Spina Bifida General Principles

Definition

 

1. Spinal dysraphism

 

Failure of the neural tube to close (i.e. spina bifida + failure of neural tube development)

 

May see one of 5 telltale skin defects 

- tail

- skin dimpling 

- sacral pit 

- hair tuft 

- lipoma 

 

Myelodysplasia: Any developmental defect of the spinal cord 

 

2. Spina Bifida Cystica

 

Vertebral laminae absent with prolapse of neural elements 

 

A.  Myeloschisis / Myelocoele

- neural plate material spread out over the surface (most severe form)

 

B.  Myelomeningocoele

- prolapse of cord & dura in defect (commonest)

 

C.  Meningocele

- prolapse of dura only

- usually no neurological deficit 

 

3. Spina Bifida Occulta

 

Congenital spinal disorder where the two halves of posterior arches fail to fuse leading to bony abnormality

- defect is hidden 

- may have diastematomyelia 

- seen in 5-10% of radiographs in normal population 

- not really related to spina bifida cystica and probably not prevented by folate

 

Epidemiology

 

1 / 1000 live births 

- varies with geographic location 

- Ireland, England, Wales - 5/1000

- Australia & USA 1/1000

 

1:20 with one affected sibling 

1:10 with second affected sibling

 

Girls > boys 

 

Aetiology

 

Multifactorial nature 

- polygenic inheritance with teratogenic enviromental factors 

 

Decreased RBC folate associated with increased risk 

- avoid folate antagonists

- folate taken prior to conception reduces rate of spina bifida by 70%

- need to take before first month of pregnancy

- 0.4 mg per day normally

- 4mg per day if have a previous child with SBC

 

Pathogenesis

 

Early problem 26th gestational day (24-28)

 

Two theories

A. Failure of neural tube to close  

B.  Initially closed tube which reopens due increased intraluminal pressure

 

The latter theory is favoured & explains other defects such as diastematomyelia etc

 

Prenatal Screening

 

Should be able to detect 90% fetus with an exposed neural defect

- small skin covered defects may be missed

 

Maternal alphafetoprotein increased 

- test at 16-20 weeks

- detects 90% of spina bifida

- will justify other investigations

- amniocentesis (spontaneous abortion risk 1:200)

 

Ultrasound

- vaginal at 10-12 weeks will identify anencephaly & some spina bifida

- standard 16-18 weeks identify anencephaly & 80% spina bifida

 

Management of early detection

- deliver by C section to avoid contamination by vaginal flora

- secondary infection which then can lead to loss of level

 

NHx

 

Survival

- without repair nearly 100% will die

- especially in pre-antibiotic day

- increase survival to 50% at 25 years

- antibiotics / selective closure / shunting

 

Neurology

- not static & there is often a decline during childhood especially first 4 years

- 60% have neurological deficiency in upper limb

- this is due to syrinx / Arnold Chiari / hydrocephalus

 

Function

- only 30% are functionally independent as adults

- only 30% will have full or part-time jobs

- 65% will have normal intelligence

 

Wheelchair

- 100% if L1 or L2 or higher

- 80% if L3, L4, L5

 

Modified Asher & Olson Classification

 

Lowest level at which Grade 3 power is available i.e. antigravity power

 

Thoracic: no grade 3 strength in lower leg muscles

L2: hip flexion

L3:      knee extension

L4:      knee flexion

L5:      ankle dorsiflexion

Sacral: ankle plantarflexion

 

i.e. L4 and below are most likely to walk

 

Clinical Features

 

1. Hydrocephalus 

 

Incidence 90% 

- of these 80% will require shunt

- inserted at time of the defect closure

 

IQ normal if no hydrocephalus 

 

Must constantly be on lookout for blocked shunt 

- deteriorating neurological function

- bulging fontanelle

- poor muscle function

 

2. Hydromyelia / Syringomelia / Syrinx 

 

Incidence 50%

- related to hydrocephalus 

- fourth ventricle communicates with the central canal of cord 

- increased hydrocephalus pushes fluid into cord 

 

Leads to

- increased lower limb paralysis & back pain

- progressive scoliosis

- weak upper extremities with increased tone

 

Usually settles with V-P shunt 

 

May need drainage prior to spinal procedure 

 

3. Arnold - Chiari Malformation: (Type II in 90%)

 

Displacement of medulla into cervical canal

- cerebellar tonsils herniated below foramen magnum on MRI

 

Symptoms   

- periodic apnea 

- stridor 

- weak / absent cry

- nystagmus 

- upper extremity spasm & weakness 

 

May resolve with shunt / if not then surgically decompress 

 

4. Tethered Cord    

 

Attachment of cord to meningocoele sac 

- prevents normal upward migration of the cord during growth

- almost universal to some degree

 

Only small number have symptoms

- buttock & posterior thigh pain 

- increased spasticity & weakness in lower extremities 

- progressive scoliosis the classic presentation is progressive 

- cavus foot deformity in young child 

- rapid deterioration in quadriceps power in teenager

 

Surgical release will halt progression but not restore function

 

5. Urinary Complications

 

One of major causes of morbidity & mortality in childhood from renal failure

 

Causes

- incontinence 

- hydronephrosis 

- recurrent UTI

 

Management

- intermittent catheterisation 

- bladder augmentation

 

6. Skin anaesthesia

 

Pressure sores major problem with casts

- hip spicas should always include feet

 

7. Latex Allergy

 

IgE mediated

 

Should always provide latex free operating environment 

- assume allergy and prevent development

 

Can screen with RAST (radioallergosorbent test) / skin test / IgE assay

- IgE assay most sensitive & specific

 

8. Fractures

 

Classic exam scenario / clinical photo

- supracondylar femoral fracture is commonest

 

Often present late 

- picture of infection (redness, swelling, warmth)

 

Treat with removable splints for short time as get very stiff

 

9. Upper Extremity Function

 

60% have abnormality of UL function

- usually weakness with increased tone

 

Risk factors

- high level

- multiple shunt revisions (ie cerebral damage from hydrocephalus)

- syrinx etc

 

10.  Orthopaedic Deformity 

 

Causes

- muscle imbalance 2° to UMN or LMN lesion

- intrauterine posture

- habitual posture after birth

- congenital malformation (eg club foot)

- arthrogryposis

 

Problems

- scoliosis

- hip FFD / Dislocation

- Knee hyperextension / flexion contracture / valgus

- teratological CTEV 

- cavus foot

- charcot foot

- ulceration

 

Orthopaedic

 

Goals

 

1.  Ambulation

- level dependent

 

2. Hips

- reduce hips if unilateral / low level / walk

- different to CP as not painful

 

3. Foot 

- keep shoeable & plantigrade 

- even if in wheelchair

- avoids ulcers and amputation

 

4.  Spine

- 80% develop scoliosis

 

5.  Prevent pressure areas

 

Always manage in spina bifida clinic

 

Muscle charting 

- should start 24 hours after birth

 

1/3 Complete LMN & loss of sensation & bowel control below affected level 

 

1/3 Complete lesion at some level but distal segment of cord preserved 

- mixed picture of intact DTR & spasticity 

 

1/3 Incomplete & some movement & sensation preserved 

 

Levels

 

L1 Level

 

Muscles

- iliopsoas grade 2 or better / some weak hip flexion

 

Position

- Hip flexed, abducted & ER

 

Ambulation

- HKAFO - hip knee ankle foot orthosis

- RGO - reciprocating gait orthosis, when one hip flexes the other extends

- adults usually wheelchair bound 

 

L2 Level

 

Muscles

- iliopsoas, sartorius & adductors grade 3 or better

- hip flexion & some adduction

 

Position

- hip flexed and adduction 

- FFD of hip may develop 

 

Ambulation

- most ambulate as children in HKAFO

- FFD may need to be corrected first 

- adults usually choose wheelchair 

 

L3 Level

 

Muscles

- quadriceps grade 3

 

Position

- hip flexed & adducted

- knee extended 

- Hip subluxation & dislocation common due to unopposed hip adduction & flexion 

 

Ambulation

- usually household ambulators 

- grade 4 quadriceps - 80% community ambulators / 98% household ambulators 

- grade 3 quadriceps -  need KAFO to walk & 88% in wheelchair 

- patients with quads & good abductors can ambulate without aids 

 

L4 Level  

 

Muscles

- medial hamstring grade 3

- Tibialis anterior 3 or better

- quadriceps grade 5

 

Position

- hip flexed & adducted

- knee extended

- ankle in varus due to T anterior

 

Ambulation

- walk in AFO 

 

Surgery often required to maintain hip & knee extension / foot plantigrade

 

L5 Level

 

Muscles

- lateral hamstrings >=3

- G medius >=2

- T posterior >=3

 

Position

- calcaneovalgus or calcaneus foot 

- need T anterior to T Achilles transfer age 3 to prevents foot drop gait

 

Ambulation

- 95% community ambulators throughout life 

 

Sacral Level 

 

Muscles

- Gastroc/Soleus >/=2 

- G medius >/=3

- G maximus >/=3

 

Position

- clawing of toes & cavus foot from intrinsic minus

 

Ambulation

- usually brace free but may need special shoes 

- ie arch supports

 

At high risk of heel ulcers due to foot imbalance / calcaneus / nil S1 protective sensation