Fusion in Adult Scoliosis

CHAPTER PREVIEW

CHAPTER SYNOPSIS:

Adult scoliosis is a common problem. Patients may have both back and leg pain. Spinal stenosis is often the underlying problem, but decompression may lead to rapid progression of deformity. Likewise, alterations in spinal biomechanics may contribute to dysfunction and require reconstruction. This chapter provides an overview of the patient evaluation, decision process for management, and treatment options for adult scoliosis.

IMPORTANT POINTS:

The central decision-making issues include:

•

Can decompression be accomplished without causing instability?
•

Is realignment necessary to effect adequate decompression?
•

What is the best approach to restore sagittal and coronal balance?
•

What is the most appropriate proximal and distal level of fusion?
•

When is anterior column support necessary as part of the fusion procedure?

Fusion surgery is an undertaking of significant magnitude, and complications, especially in an elderly population with multiple comorbidities, are common. Despite this problem, most patients feel that the results of surgery are worthwhile as long as the goals of surgery—adequate decompression, stable fixation, and restoration of sagittal and coronal balance—are achieved.

CLINICAL PEARLS:

•

Although back pain is the most common symptom of scoliosis, pain at the apex of the curve is more specific than generalized pain.
•

Radicular pain may result from direct compression on the concave side of the curve or from stretching of the nerve root on the convex side, or from both.
•

Surgical decision making must include an analysis of the degree and extent of nerve root or cauda equina compression present, and the development of a strategy to adequately decompress symptomatic areas.

CLINICAL PITFALLS:

•

Caution must be used in planning to decompress the neural elements by removing posterior structures as this can lead to spinal instability.
•

Medical co-morbidities such as uncontrolled diabetes mellitus are common in these cases and can increase the risks associated with surgical intervention.

VIDEO AVAILABLE:

N/A

The majority of the scoliosis literature has focused on the evaluation and treatment of the pediatric population. Less attention has been placed on adult scoliosis, specifically degenerative scoliosis, despite a reported prevalence rate as high as 34%. Adult scoliosis is defined as a Cobb angle of more than 10 degrees in the skeletally mature patient. The two most common types of adult scoliosis are idiopathic adolescent scoliosis of the adult (ADA) and degenerative de novo scoliosis (DDS). Other types of adult scoliosis, though much less common, include traumatic, metabolic, osteoporotic, and iatrogenic scoliosis.

Although the symptoms of progressive pain and disability are similar in ADA and DDS, the pathology and resultant treatment can be very different. Kobayashi et al. conducted a 12-year prospective study of de novo scoliosis to establish some predictive factors to distinguish it from ADA. In a population of 60 patients aged 50 to 84 years without scoliosis, 36.7% had changes of more than 10 degrees during a 12-year span. Radiographic predictors of DDS were signs of asymmetric disc degeneration such as a 20% decrease in unilateral disc height or more than 5 mm unilateral osteophyte.

Anatomically, the degenerative scoliotic curve is diseased in three planes. Axial rotation in the vertical axis, lateral translation toward the curve convexity, and translation in the sagittal axis together form a triaxial deformity. Pritchett and Bortel have shown that 55% of DDS curves displayed anterolisthesis. Thirty-four percent of adult patients with scoliosis have lateral translation, otherwise described as rotatory olisthesis, lateral spondylolisthesis, or translatory shift.

Aging effects on the spine contribute to the progressive effects on translation in the upper lumbar spine. Spinal stenosis in addition to facet joint degeneration, ligamentum flavum hypertrophy, and disc collapse contribute to reduced lumbar lordosis and nerve compression. The result is symptoms of instability, and back and leg pain.

PATIENT EVALUATION

Back pain is the most common symptom in DDS. The incidence of low back pain is not significantly more common than in the general population. The location of the back pain, however, is important to distinguish on the history. Pain at the apex of the curve is a more specific symptom. Increasing age and curve magnitude correlates with increased lateral translation and pain at the apex. Soreness is also a common symptom from unbalanced and stressed paravertebral muscles.

Radicular pain may present either on the convex or concave side of the curve. Leg pain may be the result of direct compression on the concave side or from root overstretch from the convex side of a scoliotic curve, or both. More central spinal stenosis can contribute to lower extremity pain and neurogenic claudication. Neurologic deficit, however, is rare. Spinal stenosis is more common in de novo degenerative scoliosis than the adult idiopathic variety. Cosmesis, although a common presenting symptom in adolescent scoliosis, is less of a factor in the adult degenerative population.

A patient’s history of medical co-morbidities is also important to obtain. Patients with significant symptoms from DDS are more likely to be elderly and suffering from multiple medical problems. Medical co-morbidities may complicate any type of surgery further, and thus would suggest a minimalist approach.

Schwab et al. have provided a prospective look to see which radiographic parameters correlated with pain. Lateral vertebral translation, loss of lumbar lordosis, thoracolumbar kyphosis, and L3, L4 end plate obliquity were correlated to significantly increased Visual Analog Scale pain scores ( Fig. 27-1 ). Curve magnitude and number of levels showed no significant correlation to pain scores.

TREATMENT

Patients with adult scoliosis can have any number of symptoms. Usually, some component of back pain and, to a lesser or greater extent, leg pain exists. One of the most crucial aspects in deciding whether to perform a fusion is taking an adequate history to determine specifically what the patient’s symptoms are. It is often the case that patients have had backache for many years, but this may not be the problem that has driven them to seek medical attention. More commonly, patients are willing to tolerate their backache, but it is only when they begin to experience leg symptoms (either radicular leg pain or neurogenic claudication) that they begin to feel that their symptoms are intolerable and so severely affect their quality of life that they can no longer abide them. Therefore, most of the time, surgical decision making will include an analysis of the degree and extent of nerve root or cauda equina compression present and the development of a strategy to adequately decompress symptomatic areas. Areas of central, lateral recess or foraminal stenosis may exist. At times, when the patient’s pain is primarily radicular, symptoms can be localized to a specific nerve root. Fluoroscopically guided selective nerve root blocks can help determine the percentage contribution of any one nerve root that may be contributing to the patient’s overall symptom complex and may predict the response to surgery. Any surgical procedure that decompresses the neural elements by removal of posterior structures (lamina, facet joint, ligamentum flavum) will lessen the stability of the spine. Essentially, patients with de novo adult scoliosis or progressive idiopathic scoliosis have already demonstrated some deficiency in spinal stability by virtue of their deformity. The surgeon needs to assess whether further destabilization will lead to progression, recurrent nerve root compression, and/or mechanical back pain.

Surgical reconstruction of adult scoliosis can be associated with significant complications and morbidities. Many patients have significant medical problems that can make surgery difficult or dangerous. Obesity and diabetes increase the risk for infection. Osteoporosis can make fixation with instrumentation difficult. Cardiopulmonary disease or other medical co-morbidities can make it difficult for patients to rehabilitate properly. Clearly, no patient should undergo major surgical reconstruction if other, nonsurgical treatments can give adequate pain relief. Likewise, failure of nonsurgical care is not necessarily an indication for surgical intervention if the patient is unable to tolerate surgery or rehabilitate adequately and, therefore, will not derive sufficient benefit to justify the risk of surgery.

No universally accepted classification of adult scoliosis to guide in making treatment decisions regarding fusion exists. Several authors have tried to categorize adult curves to differentiate the factors that seem to be correlated with increased pain and the need for surgical reconstruction. Common characteristics of adult curves include severe angulation of the L4-5 disc space, lateral or rotatory subluxation of L3 (and possibly L2), as well as loss of lumbar lordosis and anterior translation of the sagittal vertical axis (see Fig. 27-1 ). All of these factors have been associated with increased pain and decreased function in adult patients with deformity. In addition, degenerative spondylolisthesis may also be present, which may require stabilization and fusion as well.

To a large extent, evaluation of the mechanical stability of the spine is based on plain radiographic examination. Preoperative radiographs should include standing three-feet anterior and posterior full-length spine films, flexion and extension lateral radiographs, as well as side bending films. Detailed views of the lumbar spine may also be helpful if the full-length films do not give adequate detail. The degree of deformity present, overall sagittal or coronal imbalance, instability, and/or curve flexibility all need to be considered. An extremely stiff, highly rotated curve with large anterior or lateral bridging osteophytes may be stable enough to undergo a small unilateral laminotomy/foraminotomy in the fractional lumbosacral curve, whereas a more moderate but flexible curve requiring bilateral decompression at the apex with significant rotatory subluxation may require stabilization. Advanced imaging studies help to determine the degree and extent of stenosis present. In addition, MRI, in particular, may show significant high signal intensity on T2-weighted images in the facet joints that is an indication of incompetence and instability at that level ( Fig. 27-2 ).