Type 1 (Primary Degenerative (De Novo) Scoliosis)

Primary degenerative, or de novo, scoliosis refers to adult scoliosis in which the curve develops in a previously straight spine after skeletal maturity and most often affects the lumbar and thoracolumbar spine. Type 1 includes scoliosis secondary to iatrogenic causes, vertebral fractures, degenerative changes, and osteoporotic disease.³ Type 1 adult scoliosis is the result of a spondylotic process in that it develops from asymmetrical degeneration of the intervertebral disk at one or more motion segments. A primary degenerative curve can also be referred to as a “diskogenic” curve.² In addition, it can occur as a result of asymmetrical facet degeneration/hypertrophy. The asymmetrical degeneration of the intervertebral disk results in a coronal deviation with subsequent rotation of the vertebral body, which pivots on a facet joint.¹ The apex of type 1 adult scoliosis curves is usually between L3 and L4, L2 and L3, or L1 and L2, in descending order of frequency. In general, de novo scoliotic curves have less of a coronal plane component than type 2, or progressive idiopathic scoliosis.^11,12 Consequently, patients with primary degenerative adult scoliosis are usually affected by sagittal plane abnormalities secondary to lumbar hypolordosis or frank kyphosis (Fig. 287-1).^13–16 Patients often have significant back or radicular pain (or both) as their chief complaint from this loss of normal sagittal balance. Because de novo scoliosis is primarily the result of a degenerative process, spinal stenosis from disk degeneration and facet hypertrophy is more common in these patients than in those with progressive idiopathic scoliosis.^17,18

FIGURE 287-1 Lateral (left) and anteroposterior (right) standing 36-inch plain radiographs of a patient with primary degenerative adult scoliosis (type 1). Note the lumbar hypolordosis causing significant sagittal plane imbalance. There is also a less severe coronal plane malalignment (arrows).

Type 2 (Progressive Idiopathic Scoliosis)

Progressive idiopathic scoliosis refers to scoliotic curves that began before skeletal maturity and includes idiopathic, congenital, and paralytic curves.³ Although idiopathic curves may be asymptomatic in children and adolescents, they often cause symptoms of pain, radiculopathy, or both in adults as a result of continued curve progression and sagittal and coronal imbalance, which occurs even after skeletal maturity (Fig. 287-2).^3,19,20 In addition to pain, patients younger than 40 years have cosmetic concerns from progression of a (usually) thoracic curve.

FIGURE 287-2 Preoperative anteroposterior (AP) (A) and lateral (B) radiographs of a 55-year-old woman with pain from progressive idiopathic scoliosis. Postoperative AP (C) and lateral (D) radiographs show correction of the curvature with a combination of anterior lumbar cages and posterior spinal fixation from T3 to the ileum.

Pain

Pain is the most common complaint of adults with scoliosis and is the deciding factor for surgical intervention in approximately 85% of such cases.^3,14,21,22 The pain may be musculoskeletal or radicular in nature. Musculoskeletal back pain can be localized at the apex of the curve or at its concavity, and the areas above and below the curve may also be painful from excessive stress on the facet joints. This type of musculoskeletal pain is a result of both excessive strain and fatigue on the paravertebral muscles as they attempt to compensate for the loss of normal spinal balance, as well as a result of true spinal instability causing abnormal stress on the facet joints.² Back pain is most often associated with loss of normal lumbar lordosis.²³ Radicular pain is frequently encountered in patients with de novo scoliosis and is due to neural foraminal compression as a result of disk degeneration, bulging, and facet hypertrophy, especially on the concave side of the curve. Radicular pain may also be caused by traction of nerve roots on the convexity of the curve. Intercostal neuralgia secondary to rib cage deformity can be seen in patients with severe thoracic and thoracolumbar curves.³ The pain may be diffuse and constant in nature, or it may occur only with axial loading of the spine on standing. In the latter situation, the back and radicular pain is often relieved when recumbent because the spine, disks, facet joints, and neural foramina are unloaded.

The visual analogue scale should be used to quantify the severity of pain and is valuable in reporting changes in pain after treatment. The 36-item short-form health survey (SF-36) is a validated outcome measure that can be used to determine the effects of not only pain but also the scoliotic condition in general on the patient’s physical and mental well-being. SF-36 scores have been found by several authors to be significantly lower in adult scoliosis patients than in controls.^24,25

Neurogenic Claudication and Neurological Deficit

Neurogenic claudication secondary to lumbar stenosis often occurs in patients with primary degenerative scoliosis.²⁶ Long thoracolumbar curves fused to shorter lumbar or lumbosacral curves can be associated with areas of severe canal stenosis at the transition zone and resultant claudicatory symptoms.²

A true neurological deficit is relatively rare in adult scoliosis patients but can occur after an acute insult or decompensation in an already severely narrowed spinal canal or neural foramen. Bowel or bladder dysfunction may occasionally occur as a result of compression of the cauda equina.

Curve Progression

Progression of scoliotic curves can be manifested as changes in clothing size or height or frank alterations in body shape, such as a rib hump. Progression occurs in both adult degenerative and adult idiopathic scoliosis, although it has been found to occur more quickly in the latter group.¹⁹ Risk factors for lumbar curve progression include a Cobb angle of 30 degrees or greater, significant apical rotation, lateral listhesis of 6 mm or greater, and an intercrest line through or below the L4-5 disk space.²⁷

Cosmesis

Unlike the situation in the adolescent population, cosmesis is a relatively infrequent complaint by adult scoliosis patients. Patients younger than 40 years, however, may occasionally have a chief complaint of an unacceptable cosmetic deformity from progressive idiopathic scoliosis.

History and Physical Examination

A thorough history should include evaluation of the onset, severity, and duration of symptoms, as well as previous treatments and their relative efficacy in achieving relief of symptoms. A history of idiopathic scoliosis should be documented, in addition to symptoms of curve progression. The impact of the deformity on the patient’s overall quality of life and self-perception must be determined. Cosmetic concerns should also be addressed. Medical comorbid conditions such as osteoporosis, diabetes, obesity, and poor nutrition are documented and addressed during a thorough history. Weight loss may improve the back pain symptoms in obese patients.

The physical examination should begin with a general inspection of the patient in the standing position with knees and hips fully extended (Fig. 287-3). The location and severity of spinal curves, rib humps, sagittal and coronal balance, pelvic obliquity, curve flexibility, and any leg length discrepancies should be noted. Moreover, an assessment of hip flexibility should be performed to rule out a hip contracture as the cause of the sagittal imbalance. Improvement in posture after sitting generally indicates a hip flexion contracture. The patient should also be examined in the supine position for evidence of improvement in sagittal and coronal alignment. A rigid thoracic kyphosis is usually indicated by the persistence of a kyphotic deformity in the supine position. A thorough neurological examination is performed to assess for abnormalities resulting from compression of nerve roots or the cord (or both). Gait and reflexes should be evaluated for evidence of myelopathy from thoracic canal stenosis. A left thoracic curve, toe clawing, asymmetrical abdominal reflexes, and gait/balance difficulties may indicate that syringomyelia, a tethered cord, or a neuromuscular syndrome is the primary abnormality, and treatment should subsequently be directed at these entities.

FIGURE 287-3 Photographs of a patient with adult degenerative scoliosis being examined in the standing position. Note that overall loss of sagittal balance is evident (left) whereas coronal balance is relatively preserved (right). Pelvic obliquity is also evident.

Imaging Studies

After a thorough history and physical examination, 36-inch standing plain anteroposterior and lateral radiographs should be obtained for every adult deformity patient. For proper radiographic assessment of sagittal balance, the patient’s knees and hips must be fully extended during this examination. Dynamic lateral bending and flexion-extension radiographs are useful to assess for curve flexibility, as well as to reveal evidence of abnormal segmental motion or instability. Oblique Stagnara views can be used to evaluate kyphosis in the setting of significant rotational deformities.³

MRI, CT myelography, or both are useful to assess for neural canal or foraminal stenosis in patients with neurological symptoms. CT myelography is preferred by some because MRI is often difficult to interpret given that the scoliotic spine does not lie in anatomic sagittal or coronal alignment. Areas of significant stenosis should be decompressed during surgical intervention and before correction of the deformity. MRI of the lumbar spine can reveal evidence of degenerated intervertebral disks, which may affect fusion strategies during surgical planning, including the distal fusion level and the use of interbody grafts.

Diskography, Facet Blocks, Epidural Injections

Provocative diskography can be used as both a diagnostic and therapeutic measure for painful lumbar intervertebral disks. The presence of a positive provocative diskogram has been shown by some to be correlated with improved outcomes after lumbar fusion.²⁸ Accordingly, provocative diskography can be helpful in identifying painful lumbar intervertebral disks that should be included in the distal construct. Facet blocks are used in similar fashion to identify painful lumbar facets that should be included in the fusion. Epidural steroid injections or nerve root blocks can also be helpful in both identifying and treating symptomatic compression of neural elements.

Indications

Although the timing and type of surgical intervention must be tailored to each individual patient, there are four general indications for surgical intervention in adults with a scoliotic deformity: (1) unrelieved pain, (2) progressive deformity, (3) neurological deficit, and (4) cosmesis (rare in patients younger than 40 years). Surgical strategies and techniques for decompression of neural elements and correction of deformity are divided into anterior, posterior, and combined procedures. The choice of surgical technique is dictated mainly by the characteristics of the deformity being treated, particularly the flexibility of the main curve. Unlike adolescents, in whom flexible curves are common, adult curves are generally stiff. Whatever technique is chosen, the most important goal in correcting adult scoliosis is to achieve anatomic sagittal alignment postoperatively.³¹ Other general principles include avoiding termination of the construct at the thoracolumbar junction or at the apex of the thoracic kyphosis. This section focuses on correction of lumbar/thoracolumbar deformities (Table 287-1). Restoration of lumbar lordosis and reestablishment of anatomic sagittal balance are important goals during correction of lumbar/thoracolumbar deformities. It should be noted that these goals can be accomplished only from a posterior approach, and consequently, indications for anterior-only approaches are relatively limited in the setting of adult scoliosis of the lumbar/thoracolumbar spine.

Anterior Approaches

An anterior-only approach for correction of deformity is ideally suited for younger adults (20 to 40 years) with flexible lumbar/thoracolumbar curves, a healthy L5-S1 disk space, and no significant kyphotic deformity. Correction of deformity is achieved after complete diskectomy and interbody graft placement, followed by segmental bicortical vertebral body screw-rod fixation. Asymmetrical placement of an interbody graft in the anterior interbody space prevents the development of kyphosis during compression of the curve convexity (Fig. 287-4). All segments involved in the curve should be fused.

FIGURE 287-4 Anteroposterior (AP) (A) and lateral (B) plain radiographs of a 36-year-old woman with painful, progressive adult idiopathic scoliosis and a flexible left curve of the thoracolumbar spine. Postoperative AP (C) and lateral (D) radiographs show correction of the deformity and fusion from T10 to L2 through an anterior-only approach.

Posterior Approaches

Posterior-only approaches for correction of adult deformity are useful in older patients (≥40 years of age) with flexible lumbar/thoracolumbar curves with or without pathology of the L5-S1 disk space. It is thought that older patients have a higher risk for incisional hernia and abdominal bulging after anterior approaches than younger patients do.³ Moreover, osteopenic bone may not provide adequate fixation for vertebral body screws via an anterior-only approach, thus making pedicle screw fixation preferred for maintenance of the correction until solid arthrodesis occurs. Because of the high rates of pseudarthrosis associated with posterior-only fusions to the sacrum, an anterior interbody graft at L5-S1 can be used to provide a load-bearing interbody surface and increase arthrodesis rates at the lumbosacral junction in the setting of a degenerated or deformed L5-S1 disk space that requires fusion to the sacrum (Fig. 287-5).

FIGURE 287-5 Anteroposterior (AP) (left) radiograph of a 61-year-old man with painful adult degenerative scoliosis who had undergone a two-level transforaminal lumbar interbody fusion at L4-5 and L5-S1 3 years before evaluation. AP (middle) and lateral (right) views show correction of the curve and fusion from T10 to S1 from a posterior-only approach.

Combined (Anterior-Posterior) Approaches

Combined approaches are well suited for correction of rigid lumbar/thoracolumbar curves with or without pathology of the L5-S1 joint (Fig. 287-6). In these cases, anterior release is performed, followed by a staged or same-day posterior segmental instrumentation and fusion. Most of the correction of the deformity, including vertebral body derotation and restoration of sagittal alignment, is achieved during posterior instrumentation and fusion.

FIGURE 287-6 A, Preoperative anteroposterior (AP) radiograph of the lumbar spine in a 67-year-old woman with symptomatic de novo scoliosis of the lumbar spine. B, Postoperative AP film after anterior release and interbody cage placement. Postoperative AP (C) and lateral (D) plain films after posterior instrumentation and fusion from T9 to the ileum demonstrate excellent correction of the deformity from a combined approach.

Intraoperative Considerations

Procedures for correction of scoliotic deformity are complex and lengthy operations usually place a great deal of physical stress on the patient. Significant blood loss and fluid shifts occur during the course of these procedures, and the surgeon and anesthesiologist should be prepared to deal with these problems appropriately. Suboptimal fluid management has been shown to adversely affect the recovery of patients undergoing surgery for correction of spinal deformity.³² Packed red blood cells, fresh frozen plasma, platelets, and clotting factors should be administered in a timely fashion, beginning when blood loss is estimated to approach 1000 mL. Autotransfusion with a cell salvage system is also beneficial, although large volumes of cell-salvaged blood can induce a coagulopathy.

Intraoperative spinal cord and nerve root monitoring, including somatosensory evoked potentials, motor evoked potentials, and electromyography, should be used in every procedure for correction of deformity. Their usefulness during surgery depends on the skill of the interpreting neurophysiologist, who is another crucial member of the spinal deformity team. Motor evoked potentials are the most sensitive for detecting cord injury resulting from correction of the deformity. Pedicle screw stimulation can also be used to assess for proper screw placement.