7 Neuromuscular Scoliosis

Neuromuscular scoliosis is a coronal plane spinal curvature of 10 degrees or more, measured by the Cobb method, in the setting of muscle imbalance secondary to an underlying neuropathic or myopathic disease. Abnormal biomechanical loading secondary to this imbalance and spinal collapse results in asymmetric vertebral body growth in the skeletally immature patients, in accordance with the Hueter–Volkmann principle. Progression occurs as a result of progressive muscle imbalance and anatomical deformity. There are many neuropathic and myopathic disorders that may lead to neuromuscular scoliosis ( Table 7.1), of which cerebral palsy (CP) is the most prevalent and will be the main focus of this chapter. Cerebral palsy occurs in approximately 2 per 1,000 live births and an estimated 15 to 28% of these children will develop scoliosis, and more severe forms, such as spastic quadriplegia, have a higher incidence.^1,2

7.2 Natural History of Neuromuscular Scoliosis in Cerebral Palsy

The rate of progression relates to the magnitude of curve. Thometz and Simon observed 0.8-degree curve progression in patients with curves less than 50 degrees, whereas 1.4 degrees per year curve progression was seen in patients with curves greater than 50 degrees.³ During periods of rapid growth, severe progression can occur. The vast majority (85%) of patients with curves exceeding 40 degrees by 15 years of age progressed to 60 degrees, while only 13% of those with a curve less than 40 degrees by 15 years of age progressed to 60 degrees.⁴ Curve progression increases the magnitude of deforming forces and leads to subsequent deformity, truncal imbalance, and pelvic decompensation. The pelvis is often the end vertebra equivalent—the most tilted component with residual axial rotation of the C curve. This was described as the pelvic vertebra by Dubousset.⁵ Less frequently, pelvic obliquity presents as a compensatory fractional curve to the C curve. Pelvic obliquity alters sitting position and pressure at the typically well-distributed sitting tripod at both ischial tuberosities and pubic symphysis. Increased pressure at the ipsilateral ischial tuberosity is worsened in patients with increased pelvic tilt and can result in pressure sores.

Table 7.1 Causes of neuromuscular scoliosis

Generally, neuromuscular scoliosis develops at an earlier age than adolescent idiopathic scoliosis, but can present between 3 and 20 years of age.⁴ The flexible, postural curve tends to develop into a torsional, structural deformity with growth and finally into a stiff curve of considerable magnitude before growth is complete. Generally speaking, more severe forms of cerebral palsy are associated with greater degrees of deformity. Considering the physiological classification of CP, spastic quadriplegic patients have the highest incidence of scoliosis. Madigan and Wallace found a 64% incidence of scoliosis in institutionalized patients with CP.⁶ The risk of scoliosis correlates with ambulatory ability as graded by the Gross Motor Function Classification System (GMFCS). Children with mild gross motor function limitation have no higher risk of developing scoliosis than the general population, whereas those with limited motor function (GMFCS levels IV and V) have approximately 50% risk of developing moderate or severe scoliosis.¹

Depending on the dominant deforming forces and spasticity, patients may present with either kyphoscoliosis or lordoscoliosis. In kyphoscoliosis, progressive deformity with associated pelvic obliquity and retroversion may compromise the often-limited ambulatory function. Pelvic obliquity makes sitting difficult or even impossible. In lordoscoliosis, a patient may have extensor posturing. Progressive deformity makes sitting impossible. Patients may need to be nursed in a semi-reclined position in a wheelchair. These patients may have acute pain without relief from any sitting adaptation. Significant deformity may compromise cardiopulmonary function, gastrointestinal motility, and result in rib–pelvis impingement. Upon identification of the deformity, the most important clinical determinations are flexibility of the curve and remaining growth potential. Flexibility is determined by holding the patient up at the axillae in a sitting position or side bending over a fulcrum with the child relaxed. Pelvic obliquity is assessed by positioning the patient prone with the hips and knees hanging free. Infrapelvic causes of pelvic obliquity include hip subluxation and dislocation as well as adductor contracture. Suprapelvic causes of pelvic obliquity are from scoliosis itself. Standing 36-inch posteroanterior (PA) and lateral radiographs of the entire spine should be obtained when possible. Sitting radiographs are acceptable substitutes if the patient is unable to stand, and “sitting frames” with lateral support straps are used in some centers to obtain these with minimal external support. Curve characteristics to be noted are curve type, magnitude, and progression. Sagittal and coronal balance as well as pelvic obliquity and tilt and signs of remaining growth (triradiate cartilage and Risser’s sign) should be documented. Structural deformity is commonly detected by vertebral rotation, rib deformity, and wedging. Neuromuscular scoliosis secondary to CP should be monitored at a minimum of yearly follow-up examinations to determine curve progression, but 6-month follow-ups are appropriate for progressive or severe deformities, or for children in the midst of rapid growth during the onset of puberty. Magnetic resonance imaging (MRI) should be obtained if any suspicion for intraspinal pathology exists. Signs of intraspinal pathology include very rapid progression at a young age, increasing lumbar hyperlordosis, or a change in neurological status that may be expected with a tethered cord.

7.4 Classification of Neuromuscular Scoliosis in Cerebral Palsy

Lonstein and Akbarnia⁷ have classified neuromuscular scoliosis secondary to CP into two groups ( Fig. 7.1). Group I curves are double curves with both thoracic and lumbar components, also known as “S curves.” These curves tend to behave similar to idiopathic scoliotic curves and have a higher likelihood of preservation of ambulation ability. Group II curves have lumbar or thoracolumbar deformity that extend into the sacrum and have associated pelvic obliquity, also known as “C curves.” The long, sweeping, and collapsing curves are more typical of neuromuscular curves in patients who are wheelchair-dependent or bedridden. The apex of these curves is centered in the thoracic spine (T2–T10) or at the thoracolumbar junction (T11–L1) and have a right-sided apex. See Fig. 7.1 for examples of groups I and II curves. The majority (94%) of patients with CP who required surgery due to pelvic obliquity, poor coronal balance, and a large magnitude of curve are categorized as group II curves.⁶

7.5 Nonoperative Treatment

Pain relief, functional preservation (including sitting ability and postural control), and allowance for daily hygienic and nutritional care are of utmost importance when caring for these patients. A near-normal chin-brow vertical angle allows for visual and cognitive stimulations with motor response. Curves with less than 20 degrees of deformity are reasonable candidates for observation. Bracing is an option for patients that progress with observation, but this is dependent on the severity of the curve and neurological involvement. Spastic quadriplegic patients generally do not benefit long term from bracing. Rigid thoracolumbosacral orthoses (TLSOs) have been found to have little benefit on curve or rate of progression in patients that were braced 23 hours per day over greater than 5 years compared to observation alone.⁸ Contrastingly, Terjesen et al⁹ performed a retrospective cohort study of 86 patients with spastic quadriplegic CP and found a mean progression of 4.2 degrees per year with custom-molded TLSOs, 25% of patients less than 1 degree per year of progression per year. Soft TLSOs can assist with seating support and augment function. Improved sitting function can help with attentiveness in class, ease of care, self-image, and decreased rates of pressure ulcers. Children with flexible curves that require seating support can be fitted for offset lateral chest supports and modular seating systems on their wheelchairs. This will allow for three-point control of the coronal deformity. In ambulatory children with GMFCS I to III, rigid bracing may slow the progression of the deformity similarly to adolescent idiopathic scoliosis. Braces are commonly indicated for curves of 25 degrees or more in immature patients with significant growth remaining and should be worn for a minimum of 12 hours per day, although the optimal brace wear time is 16 to 18 hours per day. Therapeutic stretching, electrical stimulation, and botulinum toxin are lacking validity and have limited supported utility at this time.

Fig. 7.1 Curve patterns in neuromuscular scoliosis secondary to cerebral palsy. Group I curves are double curves with little pelvic obliquity that may be balanced (a) or unbalanced (b). Group II curves (c,d) are large lumbar or thoracolumbar curves with marked pelvic obliquity. (Adapted from Lonstein and Akbarnia.⁷)

7.6 Rationale for Operative Treatment

Interventions should always be weighted by assessing functional health gain, patient satisfaction, and technical success.¹⁰ All decisions to proceed with operative care for these patients should be aimed at maintaining functional health against the progressive deformity and its associated morbidity, achieving reasonable patient–caregiver satisfaction, and minimizing complications. For higher functioning patients, the goal may be different. These patients may desire more normal spinal balance, preservation of function, and greater ambulatory potential. For patients with no ambulatory potential, the aim should be to maintain independence in sitting and facilitation in care. The burden of care in this group of patients with severe learning disability may change significantly.^11,12 Surgery in this group is a palliative measure that allows families to independently care for their children at home and to keep their child involved in school and community activities. Larsson et al¹¹ discovered that overall care burden was decreased and sitting position and vital capacity were improved in patients with neuromuscular scoliosis who underwent operative treatment in a prospective cohort study. In another study of 100 spastic CP patients who underwent spinal fusion, 85% of parents interviewed indicated that they were satisfied with the result and would opt for surgery again.¹³ Caregivers believed that patients had an improved self-image. Parents and caregivers believed that surgery improved sitting ability, physical appearance, comfort, and ease of care. These results were confirmed by other studies.^14,15,16

7.7 Surgical Treatment

Surgical intervention is considered when curve magnitude exceeds 50 degrees and there is concomitant deterioration in function.^13,17,18 Even with completion of growth, there is ample evidence that these curves will progress. For curves between 60 and 90 degrees, surgery is indicated when the deformity is rigid even with remaining growth. If flexibility remains during growth, surgery can usually be delayed until 90 degrees of deformity with a posterior-only procedure. In patients with flexible curves greater than 90 degrees, sitting may be challenging and further exacerbated by the associated pelvic obliquity. Specific considerations include the level of instrumentation, early-onset scoliosis, sagittal deformity correction, pelvic and infrapelvic coronal deformity, intraoperative neuromonitoring, necessity of anterior release, intraoperative femoral traction, and intrathecal baclofen therapy.

Patients with neuromuscular scoliosis who are indicated for surgery typically undergo long-construct fusions from T1 or T2 to the sacrum and pelvis. Increased postoperative incidence of proximal curve progression and proximal junctional kyphosis has been observed if the proximal instrumented vertebra does not extend to T2 or higher, since most of these children lack adequate head control.¹⁹ Patients with pathological thoracic kyphosis may be better candidates for extension of the construct to C7. There is historical debate regarding extension of posterior spinal fusion to the pelvis. Pelvic obliquity has been shown to progress when fusion does not extend to the pelvis^3,17,20; furthermore, late revision reconstruction to the pelvis for add-on can be challenging and fraught with complications. Extension of fusion to the pelvis has been recommended in nonambulatory patients. In ambulatory patients with pelvic obliquity, extension of the fusion to the pelvis has been avoided due to concerns that it will negatively impact ambulatory function.^1,21 However, a study utilizing gait analysis at our institution demonstrated preserved ambulatory function in these patients after unit rod instrumentation to the pelvis.²² In patients who use the gluteus maximus to propel their gait due to a weak gastrocnemius, instrumentation to L5 can be considered. McCall and Hayes investigated the results of the use of a “U rod” (a unit rod construct lacking pelvic limbs) with L5 pedicle screw fixation in patients with a stable lumbosacral articulation. the L5-S1 interspace mobility was assessed on the basis of L5 tilt. Patients with more than 15 degrees of L5 tilt were instrumented with standard unit rod construct instead. Patients had similar results in both groups.²³

7.7.2 Early-Onset Scoliosis in Cerebral Palsy

Severe curves in prepubertal growth present a management dilemma. Continued observation, surgical intervention with growth-friendly spinal implants to control the curves, or early correction and fusion are all options. In one study of growing rods in CP patients, 27 patients at a mean 7.6 years of age had a 47% correction of the Cobb angle from a mean 85 degrees. However, 19 of these patients had complications, including 8 deep wound infections, 11 rod-related complications, and 6 anchor-related complications.¹⁸ There have been similar complication rates utilizing the “Eiffel Tower” vertical expandable prosthetic titanium rib (VEPTR) construct.²⁴ In one study examining early spinal fusion in 33 patients at a mean 8.3 years of age with mean Cobb’s angle of 85 degrees and minimum 5 years of follow-up with all but 2 patients being GMFCS V, there was a 28% mortality rate, with 6 patients dying between 1 and 5 years and 2 between 10 and 15 years after surgery.²⁵ Deep infection was reported in three patients. Although the ideal management plan has not been elucidated, the recently approved magnetically controlled growing rod systems that do not require repeat surgeries for lengthening purposes have been in use long enough for short-to-medium-term follow-up. Short-term studies suggest minimal proximal pullout, revision surgery, and outpatient distraction complications.^26,27,28 Generally, these authors preferred the rate of revision surgeries with magnetic growing rods as compared to those experienced with traditional growing rod systems. However, the study with the longest follow-up to our knowledge (minimum 44 months) had more sobering results. Teoh et al²⁹ reported on eight patients (five dual-rod constructs and three single-rod constructs), of which six required eight revision surgeries. These revisions were performed for rod problems (4), proximal screw pullout (3), and development of proximal junctional kyphosis (1). These authors advised using caution for utilizing magnetically controlled growing rod systems, especially for single-rod constructs.

7.7.3 Sagittal Plane Deformities

Hyperkyphosis or lordosis may develop in patients with neuromuscular disorders, with or without scoliosis. Flexible, postural deformities may be addressed in younger patients with hamstring contractures by lengthening the posterior thigh musculature and addressing the associated posterior pelvic tilt and retroversion or by wheelchair or shoulder harness modifications. However, these adaptations may not work as well in older children. The spinal column lengthens with lumbar hyperlordosis correction and shortens with hyperkyphosis correction. Tethered cord must be evaluated prior to surgical correction of lumbar hyperlordosis. Patients who have undergone a previous dorsal rhizotomy for spasticity are at an increased risk for developing pathological hyperlordosis and associated spondylolisthesis, which impact the posterior surgical exposure. Postoperative radiculitis may develop after correction of hyperlordosis and relative lengthening of the lumbar spine from nerve root tension. Lumbar hyperlordosis and associated pelvic anteversion and obliquity alter the trajectory of pelvic fixation, which is a risk factor for pelvic fixation-related complications.³⁰ Bowel perforation following medial breach of the ilium by the pelvic limbs of the unit rod has been described. Modular screw-based systems are recommended to decrease morbidity with pelvic screw placement, allow customization, and afford deformity correction.³¹

7.7.4 Pelvic and Infrapelvic Coronal Plane Deformities

Compensatory scoliosis arises from coronal plane deformities of the pelvic and infrapelvic origin. Asymmetric forces of the gluteus medius and hip adductors as well as infrapelvic pathology, including hip subluxation or dislocation contribute to pelvic obliquity. Adductor and iliopsoas release may be attempted to achieve femoral head coverage and pelvic leveling in young patients. Osteotomy of the proximal femur and pelvis may be required in older age as deformities become stiff. In these cases, spinal deformity correction should be performed prior to pelvic osteotomies for femoral head coverage.

7.7.5 Intraoperative Neuromonitoring

Spinal cord monitoring with intraoperative transcranial motor evoked potentials and somatosensory evoked potentials is controversial in this population since meaningful monitoring is difficult.³² Thirty percent of patients with severe CP may have weak or absent signals at baseline, particularly transcranial motor evoked potentials in the most severely affected children.^33,34 Intraoperative neuromonitoring changes present a management dilemma. The Stagnara wake-up test is usually not possible.³⁵ In patients that respond to intraoperative optimization of physiological parameters and surgical correction, it could potentially advert neurogenic bladder requiring urinary catheterization and maintain protective sensation even in the most neurologically involved patients. In patients who have lost signals despite optimization, staging the procedure versus in situ correction are both options and debatable. Involvement of the family in decision making is helpful to determine the best plan of care.

7.7.6 Anterior Release

Anterior release at the apical levels is indicated for stiff curves or curves greater than 90 degrees not reducible with a pull or fulcrum bend film to gain flexibility and allow correction. Anterior release at the lumbosacral region includes psoas muscle origin release, annulus release, and complete discectomy. These assist in correcting both pelvic obliquity and pelvic tilt.³⁶ Anterior surgery is associated with increased complications and morbidity. Higher rates of pulmonary and cardiovascular (coagulopathy and hypotension) complications have been reported with anterior releases.³⁷ Thoracoscopic anterior release is possible from the intervertebral disc of T4-5 to T11-12 and can reduce operative time and morbidity associated with open thoracotomy. When both anterior and posterior procedures are required, it is important to consider that evidence supports both staged (1–2 weeks apart) and same-day surgery. Some prefer the staged approach for patients with multiple medical comorbidities and severe CP.³⁸ Same-day surgery may be planned for patients with relatively good health, but may need to be reconsidered for staging with excess operative time or blood loss after the anterior release is performed. Anterior fusion to prevent crankshaft phenomenon is not necessary when rigid, segmental instrumentation with a unit rod or with pedicle screws to the pelvis is used.^39,40,41

7.7.7 Intraoperative Halofemoral Traction

Patients with kyphoscoliosis or significant pelvic obliquity can benefit from intraoperative traction.^37,42,43 In patients with lumbar hyperlordosis, bilateral use should be avoided so as to not worsen the lordosis. Unilateral traction prior to corrective maneuvers may assist in leveling the pelvis. Traction can be applied proximally through the skull with a halo or cranial tongs and distally with femoral pins, lower extremity skin taping, or securing the feet and ankles in boots attached to the operative table.

7.7.8 Intrathecal Baclofen Pump

Intrathecal baclofen is utilized to control muscle spasticity while maintaining muscle function. Patients with intrathecal baclofen pumps must have adequate padding at the pump site for prone positioning. Concurrent pump insertion during spinal deformity surgery does not increase infection risk.⁴⁴ No significant cerebral spinal fluid leak should be encountered during the insertion of the intrathecal catheter component. The pump and connecting tubing at the intrathecal sac can be safely inserted or exchanged postspinal fusion below the conus medullaris.

7.8 Surgical Advances and Outcomes

When no other alternatives would be viable, spinal instrumentation and fusion are indicated for collapsing deformities and painful sitting.⁴⁵ Harrington rods had an unacceptably high rate of pseudarthrosis (18–27%).^7,13,46,47 Segmental instrumentation with Luque’s rods and sublaminar wiring had better results than the Harrington instrumentation and obviated the need for prolonged postoperative casting.^{15,48,49,50,51} Comparing cohorts who underwent posterior-only instrumentation to a combined anterior–posterior cohort, Comstock et al found a mean correction of 51 and 57%, respectively.¹³

Progression of pelvic obliquity has been noted when the fusion does not extend to the pelvis.^13,15,20 The Galveston technique to extend the fusion across the pelvis by placing each Luque’s rod between the pelvic tables had acceptable fusion rates across the L5-S1 segment and provided good control of pelvic obliquity.⁵² However, it was associated with a high incidence of loosening associated with micromotion at the sacroiliac joints, leading to the radiographic “windshield-wiper” effect. Impacting two Luque’s rods into the pelvis with segmental fusion utilizing sublaminar wiring provides a strong construct in the sagittal plane, but a moment arm of rotation about the two rods allows for rod translation, loss of torsional control, and subsequent progression of pelvic obliquity, pseudarthrosis, and implant failure.⁵³ Luque’s rods smaller than one-fourth of an inch in diameter may be associated with increased implant failure.^20,48,54 However, intraoperative bending of one-fourth of an inch in diameter to the ideal geometry for pelvic implantation is challenging. Lonstein et al found in a cohort of 93 patients with 50% correction of the major scoliotic curve with a mean preoperative scoliosis of 72 degrees and 40% correction of pelvic obliquity at a mean follow-up of 3.8 years using a dual Luque–Galveston technique.⁵⁵ Sanders et al found that postoperative residual curve greater than 35 degrees, preoperative curves greater than 60 degrees, crankshaft deformity, and not fusing to the pelvis were all predictive of postoperative curve progression.²⁰

Bell et al developed the unit rod and this addressed some of the limitation of the dual Luque rod instrumentation.⁵³ The major design change was a proximally connected, precontoured rod that provided better rotational control compared to the independent rotational freedom between the dual Luque rods. Tsirikos et al observed a mean correction of 68% from a mean scoliotic curve of 76 degrees and pelvic obliquity correction of 71% at a mean follow-up of 3.9 years in 241 patients, which was more effective than the dual Luque rod instrumentation.³⁰ Westerlund and Dias found similar results.^39,41

Segmental instrumentation using Cotrel–Dubousset instrumentation of hooks is limited to patients with S-shaped curves without the need to extend to the pelvis. Hybrid constructs using iliosacral screws for pelvic fixation with hooks allows for 40% correction of pelvic obliquity with a posterior approach and 47% correction using a combined anterior–posterior approach.^56,57 There is a tendency of in situ rod derotation in restoring coronal correction, which does not allow a significant biomechanical advantage in reducing pelvic obliquity over a unit rod with sublaminar wires.

Iliac screws were borne from the smooth Galveston rods and iliosacral screws. They require less dissection and have better pullout strength than Galveston’s rods for pelvic fixation because they extend anteriorly beyond the pivot point of lumbosacral motion.⁵⁸ Galveston’s rods may pull out and become prominent posteriorly. Segmental pedicle screw constructs have shown substantial improvement in fusion at the lumbosacral junction while correcting pelvic obliquity and addressing seating problems. The modular nature of these systems can help with the management of osteoporotic bone, three-dimensional deformity of the pelvis (e.g., rotated pelvis), and lumbar hyperlordosis which can help to avoid early hardware failure.⁵⁹ The iliac screws are offset and connected to the rods via a connector. Careful rod engagement with adequate length distal to the tulip head of the connector is required to avoid disengagement. The use of four iliac screws at the pelvis improved bony purchase but did not eliminate loosening.⁶⁰ Implant prominence can be a problem in thin patients. Placement of the screw caudad to the natural prominence of the posterior superior iliac spine (PSIS) with bony resection may avoid this problem.

Kebaish et al popularized sacral alar–iliac (S2AI) fixation, which has the advantage of an iliac screw without the prominence, since it is placed 15 mm deeper to the PSIS.^61,62 Additionally, soft-tissue dissection is less and pullout strength is similar to an iliac screw. The screw extends across the sacroiliac joint anteriorly beyond the pivot point of the lumbosacral junction and serves as an effective flexion moment against movement at the lumbosacral junction. The tulip screw head is aligned with the instrumentation array without need for an offset connector.

Lumbar pedicle screws with reduction tabs allow for effective sagittal and coronal control while allowing reduction of pelvic obliquity when used in concert with either iliac or S2AI screws. This is particularly useful for lumbar hyperlordosis and pelvic anteversion where the trajectory of the iliac anchor would be challenging. Tsirikos and Mains demonstrated 72% correction of the major curve with a mean preoperative curve of 76 degrees along with 80% correction of pelvic obliquity from a mean preoperative 22 degrees in a cohort of adolescent CP patients who underwent correction with posterior-only pedicle screw constructs.³¹ Pedicle screw-based modular constructs allow for superior Cobb’s correction and leveling the pelvic obliquity, but the initial cost of these systems is much greater than the unit rod. However, this is offset in the long term by less implant-related complications and a lower rate of infection as demonstrated in a multicenter series.⁶³ Aside from pulmonary issues, implant-related complications and infection are the two most common complications in the operative treatment of neuromuscular scoliosis.⁶⁴

At our institution, hybrid constructs and all pedicle screw systems achieved similar results. Pedicle screws are inserted at the most caudad thoracic and lumbar vertebrae. Sacropelvic fixation is obtained with S2AI screws. A stable pelvic fixation allows a strong cantilever force to level the pelvis using dual custom rods, which are proximally connected. The reduction of the rods starts at the caudad lumbar screws and proceeds in the cephalad direction. Intervening thoracic levels are instrumented with sublaminar wiring or staggered pedicle screws. An all screw construct is used when significant correction is needed in the thoracic vertebrae.

7.9 Perioperative Management

Children with neuromuscular scoliosis tend to be medically complex and have significant preoperative risks. Risks and complications of the procedure are directly related to the severity of neurological impairment. Patients requiring nutrition through gastric or jejunal tubes, those with severe intellectual disability, lacking verbal communication and independent sitting, and epilepsy have the highest rate of complications.⁶⁵ Seizures, respiratory issues, nutritional deficiencies, gastroesophageal reflux, and gastric motility issues should be addressed preoperatively. Anesthesiologists should be made aware of children who are on ketogenic diets for seizure control, as these patients are at high risk of hypoglycemic episodes intraoperatively.

Preoperative laboratory evaluations should include a complete blood count, complete metabolic profile, urinalysis, coagulation profile, and albumin and prealbumin levels. Blood loss can be significant and a type and crossmatch of 1 to 1.5 times the patient’s blood volume should be available prior to surgery.⁴⁵ Coagulation factor replacement and core body temperature should be maintained. Despite normal prothrombin time (PT) and partial thromboplastin time (PTT) values, blood loss tends to occur earlier and in larger quantity in this population.^66,67 Cell salvage and antifibrinolytics are useful adjuncts in decreasing allogenic transfusion and blood loss.^68,69 Tranexamic acid (TXA) has been shown to be more effective than epsilon–aminocaproic acid (AMICAR) with the loading dose of 100 mg/kg over 30 minutes followed by 10 mg/kg infusion until closure.⁷⁰ This infusion should be limited to 8 hours.

Intraoperatively, the surgeon should strive to constantly communicate with the anesthesia staff. Intraoperative hypothermia is the most commonly encountered issue by the anesthesiologist, reported as high as 55%.⁷¹ This may contribute to coagulopathy, and active warming blankets with monitoring are useful to prevent hypothermia without raising the core body temperature too high. The patient is most at risk of hypothermia during induction of anesthesia and while intravenous (IV) access is being obtained prior to skin preparation and draping. Intraoperative hypotension is encountered in 15% of cases, usually related to inadequate volume replacement from chronic dehydration, increased sensitivity to anesthetic agents, and increased blood loss. Correction of kyphosis can also impede venous return to the heart and lead to hypotension, but this can be prevented by increasing the preload volume prior to the correction.⁴⁵ When hypotension during curve correction is encountered, an attempt to release pressure on the spine should be performed while increasing the rate or IV fluid and/or blood replacement. After the blood pressure has been stable for 5 to 10 minutes, it is typically safe to proceed with gradual correction after the soft tissue has creeped. If sudden hypotension with or without bradycardia occurs, anaphylaxis should be considered; unknown latex allergies are common among these patients, but reactions to colloid or blood product replacement are also possible.

Parents and caretakers are frequently not prepared for the complexity or duration of the patient’s postoperative course.¹³ Preoperative counseling of the family and caretakers should stress the potential or expectation of a prolonged intensive care unit (ICU) stay, as well as the significant possibility or anticipation of postoperative complications.

7.10 Surgical Technique

After intubation and induction of anesthesia, neuromonitoring lead placement, urinary catheterization, and the establishment of large-bore IV access, central venous catheterization (when necessary), and arterial line placement, the patient is positioned prone on a radiolucent table or four post frames. All bony prominences are padded to avoid skin breakdown. The abdomen should hang free and the hips can be allowed to gently flex with knee and thigh support to correct lumbar hyperlordosis. A free abdomen will decrease intraoperative blood loss by reducing inferior vena caval pressure.^72,73,74 Unilateral intraoperative skin traction can be utilized on the side with high pelvic obliquity during the corrective maneuver, if necessary.

After IV antibiotic and TXA administration, a standard posterior exposure to the spine is undertaken from T1 to the sacrum. Subperiosteal elevation is utilized out to the transverse processes with Cobb’s elevators. Electrocautery is used for hemostasis. The use of bipolar sealer devices should be considered, as their use has been correlated with decreased blood loss and transfusion requirements.⁷⁵ The cephalad supra- and interspinous ligaments are preserved in an effort to prevent proximal junctional kyphosis. Aggressive posterior release with facetectomies and ligamentum flavum resection creates flexibility in the rigid apical portion of the curve. Facetectomies can be performed with a rongeur, osteotome, burr, or ultrasonic bone cutting device. This should proceed from L5 to S1 in a cephalad direction to the level below the upper instrumented vertebrae. Gelfoam soaked in thrombin or other hemostatic agents can be used to control local bleeding. If additional deformity correction is needed, posterior column osteotomies (PCOs) may be performed by removing the facet in its entirety, along with the supra- and interspinous ligament, and ligamentum flavum with a combination of a Kerrison rongeur and burr.⁷⁶ The senior author uses an ultrasonic bone cutting device for the PCO. Concave osteotomy at the apical segments may be necessary. Concave release of the taut iliolumbar ligaments at the tip of the L5 transverse process may be needed for severe, stiff pelvic obliquity.

If traditional iliac screw fixation is opted for, the PSIS is next to be exposed. To avoid screw head prominence, an osteotome is used to resect a notch 1 cm caudad to the most prominent part of the PSIS. The cancellous bone between the pelvic tables is cannulated with a drill or pedicle gearshift. Successful iliac screw fixation is possible with a miniaccess approach to avoid extensive muscle dissection of the paraspinal musculature at the lumbosacral junction and outer table of the pelvis using intraoperative fluoroscopy. The “teardrop” of the ilium is visualized by tilting the image intensifier obliquely in the plane of the iliac wing and cephalad so that it is parallel to the cortical bone of the sciatic notch. Iliac screw placement in this area ensures excellent fixation in strong cancellous bone, adequate length to extend past the pivot point of the lumbosacral junction, and avoidance of the sciatic notch and acetabulum. The iliac screw is then connected to the thoracolumbar construct to level the pelvis.

If S2AI fixation is opted for, the exposure at the caudad incision is minimal. The starting point is at the midway of S1 and S2 foramen in line with the S1 pedicle screws. The screw traverses the sacroiliac joint and has the same endpoint as the iliac screw, pointing toward the anterior inferior iliac spine (AIIS) or greater trochanter for maximum purchase. The bony isthmus is usually at the 60-mm mark. A curved gearshift that points cephalad in relation to the plane of the ilium allows for longer screws to be inserted while gliding away from the direction of the hip joint.⁷⁷ A guidewire is then inserted prior to drill and screw insertion, with the typical screw size being 8 mm or more in diameter and at least 65 to 80 mm in length. In a neutral pelvis, 30 degrees of lateral angulation is expected, but this will need to be adjusted for rotational deformity. In hyperlordosis, a more horizontal trajectory will be needed.

Thoracic and lumbar pedicle screws are inserted with freehand technique.⁷⁸ The pars, mammillary bodies, and transverse processes are prepared. The pars interarticularis leads to the lumbar pedicle entry point at the intersection of the mid-transverse process and the mid-facet joints. A high-speed cortical burr is used to mark the starting point and penetrate the cortex. A curved gearshift is used to cannulate the entry point with the curve pointing laterally. Once 20 mm of depth is reached, the gearshift is removed to point medially. A pedicle probe is used to palpate superior, inferior, medial, lateral, and at the floor of the tract to ensure no breeches are appreciated. Polyaxial reduction pedicle screws are utilized for the lumbar vertebrae. For thoracic pedicles, a straight gearshift is used. The entry point of the thoracic pedicle screw is at the intersection of the mid-transverse process and slightly lateral to the mid-superior facet joint. Fluoroscopic guidance can be especially helpful for thoracic pedicle screw placement.

If sublaminar wire passage is to be performed, the spinous process of each thoracic level is removed to expose the ligamentum flavum. The laminae are preserved, as they are the basis of strength of fixation. The sublaminar space is exposed and sublaminar wires are passed at each level. Sixteen-gauge double Luque’s wires are passed at each level from T5 to T12. Wires are passed from inferior to superior after precontouring them with a radius of curvature that approximates the width of the lamina. Avoid levering off the lamina and impinging against the cord. The wire is then contoured back over the lamina and the ends of the wire are contoured to the edges of the incision, which prevents the wire from migrating away from the under-surface of the lamina as the remaining levels are instrumented. See Fig. 7.2 for an example of a pedicle screw and rod/sublaminar wire construct.

Custom-bent 5.5-mm cobalt chrome or stainless steel rods are typically used. Recognize that correction of a thoracic hyperkyphotic deformity will shorten the spine and the correction of a lumbar hyperlordotic deformity will lengthen the spine. Rods are differentially bent and connected to S2AI or iliac screws. A cross-link is placed at the cephalad part of the rods. The reduction-tab lumbar pedicle screws allow for insetting of the rod. The spine is corrected to the rod. Pushing the rod to the spine can generate substantial force at the lever arm of pelvic fixation and should be avoided to prevent fractures. Set screws over reduction pedicle screws are tightened in a cephalad direction, as are sublaminar wires (if applicable). If sublaminar wires are utilized, they should be cut 1-cm long and bent down to the lamina to avoid implant prominence. Any additional decortication can be performed at this time, followed by copious irrigation. Crushed autograft and allograft are packed posterolaterally. See Fig. 7.3 for an example of a pedicle screw and rod construct. Adding antibiotics such as vancomycin to bone graft is safe and effective for preventing acute deep wound infections.^79,80 Meticulous hemostasis and closure is performed. A drain may be utilized if meticulous hemostasis is not possible.

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