13.7 The orthopaedic management of myelomeningocoele

Myelomeningocoele or spina bifida is a congenital condition in which the embryological development of the neural tube is incomplete. The neurological effects are due to the combination of the absent or damaged neural elements at birth and the secondary effects of tethering of the spinal cord at the site of the lesion during growth.

For the orthopaedic surgeon, the main challenges are the position and stability of the hip joints and the management of foot deformities. The management of the spine itself in patients with myelomeningocoele is dealt with in Chapter 13.8.

The incidence in the United Kingdom is currently approximately 1:1000 live births. It has fallen over the last three decades particularly in Wales and Northern Ireland. This fall is probably attributable to the routine use of folate supplements in pregnancy, improved prenatal diagnosis, and the termination of affected pregnancies.

The neurological effects of a myelomeningocoele are not restricted to the musculoskeletal system. Many patients develop a hydrocephalus that requires a ventriculoperitoneal (VP) shunt and neurosurgical monitoring. Bowel and bladder function is also often abnormal and appropriate medical and surgical care essential. Hence, many centres employ a multidisciplinary approach to the management of these complex cases.

The orthopaedic goal of management is to optimize the patient’s comfort and mobility while avoiding overtreatment. Surgical treatment must be planned in the context of the individual’s abilities and circumstances; the number of surgical episodes should be minimized, and postoperative immobilization must be as brief as possible. Latex allergy has been reported in patients with spina bifida and latex-free equipment should be used in areas such as the operating theatre suite.

Whilst a rough prediction of lower limb function can be made by assessment of the level of the neurological lesion, it is not possible to make absolute or accurate forecasts of future mobility for any individual infant. Many other factors influence function. The asymmetric and often ‘patchy’ nature of the peripheral neurological lesion, the variability of the effects on the central nervous system, individual personality and drive, the possible effects of spinal cord tethering with growth, weight gain, and bone fragility are just some of these factors. Many children require the aid of orthotic devices to stabilize and support joints to achieve independent mobility and many are predominantly wheelchair users (Figure 13.7.1).

As a general rule it makes sense to treat identifiable musculoskeletal problems as simply and effectively as possible in the infant, then tailor future treatment to the individual as their particular pattern of involvement and development unfolds. In practice this involves early, minimally invasive treatment of selected hip dislocations and foot deformities in the young child, and more complex surgery where needed in older patients. It is true that with growth and associated weight changes, the child’s function may change but a change in their neurological status must also be considered and excluded by appropriate investigation (Box 13.7.1).

Hip deformities in spina bifida are associated with lesions at all neurological levels but are more common with higher lesions. An absence of muscular control appears to be the major influence on hip stability rather than muscular imbalance across the joint. Hip dislocation alone has not been shown to influence gait efficiency, sitting balance, or the formation of pressure areas around the pelvis. The hip joint may have sensation even in high lumbar lesions, however, and these patients may develop pain in subluxated or dislocated joints.

Hip flexion contractures are more troublesome in thoracic and high lumbar neurosegmental patients. In non-ambulant patients with a thoracic lesion, a progressive deformity develops which has a tendency to recur after surgical release. Well-controlled seating following surgery may be effective in younger children but a progressive deformity in the older child or adolescent is difficult to reverse.

A hip flexion deformity of more than 30 degrees in the ambulant child, with or without orthoses, is best managed with a soft tissue release to allow an upright stance and comfort when using orthotic supports and walking aids (see Figure 13.7.1B,C).

Hip dislocation, noted at birth, in lumbar and sacral neurosegmental patients can, as a rule, be reduced surgically though a medial approach in early infancy. There is no benefit to reducing the hips in patients with a definite thoracic neurosegmental lesion.

Surgery for subsequent or later subluxation or dislocation remains the subject of debate in the high lumbar neurosegmental group. No clear benefits have been demonstrated from surgical relocation in terms of gait, standing ability, or sitting balance, even for unilateral dislocations. In the event of a painful subluxation or dislocation, joint stabilization is indicated. Children with low neurosegmental levels are better candidates for surgery. Typically, this involves osteotomies above and below the joint in addition to soft tissue surgery. Unfortunately, the results of surgery are unpredictable and recurrent subluxation and dislocation does occur (Figure 13.7.2).

Muscle balancing surgery is less commonly performed now but some centres still advocate muscle transfers around the hip in association with bony surgery in patients with a low lumbar level (Figure 13.7.3 and Box 13.7.2).

As with the hip, the more severe knee flexion deformities are associated with high neurosegmental lesions and are not directly related to muscle imbalance. The late onset of a knee flexion deformity with associated hamstring tightness or an unexpected deterioration in an existing deformity should raise the possibility of a tethered spinal cord.

A knee flexion deformity of more than 30 degrees in a potential walker is an indication for soft tissue release in children below the age of 7 or 8 years. In older children, surgery is best delayed to closer to skeletal maturity at which time anterior hemiepiphyseodesis or extension osteotomies can be used to correct residual flexion. (see Chapter 13.4, Figure 13.4.8)

This is a much less common deformity. In the neonate, manipulation and serial splints or casts will achieve adequate correction in many cases. Surgical treatment can involve quadriceps lengthening with relocation of the hamstrings in patients with low lesions, or tenotomy of the patella tendon in those with no quadriceps function.

Both external and internal deformities are recognized and may be treated by derotational osteotomies. It is essential that prior to surgery any existing ankle deformity is identified.

The goal of treatment is a supple plantigrade foot: whatever the function of the patient, stiffness and deformity increase the risk of skin ulceration in a foot with impaired or absent sensation.

The principles of Ponseti’s method of foot deformity treatment (see Chapter 13.21) can be applied to the foot in spina bifida, much as they can in idiopathic cases and in arthrogryposis. Where surgery is judged inadvisable, adaptive footware can allow continued ambulation. Development of new deformities throughout childhood should raise the possibility of a tethered spinal cord.

Treatment in the neonatal period begins with manipulations and serial casts complemented where appropriate with minimal surgery to release tight tendons. Some children present with a rigid foot deformity similar to that seen in arthrogryposis, and can be treated similarly with a more prolonged series of gradual manipulations and casts. An Achilles tenotomy is usual and may need to be performed earlier than with the idiopathic foot. Relapsed or resistant deformities may be treated with more extensive surgery but at the risk of causing more stiffness in the long term. In older children, equinovarus deformities can be corrected with osteotomies, whilst many surgeons consider a triple arthrodesis as the definitive salvage procedure suitable for use from adolescence onwards. An alternative in severe deformity is the Ilizarov method of gradual correction using an external fixator. This is surprisingly well tolerated in this patient group and may avoid the problems associated with a rigid insensate foot following arthrodesis.

This foot deformity traditionally required extensive open surgery to correct the troublesome rigid rocker-bottom foot. Recently the Iowa group have described a method of serial manipulations and casts complemented by minimal surgery, derived from the Ponseti clubfoot treatment. This method has the advantages of less extensive surgery and a reduced risk of significant stiffness.

A progressive cavus deformity may indicate a tethered spinal cord and this possibility must be investigated before surgery to the foot is performed. Molded insoles can accommodate minor deformities but prominence of the metatarsal heads combined with impaired sensation is a common cause of skin breakdown and recurrent infection. Metatarsal and calcaneal osteotomies may be needed to realign the foot. Severe deformities may require triple arthrodesis or correction using the Ilizarov method.

This troublesome deformity gives an unstable base for stance and causes point-loading on the prominent calcaneum with associated risks to the skin. Management consists of serial manipulations and casts to relax the dorsal structures followed by dorsal soft tissue release and osteotomies of the mid-foot and calcaneum (Figure 13.7.4).

Rigid foot deformities in an ambulant patient with impaired sensation are associated with recurrent skin ulceration, deep infection, and osteomyelitis. In intractable cases, amputation may be a robust practical solution, particularly where the prosthesis loads through a sensate area, such as a patellar-tendon-bearing socket in a patient with a low lumbar lesion. Amputation should be delayed where possible till skeletal maturity to avoid the complication of appositional bone growth.