An Approach for Treatment of Complex Adult Spinal Deformity

Summary of Key Points

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Decision making in complex spinal problems can be made easier by applying a systematic approach.
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“Problem, Goals, Tools, Plan” is a scheme that can be used to approach complex spine problems.
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The primary driver of good clinical outcome in deformity surgery is a stable spine in neutral sagittal balance following surgery.
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Pelvic parameters, in particular, pelvic incidence, help determine optimal lumbar lordosis.
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Numerous operative techniques are available, and each has a role.
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Complication rates can be high, but outcomes are usually quite good.
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Proximal junctional failure is still an unsolved problem.

Complex spinal deformity arises from a number of pathologies. In some cases it is the large magnitude curve of idiopathic scoliosis or kyphosis. It may be the result of secondary deformity due to neuromuscular disease, congenital anomalies, infection, or trauma. The two major groups in terms of volume are decompensated deformities due to degenerative change in a preexisting scoliosis and iatrogenic deformity.

The measurement of “normal” cervical lordosis, thoracic kyphosis, and lumbar lordosis is variable. There is little or no correlation between absolute measures of lordosis kyphosis and even scoliosis on symptoms, disability, or risk of progression in adults. As long as the spine remains in balance, a wide range of deformity can be tolerated. If the spine decompensates and balance is lost, then pain, disability, and risk of progression all increase As a result, spinal balance appears to be more important in terms of symptoms and progression than the magnitude of scoliosis or kyphosis. A review by Kuntz has shown that there is only a narrow range of spinal balance and that this is highly conserved. There is a relationship between pelvic morphology and spinal alignment. There are several measurements of pelvic morphology and compensation that correlate with spinal pathology. Sacral slope, pelvic tilt, and pelvic incidence have been termed the pelvic parameters. The relationships among these parameters, especially pelvic incidence and sagittal alignment, have received a lot of interest. Clinically, spinal balance can be assessed by examining the head position of a standing patient in relation to the pelvis. In the lateral view, a plumb line from the ear canal should pass through or behind the greater trochanter. In the anteroposterior (AP) view, a plumb line from the inion should pass between the posterior superior iliac spines. Radiographically, utilizing 3-foot-long cassette scoliosis views, one can use either the C7 vertebral body or the odontoid as the starting point for a plumb line. Use of the odontoid as a marker allows assessment of cervical deformity in overall spinal balance. A plumb line from the odontoid should pass posterior to the center of rotation of the hip in the lateral plane and should fall between the medial borders of the S1 pedicle in the AP view. A plumb line from the C7 vertebral body should pass through the L5-S1 disc space. Figure 155-1 shows preoperative AP ( Fig. 155-1A ) and lateral ( Fig. 155-1B ) views of a patient with a decompensated kyphoscoliosis showing loss of both sagittal and coronal balance. Figures 155-1C and D demonstrate postoperative views of the same patient showing restoration of balance.

In many patients with spinal deformity, particularly in adults, the clinical picture can be complex and the decision making process can seem daunting. When a patient with a complex deformity presents for evaluation, it is often difficult to know where to start. Having a systematic approach to assessment and planning of treatment makes these complex patients easier to treat. A complex problem can be made easier to understand if it is broken down into its component parts. The author uses a four-part process to do this, and this chapter will use this framework to discuss the treatment of complex spinal deformity. The four components are problems, goals, options, and plans.

Define the Problem

Although it sounds simplistic, it is important to begin the process by defining the problem. In contrast to idiopathic adolescent scoliosis where the predominant focus has been on the magnitude and progression of the deformity, there are more factors to consider in adult deformity. One of the key clinical differences in adult deformity is that adults generally seek treatment for the symptoms of the deformity rather than for the deformity itself. As a result, the deformity is viewed within the context of the symptoms it produces. In addition, there are comorbidities to be considered. In many cases the patient will already have had other spinal procedures.

The first step is to gather a detailed history. What is the main presenting problem? How does it affect the patient’s quality of life? How has it changed over time? If the effect on quality of life is relatively minimal, what is the likelihood of the problem progressing? In many patients, nonoperative treatment may be a viable option even in the presence of significant deformities. It is also important to understand the patient’s perception of the problem. In the author’s experience, some patients present with few symptoms yet desire aggressive treatment because of fear that progression of the problem will lead to paralysis or death. Others present seeking information or to establish a relationship with a practitioner in case the symptoms worsen.

Comorbidities are an important part of the history if one is considering surgery. In addition to cardiovascular and pulmonary conditions, nutritional status and risk factors for osteoporosis should be considered. Poor nutritional status increases the risk of wound healing problems and infection. Osteoporosis is associated with a higher incidence of hardware failure.

If the patient has had previous surgery, it is important to know what was done. It is also important to know why the surgery was performed and the short- and long-term outcome of that surgery. Previous investigations and operative reports are valuable in the assessment if they can be obtained. In some cases, the deformity may be iatrogenic.

The physical examination should include a detailed neurologic examination. Examination of spinal alignment and balance is important. Loss of sagittal and coronal balance is associated with increased symptoms and seems to have a higher risk of progression.

Imaging studies are an integral part of defining the problem. Conventional x-rays in the standing position including the entire spine and pelvis are the standard method of assessing deformity. Lateral bending films can assess the flexibility of any coronal deformity. Supine films (often done with a bolster under the apex of the deformity) can give an assessment of the flexibility of sagittal plane deformities. Magnetic resonance imaging (MRI) is the investigation tool of choice for assessing the status of the discs and the neural axis. Computed tomography (CT) provides excellent assessment of the bony anatomy, and the use of sagittal and coronal reformatting allows a more detailed assessment of the bony architecture. If a patient has had previous surgeries, CT is a sensitive and specific method of assessing fusion status. Myelography with or without CT may make assessment of the neural axis easier in large deformities. Bone scan has historically been used for the assessment of pseudarthrosis but has been largely supplanted by CT in the author’s practice.

In those patients in whom surgery is being considered and significant comorbidities are present, general and specialty medical consultation for preoperative optimization should be utilized. Nutritional and bone health status are often overlooked in the workup and can have significant effects on outcome. Bone mineral density (BMD) testing can help to assess bone health, though the presence of degenerative changes in the spine may artificially increase BMD of the spine. Vitamin D testing and supplementation in the pre-op period should be considered, especially in regions or cultures where there is little direct sun exposure. In large magnitude thoracic deformities, pulmonary function testing should be done for risk assessment.

Goals

Once the problem has been defined, the next step is to decide on the goals of treatment. It is important to assess the patient’s goals for treatment as well the practitioner’s goals. Are these goals achievable and at what risk? Patients with minimal symptoms in daily life who have limits with high-level activities may desire a level of function that is just not achievable. Alternatively, for a patient with low demands and expectations, nonoperative treatments may provide an appropriate quality of life without the risks associated with addressing the deformity.

Prevention of curve progression is a common goal in treatment of deformity. In adult deformity, progression is unpredictable and progression of symptoms may or may not correlate with progression of the deformity. As a result, prevention of progression is not a common indication for treatment after skeletal maturity.

In general, the goals of surgical treatment are to relieve compression of neural elements, stabilize instabilities, and correct and maintain the correction of the deformity. These goals need to be accomplished with view to minimizing risk in both the short and long term. One of the primary goals of deformity treatment should be the restoration of sagittal and coronal balance. Outcome studies have shown weak, if any, correlation between correction of a Cobb angle and the outcome, but studies have shown a clear correlation between spinal balance and outcome. More recent studies have shown the importance of restoring lumbar lordosis, measured from the superior end plate of S1 to the superior end plate of L1, to equal pelvic incidence measured as the angle between a perpendicular to the midpoint of the S1 end plate and a line drawn from the midpoint of the S1 end plate to the center of the femoral heads.

Osteoporosis

Osteoporosis is common in patients with spinal deformity. It may be associated with vertebral fractures leading to increased deformity. It also affects the outcome of surgery. Though osteoporosis does not affect bone healing, it does affect the holding power of spinal instrumentation. For this reason, when considering surgery, assessment of osteoporosis is an important step. Though there is no quoted level of bone density beyond which surgery is not an option, the risks of failure increase with higher degrees of bone loss. Preoperative optimization of bone health with vitamin D testing and supplementation as required and pretreatment with teriparatide have been advocated. Clinical studies have shown a positive effect of teriparatide on fusion outcomes.

Options

Decompression Alone

In patients with a stable balanced spine and an isolated radiculopathy, one option may be to consider neurologic decompression alone. In general, compressive pathologies occur on the concavity of the deformity. If a single level can be identified either on the basis of clinical symptomatology or with nerve root blocks, then an isolated decompression may be a reasonable option. There is a risk that decompression may exacerbate deformity in these patients. Studies have shown that the results of decompression alone in the presence of scoliosis may not be as good as decompression in a normally aligned spine. Many of these studies were done with more extensive decompression than would currently be applied. Decompression alone is not an option in the presence of a rotatory subluxation or spondylolisthesis at the apex of the deformity. Anecdotally decompressions of a keyhole or laminotomy type are associated with a lower risk of progression of deformity. This option may be particularly good in elderly patients with an isolated radiculopathy and relatively minimal axial back pain.

Fusion without Instrumentation

In patients with severe osteoporosis, use of pedicle screw instrumentation may be contraindicated. In these patients an option may be fusion without instrumentation. This is reserved for patients with stable balanced deformities. In general, this is used in patients who are much older and more frail and less able to tolerate extensive procedures. There is little or no literature on this procedure, and it is difficult to compare it to other techniques as a result.

Limited Fusion

In many patients, symptoms can be isolated to a single level of pathology. An example would be a degenerative spondylolisthesis and a degenerative scoliosis. In these patients, it may be reasonable to treat only the symptomatic level. This is a somewhat controversial treatment. In a study looking at single-level fusion for degenerative spondylolisthesis in degenerative scoliosis, reasonably good results were obtained. A small number of patients needed further surgery and few if any had progression of the deformity. Some authors have criticized this technique as having an unacceptably high rate of failure. However, there are no controlled trials comparing limited fusion to more extensive fusion. There are few papers in the literature that have looked at this procedure.

Instrumented Correction and Fusion

In most complex deformity patients, some form of instrumented correction and fusion will be performed. Each option has its advantages and disadvantages. The result should be a stable balanced spine with a solid biologic fusion. Any technique that achieves this goal is a reasonable option.

In most cases, pedicle screw instrumentation will be the mainstay of instrumented fusion. This method allows for better correction of most deformities. Pedicle screws are extremely versatile and have excellent holding power. They can exert or resist forces in multiple planes. Pedicle screws tend to be weakest in pullout. As a result of their versatility, they have become the main instrumentation used in deformity correction. Hooks and wires are less commonly used as they are more technically demanding and less versatile. Hooks and wires are relatively strong in pullout but need intact posterior elements. However, they are weaker in all other vectors of failure.

Obtaining solid biologic fusion is of utmost importance for the long-term control and success of deformity correction. Fusion can be achieved through interbody, posterior, or posterior lateral arthrodesis. In general, interbody techniques have a higher fusion rate. In the lumbar spine, posterior lateral fusion is biomechanically better and more effective than a posterior laminar onlay technique. In the thoracic spine, a posterior fusion is more typically performed. The biology of fusion, choice of bone graft or bone graft substitute, and use of extenders are discussed elsewhere. In general, in complex surgery with a high risk of fusion failure, the choice of bone graft and bone graft substitutes is of high importance. The use of bone morphogenetic protein in deformity seems to lead to significantly higher fusion rates. There is limited evidence to suggest that it is cost effective in this indication. There have been concerns regarding risks of BMP, including increased risk of cancer, but a large administrative database study showed no increased risk. The use of rh-BMP-2 in this indication has not been approved by the U.S. Food and Drug Administration (FDA).

Selection of caudad and cephalad instrumentation levels is the first step in determining an operative plan. In general, the construct should begin and end at a neutral vertebra in both the sagittal and coronal planes. A neutral vertebra is defined as one that has no axial rotation, is in the central vertical axis of the spine coronally, and is in the transition zone between lordotic and kyphotic curves in the sagittal plane. In complex or degenerative deformities it is often more difficult to determine these levels than in an idiopathic scoliosis. The presence of significant disc degeneration or instability below a neutral vertebra would generally necessitate extension of the fusion beyond this. Perhaps the most controversial question is whether or not to end a fusion at the L5 vertebra. Numerous studies have looked at this issue and reached conflicting results. A series of studies by Lenke and his collaborators looked at this question and concluded that if the L5-S1 disc is relatively normal on MRI and the L5 vertebral body does not have an oblique takeoff, then preserving the L5-S1 motion segment is a reasonable option. In these patients, the incidence of repeat surgery to fuse the 5/1 level was lower than the incidence of repeat surgery for pseudarthrosis. In the presence of significant L5-S1 disc degeneration, oblique takeoff, or instability at L5-S1, the incidence of repeat surgery to fuse the 51 level was higher than the incidence of surgery for pseudarthrosis.

Numerous factors must be looked at in considering the upper stop point of the construct. The thoracolumbar junction represents a transition from the relatively mobile lumbar spine to the relatively stiff thoracic spine. Constructs extending up from the sacrum to the lumbosacral junction can create a stress riser if stopped at the junction. Typically it has been felt to be acceptable to stop such a construct at L2, but constructs longer than this should extend to T10. Studies have called this belief into question. In one study there seemed to be no clearly defined level at which the risk of subsequent surgery was lessened. In another the traditional T10 level had the highest rate of proximal junctional failure In deciding to stop in the lower thoracic spine, one must also consider whether this stop point is at the apex of the thoracic kyphosis. In patients where a fusion stops at the apex of the thoracic kyphosis, there is significant risk of proximal junctional kyphosis. In these patients it may be preferable to extend the construct up into the upper thoracic spine, typically T4 or T5.

Long fusion constructs to the sacrum have a high incidence of failure due to pseudarthrosis at L5-S1. This is due to a number of biomechanical and anatomic factors. The S1 pedicle is relatively cancellous and has a relatively short AP diameter, thus the holding power of S1 pedicle screws is less than at other levels. In addition, forces at this level are magnified due to the relatively large lever arm exerted by the pelvis. A number of strategies have been suggested to increase the fusion right at L5-S1. Primary among these is the use of interbody fusion through either an anterior or a posterior approach. This option has been shown to decrease pseudarthrosis. Studies have looked at anterior lumbar interbody fusion (ALIF) and compared it to posterior lumbar interbody fusion (PLIF) or transforaminal lumbar interbody fusion (TLIF). In these studies, none of these techniques has shown clear superiority. A study by McCord analyzed alternative fixation techniques at the lumbosacral junction, and the results led to the concept of the “pivot point,” which is the posterior disc at L5-S1. Fixation at the lumbosacral junction should extend anterior to this pivot point to increase stability. Options include sacral alar screws, S2 screws, iliac bars and screws, and iliosacral screws. Biomechanical studies show increased rigidity with the use of iliac or sacroiliac screws, and clinical studies suggest that these two fixation types are superior to sacral alar or S2 screws. In a longitudinal series by Kostuik, pseudarthrosis rates decreased from 83% to 3% with the use of interbody fusion and iliac fixation.

Many authors have advocated increasing deformity correction through the use of anterior releases and fusions. It is felt that this increases correction and fusion rate. Studies have called this into question. With the use of segmental pedicle screw fixation and alternative release techniques, equivalent deformity correction can be obtained through purely posterior procedures without the morbidity of an anterior release. These studies compared more traditional open anterior release techniques. With the advent of new or less invasive procedures and the use of interbody fusions through a direct lateral approach, the morbidity of anterior releases may be significantly less. These minimal access lateral approach and fusion techniques have been shown to give good correction, high fusion rates, and reasonably good clinical results. In the author’s practice these techniques have replaced traditional open releases and fusions. The use of these techniques at the L4-5 level should be considered cautiously. The anatomic corridor is small, and there is a relatively high rate of L3 neuropraxia. The author no longer uses minimal access lateral techniques at the L4-5 level.

Instrumentation in Osteoporosis

The presence of osteoporosis increases the failure rate of instrumented constructs in deformity surgery. Osteoporosis compromises the holding power of the implants leading to this increased failure rate. Numerous strategies have been advocated to lessen this failure risk, and Hu and colleagues, in a review article, summarized them well. Essentially these strategies are all methods of dispersing or decreasing forces across the construct. Increasing the number of fixation points decreases the stress on each element of the construct. Cement augmentation of pedicle screws has been shown to increase their pullout resistance. In general it is not necessary to cement augment all fixation points. Generally only those at the ends of the construct need to be reinforced with cement. There is relatively more loss of cancellous than cortical bone in osteoporosis, and therefore a fixation that utilizes cortical bone will be relatively stronger. As a result, laminar hooks may be a good option in a kyphosis construct if it is likely to fail in pullout. If correction can be obtained through osteotomies or releases, then loads on the hardware are more likely to be neutral and therefore the construct is less susceptible to hardware failure. Osteoporosis has been considered a relative contraindication to the use of interbody fusions. Biomechanical studies by Polly have shown that use of interbody fusion actually increases the strength and rigidity of constructs. Interbody grafts or cages placed asymmetrically can be used to obtain correction, again allowing the hardware to be in neutral and decreasing the risk of hardware failure.

Interspinous Spacers

Interspinous spacers such as the X-Stop are indicated for the treatment of spinal stenosis in the absence of deformity. In the FDA studies, scoliosis was an exclusion criterion. It has been suggested that these may be used in an off-label manner to treat stenotic symptoms in the presence of deformity. The author has used these in rare cases for patients with severe medical comorbidities and significant deformity who would not tolerate traditional surgery. The results have been mixed, but the complications have been few. Further studies may be warranted.

Osteotomies

Osteotomies are powerful tools in the treatment of complex deformity. Many of these deformities are rigid, and in the case of patients who have undergone previous surgery the deformity may be fixed due to bony fusion. Osteotomies are generally used to correct sagittal plane deformities but may also be used to correct coronal and biplanar deformities. They can be technically demanding but can give excellent clinical results.

The simplest osteotomies to perform are facet resection osteotomies as described by Ponte or Smith-Petersen. There is confusion as to nomenclature of these osteotomies. Smith-Petersen described a procedure where the facet was resected and the disc released leading to a pivot at the posterior corner of the vertebral body causing closure of the osteotomy posteriorly and extension through the disc space anteriorly. This procedure was originally described in ankylosing spondylitis. The more common facet resection and closure through a mobile disc was first described by Wilson but has been widely attributed to Ponte. For clarity, the author will use facet resection osteotomy. These osteotomies can be used anywhere there is a mobile disc. Correction of 5 to 10 degrees of kyphosis can readily be obtained, and multiple levels can be used. Some coronal correction can be obtained as well. Facet resections can also be used to increase the correction of the coronal deformity. A facet resection osteotomy augmented by an interbody fusion can increase the amount of correction obtained through this technique. An example is shown in Figure 155-2 .

If larger degrees of correction are required, then a pedicle subtraction osteotomy can be considered. This is a closing wedge osteotomy performed by removing the posterior elements, the pedicle, and a portion of the vertebral body. First described by Scudese, this powerful technique allows routine correction of 30 degrees or more. It has typically been performed at lumbar levels but can be performed safely in the thoracic spine as well. These procedures are relatively technically demanding and associated with significant complications. Clinical results are very good. Biplanar correction can also be achieved, allowing correction of deformity in more than one plane. Two basic types of pedicle subtraction osteotomy have been described. In the first of these, osteotomes are used to create a wedge, which is then removed. The alternative procedure is a decancellation osteotomy. In this procedure the vertebral is decancellized, the posterior wall reduced into the cavity, the lateral wall osteotomized, and the osteotomy closed. No comparison studies if these two techniques exist. Figure 155-3 shows the preoperative and postoperative x-rays of a patient with a posttraumatic kyphosis treated with a pedicle subtraction osteotomy to restore lumbar lordosis.

Vertebral Column Resection

In some complex high-magnitude deformities, complete resection of one or more vertebral segments may be required to correct deformity. This procedure is called a verbal column resection. It can be done through a combined anterior posterior or a posterior-only approach. An example of where this technique may be used would be an apical kyphectomy for spina bifida. This procedure can be used for both kyphosis and scoliosis and may be used to obtain biplanar correction. In some cases, the anterior column is reconstructed with a graft or cage implant; in other cases, the spinal column is shortened. These procedures are also associated with significant risks. Reasonably good clinical results have been reported.

Plans

Once the specific problem has been defined and the goals of surgery established, then the operation should be planned. Careful preoperative planning and communication of the plan to the operative team will make the procedure safer and more efficient.

In the preoperative period, steps should be taken to ensure the patient is optimally prepared for surgery. The author considers smoking cessation to be mandatory for all such procedures. Preoperative blood management consultation may help optimize hemoglobin prior to surgery. Studies have suggested an increased risk of thrombotic complications with the use of erythropoietin analogues, so the risks and benefits must be balanced. Preoperative medical cardiology and pulmonology consults should be obtained as indicated.

If a combined anterior-posterior approach is being considered, then one must decide whether to use a single-day or staged multi-day approach. Single-day procedures have the advantage of only a single anesthetic and recovery period but can result in long procedures with high blood loss. Single-day procedures may also be more demanding on the surgeon. Staged procedures may be less physically demanding for patient and surgeon. Studies that have looked at this show no clear benefit of one approach over the other. It is the author’s practice to do most of these procedures in a single day, but if a procedure is particularly complex or complications arise, it is advisable to stage them.

Complex surgeries often require a large inventory of implants. It is therefore important to coordinate with equipment suppliers to ensure an adequate supply of appropriate implants as available. The plan should include determining whether any special implants or instruments are required for the procedure. These sets should be present before beginning the procedure. If an access surgeon is being used for the approach, then the appropriate sets for this surgeon should be obtained as well.

Neurologic monitoring should be considered for all of these procedures. At the author’s institution, somatosensory and motor-evoked potentials are used for all deformities. Stimulated electromyography (EMG) monitoring is used for minimal access lateral lumbar approaches. Neurologic monitoring has been shown to decrease the risk of neurologic injury. If motor-evoked potentials are to be used, it should be communicated to the anesthesiology staff to ensure that a neuromuscular blockade is not used during the procedure.

Intraoperative red cell salvage is routinely used in complex surgeries to lessen the use of autologous blood donation.

Intraoperative imaging is facilitated by the use of a radiolucent table. X-rays taken intraoperatively in both sagittal and coronal planes allow estimation of correction obtained and implant placement. Intraoperative fluoroscopy may be used to guide implant placement. CT-based navigation systems have been shown to increase the accuracy of screw placement, particularly in significant deformities. Clinically, however, freehand placement of pedicle screws has been shown to be safe and effective. The author’s preference is to use intraoperative CT-based navigation for screw placement.

Numerous techniques have been described for determining the magnitude of deformity correction in the sagittal plane to restore balance. Perhaps the simplest way of doing this is to cut a 3-foot film at the level of the planned osteotomy, then balance the head over the pelvis and measure the subtended angle. With the advantage of digital radiography, printed 3-foot films are becoming rare and this is no longer as good an option. A second option is to measure the angle subtended between a vertical line at the pivot point of the planned osteotomy and either the C7 or C1 vertebral bodies. An osteotomy higher in the lumbar spine requires a greater angle of correction for a given amount of linear translation of the head. Ondra and collaborators have described two mathematical models for determining osteotomy correction. Although these are effective, the author finds them to be somewhat cumbersome to use in clinical practice. A much simpler method for planning correction in the lumbar spine is to aim for correcting lumbar lordosis to equal pelvic incidence.

It is generally recommended to overcorrect sagittal deformity by 5 to 10 degrees to compensate for the loss of hip extension that occurs with aging. This applies to constructs extending to the sacrum. Aging patients with a normal lumbar spine are able to compensate for the loss of hip extension by rotating the pelvis through the lumbar spine. Patients who have fusions extending to the sacrum have lost this compensation. As a result, the loss of hip extension will prevent normal stride through with gait. When this occurs, a patient who is able to stand in neutral sagittal balance will be forced to walk in positive sagittal balance in order to have a normal gait. The preoperative examination of these patients should include a careful assessment of the range of motion of the hip. Consideration may need to be given to treating hip flexion contractures, either through physical therapy or through surgical releases prior to considering osteotomies.

Even with an extensive preoperative workup, it is sometimes difficult to know how much the deformity will be corrected at the time of surgery and with successive stages of the surgery. As a result, operative plans are often flexible. Anterior interbody fusions with lordotic graft or cages may provide significant correction in patients with collapsed discs. Positioning on a four-post frame in the prone position will often provide significant correction of a deformity that did not seem flexible. If one is planning a pedicle subtraction osteotomy through a level with mobile discs, it may be advisable to obtain an intraoperative lateral x-ray after the facet resection to see if sufficient correction has been obtained through these methods to eliminate the need for the pedicle subtraction osteotomy.

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