In patients with occult spinal dysraphism and tethered SC who have undergone an untethering procedure, progressive neurologic or urologic deterioration may signal recurrent tethering of the SC, which can occur in up to 15% of patients.
From: Pediatric Surgery (Seventh Edition) , 2012
Disorders of Neural Tube Development
Nalin Gupta , M. Elizabeth Ross , in Swaiman's Pediatric Neurology (Sixth Edition), 2017
Spina Bifida Occulta
Spina bifida occulta, a confusing term, is defined as a defect in the posterior bony components of the vertebral column without involvement of the cord or meninges. It occurs in at least 5% of the population but most often is asymptomatic. The presence of a cutaneous lesion, tuft of hair, or a cutaneous angioma or lipoma in the midline of the back, is associated with spina bifida occulta in only approximately 10% of cases, although the percentage increases to approximately 50% when two or more skin lesions are present.
Gregory W.J. Hawryluk , ... Michael G. Fehlings , in Handbook of Clinical Neurology, 2012
Spina bifida occulta
SBO is characterized by deficiency of the posterior vertebral arch and arises after neural tube closure (Harris and Juriloff, 1999) as a result of deficient mesodermal migration making its ontogeny distinct from SBA (Payne et al., 1997). Indeed, the few SBO mouse mutants described (Hollander, 1976; Park et al., 1989; Payne et al., 1997) do not give rise to offspring with SBA with few exceptions (Harris and Juriloff, 2007), reviewed in Table 1.5. In humans familial occurrence has been described (Thompson and McKay, 1986). In addition to its association with cutaneous anomalies such as hairy patches, subcutaneous lipomas and capillary hemangiomas (Guggisberg et al., 2004), SBO may also be associated with polythelia (Panigrahi et al., 2008), testicular cancer (Agostini et al., 1991), and idiopathic or symptomatic epilepsy (Klepel and Freitag, 1992).
Table 1.5. Mouse mutants with spina bifida occulta
Gerald M. Fenichel , in Neonatal Neurology (Fourth Edition), 2007
Spina Bifida Occulta
Spina bifida occulta is an example of a predominantly mesodermal abnormality. The prominent bony change is the partial or complete absence of the vertebral arches with lateral displacement of the pedicles. Minor defects in the closure of the vertebral arches (defects covered by skin) are relatively common. Only in rare instances are they associated with a significant underlying deformity of the spinal cord. Scoliosis and kyphosis develop at the site of the bony abnormality when there is an underlying neural defect. While these conditions may be present at birth, they tend to become progressively severe with time. The more significant abnormalities of the cord are at its caudal extreme, where abnormal attachments may produce a tethering effect. A tethered cord is usually asymptomatic at birth but result in a traction injury to the cord and nerve roots as the child grows. The usual clinical features are disturbances of gait and sphincter control.
Georg-Christoph Korenke , in Klinikleitfaden Pädiatrie (7), 2006
Einteilung
•
Spina bifida occulta: Fehlender Schluss des knöchernen Wirbelbogens.
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Spina bifida aperta:
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Dermalsinus (Dermalfistel): Verbindungsgang zwischen Haut (oft in behaartem Pigmentfleck endend) und Spinalkanal, meist sakro-kokzygeal, oft Verwachsungen mit Dura und gutartigen Tumoren im Spinalbereich (Lipom, Dermoid).
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Meningozele: Vorwölbung der Meningen (Dura und Pia).
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Meningomyelozele (MMC): Vorwölbung von Meningen und RM.
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Offene Myelozele: MMC plus zusätzlicher Hautdefekt.
Chiari-Malformation: (90% der MMC): Herniation des unteren Kleinhirns und Hirnstamms durch Foramen occipitale magnum in zervikalen Spinalkanal → Hydrozephalus.
Thomas K. Koch , in Encyclopedia of the Neurological Sciences, 2003
Occult Spinal Dysraphism
When a spina bifida occulta is associated with neurological abnormalities, the condition is referred to as an occult spinal dysraphism. This results from a distortion of the spinal cord or roots by associated fibrous bands or masses beneath the intact dermis and epidermis. This category includes the tethered cord syndrome, spinal lipomas, diastematomyelia, and diplomyelia. Of these, the tethered cord syndrome (tight filum terminale syndrome) is the most common. Early clinical features suggestive of a potential occult spinal dysraphism include overlying cutaneous abnormalities that include a hair tuft, subcutaneous mass, pigmentary abnormalities, and dimples or tracts (Table 2). In a recent study evaluating infants with high-risk cutaneous stigmata, no infant (0 of 160) with a "simple dimple" (defined as midline, measuring <5 mm, and within 2.5 cm of the anus) had an occult spinal dysraphism.
Table 2. CUTANEOUS ABNORMALITIES ASSOCIATED WITH AN OCCULT SPINAL DYSRAPHISM
Hair tuft/patch
Subcutaneous mass
Hemangioma
Skin tag
Cutis aplasia (congenitial dermal atrophy)
Pigmented macule
Dimples and tracts
In the tethered cord syndrome, the spinal cord is fixed to the surrounding spine and usually results from a thickened filum terminale appearing to anchor the conus medullaris to the base of the vertebrae (tight filum terminale syndrome). Radiographically, this is characterized by a short, thick filum (>2 mm) and a low position of the conus medullaris. A conus below the L2–L3 disk space is always abnormal. Tethering can also be associated with a spinal lipoma, dermal sinus, or diastematomyelia and diplomyelia. Clinically, the tethered cord syndrome usually presents with slowly progressive lower extremity weakness, foot or leg length abnormalities, scoliosis, gait abnormalities, urological dysfunction, and/or changes of the myotatic reflexes. Occasionally, clinical symptoms can present abruptly. Although the pathophysiology of the symptoms and signs remains obscure, it appears that with growth there is stretching of nerve fibers and possibly vascular compromise resulting in decreased oxidative metabolism. The sudden onset of symptoms and signs may be related to sudden vascular insufficiency.
Early diagnosis and management of these lesions have been greatly aided by the use of ultrasonography in infants and/or magnetic resonance imaging (MRI). Computed tomography (CT) may be helpful for visualizing anomalous bony structures and diastematomyelia spurs. Routine radiographic studies of the spine in patients younger than 1 year of age are usually insufficient to document a bony defect due to the poor ossification of the posterior elements of the spine. Even in older children, 10% or more may have normal spine films.
Surgical intervention should be undertaken to release spinal cord tethering before there is significant clinical deterioration. Although surgical intervention will halt further neurological progression, it may not restore lost function, especially in patients who have an abrupt onset of symptoms. Following surgery for a spinal lipoma, only 25% of patients will have any improvement in their preexisting neurological status, and only 50% with a thickened filum terminale may improve. Prophylactic surgical intervention in asymptomatic children has become standard treatment to lessen the possibility of poor recovery from preexisting neurological deficits. However, the timing of surgery in the asymptomatic infant is controversial.
Diastematomyelia is a split spinal cord usually separated by a fibrous or bony septum anchoring the spinal cord to the vertebrae. Recently, the term split cord malformation (SCM) has been applied to diastematomyelia (SCM I) and diplomyelia (SCM II). The distinction between these two malformations is based on the integrity of the dural coverings and the presence or absence of intervening mesenchymal tissue. With SCM I, there are two dural sacs and a bony or fibrous spur. With SCM II, there is a single dural sac and intradural fibrous band. In either condition, there is usually progressive neurological, urological, and orthopedic deterioration. Clinical findings on examination can include scoliosis, kyphosis, leg length discrepancy, foot deformities, bladder disturbances, and a myelopathy. Infants may present with congenital scoliosis, frequently with overlying cutaneous abnormalities. Most lesions occur in the lumbosacral region and are somewhat more common in females. Detection can be accomplished by ultrasonography, even prenatally. MRI of the spine is the preferred neuroimaging technique. Surgical resection of the spur usually does not result in clinical improvement, although it can halt progression of neurological deterioration. The role of surgery before clinical deterioration occurs is controversial.
Occult malformations along the spinal canal and neuraxis can present with episodes of recurrent meningitis due to external contamination of the cerebrospinal fluid. Malformations include dermal sinuses, neurenteric fistulas, temporal bone fistulas, and basal encephaloceles or meningoceles.
Barry Mitchell BSc MSc PhD FIBMS FIBiol , Ram Sharma BSc MSc PhD , in Embryology (Second Edition), 2009
The vertebral column
The development of the vertebral column passes through three stages. Vertebrae begin as mesenchymal condensations around the notochord, which then transform into cartilaginous models. From the sixth week the ossification of vertebrae begins and usually ends by the twenty-fifth year of life.
During the initial mesenchymal stage, the sclerotome cells migrate medially towards the notochord, and meet the sclerotome cells from the other side to form the centrum or vertebral body. Each sclerotome splits into a cranial and a caudal segment (Fig. 4.5A). The cranial half of the sclerotome consists of loosely arranged cells, whereas the caudal half contains densely packed cells. The caudal half of a sclerotome fuses with the cranial half of the sclerotome below to form the vertebral body (Fig. 4.5B). From the vertebral body, sclerotome cells move dorsally and surround the developing spinal cord to form the vertebral arch. In each vertebra, the costal and transverse processes develop from the vertebral arches. The vertebral arches of each vertebra join dorsally to form the spinous processes. The formation of the vertebral body is dependent on inducing substances produced by the notochord, and that of the vertebral arch, on the interaction of sclerotome cells with the surface ectoderm.
The intervertebral disc has an outer collagenous annulus fibrosus and a central gelatinous core, the nucleus pulposus (Fig. 4.6). The annulus fibrosus develops from the densely packed lower portion of the sclerotome, whereas the nucleus pulposus is derived from the notochord. The rest of the notochord at the level of the vertebral bodies soon disappears.
Because of its formation from two sclerotomes on each side, a vertebra is intersegmental in origin. However, the spinal nerves are segmental as they emerge at the level of the corresponding somite in close relationship to the intervertebral discs.
Clinical box
A spina bifida occulta (see Chapter 10 and Fig. 10.5A) may occur when the two halves of the vertebral arch fail to fuse behind the spinal cord. This minor anomaly usually occurs in the lumbosacral region, often marked by a patch of hairy skin overlying the affected area, and is often first identified on routine radiological examination.
The notochordal tissue may persist and give rise to chordomas. Most chordomas occur in the midline, most commonly at the base of the skull or in the sacrococcygeal region. These tumours may become malignant, and infiltrate the surrounding bones, occurring more commonly in males and rarely before the age of 30 years.
Occult Spinal Dysraphism and the Tethered Spinal Cord
Gary W. Tye , ... John S. Myseros , in Spine Surgery (Third Edition), 2005
Pathology and Embryology
Although associated with other forms of occult spinal dysraphism, spinal lipomas are connective tissue and fat collections that are distinct, partially or completely encapsulated, and definitely attached to the spinal cord.25 It is thought that during the process of primary neurulation improper disjunction of surface ectoderm and neuroepithelium may lead to inclusion of fat.25 Distinct from lipomyelomeningoceles, isolated lipomas technically are fibrolipomas of the filum terminale or dural fibrolipomas, as defined by Emery and London.14 In simple lipomas the neural elements remain within the spinal canal, whereas lipomyelomeningoceles are marked by herniation of the neural elements out of the canal into the subcutaneous portion of the lipoma.16 Strictly intradural lipomas associated with an intact dura mater are lesions of subpial fat found in the cervical and thoracic spinal cord.2 In a large series reported by McLone and Naidich,33 intradural lipomas comprised 4% of the lipomas treated surgically. More common, however, are lipomas that involve the dura mater and extend from the spinal cord to the subcutaneous tissue.2,27,46
More than with the previously described dermal sinus, lipomas are associated with more severe bony changes, including scalloping of the dorsal vertebral body, widening of the interpedicular space, hemivertebrae, or even hypoplasia of the iliac wing.16 These sequelae of the mass effect associated with lipomas suggest that resultant neurologic deficits occur not only by spinal cord tethering (see Pathophysiology and Presentation) but also by direct neural compression.
In Clinical Neurology for Psychiatrists (Sixth Edition), 2007
Lower Neural Tube Closure Defects
In the most benign case, spina bifida occulta, the spine of the lumbar vertebrae simply fails to fuse. With both the underlying spinal cord and cauda equina remaining intact, this disorder usually remains asymptomatic.
In a more serious problem, meningocele, the meninges and skin protrude through a lumbosacral spine defect to form a large, CSF‐filled bulge. Although this condition may remain asymptomatic, it frequently causes symptoms originating in dysfunction of the lumbar and sacral nerves, such as leg weakness, gait impairment, bladder emptying problems, and thus progressive hydronephrosis. It also deprives the lower CNS of the multiple tissue barriers—intact skin, vertebrae, and meninges—that normally shield it from the environment. To prevent bacteria from entering the CSF through this defect and causing meningitis, infants with meningoceles must undergo neurosurgery for repair.
Meningomyelocele or myelomeningocele, the worst case, occurs far more frequently than meningocele. This malformation consists of a tangle of a rudimentary lower spinal cord, lumbar and sacral nerve roots, and meninges protruding into a sac‐like structure overlying the lumbosacral spine (Fig. 13‐7). The disrupted nerve tissue causes paraparesis, areflexia, and incontinence. In addition, defective meninges place neonates at immediate risk of meningitis. Although hydrocephalus is present in only about 25% of infants with meningomyeloceles, it develops in almost all who survive.
Neurosurgeons usually repair meningomyeloceles during the child's first week. Nevertheless, clinical deficits usually worsen in childhood and particularly during adolescent growth spurts. Although neurosurgery may protect infants from meningitis and reduce the impact of hydrocephalus, most survivors remain mentally retarded and paraplegic. In addition, as affected children physically mature, they often require urinary‐ and fecal‐diversion procedures, revisions of shunts for hydrocephalus, and further surgery on the spine.
David Myland Kaufman MD , Mark J. Milstein MD , in Kaufman's Clinical Neurology for Psychiatrists (Seventh Edition), 2013
Lower Neural Tube Closure Defects
In the most benign variety, spina bifida occulta, lumbar vertebrae simply fail to fuse. With both the underlying spinal cord and cauda equina remaining intact, this disorder usually remains asymptomatic.
In meningocele, a more serious variety, the meninges and skin protrude through a lumbosacral spine defect to form a large, CSF-filled bulge. Although this condition may remain asymptomatic, it frequently causes symptoms originating in dysfunction of the lumbar and sacral nerves, such as leg weakness, gait impairment, and bladder-emptying problems. Thus progressive hydronephrosis often complicates the deficit. Meningomyelocele (myelomeningocele), which occurs far more frequently than meningocele, is the most serious variety. It consists of a tangle of a rudimentary lower spinal cord, lumbar and sacral nerve roots, and meninges protruding into a saclike structure overlying the lumbosacral spine (Fig. 13-7). The disrupted nerve tissue causes paraparesis, areflexia, and incontinence. In addition, hydrocephalus and other brain abnormalities are comorbid in about 25% of cases. Approximately 10% of infants born with meningomyelocele die from the defect.
Meningoceles and meningomyeloceles also deprive the lower CNS of the multiple tissue barriers – intact skin, vertebrae, and meninges – that normally shield it from the environment. To prevent bacteria from entering the CSF through the defective meninges and causing meningitis, infants with meningoceles and more serious varieties must undergo neurosurgery. Therefore, neurosurgeons usually repair these defects during the infant's first week of life not to correct the paraplegia but to prevent meningitis. Most survivors of meningomyeloceles eventually require ventricular shunting. In addition, as affected children physically mature, they often require urinary and fecal diversion procedures, revision of their ventricular shunt, and further surgery on the spine. Some neurosurgeons' recent publications have described in utero or "prenatal" meningomyelocele surgery that reduces the risk of death and need for shunting, and may improve mental and motor function.
Kent R. Kelley MD , in Pediatric Secrets (Fifth Edition), 2011
Spinal cord disorders
221 Which spinal segments do each of the common reflexes test?
See Table 14-13.
222 How common are asymptomatic spinal anomalies in normal children?
Up to 5% of children have spina bifida occulta, an incomplete fusion of the posterior vertebral arches, which is usually noted as an incidental radiographic finding. The defect most commonly involves the lower lumbar lamina of L5 and S1.
223 Which sacral dimples and coccygeal pits in a newborn are concerning for an occult spinal dysraphism (OSD)?
These occur in up to 4% of newborns. Certain features are more likely to be associated with an OSD and warrant a screening ultrasound.
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Location above the gluteal crease (typically >2.5 cm from the anus)
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Deep dimples (if base cannot be visualized, do not probe because of risk for introducing an infection if a direct communication with the spinal canal is present)
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Larger size (>0.5 cm)
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Pits with cutaneous markers (lipoma, hypertrichosis, hemangioma)
Williams H: Spinal sinuses, dimples, pits and patches: what lies beneath? Arch Dis Child Educ Pract Ed 91:3p75–3p80, 2006.
Key Points:
Neonatal Sacral Findings Suggestive of Occult Spinal Dysraphism
1.
Location above the gluteal crease (typically >2.5 cm from the anus)
2.
Deep dimples
3.
Larger dimple size (>0.5 cm)
4.
Sacral pits with cutaneous markers (lipoma, hypertrichosis, hemangioma)
224 What is the recurrence rate of open neural tube defects?
Open neural tube defects (myelomeningocele or spina bifida and anencephaly) usually have multifactorial causes, but in some cases, they may be the result of mendelian recessive inheritance. The general recurrence rate is 2.5% for mothers of affected children, sisters of the mother of an affected child, and female children born to individuals with spina bifida. Daily folic acid intake of 400 mcg reduces the risk of spina bifida by as much as 70%. Serum and amniotic α-fetoprotein can detect open neural tube defects, and ultrasound is also a useful tool.
Spina Bifida Association of America: http://www.sbaa.org.
225 What are the two main features of the Chiari malformations?
Cerebellar elongation and protrusion of the foramen magnum into the cervical spinal cord. Anatomic anomalies of the hindbrain and skeletal structure result in different positioning of the various structures relative to the upper cervical canal and foramen magnum with different clinical features.
226 What are the types of Chiari malformations?
Type I is clinically the least severe and is generally asymptomatic during childhood. The presentation of a Chiari I malformation may be insidious. Epilepsy is found in a small minority of these patients. There may be paroxysmal vertigo, drop attacks, vague dizziness, and headache, which may be increased by the Valsalva maneuver. Occipital headache precipitated by exertion may progress to torticollis, downgaze nystagmus, periodic nystagmus, and oscillopsia. MRI findings in patients with Chiari I malformations include malformations of the base of the skull and of the upper cervical spine, including hydromyelia, syringomyelia, and syrinx.
Type II is the most common of those diagnosed during childhood. Medulla and cerebellum, together with part or the entire fourth ventricle, are displaced into the spinal canal. A variety of cerebellar, brainstem, and cortical defects can occur. This type is strongly associated with noncommunicating hydrocephalus and lumbosacral myelomeningocele.
Type III comprises any of the features of types I and II, but the entire cerebellum is herniated throughout the foramen magnum, with a cervical spina bifida cystica. Hydrocephalus is a common feature.
Sarnat HB: Neuroembryology, genetic programming and malformations of the nervous system. In Menkes JH, Sarnat HB, Maria BL, editors: Child Neurology, ed 7, Philadelphia, 2006, Lippincott Williams & Wilkins, pp 299–301.
Key Points:
Early Clues to Spinal Cord Compression
1.
Scoliosis producing sustained poor posture
2.
Back or abdominal pain beginning abruptly during sleep
3.
Increased sensitivity of spinal column to local pressure or percussion
4.
Bowel or bladder dysfunction
5.
Diminished sensation in the anogenital region and lower limbs
227 What is the full anatomic expression of myelomeningocele?
Children with myelomeningocele have a complex, multifaceted, congenital disorder of structure that represents a dysraphic state (i.e., a defective closure of the embryonic neural groove). In its full expression, it is typified anatomically by the following:
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The presence of unfused or excessively separated vertebral arches of the bony spine (spina bifida)
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Cystic dilation of the meninges that surround the spinal cord (meningocele)
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Cystic dilation of the spinal cord itself (myelocele)
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Hydrocephalus and the spectrum of congenital cerebral abnormalities
228 What is the likelihood that a patient with myelomeningocele will have hydrocephalus?
Hydrocephalus is seen in 95% of children with thoracic or high lumbar myelomeningocele. The incidence decreases progressively with more caudal spinal defects to a minimum of 60% if the myelomeningocele is located in the sacrum.
229 What is the usual cause of stridor in a child with myelomeningocele?
The stridor is usually caused by dysfunction of the vagus nerve, which innervates the muscles of the vocal cords. In their resting position, the edges of the cords meet in the midline; during speech, they move apart. Hence, in bilateral vagal nerve palsies, the free edges of the vocal cords are closely opposed and obstruct air flow, thereby resulting in stridor. In symptomatic patients, the motor nucleus of the vagus nerve may be congenitally hypoplastic or aplastic. More commonly, the vagal dysfunction is believed to arise from a mechanical traction injury caused by hydrocephalus, which produces progressive herniation and inferior displacement of the abnormal hindbrain. Shunting the hydrocephalus may alleviate the traction and improve the stridor. Sometimes the later recurrence of stridor indicates the reaccumulation of hydrocephalus as a result of ventriculoperitoneal shunt failure.
230 What are the principal options for managing urinary incontinence in patients with myelomeningocele?
About 80% of patients have a neurogenic bladder, which most commonly manifests as a small, poorly compliant bladder and an open and fixed sphincter. Options include the following:
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Clean intermittent catheterization, which results in more complete emptying than simple Credé maneuvers
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Artificial urinary sphincter to increase outlet resistance
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Surgical urinary diversion (e.g., suprapubic vesicostomy), which is uncommonly used
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Augmentation cystoplasty to increase bladder capacity in combination with the use of oxybutynin (a smooth muscle antispasmodic)
Blum RW, Pfaffinger K: Myelodysplasia in childhood and adolescence, Pediatr Rev 15:480–488, 1994.
231 How frequently is myelomeningocele associated with mental retardation?
Only 15% to 20% of patients have associated mental retardation. Hydrocephalus per se does not cause the mental retardation that is associated with this syndrome. (Recall that children with appropriately treated congenital hydrocephalus caused by simple aqueductal stenosis usually have normal psychomotor development.) Only severe hydrocephalus with a very thick cortical mantle predicts lower intelligence. Mental retardation is usually attributed to acquired secondary CNS infection or subtle microscopic anomalies of neuronal migration and differentiation, which may coexist with the macroscopically visible malformation of the hindbrain.
232 In an infant born with myelomeningocele, how does the initial evaluation predict long-term ambulation potential?
The level of motor function—and not the level of the defect—is most predictive of ambulation.
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Thoracic: No hip flexion is noted. Almost no younger children will ambulate, and only about one third of adolescents will ambulate with the aid of extensive braces and crutches.
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High lumbar (L1, L2): The patient is able to flex the hips, but there is no knee extension. About one third of children and adolescents will ambulate, but only with extensive assistive devices.
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Mid-lumbar (L3): The patient is able to flex the hips and extend the knee. The percentage of those able to ambulate is midway between those with high and low lumbar lesions.
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Low lumbar (L4, L5): The patient is able to flex the knee and dorsiflex the ankle. Nearly half of younger children and nearly all adolescents will ambulate, with varying degrees of braces or crutches.
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Sacral (S1-S4): The patient is able to plantar flex the ankles and move the toes. Nearly all children and adolescents will ambulate, with minimal or no assistive devices.
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