20 Growing Spine Options for Neuromuscular Scoliosis

10.1055/b-0038-162481

20 Growing Spine Options for Neuromuscular Scoliosis

Joshua S. Murphy and Burt Yaszay

Abstract

Scoliosis is a common deformity in the neuromuscular population that can interfere with sitting balance as well as pulmonary and gastrointestinal function. Nonoperative treatment has largely been ineffective in controlling neuromuscular spinal deformities. Therefore, they are geared largely toward sitting balance and posture control. Once nonoperative management is no longer effective, a number of surgical techniques have been developed to treat progressive scoliosis in a growing neuromuscular patient including growth-friendly surgery and spinal fusions. Growth-friendly surgeries include traditional growing rods, magnetically controlled growing rods, Shilla procedure, and Vertical Expandable Prosthetic Titanium Rib (VEPTR). Additional modalities include a limited anterior spinal fusion and delayed posterior spinal fusion or an early posterior spinal fusion in appropriate patients. Regardless of technique, there are many variables to consider when treating this patient population including maximizing their preoperative nutritional status and consideration of pulmonary complications and timing of surgery. Furthermore, a high complication rate is associated with growth-friendly surgeries and posterior spinal fusions in the neuromuscular population when compared to patients with idiopathic scoliosis. The surgeon has a multitude of options for treating early-onset scoliosis in the neuromuscular population. It is important to choose the appropriate procedure for each patient as these patients have not only a spinal deformity at a young age, but also other medical comorbidities that put them at risk of complications.

20.1 Introduction

Neuromuscular scoliosis is defined as an abnormal spinal curvature caused by abnormalities of the brain, spinal cord, and muscular systems. The nervous and musculoskeletal systems are unable to obtain and maintain appropriate balance of the spine and trunk. Based on the Hueter–Volkmann principle, this associated imbalance causes abnormal biomechanical load on the spine, and progressive deformity is thought to be the result of both progressive muscle imbalance and anatomic deformity.

Early-onset scoliosis (EOS) is defined as a spine deformity that is present in a child younger than 10 years of age. It is further broken down into subtypes based on the underlying cause of the deformity. Specifically, neuromuscular EOS is a scoliosis that develops in children with neuromuscular disorders including spinal muscular atrophy (SMA), cerebral palsy, spina bifida, and brain or spinal cord injury. ¹ The purpose of this chapter is to highlight the different treatment options in patients with neuromuscular early-onset scoliosis.

20.2 Nonoperative Care

Few nonoperative modalities have been effective in treating neuromuscular scoliosis. Historically, nonoperative treatment has been directed at postural control and maximizing sitting ability. Initially, observation is acceptable treatment of curves that measure 20 degrees or less. If a curve continues to progress, bracing may be an option. Olafssson et al ² published the results of 90 consecutive patients treated with a prefabricated Boston-type brace for neuromuscular spine deformity. The breakdown of patients consisted of 38 patients with spastic tetraplegia, 24 with syndrome related hypotonia, and 21 with myelomeningocele. The average success rate was 28% with 23 successful cases. They found success related to ambulation and short thoracolumbar or lumbar curves. However, nine patients ultimately underwent operation secondary to curve size, although the curve was unchanged during bracing. In conclusion, bracing was thought to be successful in only a small group of patients including those who are ambulatory, with a thoracolumbar or lumbar curve, and short curve length of approximately 5.7 vertebrae. Long hypotonic curves were found to be difficult to control with an orthosis. ²

Miller et al reviewed the results of thoracolumbosacral orthosis (TLSO) management in patients with scoliosis and a diagnosis of spastic quadriplegic cerebral palsy. They found no impact on curve or rate of progression when patients were braced 23 hours per day over a mean period of 67 months, compared to a similar cohort that was not braced and followed to spinal fusion. ³ To date, it is generally accepted that bracing in patients with CP will not alter the progression of the curve. However, it is reasonable to utilize a brace to improve muscle balance and sitting. An additional option is the use of chest supports and modular seating systems that utilize 3-point control of the coronal deformity to prop the child up and address sitting balance. ⁴

20.3 Operative Care

The decision to proceed with operative care is complex, and there are multiple factors to be considered. In general, operative treatment is considered for curve magnitudes greater than 50 degrees and significant deterioration in function. ⁵ ^, ⁶ ^, ⁷ The primary goal of surgery is to prevent progression of the spinal curve and in some cases progression of pelvic obliquity. In cases of spinal fusion, additional goals include reestablishing coronal and sagittal alignment of the spine.

20.3.1 Growing Rods

There is a growing interest in the use of growth-friendly techniques in the management of neuromuscular EOS. Historically, many authors recommended against the use of growth-friendly techniques in the neuromuscular scoliosis population secondary to the high risk of complications. However, it is well known that growing rod surgery is a safe and effective treatment for EOS as popularized by Akbarnia et al ⁸ (Fig. 20‑1). Growth assessment in these children can be challenging, as many patients with cerebral palsy and upper motor neuron disease have delayed onset of puberty and delayed bone age. In addition to serial height and weight measurements, evaluation of the triradiate cartilage status and skeletal bone age have been helpful in assessing remaining growth in patients with neuromuscular scoliosis.

Fig. 20.1 **(a)** Six-year-old male patient with progressive scoliosis. **(b)** Patient underwent placement of traditional growing rods.

Chandran et al investigated a dual growing rod system with pelvic fixation in 11 patients with SMA type 1 or 2. They found a significant improvement of postoperative Cobb angles with 50% correction and no surgical complications or reoperations. However, two patients did have postoperative medical complications including pneumonia and anemia. ⁹

In another study, McElroy et al evaluated the use of growing rods in the treatment of SMA and found there was nearly 50% correction of the major curve, improved trunk height, and improved space available for the lung ratio at final follow-up. However, they did not find any change in the rib collapse commonly seen in SMA. Additionally, they noted that patients with SMA had longer hospital stays than did patients with idiopathic EOS undergoing the same procedure. ¹⁰

McElroy et al evaluated the use of growing rods in 27 patients with CP with and without pelvic fixation. They found that growing rod constructs with pelvic fixation produced better pelvic obliquity correction (p < 0.001). However, the majority of the patients studied had at least one complication, and the cohort had a 30% deep wound infection rate. They recommended sparing use of growing rod constructs in patients with CP. ¹¹

Currently, we use dual growing rods as described by Akbarnia et al ⁸ to treat progressive EOS in our patients with neuromuscular deformity, specifically those with CP and SMA. We advise caution in regard to patient selection as these patients must be viewed as a whole in regard to size, magnitude, and location of the curve, medical comorbidities, and, in some cases, soft-tissue coverage. As previously mentioned, these patients are at an increased risk of deep wound infection, and great care must be taken in selecting the appropriate surgery for the patient. The etiology of the deformity has some impact on the rate of complications; those patients with significant spasticity, pelvic obliquity, and kyphosis are at risk of major complications.

20.3.2 Magnetic Growing Rods

In 2014, magnetically controlled growing rods (MCGR) received Food and Drug Administration (FDA) approval for use in the United States after several years of clinical application in Europe and Asia (Fig. 20‑2). Yoon et al investigated the effects on pulmonary function in children with EOS using MCGR. With a mean follow-up of 2.5 years, they evaluated six cases and found the average correction to be 34 and 36 degrees for coronal and sagittal deformities, respectively. In addition, mean improvement in postoperative forced vital capacity (FVC) and forced expiratory volume 1 (FEV1) was 14.1 and 17.2%, respectively. Importantly, there were two complications that required reoperation including a prominent rod and one rod breakage. They concluded that early intervention using MCGR was associated with significant improvement in postoperative pulmonary function testing and significant improvement in deformity correction with the added benefits of reducing repeat anesthesia and reducing surgical and psychological distress. The cost–benefit has yet to be determined. However, we believe MCGR to be a viable option in treating the growing spine as it decreases the amount of anesthesia inductions and may decrease the complication rate. ¹²

Fig. 20.2 **(a)** Five-year-old male patient with progressive neuromuscular scoliosis. **(b)** Patient underwent placement of magnetically controlled growing rods.

La Rosa et al published their results of 10 patients with EOS and the use of MCGR. They had an improvement in the coronal deformity from 65 to 29 degrees when comparing the preoperative and postoperative radiographs. In this series, they had two complications: one rod breakage and one pullout of the apical hooks. They concluded that MCGR can be effectively used in EOS and may overcome many of the common complications associated with traditional growing rods including fewer anesthesia inductions, fewer surgical scars and surgical site infections, and decreased psychological distress associated with multiple surgeries. ¹³

However, there is a paucity of literature to date investigating the effectiveness and complication rates associated with MCGRs in the neuromuscular population. The authors believe that MCGR can affect the lives of these patients for the above-mentioned reasons including outpatient lengthening that does not require anesthesia, which may decrease the complication rate and psychological stress for the patient and family. It has yet to be determined if this intervention will be safe and cost-effective for early-onset neuromuscular scoliosis.

20.3.3 Shilla Procedure

The Shilla method is a modern pedicle screw construct described by McCarthy and based on the original Luque trolley system ¹⁴ ^, ¹⁵ ^, ¹⁶ ^, ¹⁷ ^, ¹⁸ (Fig. 20‑3). Shilla utilizes an apical fusion with nonlocking polyaxial screws proximally and distally to guide a rod that is purposefully left long to minimize the need for multiple surgical lengthenings. As the spine grows, the rod slides through the nonlocking screws allowing spinal growth of the nonfused segments.

Fig. 20.3 **(a)** A 6-year-old female patient with spinal muscle atrophy type 2. **(b)** Patient underwent fusion from T10 to pelvis with placement of Shilla-type instrumentation at T2–T3.

The authors have found the Shilla procedure to be a viable option in treating early-onset neuromuscular scoliosis. This procedure allows one to obtain correction at the apex of the curve with a limited fusion and then allows for continued spinal growth at the remaining unfused segments. This is also a construct that allows continued spinal growth without having to return to the operating room for multiple lengthenings.

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