12 Dual Growing Rod Treatment
The preservation of spinal growth and prevention of pulmonary compromise in early onset scoliosis pose particularly challenging problems for clinician and patient alike. Maintaining spinal growth and achieving the necessary thoracic height are critical for expansion of the thoracic cavity and the prevention of thoracic insufficiency syndrome.
Alveolar multiplication is thought to continue up until 9 years of age, and the attainment of a vertical thoracic height of 22 cm may afford 80% of the normal forced vital capacity. 1 With these values in mind, it is essential for the clinician to understand spinal and thoracic cavity growth patterns. The first peak in spinal growth occurs during the first 5 years of life, when the T1-S1 height increases at a rate of approximately 2 cm per year. At this time, the thoracic and lumbar spine reaches approximately two-thirds of its adult height. Approximately 6 cm is gained between the ages of 6 and 10 years, and 10 cm between 10 and 18 years. 2 Dimeglio and Bonnel 3 showed that normal T1-T12 thoracic height in newborn children without scoliosis is 11 cm; it reaches 18 cm at 5 years, 22 cm at 10 years, and 26.5 cm in female adults and 28 cm in male adults. The average adult spine measures 42 to 45 cm at skeletal maturity.
Operative treatment in this patient population should be reserved for those with progressive curves in whom nonoperative measures, including casting and bracing, have failed. The correction of surgical deformity ideally aims to restore, maintain, and promote cardiopulmonary and visceral growth. Research in the treatment of this difficult problem strives for more definitive, less invasive or noninvasive options. As our knowledge and understanding of the pathophysiology and biomechanics of scoliosis increase and as more reliable, less invasive options become available, outcomes are expected to improve.
In the absence of rib anomalies or resectable congenital deformities, growth-friendly, distraction-based techniques, such as dual growing rods, currently remain the preferred and most commonly used surgical treatment for children with early onset scoliosis.
12.1 Historical Context
Fusionless instrumented techniques for early onset scoliosis have evolved to be more reliable since Harrington’s account in 1962. 4 He described a concavity-placed single rod anchored with two hooks. Hook dislocation and rod breakage ultimately obliged technique modification. Moe et al 5 later depicted a modification of Harrington’s technique through the serial lengthening of subcutaneous rods placed with a limited subperiosteal exposure at the anchor sites. They also modified the rod geometry to reduce scar formation and allow sagittal contouring. Despite improvements, similar instrumentation problems were encountered. To address anchor and rod failure, Marchetti and Faldini 6 introduced the technique of end-of-construct (foundation) fusion in 1978. Serial lengthening procedures were then performed on the mobile spine after the initial fusion procedure. Other, later notable modifications included the use of sublaminar wires, segmental fixation without arthrodesis, and Luque rod instrumentation.
Modern day growing rods as we know them were introduced in the last decade. Despite advances in technique and instrumentation, the reported outcomes and complications with the use of modern growing rods, especially single rods, have been variable and have resulted in premature fusion in some patients.
In 2000, Akbarnia and Marks 7 introduced the use of dual growing rods with posterior segmental instrumentation and limited arthrodesis of the foundations. In 2005, Akbarnia et al described the technique that most surgeons use today. 8 It has become the most commonly applied technique for dual growing rod surgery and is discussed in detail in this chapter.
12.2 Patient Evaluation
12.2.1 Physical Examination, Clinical and Radiographic Assessment
Patients with early onset scoliosis are often referred by their primary care physicians because of concern about spinal deformity. A thorough and systematic history and physical examination are critical and should be performed on all patients. The prenatal and birth history, as well as the record of achieving age-appropriate developmental milestones, should be included. Questions should be asked about factors predisposing a child to scoliosis, such as family history. The physical examination should include measurement of the height, weight, and arm span as well as an evaluation of the skin, head, neck, chest, pelvis, and extremities. A thorough neurologic examination is paramount, and abdominal reflex testing should be done; its absence may signal an underlying neuroaxial anomaly. The evaluation of the spine should include forward bending and an assessment of spinal flexibility. This may have to be done over the clinician’s knee. Scoliometry is valuable in the clinical evaluation of trunk rotation. Limb lengths should be measured, and pelvic obliquity should be assessed. Gait should be observed in the ambulatory child when possible.
A clinical assessment for early onset scoliosis should always include plain roentgenograms (anteroposterior, lateral, and full-length views) of the spine, including the neck, pelvis, and hips, to evaluate the degree of coronal and sagittal malalignment as well as scoliosis. Bending roentgenograms provide valuable information regarding curve flexibility. Traction or bolster films should also be considered. In idiopathic early onset scoliosis, measurement of the rib–vertebral angle difference (RVAD) and overlap (phase 1 or phase 2) should be evaluated to predict progression. Magnetic resonance (MR) imaging should be considered to rule out concomitant pathology involving the neuraxis and visceral structures. Computed tomography (CT) with three-dimensional reconstructions is useful for further evaluating the deformity, better visualizing any congenital anomalies, and planning surgery (e.g., pedicle screw length). To reduce cumulative exposure of the patient to radiation, an attempt should be made to schedule imaging with other specialties should more than one organ system need to be evaluated.
A multidisciplinary team approach to pre- and postoperative care is employed because many of these patients pose challenges to medical management. Pulmonary function testing should be considered before surgical intervention when possible. A preoperative laboratory and nutritional evaluation should include a complete blood cell count with total lymphocyte count, a comprehensive metabolic panel with albumin and prealbumin levels, and a bleeding profile. Appropriate medical clearances should be obtained before surgery, with a thorough anesthesia and, if necessary, pulmonary evaluation.
12.3 Treatment
12.3.1 Nonoperative Treatment
Nonoperative treatment options for early onset scoliosis include observation, bracing, and casting (Fig. 12.1). Some authors have reported utility with halo traction, but this is less desirable in our view and is reserved for selected patients with severe and rigid curves as a preoperative adjunct to correction. The flexibility of the immature rib cage may limit the transmission of force on the spine and as a whole may render nonoperative treatment ineffective. Nonetheless, nonoperative treatment modalities should be exhausted before surgical intervention is undertaken. Serial casting, such as the technique of Mehta and Morel, 9 has recently gained popularity as a surgery-delaying tactic; it includes repeated cast changes, with the patient under general anesthesia, every 4 to 6 weeks until a brace may be used. A cervicothoracic lumbosacral orthosis (CTLSO), such as the Milwaukee-type brace, is preferred to control a thoracic curve. An underarm brace, or thoracolumbosacral orthosis (TLSO), is less effective at controlling a thoracic deformity. The over-the-shoulder TLSO Kalibus brace has been historically recommended for patients as young as less than 1 year of age who have early onset scoliosis. Bracing failure, noted as curve progression or brace intolerance secondary to skin or pressure issues, should prompt consideration for surgery. Earlier correction may be considered for patients with more significant thoracic curves to prevent potential pulmonary complications.
12.3.2 Operative Indications and Timing
The optimal timing and indications to pursue operative intervention remain in question. In a level 4 survey of international surgeons treating early onset scoliosis, 10 the surgeons reported that their primary indication for growing rod treatment included curves greater than 60 degrees in patients younger than 8 to 10 years of age, with 6 months as the preferred time between lengthening procedures. Other reported indications included rigid curves, brace intolerance, and syndromic diagnoses. Despite this consensus, in actual practice, the mean curve at rod insertion was at 73 degrees at a patient age of 6 years. Lengthening procedures occurred at 8.6 months. Skeletal maturity and Risser 3 (or greater) measurements were reported as markers of the time to perform final fusion.
As is detailed in another chapter, the earlier that operative intervention is undertaken, the greater is the likelihood that complications will be encountered. 11 For this reason, prolonging observation or nonoperative treatment as long as possible may be ideal. However, most authors agree that nonfusion treatment for early onset scoliosis, such as dual growing rods, should be initiated between the ages of 4 and 7 years.
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