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Spina Bifida

  • Latin = split spine
  • Defect in neurulation
  • Unfused condition of vertebral arches with or without protrusio or dysplasia of the spinal cord or its membranes

Incidence

  • About 3 per 1000 live births in Great Britain
  • 1/200 live births in the US
  • 1.4 / 1000 in Australia
  • Spina bifida occulta seen in  25% of infants and 5% of adults
  • If one child is affected, there is 5% chance of the next child being affected, increasing to 40% if two children affected
  • Male : Female
  • Female slightly greater
  • Prenatal screening done in all pregnant woumen: elevated levels of serum alphafetoprotein: 75-80% sensitivity

Aetiology

  • Unknown
  • Great geographical variation in frequency
  • Higher incidence in certain races
  • Higher incidence in firstborn children 
  • Higher incidence in lower socioeconomic status
  • Theories 
    • Recessive inheritance with less than 1:4 ratio due to early fetal loss (Lorber)
    • Environmental factors (Von Reckllinghausen) 
    • Hamartomatous growth (Pattern)
  • Association with:
    •  Low maternal dietary folate
    • Maternal IDDM
    • Maternal hyperthermia
    • Valproic acid

Classification

  • Spina bifida occulta : Incomplete closure of laminae without cystic distension of the meninges
  • Spina bifida cystica
    • Meningocele : cystic distension of the meninges, but no neurological loss (6% of cases)
    • Myelomeningocele : cystic distension of the meninges associated with neurological loss (94%) usually of the lumbar or lumbo-sacral junction

Clinically

  • Level: Defined by the lowest active motor root
    • General Categories:
      • Upper thoracic
      • Lower thoracic
      • Upper lumbar
      • Lower lumbar
      • Sacral
    • Flaccid vs. Spastic paralysis
    • Pts with L4 function have good chance for functional walking (household or community ambulators)
    • Pts with L5 function have good chance of being community ambulators
  • Spina bifida occulta (Spinal dysraphism)
    • L5 / S1 and cervical axis most common
    • Although the skin may be intact, it is almost never normal as some midline anomaly suggests the diagnosis
    • Anomalies range from a tiny dimple or excess "down" to a large pigmented nevus or a veritable "faun's tail"
    • A bulge deep to skin is suggestive of a lesion
    • Neurological defect occurs in a very small percentage and will depend on level and extent of cord involvement
    • Associated with spinal dysraphism, tethered cord syndrome and diastematomyelia
  • Spina bifida cystica (Meningocoel or Myelomeningocoel)
    • Posture may suggest paralysis and may indicate the neurological level
    • Lower limb paralysis may be complete or incomplete, associated with urological problems
    • 85% of children, regardless of their functional level, have some form of paralytic deformity of the foot
    • Hip dislocation, genu recurvatum or flexion contracture may be evident
    • Recurvatum may be a feature at the knee, associated with talipes and claw toes in the feet
    • These deformities may develop following birth due to unbalanced paralysis, if not evident initially
    • Scoliosis occurs in 80% of the thoracic and high lumbar lesions by adulthood and curves greater than 35° at 9 years will progress
    • Anaesthetic skin may cause problems with pressure areas
    • 90% of patietns have lower urinary tract dysfunction
      • Historically this led to renal failure and high levels of mortality. New methods of urologic management have dramatically reduced morbidity and mortality secondary to urinary issues.
    • Latex hypersensitivity in 3.8 - 6.6%
      • due to exposure to latex from multiple surgical procedures, catheterization, etc...
      • Symptoms include swelling or itching in areas with latex contact
      • All patients should have all procedures done in latex-free environment
    • 50% of spina bifida children have subluxated or dislocated hips by the age of 2 years
    • Vertical talus is more often associated with myelomeningocele than as an isolated congenital deformity
    • Other vertebral anomalies such as hemivertebrae, absent vertebrae and abnormal bars are not an uncommon (15 - 20%)
    • Mental retardation in 30%
    • Children with high neurosegmental levels have more developmental delay than a child with a low lesion
    • Bone fragility is common and 20% develop pathological fractures
    • Young children are often seen with upper limb weakness and spasticity due to Arnold Chiari malformation 
    • In older children syringomyelia may produce upper limb dysfunction
    • A child that has scoliosis or deformity of rapidly increasing severity is neurologically unstable until proven otherwise (shunt malfunction, syringomyelia, Arnold Chiari malformation or tethered cord should be considered)
    • Only 30% of all patients who have a myelomeningocele are functionally independent
    • 29% lack control of bowel and bladder
  • Lipomeningocele
    • defect contains a lipoma that is intimately involved with sacral nerves
  • Diastematomyelia
    • Osseous cartilaginous, or fibrous septum in the central portion of the spinal canal that results in complete or incomplete sagittal division of the spinal cord into two hemicords.
    • Upper lumbar levels commonly involved
    • Females are affected more commonly than males.
  • Tethered cord syndrome
    • May recur after repair of myelomeningocele
    • Incidence of retethering: 11-20%
    • Occurs at 6-11 yeras of age
    • Signes: back, buttock, or lower extremity pain, progressive motor deterioration, progressive foot deformities, rapid increase in severity of lordosis or scoliosis
    • Dx: MRI with contrast
      • Must also r/o associated dermoid cyst
    • Tx: early release stops progression of spine deformity, relieves pain
  • Hydrocephalus
    • 90% of patients require VP shunt
    • Should be monitored regularly by neurosurgery
    • Acute hydrocephalus: bulging fontanelle, altered mental status, headache, N/V
    • Syrinx may develop in setting of shunt failure resulting in progressive scoliosis, motor deterioration, pain
  • Arnold-Chiari Malformation
    • Seen in 95% of children with myelomeningocele
    • Herniation of posterior fossa structures (e.g. cerebellum, brainstem) through foramen magnum
    • leading cause of death in infants
    • Sxs: intermittent apnea, stridor, nystagmus,  weak cry, upper-extremity spasticity/weakness
    • Some deformities persist/progress and require surgical decompression

X-Rays

  • Gap in the neural arch
  • Widening of the spinal canal is common
  • A bony spur of diastematomyelia should be sought
  • Bones are osteoporotic and spontaneous fracture is not uncommon
  • May heal with excessive callus
  • Other spinal deformities may be evident
    • Unsegmented bars
    • Hemivertebrae
    • Fused ribs
    • Scoliosis
    • Lordosis
    • Kyphosis

Pathology

  • Failure of development of the neural tube from the neural plate at the 4 weeks stage in utero
  • The two halves of the neural tube have failed to fuse and through this defect membranes or cord may protrude
  • The cord itself may be undeveloped (dysplastic)
  • Skin may be closed over the defect or the defect open to the environment
  • Closed defects are associated with
    • Dermal cysts
    • Lipoma of the cauda equina
    • Diastematomyelia (cord is bifurcated by bone projecting backwards from the vertebral body)
    • Partial or complete absence of the sacrum and meningocele
  • Meningocele is very rare and is merely a thecal hernia containing no neural elements
  • Myelomeningocele is a meningeal sac containing nerve roots and cord remnants, which may be adherent to the sac and protrude through the bony defect

Investigations

  • All patients with new-onset spasticity, rapidly progressive scoliosis, etc.. should be evaluated for cord tethering, hyromyelia, and shunt function

Treatment

  • Require a team approach (neurosurgery, orthopaedics urology and paediatrics and the physiotherapist and splint maker)
  • Above all, requires parental understanding and ceaseless devotion
  • If closure of defect is indicated, should intervene within 48 hours (selection of patients ethically controversial)
  • May elect not to treat, if the lesion is high and skull enlarged
  • Surgery indicated for bladder dysfunction, tethered cord, hydrocephalus and subsequent deformity
  • Forcible overcorrection and splinting is forbidden due to weak bones and skin paresis
  • Surgical correction of deformities is preferred when the child is at least several months old
  • If deformity of hip, knee and foot co-exist, correct hip then foot then the knee
  • High complication rate of procedures (infection, pathological fractures and pseudarthrosis)
  • Surgery to correct spine and limb deformities will be more rewarding when the child is neurologically stable and free of urinary tract infection

Treatment specific to regions

Hip

  • Common at L3/L4 level
  • Prime cause of hip instability is paralysis of the abductors and extensors with power remaining in the flexors and adductors in a mid-lumbar lesion
  • Unilateral dislocation: open reduction; if dislocations are bilateral, some recommend managing conservitively (controversial)
  • Open reduction, tenotomy or muscle transfer may be needed to reduce a dislocated hip
  • Early correction avoids late bony changes
  • Occasionally osteotomy or excision of the femoral head needed
  • Aim for a hip stiff enough to support the standing weight in extension and flexible enough to allow sitting
  • Iliopsoas transfer (Sharrard) : Pass tendon through a hole in pelvis to greater trochanter to redirect pull of flexors

Knee

  • Patients often have quadriceps weakness requiring KAFO
  • Correction of genu valgum needs release of contracted iliotibial band
  • For correction of flexion deformity release hamstrings, if not corrected by fixing FFD of the hip. May need to extensively release knee structures or do extension osteotomy
  • Genu recurvatum may be due to equinus of the foot

Tibia

  • Torsional deformities secondary to muscle imbalance
  • Tx: osteotomy

Foot

  • Need plantigrade foot with adequate plantar skin which is suitable for bracing
  • Perform soft tissue procedures usually at around 6 months
  • Deformities include
    • Equinus : posterior release
    • Equinovarus (most common) : postero-medial release
    • Calcaneus (strong tibialis anterior) : transfer its tendon to os calcis
    • Valgus : tendon transfer or subtalar arthrodesis
    • Cavus foot : plantar release, metatarsal +/- os calcis osteotomies
    • Vertical talus
    • Clubfoot: Most are rigid deformities requiring surgical correction
  • Fixed deformity requires bony procedures, e.g. triple arthrodesis, Grice arthrodesis, Dwyer procedure
  • Vertical talus is seen in children with thoracic and lumbar levels

Spine

Aim to maintain a stable posture for sitting

  • Scoliosis
    • Most common skeletal deformity in myelomeningocele
    • Occurs in 80% 
      • Thoracic/upper lumbar levels incidence is 95%
      • Lumbosacral level incidence is 40%
    • Natural history is progression
      • If progression is rapid, get an MRI to r/o tethered cord and neurosurg eval for shunt
    • Causes
      • Congenital spinal malformations
        • Unequal growth
        • Embryological causes
          • Failure of formation 
          • Failure of segmentation 
        • Lead to a progressive, rigid scoliosis
      • Mechanical instability due to absent\deficient posterior elements and to paralysis
      • Neurologic abnormalities caused by hydromelia and tethered cord
        • May be due to a malfunctoning shunt and if this is replaced the curve may spontaneously correct
        • If due to tethered cord, release of tether prevents progression
    • Surgical Correction:
      • High pseudoarthrosis rate
      • Infection rate up to 25%
  • Kyphosis
    • Occurs in ~15% of patients with myelomeningocele
    • Often severe with breathing  and eating difficulty
    • 2 types :
      1. Rigid type
        1. Apex ~ L1 - L2
        2. Associated with rigid lordosis in the proximal adjacent lower dorsal spine
        3. Treatment is excision of 1 or 2 vertebrae proximal to the apex
      2. Collapsing type
        1. Due to muscle weakness
        2. Can be corrected by manual pressure
        3. Not associated with proximal lordosis
    • Aim to avoid surgery for as long as possible to allow for longitudinal spinal growth
    • Need to exercise great care with use of braces
  • Lordosis
    • Excess lumbar lordosis often due to other problems, e.g. FFD of hips
  • Tethered cord is more common in children with lesions at the 4th or 5th lumbar vertebrae than thoracic 
  • Development of scoliosis at a young age often indicates tethering
  • Surgical Treatment:
    • Kyphectomy
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