Deformity Correction in the Degenerative Spine

Summary of Key Points

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Adult degenerative scoliosis arises after skeletal maturity in a previously normally aligned spine.
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Sagittal radiographic spinopelvic parameters are highly correlated with pain and disability and must be considered in the decision to pursue surgery and the surgical treatment strategy.
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Adult degenerative scoliosis is often associated with signs and symptoms of neural compression, which must also be incorporated into the surgical plan.
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Although patients with mild deformity and neurologic symptoms may be treated with simple decompression of focal fusion, more severe deformity requires a long segment fusion and possible osteotomies.
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The level of pedicle subtraction osteotomy is important for addressing spinopelvic malalignment.
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Although complications are common, outcomes remain good.

Adult degenerative scoliosis is a spinal deformity that arises after skeletal maturity. It is highly prevalent, particularly in the elderly. As such, orthopaedic and neurosurgery spine surgeons evaluate a significant number of patients with this disorder. Well-designed studies consistently demonstrate a correlation between adult spinal deformity in the sagittal plane, spinopelvic malalignment, and health-related quality of life metrics, including pain and disability. The goal of adult spinal deformity surgery is spinopelvic realignment primarily aimed at relieving pain and disability. Surgical correction is technically challenging and may be associated with significant morbidity. Overall, surgical correction of degenerative scoliosis results in long-term improvement in pain and disability. Therefore, the decision process leading to adult spinal deformity surgery is complex. This chapter focuses on the clinical evaluation, surgical decision making, surgical correction techniques, and outcomes for the adult degenerative scoliosis patient.

Adult Degenerative Scoliosis

Adult scoliosis is defined as any lateral spine curvature greater than a 10-degree Cobb angle. In contrast to progressive idiopathic scoliosis (adult idiopathic scoliosis), adult degenerative scoliosis arises de novo in a previously straight spine. The causes include degenerative changes, vertebral body fracture, osteoporosis, or iatrogenically induced. Lumbar and thoracolumbar levels are most commonly affected. Degenerative scoliosis patients are older and may have a history of prior decompression or short segment fusion surgery. There is usually a component of rotatory subluxation often at L3/4 and lateral listhesis. Curves tend to progress on average 3 degrees per year, with more rapid progression with higher magnitude curve or rotation, lateral listhesis, or an intercrest line through L5. However, there is less of a coronal curve component compared to the progressive idiopathic disease. Abnormalities in the sagittal plane, in particular global sagittal imbalance and spinopelvic malalignment, are highly associated with pain and disability. Because the primary disease process is driven by degeneration, the patient may have superimposed symptomatic degenerative arthritis, disc disease, lumbar stenosis, and foraminal stenosis, which will also need to be addressed by any planned treatment.

The mean age at presentation is 70.5 years and rates are equivalent in males and females. Adult scoliosis is highly prevalent with rates as high as 68% in asymptomatic people over the age of 60. The validated Scoliosis Research Society (SRS)–Schwab classification can be used to stratify patients based on anteroposterior and lateral radiographic parameters. The scheme utilizes four coronal curve types (thoracic only, thoracolumbar/lumbar only, thoracic and thoracolumbar/lumbar, no coronal curve) with three sagittal modifiers (pelvic incidence/lumbar lordosis mismatch, sagittal vertical axis, and pelvic tilt). This has been shown to correlate with health-related quality-of-life scores and is responsive to changes in disease state over time. As the population ages, adult spinal deformity will become an increasingly prevalent component of the modern spine surgeon’s practice.

Adult Degenerative Scoliosis

Adult scoliosis is defined as any lateral spine curvature greater than a 10-degree Cobb angle. In contrast to progressive idiopathic scoliosis (adult idiopathic scoliosis), adult degenerative scoliosis arises de novo in a previously straight spine. The causes include degenerative changes, vertebral body fracture, osteoporosis, or iatrogenically induced. Lumbar and thoracolumbar levels are most commonly affected. Degenerative scoliosis patients are older and may have a history of prior decompression or short segment fusion surgery. There is usually a component of rotatory subluxation often at L3/4 and lateral listhesis. Curves tend to progress on average 3 degrees per year, with more rapid progression with higher magnitude curve or rotation, lateral listhesis, or an intercrest line through L5. However, there is less of a coronal curve component compared to the progressive idiopathic disease. Abnormalities in the sagittal plane, in particular global sagittal imbalance and spinopelvic malalignment, are highly associated with pain and disability. Because the primary disease process is driven by degeneration, the patient may have superimposed symptomatic degenerative arthritis, disc disease, lumbar stenosis, and foraminal stenosis, which will also need to be addressed by any planned treatment.

The mean age at presentation is 70.5 years and rates are equivalent in males and females. Adult scoliosis is highly prevalent with rates as high as 68% in asymptomatic people over the age of 60. The validated Scoliosis Research Society (SRS)–Schwab classification can be used to stratify patients based on anteroposterior and lateral radiographic parameters. The scheme utilizes four coronal curve types (thoracic only, thoracolumbar/lumbar only, thoracic and thoracolumbar/lumbar, no coronal curve) with three sagittal modifiers (pelvic incidence/lumbar lordosis mismatch, sagittal vertical axis, and pelvic tilt). This has been shown to correlate with health-related quality-of-life scores and is responsive to changes in disease state over time. As the population ages, adult spinal deformity will become an increasingly prevalent component of the modern spine surgeon’s practice.

Clinical Evaluation

The clinical evaluation of the degenerative scoliosis patient begins with a thorough history. The duration, character, and magnitude of pain should be described, noting the proportion of back to leg pain. For radicular symptoms, it is important to note if they are on the same side as the concavity of the curve. Symptoms of neurogenic claudication should be elicited. A prior history of spine surgery should be documented. Medical comorbidities should also be documented. The patient should be questioned about the types of nonoperative modalities utilized and the subjective response to each. The overall impact of the deformity on the patient’s quality of life should be assessed. The patient’s subjective history can be supplemented with objective validated health-related quality of life (HRQOL) scales that have been shown to correlate with patient decision making: the visual analog scale (VAS), Oswestry Disability Index (ODI), and Short Form-36 (SF-36).

Initial physical examination should involve visual inspection of the patient standing with the knees locked. Sagittal and coronal balance should be noted, as should shoulder position and pelvic obliquity. Leg length discrepancy should be noted if present. Any patient identified to have a leg length discrepancy should be reassessed in a shoe lift to determine if there is any effect on spinopelvic alignment. Flexibility of any curves can be assessed with lateral bending. A thoracic kyphosis that persists in the supine position may indicate a rigid kyphosis ( Fig. 151-1 ). Hip flexion contracture can be evaluated by the Thomas test in which the supine patient bends and presses one leg against the lower torso while the contralateral leg is observed for knee flexion. A full neurologic examination should be performed to evaluate for signs of nerve root compression or myelopathy.

All adult spinal deformity patients must be evaluated with anteroposterior (AP) and lateral 36-inch standing radiographs. The knees and hips should be extended and locked. Coronal alignment is assessed by measuring the distance between the C7 plumb line and a vertical line through the midpoint of the sacral end plate. Global sagittal alignment is determined by the C7 sagittal vertical axis (SVA), which is measured as the distance between the C7 plumb line and the posterior superior corner of the sacrum. The pelvic incidence (PI), which is a fixed morphologic descriptor of the pelvis, should be noted as the angle between the midpoint of the two femoral heads and a line perpendicular to the midpoint of the sacral end plate. The mismatch between the PI and lumbar lordosis (LL) should also be recorded. The pelvic tilt (PT) is a dynamic measurement describing pelvic retroversion and is indicated by the angle between a vertical line from the midpoint of the femoral heads and the midpoint of the sacral end plate. Pelvic obliquity is measured on AP radiographs and is denoted by the angle between a horizontal reference line and the line between the two inferior points of the sacral ala. Dynamic radiographs, flexion extension and lateral bending, can assess for instability and flexibility ( Fig. 151-2 ). However, most adult degenerative scoliosis is rigid. Flexibility of the major curve is inversely correlated to the magnitude of the curve and increasing patient age. Magnetic resonance imaging (MRI) or computed tomography (CT) myelography is used to assess for neural compression particularly in patients with neurologic symptoms. Degenerative discs should be noted, as they may need to be treated with interbody fusion in patients with significant mechanical low back pain.

Treatment Strategies

Initial treatment is usually nonoperative and includes physical therapy, epidural steroid injections, muscle relaxants, narcotics, and nonsteroidal anti-inflammatory medications. A study of a large number of nonoperative adult spinal deformity patients found that patients with relatively mild baseline disability could return to normative disability values after 1 year of nonoperative management. Those with high baseline disability showed significant improvement but did not approach normative values. Although baseline disability scales are helpful for guiding patients to treatment modality, radiographic parameters did not predict response to nonoperative management. However, other large studies have shown no improvement in disability with nonoperative management. Therefore, patients who elect to pursue nonoperative management, especially those with significant pain and disability, should be counseled that these treatment modalities may not result in satisfactory improvement.

Patients with idiopathic scoliosis generally seek surgical evaluation for cosmetic concerns, while patients with degenerative scoliosis elect for surgical treatment due to problems with back pain, radiculopathy, neurogenic claudication, or neurologic deficits. As such, Lenke and Silva have proposed a level-based treatment algorithm for degenerative scoliosis. The Lenke-Silva levels of operative treatment range from decompression alone to long segment fusion with osteotomies and are based on the presence of leg pain or back pain, anterior osteophytes, subluxation, curve magnitude, lumbar sagittal malalignment, global imbalance, and flexibility of the deformity. Simple decompression (level I) is reserved for the subset of patients with symptoms of neurogenic claudication without back pain, and radiographic evidence of anterior osteophytes, < 2 mm subluxation, curve < 30 degrees, and good coronal and sagittal balance. Adding instrumented fusion at the level of decompression (level II) is indicated in level I patients who do not have anterior osteophytes at the level being decompressed. Level III treatment involves instrumented fusion of the entire lumbar curve for patients with deformity associated back pain, curve > 30 degrees, > 2 mm subluxation, and good coronal and sagittal balance. Combining an anterior approach for anterior spinal fusion with a posterior approach to the lumbar curve (level IV) is indicated in level III patients with mild sagittal imbalance. Lateral transpsoas approaches to the anterior interbody space offer a less invasive option ( Fig. 151-3 ). The posterior fusion can be extended into the thoracic spine (level V) for patients with thoracic decompensation or more severe global sagittal and coronal imbalance when the deformity is flexible.

Rigid deformity requires the addition of osteotomies (level VI). Smith-Petersen osteotomies (Schwab grade 2) can be used in patients who have regional deformity but reasonable global sagittal balance or in patients with milder global balance if the grade II osteotomies will meet SVA threshold goals ( Fig. 151-4 ). More severe global sagittal imbalance requires pedicle subtraction osteotomy (PSO) (Schwab grade 3 and 4). Asymmetric PSO can be used for deformity correction in patients with combined coronal and sagittal imbalance when the shoulders and the pelvis tilt in opposite directions. Vertebral column resection (VCR) (Schwab grade 5 and 6) is required for cases when the shoulders and the pelvis tilt in the same direction. Based on postoperative HRQOL scores, the following radiographic guidelines have been proposed as the goals of spinal realignment surgery; SVA < 5 mm, PT < 20 degrees, and PI-LL mismatch < 10 degrees. Approximately 5 to 10 degrees of correction can be achieved per level for Schwab grade 2 osteotomies (Smith-Petersen or Ponte). Schwab grades 3 and 4 osteotomies (PSO) can generally obtain 30 degrees of correction. In theory, the lower the level of the PSO, the more sagittal plane correction obtained. However, a large retrospective study of postoperative PSO radiographs demonstrated no correlation in change in SVA with level of PSO. Interestingly, more caudal PSOs were associated with greater reduction in PT. This is particularly important in preoperative planning, as sagittal correction strategies only aimed at correcting the SVA without considering compensatory retroversion of the pelvis may risk undercorrection.