Myelodysplasia Spine

Grant D. Hogue

Myelomeningocele Instrumentation and Fusion Techniques for Scoliosis and Kyphosis—General Principles

Preoperative Evaluation

Both scoliosis and kyphosis share the common and considerable comorbidities of myelomeningocele and require an extensive preoperative assessment and perioperative precautions.

Table 5.1 ▪ Considerations Before Surgical Intervention in Myelodysplastic Spinal Deformity

Considerations	Preoperative	Perioperative
General		Latex allergy and prophylactic broad-spectrum antibiotic coverage
Neurologic	Shunt function Tether release if symptomatic	Neuromonitoring Prophylactic tether release not routinely performed
Urologic	Urine culture Catherization schedule/size Urodynamics	Catheter/ostomy care
Soft tissue	Incision planning Tissue expansion	Closure assistance Compulsive dressing care
Pulmonary	Pulmonary function testing CPAP Sleep apnea	Supportive care
Musculoskeletal	Ambulation status Presence of hip flexion contracture(s) Seating plan Flexibility Bone age Advanced imaging and 3-dimensional models	Positioning Protection of soft tissues Traction to assist in correction Correction strategy Instrumentation strategy and profile of implants Oxygen saturation of lower extremities after correction
CPAP, continuous positive airway pressure.

Other Considerations

Urodynamics must be performed to determine consequences of cord resection
- Not commonly required in our experience, but can have devastating consequences in patients who are continent of urine
Urinary tract infections should be treated as they may increase risk of postoperative wound infection
Hydrocephalus/shunt function must be assessed

Orthopedic

Postural positioning/hip range of motion
Fusion to the lumbar and the lumbosacral area will eliminate the apparent hip flexion or extension that had occurred through the flexible spine
Procedures that increase lumbar lordosis will diminish hip flexion while a reduction in lordosis will diminish hip extension
Sitting or standing posture may be compromised
Family and patient must be informed and aware of possible need for hip surgery in the future if posture is untenable
Consideration of saving lumbar/lumbosacral motion segments when appropriate in ambulatory patients
Catheterization—Long fusions, particularly to the proximal thoracic spine, may adversely affect ability to self-catheterize

Preoperative Surgical Plan

Imaging Studies

Standing/sitting PA/lateral full-length spine radiographs
Flexibility views
Supine bending films
Traction radiographs
Lateral over a bolster for sagittal plane differences
Computed tomography (CT) scan (Figure 5.1A and B)
- Determination of bony anatomy
- Planning for anchor placement (profile and orientation)
- Creation of 3-dimensional (3D) printed models from CT scan
Magnetic resonance imaging (MRI)
- Evaluation for dura and neural tissue at bifid areas
- Presence of intrathecal differences
- Tethered cord is nearly always present
Prophylactic release not required if patient is not having neurologic or urologic deterioration
Cranial and caudal extent of instrumentation/fusion
- Scoliosis
  - Curve pattern
    - Include entire extent of Cobb deformity
    - Instrument/fuse to pelvis if it is part of the curve or there is pelvic obliquity
    - Curves with an apex in the lumbar spine will almost always require extension to the pelvis
  - Ambulation/functional status
    - Recommended to spare caudal motion segments when possible in ambulatory patients
    - Recommended to spare cranial motion segments when possible in nonambulatory patients who require upper thoracic motion for self-catheterization
  - Bone quality—poor bone density or significant dysplasia requires additional anchor points
- Kyphosis
  - Pelvic fixation is required due to significant stresses placed on instrumentation and inadequate bone stock in caudal limb of deformity

Destabilization, soft tissue release, and osteotomy: Needs determined by rigidity of the deformity

Scoliosis

Anterior releases sometimes needed

Posterior-based osteotomies

Ponte

Figure 5-1 ▪ A, The segmental anatomy of the bifid vertebral segments and pelvis is unpredictable. The pedicles in these dysplastic elements are usually angled closer to the coronal plane than in the unaffected segments, but the angles and diameters vary considerable within the vertebra. B, The asymmetric iliac-sacral relationship affects the screw placement and prominence. (Courtesy of Children’s Orthopaedic Surgery Foundation.)

Pedicle subtraction
Vertebral column resection

Kyphosis
- Kyphectomy/vertebral column resection
  - Best for rigid double curves (“S”-shaped) with thoracic lordosis
- Vertebral decancellation (“eggshell”)
  - Best for collapsing (“C”-shaped) deformities
  - Approach: anterior versus posterior versus combined
  - Anterior alone best for relatively short curve patterns that do not include the pelvis
  - Saves motion segments
  - Avoids poor posterior soft tissues
  - Variability of support for this approach in current literature
  - Posterior-alone approach is best for curves with enough flexibility that anterior releases are not required
  - Indications have expanded greatly in the era of improved posterior segmental instrumentation and stabilization techniques
  - Anterior and posterior approaches are best used for rigid curves with suboptimal bone stock
  - Posterior-only approaches are preferred when possible by the authors and will be discussed in this chapter. Anterior bone grafting and placement of structural graft is generally possible through a posterior approach if performing a kyphectomy, using vertebral column resection, or posterior interbody techniques (Figure 5.2A and B)

Instrumentation

Determine most stable fixation based on analysis of segmental bone stock and global deformity characteristics
Pedicle screws superior in bifid segments and preferred in others, though sublaminar bands/wires provide alternative or supplemental fixation
Must be low profile

Pelvic Fixation