2. Early Onset Scoliosis

Neuromuscular scoliosis is spread across a large spectrum of pathologies the manifestations of which will evolve with growth over the natural history. Each of these pathologies is unique in presentation and its response to treatment. Treatment aims to achieve the following:

• Optimal spinal growth
• Prevent spinal deformity progression
• Optimization thoracic and lung
  development
• Maintain ambulation if possible
• Improve seating comfort
• Improve general well being

Neuromuscular EOS (NM-EOS) is a heterogenous group within the EOS population. Clinical series quote 20-40% of EOS cohorts. Familiarity with the different etiologies and subsequent comorbidities and prognosis is essential in planning treatment.

Treatment which can be non-operative or surgical does provide improvements in quality of life (QOL) parameters. Surgical treatment has led to improved spinal deformity correction with modern techniques (2, 3, 4,5). High parent/caregiver and patient satisfaction rates have been reported following surgery. Watanabe et al performed a retrospective review of 84 patients/families of spastic cerebral palsy (CP) patients undergoing spinal fusion. The mean age at the time of surgery was 15.8 years (9 to 26 years). Average follow-up was 6.2 years. They reported overall satisfaction rate of 92%. Ninety three percent reported improvement with sitting balance, 94% with cosmesis, and 71% in patient’s quality of life. Functional improvements were however restricted. Satisfaction rates were lower in patients with increased complication rates and residual deformity post-operatively or in those who were less disabled pre-operatively (6).

Despite the high satisfaction scores complication rates for surgery remain high. Rumalla et al reported on neuromuscular scoliosis treated between 2002 and 2011. They examined 2154 cases. Overall complication rate was 40%. (7). Brandon et al (8) reported on a 30-year experience at a single institution on surgical site infections after posterior spinal fusion for neuromuscular scoliosis. They looked at 428 patients with average follow-up of 4.9 years. Mean Cobb angle was 74 degrees. Deep infection rate was 10.3%. More than half of these infections occurred within 3 months of surgery. 45% were polymicrobial and up to 60% were gram positive. Risk factors identified were diagnosis of spina bifida, BMI <25kg/m2 , incontinence, non-ambulation, Albumin <3.5g/dL, Zinc >60  ASA 3 grade and pelvic fixation. Other authors (9) report complication rates with a prevalence of 28% and also identify pre-operative curve magnitude >60 degrees and non-ambulatory status as risk factors. Yaszay et al (10) reported on 257 patients with follow up > 2years. They found a post-operative major complication rate of 36% and spine related re-operation rate of 14%. Treating surgeons should therefore bear in mind that complication rates with surgical management of neuromuscular scoliosis are not insignificant. It is important to ensure patients are adequately worked up for surgery.  Informed consent highlighting areas where improvement in QOL is likely to occur post-operatively will also help to manage parents/care-givers outcome expectations.

The outcomes for early spinal fusion in EOS are unclear but a retrospective study by Sitoula et al  (11) looked at 33 children who underwent spine fusion with unit-rod instrumentation between 1989 and 2006 for CP neuromuscular scoliosis, aged below 10 years at spine fusion, and with follow-up >5 years. They found that spine fusion was associated with minimal short-term and long-term morbidity, but there was 28% mortality at 10 years of follow-up and 50% predicted mortality at 15 years. Modern practice on treatment of neuromuscular scoliosis has now shifted to the use of Growing Rod technologies with the aim of preserving growth and development similar to the idiopathic group where possible. In certain cases the risks associated with this approach outweigh the benefits and early spine fusion may be the only option. Most growth-friendly constructs for neuromuscular EOS will fall into the distraction based or growth guided categories. The surgical objectives are as follows:

• Optimise spine and lung growth where possible
• Balance spine
• Correct pelvic obliquity
• Improve sitting posture
• Minimise complications

Surgical options available:

• Distraction based – Traditional growing rods (TGR), Magnetically controlled growing rods (MCGR), VEPTR
• Guided growth – Shilla, Luque trolley, modified Luque trolley, Unit Rod, Sub-laminar bands

Different surgical constructs as stated above are available for treatment of progressive neuromuscular EOS and choice will often fall to the treating surgeon depending on preference. Each system has its pros and cons. Numerous authors have published their experiences. McElroy et al performed a retrospective evaluation of 27 children with TGR through a posterior only approach. 15 of the constructs extended to the pelvis. They reported that TGRs were effective and constructs extending to the pelvis controlled pelvic obliquity more effectively. 30% of patients experienced deep wound infection (12). Tsirikos et al in 2008 reported on 287 children with unit rod instrumentation in an observational study. 241/287 had >2year follow up. Scoliosis correction was from mean Cobb angle of 76 degrees to 25 degrees (68%) and pelvic obliquity correction was from 17 degrees to 5 degrees (71%)(13). Lonstein et al in 2012 reported on the use of the Luque Galveston technique in a retrospective analysis of 93 patients. They concluded that it was a safe and effective procedure (14). Canavese et al (15) reported 49% correction in neuromuscular curves and found that a physiological kyphosis could be achieved in 88% of the patients using sublaminar bands. Gersoff et al (16) in their review of 33 patients followed up over 40 months reported no rod failures or pseudoarthrosis. They concluded that the Luque technique was effective.

More recent technologies such as MCGR and Growth guidance systems have been shown to be effective in the surgical treatment of EOS. Haapala et al (17) compared the health-related quality of life (HRQoL) and surgical outcomes of Shilla growth guidance and magnetically controlled growing rod (MCGR) treatment in patients with syndromic and neuromuscular early-onset scoliosis. They concluded that both systems offered similar correction of spinal deformity with equal number of complications but the Shilla system had less surgical procedures in patients treated for EOS when compared with MCGR instrumentation. MCGR resulted in slightly better spinal growth during the distraction period. There were no differences in the QOL measurements. The drawback was the limited numbers in this series. (17). In another study Swarup et al (18) looked at patients with spinal muscular atrophy treated surgically with growth friendly devices and the effect of these constructs and the addition of chest wall support (CWS) on spinal deformity, thorax morphology and pulmonary outcomes. There were 66 patients – 25% MCGR, 73% VEPTR and 2% unknown. They concluded that the constructs did improve the spinal deformity but those treated with CWS had better improvements in thoracic morphology compared to those without.

Despite the obvious benefits of surgery there are challenges associated with achieving good outcomes. There is an increased risk of blood loss therefore tranexamic acid and use of cell salvage is standard. In the author’s (CN) institution >40% blood loss is an indication to abort the procedure. The decision on whether or not to use pelvic fixation in ambulatory patients is complex as there is risk of impairment of mobility, which is distressing for patients and care-givers due to loss of independence. Technically, implants can be prominent with resultant skin breakdown. The surgical approach is often extensive even with growth friendly techniques, which can give rise to healing complications particularly in the distal aspect of the wound due to the risk of faecal or urinary contamination. A modified Wiltse approach (19) has been described to minimise the extensive tissue disruption normally associated with surgery through a conventional approach. The authors reported lower blood loss and comparable curve correction to the traditional midline approach.

Intra-operative monitoring

There is controversy around the usefulness of IOM in neuromuscular patients under-going surgery. Dulfer et al compared 15 patients with DMD and 15 patients with AIS to investigate the feasibility of IONM and cortical excitability. They concluded that IOM seems a feasible and valuable neurophysiological tool during scoliosis correction surgery in patients with DMD (20). Ashkenaze et al (21) reported on their series of 101 patients. They found in 28% a reliable tracing could not be obtained. Noordeen et al (22) in a retrospective review of the role of monitoring of somatosensory spinal evoked potentials (SSEP) in 99 patients with neuromuscular scoliosis showed that SSEP monitoring was useful and that a 50% decrease in the amplitude of the trace optimised both sensitivity and specificity.

Depending on aetiology and patient base line status, intra-operative neural monitoring can be considered. Sometimes due to disease severity, monitoring may not be possible and this should be discussed in advance with the patients or care-givers.

L5 or Pelvis?

The decision on where to stop the instrumentation in Neuromuscular scoliosis is multi-factorial. The magnitude of the deformity and the presence of pelvic obliquity are important but the functional status of the patient is as well. Patients with a higher GMFCS (IV or V) grade are more likely to require fixation to the pelvis compared to those with lower grades. Tondevold et al (23) in a retrospective study compared fixation to L5 and to the pelvis in non-ambulatory patients. They found that patients undergoing pelvic fixation had a greater correction of Cobb angle and pelvic obliquity with no difference in rate of complications between the 2 groups. Different techniques include Galveston technique, iliac screws, Maximum Width Construct, Dunn McCarthy, Sacral Alar Iliac (SAI) and spinopelvic trans-iliac fixation system.

Early Spine Fusion

In a landmark paper Karol (48) reviewed pulmonary function at intermediate-term follow-up in 28 patients with scoliosis who underwent thoracic fusion before the age of nine years. Forced vital capacity was <50% of normal in 12/28 patients, and two required respiratory support. Sitoula et al (49) reported on 10-year outcomes of early fusion in children with cerebral palsy. There was minimal short and long-term morbidity but 28% mortality at 10 years and 50% predicted mortality at 15 years. The decision to offer early fusion as opposed to growth friendly surgery is very much dependent on patient circumstances, natural history of the condition and surgeon experience.

The aim of non-operative management is to control curve progression and improve seating comfort. The mainstay of non-operative treatment is bracing, Wheelchair support and therapies. Recent reports (24,25) indicate that bracing does improve sitting balance and trunk support and by extrapolation leads to better neck and head control. Braces can be used to assist with wheelchair seating as well. It is usually an interim support measure in this group of patients before surgical intervention. 

Wheelchair seating in non-ambulatory patients optimises sitting comfort and improves function (26). A 3-point system of lateral support pads has been shown to offer a more symmetrical trunk posture and correction of curve angles by 35% in non-ambulatory CP patients with scoliosis (27). Other non-operative interventions include Botulinum toxin injections and intrathecal baclofen infusions which have both been shown to be effective in the management of neuromuscular scoliosis (28,29).

Achondroplasia is the result of a mutation in the gene encoding fibroblast growth factor receptor-3 (FGFR3) on chromosome 41. Inheritance is autosomal dominant but up to 80 percent of cases are caused by de novo mutations. It is the most common of the skeletal dysplasias, with an estimated incidence ranging from 1 in 30,000 to 1 in 15,000 live births^1,2. Spinal disorders commonly encountered in achondroplasia include thoracolumbar kyphosis and lumbar stenosis.

Thoracolumbar kyphosis presents in most children with achondroplasia before the age of 12 months and may reach 35 to 45 degrees before the age of 18 months.3 By age two, as children become ambulatory and gain trunk strength, kyphosis resolves in approximately 75 percent of cases³. Bracing is indicated for those children whose kyphosis does not improve by age two; the author prefers an adjustable thoracolumbar orthosis (worn full time) with a pad over the apex posteriorly.⁴ If the kyphosis does not improve with bracing, a trial of hyperextension casting that includes the thighs may be attempted.¹ Surgical treatment is an option if the kyphosis does not improve to less than 45 degrees by the age of 8 or if neurological symptoms develop (Figure 1).

Shortened pedicles and thickened laminae predispose patients with achondroplasia to the development of spinal stenosis^2,5. In addition, decreased interpedicular distance caudally makes the narrowing especially pronounced in the lumbar spine⁶. Patients may present with numbness and pain in the lower extremities, incontinence of the bowel or bladder, and decreased endurance while walking, and may, in fact, stop walking altogether². They may also place a hand on their thigh and lean forward in an attempt to relieve the symptoms of stenosis by decreasing lumbar lordosis⁴. MRI can correlate the level of stenosis with clinical findings.

A combination of bracing and supported sitting for the infant with achondroplasia has been suggested to prevent the progression of kyphosis, thereby lowering the risk of developing spinal stenosis^7,8. If a trial of conservative treatment fails, decompression and fusion is indicated to manage the stenosis. Any surgical decompression of the spine in a skeletally immature patient with achondroplasia should be accompanied by fusion in order to prevent severe kyphosis⁹. In adults, decompression should be accompanied by fusion in areas of kyphosis in most patients.

Because of the high rate of complications, spine surgery in the achondroplastic patient should be performed by spinal surgeons familiar with the patient population and aided by intra-operative neuromonitoring.

Posterior exposure may be complicated by prominent lordosis of the distal lumbar spine; reported angles range from 45.6 to 58.8 degrees and may exceed 90 degrees¹⁰. Exposure of L5 and S1 is further complicated by the overhanging iliac wings¹¹. The safest way to accomplish decompression is to first thin the lamina with a burr and then to carefully dissect it off the midline⁴.

Dural tears are not uncommon in the achondroplastic spine and may be difficult to repair given that the dura is attenuated and the nerve roots therefore tend to bulge out of the dural sac⁴. Dural allograft may be needed.

Given the relatively narrow spinal canal in achondroplasia, instrumentation designed to enter the canal (e.g., hooks and wires) should be avoided whenever possible^1,8. Pedicle screw instrumentation is instead preferred, with the caveat that pedicle morphology in the achondroplastic spine is unique⁸ (Figure 1). Given that the transverse pedicle diameter is comparable in achondroplasts and non-achondroplasts, pedicle screw diameters of 5 to 7 mm may be used⁵. However, the sagittal pedicle diameters of the achondroplastic spine are about 5 to 8 mm narrower and pedicle screws must be sized carefully⁵.

The correction of thoracolumbar kyphosis, which usually involves some shortening of the posterior column of the spine, must be done slowly and with attention to any changes in neuromonitoring. Severe focal kyphosis may be treated with either pedicle subtraction osteotomy or anterior and posterior decompression. Fusion to the sacrum in achondroplasts has recently been shown to compromise function (as measured by Short Form-36 scores) no more than more proximal fusion, though fusion to the sacrum is associated with increased post-fusion pain and increased difficulty with self-care^8,12.

Spine surgery in achondroplasia can result in specific complications, the most common of which are neurologic deficits, dural tears with cerebrospinal fluid leaks, and stenosis at other levels of the spine². Neurologic deficits have been commonly reported in series of achondroplastic deformity correction. Cerebrospinal leaks need to be treated with secure closure with or without application of a dural patch⁴. The risk of stenosis at adjacent levels may be decreased by including all potential levels, usually extending past the twelfth thoracic level proximally⁴.

Diastrophic dysplasia (DD) is an autosomal recessive condition caused by a mutation in sulfate transporter gene DTDST. Dysfunction of DTDST results in undersulfated proteoglycans, decreasing the ability of growth plate chondrocytes to respond to local growth factors and diminishing cartilage strength and resilience¹³. Disorders of the spine associated with DD are cervical kyphosis and thoracolumbar scoliosis. Other features include rhizomelic dwarfism, joint contractures, club feet, and widely abducted, hypermobile “hitchhiker thumbs.” There are estimated to be between 300 to 400 patients with DD worldwide, with most believed to be residing in Finland¹⁴.

Cervical kyphosis in DD presents between infancy and the age of 6.5, averages 35 degrees (with a range of 6 to 130 degrees), and is always associated with hypoplasia of the C3-C5 vertebral bodies¹⁵. Cervical kyphosis is reported to resolve spontaneously by the age of 7, on average, if the curve is initially less than 60 degrees¹⁵ (Figure 2).

Thoracolumbar scoliosis in DD is most commonly a double major curve that is accompanied by junctional kyphosis¹⁶ (Figure 3).

As long as the neurologic exam remains intact, cervical kyphosis measuring less than 60 degrees can be managed by close observation with a reasonable expectation of spontaneous resolution¹⁵.

Patients with early progressive scoliosis may present with substantial curves (greater than 60 degrees) before the age of 3 and will require surgical correction early, possibly as a staged procedure¹⁴. In idiopathic-like scoliosis, bracing of the thoracolumbar spine will not prevent the progression of curves but can be used to delay definitive fixation¹⁴.

Both posterior-only and combined anterior-posterior fusion have been described in patients with DD, with one recent series reporting significantly greater correction in patients undergoing antero-posterior surgery (40 percent correction) compared to those undergoing posterior-only surgery (13 percent correction)^14,16 (Figure 3).

Curves in DD tend to be very rigid due to premature degenerative changes in the facet joints and intervertebral discs; these curves are therefore less responsive to surgical correction^16,17. Failure of fixation is seen more often in DD than in other dysplasias, most likely as a result of increased the aforementioned curve rigidity as well as the decreased size and strength of the laminae and pedicles. Pseudarthrosis has also been reported as a complication¹⁶.

Because pedicles are comparatively short, a relative spinal stenosis may result but usually does not cause symptoms¹⁷. Neurologic deficits may also be due to focal kyphosis and intrusion into the spinal canal by hooks. For this reason, pedicle screws are preferred when they can be used.

Spondyloepiphyseal dysplasia (SED) has two forms: congenita (SEDC) and tarda (SEDT). SEDC is due to a variety of mutations in the COL2A1 gene that are thought to interfere with normal assembly of the type II collagen triple helix¹⁸. It is inherited in an autosomal dominant manner with an incidence of only 3 to 4 per million¹⁹. SEDT is X-linked, presenting at a later age than SEDC with a milder clinical picture. Orthopedic manifestations of SED include extreme short stature, kyphosis, scoliosis, coxa vara, equinovarus, and, in the case of SEDC specifically, delayed ossification¹⁹. Other conditions associated with SED include myopia and retinal detachment²⁰.

SED can present with hypoplasia of the odontoid or os odontoideum, resulting in atlanto-axial instability¹⁹. Fusion should be performed if there is any clinical or radiologic evidence of cord compression. The myelopathic presentation in children can include delayed motor development, spasticity, sleep apnea, and respiratory difficulty¹⁹. Thoracolumbar scoliosis is also seen in SED and can be managed with bracing in its early stages.

All patients with SED should be screened for cervical spine instability prior to scoliosis correction surgery. Airway management may be challenging due to limited flexion of the neck, odontoid hypoplasia, and atlanto-axial instability²¹. Intra-operative motor and sensory monitoring of the spinal cord is recommended.

In the management of atlanto-axial instability, it is important to determine whether atlanto-axial instability can be reduced and whether the sagittal atlas diameter (SAD) is narrowed secondary to os odontoideum²². If the SAD is narrowed, a C1 laminectomy with occipital cervical fusion is recommended.

Surgery is indicated to correct thoracolumbar deformity if the curve is greater than 50 to 60 degrees, which can happen at a young age, especially in SEDC (Figure 4). The combination of a narrowed canal and small pedicles necessitates careful selection of instrumentation²³. Cervical instrumentation may even be the best option for particularly diminutive vertebrae. The surgeon must strike a balance between (1) achieving adequate fixation and correction and (2) allowing for future growth. Given the limited growth potential of these small vertebrae, greater weight should be placed on the former objective⁴.

Complications associated with correction of atlanto-axial instability include the inability to obtain or maintain reduction of the atlanto-axial translation, in which case decompression is needed. The arch of first cervical vertebra may be bifid; in this case, where there is an absence of adequate bone surface, fusion to the occiput may be indicated. Pre-operative CT or MRI is recommended to assess this possibility⁴.

Down syndrome is the most common chromosome abnormality in humans, occurring in 1 of every 600 to 700 live births²⁴. It is caused by partial or complete trisomy of chromosome 21. Disorders of the spine associated with Down syndrome include atlanto-axial and atlanto-occipital instability. Atlanto-occipital instability is attributed to flattening of the cup-shaped superior articular surface of C1 which then allows increased movement of the occipital condyles on C1²². Ligamentous laxity is common in Down syndrome; laxity of the alar and transverse ligaments specifically may further contribute to instability of the upper cervical spine²⁴. Other spine-specific conditions associated with Down syndrome include thoracolumbar scoliosis and premature spinal degeneration in early adulthood.

Patients with Down syndrome should be screened for cervical instability with flexion-extension radiographs (Figure 5).

Several proposals have been put forth to guide clinical management of patients based on radiographic parameters (such as the atlanto-dental interval (ADI), the distance between the posterior dens and the posterior arch of C1, and the presence of os odontoideum) but the clinical picture remains paramount²⁵. Upper cervical instability without symptoms warrants closer monitoring of neurologic exams and restriction of activities that may place the cervical spine at risk, as well as a lower threshold for obtaining flexion-extension MRI²⁴. Surgical intervention is recommended if neurological symptoms develop or if displacement of the atlas exceeds 8 to 10 mm.

Management of scoliosis in Down syndrome is similar to management of idiopathic scoliosis; the first line of treatment is bracing followed by surgery if the curve progresses despite conservative management²⁴ (Figure 6).

Airway management in patients with Down syndrome may be complicated by macroglossia, mid-face hypoplasia, and instability of the cervical spine²⁶. Up to half of patients also have cardiovascular involvement and ought to undergo cardiac evaluation prior to surgery²⁶.

Posterior cervical fusion can be achieved via transarticular fixation of C1-C2 and occipito-cervical fusion using occipital instrumentation with bone graft. The technique for transarticular fixation of C1-C2 includes a starting point 3 to 4 mm lateral to the medial border of the C2-C3 facet²⁷. The keys to this technique are pre-operative CT evaluation of the vertebral artery anatomy and intra-operative fluoroscopy to guide the screw towards the anterior arch of C1 at a steep trajectory²⁷ (Figure 5). Another option is separate fixation of each level using screws in the lateral masses and pedicles^24,27.

Scoliosis curves greater than 45 to 50 degrees can be managed with standard posterior instrumentation and fusion.

Pseudarthrosis was a complication commonly associated with traditional (Gallie) fusion of the upper cervical spine. More rigid fixation has significantly decreased the rate of pseudarthrosis^22,25. As alluded to above, halo fixation may help with fusion post-operatively but there is a slight risk of infection at the pin sites²⁷. Similarly, surgical site infections are more common in Down syndrome. Other reported complications include instability in adjacent segments and neurologic deficits²².

Osteogenesis imperfecta (OI) is caused by a variety of mutations in type I collagen genes COL1A1 and COL1A2, though several other genes have recently been implicated^4,28. Genetic and clinical criteria have been used to classify OI into seven types under the expanded Sillence classification²⁹. The most salient feature of OI is increased skeletal fragility that leads to frequent fractures, and eventually to limb deformity and disability³⁰. Spinal disorders associated with OI include basilar invagination, kyphosis, scoliosis, spondylolysis, and spondylolisthesis.

Basilar invagination occurs when the cranium settles on the upper cervical spine and the atlas and dens subsequently ascend into the foramen magnum (Figure 7). Affected patients may present with headaches, ataxia, and hypotonia, and should be followed with MRI³⁰. Though rare, basilar invagination can lead to further neurologic dysfunction, hydrocephalus, and death when left untreated³⁰.

Estimates of the incidence of scoliosis in OI range from 39 to 80 percent³¹. Low bone mineral density (BMD) and biconcave vertebrae have been associated with an increased risk of progression of scoliosis. Conservative management with bracing may be worth a trial in young patients with type I OI and mild curves but is not often successful³⁰. For curves greater than 50 degrees, surgery may be indicated (Figure 8) and pre-treatment with bisphosphonates for up to a year prior to surgery can increase BMD⁴.

The surgeon should also be aware that not all patients with OI can be helped by spinal fusion. Those with minimal or absent long-bone cortices or “crumpled” ribs may not support an implant.

Pre-operative assessment of patients with OI should include lateral radiographs or MRI of the cervical spine in order to rule out basilar invagination, if the patient has not already had these studies. Basilar invagination can be managed with sub-occipital decompression (anteriorly, if necessary), upper cervical laminectomy, and occipito-cervical fusion²⁷ (Figure 7).

Pulmonary function, and history of respiratory disease should be assessed in order to estimate the likelihood that post-operative ventilatory support will be necessary; this assessment is particularly important for patients with curves exceeding 60 degrees³¹.

Scoliosis correction in OI is achieved by posterior instrumentation and fusion. Surgical exposure may be complicated by a posterior flaring of the ribs that forms a “valley” by which posterior spinal elements may be obscured⁴. Because the pedicles are thinner or irregular in cross-section and therefore difficult to image with fluoroscopy, pedicle depths should be estimated pre-operatively using radiographs since tactile and visual feedback may be limited intra-operatively. Screws should be inserted into as many pedicles as possible to distribute the load (Figure 8). The rod chosen should have a stiffness commensurate with the expected correction of the spine; excessive rigidity increases the risk of anchor cut-out⁴. In certain cases, rods from cervical or pediatric applications are most appropriate. Vertebral augmentation with cement may be needed in some cases. Extensive allograft is employed in order to bring normal collagen into the region.

In rare cases where significant correction of kyphosis is indicated, anterior column support is used to prevent cut-out of the implants. The authors try to avoid post-operative bracing in these patients because it is not only mechanically ineffective but also cumbersome.

The surgeon should also be aware that dural ectasia in patients with OI renders them susceptible to dural tears and leakage of cerebrospinal fluid.

Some authors have advocated pre-operative halo traction placement to aid in the correction of substantial curves, reporting a success rate of 80 percent for 20 patients managed by traction prior to posterior spinal fusion32. Post-operative activity restriction or even bracing for 3 to 6 months may also be necessary to achieve the optimal outcome. Potential surgical complications include breakage of laminae or pedicles by implants, instrumentation failure post-operatively resulting in loss of correction, excessive blood loss, and late pseudarthrosis.

Larsen syndrome is characterized by dislocations of the knee, hip, and elbows; equinovarus or equinovalgus; and dysmorphic facies^33,34. It has an estimated incidence of 1 in 100,000 births and has been associated with mutations in the filamin B (FLNB) gene on chromosome 334. Spinal deformities in Larsen syndrome include thoracolumbar scoliosis and cervical kyphosis caused by cervical spina bifida³⁵ (Figure 9). The apex of the cervical kyphosis is usually at the fourth or fifth cervical vertebra.

Unlike in diastrophic dysplasia, cervical kyphosis in Larsen syndrome does not improve with time and can progress to cervical dislocation and even spondyloptosis³³. Initial evaluation of the child with Larsen syndrome should include radiographs and MRI of the cervical spine. As soon as deformity is identified early posterior fusion of the cervical kyphosis is indicated in infancy or early childhood in order to prevent quadriparesis³³.

During intubation, the anesthesiologist should try to avoid further flexion of the cervical spine in order to prevent compression from the anterior side. Other anesthetic complications that have been reported in children with Larsen syndrome include malignant hyperthermia³⁶.

The spinal cord should be monitored during positioning and during surgery. Dissection posteriorly should be performed carefully in order to avoid cord damage at the levels with open laminae⁴. Localization of levels should be precise in order to avoid extension to levels above or below the desired fusion⁴ (Figure 9). Anteriorly, if corpectomy is indicated, it should begin at the upper and lower end of the gibbus (where the cord is least compressed) so that adequate perspective can be obtained⁴. If portions of the cartilage components of the vertebral bodies are left in place, they can later enlarge and lead to recurrent compression.

To prevent the progression of deformity post-operatively, recent reports recommend posterior spinal fusion only for patients with mild or flexible kyphosis and circumferential fusion for patients with severe or rigid kyphosis greater than approximately 60 degrees33.The cervical spine should be placed in a halo vest post-operatively until adequate fusion is seen.

Neurofibromatosis type 1 (NF-1) is a systemic disease caused by mutation of the NF1 tumor suppressor gene on chromosome 17³⁷. NF1 codes for neurofibromin, a mediator of proteins in the Ras pathway³⁷. The disorder is inherited in an autosomal dominant fashion and occurs in 1 in 2,500 births³⁷. Diagnosis of NF-1 is made clinically based on the presence of at least 2 of the diagnostic criteria established by the National Institutes of Health Consensus Development Conference: six or more café-au-lait spots greater than 5 mm before puberty or greater than 15 mm after puberty; 2 or more neurofibromas or at least 1 plexiform neurofibroma; axillary or inguinal freckling; optic glioma; 2 or more Lisch nodules; distinctive bony lesions; or an affected first-degree relative meeting the former criteria³⁸. Spinal disorders associated with NF-1 include scoliosis, dural ectasia, and (infrequently) cervical kyphosis (Figure 10). These and other musculoskeletal complications tend to present between the ages of 5 and 10 years³⁹.

Scoliosis curves in NF-1 are characterized as either dystrophic or non-dystrophic⁴⁰.

The dystrophic curve is usually sharply angulated, involving 6 or fewer vertebrae. Radiographic findings may include rib penciling, vertebral scalloping or wedging, and apical vertebral rotation³⁹. Dystrophic scoliosis in NF-1 presents at an early age, progresses rapidly, and responds poorly to bracing³⁹. Factors predicting increased risk of progression in dystrophic curves include a high Cobb angle, kyphosis, penciling of at least 4 ribs, and a mid- to distal thoracic apex. Patients with 3 or more dystrophic features are approximately 14 times more likely to require surgery⁴⁰. Curves less than 20 degrees can be observed at 6-month intervals; surgery is indicated for curves greater than 40 degrees (Figure 11).

Non-dystrophic scoliosis in NF-1 clinically resembles idiopathic scoliosis, albeit with an earlier age of onset, a higher risk of curve progression, and a higher rate of pseudarthrosis following spinal fusion³⁹. Non-dystrophic curves less than 25 degrees may be observed with the caveat that such curves may develop dystrophic features, especially if scoliosis presents before the age of 739,41. Curves greater than 25 degrees are amenable to bracing; however surgery is indicated for curves greater than 40 degrees³⁹.

A pre-operative MRI is indicated to assess the entire spinal canal for tumors, compression, dural ectasia, and intra-spinal rib dislocations^4,39. Pre-operative assessment should also include radiographs of the cervical spine to prevent inadvertent cord injury under general anesthesia⁴¹. Blood loss is generally greater in NF-1 compared to the general population, especially with entry into the spinal canal, and dural ectasia increases the risk of dural tears³⁹.

Cervical kyphosis may be managed posteriorly alone if dystrophic changes are not severe; if the kyphosis is greater than 50 degrees, anterior and posterior approaches may be employed⁴¹ (Figure 10). Pre-operative halo traction may help in severe curves if the kyphosis is not focal. In addition to a pre-operative MRI, skull radiographs should be obtained prior to the application of any form of traction in patients with NF-1 due to the risk of skull defects³⁹.

Non-dystrophic curves greater than 40 degrees can be managed with posterior spinal fusion and instrumentation. In children younger than 9 years of age, a growth-guiding approach is usually successful. In the presence of severe dystrophic changes (including curves measuring greater than 90 degrees), both the corrective potential and the extent of fixation are limited by an exclusively posterior approach; combined surgery produces more predictable results if fixation in a dystrophic curve seems like it will be challenging⁴¹ (Figure 11). Dystrophic curves are often associated with intra-spinal neurofibromas (known as “dumbbell lesions”) which not only limit surgical exposure but also increase the risk of intra-operative bleeding^39,42. Some surgeons prefer vertebral column resection. Pedicles are thinned in the dystrophic portion of the spine that threatens to complicate the placement of pedicle screws³⁹. The fusion mass in the dystrophic portion of the curve is also thinned.

Reported rates of pseudarthrosis range from 15 to 20 percent^39,41. If a staged anterior-posterior procedure is planned, placement of a feeding tube and hyperalimentation are recommended³⁹.

Marfan syndrome (MFS) is a systemic connective tissue disorder most frequently caused by mutations in the fibrillin-1 gene (FBN1) on chromosome 15⁴³. Disease pathogenesis is attributed specifically to the increased levels of TGF-β associated with fibrillin-1 deficiency. Inheritance is autosomal dominant (though phenotypic expression varies widely) with an estimated prevalence of 2 to 3 per 10,000 individuals⁴⁴. The diagnosis of MFS is based on the recently revised Ghent criteria that privilege two of the most salient features of the syndrome, increased aortic root diameter and ectopia lentis; the new nosology also heavily weights a known FBN1 mutation or a family history of MFS⁴⁵. Other characteristic findings in the skeletal, ocular, cardiovascular, pulmonary, integumentary, and neurologic systems each receive between 1 to 3 points; a total score greater than or equal to 7 defines “systemic involvement”⁴⁵. Features in the skeletal system include pectus carinatum (2 points), pectus excavatum (1 point), protusio acetabuli (2 points), and pes planus (1 point); dural ectasia merits 2 points while scoliosis and thoracolumbar kyphosis are each given 1 point⁴⁵.

Scoliosis is present in 63 percent of patients with MFS, kyphosis in approximately 40 percent; in the sagittal plane, curves may be increased, decreased, or even reversed44. The progression of scoliosis in MFS is faster than in the general population; curves that present before the age of 3 progress most rapidly⁴⁴. Unfortunately, bracing is not as effective in MFS as in idiopathic scoliosis. For curves between 15 and 40 degrees, bracing may be used in order to prevent or at least to delay the need for surgical intervention. Curves greater than 40 degrees, however, will almost certainly progress and bracing is therefore not recommended as more than a temporizing measure⁴⁴. Managing infantile scoliosis in MFS is particularly challenging; bracing can be used to promote upright posture if there is concomitant kyphosis but surgical correction with growing rods will eventually become necessary⁴⁶ (Figure 12).

Dural ectasia—a ballooning or widening of the dural sac in the lumbosacral spine—is found in 63 to 92 percent of MFS patients⁴⁷ (Figure 13). Increased hydrostatic pressure in the lumbosacral spine is hypothesized to cause expansion of already attenuated dural tissue⁴⁴. Dural ectasia, in turn, contributes to the increased vertebral scalloping, reduced pedicle width, and reduced laminar thickness seen in MFS⁴⁴. In adults with MFS, dural ectasias do not seem to increase in size over time; their presence is also not associated with the onset or progression of spondylolisthesis⁴⁷. Spondylolisthesis is, nonetheless, approximately twice as common in MFS as in the general population (6 percent versus 3 percent) and tends to be of higher grade⁴⁷.

Spine deformity surgery is required in 10 to 15 percent of individuals with MFS⁴⁴. Recent evidence suggests that there is no significant difference between patients with MFS and those with adolescent idiopathic scoliosis with respect to blood loss during spinal deformity correction⁴³. Nonetheless cardiac clearance should be obtained pre-operatively; intra-operatively, the thin antero-posterior diameter of the chest cavity of MFS patients should be kept in mind in order to avoid undue pressure on the ribs and therefore the heart⁴.

The presence of dural ectasia contributes to an increased rate of intra-operative cerebrospinal fluid leaks in MFS⁴³. Pre-operative MRI or CT imaging should be obtained in order to assess the bony anatomy and to delineate any ectasia. Positioning the patient in slight Trendelenburg position may decrease the prominence of the ectasia and minimize the risk of dural tears as will minimizing dissection within the spinal canal⁴. If a dural tear occurs (as happens in 8 percent of spinal fixations in MFS), closure can be attempted, a dural patch placed, and bed-rest continued for two to three days post-operatively^44,47.

The thin pedicles and laminae in certain regions of the spine in MFS can also make fixation challenging; pedicle screw fixation will require fluoroscopy and the use of narrow awls to find the pedicle center⁴. Bone mineral density, often decreased in MFS, may further undermine fixation stability.

Posterior instrumentation and fusion should include all the major curves, with consideration of alignment in both sagittal and coronal planes⁴³ (Figure 14). It is important not to fuse too short a segment of the spine; fusion to the sacrum should be considered if fusing in the lower lumbar spine, especially if distal fixation is suboptimal or if the curve is dysplastic^43,44. By fusing to the sacrum, late pain and decompensation may be avoided⁴⁴.

In the patient with infantile scoliosis, growing rods are indicated if bracing fails⁴⁶. Dual rods are employed, with proximal and distal fixation “foundations” robust enough to resist pullout⁴. A foundation of 2 vertebrae (or 3 if pedicles or laminae are dysplastic) with pairs of anchors fused proximally and distally, has proven satisfactory in our center⁴. If significant coronal imbalance exists or if the laminae or pedicles are not sufficient for solid fixation, the ilium is another option distally. Distraction is then performed once or twice per year⁴. The initial distraction followed by 5 years of growing treatment can reasonably be expected to produce at least 11 cm of additional spine length⁴⁶.

Rates of hook dislodgment, pseudarthrosis, and fixation failure in MFS have been reported to be 22 percent, 10 percent, and 21 percent, respectively⁴⁴. The failure of fixation may be due to attenuated pedicles and laminae, decreased bone mineral density, and ligamentous laxity. For these reasons, the revision rate is significantly higher than in AIS⁴³.

Because valvular incompetence and cardiac failure have been reported in the post-operative period, patients with MFS should also be followed by the cardiologist or a medical team⁴. In addition, superior mesenteric artery syndrome has been associated with the correction of significant kyphosis in MFS⁴. Other post-operative considerations include pneumothorax (a spontaneous occurrence in MFS) and hemothorax.

Ehlers-Danlos syndrome (EDS) is a connective tissue disorder caused by defects in the synthesis and post-translational modification of fibrillar collagen types I, III, and V⁴⁸. The Berlin system identified nine types of EDS. The more recent Villefranche classification system describes six subtypes of EDS, grouped according to clinical, genetic, and biochemical features⁴⁸. The incidence of EDS is estimated to be from 1 in 25,000 to 1 in 5,000 births. The most prominent features of EDS are hyperelastic skin, hyperextensible joints, and easy bruising (due to vascular fragility)⁴⁹. Scoliosis is most common in types I (classic) and VI (ocular-scoliotic). However, spinal deformity does not appear to be as common as in Marfan syndrome⁴. Spondylolisthesis can also be seen in EDS.

The scoliosis seen in EDS can become rigid and severe⁴⁹. The role and outcomes of bracing in EDS patients have not been well studied but the few mentions made in the literature suggest bracing does little to slow disease progression^50,51. Surgical correction is offered for curves greater than 50 to 60 degrees⁴. Appropriate assessment of vascular structures in type IV EDS with MRI and angiography can aid pre-operative planning⁴⁹.

Pre-operative MRI can also be used to evaluate patients for dural ectasia, the presence of which increases the risk of dural tears in the lumbosacral spine⁴.

The anesthesiologist should be aware of the increased blood loss caused by vascular fragility in EDS; reports of mean estimated blood loss range from 1,243 mL to 2,800 mL, depending on the surgical approach⁵¹. The posterior approach is associated with blood loss at the lower end of this range (mostly from small muscular and periosteal vessels) and is therefore preferred for deformity correction in EDS⁴. Because of the increased risk of significant vascular injury (e.g., to iliac vessels and segmental branches of the aorta), anterior release should be avoided whenever possible⁴⁹. If anterior vessel injury is suspected, the prudent approach is to stage the procedure, with the assistance of a vascular surgery consult. Staged, temporary internal distraction followed by segmental instrumentation may decrease rigidity and avoid the need for an anterior procedure⁴⁹.

Neurologic deficits during spinal deformity correction may be more common in EDS; proposed mechanisms for this phenomenon include increased ligamentous laxity that allows for greater spinal cord distraction and increased vascular fragility that compromises perfusion of the cord⁴.

Adequate deformity correction can be obtained in EDS but may be complicated by junctional kyphosis⁴⁹. Post-operative wound hematoma is common and can be minimized by the placement of a wound drain⁴.

At least four different varieties of Stickler syndrome (or hereditary arthro-ophthalmopathy) have been described. The membranous (type 1 vitreous) form of Stickler syndrome is associated with mutations in the COL2A1 gene while the beaded vitreous (type 2) and non-ocular (type 3) forms are associated with mutations in COL11A1 and COL11A2, respectively⁵². Types 1, 2, and 3 all share autosomal dominant patterns of inheritance, and a recessive form caused by a mutation in the COL9A1 gene has been recently described⁵³. The total incidence of all forms of Stickler syndrome is approximately 1 in 8,000, though it is suggested that the syndrome continues to be underdiagnosed^52,54.

A panel of major and minor criteria is used to diagnose Stickler syndrome⁵⁵. Characteristic craniofacial abnormalities include cleft palate or bifid uvula, micrognathia, and mid-face hypoplasia⁵⁶. Ocular defects, including myopia and retinal detachment, are found in all forms except type 3 (because COL11A2 is not expressed in tissues of the eye)⁵². Approximately 80 percent of patients with Stickler syndrome have musculoskeletal abnormalities including muscle hypoplasia, articular hypermobility, early-onset osteoarthritis, protusio acetabuli, coxa valga, and spinal anomalies⁵⁵.

Spinal abnormalities include spondylolisthesis, scoliosis, and hyperkyphosis. In one series of 53 patients with Stickler syndrome, 18 (34 percent) were found to have scoliosis⁵⁵. Of these 18 patients, 4 had curves with a left thoracic apex orientation; early MRI is indicated in the management of these cases. In general, scoliosis in Stickler syndrome can be managed conservatively with bracing; surgery is indicated if the curve does not correct (Figure 15). In that same study, only 1 of the 18 patients with scoliosis underwent surgical correction⁵⁵.

Focal thoracic kyphosis was also found in 43 percent of these patients⁵⁵. Endplate abnormalities such as Schmorl’s nodes and platyspondylia are also common in Stickler syndrome⁵⁵. Back pain affects up to 85 percent of adult patients, with a younger age of presentation compared to the general population⁵⁵.

Recent evidence suggests that valvular abnormalities are no more prevalent in patients with Stickler syndrome than in the general population, as was once thought, and that routine pre-operative echocardiography and antibiotic prophylaxis are therefore no longer indicated⁵⁷. The anesthesiologist should, however, be prepared to manage an airway potentially complicated by micrognathia or mid-face hypoplasia⁴. Standard posterior instrumentation and fusion may be used in the correction of spinal deformity.

To date, case series on outcomes of spinal deformity correction in Stickler syndrome have not been published. There is an isolated report of successful correction of thoracolumbar scoliosis with posterior spinal fusion and instrumentation⁵⁵.

Most investigators now accept four clinical forms of Neurofibromatosis: The most common form is Neurofibromatosis Type –1 (NF1) previously known as von Recklinghausen disease, which involves predominantly peripheral nervous system although it involves cells of mesodermal origin as well. It is an autosomal dominant disorder affecting about one in 4,000 persons²; multiple hyperpigmented areas (café au lait macules) and neurofibromas are characteristic. Neurofibromatosis Type-2 (NF2) is the second most common form of the disorder involving central nervous system and is associated with bilateral vestibular schwannomas and multiple spinal schwannomas. Segmental neurofibromatosis is considered to be a mosaic form of NF1 with features of NF1 present in single body segment.³ Schwannomatosis is the most recently described form manifesting itself as multiple deep painful schwannomas and is thought to represent a mosaic form of NF2.⁴

The 1987 Consensus Development Conference of the National Institutes of Health on NF-1 concluded that the diagnosis of von Recklinghausen's NF-1 was established when two or more of the diagnostic criteria listed in Table 2 were found⁵.

Other disorders of pigmentation such as McCune-Albright syndrome, LEOPARD syndrome, Noonan's syndrome and Watson's syndrome can be confused with von Recklinghausen's NF-1⁶.

Since the consensus panel meeting, specific kinds of learning disabilities and MRI abnormalities (especially in children) have been associated specifically with NF-1. These are useful even during early life.⁷ More recently, anterolateral bowing of the tibia has been considered as one of the criterion for the diagnosis of NF1.⁸

NF-1 is the most common human single-gene disorder. It affects at least one million people throughout the world. It is seen in all racial and ethnic groups. It would be conservative to estimate that half of them will suffer serious medical and social complications. The gene is fairly large sized, in the range of 300,000 base pairs. (Most genes are several tens of thousands of base pairs, and the largest known, the gene for Duchenne muscular dystrophy, extends over 2.5 million base pairs.)

In 1990, the gene locus of NF-1 in humans was discovered on the long arm of chromosome 17, and its protein product, neurofibromin, was identified 9, 10. Expression of neurofibromin is highest in neurons, oligodendrocytes, non-myelinated Schwann cells, adrenal medulla, leukocytes, and testes. Neurofirbomin act as a supressor for p21-Ras, an oncogene, and therefore, the loss of neurofibromin, as in NF-1, would lead to inability to shut off activated p21-Ras, with subsequent aberrant growth promoting signals. In this respect, NF-1 gene is a typical tumor suppressor gene and NF-1 is the most common human cancer predisposition syndrome (*1,2,3)

Direct sequencing of the NF1 gene is now available for genetic testing. In contrast to the previously used protein truncation assay which only detected 60-70% of NF1 mutations it detects the mutation in 95% and is considered as the gold standard.^{11, 12} Animal models such as knockout mouse are now available that will greatly increase our understandings of the disease and help in development of therapeutic strategies.

Routine posteroanterior and lateral cervical, thoracolumbar, and sacral radiographs are necessary when studying the deformed spine because of the potential for occult deformity in each location. Careful attention is directed on plain x-rays to the sagittal plane for evidence of abnormal lordosis, kyphosis or dystrophic changes. 

Computed tomography (CT) has been used extensively to identify the occasional abnormal structure of the spine in NF-1; it allows one to assess the spinal canal, its contents, and the associated anatomy. Three-dimensional reconstruction enhances the explicitness of the bony detail. The addition of contrast myelography to CT has allowed the surgeon to identify lesions found in and about the spinal canal. Magnetic resonance imaging (MRI) is utilized to determine the internal contents of the spinal canal and will show the presence of lesions within and about the spinal cord itself.¹⁸

The onset of spinal deformities may occur early in patients with NF1. Usually early onset scoliosis is associated with kyphosis giving rise to kyphoscoliotic deformities. Calvert et al.³⁰ presented a series of treated (n = 34) and untreated (n = 32) patients who had NF-1 and scoliosis. Seventy-five percent of patients in the non-treated group had kyphoscoliosis. The investigators reported that patients, who had severe anterior vertebral scalloping noted on the lateral view, progressed an average of 23° per year for scoliosis and kyphosis. All other patients had an average rate of scoliosis progression of 7° and kyphosis progression of 8° per year.

Some of the non-dystrophic curves exhibit a phenomenon of modulation. We defined modulation as a process by which a non-dystrophic curve acquires the features of a dystrophic curve and behaves as a dystrophic curve.¹⁶ We reported that modulation occurred in about 65% of their patients. Modulation occurred in 81% of patients who presented with scoliosis before 7 years of age and in 25% of those diagnosed after 7 years of age. In this study, rib penciling acquired through the modulation period was the only factor that was statistically significant in influencing the progression of the deformity. The rate of progression for “modulated” scoliosis and kyphosis was 12° and 8°, respectively, versus 5° and 3° for non-modulated spines. These results were based on plain radiographic findings.

Some of the recent reports with the use of MRI of spine have shown the presence of dystrophic findings in the spine before they are apparent on the plain radiographs. Based on these reports, it can be speculated that true modulation may be rare, and many of the apparent non-dystrophic curves are actually dystrophic curves which subsequently present themselves with radiographic changes of dystrophic curve giving an impression of “modulation”.

Dystrophic curvatures of less than 20° should be treated by observation. Serial spinal radiographs at 6 month intervals should be obtained to check for progression of the deformity.²³ Bracing of progressive dystrophic curvatures is ineffective and surgery is usually recommended.^{15, 22, 24} For adolescent patients with dystrophic curvature greater than 20° to 40° of angulation, a posterior spinal fusion with segmental spinal instrumentation is recommended.^{15, 28} In more severe dystrophic scoliosis, anterior fusion should be performed in addition to posterior fusion, to increase the fusion rate and to reduce the risk for progression despite solid posterior fusion. Preoperative halo traction may be beneficial for the treatment of severe curves, including those with kyphoscoliosis.^{15, 31-33} It allows gradual and controlled soft tissue relaxation and curve correction before surgery or between staged surgeries; however, it is contraindicated in patients who have cervical kyphosis. Daily neurological evaluations are mandatory to avoid spinal or cranial nerve injuries. Nutrition is also paramount during this time. We use supplemental naso-jejunal feeding in between stages to decrease the protein depletion that is seen in staged patients.^{25, 34} We recommendanterior release, nasojejunal tube alimentation, and craniofemoraltraction for rigid curves of >90°. For curves >100°in any plane, anterior as well as posterior release followed bynasojejunal tube alimentation and craniofemoral traction is recommended (see Fig. 6).

The dystrophic curves that are present in late juvenile and early adolescent period pose a challenge to the surgeon. These curves have a high rate of pseudoarthrosis following a posterior spinal fusion.^{18, 23, 27} A combined anterior and posterior spinal fusion has been recommended in these patients to decrease the rate of pseudoarthrosis and crank-shaft.^35-38 We have used off label BMP in these surgeries, but not enough cases with adequate follow up have been done to validate its efficacy. We also recommend the use of segmental instrumentation to reduce the rate of curve progression after arthrodesis. In our experience, an early fusion of the spine in this age group does not significantly alter the final height and its benefit outweighs the risk of severe progression. Furthermore, the dystrophic segments have very limited growth potential to begin with.²⁹

Dystrophic curves in infants, toddlers and early juvenile patients present even more of a challenge. In this age group, a spinal fusion can certainly have a significant effect on overall height as well as the size of the thoracic cage. Smaller size of the vertebrae can pose difficulty in the instrumentation. On the other hand, progression of the curve itself can significantly distort the thoracic cage which can lead to cardio-thoracic decompansation.

The so-called “growing rods” have been used successfully in the treatment of early onset idiopathic curves. These devices have been shown to prevent the progression of the curve while preserving the longitudinal growth of the spine.³⁹ The currently available dual growing rods have been shown to be superior to the previous versions of submuscular single growing rods.⁴⁰ We have used dual growing rods on early-onset dystrophic curves with a great deal of optimism.

We have used the growing rods directly with fusion of the cranial and caudal anchors only in the patients with flexible curves less than 60°. Traditionally, this is followed by a period of bracing and lengthening every 6 months. In larger and stiffer curves, we recommend anterior annulotomies (with or without thoracoscope) without fusion to preserve growth. This is followed by insertion of the growing rods and routine lengthening at 6 months interval.

In certain cases, traditional use of hooks as anchor point may not be feasible (Figure 2). In these cases, use of pedicle screws as anchor points in the spine is advantageous.

The use of growing rod instrumentation in NF1 is also associated with a high incidence of complications (Figure 3). The high rate of complications has also been reported for idiopathic patients.³⁹ The most common complication we have encountered is proximal juctional kyphosis. This is especially common in the patients with high thoracic or cervicothoracic curves. An all screw construct may be less problematic. In these patients, we currently do not perform routine lengthening. Other complications encountered are infection and rod breakage.

Although the use of growing rod instrumentation is associated with higher complication rate, its benefits outweighs the risk in patients with early onset dystrophic scoliosis. Our early results with the use of growing rods remain encouraging. This is a promising technique made especially useful because most dystrophic curves are early onset.

Kyphoscoliosis

Kyphoscoliosis seen in NF-1 is distinguished by the predominance of kyphosis (>50 degrees on the lateral radiograph) associated with scoliosis; acute posterior angulation is a typical sign. The vertebral bodies are frequently so deformed and attenuated at the apex that it may be impossible to identify them on routine radiographs.

Patients with dystrophic angular kyphosis respond poorly to posterior fusion alone. This is a potentially aggressive deformity and should be aggressively pursued. Good results are consistently obtained only in those patients who have both anterior and posterior fusion; however, not every patient obtains solid fusion following these procedures. Technically inadequate anterior procedures have been considered the reason for failure; however, pressure erosion from enlarging neurofibromas, dural ectasia, and meningoceles may prevent safe exposure to the front of the spine. Most important, the entire structural area of the deformity should be fused anteriorly with complete disc excision and strong strut grafting, preferably from the fibula, as well as rib and iliac crest graft. No soft tissue should be allowed to interpose between the grafts, and all grafts should have contact with each other and with the spine.

Because of the association of paraplegia with kyphoscoliosis, there has been a tendency to perform laminectomies. Laminectomy alone for kyphoscoliosis cord compression is absolutely contraindicated; the inciting lesion is usually anterior, and the compression cannot be visualized from behind. Also, the removal of the posterior element predisposes the patient to unstable postlaminectomy kyphosis and removes valuable bone stock required for posterior spinal fusion.

The authors strongly recommends anterior and posterior fusion for all dystrophic kyphotic curvatures greater than 40° coronal Cobb angle. If the kyphosis is greater than 50°, a strong anterior strut graft (preferably fibula) should also be performed.

A complete spine MRI or a complete high-volume CT myelogram should be performed prior to surgical treatment. If there is spinal cord impingement, the problem should be approached directly--anteriorly with partial corpectomy for anterior lesions and a hemilaminectomy for posterior ones, both to be followed by anterior and posterior fusions. The patient should be re-imaged six months postsurgery, with augmentation of the fusion mass if there is any evidence of weakness of the fusion mass.

Lordoscoliosis

Lordoscoliosis has been reported in only a small percentage of patients with NF-1. (Figure 4) It is well known that thoracic lordosis (hypokyphosis) predisposes to a significant decrease in pulmonary function and mitral valve prolapse ^{41, 42}

Spondylolisthesis

The deformity is usually the result of increased diameter of the spinal canal, with pathologic elongation and thinning of the pedicles giving rise to a pathologic forward progression of the anterior elements of the spinal column. Dural ectasia with meningoceles,or interstitial hypertrophic neurofibromas with involvement of the lumbosacral roots exiting the spinal canal through the neuroforaminae, is the cause of the problem. An MRI or large-volume CT myelogram is necessary to identify the character of the soft tissue affecting and surrounding the vertebral elements before considering surgery. The vertebral bodies are secondarily affected and appear to be thin and dystrophic; the smaller vertebral bodies and narrower pedicles may preclude use with pedicle screws. Every effort should be made to achieve anterior and posterior fusion.

Paraplegia

It is possible that neurologic compromise may be related to tumor, structural instability of the vertebral column complex, dural ectasia, vertebral destruction, neurofibromas, neurosarcomas, fibrofatty tissue reaction, severe kyphosis, vertebral subluxation, dislocation, protrusion of ribs into the spinal canal, or progressive dystrophy of the bony elements of the spine. A neoplasm is usually responsible for paraplegia in older patients, whereas spinal malalignment or ribs displacing into the spinal canal is the most common cause in younger individuals. Rockower et al.⁴³ reported two patients who, because of vertebral body instability and displacement secondary to neurofibromatous tissue encroachment, developed paraplegia. The problem was solved by carefully monitored traction and spinal fusion. Traction should be used very rarely when the deformity is mostly kyphotic. Traction should be used only with flexible kyphosis--never if the kyphosis is rigid. If the kyphosis is rigid, an anterior release, disc excision, and fusion followed by posterior spinal fusion are recommended.⁴⁴

Unrecognized rib penetration into the spinal canal with spinal cord compromise could be a source of paraplegia that, prior to current imaging technology was thought to be the natural course of NF-1 with kyphoscoliosis.

Those with severe spinal curvatures without significant kyphosis and with evidence of paraplegia should be assumed to have intraspinal lesions until proved otherwise. An MRI or a high-volume CT myelogram is done in the prone, lateral, and supine positions. If the kyphosis is mobile and no intraspinal tumor is present, the patient should be placed in halo-assisted traction; this must be done with extreme caution and neurologic monitoring; it should definitely not be performed if the kyphosis is rigid. Even if the kyphosis is mobile and there is paraplegia, the author recommends somatosensory evoked potential monitoring during traction. If a tumor is anterior, immediate anterior excision, spinal cord decompression, and fusion should be carried out; if the lesion is posterior, a hemilaminectomy with tumor excision and posterior spinal fusion should be performed. If total laminectomy is required, posterior spinal fusion is mandatory.

Dural ectasia is a circumferential dilatation of the dural sac which is filled with proteinaceous fluid. The slow expansion of the dura results in erosion of the surrounding osseous structures resulting in widening of the spinal canal, thinning of the laminae, and ultimately destabilization of the spine. Similar lesions are seen in other connective tissue disorders e.g. Marfan’s syndrome and Ehler Danlos syndrome, although cause of these lesions in NF1 is not known.

During this process, the neural elements are not affected. As a result of slow nature of this process and enormous widening of the spinal canal the neural elements have adequate room for accommodation, and there may be severe angular deformity and distortion without neurological deficit. The patients remain neurologically intact until later in the course of the disease process when destabilization of the vertebral column jeopardizes the neural elements. Dislocation of the vertebral column due to dural ectasia has been reported in the literature.⁴⁵ The destabilization at the costovertebral junction can result in penetration of the rib head into the spinal canal with neurologic compromise (Figure 1).^{44, 46}  The presence of rib head or the neurofibroma in the spinal canal can result in intra-operative neurological deficit if instrumentation is used for correction of the curve without adequate decompression.

Dural ectasia can be readily seen on high-volume computed tomographic (CT) myelography or contrast-enhanced MR imaging and is recommended before surgical intervention is undertaken for dystrophic curves. Higher imaging studies help to demonstrate extremely thin laminae; in which case dissection by electocautery rather than by periosteal elevators are recommended during surgical exposure to avoid direct injury to the neural elements/dura by plunging into the spinal canal. Surgical spinal stabilization and fusion does not alter the course of dural ectasia. Dural ectasia can result in failure of the primary fusion or the expanding dura ultimately can destroy a solid fusion leaving behind the instrumentation.