Kirk W. Dabney and Freeman Miller
DEFINITION
Neuromuscular spinal deformity is a result of an abnormal neuromuscular system in childhood, as in cerebral palsy, muscular dystrophy, spinal muscular atrophy, and so forth. It may be related to a pathologic abnormality in muscle tone, motor control, or weakness or a combination.
While 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 or thoracolumbar with associated pelvic obliquity (FIG 1).
Since 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 scoliosis or sagittal plane spinal deformity in neuromuscular disorders differs depending on the cause of the specific neuromuscular disease. In general, however, most neuromuscular spinal deformities are largely due to muscle imbalance (low tone or high tone) and abnormal postural reflexes.
The natural history of neuromuscular scoliosis is usually that of slow progression, beginning with the development of a flexible scoliosis in middle childhood and the more rapid development of a more fixed scoliosis during the adolescent growth spurt. Some neuromuscular conditions are associated with a more progressive scoliosis than others.
The clinician must weigh the progressive characteristics of scoliosis within each neuromuscular disease with the natural history of the disease itself when deciding on treatment.
The pathogenesis and natural history of some of the more common disorders associated with neuromuscular spinal deformity and spinal deformity 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. In modern society, it has become the most common cause of neuromuscular spinal deformity.
The natural history of neuromuscular scoliosis in cerebral palsy is frequently that of progression. The rate of progression can be very severe in adolescent years (2 to 4 degrees per month).
Progression also occurs after skeletal maturity, and in curves greater than 40 degrees it may occur at a rate of 2 to 4 degrees per year.16
Curves in the 60to 90-degree range begin to affect sitting, 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 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.5
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.
The prevalence of scoliosis approaches 100%.14 For this reason, surgery is done soon after the child becomes nonambulatory, before an irreversible decline in forced vital capacity occurs.
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.
FIG 1 • Typical neuromuscular curve pattern in a child with quadriplegic-pattern cerebral palsy. A. Radiograph of long thoracolumbar curve with pelvic obliquity. B. Clinical picture of this child with poor sitting balance.
While the level of the spinal cord defect influences the clinical presentation of the disease, 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 will develop scoliosis.17
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
This condition 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 gene (SMN) and neuronal apoptosis inhibitory gene (NAIP).15
Clinically, progressive muscular weakness occurs, and eventual pulmonary compromise is common.
Three forms of this disease exist:
Type 1 (early, acute Werdnig–Hoffmann)
Type 2 (intermediate, chronic Werdnig–Hoffmann)
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 starts in the first decade. Thoracolumbar and single 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.1
Friedreich 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 is present in about 50% of patients.7
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.13 The child's development is normal until 6 to 18 months of age, followed by a 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.6
A long C-shaped thoracolumbar pattern is common. Bracing is typically 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.3
The predominant curve type is a long C-shaped curve. 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 progression in established curves greater than 20 degrees.
PATIENT HISTORY AND PHYSICAL FINDINGS
The medical history is critical for this group of patients.
In patients with cerebral palsy, the medical history correlates very strongly with postoperative complications. This appears to be true also in patients with Duchenne muscular dystrophy and spinal muscular atrophy.
Important historical information includes respiratory status, cardiac status, gastrointestinal status (eg, gastroesophageal reflux, nutritional intake), and the presence of a seizure disorder.
Physical examination should assess sitting or standing balance, the pelvic obliquity, and curve magnitude and stiffness (including the curve's coronal, sagittal, and rotational components).
Coronal plane 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, which is common in many neuromuscular diseases.
A complete neurologic examination should also be performed.
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.
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.
If intraspinal pathology is suspected, especially in the ambulatory patient, a preoperative magnetic resonance imaging (MRI) scan should be obtained.
DIFFERENTIAL DIAGNOSIS
Some neurologic diseases can look similar.
It is important to diagnose progressive neurodegenerative disorders in which mortality from the disease is more rapid than the progression of the spinal deformity.
NONOPERATIVE MANAGEMENT
While there was initially some historical enthusiasm for the treatment of neuromuscular scoliosis with casting or bracing, orthotic management has been found to have little or no impact on neuromuscular deformity.
Flexible curves in younger children may require seating modifications (hip guides and offset lateral seat supports) or a soft thoracolumbar orthosis to maintain balanced seating until the child is at optimal sitting height.
Orthotic treatment does not affect the rate and eventual progression of neuromuscular scoliosis.
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 a restrictive type of pulmonary involvement, 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 greater than 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.
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 also benefit from surgical correction.8
Typically during the middle part of adolescent growth, the scoliosis becomes much larger and begins to progress and stiffen. Surgical instrumentation and fusion is recommended at this time.
Preoperative Planning
Technical Considerations
Two main technical preoperative questions require careful consideration:
Is fusion to the pelvis necessary?
Is an 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 or T2 down to the sacrum if there is 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 still consider fusion to the pelvis to prevent the development of late pelvic obliquity.
Some children with Duchenne muscular dystrophy who have no pelvic obliquity are an exception and can be treated with fusion ending at L5.
The gold standard for neuromuscular scoliosis is Luque rod instrumentation (with Galveston extension for the pelvis), crosslinkage to prevent rod shift and rotation, and sublaminar wires.
The unit rod incorporates these concepts into one instrumentation system2,4,10,13 (FIG 3A,B).
The unit rod has a prebent sagittal contour and comes in sizes of 250 mm to 450 mm. Both quarter-inch and 3/16-inchdiameter rods are available. The quarter-inch rod should be used whenever possible, reserving the 3/16-inch rod for patients with a very thin gracile pelvis.
Some surgeons are using pedicle screws for segmental fixation, especially if there is a severe rotational component to the curvature. Caution should be taken when the bone is severely osteopenic, as the pedicle screws may pull out of the bone.
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. C–E. Cantilever effect of the rod correcting pelvic obliquity and scoliosis. The rod is gradually pushed to each vertebra and each wire is tightened, gradually correcting the deformity using transverse forces. F. Anterior release: wedge resections of the discs are performed around the apical vertebrae if the spinal deformity is stiff.
The unit rod is especially powerful as a cantilever to correct pelvic obliquity (FIG 3C–E).
Anterior release for scoliosis is required for larger stiff curves that do not bend out on the bending test (generally greater than 90 degrees) (FIG 3F).
Anterior release is also recommended for severe hyperlordotic and hyperkyphotic spinal deformities.8
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.
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.
Typeand cross-matched blood (up to twice the patient's blood volume), fresh-frozen plasma, and platelets should be available.
Good vascular access is required, often through central venous access.
Another consideration is the use of spinal cord monitoring, the role of which is unclear in many patients with neuromuscular scoliosis. On the one hand, most children with neuropathies and myopathies can be monitored, while most severely retarded quadriplegic cerebral palsy patients with poor motor function cannot be reliably monitored. In addition, it is hard to justify removing implant hardware if there are signal changes in the child with minimal motor function since the risk of a 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.
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 screws pulling out of osteopenic bone.
Any nonambulatory child with a history of low-impact long-bone fracture should be checked for low bone density using dual-energy x-ray absorptiometry (DEXA scan).
Children on seizure medication should have calcium, phosphorus, and vitamin D levels measured.
FIG 4 • 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.
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 4).
We have adapted special radiolucent posts for the table that can be spaced at a narrower distance compared to the standard posts.
The hips and knees are bent to minimize lumbar lordosis and to optimize insertion of the limbs of the rod into the pelvis. All bony prominences should be well padded with eggcrate foam.
Many children with cerebral palsy have significant contractures, making their extremities hard to position. They should be positioned with minimal tension on the joints.
TECHNIQUES
EXPOSURE
A posterior approach to the spine is performed from T1 to the sacrum.
A complete subperiosteal exposure of each vertebra is performed, followed by exposure of the outer wing of each iliac crest down to the sciatic notch and the bottom tips of the posterior superior iliac spines.
PELVIS PREPARATION
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 less than 45 kg and 15 mm past the hook in children greater than 45 kg.
The right or left drill guide is next inserted into the right or left sciatic notch, respectively.
The lateral handle of the drill guide is placed parallel to the pelvis (iliac crests) while the axial handle is held parallel to the body axis.
The pelvis is drilled from the inferior tip of the posterior superior iliac spine in a line just superior and anterior to the sciatic notch, where the bone is densest (TECH FIG 1).11
The hole is probed to make certain that the pelvic cortex or the sciatic notch is not penetrated.
The drill hole can be temporarily packed with Gelfoam to control bleeding.
TECH FIG 1 • A. Optimal drill hole placement anterior and superior to the sciatic notch. B. With severe lordosis, the drill hole starting point is more anterior and aims more posterior.
LUQUE WIRE PASSAGE
After the spine is completely exposed and 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 lamina.
The radius of curvature for the wire bend must approximate the width of the laminae to allow safe passage of the wire.
Two double wires are passed at the L5 and the T1 lamina only, while a single wire is passed at each of the other levels (TECH FIG 2A–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 2F).
This helps the wires from getting inadvertently pushed into the spinal canal and allows for easier wire organization.
TECH FIG 2 • 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.
ROD SELECTION AND INSERTION
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 3A).
The proper-length rod should reach T1 (TECH FIG 3B).
A rod one length shorter should be chosen if there is severe kyphosis because the spine shortens with correction.
With severe lordosis, a rod one 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 several levels if necessary.
If the rod is more than 2 cm long, it may be 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 (about 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 3C).
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 half to three quarters of this pelvic limb of the rod first and then inserts 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 limbs into the pelvis, alternatively impacting each pelvic leg and making certain to direct each of the legs in the direction of the previously drilled holes.
At this point, intraoperative fluoroscopy should be used to confirm the correct placement of the rod limbs within the pelvis.
Caution: 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 either the pelvic limbs of the rod to pull out of the pelvis or fracture of the ilium.
TECH FIG 3 • 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). 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. D. 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.
The surgeon should push the rod to line up with the L5 lamina only and then twist the wires (we suggest a jet wire twister). The wires are cut 10 to 15 mm long.
Now the rod is pushed to L4 and the wires are twisted and cut.
Next 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 (TECH FIG 3D).
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 4A).
We mix the last 60 cc of allograft with four 80-mg vials of gentamicin. 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.
The fascia is closed tightly.
No drain is used.
The subcutaneous tissue and skin are meticulously closed.
Final radiographs are taken to confirm coronal and sagittal alignment (TECH FIG 4B–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 4E,F).
TECH FIG 4 • 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 Figure 1 shows postoperative correction of coronal plane deformity. Clinical photographs show correction of pelvic obliquity (C) and good sagittal plane alignment (D). Preoperative (E) and postoperative (F) lateral radiographs of patient with severe hyperlordosis corrected with unit instrumentation and pedicle screws used to correct lordosis in the apex of the deformity.
POSTOPERATIVE CARE
Neuromuscular patients are managed in the intensive care unit postoperatively.
Most children remain intubated and are ventilated over a 2to 5-day period. This allows for easier respiratory management and pain management.
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.
Hypertensive episodes are avoided by maintaining increased fluid intake and pressor support as needed. Urine output should be maintained at a minimum of 0.5 cc/kg/hour.
Most children require aggressive postoperative nutritional support with central hyperalimentation.
Typically, a tunneled central venous catheter (Hickman) is placed at the time of surgery.
Gastrostomy tube feedings can be started as soon as bowel sounds are present.
Gastrojejunostomy or nasojejunostomy tubes may be started as an alternative to hyperalimentation.
Pancreatic enzyme levels are monitored carefully postoperatively, as elevated amylase and lipase levels are common and indicative of subclinical pancreatitis.
Oral or 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.
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.4
In a subset of 24 ambulatory cerebral palsy patients who underwent posterior spinal fusion with unit rod instrumentation, all patients had preservation of their ambulatory status.20
Sagittal plane spinal deformity is also well corrected with unit rod instrumentation. Lipton et al8 showed relief of symptoms and correction of sagittal plane spinal 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.18Positive 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 also 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.19
COMPLICATIONS
Complications are common but are 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.9
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· Bell DF, Moseley CF, Koreska J. Unit rod segmental spinal instrumentation in the management of patients with progressive neuromuscular spinal deformity. Spine 1989;14:1301–1307.
· Dearolf WW III, Betz RR, Vogel LC, et al. Scoliosis in pediatric spinal cord–injured patients. J Pediatr Orthop 1990;10:214–218.
· Dias RC, Miller F, Dabney K, et al. Surgical correction of spinal deformity using a unit rod in children with cerebral palsy. J Pediatr Orthop 1996;16:734–740.
· Karol LA. Scoliosis in patients with Duchenne muscular dystrophy. J Bone Joint Surg Am 2007;89A:155–162.
· Keret D, Bassett GS, Bunnell WP, et al. Scoliosis in Rett syndrome. J Pediatr Orthop 1988;8:138–142.
· Labelle H, Tohme S, Duhaime M, et al. Natural history of scoliosis in Friedreich's ataxia. J Bone Joint Surg Am 1986;68A:564–572.
· Lipton GE, Letonoff EJ, Dabney KW, et al. Correction of sagittal plane spinal deformities with unit rod instrumentation in children with cerebral palsy. J Bone Joint Surg Am 2003;85A:2349–2357.
· Lipton GE, Miller F, Dabney KW, et al. Factors predicting postoperative complications following spinal fusions in children with cerebral palsy. J Spinal Disord 1999;12:197–205.
· Maloney WJ, Rinsky LA, Gamble JG. Simultaneous correction of pelvic obliquity, frontal plane, and sagittal plane deformities in neuromuscular scoliosis using a unit rod and sublaminar wires: a preliminary report. J Pediatr Orthop 1990;10:742–749.
· Miller F, Mosely C, Koreska J. Pelvic anatomy relative to lumbosacral instrumentation. J Spinal Disord 1990;3:169–173.
· 12. Rinsky LA. Surgery of spinal deformity in cerebral palsy: twelve years in the evolution of scoliosis management. Clin Orthop Relat Res 1990;253:100–112.
· Smeets E, Schollen E, Moog U, et al. Rett syndrome in adolescent and adult females: clinical and molecular genetic findings. Am J Med Genet A 2003;122:227–233.
· Smith AD, Koreska J, Mosely CF. Progression of scoliosis in Duchenne muscular dystrophy. J Bone Joint Surg Am 1989;71A: 1066–1074.
· Sucato DJ. Spine deformity in spinal muscular atrophy. J Bone Joint Surg Am 2007;89A:148–154.
· Thometz JG, Simon SR. Progression of scoliosis after skeletal maturity in institutionalized adults who have cerebral palsy. J Bone Joint Surg Am 1988;70A:1290–1296.
· Trivedi J, Thompson JD, Slakey JB, et al. Clinical and radiographic predictors of scoliosis in patients with myelomeningocele. J Bone Joint Surg Am 2002;84A:1389–1394.
· Tsirikos AI, Chang WN, Dabney KW, et al. Comparison of parents' and caregivers' satisfaction after spinal fusion in children with cerebral palsy. J Pediatr Orthop 2004;24:54–58.
· Tsirikos AI, Chang WN, Dabney KW, et al. Life expectancy in pediatric patients with cerebral palsy and neuromuscular scoliosis who underwent spinal fusion. Dev Med Child Neurol 2003;45: 677–682.
· Tsirikos AI, Chang WN, Shah SA, et al. Preserving ambulatory potential in pediatric patients with cerebral palsy who undergo spinal fusion using unit rod instrumentation. Spine 2003;28:480–483.