Adult degenerative deformity usually presents as a mild curve, which is rarely greater than 30 degrees unless it is superimposed on an adolescent-onset curve. Symptomatic lumbar curves tend to be larger in the idiopathic group than in the degenerative group.¹ Degenerative disc disease and osteoporosis are major contributing factors in adult-onset deformity. In these adult deformities, vertebral structural changes with lateral olisthesis are typically associated with degenerative disc and facet joint arthrosis. Adult deformity may also present as a sequela after a decompression for spinal stenosis or spinal fusion for degenerative disc disease. In primary as well as secondary deformities, the degenerative process plays a central role and leads to loss of lumbar lordosis, not infrequently progressing to thoracolumbar kyphosis.

Natural History

Idiopathic Curves

Untreated adolescent idiopathic curves are known to progress after skeletal maturity ²^–⁴. On long-term follow-up of patients with adolescent scoliosis at the University of Iowa, Weinstein et al reported that 68% of the curves progressed after maturity. Thoracic curves progressed at 1 degree per year, thoracolumbar at 0.5 degree per year. Factors associated with curve progression were Cobb angle greater than 30 degrees, apical vertebral rotation more than 30%, presence of lateral olisthesis, and a poorly seated L5 vertebra over S1 in lumbar curves ⁴.

Degenerative Curves

Pritchett and Bortell reported on the natural history of degenerative scoliosis in 200 patients. The number of vertebrae involved in the curve were from 3 to 6 (mean 3), with the apex commonly located between L2 and L3, and with 68% of the curves being left-sided. While degenerative spondylolisthesis was noted in half the patients, lateral listhesis was even more common (78%). They found that all the curves with the intercrestal line passing through L5 or the L4-5 interspace with vertebral rotation of 2 or more on the Nash and Moe scale progressed, as did curves greater than 30 degrees with lateral listhesis of 6 mm or more ⁵.

Korovessis et al. followed up 91 adults with de novo spinal deformity for a period of 3.7 years. The average curve size was 16.5 degrees (range 10° to 36°). Risk factors for progression were lateral olisthesis, a high Harrington factor (the Cobb angle divided by the number of vertebrae involved in the curve), and the disc index ⁶. In a similar study, Perennou et al. also reported a curve progression of 10 degrees or more in 73% of their patients over a follow-up period of 10 to 30 years, at an average of 3 degrees per year ⁷.

Imaging Evaluation

Radiographic studies for diagnosis and evaluation of adult scoliosis include full-length standing radiographs, bending films, hyperextension films, CT myelograms, and MRI. Assessment of bone mineral density will provide information regarding the presence and severity of osteporosis.

Standing radiographs with hips and knees in extension are necessary to evaluate the extent of the deformity and to assess sagittal and coronal balance. Supine side-bending radiographs may not be useful in degenerative scoliosis, but are useful in idiopathic scoliosis to assess curve rigidity and flexibility. Other options include traction views and fulcrum-bending views.⁸ Curve location, curve magnitude, number of levels involved, curve direction, and rotation should be evaluated on the radiographs. The presence of anterolisthesis, the maximum lateral olisthesis, the height of the residual disc spaces, and the presence of osteoporotic compression fractures are the radiographic factors that impact curve progression.

Achievement of coronal and sagittal balance is more important in adults than correction of deformity. Coronal balance is defined by the distance of the C7 plumb line from the central sacral vertical line (CSVL) on standing radiographs. Lateral trunk shift (LTS) measurement is also useful in thoracolumbar curves and is defined as the distance between the midpoint of the horizontal line drawn to the edges of the ribs at the apex of the deformity and the CSVL. (Figure 52-2)

FIGURE 52-2 A, Preoperative AP radiograph of single thoracic scoliosis. B, Preoperative lateral image with no obvious sagittal deformity. C, Right side-bend. Moderate thoracic curve flexibility. D, Left side-bend shows complete improvement in lumbar compensatory curve.

Global sagittal balance evaluation is essential, as this may have a major role in causation of symptoms in adult deformity. In adult scoliosis, the sagittal contour may vary from hyperlordosis to frank kyphosis. Sagittal vertical axis (SVA) measurement quantifies the global sagittal balance and is the distance of the C7 plumb line from the posterosuperior corner of the lumbosacral disc. The SVA usually falls anterior to the thoracic spine and passes posterior to the apex of the lumbar lordosis. Sagittal balance is considered positive when SVA falls anterior to the S1 body and negative when it falls posterior to the S1 body.

It is found that as lumbar lordosis reduces with progressive disc degeneration, the sacropelvis rotates posteriorly, leading to a vertical sacral inclination with hip extension. In the presence of hip flexion contractures, this compensatory mechanism may be compromised, leading to worsening of sagittal imbalance.

Patients with radiculopathy, with or without neurological deficit, and patients with neurogenic claudication should be evaluated with an MRI or a postmyelogram computed tomography scan. MRI can provide detailed information about central, lateral recess, and foraminal stenosis. The extent of disc degeneration can be assessed on MRI, which may be helpful with decision-making regarding the extent of fusion.

CT myelogram with sagittal and coronal reconstructions provides better bony details in cases of severe rotational deformity or in the presence of metal implants. Diskography is usually not beneficial in adult scoliosis for determining levels of fusion.

The Role of Conservative Management

A commonly described prerequisite to surgical intervention is the lack of response to conservative care. Even though multiple nonsurgical options are advocated for adult scoliosis, there is currently a lack of evidence in the literature regarding the efficacy of these treatment options. Everett et al reviewed the literature on nonsurgical treatment options for adult scoliosis. They concluded that in the conservative treatment of adult deformity, there is level IV evidence for the role of physical therapy, bracing, and chiropractic care, while there is level III evidence for injections .⁹

Still, most surgeons would attempt nonsurgical treatment as the first option. The goal of conservative treatment is pain relief, and any safe conservative care option that a patient can use to obtain relief reasonable. At the least, this is likely to improve the conditioning of the patient and promote weight loss, which may eventually improve the surgical outcome.

Indications for Surgery

Adult scoliosis patients fall into two broad categories when they present as surgical candidates. The first category is that of younger patients less than 50 years old, who mostly present with untreated idiopathic curves that have progressed to greater than 50 to 60 degrees and have become painful and symptomatic. Chronic, disabling pain refractory to conservative management and/or significant and cosmetically unacceptable deformity are indications for surgery.

The second category is that of patients over the age of 50, who present mostly with degenerative curves or with idiopathic curves worsened by superimposed degenerative changes. In these patients, surgery is most likely to be indicated for progressive deformities with sagittal or coronal plane imbalance, or for refractory back or radicular pain with or without symptoms of spinal stenosis. Although compromised pulmonary function has also been suggested as an indication, Korvessis et al did not find any difference in pulmonary function in adult scoliosis patients compared with age-related changes in normal persons at an average of 23 years follow-up.⁶

Surgical Planning

A multitude of factors impact surgical decision-making in this patient population. Achievement of coronal and sagittal balance is the most important goal for many patients. A balanced spine orients the skull so that it is placed over the pelvis. This reduces paraspinal muscle fatigue and pain, improves patient satisfaction, improves cosmesis, and reduces the risk of complications associated with persistent decompensation in the sagittal or coronal plane. A well-balanced spine in the sagittal plane has been found to correlate with a better self-image score in adult deformity patients.¹⁰ While extensive surgery might be required to achieve an adequately decompressed and well-balanced spine, the individual surgical plan needs to be matched with the overall health, medical fitness, and expectations from surgery for every patient. Medical and social factors that are known to correlate with poor outcome are nutritional deficiency,¹¹ chronic respiratory conditions,¹² diabetes,¹³ smoking,^14,¹⁵ coronary or cerebrovascular artery disease, and osteoporosis.¹⁶ Osteopenia is a major concern, especially if significant deformity correction is one of the goals. Segmental fixation can create a large surface area for force transmission and possibly prevent fixation failure. Medical treatment of osteoporosis with daily subcutaneous injections of parathyroid hormone for 2 to 6 weeks has been shown to enhance spinal fusion, in animal models.^17,¹⁸

If an anterior and posterior fusion is planned, a same-day procedure is preferable to a staged procedure, as nutritional status has been found to take 6 to 12 weeks to return to the baseline after posterior surgery.¹⁹ Use of parenteral nutrition has been advocated if a staged procedure is planned, to improve the nutritional status before the second stage.²⁰

The Role of Decompression Only in Adult Scoliosis Surgery

In carefully selected patients with degenerative scoliosis, performing a decompression alone without an instrumented fusion may be an option. If the patient presents with symptoms of neurogenic claudication and minimal back pain, it is possible that the patient will get relief with a trial of epidural steroids. If such patients have collapsed disc spaces without any evidence of anterolisthesis or lateral listhesis, they can be treated with decompression alone or decompression with an in situ fusion without instrumentation. Frazier et al. assessed the relationship between preoperative scoliosis and clinical outcome after a decompression only procedure for spinal stenosis in 90 patients with degenerative scoliosis. They inferred that the presence of preoperative scoliosis was associated with less improvement in back pain in these patients postoperatively; however, there was no correlation between preoperative scoliosis and satisfaction or improvement in leg pain and walking capacity after a decompression-only procedure ²¹.

The Role of Deformity Correction and Fusion

The natural history of adult deformity has been detailed earlier. The role of deformity in the causation of symptoms is not entirely clear. However, it is important to understand these issues to analyze the role of deformity correction in the treatment of adult scoliosis.

The Role of Deformity in the Clinical Presentation

Early studies indicated that the incidence of back pain in adult scoliosis patients is about the same as in age-matched controls. Kostuik found a 60% incidence of back pain in adult patients with scoliosis, which was similar to that noted in patients without spinal deformity ²². In other studies, patients with adult scoliosis were found to have more severe back pain as compared to controls, especially if the curve progressed beyond 45 degrees²³. In more recent studies, Weinstein et al. have reported that chronic back pain was present in 61% of the scoliotic patients as compared to 35% of the controls²⁴. Schwab et al. found a highly significant correlation between the severity of pain in adult scoliosis patients and the presence of lateral olisthesis and obliquity of L3 and L4 endplates on plain radiographs¹. Jackson et al. had found the fractional lumbosacral curves most disabling and painful. They reported that while scoliosis greater than 40 degrees and kyphosis greater than 50 degrees correlated with pain, rotational deformity had the highest correlation with pain²⁵. More recently, Buttermann et al. analyzed the correlation between degenerative disc findings on MRI with pain in scoliosis patients. In adult scoliosis patients, they found that the pain typically corresponded to the apex of the curve or to the lumbosacral junction. They found a higher incidence of disc degeneration and inflammatory end plate changes in adult scoliotics than asymptomatic controls. When compared with symptomatic patients with disc degeneration without a deformity, adults with scoliosis had a higher incidence of disc degeneration and inflammatory end plate changes at proximal lumbar levels (T12 – L3)²⁶.

The role of osteoporosis in the causation of adult deformity is well known. Osteoporotic fractures may cause pain, in addition to their contribution to the deformity. Radicular pain in the lower extremities is caused by degenerative changes in adult scoliosis. Root entrapment is more common in the concavity of the curve ^7,²⁵. In 200 patients with adult scoliosis, Pritchett et al. had found a 72% incidence of neurogenic claudication and a 45% incidence of neurological symptoms in the lower limbs, most commonly paresthesias ⁵.

Spinal balance in sagittal and coronal plane can be adversely affected in adult scoliosis. Poor spinal balance is known to worsen the functional status in these patients, and can be quite disabling. Pain in adult scoliosis may arise from muscle fatigue due to abnormal biomechanics caused by the deformed and poorly balanced spine. Glassman et al studied the impact of spinal balance on clinical symptoms in 298 adult scoliosis patients with or without prior surgery. They reported that positive sagittal balance led to greater pain, poor function, and poor self image in patients with or without prior surgery while coronal balance of more than 4 cm correlated with greater pain and poor function. Additionally, the severity of symptoms was found to increase linearly with worsening sagittal imbalance. In terms of location, thoracic curves were better tolerated than thoracolumbar or lumbar curves; however, the magnitude of the curve had a poor correlation with functional status ^27,²⁸. In patients with adult degenerative lumbar or thoracolumbar scoliosis, Ploumis et al. reported that coronal imbalance more than 5 cm affected bodily function and moderate to severe lateral olisthesis (more than 6 mm) correlated with higher bodily pain, while sagittal balance did not show a good correlation with functional results ²⁹

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