Spinal Fusion for Neuromuscular Scoliosis

 

 

 

DEFINITION

Neuromuscular diseases are heterogeneous between and within diseases and are due to a vast number of pathologies involving the brain, spinal cord, peripheral nervous system, and muscle.

Neuromuscular spinal deformity is a result of neuromuscular disease which occurs during childhood, including cerebral palsy, muscular dystrophy, spinal muscular atrophy, etc. It may be related to a pathologic abnormality in muscle tone, motor control, weakness, or a combination.

Although neuromuscular scoliosis (coronal deformity) is the most common neuromuscular spinal deformity, sagittal plane deformity (hyperlordosis and hyperkyphosis) may also occur.

 

 

ANATOMY

 

The curve patterns of neuromuscular scoliosis are most commonly lumbar and thoracolumbar with associated pelvic obliquity (FIG 1).

 

Because many children are nonambulatory, associated pelvic obliquity affects sitting balance.

 

Ambulatory neuromuscular patients often have decompensation, with the inability to center their head over the center sacral line.

 

PATHOGENESIS AND NATURAL HISTORY

 

The biologic basis of both scoliosis and sagittal plane spinal deformity in neuromuscular disorders differs depending on the specific neuromuscular disease. In general, however, most neuromuscular spinal deformities are largely due to muscle imbalance (high tone or low tone) and abnormal postural reflexes.

 

 

 

FIG 1 • Typical neuromuscular curve pattern in a child with quadriplegic-pattern cerebral palsy. A. Child with poor sitting balance. B. Radiograph showing long thoracolumbar curve with pelvic obliquity.

 

 

The natural history of neuromuscular scoliosis is typically that of progression, beginning with the development of a flexible scoliosis, often in middle childhood, and the more rapid progression to a more rigid scoliosis during the adolescent growth spurt. Some neuromuscular conditions are associated with a more progressive scoliosis than others.

 

The pathogenesis and natural history of some of the more common neuromuscular disorders associated with spinal deformity and the spinal deformity itself within the disease follow.

 

Cerebral Palsy

 

Cerebral palsy is a heterogeneous disorder that is characterized by a static lesion (eg, injury, congenital defect) to the immature motor cortex of the brain.

 

The natural history of neuromuscular scoliosis in cerebral palsy is relentless progression. Progression is most common in spastic quadriplegic cerebral palsy. The rate of progression can be severe in adolescent years (2 to 4 degrees per month).

 

Progression also occurs after skeletal maturity. In curves greater than 40 degrees, it may occur at a rate of 2 to 4 degrees per year.25

 

Curves in the 60- to 90-degree range begin to effect sitting balance, arm control, and head control. Further progression may prevent the child from sitting in an upright position.

 

Conservative treatment with chair modifications and bracing is only a temporary treatment and does not stop curve progression. Conservative treatment is especially helpful in the younger child with a flexible scoliosis to temporarily maintain upright sitting posture. This will allow the spine to grow to its maximum size (to achieve maximum sitting height) so that the resulting fusion can correct the spinal deformity without limiting growth.

 

Muscular Dystrophy

 

Duchenne muscular dystrophy is a sex-linked recessive disorder involving a defect on the Xp21.2 locus of the X chromosome resulting in a marked decrease or absence of the protein dystrophin.11

 

 

Affected children become progressively weaker with age, eventually becoming nonambulatory. Death typically occurs in the second or third decade secondary to pulmonary or cardiac failure.

 

Scoliosis is almost universal when the child becomes nonambulatory, and curve progression correlates strongly with a decline in respiratory function.

 

In the past, the prevalence of scoliosis approached 100%.22 For this reason, surgery was previously recommended soon after the child became nonambulatory before an irreversible

 

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decline in forced vital capacity occurred. Now with the advent of corticosteroids, the life expectancy of children with Duchenne muscular dystrophy is extended with a reported delay or prevention of the severity of scoliosis with long-standing use of corticosteroids.1, 13, 15 The risk of progression decreases if the scoliosis develops

after 14 years of age.31 Pulmonary function decreases as the natural history of the disease and scoliosis magnitude progresses. Scoliosis surgery should be done before the forced vital capacity decreases to less than 30%.

 

Myelomeningocele

 

Myelomeningocele, a congenital malformation of the nervous system, is due to a neural tube defect and results in a spectrum of sensory and motor deficits.

 

Although the level of the spinal cord defect influences the clinical presentation of the condition, neurologic deterioration may occur at any age owing to hydrocephaly, hydrosyringomyelia, Arnold-Chiari deformity, and tethered cord syndrome.

 

In general, the higher the level of the defect, the higher the prevalence of scoliosis. Almost 100% of thoracic level paraplegic patients develop scoliosis.26

 

A long C-shaped curve is associated with a high level of paralysis and usually occurs at a young age.

 

Hydromyelia and tethered cord syndrome may also be associated with scoliosis and should be suspected if the scoliosis onset is more sudden and associated with other symptoms of acute neurologic deterioration.

 

Bracing in younger children can be attempted to slow progression, but it does not stop eventual progression.

 

Spinal Muscular Atrophy

 

Spinal muscular atrophy is an autosomal recessive disorder resulting in spinal cord anterior horn cell degeneration. Two genes on the chromosome 5q locus have been found to be associated with this disorder:

survival motor neuron (SMN) gene and neuronal apoptosis inhibitory (NAIP) gene.24

 

 

Clinically, progressive muscular weakness occurs and eventual pulmonary compromise is common. Three forms of the disease exist:

 

Type 1: early, acute Werdnig-Hoffman

 

 

Type 2: intermediate, chronic Werdnig-Hoffman Type 3: late, Kugelberg-Welander type

 

Most children with the early form of the disease die at an early age and therefore do not require treatment.

 

Most children with the intermediate and late type who survive into adolescence develop a progressive spinal deformity. The curvature typically develops in the first decade. Thoracolumbar and thoracic patterns are most common.

 

One-third of patients have an associated kyphosis in the sagittal plane. Bracing is ineffective at preventing curve progression but may delay progression in the very young patient to allow further growth of the spine.2

Freidreich Ataxia

 

This autosomal recessive disorder results in a slowly progressive spinocerebellar degeneration. A defect on chromosome 9 has been identified.

 

The incidence of scoliosis is 100%, and progression is related to the age of disease onset. When disease onset is prior to age 10 years and scoliosis onset is before 15 years, scoliosis progression is usually greater than 60 degrees.

 

Progressive scoliosis requiring surgery occurs in about 50% of patients.14

 

 

Curve patterns are similar to idiopathic scoliosis: double major, single thoracic, and thoracolumbar.

 

Orthotic treatment may slow but usually does not prevent progression.

 

Rett Syndrome

 

This is an X-linked disorder that affects females almost exclusively. Some children have a mutation on the

MECP2 gene.21 The child's development is normal until 6 to 18 months of age, followed by rapid deterioration in cognitive and motor function.

 

After the initial deterioration in function, the neurologic picture may become relatively static for years. The clinical spectrum is variable, with some children remaining ambulatory and others becoming wheelchair bound.

 

 

Rett syndrome may be mistaken for cerebral palsy. Scoliosis has been reported in up to 80% of patients.12

 

A long C-shaped thoracolumbar pattern is common. Bracing is usually ineffective, and curve progression is

common. Surgical stabilization allows maintenance of sitting balance.

 

Spinal Cord Injury

 

 

Spinal cord injury in the skeletally immature child is associated with a nearly 100% incidence of scoliosis.7 The predominant curve type is a long C-shaped curvature. The younger the child, the higher the progression.

 

Prophylactic bracing may be effective in smaller curves (under 20 degrees). There are no data to support that bracing is effective in preventing progress in established curves greater than 20 degrees.

 

PATIENT HISTORY AND PHYSICAL FINDINGS

 

An accurate medical history is crucial for patients with neuromuscular disease.

 

 

In patients with cerebral palsy, the medical comorbidities strongly correlate with postoperative

complications.17 This appears to also be true in patients with Duchenne muscular dystrophy, spinal muscular atrophy, and other neuromuscular disease.

 

Important historical information includes respiratory status, cardiac status, gastrointestinal status (eg, gastroesophageal reflux, nutritional intake), bone health (low bone density and history of fracture), and the

presence of seizure disorder.

 

Physical examination should assess sitting or standing balance, the pelvic obliquity, curve magnitude, and stiffness (including the curve's coronal, sagittal, and rotational components).

 

 

Coronal stiffness is best assessed by performing the side-bending test (FIG 2).

 

The physician should also assess for the possible coexistence of hip subluxation or dislocation, common in many neuromuscular diseases.

 

A complete neurologic examination should also be performed.

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

Anteroposterior (AP) and lateral radiographic views should be obtained to assess the Cobb angle and pelvic obliquity in the coronal plane and lumbar lordosis and thoracic kyphosis in the sagittal plane.

 

 

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FIG 2 • Side-bending test. Patient is being bent over the examiner's thigh at the apex of the curve. If the patient's curve reverses and the pelvis levels to perpendicular to the trunk, the curve is still flexible enough to correct through posterior fusion and instrumentation alone. If not, an anterior release is performed.

 

 

If intraspinal pathology is suspected, especially in the ambulatory patient, a preoperative magnetic resonance imaging (MRI) scan should be obtained.

 

If severe low bone density is suspected (history of multiple fractures), dual energy x-ray absorptiometry (DEXA) scan is recommended to assess bone density and potential need to treat.

 

DIFFERENTIAL DIAGNOSIS

Some neurologic diseases can look similar.

It is important to diagnose progressive neurodegenerative in which mortality from the disease is more rapid than the progression of the spinal deformity.

 

NONOPERATIVE MANAGEMENT

 

Although there was initially some historical enthusiasm for the treatment of neuromuscular scoliosis with casting or bracing, orthotic management is rarely able to halt progression of neuromuscular scoliosis.

 

Flexible curves in younger children may require seating modifications (hip guides and offset lateral seatback supports) or a sort thoracolumbar orthosis to maintain balanced seating until the child is at optimal sitting height.

 

 

SURGICAL MANAGEMENT

Indications

The indications for spinal fusion in neuromuscular scoliosis depend largely on the natural history of the specific neuromuscular disease and the natural history of the scoliosis within the specific disorder.

Examples of two neuromuscular diseases with different indications are Duchenne muscular dystrophy and cerebral palsy.

Duchenne Muscular Dystrophy

The major comorbidity in Duchenne muscular dystrophy is restrictive lung disease, with forced vital capacity dropping dramatically with scoliosis progression.

Due to the natural history, the indication for fusion is a scoliosis curvature greater than 25 degrees and forced vital capacity above 35%.

Cerebral Palsy

The indications for spinal fusion in children with cerebral palsy are a scoliosis curve magnitude approaching 60 degrees in the older child, especially if the curve is becoming stiff by physical examination.

Surgical correction is indicated when the child is not tolerating seating with a combination of either seating adjustments or a soft orthosis. This is usually done before the curvature reaches 70 degrees when the risk of complications increases.17

Less commonly, sagittal plane spinal deformity, hyperlordosis, and kyphosis will cause seating problems or back pain. Cerebral palsy patients with sagittal plane spinal deformity of 70 degrees or more causing

seating difficulties or back pain can benefit from surgical correction.16

Typically during the middle part of adolescent growth, the scoliosis becomes much larger and begins to stiffen. Surgical instrumentation and fusion are recommended at this time.

 

Preoperative Planning

Technical Considerations

 

Three main technical preoperative considerations require careful consideration:

 

 

Is fusion to the pelvis necessary?

 

 

Is there a significant rotational component to the scoliosis that is contributing to difficulty in seating? Is anterior release (discectomies around the stiff portion of the curve) necessary?

 

The only treatment that has made a definitive impact on neuromuscular spinal deformity is instrumentation and fusion.

 

The standard surgical procedure for neuromuscular scoliosis is a posterior spinal fusion with segmental instrumentation from T1 to T2 down to the pelvis if there is a significant pelvic obliquity.

 

Even if the pelvis is not involved in a severely involved nonambulatory patient or an ambulatory patient with a poor “righting reflex,” the surgeon should consider fusion to the pelvis to prevent the development of late pelvic obliquity. However, with modern pedicle screw instrumentation, complete correction of the lumbar spine to L5 may prevent subsequent development of pelvic obliquity or so that in the era sublaminar wire fixation.

 

The unit rod incorporates these concepts into one instrumentation system (FIG 3) as well as the concept of cantilever correction.3, 9, 18, 20

 

Newer methods of instrumentation allow modularization of the unit rod concept and cantilever correction by combining pelvic screws, precontoured rods, and a proximal connector (FIG 4).

 

Both the unit rod and the precontoured rods (in the modular unit rod construct) have prebent sagittal contour.

 

 

The unit rod comes in lengths from 250 to 450 mm.

 

Both 3/16- and 1/4-inch diameter rods are available. The 1/4-inch rod is used whenever possible, reserving the 3/16-inch rod for patients with a very thin gracile pelvis.

 

With the modular system, precontoured rods are connected with a proximal connector, in addition to pelvic screw with diameter (7 to 10 mm) and length (65 to 100 mm) that can be selected according to pelvic size.

 

Some surgeons are using pedicle screws instead of wires for segmental fixation, especially if there is a severe rotational

 

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component to the curvature or pelvis. Caution should be taken when the bone is severely osteopenic, as the pedicle screws may pull out of the bone. Screws can be supplemented by wires or sublaminar cables as necessary.

 

 

 

FIG 3 • A. The unit rod is available commercially in a range of sizes. B. Drill guides are provided for placement of the pelvic limbs as well as the impactor and pusher for the rod.

 

 

The unit rod (FIG 5A-C) and the modular unit rod (see FIG 4) are especially powerful as cantilevers to correct pelvic obliquity.

 

Anterior release for scoliosis is required for larger stiff curves that do not bend out on the bending test (generally

>90 degrees) (FIG 5D).

 

 

Anterior release is also recommended for severe hyperlordotic and hyperkyphotic spinal deformities.16

 

Other Preoperative Considerations

 

The general medical condition of the child should always be considered first. Many children with neuromuscular conditions will have comorbidities such as pulmonary disease, cardiac disease, seizure disorder, poor nutrition, and so forth.

 

 

 

FIG 4 • A. Lateral profile of the prebent rods with built-in thoracic kyphosis and lumbar lordosis. B. AP profile of the prebent rods connected via the lateral connectors to the iliac screws. (B: Courtesy of DePuy Synthes Spine.)

 

 

All patients with complex preoperative medical conditions should have the appropriate preoperative workup.

 

The surgeon and anesthesiologist should plan for the possibility of large intraoperative blood loss.

 

 

Type and cross-matched blood (up to twice the patient's blood volume), fresh frozen plasma, and platelets should be available. In addition, consider the use of cell-saver blood.

 

 

The use of antifibrinolytic such as tranexamic acid or Amicar can successfully decrease overall blood loss.8 Good vascular access is required, often through central venous access.

 

Another consideration is the use of spinal cord monitoring. Most children with neuropathies, myopathies, and mild to moderate cerebral palsy (without severe motor cortex involvement) can be monitored using a

combination of somatosensory and motor evoked potentials.10 On the other hand, only about 40% of children with severe quadriplegic cerebral palsy and poor motor function can be monitored. In addition, it is difficult to justify removing implant hardware if there are signal changes in the child with minimal motor function because the risk of repeat operation to reimplant hardware is quite high in this population.

 

 

As a general rule, any child with ambulatory or functional standing (able to assist with standing transfers) should have somatosensory and motor evoked potential monitoring attempted. There may also be some efficacy in monitoring neuromuscular patients with intact sensation and bowel and bladder control.

 

Any child with neurogenic bladder should be carefully evaluated for urinary tract infection preoperatively, and if present, should be treated to clear the urine prior to surgery.

 

A final preoperative consideration is the bone density of the child undergoing spinal fusion. The child who is nonambulatory, poorly nourished, and on seizure medication is at highest risk. Children with low bone density may be difficult to instrument owing to the possibility of sublaminar wires pulling through or pedicle screws pulling out of osteopenic bone.

 

 

Any nonambulatory child with low-impact long bone fracture should be checked for low bone density using DEXA scan.

 

Children on seizure medication should have calcium, phosphorous, and vitamin D levels measured.

 

Patients with bone density two or more Z scores below the mean should be considered for treatment using intravenous pamidronate.

 

Positioning

 

The patient is positioned prone on a Jackson table (a Relton Hall frame can also be used) with the abdominal area free (FIG 6).

 

We have adapted special radiolucent posts for the table that can be spaced at a narrower distance compared to the standard posts.

 

Some surgeons prefer intraoperative traction, using a combination of skin traction, halo traction, or halo femoral traction depending on surgeon preference and experience. Establishing good deformity correction with preoperative traction can dramatically improve results especially when bone density is very low and indirect correction is safer.

 

 

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FIG 5 • A-C. Cantilever effect of the rod correcting pelvic obliquity and scoliosis. The rod is gradually pushed to each vertebra, and each wire is tightened, progressively correcting the deformity using transverse forces. D.

Anterior release. Wedge resections of the discs are performed around the apical vertebra if the spinal deformity is stiff.

 

 

The hips and knees are bent to minimize lumbar lordosis and to optimize insertion of the limbs of the rod into the pelvis when using the unit rod. All bony prominences should be well padded.

 

Many children with cerebral palsy have significant contractures, making their extremities hard to position. They should be positioned with minimal tension on the joints.

 

Urinary catheters should be free flowing, especially children with neurogenic bladder with a vesicostomy or other bladder reconstruction.

 

 

 

FIG 6 • A,B. Positioning the patient should leave the abdomen free and minimize lumbar lordosis by allowing the knees to hang low to optimize pelvic limb placement. If necessary, an unscrubbed assistant can push up on the abdomen (arrow in A) to aid in the pelvic limb insertion with severe lordosis.

 

Approach

 

A posterior approach to the spine is performed from T1 to T2 to the sacrum.

 

A complete subperiosteal exposure of each vertebra is performed followed by exposure of the outer wing of the iliac crest down to the sciatic notch and the bottom tips of the posterior superior iliac spine (PSIS).

 

Alternatively, if using iliac screws, exposure of S2 to prepare for an S2 iliac approach can also be performed.6,

23

 

 

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TECHNIQUES

• Pelvic Preparation

Posterior Superior Iliac Spine Placement

A drill hole is made between the outer and inner cortex of the ilium with a drill bit. Before drilling, the drill bit is marked 10 mm past the drill guide's hook for the sciatic notch in children who weigh less than 45 kg and 15 mm past the hook in children heavier than 45 kg.

The right and left drill guide is next inserted into the right and left sciatic notch, respectively.

The lateral handle of the drill guide is placed parallel to the pelvis (iliac crests), whereas the axial handle is held parallel to the sacrum.

The pelvis is drilled from the inferior tip of the posterior iliac spine in a line just superior and anterior to the sciatic notch, where the bone is densest.19

To confirm proper placement, a fluoroscopic view is taken with drill bit or pedicle probe in place parallel with its trajectory (TECH FIG 1).

 

 

 

 

TECH FIG 1 • PSIS placement. A. Optimal drill hole placement anterior and superior in the sciatic arch.

B. With severe lordosis, the drill hole starting point is more anterior and aims more posterior. C-F. Intraoperative AP and oblique views showing proper placement of pelvic screw. C,D. The AP views show the trajectory of the pedicle probe from the PSIS to just superior and adjacent to the sciatic notch and the final screw position at least 1 cm lateral to the notch. E,F. The oblique views are taken parallel with the probe and show the probe and the final screw position between the inner and outer cortex just superior to the sciatic notch, which appears as a teardrop. (C-F: Courtesy of DePuy Synthes Spine.)

 

 

The hole is probed to ensure that the pelvic cortex or sciatic notch is not penetrated.

 

The drill hole is countersunk if a pelvic screw will be used so as to prevent prominence of the screw.

 

Pelvic screw fixation of largest diameter possible (usually a 7- to 10-mm diameter) is placed in this trajectory and should be of sufficient length to pass the sciatic notch by at least 1 cm.

 

We prefer to use a closed polyaxial screw head to maximize the rigidity of the final rod-pelvic screw construct.

 

Typically, we use pelvic screws alone, but when additional fixation is needed to improve the rigidity of pelvic fixation, we add S1 screws. We prefer this over sacral screw fixation alone because pelvic screw

 

fixation provides a better lever arm to correct both pelvic obliquity and sagittal plane pelvic deformity. The drill hole can be temporarily packed with Gelfoam to control bleeding if the unit rod is to be placed.

 

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S2 Alar Iliac Placement

 

 

Alternatively, pelvic screws can be placed using the medial portal as described by Chang et al6 and

Sponseller et al.23 The start point approximately 1.5 cm deeper than the traditional entry from the PSIS placement.

 

Advocates for this method state that there is less exposure time, less bleeding, and that the screw head is less prominent. Also, because the start point is in line with L5 and S1 pedicle screws, offset rod connection can be avoided if pedicle screw instead of wire fixation is being used.

 

The starting point for the screw is 2 to 4 mm lateral and 4 to 8 mm inferior to the S1 foramen (TECH FIG 2A-E); minimal muscle stripping and dissection is needed.

 

A sharp awl or burr is used to mark the starting point and penetrate the cortical bone.

 

 

 

TECH FIG 2 • S2 alar iliac (S2AI) placement. A. The starting point of the sacroiliac (SAI) screw is a point

between the S1 and S2 foramen, along the lateral border, in line with an S1 pedicle screw. B. From the starting point, one should aim for the anterior inferior iliac spine (AIIS), palpating the tip of the ipsilateral greater trochanter. C-E. Axial cross-section, posterior, and lateral iliac views, respectively, of the screw pathway in the ilium. (Radiographic confirmation of this placement is similar to TECH FIG 1C-F). The S2AI pathway allows the iliac screw to line up with the lumbar and sacral pedicle screws (F), so no offset connection is needed when securing the longitudinal rods as is needed using the PSIS placement (G). (Courtesy of DePuy Synthes Spine.)

 

 

Then, a drill or pedicle gearshift is used to enter the cancellous bone of the sacrum directed toward the dorsal aspect of the sacroiliac joint into the ilium.

 

The trajectory is lateral (approximately 40 degrees to the horizontal plane) and 20 to 30 degrees caudal (this depends on pelvic tilt), and fluoroscopy is helpful to guide this trajectory as described in the PSIS approach earlier.

 

Once in the ilium, the pathway is 1 to 2 cm above the sciatic notch directed toward the anterior inferior iliac spine (TECH FIG 2F,G).

 

 

 

The hole is probed with a pedicle probe to ensure that the pelvic cortex or sciatic notch is not penetrated. A pelvic screw (65 to 100 mm long; 7 to 10 mm diameter) is placed at this time.

 

• Luque Wire Passage

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  After the spine is completely exposed and the pelvis is prepared, the spinous processes are completely removed and the ligamentum flavum is carefully removed to expose the sublaminar spaces.

   

  Double Luque wires are bent (prebent wires are also available) and passed under the lamina from the lamina of L5 up to and including the T1 or T2 lamina.

   

  The radius of curvature for the wire bend must approximate the width of the laminae to allow safe passage of the wire.

   

   

   

  TECH FIG 3 • When passing wires, it is important to roll the wires under the lamina (A-D), being careful not to catch the tip under the lamina (E), which will lever the wire into the canal and place pressure on the spinal cord. F. Wires are bent down to the midline in the middle and the ends are bent down flat against the paraspinous muscles.

   

   

  Two double wires are passed at the L5 and the proximal most vertebra (T1 or T2) only, whereas a single wire is passed at each of the other levels (TECH FIG 3A-E).

   

  Wires are pulled to equal length and next bent, with the midline bent flat down onto the spinous process beds and the beaded end flat down onto the paraspinous muscles (TECH FIG 3F).

   

  This helps the wires from getting inadvertently pushed into the spinal canal and allows for easier wire organization.

   

   

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• Rod Selection and Insertion

Unit Rod

 

After the wires are passed, the length of the unit rod is selected.

 

This is done by placing the rod upside down with the corner of the rod placed at the drill hole on the elevated side of the pelvis (TECH FIG 4A).

 

The proper length rod should reach either T1 or T2 (the selected proximal end point) (TECH FIG 4B).

 

A rod one length shorter should be chosen if there is severe kyphosis because the spine shortens with correction.

 

With severe lordosis, a rod length longer should be chosen because the spine lengthens with correction.

 

It is best to err on the side of the rod being too short because the wires can be brought down to the rod two or three levels if necessary.

 

 

If the rod is more than 2 cm long, it may become too prominent under the skin. In such cases, cutting the rod and cross-linking the rod may be advisable.

 

Facetectomy and decortication of the transverse processes are performed. Corticocancellous allograft (crushed) bone is added (180 to 240 mL).

 

Insertion of the rod involves crossing the pelvic limbs of the rod to insert them into the previously drilled pelvic holes (TECH FIG 4C).

 

In patients with pelvic obliquity, the pelvic limb of the rod is placed into the drill hole on the low side of the pelvic obliquity first, with this side crossed underneath the other limb.

 

With the rod impactor, the surgeon inserts three quarters to half of this pelvic limb first and then insert the opposite pelvic limb, using a rod holder to direct it into the correct direction of the previously drilled hole.

 

The rod impactor is next used to drive the rod limbs into the pelvis, alternatively impacting each pelvic leg and making certain to direct each of the legs into the previously drilled holes.

The Modular Unit Rod Construct

 

After the right and left pelvic screws are placed, the fixed lateral rod connector is connected to each pelvic screw, the wires are

 

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passed, the precontoured rods are connected to the fixed lateral connectors, and the proximal closed connector is placed at the proximal end of the rods (TECH FIG 5A).

 

 

 

TECH FIG 4 • A. Measuring for the proper rod length is one of the most difficult aspects of the surgery and is done by turning the rod upside down and placing the top of the rod at T1 and the bottom corner of the rod at the drill hole in the pelvis. B. The spine shortens (top) as kyphosis is corrected and lengthens (bottom) as excessive lordosis is corrected to normal (center). (continued)

 

 

TECH FIG 4 • (continued) C. The pelvic limbs of the unit rod are crossed to insert them into the drill holes into the pelvis. They are gradually impacted 1 cm at a time, alternating between the right and left limbs, until each is completely within the pelvis.

 

 

Critical to the correction is to attach and secure each of the precontoured rods to the iliac screws with the fixed lateral connectors so that each of the rods is perfectly perpendicular to the horizontal axis of the pelvis and that the sagittal contour of the rods is aligned with the sacrum.

 

 

 

TECH FIG 5 • A. AP profile of the modular unit rod construct with precontoured rods connected to the pelvic screws in the PSIS position (S2AI pathway can also be used after the wires have been passed). The connection should make the rods perpendicular to the horizontal axis of the pelvis to maximize cantilever correction. A distal cross-connector and proximal closed connector make the construct rigid. The rods should match in both length and contour with rotation matched before final tightening of the connectors. B. Lateral contour of the prebent rods in line with the sagittal profile of the sacrum. C. There is a line on the posterior contour of the rod to help line it up with the sacrum. (Courtesy of DePuy Synthes Spine.)

 

 

The sagittal bend (TECH FIG 5B,C) should be identical on each rod and should also be aligned so that the contour matches from proximal to distal. If these steps are not meticulously done, the pelvic obliquity will not be fully corrected with the cantilever maneuver. Once this is done, the set screws at each connection (the pelvic screws, lateral connectors, and proximal connector) are tightened and torqued down onto the rod.

 

If the top of the rod is too long, it can be cut in situ and the proximal connector adjusted. A drop entry cross-connector can be added at the thoracolumbar junction to augment the stability of the construct. This foundation from the pelvic screws up to the proximal connector serves as modular constructed unit rod which is now ready to serve as a cantilever to correct the spinal deformity.

Cantilever Correction

 

The surgeon should not try to see if the rod fits by pushing it down into the wound completely in one move, as this may cause the pelvic limbs of the rod or the pelvic screws to pullout of the pelvis or fracture the ilium.

 

The surgeon should push the rod to line up with the lamina only (TECH FIG 6A,B) and then twist the wires being careful not to overtighten (we suggest a jet wire twister). It is important that the remaining spinous process lies in the midline. The wires are cut 10 to 15 mm long.

 

The rod is pushed to L4 and the wires are twisted and cut.

 

Then, the rod is pushed to L3 and the wires are twisted and cut.

 

This process continues one level at a time until the surgeon reaches T1 or T2 (TECH FIG 6C,D).

 

 

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TECH FIG 6 • A. Once the foundation is instrumented, the rod construct is manually pushed down at each level with a rod pusher (similar to the unit rod) at each level before tightening wires (if sublaminar wires are to be used). B. The rod is manually pushed down at each level with a rod pusher before tightening the wires. This is important to prevent wire breakage or cutout through the lamina. It is important to keep the center of the unit rod at the spinous process. C,D. Preoperative and postoperative AP radiographs. (A,C,D: Courtesy of DePuy Synthes Spine.)

• Thoracic Scoliosis and Kyphosis

   

  Spinal curvatures in the thoracic region are more difficult to correct with cantilever correction.

   

  In such cases, starting distally at the pelvis or in the lumbar spine leaves a short lever arm at the proximal end of the rod by the time one reaches fixation in the thoracic spine, making it difficult to center the head over the remainder of the thorax and pelvis.

   

  This type of curvature is difficult to correct with the traditional unit rod because the unit rod requires distal fixation into the pelvis first (TECH FIG 7A).

   

  With this type of curvature, a reverse cantilever (proximal to distal) can be performed (TECH FIG 7B-D).

   

  After exposing the spine and pelvis, pelvic screws and sublaminar wires are placed as previously described.

   

   

   

  TECH FIG 7 • A. It is difficult to cantilever this type of thoracic curvature using the unit rod due to insufficient lever arm. B. This diagram shows proximal to distal cantilever technique that can be used for thoracic scoliosis. (continued)

   

   

  P.783

   

   

   

  TECH FIG 7 • (continued) C,D. Preoperative and postoperative AP radiographs. (Courtesy of DePuy Synthes Spine.)

   

   

  The rod construct is then preassembled by first connecting the pre-contoured rods with the proximal closed rod connector at the top and placing a cross-connector in the lumbar region. The rods should be parallel from proximal to distal with respect to their contour.

   

  Next, the top of the rod construct is secured using sublaminar wires from T1 down to the apex of the curvature.

   

  After the apical vertebra is secured to the rod, cantilever correction can be performed by gradually pushing the rod down to the next more distal vertebra, tightening the sublaminar wire, pushing the rod down to the next more distal vertebra, and then tightening the wire, performing the same maneuver progressively down the spine until the pelvis screws are reached.

   

   

   

  TECH FIG 8 • A,B. The proximal to distal cantilever technique can be used for thoracic kyphosis. C,D.

  Preoperative and postoperative radiographs. (Courtesy of DePuy Synthes Spine.)

   

   

  The fixed rodded lateral connectors are then used to connect the rod to the pelvic screws.

   

  Using this “proximal to distal” cantilever technique for cantilever correction allows for a better lever arm to correct thoracic scoliosis as well as thoracic kyphosis (TECH FIG 8) and to center the head over the trunk.

   

  P.784

• Completion and Wound Closure

   

  All wires are bent down into the midline of the rod and directly caudally. This allows easier exposure of the

   

  rod and wires if reoperation should ever become necessary. The remaining bone graft is applied (TECH FIG 9A).

   

  We mix the remaining 60 mL of allograft with either gentamicin (three or four 80-mg vials)4 and, more recently, vancomycin (500 mg for smaller children, 1000 mg for larger children [>50 kg]). This has lessened the postoperative infection rate.

   

  If the child is thin and the sacrum is prominent, the sacral spinous processes and lateral processes are trimmed.

   

  The sacral lamina and lateral processes can be completely removed if they are severely prominent.

   

   

   

  TECH FIG 9 • A. Wires are passed and then twisted in a clockwise direction (1). Wires are cut about 1 cm and then bent to the midline (2). Allograft bone (yellow) is placed out laterally along the transverse processes and is impacted into the facet joints after facetectomy (3). B. AP radiograph of the patient in FIG 1 shows postoperative correction of coronal plane deformity. Clinical photographs show correction of pelvic obliquity (C) and good sagittal plane alignment (D). E,F. Preoperative and postoperative lateral radiographs of patient with severe hyperlordosis corrected with unit instrumentation and pedicle screws used to correct lordosis in the apex of the deformity.

   

   

  The fascia is closed tightly (any leakage may predispose to infection, especially in the lower part of the spine and if the child is incontinent of urine and stool).

   

  No drain is used.

   

  The subcutaneous tissue and skin are meticulously closed.

   

  Final radiographs are taken to confirm coronal and sagittal alignment (TECH FIG 9B-D).

  In patients with hyperlordosis, pedicle screws with reduction posts are useful in the apex of the sagittal plane deformity to aid in the correction (TECH FIG 9E,F).

  If plastic surgery expertise is available, flap closure by a plastic surgery reconstructive team may lead to lower rates of wound breakdown and deep infections.

   

   

   

  P.785

   

  PEARLS AND PITFALLS
  	Severe ▪ Constant communication between the surgeon and the anesthesiologist is intraoperative critical. Type and crossmatched packed red blood cells (1.5-2 times blood hypotension may volume), fresh frozen plasma, and platelets should be available. suddenly occur, especially after decortication.   Hypothermia ▪ Hypothermia can be avoided by keeping the room temperature high and using a heated ventilator, a warmer for intravenous fluids and blood, and an airflow heating device.   Excessively stiff ▪ The surgeon should recognize stiffness preoperatively on the physical scoliosis or examination or bending radiographs to plan for anterior release. accompanying sagittal plane deformity (hyperkyphosis or hyperlordosis)   Rod insertion ▪ Using the wires to pull the rod down to the lamina may cause the wires to cut through the lamina.   Pelvic insertion of ▪ Difficulty occurs as the surgeon attempts to insert the pelvic limb of the rod rod limb in severe and cannot get the rod anterior enough to steer the rod into the drill holes. lordosis This may allow the rod to perforate into the sciatic notch or through the inner pelvic table.

  • Relaxing the push on the rod between levels while correcting the major curve may cause an “unzipper” effect, with several wires tearing through lamina or breaking from too much force on the end vertebra.

  • The surgeon should use a rod holder to prevent the pusher from slipping off the rod as the top of the rod is approached.

  • The force from pushing may become large, preventing the patient from being ventilated or causing a drop in blood pressure. If this occurs, the surgeon should relax the push on the rod just enough to allow ventilation and return of pressure.

  • Intraoperative fluoroscopy should be used to check proper placement of the pelvic limbs. If pelvic penetration of the rod occurs, the penetrated rod limb should be cut, reinserted into the pelvis, and reconnected with an end-to-end

   

  or side-to-side connector.

  • Alternatively, if severe lordosis is present, the modular unit rod concept with separate insertion of pelvic screws may be performed instead of the unit rod which allows easier placement of the pelvic portion of the instrumentation with separate attachment of the rods.

     

    Misjudgment of rod length

• If the rod is too long and prominent, both rods can be cross-linked together and then cut at the T1 vertebra. If the rod length is misjudged too short by more than two levels, the top of another unit rod can be connected with end-to-end connectors. This is important when there is excessive kyphosis to prevent drop-off of the spine over the top of the rod.

   

  Wires cut through lamina

  • Only enough bone should be removed to allow wires to pass through the sublaminar space. Wires should not be used to pull the rod to the lamina. This may also be due to inadequate anterior release in a stiff deformity.

     

    Pedicle screw pulling out of bone

  • A larger diameter screw may be placed or a sublaminar wire may be added at the level where the screw is beginning to back out to add to the fixation.

 

POSTOPERATIVE CARE

 

Neuromuscular patients are managed in the intensive care unit postoperatively in most cases in most centers

 

If blood loss is not excessive and the anesthesiologist feels the child can be extubated, the breathing tube is removed. Some children remain intubated and are ventilated for 2 to 5 days. This latter group of children requires more intensive respiratory management.

 

Pain management consists of short-acting narcotic (fentanyl) drip and management of spasticity using diazepam. Oral pain management can be started on the third or fourth postoperative day.

 

Core body temperature should be increased to 37° C and maintained. Blood clotting is impaired by low body temperature below 33° C, which can easily develop in this patient population.

 

Hypotensive episodes are avoided by maintaining increased fluid intake and pressor support as needed. Urine output should be maintained at a minimum of 0.5 mL/kg/hour.

 

Most children require aggressive postoperative nutritional support.

 

 

Gastrostomy tube feedings can be started as soon as bowel sounds are present.

 

If bowel sounds are not present, gastrojejunostomy or nasojejunostomy feedings are attempted.

 

Central hyperalimentation is started if feeding through the gut is not tolerated. A tunneled central venous catheter (Hickman) is placed at the time of surgery. This is discontinued as soon as central access is no longer needed to avoid the risk of line infection.

 

Pancreatic enzyme levels are monitored carefully postoperatively, as elevated amylase and lipase levels are common and indicative of subclinical pancreatitis.5

 

Oral and gastrostomy feedings should be delayed if these values are increasing above normal.

 

Adequate nutritional intake for optimal wound healing usually requires about 1.5 times the child's normal preoperative requirements and is continued up to 1 month postoperatively.

 

Proper wheelchair assessment postoperatively is also important.

 

 

P.786

 

 

OUTCOMES

Unit rod instrumentation achieves a scoliosis correction of 70% to 80% of the preoperative curve magnitude and an 80% to 90% correction of pelvic obliquity.9, 30

In a subset of 24 ambulatory cerebral palsy patients who underwent posterior spinal fusion with unit rod instrumentation, all patients have preservation of ambulatory status.29

Sagittal plane spinal deformity is also well corrected with unit rod instrumentation. Lipton et al16 showed relief of symptoms and correction of sagittal plane deformity in 24 cerebral palsy patients with hyperlordosis and kyphosis after unit rod instrumentation.

In one survey of 190 parents and caretakers assessing functional improvement of children with cerebral palsy after posterior spinal fusion, 95.8% of parents and 84.3% of caretakers would recommend spinal

surgery again.27 Positive responses included improved appearance, overall function, quality of life, and ease of care.

Overall life expectancy of the cerebral palsy child after posterior spinal fusion is critically important. A survival analysis showed that the presence of severe preoperative thoracic hyperkyphosis and the number of postoperative days in the intensive care unit correlated with decreased life expectancy after evaluating a

number of variables.28

 

COMPLICATIONS

Complications are common but usually not life-threatening and range from minor to major. They include excessive intraoperative bleeding, neurologic complications, atelectasis, pneumonia, prolonged postoperative ileus pancreatitis, wound infection, and so forth.

Mechanical or technical complications also occur and include rod or wire prominence, pseudarthrosis, rod penetration through the pelvis, curve progression after fusion due to crankshafting, and so forth.

In one study, the curve magnitude, preoperative pulmonary status, and degree of neurologic involvement had the highest correlation with postoperative complications.

Infection rates vary but should be expected in about 10% of cases, even when all conditions are optimized. Family should be counseled and prepared for high rate of perioperative problems.

 

 

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    Pediatr Orthop 1990;10:742-749.

     

     

19. Miller F, Moseley C, Koreska J. Pelvic anatomy relative to lumbosacral instrumentation. J Spinal Disord 1990;3:169-173.

     

     

20. Rinsky LA. Surgery of spinal deformity in cerebral palsy. Twelve years in the evolution of scoliosis management. Clin Orthop Relat Res 1990;(253):100-109.

     

     

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31. Yamashita T, Kanaya K, Yokogushi K, et al. Correlation between progression of spinal deformity and pulmonary function in Duchenne muscular dystrophy. J Pediatr Orthop 2001;21(1):113-116.