Online Exclusive Spine Focus Section: Early Onset Scoliosis and Growing Rods
The management of scoliosis in patients less than 10 years of age has significantly changed over the last 20 years. This change can be attributed to advances in spinal instrumentation and techniques, and its impact on pulmonary function in the growing child.1 Surgical management, in general, has been reserved for those patients with progressive, moderate to severe spinal deformities. The classic spinal instrumentation for the growing spine consists of dual-rod spinal construct, with fixation to the spine through 2-level fusion foundations, 1 cephalad and 1 caudad.2–4 By actively distracting the spine across the construct the spinal deformity can be partially corrected, and then maintained without an intercalary posterior spinal fusion. This “intermittent distraction growing rod” (IDGR) construct improves spinal deformity but also limits normal spinal motion across the instrumented segments. Over time the spines with IDGR constructs get stiffer, which has been demonstrated by the need for greater distraction forces and less linear distraction at each sequential IDGR lengthening.5,6 In addition, IDGR constructs typically require operative lengthening under general anesthesia commonly performed at 6-month intervals, to accommodate the interval spinal growth.
In response to the shortcomings of IDGR constructs a new spinal construct was designed and called the SHILLA GROWTH GUIDANCE SYSTEM (SHILLA).7 This construct, based on the concept of the Luque trolley, guides or modulates spinal growth along a set of parallel spinal rods, without the use of active distraction.8 With the evolution of spinal instrumentation, the use of pedicle screws placed without subperiosteal dissection, instead of sublaminar wires, greater spinal growth, and better correction and control of apical rotation, when compared with the Luque trolley, will hopefully be demonstrated. One of the initial, documented benefits of this construct is a decrease in the overall number of surgeries when compared with IDGR constructs.9 Critics of the SHILLA construct have questioned its ability to optimize T1-S1 spinal growth and control the coronal plane deformity. To date there have been no studies which have directly compared IDGR to SHILLA in patients with progressive spinal deformity. The purpose of this study was to: (a) compare the correction of the Cobb Angle of the major curve—both immediate and long term; (b) spinal growth within the thoracolumbar spine; and (c) secondary surgeries of SHILLA and IDGR in the treatment of children (less than 10 y of age) with progressive spinal deformity.
This was a retrospective study of the SHILLA construct used as an alternative treatment to IDGR to support an HDE submission for Food and Drug Administration (FDA) approval. Patients were collected from 2 US tertiary-care pediatric hospitals with expertise in IDGR and SHILLA constructs for the management of spinal deformity. IRB approval was obtained at both institutions and required parental consent for patient participation. The inclusion criteria were progressive scoliosis in a patient less than 10 years of age at index procedure, with a minimum of 6 vertebral levels within the IDGR or SHILLA constructs. A preoperative major curve Cobb angle >40 degrees and rib-vertebral angle difference >20 degrees was necessary for any infantile scoliosis patients. Patients were excluded if the surgical procedure included fixation at the occipital or cervical levels or if bone morphogenic protein was implanted. The IDGR and SHILLA constructs were all stainless steel systems with rods diameters of 4.5 and 5.5 mm. Cephalad and caudad foundations (2 vertebra) were with pedicle screws in all cases. The IDGR constructs had long, axial connectors for the planned distractions/lengthenings, and no side-to-side connectors were used. Patients with the diagnoses of idiopathic, congenital, neuromuscular, and syndromic scoliosis were included in the analysis. Preoperative major curve Cobb had to be >40 degrees, with the major deformity in the thoracic and/or lumbar spine and with surgical intervention at any level(s) from T1 to the pelvis. Surgical treatment consisted of either an IDGR or SHILLA construct at the surgeon’s discretion. Patients were excluded if they had insufficient medical records or radiographic data, or parental consent could not be obtained. Minimum follow-up was 6 months after the index procedure.
Adverse events (AEs) were identified and recorded. Target level, per the FDA, was defined as the anatomic area being treated. A spinal event at a target level was defined as an event involving the spinal anatomy. Examples include fractures of spinous processeses, foraminal stenosis, uncorrected pelvic obliquity, increased kyphosis, scoliosis with prominence, and popping/clicking of implants.
After identification of study population a review of all radiographic studies and medical records was completed by individuals not involved with the patients’ surgical care. Assessment of axial plane deformity (ie, scoliometer measurements, computed tomography, etc.…) were not routinely obtained in this patient population and were not collected for analysis. Pulmonary function tests and computed tomography lung volume studies were not routinely obtained in this patient population during the study periods. Seventy-nine patients were initially identified as possible based on diagnosis and age at surgery, however, only 25 were actually able to meet inclusion criteria. Five patients did not meet criteria, 13 did not return study consent, 22 declined, 10 were unable to be located, and 2 did not receive study treatments. For comparison over the study period 5 patients underwent spinal casting for early onset scoliosis at the 2 institutions. The study population consisted of 19 SHILLA and 6 IDGR patients. Group demographics were similar between the 2 groups and are detailed in Table 1.
The major curve location for the SHILLA group was proximal thoracic in 1 patient, main thoracic in 14 patients, and thoracolumbar in 4 patients. All IDGR patients had the major curve in the thoracic spine. Mean follow-up was 3.8 years for SHILLA (1.1 to 7.0) and 3.6 years for IDGR (1.8 to 7.0). The mean operative time for the index procedures was 5.2±1.0 hours for SHILLA and 4.4±2.0 hours for IDGR, with mean intraoperative estimated blood loss of 389±237 mL for SHILLA and 235±294 mL for IDGR. Hospital stay averaged 5.1±1.6 days for SHILLA and 6.7±3.2 days for IDGR (Figs. 1, 2).
The initial major curve magnitude was 70.3±19.7 degrees for SHILLA and 68.3±15.2 degrees for IDGR, which decreased postoperatively to 22.4±12.7 degrees (68.1% improvement) and 32.2±7.0 degrees (52.9% improvement), respectively (Figure 3). During the first 4 years the correction for SHILLA varied from 40.5% to 53.4% and for IDGR from 40.9% to 56.9% (Fig. 3). Preoperative T1-S1 length was 28.7 cm for SHILLA and 29.0 cm for IDGR. At final follow-up, T1-S1 length was 32.9±4.6 cm for SHILLA (4.2 increase) and 34.0±2.19 cm (5.0 cm increase) for IDGR. T1-S1 measurements by year postoperatively are detailed in Figure 4. The average growth per month from T1-S1 was 0.14±0.28 cm for SHILLA and 0.11±0.09 cm (P=0.75) for IDGR. Preoperative T1-T12 length was 15.8±3.0 cm for SHILLA and 17.3±1.5 cm for IDGR. At final follow-up, T1-T12 length was 18.9±3.6 cm for SHILLA and 20.5±1.9 cm for IDGR. The change from preoperative to final follow-up was 3.0±3.2 cm for SHILLA and 2.8±1.3 cm for IDGR (P=0.99). Average growth per month from T1-T12 was 0.10±0.10 cm for SHILLA and 0.10±0.0 cm for IDGR.
The sagittal T2-T12 Cobb preoperatively was 36.3 degrees for SHILLA and 30.0 degrees for IDGR (Fig. 5). At 3-year follow-up, SHILLA was 51.0 degrees (14.7 degree increase) and IDGR 35.5 degrees (5.5 degree increase), as detailed in Figure 5. Over the 3- to 5-year postoperative time period, the SHILLA group had more kyphosis (7 to 15 degrees) when compared the IDGR group (0 to 6 degrees), however, the sagittal alignment (kyphosis) did not change over time. In addition, there were fewer patients in the SHILLA group which reached the 4- to 5-year follow-up which creates some bias in the data. The sagittal T12-S1 preoperatively was −44.6 degrees for SHILLA and −55.0 degrees for IDGR. At 3-year follow-up, SHILLA was −57.0 degrees (12.4 degree increase in lordosis) and IDGR 52.0 degrees (3.0 degree decrease in lordosis). There was only 1 IDGR patient with sagittal measurements obtained at 4-year follow-up. The changes in the sagittal T12-S1 measurement likely reflect patient compensation to the primary changes in the sagittal T2-T12 created by the 2 constructs. The SHILLA group has an increase in T2-T12 kyphosis of 14.7 degrees and an increase in T12-S1 lordosis of 12.4 degrees. The IDGR group had a 5.5 degree increase in T2-T12 kyphosis and an increase of 3.0 degrees in T12-S1 lordosis.
Overall, there were 29 secondary surgeries related to the index procedure in 12 of the 19 SHILLA patients (63.2%) and 40 secondary surgeries related to the index procedure in all 6 of the IDGR patients (100%) related to the index procedure. Hence the mean overall reoperation rate, and need for general anesthesia, was lower for the SHILLA group at 1.5 and 6.7 (P=0.0003) for the IDGR group. Closer analysis of the IDGR secondary surgeries documented 10 were “unplanned” and 30 were “planned” surgeries, meaning they occurred near or at the time of a “planned” lengthening procedure. Hence, simply based on the chronologic scheduling of a procedure 6 IDGR patients underwent an “unplanned” procedure which decreases the secondary “unplanned” surgery rate to 1.7/patient in the IDGR group (similar to the SHILLA group; 1.6 per patient). Of the “unplanned” surgeries there were 6 GR revision surgeries, 3 irrigation and debridements, and 1 conversion to a posterior spinal fusion (after construct breakage). However, of the “planned” surgeries in the IDGR group 22 were isolated lengthenings and 8 were lengthenings plus revision of the implants for hook/screw dislodgement or rod breakage. Hence secondary surgeries in the IDGR group, excluding isolated lengthenings, were 18 for a rate of 3.0 per patient, double the rate for the SHILLA group. All secondary surgeries in the SHILLA group were “unplanned,” which includes surgeries of rod exchanges because spinal growth pushed the SHILLA screws to grow off the rods (cephalad and caudad), an expected phenomena. There were no intraoperative complications or AE in either group. According to FDA definitions there were implant-associated AEs in both groups. There were 31 AEs in 13 SHILLA patients (68.4%) and 11 AEs in 6 IDGR patients (100%). Tables 2 and 3 detail the AEs by the relation to the implants and those associated with the surgical procedure. There was 1 deep surgical site infection in the SHILLA group and 1 in the IDGR group.
The development of Harrington instrumentation in the 1960s enabled surgeons to directly correct and control spinal deformity. In one of the first reports on growing rods, Moe and colleagues reported in 1984 on 20 patients managed with Harrington instrumentation without fusion. This distraction-based construct permitted a mean gain in spinal length of 3.8 cm but documented a 50% complication rate.10 In a follow-up study, Klemme et al11 expanded this study to 67 children treated over a 21-year time period. They reported a 3.1 cm gain in length over the instrumented levels over a mean 3.1 years of follow-up.11 Preoperative major curve magnitude was 67 degrees and at final follow-up was 47 degrees. These early studies demonstrated the efficacy of the growing spine concept but the complication rate was significant. Subsequent studies have confirmed a high complication rate for growing rods.4,12,13
In 1982 Luque reported on another encouraging surgical approach to spinal deformity in the growing child: the Luque trolley. This method corrects and then passively guides spinal growth through the use of multiple sublaminar wires and dual spinal rods. Unfortunately, follow-up studies at other centers demonstrated small gains in spine height, significant loss of deformity correction, and spontaneous spine fusion.14,15 This passive growth guidance concept fell out of favor, until improvements in spinal instrumentation which permit placement of pedicle screws which would glide on the rod instead of being rigidly fixated to the rod. By avoiding the deep dissection and intracanal placement that was needed for placement of sublaminar wires, the pedicle screws could be placed with fluoroscopic guidance thereby avoiding subperiosteal dissection. Early reports have demonstrated encouraging results with the technique euphemistically called the “SHILLA technique.”7,9,16 Subsequently, others have reported the ability to safely place pedicle screws in infantile and juvenile patients with an intrapedicular placement accuracy of 99%, no insertional or short-term complications, and a 0.4% long-term screw complication rate.17 Demonstrating the safety of pedicle screws in this patient population is essential for both IDGR and SHILLA, however, pedicle screws are an absolute necessity in SHILLA constructs (but not IDGR constructs) as they are currently being implanted.
Rigidly fixating the immature spine during growing rod treatment has raised concerns of “autofusion” of the instrumented spines. Two recent studies, from different institutions, have reported similar results: the longer the spines have been instrumented, the stiffer the spines become. Sankar et al6 reported a multicenter review of 38 patients with dual growing rod constructs whose mean age was 5.7 years. Cobb measure improved from 74 degrees preoperatively to 36 degrees postoperatively and this measurement did not change significantly during the study follow-up period. The average T1-S1 length gain was 1.76±0.71 cm. The T1-S1 gain decreased with repeated lengthening (P=0.007) and over time (P=0.014). Noordeen et al5 reported a single-institution study analyzing 60 consecutive distractions in 26 early-onset scoliosis patients whose mean age was 6.49 years and preoperative major curve Cobb measure was 70.2 degrees. The force required to distract the spine doubled at the fifth lengthening procedure compared with early lengthening (P<0.01). In addition, the mean length achieved at each distraction diminished with ≤8 mm achieved by the fifth lengthening. Cahill et al2 reported on 9 skeletally immature patients who underwent IDGR treatment at mean age at implantation 4.8 years. After a mean 8.3 lengthenings/revisions and 7.2 years of lengthening, 8 of the 9 patients (89%) demonstrated autofusion (mean 11 levels) at time of definitive fusion surgery. The concerns and issues of autofusion secondary to instrumentation of the immature spine, as it relates to the SHILLA constructs, is unknown at the present time. During conversions of SHILLA constructs to definitive spinal fusion occasional spot facet fusions have been observed by the authors, and were seen at the motion segment immediately cephalad to the apical fusion. These spot facet fusions were not evident on plain radiographic evaluations. Theoretically, minimizing autofusion of the immature spine will maximize T1-S1 growth and permit better final correction of the spinal deformity at the definitive spinal fusion.
There were no intraoperative complications or AEs in either group. According to FDA definitions there were implant-associated AEs in both groups, with 31 AEs in 13 SHILLA patients (68.4%) and 11 AEs in 5 IDGR patients (83.3%). Tables 2 and 3 detail the AEs by the relation to the implants and those associated with the surgical procedure. Bess et al13 published a multicenter study group study on 140 patients who underwent 897 growing-rod procedures over a 19-year period. At least 1 complication occurred in 58% of patients with a 24% complication risk increase with each additional surgical procedure performed. Akbarnia et al12 documented 48% of IDGR patients having a complication. The complications reported in this study are likely higher than in these published reports due the FDA definitions as to what constitutes an AE.
There are several drawbacks or shortcomings of the current study. The first is the short follow-up for growth-friendly procedures. The data in this study was the same which was submitted to the FDA for approval of the SHILLA set plugs, per the FDA recommendations. Longer follow-up is necessary to more adequately assess complications, spine growth, and deformity correction. Secondly, there is only 2-dimensional measurements for this analysis. The use of 3-dimensional imaging was not part of the authors’ preoperative assessment, due to cost and concerns of radiation exposure. Because of the absence of transverse plane measurements we are unable to assess the apical rotation of the spine in either group. Finally, there are few patients in the GR group (n=6). The FDA had very specific criteria for this study, which eliminated many of the GR patients.
One of the significant advantages of the SHILLA procedure over IDGR is the 78% decrease in reoperations in this study, an average of 6.7 procedures/patient in the IDGR group and 1.5 procedures/patient in the SHILLA group. In addition, 37% (n=7) of the SHILLA patients did not have a single reoperation during the study period. Implant breakage and fixation pullout are inherent problems with both constructs which usually requires a reoperation. However, the main reason for the significant reoperation rate between the 2 groups is the need for routine, typically every 6 months, lengthening for IDGR constructs. This problem is being addressed in the new magnetic autolengthening devices have proven proof of concept in animal models and are now being used in experimental human trials.18–22
The SHILLA GROWTH GUIDANCE SYSTEM compares favorably with traditional IDGR constructs in terms of correction of the major curve, spinal length and growth, and maintenance of sagittal alignment. The >4-fold decrease in additional surgeries makes the SHILLA GROWTH GUIDANCE SYSTEM a comparably effective alternative to IDGR constructs, with fewer additional surgeries.
The authors would like to thank Frances L. McCullough and June C. Smith for all of their hard work in assisting with data collection.
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Keywords:Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.
SHILLA; growing spine; early-onset scoliosis; growing rod