Diagnosis and Treatment
Degenerative spondylolisthesis (DS) is a very common spinal pathology among patients 55-60 years old and older. As opposed to isthmic or lytic spondylolisthesis, degenerative subluxation predominantly affects the L4-L5 level and much less frequently L5-S1 or L3-L4 levels. The degree of slip rarely exceeds Grade 1. As it is quite clear from the name of the pathology, the underlying problem is a progressively developing degeneration of the intervertebral disc and osteoarthritis of the facet joints. There is a difference in opinions whether disc degeneration is a primary trigger for the development of subluxation, and facet joint disruption is a secondary factor, or vice versa the orientation of the facet joints also plays an important role in DS. It is believed that a more sagittal orientation of the joints predisposes the segment to development of the degenerative slip. In any event, it takes quite a few years and not infrequently even decades for the segment to develop enough weakness to allow for subluxation.
The clinical picture is extremely variable and ranges from lack of any symptoms to debilitating conditions. The following are the most typical syndromes seen in a clinical setting, either separately or in any possible combination with others. Clear understanding and precise diagnosis of these syndromes is prerequisites for adequate treatment.
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 haemorrhage 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.
Diagnosis of DS is based on clinical and radiological findings. It is necessary to mention that DS is frequently a totally asymptomatic condition and is discovered incidentally during routine spinal radiography. However, complaints of an older person of activity related back and/or leg pain responding quickly to rest should raise the suspicion of possible DS. The basic diagnosis is very easily established with the help of plain radiography. Analysis of specific anatomical details requires more sophisticated imaging studies, such as CT or MRI scanning. Standing and flexion-extension X-rays help to appreciate the degree of instability. Myelography and CT-myelography have proven useful and sometimes indispensable for the assessment of the degree of spinal canal stenosis. Thorough analysis of radicular pain pattern and careful neurological examination and in some cases selective diagnostic nerve root injection help to more accurately identify the source of radiculitis or radiculopathy.
Differential diagnosis does not present difficulties. Lytic spondylolisthesis is most commonly seen at the L5-S1 level. The presence of pars defect and lack of characteristic arthritic changes of the facet joints makes differential diagnosis easy. Another possible cause of subluxation is previous laminectomy and facetectomy. Diagnosis of this problem is quite obvious, considering the history and radiological findings.
As it was stated above, DS is often asymptomatic and does not require any treatment, with the exception of general recommendations for low back care. Patients with symptoms of instability may respond very well to a program of physical therapy and stability exercises. Intermittent bracing, job modification, education in proper body mechanics may lead to substantial and lengthy improvement of the symptoms.
Radiculitis, especially acute or subacute could be treated with epidural injection of steroids. Surgical treatment may become indicated in patients, whose symptoms are chronic, not responding to appropriate conservative treatment, and incapacitating. As with many other spinal conditions, surgical results are more gratifying if surgery is performed for radicular symptoms, rather than for relief of low back pain. Radiculitis or radiculopathy is causes by much better defined an understood anatomical changes than axial back pain, and therefore is much more successfully managed by well planned and executed surgical operations.
The most frequently seen syndrome of the traversing root compression is fortunately the most successfully treatable one. Considering the fact that compression is present at very small segment of the root, adequate decompression with excellent results can be accomplished using a unilateral approach with minimal laminotomy. However, adequate resection of the medical portion of the superior articular process must be performed widely enough to expose the pedicle. A synovial cyst or synovial chondroma can be also removed with the approach. An operation of this extent does not increase instability and does not require fusion. Long incision, wide and bilateral stripping of the muscles, extensive laminectomy can and must be avoided.
Central spinal stenosis obviously needs more extensive decompression. However, the need for this should be determined on clinical, but radiological basis. Only those patients who present with a definite picture of neurogenic claudication are candidates for central decompression. There is no direct relationship between the degree of stenosis demonstrated on imaging studies and the severity of the symptoms. Prophylactic decompression based only on the radiological diagnosis is not appropriate. Dealing with symptomatic central stenosis one has to realize that compression of the thecal sac is present at an only very short segment and total laminectomy and more than medial facetectomy are not necessary and could be detrimental. At the same time, the segment of very thick and dense yellow ligament contributing to the compression of the dura has to be carefully removed. The need for fusion along with central decompression is somewhat controversial and definitely increasing with wider decompression. The best clinical long term results, according to published data, are being achieved with non-instrumented fusion, although there are advocates of a more aggressive approach with instrumented fusion by way of pedicle screw fixation or interbody fusion techniques using threaded fusion cages.
The most challenging situation is the compression of the exiting nerve root within the foramen. Adequate decompression under these circumstances calls for extensive facetectomy, with the threat of increasing instability and subluxation. Besides, without help to keep the foramen open following decompression, recurrent foraminal stenosis is all but inevitable. In these cases instrumented dorsolateral or interbody fusion become procedures of choice.
Case 1. 62-year-old female with 2 year history of progressive neurogenic claudication. Within the last several months has been unable to be on her feet longer that for a few minutes and could not walk practically any distance due to profound numbness and weakness in the leg. The level of back and leg pain is minimal. Perfectly comfortable while sitting or at bed rest Previous history is quite unremarkable, no injury, a few episodes of mild low back pain. Physical examination revealed excellent range of motion, no spasm, neurologically intact, no typical signs of radiculitis. Plain radiographs showed grad 1 subluxation at the L4-L5 level. CT Myelogram demonstrated a severe degree of degenerative arthropathy of the L4-L5 facet joints with the development of degenerative spondylolisthesis and an extremely severe degree of central spinal stenosis with complete myelographic block.
Laminotomy and medical facetectomy with removal of hypertrophied yellow ligament and noninstrumented postero-lateral fusion was performed without complications and with minimal blood loss. One year postoperatively the patient can walk up to a mile with only slight back pain.
Case 2. 71-year-old female with no significant history of back problems became acutely symptomatic with the development of severe right leg pain, posteriorly and laterally, extending into the dorsum of the foot with numbness and weakness of the right root. Examination showed signs of acute L5 radiculopathy including sensory deficit and partial foot drop. MRI scan demonstrated degenerative spondylolisthesis at the L4-L5 level. Soft tissue density, originating from the right L4-L5 facet joint and extending into subarticular recess was visualized. The patient was taken to the operating room on an urgent basis. Minimal laminotomy and facetectomy were performed only on the symptomatic side. Acute hemorrhage into a synovial cyst was found with severe compressing of the L5 nerve root. The cyst was removed, blood clots evacuated. No fusion was necessary due to a very limited bone removal and absence of history of chronic back pain. The leg pain was immediately and completely eliminated following surgery. Muscle strength and sensorium were restored to a normal level within the next few days.
Case 3. 55-year-old female with quite a long history of mechanical low back pain and known diagnosis of degenerative subluxation of L4 on L5 was managed with conservative treatment for a number of years until she began to develop progressively increasing pain in the left anterior thigh and shin. The pain became eventually intolerable. She also began to complain of weakness in the proximal part of the leg. Neurological examination revealed weakness of the quadriceps femoris and anterior tibial muscles, absent left knee reflex. CT scan demonstrated a severe degree of foraminal compression of the L4 nerve root as a result of degenerative slip, collapse of the disc space extension of the annulus of the disc into the forearm.
Considering the fact that adequate decompression of the exiting nerve root requires extensive facetectomy and also because of severe disc collapse and lateral spinal stenosis, dorsolateral fusion was performed using pedicle screws instrumentation and slight distraction in order to keep the forearm open. The leg pain disappeared immediately following the procedure. Muscle strength returned to normal within 3 months after the operation. The patient developed solid fusion and remains asymptomatic 3 years postoperatively.
Alexander Lifson, M.D.