Clinical StudyReducing radiation exposure in early-onset scoliosis surgery patients: novel use of ultrasonography to measure lengthening in magnetically-controlled growing rods
Introduction
Scoliosis is a three-dimensional deformity [1], [2] of the spine, characterized by lateral deviation in the coronal plane. Most patients require no treatment, however, in a small subset, the lack of appropriate treatment can lead to the compromise of pulmonary function and unacceptable cosmesis [3], [4], [5]. Early-onset scoliosis (EOS) begins before the age of 5 years and is independent of etiology [6], which includes both congenital and idiopathic infantile types. Spinal deformity at this young an age presents a particular challenge because the spine, thoracic cage, and its contents are all growing rapidly. As such, the thorax cannot support normal lung maturation and respiration [7]. To prevent progression of spinal deformity, bracing, casting, and spinal fusion have all been used [8], [9], [10], but conservative measures fail to prevent progression in young patients [8], [9], [10]. In addition, spinal fusion in the skeletally immature child will result in loss of normal spinal growth [8], [9], [10], with consequent poor respiratory and cosmetic effects [11].
Growing rods are spinal implants that guide spinal growth. They have been used to address the limitations of both bracing and surgery in patients with EOS [12], [13], [14], [15], [16]. Traditionally, distraction (ie, lengthening of the rods) of these systems required invasive, open surgery under general anesthesia every 6 months until skeletal maturity is reached. Such a frequent procedure can lead to potential intraoperative complications, repeat hospitalization, increased health care costs, and a psychological impact for the child and parent [5], [17]. To minimize the limitations of this procedure to patients and their families, a magnetically-controlled growing rod (MCGR) system was developed that had been validated in animals [18] and its safety and efficacy has been noted in humans [18], [19].
With the use of the MCGR system, distraction can take place regularly and potentially frequently in the outpatient clinic to more closely mimic the normal growth of the spine. At the authors' institution, we have distracted the implant on a monthly basis, with distractions of approximately 2 mm at each visit to parallel normal physiologic growth. However, such frequent distractions may inconvenience the parent and child. More importantly, distraction is measured and documented through the use of pre- and postdistraction plain radiographs, which has led to concerns about the amount of ionizing radiation exposure in children. Ionizing radiation is known to cause cell death and genetic mutation and is associated with cancerous and noncancerous diseases [20], [21]. In fact, excess amounts of ionizing radiation exposure in children with scoliosis has led to the development of breast cancer and increased mortality [22], [23], [24].
Ultrasound is a noninvasive, nonionizing imaging modality with increasing scope of applications, including the measurement of stents implanted in the human body [25], the relationship of nerves to orthopedic implants [26], and the evaluation of mobile bearings in knee arthroplasty [27]. The use of ultrasound scanning had been reported in the measurement of leg length discrepancy [28], assessment of new bone formation during limb lengthening [29], and the measurement of fetal spine length in utero [30].
As such, in an attempt to reduce the number of plain radiographs required to monitor and chart the distraction of the MCGRs, the following study was undertaken to determine the feasibility and reproducibility of the novel use of ultrasonography to measure rod distractions.
Section snippets
Materials and methods
Six patients who have been treated with the MCGR for scoliosis were volunteered by their parents to participate in the study, and informed consent was taken when they attended for routine outpatient lengthening at a single institution. They had a mean age of 12.5 years (range: 8–16 years). There were two males and four females. The diagnoses of these cases were idiopathic scoliosis (n=2), neurofibromatosis (n=1), Ehlers-Danlos syndrome (n=1), Noonan syndrome (n=1), and Charge syndrome (n=1).
To
Results
One patient was selected to determine the optimum reference point on ultrasound. Over nine sets of measurement, the mean screw distance was 14.04 mm (SD: 0.27 mm) and the mean neck of the rod distance was 8.31 mm (SD: 0.12 mm) on the MCGR (Fig. 5). Because the variance was less in the distance of the rod's neck, this reference point was selected as the most optimal.
With respect to interrater reliability, assessment of the rod's neck distance on ultrasound was performed in three patients,
Discussion
This study is, to our knowledge, the first to explore the use of ultrasonography to measure changes in spinal implant length. To demonstrate its feasibility and reliability, we first identified reproducible reference points on the implant that could be used for measurements. We then demonstrated that these measurements had good intra- and interobserver reliabilites and that they were comparable with measurements taken from radiographs.
The reliability of ultrasonography to measure an implant
Conclusions
Our study is the first, to our knowledge, to demonstrate the reliability of using ultrasound technology to assess rod lengthening in patients with EOS undergoing surgical treatment with the MCGR. This practical and easy to administer technique can change clinical practice by decreasing the frequency of plain radiographs and the associated cumulative ionizing radiation exposure in the developing child.
Source of funding
Ellipse Technologies Incorporated purchased a 64 mm ultrasound probe to facilitate image capture for this study. Ellipse Technologies Incorporated was not involved in any of the surgical procedures, distractions, ultrasound assessments, data collection, analysis or interpretation of the results, writing or editing of the manuscript, or the decision to submit the study for publication.
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Cited by (0)
FDA device/drug status: Not approved for this indication (Magnetically-controlled growing rods for scoliosis).
Author disclosures: OMS: Nothing to disclose. EJO: Nothing to disclose. DS: Board membership: Journal editorial board member; Grants/grants pending: Research Grants Council (F, Paid directly to institution). CHB: Nothing to disclose. KDKL: Nothing to disclose. KMCC: Consultancy: Ellipse Technologies (B, Paid directly to institution); Grants/grants pending: Research Grants Council (F, Paid directly to institution); Travel/accommodations/meeting expenses unrelated to activities listed: AOSpine (B, Paid directly to institution).
The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com.
Disclosures: KMCC has received grant and research support from Ellipse Technologies for previous studies. OMS has received a travel grant from Ellipse Technologies after the conclusion of this study. Ellipse Technologies purchased a 64 mm ultrasound probe to facilitate image capture for this study. The authors have no other financial or competing interests to disclose in relation to this work.