CLINICAL SIGNS AND COURSE
The spinal cord defect associated with spina bifida is often associated with other malformations. This results in a multisystemic process that leads to a variety of health problems and potentially life-threatening complications. Motor and sensory deficits vary according to the level and extent of spinal cord involvement (52-54).
In the care of individuals with spina bifida, two levels are often described: the anatomic level of the lesion and the neurologic level of functional involvement. In terms of the level, it is the neurologic or functional level that gives health care providers prognostic information with respect to long-term expectations and functional outcomes. Spinal cord involvement may result in asymmetric motor and sensory deficits. Sensory deficits usually follow a dermatomal pattern and may not affect all sensory modalities equally (52,53).
Neurogenic bladder and bowel dysfunction may be present in all patients because of the distal level of innervation of the bladder and bowel. This is true even if there is no apparent motor deficit in the legs.
In the following discussion, clinical signs of muscle weakness are described. These functional neurologic levels may not directly reflect the anatomic level of the malformation.
Musculoskeletal deformities related to muscle imbalance may present serious clinical concerns. Deformities may be static deformities present at birth or may develop over time. Figure 15.1 summarizes segmental innervation, preserved muscle function, and musculoskeletal complications typical of various levels of spinal cord malformation. Providers must keep in mind that the overall functional outcome for the individual is related in part to neurologic level, in addition to other associated CNS, psychosocial, and medical issues.
Thoracic-level malformations spare the upper extremities, with the exception of decreased ability to abduct the fifth digit (thoracic level 1 = Tl). There is usually partial innervation of the abdominal and intercostal musculature, which may result in respiratory dysfunction or insufficiency. Kyphosis and kyphoscoliosis may result from trunk weakness and be more prominent in individuals with vertebral anomalies (55). The legs may be flaccid or show signs of spasticity when some portion of the distal spinal cord is preserved (56). The lack of volitional movements combined with the effect of gravity leads to lower extremity deformities. The usual lower extremity posture in the supine position is partial hip external rotation, abduction, and ankle plantar flexion from gravity. Knee flexion contractures and equinus foot deformities develop from sitting. Hip flexion contractures with compensatory lumbar lordosis increase any pre-existing kyphosis or kyphoscoliosis (56).
Hip flexors and hip adductors are innervated at the LI to L2 levels. With L2 sparing, knee extensors have partial innervation but are not at full strength. The distal lower extremity muscle strength is absent. The distribution of muscle imbalance—hip flexion and hip adduction with absent hip extension and hip abduction—leads to the development of contractures and early paralytic hip dislocation. Pelvic obliquity seen in asymmetric hip pathology enhances scoliosis. Gravity-related foot equinus deformity may develop (56).
Ambulation during young childhood is typical with the use of bracing and assistive devices. Long-term ambulation through adulthood is less likely as priorities change and there are further increases in the already high-energy demands of walking (54). The extent of bracing necessary to achieve ambulation is usually related to the amount of active knee extension.
Innervation of the hip flexors, hip adductors, and knee extensors is usually complete; however, hip abductors and hip extensors remain weakened. Coxa valga and acetabular dysplasia are still a concern. Typically, hip dislocation occurs later at the L4 to L5 segmental levels. Newborns with a well-defined lesion sparing L4 lie in a typical position of hip flexion, hip adduction, and knee extension. When the L5 segment is spared, the gluteus medius, gluteus maximus, and hamstrings have partial strength and knee extensor contracture is less likely. Because the tibialis anterior is unopposed by its plantarflexion and everter antagonists, a calcaneo-varus foot deformity develops. If the peroneus muscles are spared, the varus is eliminated. Although the plantar flexors are partially innervated, they are not strong enough to counter the strong force of the ankle dorsi-flexors (56).
Active plantarflexion is stronger and some toe movements are present. Intrinsic foot muscles remain weak and may result in a cavus foot deformity with clawing of the toes (56).
FIGURE 15.1 Musculoskeletal, sensory, and sphincter dysfunction by segmental level.
Partial or complete absence of sensation predisposes individuals with spina bifida to skin injuries because of decreased ability to perceive pressure, pain, trauma, or heat (52-54,57). Skin breakdown tends to occur over areas of prominence and weight-bearing. The lower back, inter-gluteal, perineum, feet, heels, and toes are the sites of predilection, but any area with sensory loss may be affected. Scoliotic and kyphotic prominences are areas prone to breakdown (55). Pressure ulcers often heal slowly, tend to get infected, and often recur. A refractory pressure ulcer may be a symptom of a tethered cord. Long-standing ulceration with deep tissue necrosis may spread to bone and lead to acute or chronic osteomyelitis. Weight-bearing is often on the anesthetic heel, and a deep ulcer can lead to osteomyelitis of the os calcis (56).
Other complications of denervation include vasomotor instability, neuropathic Charcot joints, and osteoporosis in individuals with extensive lower extremity weakness (54,55,57,58).
Sensation may be decreased with regard to sexual function thus causing different issues for males and females. Please see the section on Long Term Aging With a Neural Tube Defect where this is discussed in more detail.