Spina Bifida

Spina bifida describes an incomplete closure of the spine that occurs very early in development, when the neural tube is forming. It is helpful to picture the condition as a spectrum rather than a single entity, because the forms differ enormously in their consequences for the spine and the nervous system.

Spina bifida occulta is the mildest and commonest form. Here a vertebra, most often in the lower lumbar or sacral region, has a small gap in the bony arch that would normally close over the back of the spinal canal. The cord and its coverings remain inside the canal and the skin over the area is usually intact. In the great majority of people this is an incidental finding on an X-ray taken for another reason, causes no symptoms, and has no bearing on health.

The closed, or occult, spinal dysraphisms are a more complex group in which the back of the spine has not formed normally but the skin is intact, sometimes with a marker such as a dimple, a tuft of hair, a fatty lump or a birthmark over the lower spine. Within this group the cord may be tethered, fixed in place by a thickened filum, a fatty mass or a bony spur, rather than hanging free as it normally would.

Myelomeningocele is the severe, open form and the one that dominates the spinal surgeon's view of the condition. Here the neural tube has failed to close over a segment of the back, so that the spinal cord and the membranes around it bulge outward through a defect in the vertebrae, skin and muscle, often as a sac on the surface of the back at birth. The exposed and maldeveloped cord does not function normally below the level of the lesion, which produces weakness or paralysis, altered sensation and disturbance of bladder and bowel.

The first factor is the bony deficiency itself. In an open lesion, the vertebrae at the level of the defect are split at the back, their posterior elements widely spread apart or absent, and the muscles that should attach to them are deficient or unbalanced. The spine is therefore missing part of its natural bracing at the back, the very structure that normally resists forward collapse and helps hold the column straight.

The second is the muscle imbalance that follows the cord injury. Because the cord is damaged from a certain level downward, the muscles of the trunk and around the spine are paralysed or weakened in a pattern that depends on that level. When some muscles pull and their opposing muscles do not, the growing spine is drawn progressively out of line.

The third is the cord itself. The maldeveloped cord may be tethered at the site of the original defect or by associated abnormalities, and a tethered cord that is placed under tension as the child grows can drive or worsen deformity. Layered on top of all this, there may be congenital anomalies of the vertebrae, such as hemivertebrae or fused segments, present from birth.

Scoliosis is among the most frequent and most important spinal problems in myelomeningocele. Reported rates are high and rise with the severity and height of the lesion, with the literature describing scoliosis in a large proportion of children with myelomeningocele and in the majority of those with higher-level lesions by adolescence.

Children with high lesions, in the thoracic region, have the greatest paralysis of the trunk muscles, the least ability to walk, and by far the highest rates of scoliosis. As the lesion level descends through the lumbar segments to the sacral region, more muscle function is preserved, more children are able to walk, and the rates of scoliosis fall accordingly.

The curves themselves tend to be of two broad kinds, and they often coexist. Some are congenital, arising from malformed vertebrae present from birth. Others are developmental and paralytic, arising over time from the muscle imbalance and the absent posterior bracing, and these tend to be long, sweeping curves that often extend down into the pelvis and are accompanied by pelvic obliquity.

In a proportion of children with thoracolumbar myelomeningocele, a sharp, angular kyphosis is present from birth, sometimes called a gibbus. At the apex of this deformity the spine is bent acutely forward, and because the posterior elements of the vertebrae are absent or splayed, there is nothing at the back to resist the collapse. The result can be a rigid, prominent and progressive forward angulation, often centred in the lumbar region, that worsens as the child grows.

The sharp prominence at the apex stretches the overlying skin tightly over the bony point. In a child whose skin is already insensate over that region, the combination of pressure, prominence and absent sensation is a recognised source of skin breakdown and ulceration over the apex. A large kyphosis can also compromise sitting balance, force the child into an awkward posture, and crowd the contents of the abdomen and chest.

A tethered spinal cord is one that is abnormally fixed in position. In spina bifida this is common, both in the open myelomeningocele, where scar tissue and the abnormal anatomy can fix the cord, and in the closed dysraphisms. As a child grows, the spine lengthens, and a cord that is fixed at its lower end is placed under increasing tension. The literature on tethered cord describes a syndrome in which this tension is associated with the development or progression of spinal deformity, particularly scoliosis, alongside changes in strength, sensation, gait and bladder function.

A good deal of attention has been given to whether releasing the tethered cord, an operation called untethering, can influence the course of an associated scoliosis. The published series describe mixed findings. Some report that untethering can stabilise or even improve curves in selected children, particularly when the curve is still relatively small and flexible. Others find that established, larger curves tend to continue to progress despite release.

Alongside the open defect itself, the spine in spina bifida frequently carries congenital anomalies of the individual vertebrae. The commonest of these are failures of formation, such as a hemivertebra, where only half of a vertebra has developed, and failures of segmentation, where two or more vertebrae are partly fused together by a bar of bone. A hemivertebra acts like a wedge inserted into the column, tilting the spine to one side, while an unsegmented bar tethers one side of the spine and prevents it from growing evenly.

Because the cord is damaged, the skin below the level of the lesion is insensate, meaning it cannot feel pressure, friction or the warning discomfort that normally prompts a change of position. This matters greatly wherever a bony prominence presses against the skin from within. A severe kyphosis, with its sharp apex, is the clearest example: the skin is stretched over a prominent bony point that it cannot feel, and the combination of unrelieved pressure and absent protective sensation is a well-recognised setting for skin breakdown and ulceration.

Wound healing problems and deep infection are reported far more frequently after spinal fusion in myelomeningocele than after most other spinal operations. The reasons lie in the deficient and scarred soft tissues over the back, the insensate skin, the often poor nutritional and general health of severely affected children, the presence of a ventricular shunt, and contamination from a neuropathic bladder and bowel.

Beyond infection, the literature describes high rates of other problems: failure of the bone to fuse, known as pseudarthrosis; loosening, breakage or prominence of the metalwork; and the need for further surgery. The deficient posterior bony elements give the surgeon less native bone to fuse to and fewer secure points of fixation.

A recurring and characteristic feature is the frequent need to extend the fusion down to the pelvis. Because the long paralytic curves of myelomeningocele so often involve pelvic obliquity and extend into the sacrum, achieving a balanced, level pelvis for sitting frequently requires anchoring the lower end of the construct into the pelvis itself.

Almost all children with myelomeningocele have an associated abnormality at the base of the brain called the Chiari II malformation, in which the lower part of the brain and brainstem are displaced downward through the opening at the base of the skull into the upper spinal canal. This is closely linked to hydrocephalus, a build-up of fluid within the brain, which very commonly requires a shunt, a tube that drains the fluid away, usually placed in early life.

These features interact with the spinal picture in ways that matter. The Chiari II malformation involves the junction between the brain and the cord, and changes here can produce or contribute to neurological symptoms. Hydrocephalus and the function of the shunt are part of the wider neurological balance of the child; a shunt that is not working well can cause a change in neurological state, which in turn may be relevant to the cord and the spine.

For spina bifida occulta and many of the milder forms, there is often no consequence for the spine at all. For myelomeningocele the picture is more involved, and the height of the lesion is the strongest guide: higher lesions carry greater paralysis, lower rates of walking, and far higher rates of severe scoliosis and kyphosis, while lower and sacral lesions are associated with less severe spinal problems. Where surgery is undertaken, the literature describes both its considerable value in restoring sitting balance and controlling deformity, and its considerable risks.

This page is general medical education and is not a substitute for individual advice. New or worsening weakness, numbness, saddle numbness or any disturbance of bladder or bowel control requires urgent assessment.

• —Mummareddy N, Dewan MC, Mercier MR, Naftel RP, Wellons JC, Bonfield CM, et al. Scoliosis in myelomeningocele: epidemiology, management, and functional outcome. J Neurosurg Pediatr. 2017;20(1):99–108.
• —Heyns A, Negrini S, Jansen K, et al. The prevalence of scoliosis within Belgian myelomeningocele population and the correlation with ambulatory status and neurological comorbidities. Spinal Cord. 2021;59(10):1053–1060.
• —Trivedi J, Thomson JD, Slakey JB, Banta JV, Jones PW. Clinical and radiographic predictors of scoliosis in patients with myelomeningocele. J Bone Joint Surg Am. 2002;84-A(8):1389–1394.
• —Müller EB, Nordwall A. Prevalence of scoliosis in children with myelomeningocele in western Sweden. Spine. 1992;17(9):1097–1102.
• —Lindseth RE, Stelzer L Jr. Vertebral excision for kyphosis in children with myelomeningocele. J Bone Joint Surg Am. 1979;61(5):699–704.
• —Carstens C, Koch H, Brocai DR, Niethard FU. Development of pathological lumbar kyphosis in myelomeningocele. J Bone Joint Surg Br. 1996;78(6):945–950.
• —Mintz LJ, Sarwark JF, Dias LS, Schafer MF. The natural history of congenital kyphosis in myelomeningocele. Spine. 1991;16(8 Suppl):S348–S350.
• —Niall DM, Dowling FE, Fogarty EE, Moore DP, Goldberg C. Kyphectomy in children with myelomeningocele: a long-term outcome study. J Pediatr Orthop. 2004;24(1):37–44.
• —Comstock SA, Cook PC, Leahey JL, El-Hawary R, Hyndman JC. Posterior kyphectomy for myelomeningocele with anterior placement of fixation. Clin Orthop Relat Res. 2011;469(5):1265–1271.
• —Akbar M, Bremer R, Thomsen M, Carstens C, Abel R. Kyphectomy in children with myelodysplasia: results 1994–2004. Spine. 2006;31(9):1007–1013.
• —Reigel DH, Tchernoukha K, Bazmi B, Kortyna R, Rotenstein D. Change in spinal curvature following release of tethered spinal cord associated with spina bifida. Pediatr Neurosurg. 1994;20(1):30–42.
• —McLone DG, Herman JM, Gabrieli AP, Dias L. Tethered cord as a cause of scoliosis in children with a myelomeningocele. Pediatr Neurosurg. 1990–91;16(1):8–13.
• —Mehta VA, Bettegowda C, Ahmadi SA, et al. Spinal cord untethering and scoliosis in patients with myelomeningocele. J Neurosurg Pediatr. 2011;8(2):155–162.
• —Pierz K, Banta J, Thomson J, Gahm N, Hartford J. The effect of tethered cord release on scoliosis in myelomeningocele. J Pediatr Orthop. 2000;20(3):362–365.
• —McGirt MJ, Mehta V, Garces-Ambrossi G, et al. Pediatric tethered cord syndrome: response of scoliosis to untethering procedures. J Neurosurg Pediatr. 2009;4(3):270–274.
• —McMaster MJ, Ohtsuka K. The natural history of congenital scoliosis. J Bone Joint Surg Am. 1982;64(8):1128–1147.
• —Hedequist D, Emans J. Congenital scoliosis: a review and update. J Pediatr Orthop. 2007;27(1):106–116.
• —Banta JV, Drummond DS, Ferguson RL. The treatment of neuromuscular scoliosis. Instr Course Lect. 1999;48:551–562.
• —Tsirikos AI, Wordie SJ. The surgical treatment of spinal deformity in children with non-ambulatory myelomeningocele. Bone Joint J. 2021;103-B(6):1133–1141.
• —Sponseller PD, Yang JS, Thompson GH, et al. Pelvic fixation of growing rods: comparison of constructs. Spine. 2009;34(16):1706–1710.
• —Geiger F, Parsch D, Carstens C. Complications of scoliosis surgery in children with myelomeningocele. Eur Spine J. 1999;8(1):22–26.
• —Hatlen T, Song K, Shurtleff D, Duguay S. Contributory factors to postoperative spinal fusion complications for children with myelomeningocele. Spine. 2010;35(13):1294–1299.
• —Sponseller PD, LaPorte DM, Hungerford MW, Eck K, Bridwell KH, Lenke LG. Deep wound infections after neuromuscular scoliosis surgery. Spine. 2000;25(19):2461–2466.
• —Stevenson KL. Chiari Type II malformation: past, present, and future. Neurosurg Focus. 2004;16(2):E5.
• —Tubbs RS, Oakes WJ. Treatment and management of the Chiari II malformation. Childs Nerv Syst. 2004;20(6):375–381.
• —Copp AJ, Adzick NS, Chitty LS, Fletcher JM, Holmbeck GN, Shaw GM. Spina bifida. Nat Rev Dis Primers. 2015;1:15007.

This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.