18 Surgical Treatment and Outcomes
Neuromuscular disorders comprise a very diverse group of conditions. The most common myopathic form is Duchenne muscular dystrophy, and the most common neurogenic form is spinal muscular atrophy (SMA). The majority of patients with early onset neuromuscular scoliosis have SMA, which is an autosomal recessive disorder presenting in early childhood (homozygous mutation of survival motor neuron gene 1 on chromosome 5 and predominant skipping of survival motor neuron gene 2). Patients with SMA exhibit degeneration of the anterior horn cells of the spinal cord. The diagnosis is based on a combination of clinical features (hypotonia and absent reflexes), an electromyogram showing fibrillation and muscle denervation, muscle biopsy, and DNA genetic testing with polymerase chain reaction (PCR), which is a conclusive method for diagnosing the condition. 1
This disorder has been classified into four types based on the age of the patient at presentation. Type 1 develops before the age of 6 months, type 2 at 6 to 18 months, and type 3 after the age of 18 months. Type 4 is benign and has an onset after 30 years. Scoliosis is present in more than 70 to 80% of patients with SMA. More specifically, all patients with type 2 SMA develop scoliosis by the age of 3 years, and by the age of 10, they develop significant curves of more than 50 degrees. Therefore, surgical intervention is at some time indicated for all children with type 2 SMA. 2
SMA, like Duchenne muscular dystrophy, can have an effect on several systems, so that multidisciplinary evaluation and treatment are required. Progressive muscular weakness can result in pulmonary restriction, usually joint contractures, and nutritional disorders. The development of severe curves at a very young age poses unique challenges, and attempts at prophylactic or early bracing have not prevented curve development and progression. An immediate effect of this is difficulty breathing and restricted growth of the chest wall in the longer term. The spinal deformation is mostly a progressive, c-shaped thoracolumbar curve with the development of pelvic obliquity. An increase in either kyphosis or thoracic lordosis can be part of the deformity. The consequences of the deformity are loss of sitting balance, shortening of the trunk, and compression of the heart and lungs. The mobility of the ribs is reduced by rotation and deformation of the trunk; as a result, the breathing capacity is further decreased.
In this chapter, we describe our approach to the management of patients with early onset neuromuscular scoliosis (SMA in particular). Our discussion includes the preoperative assessment, our operative preference for self-growing rods, and the postoperative care required by this group of very delicate patients.
18.1 Indications for Surgery
Studies have shown that bracing is ineffective in preventing the progression of spinal deformity in patients with neuromuscular disorders. Spinal surgery is considered the primary treatment option for correcting severe scoliosis in neuromuscular disorders. It can improve the patient’s cardiopulmonary function, sitting balance, appearance, and quality of life. However, in this population, surgery is considered a major intervention associated with high risk. A careful preoperative evaluation is necessary, and this should not be restricted to the spinal deformity itself; it must also include anesthetic management, pediatric cardiopulmonary care, postoperative intensive care, and postoperative rehabilitation.
We believe that surgery is indicated for those patients who have early onset neuromuscular scoliosis with rapidly progressing curves, which includes all children with type 2 SMA. We favor surgical treatment with growing constructs, to provide early correction of progressive curves and allow guided growth of the spine. This should, in theory, protect lung function and improve daily care of the children, including their mobilization with use of a wheelchair.
18.1.1 Preoperative Assessment
Preoperatively, respiratory function should be assessed in regard to both the timing of surgery and possible postoperative complications. The relationship between preoperative pulmonary function and postoperative complications is a little vague. 2 Wang et al have considered this issue at length, and their recommendations include preoperative sleep studies and closely monitored postoperative care, with extubation to noninvasive bi-level positive airway pressure therapy in patients who have marginal respiratory function. 3
Attention should also be given to nutrition, bowel and bladder function, contractures, blood coagulation, and medication during the preoperative phase. A decision about resuscitation should be discussed with the parents, as well as the possibilities of a need for ventilation and/or tracheostomy. Patients and parents should be well informed about all aspects of the treatment, including the aims of surgery, and possible adverse events and their consequences in regard to daily functioning.
18.1.2 Perioperative Management
We recommend hypotensive anesthesia, the use of cell salvage and tranexamic acid, hemodilution, hemodynamic monitoring, and careful positioning of a nasogastric tube and a Foley catheter or indwelling urinary tract catheter. It is also important to maintain normothermia to prevent hemorrhagic complications and clotting problems. The use of anticholinergic agents should be avoided. Throughout the surgery, we use both somatosensory evoked potential (SSEP) and transcranial motor evoked potential (Tc-MEP) spinal cord monitoring.
18.1.3 Postoperative Management
The postoperative care should be conducted by an experienced multidisciplinary team of specialists: surgeons, a pediatric intensive care team, and rehabilitation specialists. The patient is admitted to the pediatric intensive care unit, especially as the threat of respiratory insufficiency requires intensive monitoring. A physiotherapist can coach the child in respiratory techniques and coughing.
The rehabilitation specialist verifies that adequate care is provided at home and coordinates the adaptation of facilities. The (electric) wheelchair may need to be adapted to support a position in which sitting and head balance can be maintained with the least effort on the child. Finally, in consultation with the general practitioner, temporary home care may need to be organized. 2 We do not recommend postoperative spinal braces because modern instrumentation is well suited to provide the required stability.
18.2 Surgical Options
As we have already mentioned, surgical treatment options for early onset neuromuscular scoliosis include both spinal fusion and growth-sparing techniques. Fusion techniques, however, inhibit spine and thoracic growth, and it is well-known that pulmonary development is not complete at birth. Thus, the thoracic deformity caused by scoliosis may adversely affect lung maturation up to the age of 8 years by inhibiting growth of the alveoli and pulmonary arterioles. Spinal growth peaks during the first 5 years of life and then diminishes from 5 to 10 years before increasing again. 4 Therefore, the early treatment of progressive curves without fusion becomes important to improve respiratory and visceral development and to normalize spinal growth as much as possible.
A surgical solution includes posterior spinal stabilization with growing rods. Dual growing rod techniques involve short fusion at the foundation sites and the placement of rods spanning the deformity. However, the rods need to be lengthened approximately every 6 months, with definitive spinal fusion performed after maximal spinal growth has occurred. 5 We have used a self-growing construct system over the last 20 years, which precludes the need for rod lengthening every 6 months. There is no doubt that the one procedure with general anesthesia used for this definitive self-growing rod construct is preferable to the multiple procedures with anesthesia used for the application of other systems.
18.2.1 Surgical Technique for the Self-Growing Rod Construct
Luque and Cardoso developed segmental spinal instrumentation to avoid the need for prolonged bracing while allowing further spinal growth in infantile or juvenile onset scoliosis. 6 Their initial report on a sample of 50 patients (mean follow-up, 23 months) showed Cobb angle correction from 73 to 22 degrees, and mean instrumented segment growth was 2.6 cm over 2 years. A subsequent report on paralytic scoliosis showed maintained correction and continued growth. Further reports on the Luque trolley in paralytic scoliosis secondary to poliomyelitis and in other types of scoliosis describe some problems of spontaneous fusion, modest spinal growth, loss of correction, and rod fracture.
Our self-growing rod construct is based on the Luque principles. After the patient is placed in a prone position and appropriately draped and prepared with padding at all pressure points, we perform a midline incision spanning the segment of the spine to be instrumented. Fixed spinal anchors (pedicle screws) and gliding spinal anchors (sublaminar wires free to travel along the rods) are then inserted. At the fixed proximal and/or distal anchorage points, a classic subperiosteal dissection is performed because these segments are to be fused. At the apex of the deformity, gliding anchors in the form of sublaminar wires are placed for maximal apical translation and deformity correction. We carefully perform midline laminotomies, partially remove the ligamentum flavum, and insert the sublaminar wires. Two double-stranded, short, closed-loop sublaminar wires are used in conjunction with the simple instrumentation designed by the senior author [SHM] at each level. These double-stranded looped wires, each measuring 1 mm, are available in three different lengths for different areas of the spine. The technique of wire passage and the modified instrumentation are detailed elsewhere. 7 The dissection at the gliding anchors is kept to a minimum by using extraperiosteal techniques (and muscle-sparing techniques to a degree) to avoid spontaneous fusion. Two pairs of 5-mm titanium rods are positioned, and the wires are tightened over in a standard fashion. A classic apical translation reduction maneuver is performed to correct the deformity.
We looked at the results of the use of self-growing rod constructs 8 at our institution between 1998 and 2010. From 1998 to 2006), we used the h-bar construct (n = 6). Two l-shaped rods are connected with two h-bars at the proximal and distal ends and secured to the spine with sublaminar wires (Fig. 18.1). In this construct, spinal growth is provided at the proximal part of the fixation by migration of the h-bars cephalad (Fig. 18.2). The rectangular shape created by the h-bars controls rotational forces and maintains the correction, yet allows spinal growth. In this first group of patients, a sufficient length of the rods was left free proximally to allow future spinal growth. We feel that fixation to the pelvis is preferable in all patients because it reduces the chance of loss of correction of sagittal and coronal balance in the long term.
From 2006 to 2010, we used a new hybrid self-growing rod (n = 10). This consists of a combination of screws, four rods, and sublaminar wires. In this construct, two contoured rods are secured to the proximal and distal screws on each side, proximally and distally. The distal rods are also fixed to the pelvic screws directly. The middle section of the spine between the proximal and distal screws is secured by sublaminar wires.
Fixation to the pelvis (including S1 and the ilium) was performed in all cases in both groups. The mean age of the patients in our series was 7 years (range, 5–8; Fig. 18.3 and Fig. 18.4). The new construct had the advantage of sound fixation proximally and distally, and this strong foundation could prevent proximal and distal junctional kyphosis and also provide a long space for spinal growth between screws. This is, we feel, advantageous in young children with a great deal of growth potential. The diagnoses in our series were type 2 SMA (n = 6), type 3 SMA (n = 3), hypotonia (n = 2), muscular dystrophy (n = 4), and cerebral palsy (n = 1). The mean follow-up period for group 1 was 11 years and for group 2 was 2 years. 8
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