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