Spinal Stenosis with Spondylolisthesis

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15 Spinal Stenosis with Spondylolisthesis

Vincent J. Miele, Sumeet Vadera, Edward C. Benzel

KEY POINTS

• In the majority of cases patients with spinal stenosis and degenerative spondylolisthesis may undergo a traditional laminectomy.

• Several factors, including the mobility of the listhesis, character of the slip (lateral listhesis), presence of an associated degenerative scoliosis, and the presence of axial pain are weighted in favor of adjunct fusion.

• If fusion is required, it can be performed with or without instrumentation. Generally, instrumentation increases the morbidity of the patient.

• Factors to consider when deciding on instrumentation include the amount of instability, age of the patient, bone quality, presence of comorbidities, amount of levels requiring decompression, and factors that predict worsening of listhesis (see previous point).

• New technologies, such as biologics used to promote fusion, minimally invasive techniques, and motion preservation technology are promising but have limited data proving efficacy.

Spinal stenosis accompanied by spondylolisthesis is a common diagnosis encountered by the spinal surgeon. Although nonoperative treatment consisting of antiinflammatory medications and epidural steroid injections is effective in some patients, many patients with severe symptoms are not helped by this strategy.^1,² In the group that fails conservative therapy, decompression has been shown to be an effective treatment modality.²^–⁴ Although numerous studies have clearly demonstrated the beneficial effects of decompressive laminectomy, the fear of creating instability often limits this procedure’s application. The concomitant presence of spondylolisthesis increases this likelihood. Controversy also persists regarding the virtues of concomitant spinal fusion in this patient population, which is often elderly. When fusion is chosen, the decision of whether or not to use instrumentation must be made. Fortunately, the management of this condition has evolved over the past several decades and numerous prospective randomized trials have been performed assessing the influence of fusion and instrumentation following decompression.

To treat a patient with spinal stenosis with degenerative spondylolisthesis, the clinician should have a basic knowledge of the epidemiology, diagnosis, and management of this condition. This chapter addresses specific situations in which individuals will have a high incidence of instability and progression of deformity without fusion. In addition, laminectomy without fusion may be considered. It will also discuss certain patient populations in which the better part of valor might be a limited decompression without fusion or a fusion without instrumentation. Finally, new techniques such as the use of biologics, motion preservation devices, and soft tissue stabilization will be discussed.

Part One: Understanding the Condition

Pathophysiology

As the spine ages, the accumulation of years of axial loading and rotational strains may lead to disc degeneration, facet arthrosis with hypertrophy, thickening or buckling of ligamentum flavum, and osteophyte formation. This cascade of degenerative changes can result in the development of central canal or foraminal narrowing with resulting neural compression characterized by low back, buttock, and lower extremity pain.¹ They can also result in varying degrees of spinal instability and, depending on the anatomic predisposing factors, the vertebra develops either anterolisthesis or retrolisthesis. Spondylolisthesis, the slippage of one vertebra relative to the adjacent vertebrae, often results from asymmetric degeneration of the disc, the facet joints, or both.

Once degenerative spondylolisthesis begins, the imbalance in stress can lead to an asymmetric deformity, which further aggravates the asymmetric loading and results in a vicious circle that promotes progression of instability. As the listhesis progresses with the narrowing of the intervertebral disc, subsequent changes in the motion segment include spur formation, subchondral sclerosis, ligamentous hypertrophy and ossification, together with hypertrophic facet arthrosis. These secondary changes have a natural tendency to restabilize the motion segment.

The deformity may occur in any of three axes: axial rotation on the vertical axis, lateral translation, and anterior translation in the sagittal plane. The types of spondylolisthesis that can occur are therefore rotatory olisthesis (rotational subluxation of one vertebral body upon another), lateral subluxation, and translatory shift. A listhetic segment is defined as fixed if less than 2-mm translation occurs on flexion/extension radiographs. If a translation occurs that is greater than 2 mm, the listhetic segment is considered mobile.

Degenerative spondylolisthesis is commonly associated with symptomatic stenosis as well as degenerative scoliosis. The primary pathology in degenerative scoliosis is lateral listhesis, coupled with lateral wedging of the vertebral body and angulation secondary to asymmetric degeneration of the facet joints.

Epidemiology

Degenerative spondylolisthesis is a relatively common pathology. A recent study involving a large series in an Asian population reported an overall incidence of 8.7%. It typically is found in individuals older than 50 years. It is also more common in women than men, which is thought to be secondary to the increased ligamentous laxity in the former.

The level L4-L5 is most commonly affected overall by degenerative spondylolisthesis. Anterolisthesis is more common in the lower lumbar segments in females, whereas retrolisthesis in the upper lumbar segments is equally common in both sexes. When disc degeneration occurs, the motion segment often settles into an anterolisthesis.

Natural History

The majority of patients with a history of significant neurogenic claudication or vesicorectal symptoms have been shown to have poor outcomes without intervention. A prospective observational cohort study assessing the long-term outcomes (8- to 10-year follow-up) of patients with lumbar spinal stenosis treated either surgically or nonsurgically has demonstrated increased leg pain relief and greater back-related functional status in patients who initially received surgical treatment. Although degenerative spondylolisthesis has been shown to progress in 25% to 30% of patients, it fortunately rarely progresses to more than 30% of the subjacent vertebra. Some studies have demonstrated that as the pathology progresses and the disc space collapses, back pain can improve spontaneously.

Part Two: Clinical Decision Making

Evaluation

Patients with spinal stenosis and degenerative spondylolisthesis present with neurogenic claudication, radiculopathy, intermittent episodes of axial mechanical back pain, and vesicorectal disorder. L5 is the most commonly associated radiculopathy. This is because for a patient with spondylolisthesis at L4-L5 (the most commonly affected level), the L5 nerve root is usually compressed in the lateral recess. Less frequently, the vertebral body movement causes narrowing of the foramen and L4 nerve root compression. Specifically, this foraminal stenosis is the result of anterosuperior subluxation of the caudad superior articular facet from decreased disc height, hypertrophied ligament and disc material, and osteophyte formation in the posterolateral corner of the vertebral end plate. This can compress the exiting nerve root against the superior pedicle. The origin of the axial mechanical back pain component of the disorder can be primarily discogenic or related to facet degeneration, which is often difficult to distinguish. Generally, if the discomfort is primarily secondary to disc disease, it worsens with forward bending. Additionally, the patient often complains of a catching pain in the low back that tends to climb up the body that occurs when rising from a forward bent posture. The patient also often supports his or her weight by placing his or her hands on the knees and thighs. Pain that arises primarily from the facet joints is often worsened by extension and rotation of the spine and is often associated with paravertebral tenderness.

Obviously, a thorough vascular examination is imperative to identify a peripheral vascular component of the symptoms. A patient presenting with atypical symptoms (e.g., night pain, rest pain) should be evaluated for other etiologies, such as a tumor, acute compression type fracture, or infection.

Imaging Studies

Imaging studies used to evaluate spinal stenosis with degenerative spondylolisthesis should focus on two goals. First, determining the extent of central and foraminal stenosis and secondary neural impingement. Magnetic resonance imaging (MRI) is most useful in this regard and can help differentiate between varying causes of stenosis, such as synovial cysts and ligamentum flavum hypertrophy. If MRI is contraindicated, a computed tomography (CT) myelogram can also be used. This information is needed to design an appropriate strategy to treat the patient’s radicular complaints. Secondly, imaging should focus on quantifying the amount of instability present in the spondylolisthetic segment and specific characteristics that portend an increased risk of progression. This information is necessary when determining how aggressive a decompression should be attempted and if additional stabilization techniques will need to be employed. These studies should include upright weight-bearing anteroposterior and lateral radiographs of the lumbar spine and pelvis, as well as flexion and extension views. An alternative method is to compare standing lateral radiographs with radiographs taken with the patient in supine hyperextension using a pillow. Lack of motion suggests a component of secondary stabilization. Though it is unclear what magnitude of slip is considered unstable, most studies define instability as listhesis greater than 2 mm.

Specific Patient Populations and Situations

Elderly

The aging baby boomer generation is leading a shift in demographics toward a “gray society,” and over the next 25 years a significant proportion of the population in industrialized societies will be over 65 years old. Since both symptomatic spinal stenosis and spondylolisthesis typically appear between the fifth and seventh decades of life (40-60 years), these conditions frequently coexist in this populace, and many patients with these conditions will become surgical candidates. While decompression of disabling lumbar spinal stenosis may lead to a significant improvement in quality of life, concerns about potential medical complications in this sometimes fragile population and uncertainty about the expected outcome of operative treatment make many surgeons apprehensive about big surgeries, such as decompression with arthrodesis.

Some controversy exists as to whether age should be considered an independent risk factor for surgery. Many authors report no difference in outcome or rate of complications between elderly and younger patients of comparable health.⁷ Therefore advanced age alone should not be a contraindication for surgery. Some studies, on the other hand, have demonstrated that increasing age can be an independent risk factor for surgery, especially if the patient is older than 60 years.⁵ One such study noted a 41% complication rate (14% major and 27% minor) for patients 41 to 60 years of age and a 64% complication rate (24% major and 40% minor) for those 61 to 85 years of age (27). Pulmonary complications were the most common major complications and genitourinary problems were the most common minor complications. Age more than 60 years was therefore found to be a significant risk factor for perioperative complication.

It has also been reported that decompressive surgery in the elderly population can be effective without the need for supplemental fusion, and many authors therefore do not recommend fusion in patients older than 70 years. This is partly because the risk of developing postoperative instability in this age group appears to be small because of some intrinsic stability afforded by the spondylosis and spondylarthrosis that occur as the spine ages as well as the decreased activity level of this population.⁵

If decompression without supplemental fusion is performed in this population, care should be taken to limit the number of levels decompressed. It has been shown that the probability of developing postoperative spondylolisthesis increases with the number of levels decompressed; (6% for 2 levels progressing to 15% for 3 or more levels). Other strategies (which will be discussed later in this chapter) that may be employed in the elderly include noninstrumented fusions and minimal bone removal.

Multiple Comorbidities

Patients who have multiple comorbidities, such as cardiac disease, vascular disease, or diabetes have an increased risk for postoperative complications.^6,⁷ The preoperative evaluation and optimization of patients with these conditions is critical. The addition of an arthrodesis increases the length of anesthesia as well as the amount of blood loss. Both of these factors can delay recovery time, and patients with multiple comorbidities are therefore more likely to require an extended rehabilitation period. These factors should all be considered when deciding upon the advisability of supplemental fusion with decompression. Finally, for patients with a limited life expectancy, treatment should be focused on obtaining an immediate improvement in quality of life without subjecting the patient to a prolonged and painful recovery period.

Several studies in the literature have examined the relationship between preoperative comorbidities and postoperative complications. Although there is a link between certain risk factors and postoperative mortality, increasing American Society of Anesthesiology (ASA) physical status class has been shown to be one of the best independent predictors of mortality. Previous studies have reported an increasing rate of postsurgical mortality with increase in the ASA class. In fact, increasing morbidity and mortality rates have been prospectively demonstrated with an increase in the ASA class in a large population where the mortality rate increased from zero to 7.2% from ASA class 1 to ASA class 4, respectively.⁷