DEFINITION

Adult scoliosis is a coronal deformity of the spine, typically also involving axial and sagittal plane abnormalities.

Adult scoliosis can be categorized by patient presentation.11

One group, predominantly defined by lumbar stenosis and neurogenic claudication with degenerative deformity, has surgical management typically achieved by posterior lumbar procedures.

A second group, categorized by progressive deformity, with or without back pain, is more frequently treated with combination anterior and posterior procedures that may involve the thoracic spine to achieve surgical goals.

Although the surgical principles and techniques used to address these different categories are similar, important variations exist.

 

 

ANATOMY

 

Anatomic characterization of adult spinal deformity involves the coronal, sagittal, and axial plane.

 

Lumbar degenerative scoliosis may be characterized by loss of lordosis and intervertebral disc height as well as listhesis in the anteroposterior, lateral, or rotary direction (FIG 1A,B).

 

Long curves, typically the result of a preexisting spinal deformity, may involve the entire thoracolumbar spine and may be associated with a significant rotational component (FIG 1C,D).

 

PATHOGENESIS

 

Adult scoliosis develops either as the progression of a spinal deformity that was present in adolescence or as the development of a deformity related to other spinal disorders.

 

The progression of the adolescent spinal deformity is related to increasingly unbalanced forces in the axial skeleton over time.

 

De novo adult deformity is commonly the result of degenerative disease and may also be related to osteoporotic fragility fractures of the vertebrae, resulting in a deformity frequently associated with spinal stenosis and mechanical back pain.

 

NATURAL HISTORY

 

The progression of an adolescent deformity is often seen as a long thoracolumbar curve in the adult.

 

Curves that reach a magnitude of more than 50 degrees are likely to progress, resulting in symptom exacerbation.

 

As patient age increases, curve flexibility typically decreases.

 

Lumbar degenerative curves typically involve fewer segments and may be limited to the lumbar spine.

 

Degeneration and deformity can cause central, lateral recess, and neural foramen stenosis as a result of the following:

 

 

Loss of intervertebral height Hypertrophy of facet joints

 

 

Hypertrophy and buckling of the ligamentum flavum Compression deformities

 

Neurogenic claudication, as well as radiculopathy and back pain, may result.

 

PATIENT HISTORY AND PHYSICAL FINDINGS

 

Determining the reason for the patient's presentation is the first step in establishing the goals of surgical treatment.

 

Patients with extensive thoracolumbar deformity may present with concerns related to curve progression with an impact on the following:

 

 

 

 

Balance Ambulation Pain Cosmesis

 

Patients with lumbar degenerative scoliosis classically present with complaints of neurogenic claudication or radiculopathy.

 

Hip and knee flexion contractures, related to the typical forward-flexed ambulation that limits the symptoms of neurogenic claudication, may be found (FIG 2).

 

Major focal neurologic abnormalities are unusual in this patient group, although relatively mild degrees of weakness in the tibialis anterior and extensor hallucis longus are not uncommon.

 

Physical examination should include the following:

 

Assessment of sagittal balance based on lateral observation of the patient standing with knees extended. A plumb line is dropped from the ear and the deviation (anterior or posterior shift) at the greater trochanter is measured, as is the regional (lumbar) lordosis and (thoracic) kyphosis. An upright posture with head over trunk and trunk over pelvis is a critical treatment goal.

 

Assessment of coronal balance based on posterior observation of the patient standing. A plumb line is dropped from the occiput and the deviation (leftward or rightward shift) at the sacrum is measured. A centered posture reduces gait abnormality.

 

Observation and palpation of the vertical relationship of the right and left acromions with the patient standing. Shoulder asymmetry may indicate coronal postural compensation to maintain upright stance.

 

Observation and palpation of the vertical relationship of the right and left iliac crests with the patient standing on the right, left, and both legs. Pelvic obliquity may be a primary or compensatory mechanism with spinal deformity.

 

Assessment of hip and knee range of motion. Long-standing sagittal plane deformities, as well as neurogenic claudication, may result in hip and knee flexion contractures.

 

Neurologic examination: Focal findings may be uncommon, but a thorough examination must be performed.

 

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Neurologic abnormalities should prompt total spine magnetic resonance imaging (MRI) to screen for tethered neurologic elements or other morphologic abnormalities.

 

 

 

 

FIG 1 • A,B. Degenerative lumbar scoliosis, with mild degree of deformity, in PA (A) and lateral (B) radiographs. Small lateral, rotary, and anterolistheses are seen, with significant loss of disc height, osteophyte formation, and subchondral sclerosis. The coronal deformity is limited to the lumbar region. C,D. A longer scoliosis, and of more significant degree, involving the lumbar and thoracic regions, and associated with rotational deformity, is shown in PA (C) and lateral (D) radiographs.

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

Radiographs

 

 

Standing posteroanterior (PA) radiographs on 36-inch cassettes characterize the spinal deformity by The magnitude of primary and compensatory curves, by the Cobb method (FIG 3)

 

Coronal balance: the relationship between the C7 plumb line and center of S1 on PA views (FIG 4)

 

The apical vertebrae (most laterally deviated; FIG 5A)

 

 

 

FIG 2 • Neurogenic claudication is frequently associated with this gait abnormality. A forward-flexed posture may provide postural relief of posterior foraminal stenosis but typically alters the sagittal balance, as depicted here. Hip and knee flexion contractures may be associated.

 

 

 

The stable vertebra (caudal vertebra that is transected by the z-axis; FIG 5B) Rotary and lateral listhesis

 

 

Standing lateral radiographs on 36-inch cassettes characterize the spinal deformity by Regional lordosis and kyphosis (FIG 6)

 

Sagittal balance: the relationship between the C7 plumb line and center of S1 on lateral views (FIG 7)

 

Anterolisthesis or retrolisthesis

 

 

Right- and left-bending PA radiographs (FIGS 8 and 9) are used to Evaluate spinal flexibility

 

Determine the structural or nonstructural nature of the curve

 

 

 

FIG 3 • The Cobb method is used to measure the coronal deformity. Vertebral endplates (or the margins of pedicles) are used to extend lines as depicted for each of the curves involved. Lines orthogonal to these are then compared to determine the scoliosis angle. Vertebrae are typically selected to maximize the Cobb angle on each measurement.

 

 

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FIG 4 • Coronal balance is evaluated on the standing PA radiograph. A virtual plumb line is dropped from the center of C7. The lateral distance between that plumb line and the center of S1 is then measured. (Left to right) Negative coronal decompensation, coronal compensation, and positive coronal decompensation. CSVL, center sacral vertical line.

 

 

 

FIG 5 • A. The apical vertebra is defined as that which is most deviated laterally on the PA radiograph. B. The stable vertebra is defined as the caudal vertebra that is transected by the vertical plumb line extending from the center of S1 on the standing PA radiograph. CSVL, center sacral vertical line.

 

 

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FIG 6 • Regional lordosis and kyphosis are measured on the standing lateral radiograph. Typically, the vertebral endplates are used as references for measurement.

 

 

 

FIG 7 • Sagittal balance is evaluated on the standing lateral radiograph. It is measured as the anterior (positive) or posterior (negative) distance between the C7 plumb line and the center of the L5-S1 disc space.

 

 

Supine traction radiographs may also be used to evaluate curve flexibility.

 

Computed Tomography Scans

 

Computed tomography (CT) images, reformatted in the plane of the superior endplates of each vertebra, can be used to measure pedicle dimensions, assess for potential auto fusions (that may impact curve flexibility and surgical correction), and assess local bone quality (osteoporosis, sclerosis, osteophyte density); all of which is used for preoperative planning.

 

Plain radiographs and CT images can be used to assess the degree of bone loss and tailor the reconstructive techniques to the bone quality of the patient.

 

Magnetic Resonance Imaging

 

MRI is used to assess neurologic compression (FIG 10) as well as the status of the disc, ligamentum flavum, and other soft tissues.

Dual-Energy Radiographic Absorptiometry

 

 

 

Dual-energy radiographic absorptiometry (DEXA) is often performed for patients with identified risk factors: History of fracture as an adult or fracture in a first-degree relative

26

 

 

 

 

FIG 8 • A,B. Bending radiographs aid in determining the flexibility of the spinal curves and are also used to determine the structural or nonstructural nature of the curves. This patient has a relatively rigid deformity.

 

 

 

FIG 9 • Regional bending (A,C-E) and full-length standing (B) radiographs characterize this as a flexible deformity. A,C. The thoracic bending films demonstrate near-complete correction of the thoracic curve. D,E. The lumbar bending films also demonstrate nearcomplete correction of the lumbar curve.

 

 

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FIG 10 • A-C. MRI is particularly useful in evaluating patients with neurologic symptoms such as claudication. It is used to assess neurologic compression as well as the status of the disc, ligamentum flavum, and other soft

tissues.

 

 

 

 

White race Advanced age Smoking

 

 

 

Low body weight Female gender Dementia

 

Poor health or general fragility

 

Provocative Tests

 

Discography, although not 100% accurate, can be useful to assess for painful segments and evaluate the competence of the disc annulus, particularly in the lower lumbar spine.

 

Facet blocks have been employed to determine levels that should be included, or need not be included, in the fusion. This may be particularly relevant at the lumbosacral junction.

NONOPERATIVE MANAGEMENT

 

 

A physical therapy regimen may be tried, focusing on the following: Stretching and core-strengthening exercises

 

Postural training

 

Gait training

 

 

Resolution of hip and knee flexion contractures General conditioning

 

Nonsteroidal anti-inflammatory medications may be used if safely tolerated.

 

SURGICAL MANAGEMENT

 

The treatment of adult scoliosis is complex because of the global nature of the spinal deformity and the multiple causes of this disorder.

 

Efficiency, safety, and effectiveness in meeting surgical goals are each optimized by a well-designed procedure.

 

Preoperative Planning

 

Preoperative planning is instrumental to a successful treatment algorithm; avoiding both short- and long-term complications is paramount.

 

 

In 1968, the complications associated with surgical correction of adult deformity were quite significant17: Five percent risk of death

 

Six percent risk of major neurologic deficit

 

 

Twenty percent risk of correction loss Ten percent risk of deep infection

 

Forty percent risk of major medical complication

 

With advances in surgical and anesthesia techniques, neurophysiologic monitoring, and improvements in

perioperative management, these risks have been decreased.1

 

The patient with adult scoliosis may carry a myriad of comorbidities that may increase the risk of a spinal operation or even contraindicate it. A complete preoperative assessment of those considering surgical treatment provides the opportunity to minimize risks by optimizing health status.

 

 

Modifiable conditions that affect surgical risk include the following: Tobacco smoking

 

History of asthma or chronic obstructive pulmonary disease

 

 

Coronary or cerebrovascular disease Diabetes

 

 

 

Nutritional deficiency Osteoporosis Depression

 

Current significant life stressors

 

Collaboration with consulting medical specialists who are trained in perioperative management is an important technique to optimize outcomes for patients with adult scoliosis.

 

Anesthesia colleagues familiar with this surgical course may also reduce risks.

 

Certain medical considerations directly affect the selection of surgical techniques for a patient with adult scoliosis.

 

Assessment of bone quality plays a critical role in the design of the operation.

 

 

Osteoporosis is the rule, not the exception.13 Although bisphosphonate medications may be helpful (and common) in treating osteoporosis, they inhibit osteoclastic bone resorption, which may have a negative impact on fusion biology.

 

 

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Approach

 

Posterior surgical approaches are typically used for the treatment of adult deformity correction.

 

 

Anterior surgery may be used alone in isolated cases but is more frequently combined with posterior surgery to augment the deformity correction, reconstruction, or both.

 

Anterior exposure allows the soft tissue releases and interbody reconstruction that are often required for adequate coronal and sagittal deformity correction. Interbody reconstruction can help with decompression of the neurologic elements, particularly by restoring the height of the neural foramen.

 

TECHNIQUES

• Fixation Strategies for Osteoporotic Bone

Pedicle screw fixation is less effective in osteoporotic bone.5 Trabecular bone is predominantly affected by osteoporosis.

Because pedicle screws have cortical contact limited to the pedicle isthmus, a “windshield wiper” mode of

failure may lead to screw loosening.

Fixation strategies for osteoporotic bone include the following4: Taking advantage of the relatively stronger cortical bone

 

 

Augmenting the fixation of a pedicle screw within the existing trabecular bone

 

Extending the fixation, that is, to the pelvis, in order to “protect” the fixation in the sacrum, to prevent sacral fracture.

 

Bone implant interface complications in the osteoporotic spine can be reduced by various methods.

 

Sublaminar wires, laminar hooks, and pediculolaminar fixation take advantage of the cortical bone composition of the posterior spinal lamina.

 

Fixation of pedicle screws within osteoporotic trabecular bone may be improved by polymethylmethacrylate (PMMA) cement augmentation.21

 

Fluoroscopy is used to visualize the placement of 2 to 3 mL of PMMA per pedicle to ensure that cement does not migrate to the neural elements.

 

 

 

TECH FIG 1 • These radiographs depict both the straight ahead trajectory (uppermost and lowermost vertebrae on these images) and the anatomic trajectory (central three vertebrae on these images) for thoracic pedicle screws. Alternating trajectories at adjacent segments may help improve fixation.

 

 

Calcium sulfate paste may also be used; this has the theoretical advantage of becoming replaced by bone over time.

 

Modified pedicle screws may also be used, including conical screws, hydroxyapatite-coated screws, and expandable screws.

Pedicle Screw Selection and Placement

 

 

Screw pullout strength is improved when high insertional torque is achieved with the following: Undertapping (or not tapping) the screw path

 

Tapered screws. These are limited by the absolute restriction that they cannot be reversed or backed out;

such an action would remove the screw's contact with the bone.

 

Larger diameter screws. Increased cortical contact may increase insertional torque but may increase the risk of pedicle fracture as well.

 

Longer screws: Bicortical purchase can increase screw pullout strength but may pose the possibility of injury to abdominal or vascular structures.

 

Loss of proximal fixation in the thoracic spine can be reduced by placing thoracic pedicle screws with alternating “anatomic” and “straight ahead” trajectories; this increases fixation by changing the mode of potential failure from straight “pull out” to a required “plow out” mode. This principle has been effective with long bone fracture treatment, using fixed-angle divergent or convergent fixation in metaphyseal bone (TECH FIG 1).

 

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• Fusion and Bone Grafting

 

Establishment of a solid fusion is critical.

 

The pseudarthrosis rate in one large series of adult deformity patients after long fusion procedures was 24%. Statistically significant risk factors for pseudarthrosis in that study included11

 

 

Thoracolumbar kyphosis Hip osteoarthritis

 

 

Use of a thoracoabdominal (vs. paramedian) approach Positive sagittal balance greater than 5 cm

 

 

Age older than 55 years Incomplete sacropelvic fixation

 

These risk factors emphasize the importance of surgically establishing the proper mechanical environment, including overall sagittal balance and appropriate fixation.

Bone Graft Selection

 

Appropriate graft selection may reduce pseudarthrosis risk.

 

Bone grafts and alternatives may serve multiple roles in the surgical treatment of adult scoliosis; fusion-promotion and deformity-correction techniques both may influence graft selection.

 

An anterior interbody graft may need to be structural to correct a deformity.

 

If a structural graft is used anteriorly first, it is with the anticipation that further deformity correction at that segment will be limited by posterior manipulation.

 

Anterior structural interbody grafts can be instrumental in preventing a kyphosis when the convexity of a deformity is compressed in a reduction maneuver.

 

Structural grafts can be placed with a bias toward the concavity in order to assist in the deformity correction.

 

Structural interbody grafts serve a critical role in supplementing the stability of a reconstruction, particularly at the caudal end of a construct, at the lumbosacral junction.

 

Morselized grafts may allow for deformity correction by subsequent posterior manipulation.

 

Our typical strategy is as follows:

 

Use structural grafts at the caudal end of the construct (two to four levels).

 

Overzealous posterior manipulation can cause loosening or displacement of an anterior structural graft.

 

Use morselized graft rostrally.

 

Subsequent deformity correction during the posterior procedure will be limited mainly to those levels with

morselized (or no) anterior graft.

Interbody Graft Materials

 

 

Graft selection is guided by the following: The goal of fusion success

 

The potential use of structural roles for the graft

 

 

The risk of potential complications and other shortcomings Costs

 

 

Interbody grafts may be composed of the following: Bone (autograft or allograft)

 

Metal

 

 

 

Carbon fiber Polyetheretherketone (PEEK) Other synthetic materials

 

To reduce the risk of graft subsidence, a graft with a modulus of elasticity similar to that of the native bone can be employed.

 

Iliac crest autograft may be the best modulus match but is associated with well-established harvest-related morbidity.

 

In osteoporosis, we have used allograft harvested from the iliac crest of a donor, which offers the following:

 

A relatively high proportion of trabecular to cortical bone compared to a long bone allograft and an appropriate modulus match

 

More rapid biologic incorporation of trabecular grafts

 

Carbon fiber and PEEK interbody cages offer a lower (and more closely matched) modulus compared to metal cages; we typically avoid metal cages in the reconstruction of osteoporotic spinal deformities.

 

 

Autograft remains the gold standard material for establishing a solid arthrodesis but has shortcomings: Morbidity of iliac crest autograft harvest

 

 

 

Chronic donor site pain Postoperative hematoma, infection Nerve or vessel injury

 

 

Iliac graft harvest may be undesirable when iliac instrumentation is planned. Autograft may be insufficient for an extensive thoracolumbar fusion.

 

Autograft alternatives include allograft products, synthetics, and bone morphogenetic proteins (BMP).

Bone Morphogenetic Protein

 

The fusion efficacy of BMP-2 has been demonstrated in patients with adult spinal deformity.

 

Seventy adult patients underwent scoliosis fusion with anterior or posterior BMP-2 application, with either local bone graft only (posterior) or no bone graft (anterior), obviating rib, iliac crest, or other autograft harvest morbidity.

 

Fusion rates were satisfactory, with 96% anterior fusion success and 93% posterior fusion success.14

 

The use of BMP-2 in spine surgery has been popularly criticized, however. Independent meta-analyses organized through the Yale Open Data Access (YODA) project have reported decreased efficacy and

increased risk, as compared to what was reported in prior industry supported trials.8,23

 

 

Attention to certain surgical techniques may reduce the risk of complications and may also improve efficacy. The risks associated with the use of BMP in the cervical spine include25

 

Complications related to soft tissue swelling

 

 

Inappropriate bone formation Accelerated graft resorption

 

In the lumbar spine, there also have been reports of undesirable effects, including

 

 

 

Inappropriate bone formation around neural elements15 Postoperative radiculitis

 

Retrograde ejaculation

 

Accelerated resorption of interbody grafts, increasing the risk of pseudarthrosis, has also been reported in a study of singlelevel uninstrumented anterior lumbar interbody fusion (ALIF).20

 

Structural allograft with appropriate doses of BMP at the lower two to four levels in adult thoracolumbar fusions can, however, be used with minimal risks of complications.

 

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Example: BMP-augmented transforaminal lumbar interbody fusion (TLIF) Care is taken to reduce the risk of inappropriate bone formation.

 

These steps may help ensure maintenance of the BMP and limit the BMP from affecting adjacent tissues:

 

 

 

Irrigate before the placement of the BMP packed cage, not afterward. Pack the BMP sponge entirely within the cage, avoiding “overstuffing.” Place additional sponge only anterior to the cage.

 

Use a repairable “trapdoor” annulotomy.

 

A three-sided annular flap is created, hinging medially, such that when the flap is held open with sutures at its corners, it augments the protection of the thecal sac.

 

After discectomy and placement of BMP, anterior graft, and TLIF cage, the annulotomy is repaired with suture and augmentation of the closure with an adjuvant sealant.

Sagittal Balance

 

One of the most important principles in the surgical treatment of adult scoliosis is achieving and maintaining a proper sagittal balance.

 

Balanced spinal posture with neutral positioning

 

 

Provides for decreased energy requirements with ambulation Limits pain and fatigue

 

Improves cosmesis and patient satisfaction

 

Limits complications associated with unresolved (or new) deformities

Fusion Level Selection

 

 

Sagittal balance must be achieved. Junctional problems must be avoided.

 

Presenting symptoms can guide level selection.

 

Discography can be useful to assess for painful segments, particularly in the lower lumbar spine, that may be incorporated in the fusion.

 

Facet blocks have been employed to determine levels that should be included or need not be included.

This may be particularly relevant at the lumbosacral junction.

Radiographs

 

36-inch standing PA and lateral

 

PA (left and right) bending views, to determine if the main curves are structural

 

If the Cobb angle is greater than 25 degrees on side-bending radiographs, then it is considered to be a structural curve.

 

Curve magnitude and flexibility and the apical vertebral translation of the thoracic and lumbar curves are measured.

 

 

The relationship between the C7 plumb line and the center sacral vertical line is considered. Radiographic signs of degenerative disease are categorized.

 

Listheses (rotary and lateral) are noted. Degenerative segments often are associated with stenosis; this must be considered in the treatment algorithm.

Fusion to the Sacrum and Pelvis

 

Extension of the fusion to the sacrum and pelvis for the adult scoliosis patient is an important and controversial subject. There is no consensus as to the best strategy for all clinical scenarios, but certain guidelines and lessons have been developed.

 

There is a relatively high rate of pseudarthrosis (and other complications) after L5-S1 fusion.7 For these reasons, in part, avoiding fusion to the sacrum whenever possible has been advocated.

 

 

Certain scenarios do require lumbosacral fusion: Symptomatic L5-S1 spondylolisthesis

 

Other instability

 

Oblique take-off with over 15 degrees of scoliosis at the L5-S1 segment often requires reduction and fusion for adequate correction of deformity.

 

For correction of lumbar hypolordosis to achieve proper sagittal balance

 

The risk of pseudarthrosis at the lumbosacral junction can be limited by the following:

 

 

Employing combined approaches to perform a meticulous 360-degree fusion at the L5-S1 segment BMP may be applied within an interbody device at L5-S1 to increase the chances of solid arthrodesis.

 

Extending the fusion construct to the ilium, using iliac screws, S2 alar screws, sacroiliac (SAI) screws, or other distal fixation methods

 

 

Anterior instrumentation has been advocated with Fixed-angle plates

 

Vertebral body compression screws

 

Isolated posterior instrumentation may be satisfactory if good bicortical purchase is achieved with sacral screws with high insertional torque.

 

Additional fixation is required, however, in many cases, and extension to the pelvis can satisfy this need.

• Degenerative Lumbar Scoliosis

   

  The patient with adult lumbar scoliosis typically has some component of back pain and may also present with radiculopathy or claudication.

   

   

  For the typical patient presenting with stenosis complaints, decompression of the neural elements is a priority. Deformity correction with proper sagittal balance also is a critical goal of surgery.

   

  Loss of lumbar lordosis is associated with increased pain.22

   

  Restoration of proper sagittal balance is the most important factor associated with clinical outcome.9

   

  The typical patient presents with hypolordosis and varying degrees of scoliosis, typically associated with relatively flexible

   

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  thoracic compensatory curves less than 30 degrees or no thoracic curve (TECH FIG 2A,B).

   

   

   

   

  TECH FIG 2 • A,B. Radiographs of a patient with degenerative lumbar scoliosis. Rotatory and lateral listheses are seen on the PA view (A) and the typical hypolordosis is seen on the lateral view (B) preoperatively. C,D. Lumbar radiographs of a typical patient with degenerative scoliosis limited to the lumbar region. The lateral listhesis is seen at L3-L4 (C) as well as the typical loss of lumbar lordosis (D). In another patient, obliquity at L4-L5 is seen in the preoperative PA radiograph (E), with focal loss of disc and neuroforaminal height seen on the preoperative lateral radiograph (F).

   

   

   

   

  Common radiographic findings include the following: Degenerative disease, most commonly at L5-S1 Rotary subluxation at L3-L4 (TECH FIG 2A,D)

   

  Obliquity at L4-L5 (TECH FIG 2A,F)

   

   

  The choice of surgical approach for the treatment of lumbar adult scoliosis depends on the following: The levels of the pain-generating segments

   

  The flexibility of the curve

   

   

   

  TECH FIG 3 • A,B. After decompression of the patient in TECH FIG 1A,B, spinal reconstruction is achieved with recreation of coronal ( A) and sagittal ( B) balance. C,D. In the patient in TECH FIG 1E,F, postoperative reconstruction after decompression of the neural elements recreates lumbar lordosis to achieve proper sagittal balance.

   

   

   

  The coronal obliquity of the distal vertebrae The extent of the curve

   

  Although in situ fusion may be an option for patients with small-magnitude deformity and poor bone quality, typically, restoration of lordosis and coronal realignment are desired (TECH FIG 3). This can be accomplished with a variety of methods, many of which require restoration of anterior interbody height.

   

  32

• Transforaminal Lumbar Interbody Fusion for Deformity Correction and Reconstruction

   

  TLIF may achieve these goals with a posterior-only approach.

   

  To assist in correction of the deformity, the cage may be biased to the concavity of the scoliosis to address the coronal plane.

   

  After facetectomy and posterior compression, lordosis can be restored.

   

  In general, a posterior interbody technique (posterior or thoracic lumbar interbody fusion) is less effective than an anterior interbody approach for restoring lordosis.

   

  The use of an operating table that produces extension of the lumbar spine (Jackson) to maximize positional lordosis is critical.

   

  The decision of the levels to include in the treatment of a degenerative lumbar deformity may be determined by a variety of influences.

   

   

  It can be useful to preoperatively determine which segments contribute to a patient's pain. The apex of the deformity is included (typically L3 or L4).

   

  Levels that are severely degenerated may also be included, particularly if they exhibit lateral or rotary listhesis.

   

• Transpsoas Lateral Lumbar Interbody Fusion for Deformity Correction and Interbody Fusion Lateral lumbar interbody fusion (LLIF) is an alternative to anterior and posterior interbody fusion, with excellent applications to deformity.16

 

The lateral approach provides excellent access for discectomy and interbody fusion (TECH FIG 4).

 

It also accommodates excellent deformity correction via

 

The placement of large interbody devices, which span the apophyseal ring and marginal vertebral cortex

 

Complete resection of the lateral annulus and lateral osteophytes, without disruption of the anterior and posterior longitudinal ligaments

 

In many cases, it can also provide indirect decompression of the neural elements by restoring segmental height and alignment.10,18

 

LLIF has been found to be generally safe and effective in comparison to ALIF and TLIF, but it has been frequently associated with adverse anterior thigh symptoms, particularly when operating at L4-L5.3,6

 

 

TECH FIG 4 • These standing radiographs depict the coronal and sagittal correction associated with interbody reconstruction from a lateral (L3/L4 and L4/L5) and posterior (L5/S1) approach. Note that little to no deformity correction was required from the posterior instrumentation. The coronal correction (A-C) and the sagittal correction (B-D) was achieved with interbody surgery alone. Panel A depicts that the preoperative apical vertebrae is L2, and the central sacral line bisects T11. By maximizing the interbody correction at the focal segments, however, this patient required a relatively short-segment fusion from L3 to S1.

 

 

 

Surgical techniques proposed to limit the risk of adverse anterior thigh symptoms include24 the following: Direct visualization of the transpsoas approach (via single incision)

 

Direct dissection through psoas (to limit crush or other trauma to muscle and nerve plexus)

 

Accessing the disc through a portal just anterior to midbody; this may limit the risk of encountering a nerve (typically found posterior) and may also limit the pressure on the nerve between the retractor and the transverse processes (TP).

 

Performing discectomy and fusion expeditiously; this may limit the nerve injuries related to prolonged compression between the retractor and the TP.

 

Avoiding or limiting opening the retractor to limit the degree of compression on the nerves that lie between the retractor and the TP.

 

Using intraoperative neuromonitoring (IONM) that includes motor evoked potentials (MEP), almost all nerve injuries have

 

33

gone undetected by the traditionally used mode of IONM (electromyography [EMG]) because the most typical mode of nerve injury (prolonged compression) does not generate a nerve depolarization. MEP however can be used to detect nerve dysfunction related to this slow and progressive mode of injury. We

have found this to be very useful in our practice.

 

Other LLIF surgical techniques that have been helpful when treating spinal deformity in our practice include the following:

 

Being aware of the effect of the deformity on the location of the retroperitoneal structures (vessels, psoas, lumbosacral plexus) in relation to the planned approach

 

Determine the side of the approach (left vs. right) by the coronal plane deformity; L4-L5 typically can only be approached from the convexity due to the relationship with the iliac crest. Other levels may be best approached from the concavity, however, so that multiple levels can be accessed through a single small lateral incision (TECH FIG 5).

 

Ensuring that the patient is positioned with the operative vertebrae orthogonal to the walls and floor of the room will ensure that a path straight down is also straight across the disc. This may reduce the risk of inadvertently traversing posteriorly (into spinal canal and contralateral foramen) or anteriorly (into vessels).

 

 

 

TECH FIG 5 • Approaching from the concavity of the lumbar curve (in this case, from patient's right side) may allow multiple levels to be approached from a small single-skin incision. Also L4/L5 can typically be approached only from the concavity of lumbar curves because the iliac crest typically would prevent the approach from the other side. In this case, L4/L5 is best approached from the patient's right side. In treating

single-level, coronal-deformed segments, however, it may be easier to enter the interbody space from the convexity because interbody access is less frequently prevented by osteophytes and because it may be easier to perform the discectomy from the “open” side of the disc.

 

 

Positioning the interbody device anteriorly to favor lordosis while positioning the device posteriorly bias to favor restoration of the foramen height and improve the degree of indirect neurologic decompression

Selection of Fusion Levels

 

There is no general consensus as to where a lumbar construct should terminate cranially, but it should be at least at a stable end vertebra (ie, the cranial-end level of the fusion construct should be bisected by the center sacral line on a lateral radiograph).

 

If the goal is to treat neurogenic claudication, relieve stenosis, and prevent future progression, a short-segment construct (often L2-L5) is sufficient if adequate lordosis is attained and the cranial and caudal vertebrae are well balanced.

 

In many scenarios, however, such as when the Cobb angle is from L1 to L5, it is necessary to continue the fusion cranially past the thoracolumbar junction.

 

When this is the case, one should take care not to end the fusion at the thoracolumbar junction or at the apex of the thoracic kyphosis.

 

Extending the fusion to the thoracolumbar junction provides fixation into the more stable rib-bearing vertebrae and is more likely to terminate within the sagittal plumb line, reducing the risk of instrumentation failure or junctional kyphosis.

 

 

A frequent decision-making dilemma is where to end the caudal end of the fusion reconstruction. Accepted indications to fuse to the sacrum include2 the following:

 

Spondylolisthesis or previous laminectomy at L5-S1 (TECH FIG 6A)

 

 

Stenosis requiring decompression at L5-S1 Severe degeneration

 

An oblique takeoff (above 15 degrees) of L5 (TECH FIG 6A)

 

 

Fusions to the sacrum in adults with lumbar scoliosis have been found to Require more additional surgery than those to L5

 

Have more postoperative complications

 

 

On the other hand, fusions to L5 have been associated with the following: A 61% rate of adjacent segment disease

 

An associated shift in sagittal balance

 

When fusion to the sacrum is performed, iliac fixation should be considered, particularly if the fusion includes more than three levels (TECH FIG 6C,D).

 

 

Augmentation of the lumbosacral reconstruction with interbody fusion at L5-S1 Improves biomechanical stability19

 

Reduces the risk of lumbosacral pseudarthrosis12

 

A structural graft at L5-S1 can

 

 

Recreate lordosis, partially restoring sagittal balance Diminish stenosis by restoring intervertebral height

 

Hip and knee flexion contractures can be common in this group, with patients accustomed to ambulating with flexed posture.

 

A flexion contracture at the hip limits the patient's ability to extend the sagittal plumb line posterior to the hips.

 

It may be necessary to address the patient's hip pathologies before planning any surgical correction of a spinal deformity.

 

 

34

 

 

 

TECH FIG 6 • These standing radiographs were performed on 36-inch cassettes before and after scoliosis fusion from T4 to the ileum. A,B. Iliac fixation was motivated, in part, by the obliquity at the lumbosacral junction. Concerns related to this patient's osteoporosis led the surgeons to use a combination of fixation techniques, including pedicle screw fixation and sublaminar wiring, to take advantage of the relatively well-preserved cortical bone. There is restoration of coronal (C) and sagittal (D) balance.

Thoracic and Lumbar (Double Curve) Scoliosis

 

 

Patients with double major adult scoliosis may present with axial skeletal pain. Complaints of progressive deformity may be manifested as follows:

 

 

 

Changes in balance Gait abnormalities Alterations in cosmesis

 

The surgical treatment of double-curve scoliosis often combines anterior and posterior procedures (TECH FIG 7).

 

Long deformities that are relatively inflexible may require anterior releases to accomplish effective reduction and fusion with posterior surgery.

 

 

 

TECH FIG 7 • A-D. This long thoracolumbar scoliosis was treated with a fusion from the upper thoracic spine to L5. To reduce the risk of pseudarthrosis at the caudal end of the construct and to assist in the recreation of lordosis, structural interbody grafts were placed in the three most caudal disc spaces of the fusion, with morselized graft above, after release of the anterior interbody soft tissues were performed. Subsequently, a posterior fusion was performed with pedicle screw instrumentation.

 

 

In part because of the typical degeneration in adult patients, fusions into the caudal lumbar spine are more frequently required.

 

Bending films determine whether the lumbar flexibility is adequate for the scoliosis to “bend out” (see FIGS 8 and 9).

 

Curve stiffness is related to both patient age and curve magnitude.

 

 

Flexibility decreases by 10% with every 10-degree increase in coronal deformity beyond 40 degrees. Flexibility decreases by 5% to 10% with each decade of life.

 

The correction of a double-curve deformity can be accomplished with a variety of methods. The primary goal of achieving a proper sagittal balance must be emphasized. Reduction of the coronal and rotational deformities follows in priority, with the goal of

 

35

establishing coronal balance and reduction of rib asymmetry for enhanced cosmesis and patient satisfaction, if possible.

 

Analogous to the design of the operation for adult lumbar deformities, the decision of whether to extend the fusion to the sacrum may be difficult.

 

 

Lumbosacral fusion is recommended when Decompression of L5-S1 stenosis is required

 

There is a fixed obliquity over 15 degrees at L5-S1 (see TECH FIG 6B)

 

Long fusions to the sacrum increase the risk of pseudarthrosis and reoperation. These may be minimized by anterior augmentation and iliac fixation, as previously discussed (see TECH FIG 7).

 

The cranial end of the fusion should include the thoracic curve and should not stop caudal to any structural aspect of it.

 

 

 

TECH FIG 8 • A,B. Monoaxial or uniaxial screws are placed into the pedicles of the vertebrae that will be manipulated. C,D. After one prebent rod (usually the left rod by convention) is placed and rotated in the usual manner to reduce the coronal deformity and attain a proper sagittal relationship, it is locked to screws at the thoracolumbar junction and at the cranial and caudal limits of the construct. Reduction tubes are then placed onto the fixed screws at the thoracolumbar junction, which we refer to as the mainland for purposes of the reduction. E. An array of tubes is placed onto the screws of the thoracic cascade, where the greatest rotational deformity typically exists. F. These secondary tubes are then aligned toward the mainland vertebrae, effecting the rotational reduction, and locked to the rods. G. Rotational reduction is then applied one vertebra at a time in the lumbar region, caudal to the mainland, because the lumbar lordosis often limits the application of more than one set of reduction tubes concurrently. H. The prebent contralateral rod is then placed and locked to screws at the thoracolumbar junction as well.

 

 

All fixed deformities and subluxations should be included in the fusion.

 

Rod cross-links increase the stiffness of long constructs and are recommended (see TECH FIG 7C). They should be avoided at the thoracolumbar junction, however, where they may increase the risk of

 

pseudarthrosis.11 Vertebral derotation

 

Curve stiffness may limit the surgeon's ability to reduce the rotational deformity in the adult population.

For relatively flexible rotational deformities, rotational reduction can be achieved with effective improvement in trunk symmetry, which can significantly improve patient satisfaction (TECH FIG 8).

Additional release maneuvers may be necessary in stiff curves, including thoracoplasty, concave rib osteotomies, and aggressive facetectomies.

 

 

 

36

 

PEARLS AND PITFALLS

 

Reduction of complications associated with BMP

• The surgeon should minimize the dose of BMP specific to each application.

• The surgeon should minimize diffusion of the protein from the site of desired action.

   

  • Meticulous hemostasis should be achieved before BMP implantation; a postoperative hematoma may provide an avenue for the spread of the protein.

  • Wound irrigation should be performed before BMP implantation, not afterward.

  • The BMP should be contained within a rigid structure to limit compression of the implant to prevent pressure-induced diffusion.

  • A barrier should be created between the protein implant and sensitive tissues. Thrombin glue has been used to seal the epidural space from the BMP.

  • Hemostatic sponges and suction drains may permit protein to migrate to adjacent tissues and should not be placed adjacent to the protein implant.

 

Prevention of adjacentsegment disease

• The preoperative status (or health) of the segment or disc is the greatest predictor for the development of adjacent segment disease.

• For the population with adult scoliosis, where some identifiable degenerative disease is nearly ubiquitous, this is particularly relevant.

   

  • The surgeon should not end a fusion adjacent to a severely degenerated disc.

  • The surgeon should not end a fusion adjacent to a segment with fixed obliquity or subluxation.

  • The surgeon should preserve the supra-adjacent facet.

  • The surgeon should preserve the intraspinous and the supraspinous ligaments.

  • The surgeon should not violate the cranial disc space or facet joint with pedicle screws.

 

POSTOPERATIVE CARE

 

 

If a brace is used, it must be custom-molded postoperatively after surgical deformity correction is accomplished. Application of a preoperatively molded brace is counterproductive and should be avoided.

 

Postoperative physical therapy regimen should focus on the following:

 

Range-of-motion and flexibility improvement, often in response to chronic hip and knee loss of motion or contractures

 

 

Gait training, to include balance rehabilitation General conditioning

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