Adult Deformity

Daniel G. Kang

Keith H. Bridwell

Adult spinal deformity encompasses various etiologies that contribute to an alteration in the three-dimensional structure of the human spine. Patients typically seek treatment based on a combination of symptoms, including back pain, radicular pain, paresthesias, lower extremity weakness causing difficulty with ambulation, and progression of deformity. Spinal deformity is typically described based on the involved region of the spine and whether the curvature occurs in the coronal plane (scoliosis) and/or sagittal plane (kyphosis/lordosis). In addition, with progressive spinal deformity or worsening degenerative changes, there may be significant axial plane (rotation) deformity and translation (anterior, posterior, or lateral listhesis) of spinal segments. Another important distinction for adult scoliosis is whether the spinal deformity had its onset before skeletal maturity with progression over time (idiopathic) or developed in adulthood (de novo). The following chapter will discuss the evaluation and treatment of adult scoliosis, as well as iatrogenic sagittal spinal deformity in ambulatory patients without other neuromuscular disorders or congenital etiologies.

Normal Spinal Alignment

Understanding the normal alignment of the human spine is important for evaluation and treatment of spinal deformity. In the coronal plane, there is normally no curvature of any spinal segment. The Scoliosis Research Society (SRS) has defined scoliosis as a coronal curvature greater than 10 degrees using the Cobb angle measurement technique (bisected lines from the superior end plate of the cephalad most tilted vertebra to the inferior end plate of the caudad most tilted vertebra) (Fig. 23.1). On a standing anteroposterior radiograph, a vertical line (plumb) from the tip of the C2 vertebra (dens) or the middle of C7 (if unable to visualize C2) should bisect each caudal vertebra through the center of the sacrum. Deviation of the plumb line from the center sacral vertical line (CSVL) is termed the coronal vertical axis (CVA) and can be increased to the left or right with a large scoliosis, although patients with double curves that are similar in magnitude may lead to no or minimal coronal imbalance.

In the sagittal plane, each spinal region has normal kyphotic or lordotic curvature that changes from birth up to early adolescence. At skeletal maturity, there is normally cervical lordosis (range, 20- to 40-degree lordosis), thoracic kyphosis (range, 20- to 60-degree kyphosis), and lumbar lordosis (range, 30- to 80-degree lordosis). The apex of thoracic kyphosis usually falls between T6 and T8, and in the lumbar spine two-thirds of lordosis occurs between L4 and the sacrum. In addition, 80% of lumbar lordosis occurs through wedging of the intervertebral disks, and only 20% is derived from the trapezoidal osseous morphology of the vertebral bodies. Therefore, sagittal plane curvature can be affected with advancing age and degeneration of intervertebral disks, causing increased kyphosis in the thoracic spine, and loss of lordosis in the cervical and lumbar spine, gradually leading to sagittal imbalance. On a standing lateral radiograph, a vertical line (plumb) from the center of the C7 body should intersect with the posterior-superior body of the S1 segment, and anterior or posterior deviation is termed the sagittal vertical axis (SVA) (Fig. 23.2). Sagittal imbalance with anterior (positive) SVA greater than 5 cm and coronal imbalance greater than 4 cm have been found to correlate with worse patient-reported outcomes scores, and are important parameters in the surgical decision-making process.

Also important in the evaluation of sagittal plane deformity is an understanding of normal spinopelvic parameters, and their relationship to sagittal balance. Pelvic tilt (PT), sacral slope (SS), and pelvic incidence (PI) are defined by the following relationship: PI = PT + SS.

PT is defined as an angle between the vertical reference line and a line from the center of the cephalad S1 end plate to the center of the femoral heads.
SS is defined as an angle between the horizontal reference line and the cephalad S1 end plate.
PI is defined as an angle between a line perpendicular to the center of the cephalad S1 end plate and a line from the center of the cephalad S1 end plate to the center of the femoral heads.

Figure 23.1 Sagittal alignment showing the C7 plumb and its typical relationship relative to the sacrum.

Additional spinopelvic relationships that have been described include:

PI = lumbar lordosis ± 9 degrees
PI = lumbar lordosis + thoracic kyphosis + 45 degrees

Figure 23.2 Sagittal alignment of the spine showing the Cobb method of quantifying spinal deformities.

Patient Assessment

Clinical Manifestations

A thorough history and physical examination are essential for identifying and treating specific factors resulting in symptoms and functional limitations. Adult spinal deformity is typically appreciated by the patient as a loss of trunk height, change in trunk contour, shoulder
asymmetry, shift in the position of the head relative to the pelvis (global balance), as well as changes in the fit of clothing. Mild-to-moderate scoliotic deformities may be well tolerated, especially when global balance is maintained. However, larger curves and curves with advanced degeneration in the thoracolumbar or lumbar regions tend to be symptomatic, with mechanical instability and neural compression collectively contributing to clinical presentation. Patients often present with a combination of symptoms, including:

Mechanical upper or lower back pain
Radiating lower extremity pain
Paresthesias
Lower extremity weakness

Axial upper or lower back pain is a common presenting symptom, and may represent mechanical instability at the degenerated segments or paraspinal muscle fatigue from the body’s attempt to maintain an upright posture in the setting of regional and global imbalance. Radicular symptoms can occur from loss of foraminal height due to disk degeneration (up-down foraminal stenosis), narrowing of the foramina along the concavity of the major and fractional curves, traction of nerve roots on the convexity of the curve, an acute disk herniation, lateral recess stenosis from facet joint overgrowth, facet joint cysts, and ligamentum flavum hypertrophy. These degenerative changes may also contribute to central stenosis, particularly in patients with underlying congenital spinal stenosis, and development of neurogenic claudication and associated complaints such as lower extremity weakness/fatigue, difficulty with gait, decreased walking distance tolerance, and increased use of ambulatory assistive devices. The bicycle-treadmill test is used to differentiate neurogenic claudication from vascular claudication, and can also provide information regarding the cardiopulmonary fitness of possible operative candidates. Adult spinal deformity patients may also have concomitant degenerative changes in the cervical or thoracic spine, and central stenosis in these regions may cause myelopathic symptoms and long tract signs from spinal cord compression, which would warrant advanced imaging and careful evaluation of the entire spinal column. Patient hip range of motion should also be assessed because hip flexion contractures may occur in patients with severe sagittal imbalance.

Imaging Studies

Radiographic evaluation should include a full-length (36-in) standing anteroposterior and lateral views of the spine, with the patient’s hips and knees extended to assess regional and global balance. Other important factors to be noted on standing anteroposterior radiographs include the presence of significant pelvic obliquity or shoulder height imbalance. Supine full-length anteroposterior and lateral views allow assessment of spontaneous deformity reduction with gravity forces removed. In addition, supine flexibility radiographs in the coronal (side bending to the left and right) and sagittal (passive extension over a bolster) plane also provide valuable information regarding the rigidity of the curves. Passive extension over a bolster is a useful technique for sagittal deformities which seem stiff or stuck on initial evaluation, and surprisingly correct after lying over a bolster for 5 to 10 minutes. However, flexibility assessment films can be limited by patient effort and pain, as well as radiology technician training and experience, and thus should be evaluated in conjunction with other imaging studies to completely understand the nature of the patient’s spinal deformity. Upright dynamic flexion and extension lateral radiographs may be used to demonstrate pathologic motion, such as increased listhesis or disk wedging, hypermobility of segments immediately adjacent to a fusion construct, or for motion in a previously fused segment. Degenerative changes at the lumbosacral junction, and regional anatomy, may be better visualized with short cassette radiographs, using “cone-down” views, as well as a true anteroposterior lumbosacral radiograph (Ferguson anteroposterior view), which is obtained with the beam angled cephalad to match lumbosacral lordosis. These radiographic studies must be carefully evaluated for transitional lumbosacral anatomy, extent of facet and disk degeneration, and pedicle morphometry. Cobb angle measurements, regional and global balance measurements, and spinopelvic parameters are also important factors for surgical decision making.

Advanced imaging is indicated for patients with radicular pain or neurologic symptoms. Typically a magnetic resonance imaging (MRI) is recommended, although it is not uncommon for older patients to be unable to obtain an MRI for various reasons (e.g., presence of a pacemaker, non-MRI compatible surgical devices/implants). Also, in patients with previous spinal instrumentation, artifact from metallic implants may cause difficulty with MRI interpretation. An alternative to MRI is myelography followed by thin-cut (1-mm) computed tomography (CT), which may provide a better assessment of central and lateral recess stenosis compared to MRI, whereas MRI is most helpful for assessing disk degeneration and foraminal stenosis. CT images with three-dimensional reconstruction are also helpful in surgical planning to further evaluate the extent of spondylotic changes, identify segments with autofusion, and allows for sizing and planning of spinal fixation points; furthermore, for revision surgery, CT allows assessment of the location and extent of previous decompressions, healing status of previously fused segments, and the position of prior spinal instrumentation. Some surgeons use provocative discography for diagnostic assessment and for choosing the distal fusion level. However, there remains controversy on the reproducibility and reliability of this diagnostic modality, as well as concerns that iatrogenic trauma
from the procedure may increase the risk of progressive disk degeneration.

Adult Scoliosis

As previously noted, there are two distinct types of adult scoliosis:

Adult idiopathic scoliosis
Adult de novo scoliosis

These two types of adult scoliosis are differentiated from adolescent idiopathic scoliosis, as the progression and treatment of adult scoliosis is due to degenerative changes and mechanical instability, not longitudinal growth of the spine. Adult idiopathic scoliosis is used to describe patients with a history of adolescent idiopathic scoliosis, with or without progression of curve magnitude, and development of superimposed degenerative changes. Adult de novo scoliosis, also termed primary degenerative scoliosis, typically develops after age 40 and in the lumbar spine without any significant thoracic deformity. De novo scoliosis usually begins and then progresses with intervertebral disk degeneration, with subsequent abnormal motion, ligamentous laxity, and posterior facet degeneration (Table 23.1). As the intervertebral disk and posterior osteoligamentous complex become incompetent, there may be mechanical instability, lateral listhesis, rotatory subluxation, and progressive scoliosis. An additional type of adult scoliosis, which will not be discussed, is secondary to altered vertebral anatomy which can be from prior spinal surgery or trauma causing instability, as well as metabolic bone disease, spinal tumors, or metastatic disease causing spinal deformity.

Natural History

The natural history of adult idiopathic scoliosis is variable and not completely understood. Usually, smaller curves (<45 degrees) and curves in patients with good overall spinal alignment progress little over time. Conversely, larger curves and curves associated with global imbalance may progress at a rate of 1 degree or more per year during adulthood. Older patients with de novo degenerative scoliosis curves may progress at a rate of 3 degrees or more per year. In general, thoracolumbar and lumbar curves are more likely to progress than more stable thoracic curves. Also, with advancing age, the rate of progression may increase as patients undergo progressive degenerative changes in the disks, facets, and ligaments.

TABLE 23.1 COMPARISON OF CLINICAL CHARACTERISTICS ASSOCIATED WITH ADULT IDIOPATHIC SCOLIOSIS AND DE NOVO SCOLIOSIS

	Adult Idiopathic Scoliosis	Adult De Novo Scoliosis
Presenting Complaints	Back pain, cosmesis, loss of trunk height, global imbalance	Back pain, loss of trunk height, leg pain, leg paresthesias, leg weakness, neurogenic claudication, global imbalance
Physical Findings	Partially flexible curve, neurologically intact	Typically rigid primary curve and fractional curve, painful motion, lumbar radiculopathy
Radiographic Findings	Early degenerative changes, loss of disk height, mild-moderate facet arthrosis, typically good bone quality	Moderate-to-severe degenerative changes, collapsed disk space, end plate sclerosis, osteophyte formation, listhesis, possible osteoporosis, and vertebral compression fractures
Progression	Onset of curve during childhood, large curves (>45 degrees) can progress up to 1 degree per year	Onset of curve in 5th or 6th decade, thoracolumbar and lumbar curves can progress 3 or more degrees per year

Nonsurgical Treatment

A trial of nonsurgical treatment is indicated for most patients presenting with adult scoliosis, particularly those with mild deformity and a primary complaint of mechanical back pain. In addition, nonsurgical treatment may be recommended for some patients with large deformities or spinal imbalance because various organic and psychosocial factors make them poor candidates for surgical intervention. Nonsurgical treatment should involve a combination of modalities, and typical recommendations include nonsteroidal anti-inflammatory medications, physical therapy for core strengthening, low-impact aerobic fitness, weight management, and smoking/tobacco cessation. In rare cases, an orthotic brace, such as a thoracolumbar or thoracolumbosacral orthosis, is recommended for temporary pain relief. However, bracing in adult scoliosis typically does not alter the natural history or progression of deformity, and may cause deconditioning of the paraspinal extensor muscles and place the patient at risk for skin complications. Narcotic pain
medications are avoided, and a pain management specialist may be consulted to provide optimization of nonnarcotic pain medications (e.g., gabapentin, pregabalin), muscle relaxants (e.g., cyclobenzaprine, methocarbamol), and if needed a pain specialist may prescribe a short period of narcotic pain medications. However, when operative treatment is decided for a patient, we encourage significantly reducing or completely discontinuing all narcotic pain medications to avoid pain control problems postoperatively.

Surgical Intervention

Indications

Some patients with adult scoliosis require surgical treatment, and appropriate indications include:

Large spinal curvature based on Cobb measurement, significant vertebral rotation or listhesis, and/or global spinal imbalance (coronal or sagittal plane)
Documented deformity progression or worsening global spinal balance (coronal or sagittal plane)
Axial or radicular pain, causing significant impact on quality of life and functional activities, which has not responded to nonsurgical measures
Pulmonary dysfunction related to the spinal deformity

In addition, surgical candidates should have a good overall state of health, a stable emotional state, and a functional social support structure to assist with rehabilitation and ensure compliance with postoperative care and instructions. However, because the typical presenting age of adult spinal deformity patients is between 50 and 60 years, medical comorbidities such as diabetes, autoimmune disorders, and cardiac and vascular disease can significantly impact surgical outcomes and should be optimized through an interdisciplinary approach with the patient’s primary care physician, anesthesiologist, and medical specialists. Also, modifiable risk factors such as smoking, tobacco use, malnutrition, hypovitaminosis D, osteoporosis, and skin compromise should be addressed before surgery to reduce the risk of perioperative complications.

Surgical Decision Making and Selecting Fusion Levels

Surgical decision making is individualized for each patient based on several major factors, including the patient’s symptomatology, age, physical and radiographic findings, general medical health, and the patient’s expectations with regard to the outcome of surgery. As previously mentioned, medical optimization and detailed preoperative planning are absolutely critical to minimizing complications and maximizing success of the surgical intervention.

The optimal surgical treatment strategy uses the smallest magnitude of surgery to improve the patient’s symptoms, while reducing the risk of perioperative complications, as well as providing a durable result that will allow sustained improvement in the patient’s quality of life and function.

Young adults with idiopathic scoliosis typically do not have significant lumbar degenerative changes and have good bone quality for spinal fixation. Therefore, principles of selecting fusion levels for these patients are similar to those with adolescent idiopathic scoliosis. The upper and lower instrumented vertebrae (UIV and LIV) should be stable (vertebra most closely bisected by the CSVL) and neutral (least-rotated vertebra). In the sagittal plane, the construct should not end in an area of significant regional kyphosis, and ideally should extend into a segment that is straight or lordotic. Stopping a fusion at the apex of a sagittal kyphosis is almost always a mistake, because a progressive junctional kyphosis commonly follows. Another important concept to avoid junctional kyphosis includes careful attention when contouring the construct to maintain or reconstitute normal sagittal parameters, particularly lumbar lordosis.

Older adults with idiopathic scoliosis can present with significant degenerative changes in the distal lumbar spine and stiff fractional curves, and patients with de novo scoliosis by etiology have degenerative changes that have caused the spinal deformity. In both types, fusion levels should be selected to include segments with subluxation, listhesis, rotational deformity, segments with severe disk degeneration (e.g., presence of vacuum disk phenomenon), segments of neural compression and spinal stenosis requiring decompression, and levels with previous decompression and posterior column deficiency. When determining the extent of curve correction, careful attention should be directed at the fractional curve, which should be corrected to be parallel to the sacrum. Coronal imbalance may be a problem if significant correction of the major thoracolumbar or lumbar curve is achieved and a stiff fractional curve is left uncorrected. Therefore, if unable to completely correct the fractional curve, the major curve should only be corrected to the extent that will maintain coronal balance.

In general, distal lumbar segments with only mild degenerative changes, with no underlying central, lateral, or foraminal stenosis, do not need to be included in the fusion. However, controversy remains regarding the inclusion of distal segments with moderate disk degeneration. If the LIV is chosen above the degenerated level, there is a theoretical increased risk for accelerated adjacent segment degeneration due to increased forces at the bottom of a fusion construct. Particularly for fusions stopping at L5, the lumbosacral motion segment may develop a “transition syndrome” resulting in pain, radiculopathy, and forward shift in sagittal balance, and therefore a potentially higher risk for subsequent reoperation. These concerns should be compared to the potential risks of including additional fusion levels, such as longer operative time with greater blood loss, as well as higher rates of pseudarthrosis and complications. The risk of additional fusion levels may be a greater concern for long fusion constructs that extend across the lumbosacral junction. Long fusions that stop at or above L5 instead of crossing the lumbosacral junction obviate the difficulties with obtaining and maintaining lumbosacral fixation, possibly avoid the necessity for adjunctive
anterior discectomy and fusion, and may reduce the risk of infection from fecal contamination by avoiding a distal surgical incision. Therefore, stopping the fusion at or above L5 should always be considered because preservation of the native motion segments, especially at L5–S1, offers multiple theoretical advantages. However, certain indications may necessitate extending the construct across the lumbosacral junction such as advanced degeneration of the L5–S1 disk, oblique take-off or tilt of L5 on the sacrum, previous L5–S1 decompression, or presence of spondylolysis or spondylolisthesis. Ultimately, the decision of whether to stop a long fusion at or above L5 versus extending across the lumbosacral junction should be evaluated on a case-by-case basis with consideration of the patient’s spinal deformity, global spinal alignment, degenerative status of the distal lumbar and L5–S1 disks, and perioperative medical risk stratification (Table 23.2).

TABLE 23.2 ADVANTAGES OF TERMINATING A LONG FUSION AT L5 VERSUS THE SACRUM-PELVIS

Only gold members can continue reading. Log In or Register to continue