Pelvic Fixation for Neuromuscular Scoliosis

 

 

 

DEFINITION

Neuromuscular scoliosis (NMS) is a spinal deformity in the coronal plane in patients with abnormal myoneural pathways of the body.16

Pelvic fixation refers to the anchorage of spinal fixation to the sacrum or ilium or both.

 

 

ANATOMY

 

The pelvis can accommodate large screws that aid in the correction of pelvic obliquity while also providing a stable base in long fusion constructs.

 

In adolescents, the mean length of the sacral alar iliac (SAI) screw pathway is 106 mm, whereas that of the posterior superior iliac spine (PSIS) to anterior inferior iliac spine pathway (for standard iliac screws) is 123 mm (FIG 1).

 

The narrowest mean width of the ilium is 12 mm for the right or left side, indicating that the SAI pathway can accommodate large-diameter screws for increased bone purchase.

 

The average depth below the skin of the SAI screw insertion point is 52 mm, whereas that for the PSIS

insertion point7 is 37 mm. This difference of 1.5 cm is important for the patient with neuromuscular deformity who has vulnerable skin because he or she spends most of the time in a recumbent position.

 

It has been shown that intrapelvic asymmetry between the right and left side is common in patients with

NMS.12 A firm grasp not just of normal anatomy but also of the patient's individual anatomy is vital in placing screws in the right trajectory.

 

 

 

FIG 1 • In space, three-dimensional CT imaging of SAI pathway. (Modified from Chang TL, Sponseller PD, Kebaish KM, et al. Low profile pelvic fixation: anatomic parameters for SAI fixation versus traditional iliac fixation. Spine 2009;34:436-440.)

 

 

The sacroiliac joint is composed of hyaline cartilage anteriorly and fibrocartilage posteriorly. An SAI screw traverses the hyaline cartilage of the sacroiliac joint 60% of the time.21

PATHOGENESIS

 

The Scoliosis Research Society has classified the abnormal myoneural pathways that cause NMS into the following categories6:

 

Neuropathic

 

 

Upper motor neuron: cerebral palsy, spinocerebellar degeneration (Friedreich ataxia, Charcot-Marie-Tooth disease, Roussy-Lévy disease), syringomyelia, spinal cord tumors, spinal cord trauma, Rett syndrome

 

 

Lower motor neuron: poliomyelitis, traumatic, spinal muscular atrophy, dysautonomia Combined upper and lower pathologies: myelomeningocele

 

Myopathic

 

 

 

 

 

 

Arthrogryposis Muscular dystrophy Fiber-type disproportion Congenital hypotonia Myotonia dystrophica

NATURAL HISTORY

 

The rates of spinal deformity are high in patients with NMS, including 20% to 70% of patients with cerebral

palsy (depending on the amount of trunk control), 60% of patients with Friedreich ataxia, 80% of patients with spinal muscular atrophy, 86% of patients with familial dysautonomia, 50% to 90% of male patients with Duchenne muscular dystrophy, and nearly 100% of patients with traumatic quadriplegia or thoracic level

paraplegia before skeletal maturity.4

 

Unlike adolescent idiopathic scoliosis, most curves in patients with NMS tend to progress.

 

Pelvic obliquity of 15 degrees or more in patients with NMS will likely worsen after spinal fusion if pelvic fixation is not included as part of the instrumentation construct.18

PATIENT HISTORY AND PHYSICAL FINDINGS

 

The importance of understanding a patient's baseline function cannot be understated.

 

Patients with NMS have a wide range of motor and sensory function. Knowledge of this fact is important for postoperative comparison. This baseline should be recorded in the chart, and the patient should be reexamined immediately before surgery. Does he or she move the toes to command or only spontaneously? Is he or she able to ambulate? These questions should be answered by physical examination before surgery begins.

 

 

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FIG 2 • Standard preoperative radiographs to obtain before deformity correction in NMS. A. Anteroposterior upright radiograph of the neuromuscular curve. B. Lateral upright radiograph showing operative kyphosis and

lordosis. C. Anteroposterior radiograph of the patient in traction. Notice the improvement of the curve to approximately 75 degrees in the coronal plane as compared with the anteroposterior radiograph in A. D. Anteroposterior radiograph of the pelvis revealing the degree of pelvic obliquity and the location of the baclofen pump.

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

 

Standard posteroanterior and lateral 3-foot upright scoliosis radiographs (FIG 2A,B) should be obtained. The rigidity of the curve is assessed by obtaining traction or fulcrum radiographs (FIG 2C).

 

Pelvic obliquity, sagittal alignment, and the status of the patient's hips are assessed to help with positioning of the patient on the day of surgery (FIG 2D).

 

If a baclofen pump is present, the side it is on should be identified to help with the surgical approach.

DIFFERENTIAL DIAGNOSIS

It is important to make sure that the patient's scoliosis is truly neuromuscular and does not fall in other categories such as congenital, idiopathic, or syndromic scoliosis.

Congenital scoliosis is caused by a failure of vertebral formation or segmentation during the fourth to fifth week of gestation. Syndromic scoliosis is discerned by certain pathognomonic features of the suspected diagnosis such as the ligamentous laxity, arachnodactyly, and dolichostenomelia seen in Marfan syndrome.

 

 

NONOPERATIVE MANAGEMENT

 

Bracing

 

 

Bracing in patients with NMS is ineffective in preventing progression of the curve and resultant pelvic obliquity.22

 

If bracing is used, it is often a soft thoracolumbosacral orthosis to help with sitting balance for a flexible curve.

 

Additional nonoperative interventions include sitting supports, custom seating, and functional sitting programs.9

SURGICAL MANAGEMENT

 

Posterior spinal fusion has not been shown to prolong the life of patients with NMS, but it often increases the quality of life through improving trunk balance, sitting position, and comfort; through correction of pelvic obliquity; and by prevention of further progression of their curve.20, 24

 

Historically, fusion to the pelvis was thought to be difficult with associated poor outcomes; however, major advances in spinal fusion techniques have improved outcomes significantly.

 

 

In the 1980s, Luque14 introduced segmental spinal instrumentation using sublaminar wires to better control progressive deformity in patients with postpoliomyelitic scoliosis.

 

The Cotrel-Dubousset instrumentation system8 further expounded on Luque's findings by adding hooks and pedicle screws to the construct and introducing the concept of derotation of the spinal deformity.

 

In 1988, Allen and Ferguson1 introduced the Galveston technique, involving fixation to the pelvis using an L-shaped rod inserted at the PSIS and placed between the inner and outer tables of the ilium. The Galveston technique improved caudal fixation in long fusions and brought to the forefront the importance of pelvic fixation.

 

In 1989, Bell et al3 built on the Galveston technique with the unit rod, which was one continuous rod with precontoured bends for kyphosis and for fixation to the pelvis. It was developed to counteract translation of one rod with

 

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respect to the other and to resist rotation of the pelvis around the caudal ends.

 

 

The iliosacral screw11 was a natural progression and provided increased caudal purchase because it

traversed both cortices of the ilium before entering the S1 pedicle. Its main disadvantage was the extensive soft tissue dissection required to place it in the correct position.

 

The most recent development in pelvic fixation is the SAI screw.

 

 

Its start point is on the sacrum, avoiding the extensive soft tissue dissection needed to use the PSIS as a start point.

 

As described by McCord et al,17 the stiffness of a construct connected caudally to SAI screws is greatly increased because of the marked anterior extension past the lumbosacral pivot point.

 

The start point for the SAI screw is 1.5 cm deeper than that the unit rod, avoiding many of the complications associated with the latter, such as prominence and backout.

 

Implants used for SAI fixation may include standard large screws, cannulated screws, and favored-angle screws. Some have a smooth shank and others have a dual-lead thread.

 

Preoperative Planning

 

The decision to fuse to the pelvis depends on the curve pattern and preoperative trunk control. Curves with an apex above the thoracolumbar junction and an end vertebra above L4 may not require fusion to the pelvis.

Patients with NMS who have a reasonable ability to sit independently with a balanced pelvis may not require fusion to the pelvis, especially if it would limit their function.

 

Preoperative traction radiographs help to determine the flexibility of the curve, but the curves of most patients with NMS progress caudally if left unfused, so extension down to S2 is common.

 

Another variable is from how far cephalad to fuse. As a general rule, all vertebrae within the main coronal and sagittal curves, as well as any proximal thoracic curve larger than approximately 30 to 35 degrees, should be included in the fusion.

 

The decision on whether or not to use traction via Gardner-Wells tongs should be made during preoperative planning. It is our preference to use proximal traction via Gardner-Wells tongs for all patients with NMS undergoing primary posterior spinal fusion.

 

 

 

FIG 3 • Positioning the patient for surgery. A. When positioning the patient on the modified Jackson table, the clinician should place the superior pad three fingerbreadths below the sternal notch, the middle pad under the anterior superior iliac spine, and the inferior pad under the midthigh (not pictured). B. The patient's legs can be placed in a padded sling, which can be tightened or loosened to affect the amount of lordosis assumed intraoperatively after the posterior elements have been released. C. Once the patient is turned to the prone position, the desired amount of weight is added to the rope attached to the Gardner-Wells tongs.

 

 

Some degrees of pelvic obliquity can be corrected with distally in addition to proximal traction. The senior author prefers to use skin traction when distal traction is required. A prerequisite for use of distal extremity traction is the absence of hip or knee flexion contractures greater than 30 degrees.

 

The use of antifibrinolytic agents such as tranexamic acid, aprotinin, or epsilon-aminocaproic acid should be decided on preoperatively.

 

 

Tranexamic acid has been shown to decrease blood loss and the need for transfused blood products in patients requiring vertebral column resections for the correction of their deformity.19

 

Tranexamic acid works by competitively binding to and inhibiting plasminogen and plasmin, which would otherwise break down fibrin, the principle component of clot formation in the body.

 

Positioning

 

Starting 1 cm superior to the pinna, the skin is injected down to the skull with approximately 1 mL of lidocaine. While the patient is supine, Gardner-Wells tongs are placed at the anesthetized sites and the screws are tightened to the appropriate torque.

 

The patient is turned, and the pads are adjusted on the modified Jackson table so that the superior pad is three finger-breadths below the sternal notch, the middle pad is under the anterior superior iliac spine, and the inferior pad is under the midthigh (FIG 3A).

 

The distal legs are placed in a padded sling, which can be tightened or loosened to affect the amount of lordosis assumed intraoperatively after the posterior elements have been released (FIG 3B).

 

Once the patient is properly positioned, weight is attached to the Gardner-Wells tongs (FIG 3C).

 

 

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Approach

 

The approach is performed by standard technique with a midline incision down to the spinous processes, with subperiosteal dissection.

 

When exposing the sacrum, it is often helpful to place a bend in the electrocautery to assist in removing the soft tissues from the sacral surface. The clinician should be alert for spina bifida occulta in the sacrum, which occurs in up to 12.4% of the population.10

 

Before any pedicle screws are placed, it is important to decide whether correction of the patient's deformity will be made from distal to proximal or from proximal to distal. The senior author prefers to correct from distal to proximal; however, the other approach is used if the patient has substantial proximal thoracic kyphosis or focal proximal thoracic scoliosis.

 

TECHNIQUES

• Placement of S1 Screws

   

  Once the sacrum is exposed, a distractor is placed between the spinous processes of L5 and S1. If it is truly at the correct level, the sacrum will move as one complete unit during gentle distraction.

   

  The start point for the S1 screw is at the base of the superior articular process of S1 (TECH FIG 1A).

   

  The path is initially made with a starting awl and then widened with a dilator or tapped. The trajectory should be angled 25 degrees medially and toward the sacral promontory, which has been shown to

  increase insertional torque by up to 99%.13 The ideal position for the tip of the screw is in the cortical bone at the acute angle of the anterior sacrum with its endplate. The screw at this level is typically 7 to 8 mm in diameter ( TECH FIG 1B).

   

   

   

  TECH FIG 1 • Technique for placement of S1 screw. A. The start point for the S1 screw (red dot) is at the base of the superior articular process of S1. B. With a start point at the base of the superior articular process of S1, a starting awl is used to create the screw pathway, aiming 25 degrees medially and

  toward the sacral promontory. C. Final position of S1 screws.

   

   

  Finally, the S1 pedicle screw is inserted and the head is turned until the opening for the rod is in line with the future position of the rod (TECH FIG 1C).

• Placement of Sacral Alar Iliac Screws

   

  The typical start point for the SAI screw is 25 mm inferior to the S1 endplate and 22 mm lateral from the midpoint of the S2 body (TECH FIG 2A).

   

  With the starting awl and a trajectory angled 40 degrees laterally and 40 degrees caudally, the desired screw pathway is created (TECH FIG 2B).

   

  Mild resistance will be felt crossing the sacroiliac joint with the awl. If too much resistance is felt after passing the sacroiliac joint, it is from the lateral table of the ilium. If this occurs, the awl should be backed out and the trajectory should be made more vertical to avoid hitting the lateral wall.

   

  Fluoroscopy is used to confirm that the awl is in the desired position in the ilium. The awl should cross the sacroiliac joint and the ilium just cranial to the sciatic notch (TECH FIG 2C).

   

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  A depth gauge is used to measure the length of the screw pathway. The senior author prefers to place screws 90 mm in length, with diameters of 8, 9, or 10 mm. Doing so allows the pelvis to be manipulated when correcting pelvic obliquity, even in the presence of osteoporosis.

   

  A guidewire is inserted, and fluoroscopy is used to confirm it is still in the desired screw trajectory (TECH FIG 2D,E).

   

   

   

  TECH FIG 2 • Technique for placement of SAI. A. The start point for the SAI screw (red dot) is 25 mm inferior to the S1 endplate and 22 mm lateral from the midpoint of the S2 body. B. The starting awl is used to create the desired screw pathway with a trajectory angled 40 degrees laterally and 40 degrees caudally. C. The desired trajectory is confirmed while advancing the starting awl under fluoroscopy. D. The guidewire is inserted and impacted into the anterolateral bone of the SAI screw pathway. E. It is confirmed under fluoroscopy that the guide-wire is still in the desired trajectory. F. The SAI screw is inserted over the guidewire and advanced into the sacrum and ilium. G. It is confirmed fluoroscopically that the guidewire is not bending while the SAI screw is advanced.

   

   

  The screw is inserted over the guidewire, and another fluoroscopic image is obtained to confirm that the guidewire is not bending (TECH FIG 2F,G). Before the screw is advanced completely, a sternal needle driver is used to partially pull out the guidewire.

   

  The SAI screw should be advanced until the top of the screw is at the same height as, and in line with, the S1 and L5 pedicle screws.

   

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• Confirmation of Sacral Alar Iliac Screw Position

   

  With time and repetition, it is possible to know by tactile feel alone that the SAI screw is within the column of bone in the ilium.

   

   

   

  TECH FIG 3 • A teardrop view is obtained to confirm the placement of the SAI screw by advancing the Carm 30 degrees over the top of the patient so that it is colinear with the head of the SAI screw. Then the top of the C-arm is lowered 30 degrees closer to the patient's body.

   

   

   

  If radiographic confirmation is desired, the C-arm should be positioned for a “teardrop view.” The C-arm is advanced 30 degrees over the top of the patient.

   

  Then, the radiology technician lowers the top of the C-arm 30 degrees closer to the patient's body

  (TECH FIG 3).

• Correction of Pelvic Obliquity

   

  The length of the instrumented spine is measured, and the rods are cut accordingly.

   

  At least 2 cm of the rod must extend distally below the SAI screw to allow space for any distraction or compression required.

   

  A T-square instrument is placed on top of the spine with the horizontal arms parallel to the superior dome of the acetabulum bilaterally and the vertical arm in line with the center sacral vertebral line (TECH FIG 4A). If adequate balance has been achieved, the top of the T-square instrument will cross the vertebral

  body of T1.2

   

   

   

  TECH FIG 4 • A. A T-squared instrument is placed with the horizontal arms parallel with the pelvis and the vertical arm in line with the assumed central sacral vertebral line. B. It is confirmed with fluoroscopy that that horizontal arms of the T-squared instrument are parallel with the superior dome of the acetabulum. Then the C-arm is moved to the top of the spine and, if the deformity has been adequately corrected, the top of the T-squared instrument will cross the vertebral body of T1.

   

   

  If pelvic obliquity is present, the top of the T-square instrument will not cross the T1 vertebral body. Confirmation that the T-square is sitting in the appropriate position should be obtained fluoroscopically.

   

  Once there is fluoroscopic confirmation of the direction in which the pelvis is guiding the spine, the concavity should be distracted or the convexity should be compressed directly off of the SAI screws to obtain a full correction. Additional options are to distract, compress, or contour the spine in situ.

   

  After correction, the clinician should recheck that the spine is balanced over the pelvis with the T-square instrument.

   

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• Working Around a Baclofen Pump

   

  Many patients with NMS have increased muscular tone that requires baclofen pumps to keep them

  functional. It is important to work around these pumps while still achieving the desired correction of the deformity.

   

  Preoperative evaluation should note on which side the baclofen pump is located.

   

   

   

  TECH FIG 5 • The baclofen pump is isolated as it exits the spine then dissected from the surrounding tissues to allow insertion of the pedicle screws and corresponding rods.

  Once dissection reaches the spinous processes, subperiosteal dissection of the soft tissues should be started on the side with the baclofen pump.

  Once the baclofen pump catheter is identified, it can be followed superficially to release it from the surrounding soft tissues. The goal is to get enough slack in the catheter to safely place the pedicle screws and slide the rod underneath it (TECH FIG 5).

   

   

   

  PEARLS AND PITFALLS

   

  Approach ▪ Patients with NMS with long fusion constructs are at risk for proximal junctional kyphosis. Attempts should be made to avoid this complication by not disrupting the soft tissue attachments of the most cephalad instrumented levels.

   

  Choosing levels to instrument

  • The L5 level in patients with NMS is often difficult to instrument secondary to the severe curves and dysplastic pedicles in this patient population.

  • In such cases, it is the senior author's preference to instrument the L4, S1, and S2 levels.

  • S1 screws are much more useful in osteoporotic bone where more points of fixation are needed caudally. They should engage the “tricortical portion” of the sacrum.

     

    Placement of SAI screws

• When cutting the rod, the clinician should leave 2 cm of rod distal to the SAI screw to allow for any subsequent distraction or compression.

• When advancing the SAI screw over the guidewire, the clinician should fluoroscopically check that the wire is not bending as the screw head begins to seat into sacrum.

• Marked resistance is felt while advancing the SAI screw usually indicates that the screw is hitting the lateral cortex of the ilium. The screw should be reversed and the trajectory made more vertical and less oblique.

• The SAI screw should be torqued before any correction of pelvic obliquity is attempted.

   

  Fusion ▪ While decorticating the spine to ensure a fusion, it is important to decorticate the area where the sacral ala meets the ilium.

  • Our practice is to partially release the muscle from the undersurface of the iliac tuberosity, which relaxes the posterior paraspinous muscle and eases the closure. It also allows for fusion mass to bridge to the ilium as well as the sacrum, strengthening the fusion at the level of the SAI screw.

     

    Postoperative imaging

• It is rare to see mild lucency around the SAI screws. However, if present, it does not necessarily indicate loosening and as of yet does not have clinical significance.

 

 

POSTOPERATIVE CARE

 

When the patient is extubated and alert, the neurologic examination is repeated to make sure there has been no worsening from preoperative evaluation levels.

 

Packed red blood cells are transfused as necessary; our threshold for transfusion is a hemoglobin less than 7 g/dL.

 

If the patient is nonambulatory, we obtain supine scoliosis radiographs once the patient is transferred to the floor.

 

Dressings are changed on the second postoperative day and then as needed thereafter.

 

 

OUTCOMES

In one study, the 2-year outcomes of patients with NMS who underwent spinal fusion with SAI pelvic fixation were compared with those of control patients who underwent spinal

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fusion with pelvic fixation involving sacral and iliac screws through a PSIS insertion.23

There was no statistically significant difference in correction of Cobb angle between the SAI and control groups.

There was a greater improvement of pelvic obliquity in the SAI than in the control group.

Patients in the SAI group experienced no episodes of deep surgical site infections, whereas the control group had three cases.

In the SAI group, there were no cases of screw prominence, late skin breakdown, or anchor migration.

To date, more than 200 patients have undergone pelvic fixation with SAI screws at our institution, and there is a trend overall to less skin breakdown secondary to screw prominence, less cases of screw backout, and less cases of deep surgical site infection as compared with patients with iliosacral screws

and other forms of pelvic fixation.23

 

COMPLICATIONS

It has been estimated that the risk of surgical site infection is between 3.7% and 8.5% in patients with NMS.15

At our institution, numerous steps are taken to prevent infection.

After the spine has been fully instrumented, povidoneiodine is poured into the incision and is allowed to sit for 20 seconds (FIG 4A).

Before the incision is finally closed, vancomycin powder is sprinkled onto the hardware and the surrounding soft tissues (FIG 4B).

If allograft is used, it is soaked in gentamicin.5

A one-quarter-inch Hemovac drain (Zimmer, Warsaw, IN) is usually placed on straight drain to prevent pooling of blood.

The incision is closed with interrupted figure-of-eight sutures to ensure a watertight closure.

 

Because of the changed body alignment, the clinician should watch for pressure concentration in the ischium or coccyx when the patient first sits.

 

FIG 4 • A. In addition to standard measures, a povidone-iodine solution is poured into the incision as prophylaxis against deep surgical site infection. B. Vancomycin powder is poured into the surgical site as prophylaxis against surgical site infection.

 

 

 

REFERENCES

1. Allen BL Jr, Ferguson RL. The Galveston experience with L-rod instrumentation for adolescent idiopathic scoliosis. Clin Orthop Relat Res 1988;(229):59-69.

    

    

2. Andras L, Yamaguchi KT Jr, Skaggs DL, et al. Surgical technique for balancing posterior spinal fusions to the pelvis using the T square of Tolo. J Pediatr Orthop 2012;32:e63-e66.

    

    

3. Bell DF, Moseley CF, Koreska J. Unit rod segmental spinal instrumentation in the management of patients with progressive neuromuscular spinal deformity. Spine 1989;14:1301-1307.

    

    

4. Berven S, Bradford DS. Neuromuscular scoliosis: causes of deformity and principles for evaluation and management. Semin Neurol 2002;22:167-178.

    

    

5. Borkhuu B, Borowski A, Shah SA, et al. Antibiotic-loaded allograft decreases the rate of acute deep wound infection after spinal fusion in cerebral palsy. Spine 2008;33:2300-2304.

    

    

6. Bradford DS. Neuromuscular spinal deformity. In: Bradford DS, Lonstein JE, Moe JH, et al, eds. Moe's Textbook of Scoliosis and Other Spinal Deformities, ed 2. Philadelphia: WB Saunders, 1987:271.

    

    

7. Chang TL, Sponseller PD, Kebaish KM, et al. Low profile pelvic fixation: anatomic parameters for sacral alar-iliac fixation versus traditional iliac fixation. Spine 2009;34:436-440.

    

    

8. Cotrel Y, Dubousset J. A new technic for segmental spinal osteosynthesis using the posterior approach [article in French]. Rev Chir Orthop Reparatrice Appar Mot 1984;70:489-494.

    

    

9. Driscoll SW, Skinner J. Musculoskeletal complications of neuromuscular disease in children. Phys Med Rehabil Clin North Am 2008;19: 163-194.

    

    

10. Eubanks JD, Cheruvu VK. Prevalence of sacral spina bifida occulta and its relationship to age, sex, race, and the sacral table angle: an anatomic, osteologic study of three thousand one hundred specimens. Spine 2009;34:1539-1543.

     

     

11. Farcy JP, Rawlins BA, Glassman SD. Technique and results of fixation to the sacrum with iliosacral screws. Spine 1992;17(6 suppl):S190-S195.

     

     

12. Ko PS, Jameson PG II, Chang TL, et al. Transverse-plane pelvic asymmetry in patients with cerebral palsy and scoliosis. J Pediatr Orthop 2011;31:277-283.

     

     

13. Lehman RA Jr, Kuklo TR, Belmont PJ Jr, et al. Advantage of pedicle screw fixation directed into the apex of the sacral promontory over bicortical fixation: a biomechanical analysis. Spine 2002;27:806-811.

     

     

14. Luque ER. The anatomic basis and development of segmental spinal instrumentation. Spine 1982;7:256-259.

     

     

15. Mackenzie WGS, Matsumoto H, Williams BA, et al. Surgical site infection following spinal instrumentation for scoliosis: a multicenter analysis of rates, risk factors, and pathogens. J Bone Joint Surg Am 2013;95:800-806.

     

     

16. McCarthy RE. Management of neuromuscular scoliosis. Orthop Clin North Am 1999;30:435-449.

     

     

17. McCord DH, Cunningham BW, Shono Y, et al. Biomechanical analysis of lumbosacral fixation. Spine 1992;17:S235-S243.

     

     

18. Modi HN, Suh SW, Song HR, et al. Evaluation of pelvic fixation in neuromuscular scoliosis: a retrospective study in 55 patients. Int Orthop 2010;34:89-96.

     

     

19. Newton PO, Bastrom TP, Emans JB, et al. Antifibrinolytic agents reduce blood loss during pediatric vertebral column resection procedures. Spine 2012;37:E1459-E1463.

     

     

20. Obid P, Bevot A, Goll A, et al. Quality of life after surgery for neuromuscular scoliosis. Orthop Rev (Pavia)

    2013:5:e1.

     

     

21. O'Brien JR, Yu WD, Bhatnagar R, et al. An anatomic study of the S2 iliac technique for lumbopelvic screw placement. Spine (Phila Pa 1976) 2009;34:E439-E442.

     

     

22. Olafsson Y, Saraste H, Al-Dabbagh Z. Brace treatment in neuromuscular spine deformity. J Pediatr Orthop 1999;19:376-379.

     

     

23. Sponseller PD, Zimmerman RM, Ko PS, et al. Low profile pelvic fixation with the sacral alar iliac technique in the pediatric population improves results at two-year minimum follow-up. Spine 2010;35: 1887-1892.

     

     

24. Watanabe K, Lenke LG, Daubs MD, et al. Is spine deformity surgery in patients with spastic cerebral palsy truly beneficial?: a patient/parent evaluation. Spine 2009;34:2222-2232.