19 Best Surgical Strategies for Sitting Comfort
Children with neuromuscular disorders are often unable to walk and depend on wheelchairs for mobility. It is therefore doubly unfortunate for them that these disorders are also a potent cause of spinal deformity, which can make sitting comfortably in a wheelchair almost impossible. Untreated, they typically sit with a tilt to one side, requiring lateral support or the use of their arms to remain upright. The spine is scoliotic and often hyperlordotic or hyperkyphotic; this results in restriction of the chest and abdominal capacity, with the lower costal margin impinging painfully on the pelvis. The pelvis is tilted, causing an uneven and painful distribution of pressure in the weight-bearing areas, and the hips are asymmetrically positioned, with one or both often dislocated, causing further discomfort (Fig. 19.1).
The main aim of treatment for neuromuscular scoliosis in wheelchair-dependent children is to improve their sitting comfort. The components of this treatment are the following: positioning the center of gravity of the trunk in the stable zone within the four corners of the sitting position, which are the ischial tuberosities and the posterior aspect of the thighs; making the trunk sufficiently straight that the thoracic and abdominal cavities can maintain a physiologic capacity; and positioning the pelvis and hips in relation to the spine so that the sitting pressure is distributed evenly.
The surgical strategy to achieve these aims requires a careful assessment of every aspect of the child’s condition and lifestyle, how they are affected by the spinal deformity, and how this is likely to change in the future. The assessment should be carried out by the spinal surgeon in collaboration with the other physicians and other health care professionals who are usually already involved in the child’s care. An understanding needs to be reached by all concerned, in particular the caregivers and in so far as is possible the child, of what is the best outcome of treatment that can be hoped for, what is the likelihood of achieving it, and what risks are involved. The surgery typically requires the correction of severe and stiff deformities of the spine and spinopelvic junction. It is technically demanding with a risk for significant complications, and it is seldom possible to achieve a perfect correction of the spinal curvature or a perfect sitting position. Nonetheless, with an appropriate preoperative assessment involving a multidisciplinary team, and with careful patient selection and surgical planning and execution, it is usually possible to improve the basic requirement of these children to be comfortably seated and to prevent or lessen the worsening of their sitting position that usually accompanies growth.
19.1 Natural History of Neuromuscular Scoliosis
The neuromuscular conditions that affect children are highly likely to cause scoliosis. Polio, now almost eradicated worldwide, has left a legacy of neuromuscular spinal deformity and loss of walking ability in countries where it was until recently endemic. In developed countries, cerebral palsy is the condition most commonly underlying neuromuscular deformity, although several other early onset neuromuscular conditions—for example, spinal muscular atrophy, Duchenne muscular dystrophy, and spinal dysraphism—cause similar problems, each with its own characteristics.
In general, the more severe the neurologic problem, the more likely it is that scoliosis will develop. This was demonstrated by Saito et al in 1998 1 in a review of 79 untreated, institutionalized patients with cerebral palsy in whom the progression of scoliosis was monitored with serial radiographs. Scoliosis affected 68% of these patients, and it was found that the progression of spinal deformity correlated with the severity of their condition, as assessed by their ambulatory ability. No patients who were able to walk developed curves of more than 60 degrees; in contrast, 29% of those who were wheelchair-bound developed curves of more than 60 degrees, and all did who were bedridden (Fig. 19.2). These findings were very similar to those of McCarthy et al, 2 who in 2006 found an overall incidence of scoliosis of 20% in patients with cerebral palsy but of 62% in nonwalkers (Fig. 19.3).
Several publications have shown that musculoskeletal problems in children with cerebral palsy, such as scoliosis and hip dislocation, are becoming more common in developed countries, where the improved medical care of preterm neonates is increasing their survival. Although the incidence of cerebral palsy in babies of normal birth weight remained constant from 1980 to 1998, at between 2 and 3 per 1,000 births, 3 the survival of low birth weight and premature infants, in whom cerebral palsy is much more common, increased markedly during this same time. 4
Typically, children with cerebral palsy have low muscle tone at birth and no deformity or joint contractures. However, the muscles affected by the neurologic injury become hypertonic at an early age, and joint contractures, including spinal deformity, often develop between 5 and 10 years. The typical spinal deformity involves the whole spine in a single long c-shaped curve with an associated tilt of the pelvis and deformities of the hips, one or both of which often dislocate. This makes sitting (and for those able to, standing and walking), increasingly difficult.
19.1.1 Duchenne Muscular Dystrophy and Spinal Muscular Atrophy
In Duchenne muscular dystrophy, the progressive nature of the muscle weakness leads to a loss of ambulation around the age of 8 to 10 years, and respiratory compromise starts to become apparent at about 12 years. In spinal muscular atrophy, similar considerations apply, although the different subtypes progress at different rates. The purpose of surgery for children with these two progressive conditions, like scoliosis surgery for other wheelchair-bound children, is first to optimize sitting balance and free the arms from providing trunk support, allowing hand function, and second to protect lung capacity from the effects of spinal collapse, thus improving quality of life and increasing life expectancy.
The timing of surgery is ideally during the surgical window when bone growth has been sufficient to allow secure spinal fixation but the child has not yet reached the point of serious (>50%) loss of vital capacity. In Duchenne muscular dystrophy, this is usually around age 12, when the Cobb angle is small and pelvic obliquity has not yet become an issue. The advantages of operating at this age rather than later are that the distal extent of fixation can be kept at L5 rather than the pelvis, and the operative time, blood loss, complications, and hospital stay are all reduced. 5 , 6
19.1.2 Myelomeningocele
Scoliosis and hyperkyphosis are common in patients who have myelomeningocele, with the more proximal lesions resulting in more severe neurologic loss and a higher incidence of spinal deformity. More than 80% of patients with a thoracic lesion have a spinal deformity, whereas in those with a lumbar or sacral lesion, the incidence is about 20%. 7 As in most children with a neuromuscular spinal deformity, the severity increases with growth. Pelvic tilt in both the coronal and sagittal planes often accompanies the spinal deformity, and in addition, there may be developmental abnormalities of the pelvis itself. The effect of the deformity on seating is compounded by the associated numbness of the saddle area. Together with urinary and fecal incontinence, this numbness makes skin care a lifelong problem.
Hyperkyphosis, typically in the thoracolumbar or lumbar spine, results in forward tilting of the pelvis and forward displacement of the distribution of sitting pressure. Correction is made more difficult by the presence of scarring from the myelomeningocele and any closure surgery that may have been performed. Scarring, together with anesthetic skin, makes for problems with wound healing. The technique requires shortening of the spine, either by posterior subtraction osteotomy at multiple levels or by excision of the apical vertebrae (kyphectomy), usually accompanied by transection and ligation of the thecal sac. Even in experienced hands, these operations are demanding and carry significant risks. 8 , 9
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