Surgery for Spina Bifida

Surgery for spina bifida involves a variety of neurosurgical, orthopedic, and urologic procedures. Surgical procedures include the following:

• Closure of the defect over the spinal cord
• Spinal deformity reconstruction
• Lower-extremity deformity correction

Without closure of the defect, survival is jeopardized. Closure may become more frequently an antenatal procedure. ^{[1, 2, 3]}  Beyond closure, other needed neurosurgical procedures may include shunting for hydrocephalus, including normal-pressure hydrocephalus. Many urologic procedures may be required for the neurogenic bladder.

In the preantibiotic era, persons with spina bifida were not expected to survive, because the spinal cord and, thus, the central nervous system are exposed in this disease. Those who did survive had severe handicaps. Debate over whether surgical treatment should be offered or whether the disease should be allowed to take its natural course has been resolved in favor of treatment. The results of withheld treatment are well documented, with most patients dying within the first 6-12 months.

Malcolm Menelaus pioneered many advances in the treatment of patients with spina bifida and summarized them in his classic book The Orthopaedic Management of Spina Bifida Cystica. ^[4]

Some have viewed the connection between spina bifida and hydrocephalus in a unified sense, ^[5] so that spina bifida is considered a consequence of fetal hydrocephalus.

Spinal deformity is common in patients with spina bifida and can be difficult to treat. Complications are frequent, and some question the benefits of spinal-deformity correction in persons with myelomeningocele. ^[6]  The literature has failed to document a significant quality-of-life improvement with fusion. ^{[7, 8]}

Infection is common, particularly in spina bifida patients with a neurogenic bladder. An increased risk exists with any operative procedure. Retethering of the spinal cord frequently occurs and may manifest urologically and orthopedically. Any suspected change in muscle status, which must be monitored serially, or urologic status may be a sign of retethering. ^[9]

Spinal-deformity reconstruction may be rendered particularly challenging by posterior-element deficiencies. These can lead to instrumentation and fusion failures, infection from the neurogenic bladder, and distal ulcers from insensate skin. Anterior procedures are being combined more frequently with the posterior approach to produce a satisfactory fusion.

Lower-extremity procedures are necessitated by muscle imbalance forces. These procedures, particularly hip reduction, have been the most controversial. Opinions differ as to whether they aid in seating and ambulation. Gait analysis has been used to analyze specific candidates who possess motor strength in the quadriceps in the range of "good plus" and who also have hip dysplasia or dislocation.

Procedures distal to the hip often are similar to those for polio but generally are aimed at maintaining the ability to brace the limb to maximize accessibility and independence. These procedures are directed toward reducing deformity, releasing contractures, and balancing muscle forces from the variable neurologic lesions.

The orthopedic surgeon plays a large role in the treatment of patients with spina bifida, in addition to surgical intervention. This role includes long-term monitoring of neurologic status, motor strength, and joint range of motion (ROM). Because many patients require some degree of bracing, examination for skin irritation and breakdown and observation of ambulation to assess the functional utility of the braces are helpful in detecting any change in condition or the need for treatment modification

For more information on this topic, see Spina Bifida.

Pertinent anatomy includes neural innervation, particularly of the lower extremities. Examination of neurologic deficit helps determine the functional level at which the spina bifida cystica lesion has interrupted function.

The myelomeningocele lesion (see Guidelines below) is unique; its effects are significantly different from those of poliomyelitis, in which anterior horn cells are injured. Thus, with a myelomeningocele, motor function and sensation are affected. The symptoms are also unlike those of cerebral palsy, in which spasticity is common. This is because the spina bifida lesion is generally flaccid, though in some cases a myelomeningocele may be associated with a measure of spasticity. (See the images below.)

The severity of the neurologic impairment is based on the patient's neurosegmental level, which is determined through careful assessment of lower-extremity function. Sharrard developed the first and most commonly used system, based on the lowest normally functioning motor level. ^[10]  The International Myelodysplasia Study Group developed a system with more explicit criteria for assigning neurosegemental levels. 

An oversimplified system that the author finds convenient is as follows:

• L1 - Hip flexion
• L2 - Hip adduction
• L3 - Knee extension
• L4 - Knee flexion (medial hamstrings) and ankle dorsiflexion
• L5 - Hip abduction and extension
• S1 - Ankle plantarflexion

It should be kept in mind, however, that manual muscle testing is not reproducible until age 5 or 6 years and can be subjective.

Once the complexity of the actual neurologic deficit has been recognized, it is clinically useful—because the function and treatment of patients with spina bifida follow broad guidelines—to categorize these patients into general groups. Generally, neurologic levels are grouped as follows:

• Thoracic
• Upper lumbar (L1-3)
• Lower lumbar (L4-5)
• Sacral

Independent ambulation generally is a function of having an intact quadriceps with good-plus or excellent-plus strength levels. Patients who do not have adequate quadriceps function (ie, those with thoracic- and upper-lumbar-level spina bifida) may require long-leg braces and bilateral Lofstrand crutches or may be restricted primarily to a wheelchair. However, a study by Bartonek and Saraste found that only 21 of 53 patients achieved expected ambulatory potential on the basis of manual muscle tests, and 22 of 53 did worse than expected. Patients who did not achieve expected ambulation potential had worse balance, more spasticity, and a greater number of shunt revisions. ^[11]

In 1986, Mazur et al found that 46% of spina bifida patients had some spasticity: 9% in the upper extremity, 24% in the lower extremity, and 13% in both upper and lower extremities. ^[12] Patients with spasticity had more orthopedic procedures, more hospital days, and more days in casts and were less likely to walk.

The ability to ambulate is described according to the following functional levels, developed by Hoffer et al ^[13] :

• Community ambulatory - Indoors or outdoors, crutches with or without braces
• Household ambulatory - Only indoors, crutches with or without braces
• Nonfunctional ambulatory - Wheelchair, crutches, and braces, in therapy
• Nonambulator - Wheelchair bound

Swaroop and Dias described a spina bifida classification system in which patients can be categorized into one of the following three groups on the basis of neurosegmental level and accompanying functional and ambulatory capacity ^[14] :

• Group 1 (high-level lesion, weak quadriceps < 3/5) - Limited walking until early adolescence; reciprocating gait orthosis or hip-knee-ankle-foot orthosis (HKAFO)
• Group 2 (low lumbar level, quadriceps >3/5) - Knee-ankle-foot orthosis (KAFO), ankle-foot orthosis (AFO) and crutches; 80% of patients walk into adulthood
• Group 3 (sacral level, gluteus > 3/5) - Patients walk with or without AFOs and 90% walk into adulthood; those with high-sacral disease lack gastrocnemius-soleus function and ambulate with AFOs and no support; those with low-sacral disease retain gastrocnemius-soleus function and ambulate without braces or suport

A review of 84 patients from an adult clinic (minimum age at follow-up, 20 years; mean, 31 years; range, 20-64 years) found that 42 had normal IQs, 70% never needed a neurosurgical shunt, 44% had regular education, 8% had college degrees, 56% were unemployed, 30% lived independently, 23% were either married or divorced (with nine normal offspring), 85% dressed themselves, 65% shopped independently, and 54% drove. ^[15]

Additionally, 31% were thoracic (all used wheelchairs), 12% were L1-3 (all but one used wheelchairs), 33% were L4-5 (78% used wheelchairs at least part time), and 24% were S1 and below (all walked). ^[15] Furthermore, 54% experienced decubitus ulcers, and as a consequence, four required major extremity amputations. Spinal fusion protected sitting balance, but hip surgery did not produce congruent hips and occasionally resulted in debilitating stiffness; pressure sores resulted in partial foot amputations despite plantigrade feet.

Patients with spina bifida have variable neurologic deficits that characteristically cause deformity as a result of imbalance in muscle forces. Unopposed muscle pull can cause spinal deformity, progressive lower-extremity contractures, hip dislocations, and, less commonly, dislocations in other joints.

The assessment of the patient with spina bifida should focus on function (ie, accessibility, gait, and independence), and treatment should be directed at addressing any deformity that interferes with the patient's potential. When serial follow-up examinations demonstrate worsening function associated with progression of a deformity, surgery should be considered to correct the deformity in combination with release of the deformity and rebalancing of muscle forces around the involved joint as necessary.

Because neurologic impairment is associated with most functional problems, any corrective surgery would presuppose a stable neurologic status. In the patient with spina bifida, a tethered cord may represent a changing neurologic situation that, until it is addressed, would contraindicate any surgical procedures. Hydrocephalus, Arnold-Chiari malformation and syringomyelia can also cause a decline in neurologic function. 

Spasticity is relatively common in persons with spina bifida, and deformity may be secondary to muscle spasticity versus an unopposed muscle. For example, a patient with excessive ankle dorsiflexion may have spasticty of the anterior tibialis versus lack of ankle plantarflexors. A spastic muscle should be released and never transferred.

Scoliosis, most commonly paralytic scoliosis, accounts for about 90% of spinal abnormalities in spina bifida. ^[16] Paralytic scoliosis is characterized by a single long curve, midthoracic to sacral, often with pelvic obliquity. Paralytic scoliosis is associated with difficulties balancing when sitting and with ischial pressure sores. 

Congenital curves may arise at any level and often are associated with vertebral-body abnormalities, such as defects of segmentation and formation, as well as mixed defects. Many curves may have associated syringomyelia.

The likelihood of developing a scoliotic curve of more than 30° varies with the level of the myelomeningocele. In spina bifida patients at age 20 years, the approximate prevalence is as follows:

• Thoracic myelomeningocele - Almost 90%
• High lumbar myelomeningocele - 80%
• Low lumbar myelomeningocele - 25%
• Sacral myelomeningocele - 10%.

Bracing can be used to improve sitting posture, but it does not stop curve progression. Surgey may be indicated for patients with any of the following:

• Very large curves (>50º)
• Progressive problems with recurrent pelvic pressure sores
• Gross pelvic obliquity
• Unacceptable cosmetic deformity, particularly with back pain

Historically, an anterior and posterior procedure was recommended to achieve a reliable arthrodesis. ^[17] ; however, pedicle screw fixation has decreased the need for anterior surgery while achieving greater curve correction and improvement in lumbar lordosis. ^[18]  For nonambulatory patients, the posterior fusion and instrumentation should extend to the pelvis.

Sponseller et al described an anterior-only surgical technique that can be succesful in a very select group of patients (thoracolumbar curve < 75, compensatory curve < 40, no increased kyphosis, and no syrinx). ^[19] Anterior-only surgery avoids a posterior incision over skin that can be already compromised and at risk for infection.

Tethered cord has been associated with the development of scoliosis, and opinions are mixed regarding the role of tethered cord release and its impact on scoliosis. Pierz et al found that tethered cord release was not helpful in patients with scoliosis greater than 40º or in patients with thoracic-level spina bifida. ^[20]   Mummareddy et al performed a meta-analysis and found that tethered cord release is potentially beneficial to some but not all myelomeningocele patients with scoliosis; patients more likely to benefit are those with smaller curves and lower-level lesions. ^[21]

The high complication rate for scoliosis surgery in spina bifida—up to 58%—makes some question the benefit of this surgery. Sitting balance may be the only measurable parameter that can be improved by means of surgical treatment. ^[6]

Kyphosis of variable severity occurs with high-level spina bifida cystica. Above the T12 level, more than 60% of patients have kyphosis, whereas below that level, only about 10% have a measure of kyphosis. ^[17] Patients with kyphosis greater than 65° have insidious progression; the extensor muscles become flexors when they migrate to a position anterior to the spinal column and thus become a deforming force.

Kyphosis can be associated with a high level of chronic skin ulcerations, difficulty sitting, and problems with access for urinary diversion. It can also lead to early satiety secondary to the chest putting pressure on the abdomen. Kyphosis management varies with the age of the child and the severity or stiffness of the kyphosis. 

In neonates, a rigid kyphosis may interfere with sac closure. Decancellation of the apical vertebra can reduce the kyphosis and allow sac closure.

In young children with flexible kyphosis, bilateral rib-based distraction (eg, with the Vertical Expandable Prosthetic Titanium Rib [VEPTR] device) to the pelvis has been described. ^[22] This technique is especially intriguing because it is relatively minimally invasive and effectively corrects gibbus deformity in the growing child without early vertebral-column resection and fusion.

Young children with stiff kyphosis are especially challanging because an extensive fusion should be avoided to allow for continued truncal growth., Two techniques have been described that resect the kyphosis and allow continued growth of the spine and this was reported by Bas et al. ^[23]

Surgical reduction of the stiff kyphosis can be accomplished via osteotomy or a decancellation procedure; the latter technique may be associated with fewer complications. ^[24]

Sacral agenesis may occur in association with a myelomeningocele, and diastematomyelia can be associated with a tethered cord and other complications. Spondylolisthesis may be present, particularly with hyperlordosis. (A common condition, hyperlordosis results from the imbalance of functioning flexors unopposed by the extensors, which have a higher innervation and may be absent.)

Lordosis is never found at birth, but fixed flexion deformities of the hip and lumboperitoneal shunting have been associated with a significant incidence of hyperlordosis. This may be the result of muscle imbalance, particularly pertaining to the hips, or it may be caused by posterior scarring from other spinal surgery. The problem may require an anterior wedge resection or posterior fusion to prevent interference with ambulation.

A sequential study of the lumbosacral angle documented that it did not correlate with tethered cord syndrome. ^[25] Furthermore, the incidence of spondylolisthesis, which may be associated with tethered cord syndrome and pelvic imbalance, may be treated with in-situ fusion in selected cases. ^[26]

Hip abnormalities are relatively common in spina bifida, and it is therefore important to be cognizant of the natural history. Approximately 80% of upper-lumbar-level patients have some degree of hip dysplasia or dislocation, and the failure rate for hip surgery in this group is very high.  Management has ranged from ignoring the dislocation to treating it aggressively, but treatment is generally more aggressive in patients with the potential to ambulate, such as those with strong quadriceps muscles, good ROM of the hip, and a level pelvis.

In the 1960s, Sharrard popularized an operation for paralytic dislocation of the hip ^[27] in which the iliopsoas was transferred through an opening created in the ilium, with the muscles balanced by a reattachment to the trochanter for abduction and extension forces. This procedure, along with several others, could successfully reduce the hip but often did not result in functional improvement. Many patients developed restricted ROM and pathologic fractures that compromised the functional result.

Subsequent studies of functional results found that the presence of a concentric reduction did not lead to improvements in hip ROM or the ability to ambulate. Current treatment of hip dislocation in spina bifida focuses on maintaining hip ROM with contracture release or femoral osteotomy while avoiding open reduction. ^[14]

Hip flexion contractures over 20-30º impair ambulation and can be treated with soft-tissue releases for high-level patients. Proximal femoral extension osteotomies, which preserve muscle strength, can be performed for L4-5 ambulatory patients.

Generally, flexion deformities of the knee occur in patients with weak quadriceps muscles, and only one third of patients with flexion contractures of more than 10° can maintain ambulatory status. These contractures should be braced when they progress past 10-20°, and a posterior release procedure should be performed at 20-40°.

Hyperextension or recurvatum deformity with limited flexion is associated with a poor prognosis for ambulation, especially when it prevents a normal alignment in a young child. An older child may require a quadricepsplasty or femoral osteotomy, particularly in cases of valgus alignment. Newborns with spina bifida can present wtih knee recurvatum or congenital knee dislocation. Serial stretching and splinting are usually successful in achieving full flexion. Percutaneous quadriceps release can be performed if full flexion is not achieved.

Knee valgus can occur in ambulatory patients with weak hip abductors secondary to a combination of crouch, Trendelenburg gait, and excessive tibial torsion. This can lead to excessive transverse motion through the knee with subsequent knee laxity, pain, and cartilage damage. Treatment can consist of an HKAFO to protect the medial knee, crutches, and/or tibial derotational osteotomy to correct the excessive tibial torsion.

Foot and ankle problems are very common in spina bifida and may present as calcaneus, equinus, varus, valgus, or a combination of deformities. For ambulatory patients, the goal of treatment is a plantigrade, supple, and braceable foot with preserved ROM. For nonambulatory patients, the goal is reasonable foot position that permits easy shoeing.

Clubfoot (talipes) is one of the most common foot deformities seen in spina bifida and may arise from several causes, including muscle imbalance, spasticity, and contractures. It is more frequent in higher-level lesions and traditionally has been treated with soft-tissue releases. Serial casting has been associated with skin breakdown, but there are reports of the Ponseti method being successful in spina bifida. If a recurrence is encountered, soft-tissue releases are the first step, followed by traditional posteromedial release if necessary. The goal is to have a plantigrade foot by age 12 months when the child begins a standing program.

For the recurrent multiply operated clubfoot in children younger than 10 years, talectomy is a reasonable option. Simultaneous fusion of the calcaneocuboid joint will help prevent loss of correction. A triple arthrodesis can be performed if the patient is older than 10 years, but one must ensure that the foot is plantigrade. Some feel that foot fusions should be avoided in spina bifida on the grounds that they can lead to skin breakdown.

Equinus can be seen with all neurosegmental levels but especially in thoracic-level and high-lumbar-level patients. The cause may be muscle imbalance, gravity, or spasticity. Nonsurgical treatment consists of stretching and casting followed by braces. If this fails, soft-tissue release of the tight posterior structures can be performed. Capsulotomy may be necessary in severe cases.

Congenital vertical talus presents with rocker-bottom foot position and can be treated with serial casting to stretch out the tight dorsal structures. If the talonavicular joint remains subluxated, limited dorsal soft-tissue releases can be performed if necessary.

Calcaneus or calcaneovalgus occurs in as many as one third of patients with spina bifida, mostly in those whose neurosegmental level is L4-5. The contracture may be secondary to unopposed muscle pull or spasticity; it can also be secondary to prolonged walking in the crouch position without braces.

Unopposed tibialis anterior activity may create a calcaneus deformity and can be treated with simple release of the tibialis anterior (especially if it is spastic) or with posterior transfer of the muscle through the interosseous membrane to the calcaneus. Because the transferred tibialis anterior is too small to create sufficient ankle plantarflexion power, the patient will still require an AFO. Patients with calcaneovalgus can be treated with soft-tissue releases of the tight extensors and evertors of the foot.

A cavus deformity may be associated with a lower neurologic lesion. The lesion is sometimes at S2 and can produce intrinsic tightness, which may respond to a Steindler plantar fascial release from the heel or a Dwyer calcaneal osteotomy. At maturity, a triple arthrodesis is very successful.

Ankle valgus can be located at the tibiotalar joint or can be subtalar. If the valgus is at the tibiotalar joint and the patient has at least 2 years of remaining growth, guided growth can be utilized to correct the deformity. An eight-Plate (Orthofix, Lewisville, TX) placed across the distal medial physis can act as a medial tether, and the lateral side can grow, thus correcting the valgus. Guided growth can also be accomplished with a fully threaded screw placed through the medial malleolus, across the physis, and into the distal tibial metaphysis.

If the patient has less than 2 years of growth remaining, a distal tibial osteotomy can be performed. The valgus can be located at the talocalcaneal joint, and this requires a medial sliding calcaneal osteotomy if the deformity cannot be controlled with an AFO.

Patients with myelomeningocele can have several complications, of which fracture is one of the more common; 22% of spina bifida patients have a significant fracture in their lifetime. Fracture may occur in association with a significant surgical procedure, such as hip reduction or spine surgery. During the postoperative period, patients are not upright and have disuse osteoporosis complicating their already present osteopenia.

Fracture may occur without pain and often is associated with an elevated temperature and redness, swelling, and warmth in the fracture area. An associated pressure injury sometimes occurs. In some cases, the erythrocyte sedimentation rate (ESR) and white blood cell (WBC) count are mildly elevated in reaction to the swelling. In other instances, radiographs reveal marked periosteal elevation and exuberant callus, which occurs because the fracture is adjacent to a Charcot joint. Osteomyelitis and septic arthritis are differential diagnoses.

Management includes inspection of the skin in cases of stable fracture, as well as possible immobilization using existing braces (locked on a 24-hour basis) or plaster immobilization. In some cases, open reduction with internal fixation (ORIF) is required for reasonable function.

Patients who have had a major surgical procedure are best treated as soon as possible because early treatment may diminish the fracture rate. A study of patients who underwent hip reduction revealed that placing the patient back in some form of cast or HKAFO brace in an upright position in the immediate postoperative period eliminated fracture; prior to the institution of this postoperative weightbearing, 22% of patients sustained fracture on follow-up. ^[28]

Patients with spina bifida have an increased incidence of sensitivity to latex, which can cause anaphylactic reactions. Anecdotally, the author witnessed an unsuspected reaction during ORIF of a femoral fracture. Although the child undergoing the procedure had had prior operations without incident, upon dissection down to the fracture, anaphylaxis with complete arrest occurred when the author's gloved finger touched the bone. After resuscitation and glove change, the procedure was completed uneventfully.

Risk factors for latex sensitivity, beyond having a myelomeningocele, include multiple operations, particularly in the first year of life. The most common source of latex exposure is balloons, followed by latex gloves. Treatment with latex-free materials has been shown to reduce the incidence of reactions; these materials may also diminish sensitization, and they can familiarize the staff with the allergy problem and with substances that may contain latex that would not otherwise be suspected.

The Congress of Neurological Surgeons (CNS) issued clinical practice guidelines for pediatric myelomeningocele in September 2019. ^[29]  Recommendations included the following:

• Antenatal myelomeningocele repair is recommended in fetuses who meet fetal and maternal Management of Myelomeningocele Study (MOMS)-specified criteria for antenatal surgery to decrease the likelihood of shunt-dependent hydrocephalus.
• The method of myelomeningocele closure chosen should be based on differences between antenatal and postnatal repair in terms of the need for permanent cerebrospinal fluid diversion, in addition to other relevant fetal and maternal factors.
• In fetuses with antenatally diagnosed myelomeningocele who meet fetal and maternal MOMS inclusion criteria, antenatal myelomeningocele closure is recommended. It may improve short-term ambulatory status (at age 30 months).
• The long-term benefit of antenatal closure on ambulatory status has not been determined. Children who have undergone antenatal or postnatal closure should be monitored closely for tethered spinal cord and resulting loss of ambulatory function.
• It is unknown whether myelomeningocele closure performed within 48 hours of birth decreases the risk of wound infection.
• If myelomeningocele closure is delayed beyond 48 hours, antibiotic therapy should be initiated.
• Whether ventricular size and morphology affect neurocognitive development is unknown.
• Children who have undergone antenatal or postnatal myelomeningocele closure should be monitored for tethered cord syndrome and/or inclusion cysts; antenatal closure has been shown to increase the risk of recurrent tethered cord, more so than postnatal closure.