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Online Exclusive Spine Focus Section: Early Onset Scoliosis and Growing Rods

Staged Growing Rods With Preimplantation of Spinal Anchors for Complex Early Onset Scoliosis

Gomez, Jaime A. MD*; Grzywna, Alexandra BA; Hanstein, Regina PhD*; Emans, John B. MD; Hresko, M.Timothy MD; Hedequist, Daniel MD; Karlin, Lawrence I. MD; Glotzbecker, Michael P. MD

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Journal of Pediatric Orthopaedics: December 2017 - Volume 37 - Issue 8 - p e606-e611
doi: 10.1097/BPO.0000000000000957
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Abstract

Early onset scoliosis (EOS) is defined as a significant spinal deformity before the age of 10. It has many etiologies, such as congenital anomalies, neuromuscular disease, associated syndromes, or idiopathic causes.1 Progressive spinal deformity in early life leads to disturbance of normal lung development and pulmonary function,2–8 with a natural history of reduced life-expectancy.9 Therefore, EOS treatments are intended to correct spinal deformity and expand the chest wall in an effort to improve patients’ long-term quality of life.10,11 Currently, distraction-based treatment is the most popular surgical management method for EOS in the United States.12 Methods include traditional dual growing rod (GR), magnetically controlled GR (MCGR), and vertical expandable prosthetic titanium rib (VEPTR). Distraction-based devices have been found effective in improving or controlling severe deformities in the coronal and sagittal planes.13–15 However, the complication rate of distraction-based treatment is high16,17 due to the presence of critical health comorbidities,18,19 the need for multiple surgeries,1,14,20,21 and implant-related complications.16,22

Progressive EOS patients with poor bone quality and a large deformity, especially hyperkyphosis, have high risk of neurological injury and construct failure.16,22,23 In this complex group of patients, a 2-stage GR technique has been utilized in an effort to facilitate spinal deformity correction, avoid neurological complications, and reduce risk of implant failure. In addition, in the event of an intraoperative neurological event, we believe 2-stage GR technique allows for safe placement of the rods and enhances correctability. In the late seventies, Marchetti and Faldini24 described a 2-stage technique in which 2 vertebrae at each end of the curve were fused in the first surgery, and hooks were placed at a second surgery 6 months later.25 Modern GR techniques describe establishing anchors and inserting rods in a single stage.13,26,27 The objective of this report is to describe a single center’s results of treating complex EOS patients using modern growing instrumentation with a 2-stage technique.

METHODS

After institutional review board approval was obtained, EOS patients who had insertion of a GR device in 2 stages between 2006 and 2013 were identified. Surgeries were performed by 5 different surgeons at 1 center. Inclusion criteria included diagnosis of EOS, implantation of a GR construct at 2 separate surgeries, and minimum 2-years follow-up after index surgery. Single-stage GR implantations were excluded.

The decision for 2-stage technique was clinical decision-making based on surgeon’s discretion. Staging was either planned before surgery or elected based on intraoperative events. In either case, insertion of the GR system was performed in 2 stages. At stage 1, the proximal and distal bone anchor sites were established by an instrumented fusion. The proximal anchor sites were instrumented with 4 to 6 hooks. In 1 patient with hyperkyphosis, sublaminar wires were used. All distal anchor sites were instrumented with 4 screws, 2 on each side. Autograft and/or allograft bone was placed between vertebrae. Small, short rods were inserted to keep instrumentation in alignment. The anchor fusion sites were allowed to heal in situ, and stage 2 was scheduled at least 3 months later. One patient who presented with severe rotational deformity was casted immediately after anchor placement to facilitate derotation. Four patients were discharged with a Boston TLSO brace to protect the hardware while integrating with the bone in the immediate postoperative period. Patients were placed in halo-gravity traction in the month prior to stage 2 unless contraindicated by their condition. Contraindications for HGT include: congenital kyphosis, previous spinal cord tumor resections, residual neurological deficits, and cord tethering.25 At stage 2, distraction rods were inserted that spanned the proximal and distal anchor sites. In some patients, 1 to 2 crosslinks were added. After this 2-stage implantation, patients underwent routine serial lengthenings.

Patient data retrospectively collected included age, diagnosis, scoliosis etiology, past medical history, indications for GR surgery and staging. Patients were classified using the Classification of Early Onset Scoliosis (C-EOS).28 Surgical characteristics including foundation healing time, number, and frequency of lengthening procedures were analyzed. Complications were collected and scored using the classification system described by Smith et al.29 Radiographic measurements including Cobb and kyphosis angles were evaluated before stage 1, after halo-gravity traction, after stage 2, and at last follow-up.

Eight patients (6 males, 2 females) were identified. Subjects were a mean age of 5.4 (range, 3.4 to 7.9) years at stage 1. Five (63%) had syndromic scoliosis. GR implantation was undertaken in 4 patients for severe coronal deformity and 4 for hyperkyphosis. Three patients had failed nonoperative scoliosis treatment (casting or bracing). Two patients had previously failed GR or VEPTR constructs due to proximal instrumentation-bone failure (Table 1).

TABLE 1
TABLE 1:
Surgical Characteristics

RESULTS

Staging was either planned or unplanned. Four patients had planned staging due to preoperatively identified poor bone quality such as osteogenesis imperfecta or osteoporosis defined as T-score 2.5 SDs below the mean. Those with planned staging had no intraoperative complications during stage 1 or 2. Four patients had unplanned staging: 3 patients due to neurological changes, and 1 patient due to poor bone quality identified intraoperatively. In the patients with neurological changes, 2 were detected by neuromonitoring when the rods were placed, and 1 had paraplegia recognized postoperatively. In the 2 recognized intraoperatively, releasing distraction and improving hemodynamic parameters did not improve neurological function. All 3 patients’ signals returned when rods were removed. At stage 2, rods were placed without changes to motor and sensory-evoked potentials, or any other intraoperative complications.

Five patients were placed in halo-gravity traction a mean of 33 (21 to 56) days before stage 2. Their Cobb angles improved from mean 87 (range, 67 to 97) degrees before halo placement to mean 62 (range, 35 to 79) degrees in traction.

Mean time between stage 1 and 2 was 23 (15 to 45) weeks. Patients had lengthenings every 6 months for traditional GR and every 3 months for MCGR. The cohort had mean 7 (range, 3 to 16) lengthenings at final follow-up. Major coronal Cobb angle improved from preoperative mean 81 (61 to 94) to 41 (range, 24 to 60) degrees after stage 2 and remained at a mean 40 (27 to 53) degrees at last follow-up (Table 2). Kyphosis was controlled from 45 (10 to 76) degrees preoperatively to 38 (9 to 61) degrees after stage 2 to 41 (17 to 65) degrees at most recent follow-up. Radiographic images to illustrate results are shown in Figure 1.

TABLE 2
TABLE 2:
Patient Characteristics
FIGURE 1
FIGURE 1:
Patient posterior-anterior (top) and lateral (bottom) radiographs at stage 1, 2, and most recent follow-up.

Disease-related complications over course of treatment included 3 patients with pneumonia and 2 patients with lower extremity fractures. Device-related complications included superficial wound problems (4 patients), broken rods (2 patients), proximal migration (2 patients), and implant prominence (1 patient). Amongst the 8 subjects, there were 2 unplanned returns to the OR, in addition to the 4 unplanned stage 2 surgeries. Superficial wound problems encompassing dehiscence, contact dermatitis, eschar formation, and delayed healing (Smith Grade I, nonsurgical treatment) were the most common, occurring 7 times in the 4 patients (Table 3). One patient with Prader-Willi syndrome and high body mass index had 5 broken rods over 8.5 years of lengthening treatment. Three broken rods were replaced at regularly scheduled lengthenings, 2 necessitated premature lengthenings (Smith Grade IIA, requiring 1 unplanned surgery). In the 2 patients with proximal migration, the fusion mass migrated with the instrumentation, but the instrumentation remained embedded in bone. This was observed on x-ray and adjusted at a regularly scheduled lengthening. At a mean final follow-up of 4.9 (2.0 to 9.4) years, no patients had instrumentation-bone failure of the GR construct.

TABLE 3
TABLE 3:
Complications

DISCUSSION

In traditional dual GR technique, short fusions are made at foundation sites with hook or screw anchors, and GRs spanning the deformity are placed in a single-stage procedure.26 Prior studies have shown that the most deformity correction occurs with this initial procedure.17 However, in patients with poor bone quality, maximal correction force may not be utilized due to concern for implant-bone failure. In patients with poor bone quality, 2-stage surgery give time for the foundations to fuse before the rods are placed. We hypothesize this creates more stable anchor sites, allows for a greater deformity correction at stage 2, when distraction rods are inserted, and reduces the risk of postoperative hardware pull-out. In the event of intraoperative neurological changes, 2-stage surgery can also be implemented to avoid permanent neurological damage and enhance later correctability. Staged procedures have been advocated in other types of surgery, such as spine fusion in adult scoliosis, in cases of coagulopathy or hypotension.30

We found the 2-stage strategy enabled correction of coronal deformity (−50%) and stabilization of sagittal deformity (−8%) in patients with high risk of implant failure. Changes to coronal and sagittal deformity were obtained with initial distraction rod placement and did not change significantly with subsequent lengthenings, similar to previously published reports.17,31,32 Other studies have reported Cobb angles 75 to 83 degrees preoperative to 47 to 56 degrees postoperative, with percent Cobb angle correction varying from 32% to 40%.16,31,32 Our results suggest that 2-stage GR technique allows for greater correction, but such conclusions are limited by a small sample size.

In between stage 1 and 2, halo-gravity traction can be used for gradual curve correction. Because patient is awake, neurological function can be monitored as traction increases, decreasing the risk of neurological deficits.33 Traction also loosens up spinal ligaments to prevent neurological change when GR are placed to maintain curve correction.34 Halo-gravity traction was not used in 3 patients. Two patients had very flexible curves, and 1 patient with osteogenesis imperfecta had insufficient bone stock.

Patients treated with the 2-stage technique encountered a 29% complication rate per surgery over average 5 (minimum 2) years of GR treatment. Previous studies have reported complication rates per surgery between 20% to 47%,16,32 which represent heterogenous populations including idiopathic or idiopathic-like patients, whereas this case series represents our most challenging patients. Importantly, none of the complications we faced necessitated multiple surgical interventions or abandoning treatment. Patients who had failed single-stage distraction-based instrumentation (VEPTR or GR) in the past could be treated with regular lengthenings. Nonetheless this technique is not a panacea for all GR complications, as our patients continued to have superficial wound complications and the structural integrity of the rod was subject to fracture. Furthermore, the proximal anchors continue to experience stress as shown by migration of the fusion mass with the instrumentation in 2 patients. Notably, however, the proximal anchors were still attached to bone, which was noted and resolved at regularly scheduled lengthenings, instead of pulling out and requiring emergent surgery. Thus, establishing solid proximal and distal anchors before placing distraction instrumentation may create more stable foundations.

Other studies have shown the risks of GR surgery in complex EOS patients such as the ones in this study. Patients with hyperkyphosis have been shown to have 3.1 times greater complications than hypokyphotic or normo-kyphotic patients, and syndromic diagnosis predicts 2.9 times greater likelihood of implant complications.35 Cobb angle >90 degrees has significantly higher rate of proximal anchor failure.36 In an analysis of implant-related complications requiring unplanned surgery, proximal anchor failure was the most prevalent (43%).31 Proximal anchor failure also raises the risk of neurological damage.37 Stable anchors accomplished by the 2-stage technique described by this report provide a preventive method.

Three patients in this study have been converted from traditional to MCGR systems. They have undergone at least 2 outpatient lengthenings. None have experienced complications. One drawback to the MCGR is the thicker diameter rods necessitated by the magnetic technology may increase the risk of proximal anchor failure.38 Thus, this 2-stage technique may have applicability in the setting of complex index MCGR cases, but has yet to be fully evaluated.

Limitations of this case series include its retrospective nature and small sample size. Although there is no control group, this technique was used in our most challenging patients with outcomes and complications that compare favorably to other published results. Although these study limitations could be eliminated by a prospective study, randomizing single-stage versus 2-stage procedures raises ethical and practical concerns given the heterogeneity of patients.39,40 Ultimately tracking long-term follow-up such as this case series provides clinical indications.

Here, we report that in cases of complex EOS, the 2-stage insertion of a GR system is a safe technique with encouraging results. With the reported complication rates of GR treatment so high, efforts to decrease complications such as the one described by this paper are imperative.

CONCLUSIONS

Two-stage GR placement technique can be utilized in complex EOS patients with hyperkyphosis and poor bone quality, or in the event of neurological changes. Anchor foundations are allowed to heal for at least 3 months before lengthenings. Halo-gravity traction can be used in between stage 1 and 2. Patients with neurological changes fully resolved, and no patients had instrumentation-bone failure with minimum 2-year follow-up. Satisfactory coronal correction and sagittal stabilization were obtained, indicating the 2-stage GR technique can be effectively used in EOS.

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Keywords:

scoliosis; early onset; kyphosis; growing rod; traction; orthopaedics; ribs; spine; staged surgery

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