar lordosis is equally influenced by the shape of the vertebral bodies and intervertebral discs; each of these structures account for about 50% of the variation of the angle of lordosis in adults. Lumbar lordosis is usually described by the anatomical parameter ‘lordosis angle.’ All lumbar segments are measured (L1-L5), wherein an upper limit of the angle is the upper endplate of the L1 body, lower endplate of S1 body. The lumbar lordosis is represented by ‘β’ – the lordosis angle.
Most researchers agree that the lumbar lordosis angle positively and strongly associated with spondylolysis and isthmic spondylolisthesis. The amount of lumbar lordosis is either a consequence, or reason for the development of osteoarthritis of the facet joints. Increasing of the lordosis angle is considered as a risk factor for progression of spondylolysis and ventral displacement of the affected vertebra.
A 42 year old man presented with low back pain with neurogenic intermittent claudication. He was operated using L4-L5 decompressive laminectomy with Posterolateral fusion using pedicle screw fixation.
Verbiest in 1954 defined relative LSS as an anteroposterior canal diameter between 10 and 12 mm whereas absolute LSS as a diameter less than 10 mm. The most frequently applied criteria were measurement of the anterior-posterior diameter of the osseous spinal canal and of the cross-sectional area of the dural sac for central stenosis as well as measurement of the height of the recess for lateral stenosis.
Schonstrom established criteria for diagnosis of lumbar canal stenosis; absolute spinal stenosis (Dural sac cross sectional area of 0-74 sq. mm) relative spinal stenosis (75-99 sq. mm) and no spinal stenosis (>100 sq. mm).
Sedimentation Sign (SedSign) :On supine Lumbar MRI scans that in patients with no suspected LSS, owing to gravity, the lumbar nerve roots sink to the dorsal portion of the dural sac. Conversely, in patients with LSS, such cauda equina nerve root sedimentation was rarely observed. A positive SedSign was defined as the absence of sedimented nerve roots. The Sign was reported to be 94% sensitive and 100% specific for severe LSS. However, a positive SedSign is not sufficient in and of itself to diagnose LSS.
The neurologic examination typically is normal, and findings when present are usually mild motor weakness or sensory changes. Both of these symptoms usually improve with conservative treatment, but in refractory cases, surgical intervention is indicated.
The only well known absolute indication for surgical neurogenic decompression in patients with lumbar radiculopathies is cauda equina syndrome. CES includes a famous triad of bilateral Achilles areflexia, saddle anesthesia, and sphincter disturbances, but these findings are observed in only half of the patients. Therefore, the clinicians should not wait too long to observe all the three features of the syndrome.
In other patients with signs and symptoms of LSS, a three-month trial of aggressive conservative treatment is usually recommended, but after this time period, surgery has been found to be associated with significant improvement in all primary outcomes.
In ordinary LSS, radicular complaints (other than CES) are usually relative surgical indications, even though most of the authors recommend early neural decompression when the radicular pain is present even at rest.
The primary goal of neurologic decompression in LSS is to improve the radicular pain. The primary goal of spinal fusion is to improve the regional back pain.
Spinal fusion is usually achieved by applying autogenous or allogenous bone graft over the decorticated bone surfaces. Instrumentation may be used to improve the fusion rate and to correct the underlying deformity. Instrumentation may increase the fusion rate (especially in multilevel fusion), but it is not necessarily associated with improvement in the recovery rate. Solid radiographic fusion does not guarantee a successful outcome.
In appropriately selected patients, fusion can stabilize the unstable lumbar vertebrae and also eradicate the source of pain originating from the diseased intervertebral disc or facet joints. Appropriate indications for lumbar fusion are usually categorized into two major groups; preoperative and intraoperative indicators.
- Failed back surgery syndrome
In the patients with a history of previous lumbar surgery who present with instability, deformity (flat back), or recurrence, if revision surgery is found to be necessary, fusion is probably indicated, because revision often requires more resection of the stabilizing structures.
- Degenerative instability
In patients with debilitating lumbar degenerative spondylolisthesis with spinal stenosis, surgery compared to non surgical treatment can provide substantial improvement in pain and function at least for a period of two years. When the chief complaint of the patient is a refractory low back pain and no significant stenosis is apparent on imaging studies, fusion is recommended (without any accompanying decompression).
- Correction of the deformity
Whenever it is necessary to correct the underlying deformity as well as spinal stenosis, instrumented fusion is needed. Correction of the spinal deformities such as degenerative scoliosis or degenerative kyphosis in elderly patients is a major operation, and it should be performed only in patients who have appropriate indications.
- Symptomatic spondylolysis
Spondylolysis is such a common radiologic finding (6% of general population), and some authors consider it as a normal variation like sacralization, lumbarization, or spina bifida occulta. Only a limited number of patients with spondylolysis, particularly at L5 vertebra would require surgery.
- Refractory degenerative disc disease
MR imaging findings such as endplate changes eg Modic changes and presence of disc degeneration are found to increase the possibility of a discogenic origin of pain. In patients with underlying degenerative disc disease and in whom other pathologies are completely ruled out, spinal fusion especially with an intervertebral cage may be recommended.
- Adjacent segment disease
In the patients in whom the stenotic segments are located adjacent to a previously fused or immobilized segment, neural decompression with instrumented fusion is preferred. As more stress is concentrated on this segment, even with limited neural decompression, the probability of postoperative instability is high.
- Extensive decompression
Spinal fusion is recommended in the patients who underwent
- Bilateral facetectomy>1/3–1/2
- Excision more than 50% of the pars interarticularis
- Bilateral discectomy in addition to partial facetectomy
The relative efficacy of various surgical options for treatment of spinal stenosis remains uncertain. Decompression plus fusion is not more effective than decompression alone.