Management of Degenerative Scoliosis

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Chapter 185 Management of Degenerative Scoliosis

Scoliosis refers to an abnormal curvature of the spine and is classically defined radiographically as a coronal curve greater than 10 degrees. As a more comprehensive three-dimensional understanding of the spine has evolved over the last several decades, scoliosis now represents a complex curvature of the spine in the coronal, sagittal, and axial planes. Over much of this past century, the term scoliosis has generally referred to young patients with congenital or idiopathic curves that occurred during childhood or adolescence. A more comprehensive term, known as spinal deformity, likely encompasses the breadth of spinal curves that occur from congenital, idiopathic, degenerative, syndromic, neuromuscular, traumatic, and iatrogenic causes. In this chapter, the focus is adult degenerative scoliosis. Although curve characteristics and patient complaints may be similar in some respects, management of adult scoliosis and goals of treatment often differ vastly from the approach to young patients presenting with spinal deformity.

Terminology

Adult patients presenting with spinal deformity in the absence of previous surgery, trauma, or syndromic or neuromuscular causes are classically placed into one of two categories. The first main category of adult scoliosis involves patients who previously possessed a spinal deformity at a much younger age in the form of infantile, childhood, or adolescent idiopathic scoliosis. Such patients become symptomatic during adulthood likely from a progression of these curves with or without superimposed degenerative changes. The second major category of adult scoliosis involves patients without preexisting scoliosis who develop spinal deformity as a result of adult-onset degenerative changes (e.g., disc degeneration, facet joint arthropathy, osteoporosis, and vertebral body compression fractures).¹^–² This latter condition is classically referred to as de novo or adult degenerative scoliosis. Differentiating between these two is often determined based on history, symptoms, and imaging.

With regard to history, patients with preexisting curves might acknowledge the presence of their curve since adolescence or young adulthood, which may be corroborated by past photographs. In terms of presenting symptoms, patients with de novo scoliosis typically complain of low back pain, neurogenic claudication, and/or radiculopathy in keeping with most patients with degenerative spine pathology. They might also present with progressive deformity and spinal imbalance leading to severe axial back pain, but such symptoms occur more commonly in patients with preexisting scoliosis. Finally, with regard to imaging, patients with previous idiopathic curves often exhibit larger curves that span more spinal segments, often extending over the thoracic and lumbar regions. These curves may also be associated with significant rotational components. With de novo patients, curves more commonly center on the lumbar region, focally span fewer segments, involve listhesis or focal rotation of one vertebral body over another, and involve degeneration of the lumbosacral junction. Although these generalizations are associated with each type of adult scoliosis, such characteristics are not specific (Table 185-1). For the remainder of the chapter, a general view of de novo scoliosis is discussed.

Table 185-1 Factors that Help Differentiate De Novo or Adult Degenerative Scoliosis from Preexisting Idiopathic Scoliosis Presenting in the Adult

Factor	De Novo or Adult Degenerative	Previous Idiopathic Curve
History of previous curve	No	Yes
Age	60s	40s
Sex	Male > female	Female > male
Stenosis	Common	Uncommon
Curve magnitude	Smaller (15-50 degrees)	Larger (35-80 degrees)
Location	Lower lumbar	Thoracolumbar or lumbar
Length (in spinal segments)	<5 levels	>5 levels
L5-S1 involvement	Yes	No
Neurological dysfunction	50%-90%	7%-30%
Imbalance, coronal	No	Yes
Imbalance, sagittal	Yes	No

Clinical Presentation

In the younger populations with scoliosis, progressive deformity and cosmetic concerns are often the reasons for clinical presentation, but in the adult population, pain is the most common reason for presentation (up to 90%).³^–⁴ This latter group of patients might complain of radicular pain due to neural compression, often on the side of the lumbar concavity. However, complaints of axial pain are common, believed to result from muscle fatigue and spasm over the convexity of the curve.¹ Like younger patients with scoliosis, pulmonary compromise occurs only with severe thoracic curves (more than 80 or 90 degrees).¹ More commonly though, patients with thoracolumbar deformity with or without kyphosis complain of early satiety with eating because the rib cage can severely indent the abdomen, preventing gastric filling. When evaluating patients, surgeons must try to gain an understanding of the curve’s progression rather than assume the patient is presenting with back pain because degenerative processes have became too debilitating. For instance, a rapidly progressive curve might signify an underlying degenerative neurologic condition (e.g., spinal cord tumor, syrinx). In the absence of this diagnosis, the greatest threat to the patient’s health may be overlooked.

Radiographic Evaluation

Plain Films

Scoliosis films include three-foot (36-inch) standing posteroanterior (PA) and lateral radiographs at the very minimum. On PA films, Cobb angles are used to measure curves in the coronal plane. First, curves should be measured so as to create the greatest curve angle, and the levels at the top and bottom of such curves should be noted. These curves are used as the foundation to define clinical curve progression. Second, the relationship of the center sacral line to C7 should be documented so as to determine the presence of coronal imbalance or trunk shift (Fig. 185-1). This line bisects a line passing through both iliac crests and ascends perpendicularly. Emami and colleagues have defined coronal imbalance as greater than 25 mm of lateral offset of this plumb line.⁵ Finally, bending films, traction films, or push-prone films can be used to explore the flexibility of the curves. Such maneuvers can help identify the primary structural curves of the scoliosis, because smaller curves can flatten out on such imaging. In addition, these images might yield information on the flexibility of such curves so that surgeons can quantify the ease or difficulty with which curves may be corrected by surgery.

FIGURE 185-1 Technique for measuring coronal balance.

(From Glassman SD, et al. Correlation of radiographic parameters and clinical symptoms in adult scoliosis. Spine (Phila Pa 1976) 30:6 682-688, 2005.)

On the lateral films, thoracic kyphosis, lumbar lordosis, and pelvic parameters (especially pelvic incidence) should be measured first. Second, the C7-plumb line and/or T1 tilt should be measured to help determine the patient’s overall sagittal balance (Fig. 185-2). Such measurements are exceedingly important because multiple studies have shown that the quality of life in patients with adult degenerative spinal deformities is highly correlated with sagittal balance, both preoperatively and following spine surgery.⁶^–⁷ “Normal” sagittal balance is classically defined as a C7 plumb line that passes 2 to 4 cm posterior to the ventral S1 vertebra or 1 cm posterior to the L5–S1 disc space.⁸^–⁹ An offset of greater than 40 mm has been defined as sagittal imbalance.⁵ As with the coronal films, bending films can be taken from the lateral view. Such images are often referred to as extension films or supine films, and these can be taken with a bump under the patient’s kyphosis while lying supine. The goal is for the surgeon to estimate how much flexibility there is in the sagittal plane, once again to provide information preoperatively regarding the potential ease or difficulty the surgeon might face in the operating room during deformity-correction maneuvers.