Identifying complications and failure modes of innovative growing rod configurations using the (hybrid) magnetically controlled growing rod (MCGR) and the spring distraction system (SDS)

Health-related quality of life in early onset scoliosis patients treated with the spring distraction system: what to expect in the first 2 years after surgery

PURPOSE

The Spring Distraction System (SDS) is a novel "growth-friendly" implant for the treatment of Early-Onset Scoliosis (EOS). This prospective study aims to determine the evolution of the "24-Item Early-Onset Scoliosis Questionnaire" (EOSQ-24) scores during 2-year follow-up after SDS surgery. Secondary aims include investigating the relation between EOSQ-24 scores and EOS etiology, and evaluating the impact of an unplanned return to the operating room (UPROR) on HRQoL.

METHODS

All SDS patients with at least 2-year follow-up were included. Caregivers completed the EOSQ-24 pre-operatively, post-operatively, and at 6, 12, and 24 month follow-up. Mean total and -domain scores were graphed over time. Repeated-measures ANOVA analyzed the influence of etiology on EOSQ-24 scores. Multiple regression analyzed associations between UPRORs and EOSQ-24 scores.

RESULTS

Forty-nine patients were included. Mean total EOSQ-24 scores decreased from 70 pre-operatively to 66 post-operatively, then gradually increased to 75 (24 months). Most domains exhibited changes over time, with initial declines, but eventually surpassing pre-operative levels after 2-year follow-up. Neuromuscular/Syndromic patients had lower scores, but showed similar improvements over time compared with other etiologies. Multiple regression showed lower Parental Burden domain score (- 14 points) in patients with UPRORs, although no significant reductions were found in total score, or in other domains.

CONCLUSION

HRQoL decreases immediately following SDS surgery but quickly recovers and exceeds pre-operative levels at 2-year follow-up in all domains. Neuromuscular/Syndromic patients have lower initial scores, but progress similarly over time. UPRORs do not influence EOSQ-24 scores, except for a negative impact on the Parental Burden domain in the short term.

LEVEL OF EVIDENCE

III.

Growing rods in Early Onset Scoliosis: The current scenario

Background and aims

The treatment of early onset scoliosis is a challenge. Some curves resolve spontaneously, while the more aggressive ones require surgical intervention. Several surgical strategies have been explored in this unique group of patients, though the distraction based growing rods are the mainstay of treatment. The aim of this paper is to consider the current scenario with the surgical treatment for early onset scoliosis with growing rods.

Methods

This is a narrative review that explores the various types of growing rod options that are currently available. The results, as reported in literature, are discussed. The complications and problems with the commonly used growing rods are explored, based on the reported literature and on retrieval analysis that we have published. We discuss some of the newer modifications of growing rods.

Results

There is no real consensus on the ideal timing for the surgery or ways to assess the outcomes of the treatment. The Cobb angle measurement and measures of thoracic growth are surrogate markers. The main indication for surgery is to an increase in the thoracic dimensions and allowing for lung growth. Measures that are linked to lung function are more useful. We report some newer MRI scanning technology. Distraction-based growing rods have been reported to produce consistent and good results. Frequent return to theatre with the Traditional Growing Rods (TGR) and the metallosis related problems with the MCGR are reported.

Conclusions

We have learned a lot from the TGR and MCGR experiences. There is a scope for ongoing research to improve the design of the implant systems and better assess the outcomes on lung function. This review outlines these and helps identify the future trends.

Three-dimensional correction of scoliosis by a double spring reduction system as a dynamic internal brace: a pre-clinical study in Göttingen minipigs

BACKGROUND CONTEXT

Adolescent idiopathic scoliosis (AIS) is a major skeletal deformity that is characterized by a combination of apical rotation, lateral bending and apical lordosis. To provide full 3D correction, all these deformations should be addressed. We developed the Double Spring Reduction (DSR) system, a (growth-friendly) concept that continuously corrects the deformity through two different elements: A posterior convex Torsional Spring Implant (TSI) that provides a derotational torque at the apex, and a concave Spring Distraction System (SDS), which provides posterior, concave distraction to restore thoracic kyphosis.

PURPOSE

To determine whether the DSR components are able to correct an induced idiopathic-like scoliosis and to compare correction realized by the TSI alone to correction enforced by the complete DSR implant.

STUDY DESIGN/SETTING

Preclinical randomized animal cohort study.

PATIENT SAMPLE

Twelve growing Göttingen minipigs.

OUTCOME MEASURES

Coronal Cobb angle, T10-L3 lordosis/kyphosis, apical axial rotation, relative anterior lengthening.

METHODS

All mini-pigs received the TSI with a contralateral tether to induce an idiopathic-like scoliosis with apical rotation (mean Cobb: 20.4°; mean axial apical rotation: 13.1°, mean lordosis: 4.9°). After induction, the animals were divided into two groups: One group (N=6) was corrected by TSI only (TSI only-group), another group (N=6) was corrected by a combination of TSI and SDS (DSR-group). 3D spinal morphology on CT was compared between groups over time. After 2 months of correction, animals were euthanized.

RESULTS

Both intervention groups showed excellent apical derotation (TSI only-group: 15.0° to 5.4°; DSR-group: 11.2° to 3.5°). The TSI only-group showed coronal Cobb improvement from 22.5° to 6.0°, while the DSR-group overcorrected the 18.3° Cobb to -9.2°. Lordosis was converted to kyphosis in both groups (TSI only-group: -4.6° to 4.3°; DSR-group: -5.2° to 25.0°) which was significantly larger in the DSR-group (p<.001).

CONCLUSIONS

The TSI alone realized strong apical derotation and moderate correction in the coronal and sagittal plane. The addition of distraction on the posterior concavity resulted in more coronal correction and reversal of induced lordosis into physiological kyphosis.

CLINICAL SIGNIFICANCE

This study shows that dynamic spring forces could be a viable method to guide the spine towards healthy alignment, without fusing it or inhibiting its growth.

Surgical treatment of neuromuscular Early Onset Scoliosis with a bilateral posterior one-way rod compared to the Spring Distraction System: study protocol for a limited-efficacy Randomized Controlled Trial (BiPOWR)

BACKGROUND

Early Onset Scoliosis (EOS) is a progressive spinal deformity in children, and a potentially life-threatening disease. "Growth-friendly" surgical techniques aim to control the deformity, while allowing the spine and trunk to maintain growth. Current "growth-friendly" systems such as the traditional growing rod (TGR) and magnetically controlled growing rod (MCGR) have limitations that reduce their efficacy and cost-effectiveness. Recently, two "growth-friendly" systems have been developed that mitigate many of these limitations, the Spring Distraction System (SDS) and the One Way Self-Expanding Rod (OWSER). The purpose of the multicenter BiPOWR trial is to investigate, describe and compare the 1-year limited-efficacy and -safety of both strategies in the treatment of neuromuscular EOS.

METHODS

After informed consent, 28 neuromuscular EOS patients will be randomized to receive either the SDS or the OWSER. Patients and caregivers will be blinded to allocation until after surgery. Primary outcomes will be maintenance of coronal curve correction and the occurrence of serious adverse events. In addition, spinal growth, implant lengthening, and perioperative findings are recorded systematically. At each follow-up moment, the Early Onset Scoliosis Questionnaire (EOSQ-24) will be used to assess health-related quality of life. All outcomes will be compared between groups.

DISCUSSION

The BiPOWR trial is the first randomized controlled trial that compares two specific "growth-friendly" implants in a specified EOS population. It will determine the 1-year limited-efficacy and safety of the SDS and OWSER implants.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT04021784 (13-06-2019). CCMO registry: NL64018.041.17 (06-05-2019).

The Spring Distraction System for Growth-Friendly Surgical Treatment of Early Onset Scoliosis: A Preliminary Report on Clinical Results and Safety after Design Iterations in a Prospective Clinical Trial

Background: The Spring Distraction System (SDS) is a dynamic growth-friendly implant to treat early onset scoliosis (EOS). Previous SDS studies showed promising results in terms of curve correction and complication profile. Nevertheless, complications did occur, which led to modifications in the implant design. The main iterations were a larger rod diameter and a more sagittal stable sliding mechanism. The purpose of this study was to investigate the performance of these iterations. Methods: All patients treated with the modified SDS and >1 year follow-up were included. Radiographic outcomes, severe adverse events (SAEs), unplanned returns to the operating room (UPRORs) and health-related quality of life (HRQoL) were investigated. Results: Seventeen EOS patients (three congenital, four idiopathic, nine neuromuscular, one syndromic) were included. Mean age at surgery was 9.5 ± 2.5 years. Similar to the first generation SDS, about 50% initial correction was achieved and maintained, and spinal growth was near physiological. Most importantly, SAEs and UPRORs were diminished and favorable with 0.10/patient/year. In addition, HRQoL increased during the first year postoperatively, indicating the implant was well accepted. Conclusion: These preliminary results indicate that the iterations of the SDS are effective in terms of reducing SAEs and UPRORs and increasing HRQoL in patients with EOS.

Finite Element Comparison of the Spring Distraction System and the Traditional Growing Rod for the Treatment of Early Onset Scoliosis

STUDY DESIGN

Finite element analysis (FEA).

OBJECTIVE

The aim of this study was to determine biomechanical differences between traditional growing rod (TGR) and spring distraction system (SDS) treatment of early-onset scoliosis.

SUMMARY OF BACKGROUND DATA

Many "growth-friendly" implants like the TGR show high rates of implant failure, spinal stiffening, and intervertebral disc (IVD) height loss. We developed the SDS, which employs continuous, dynamic forces to mitigate these limitations. The present FEA compares TGR and SDS implantation, followed by an 18-month growth period.

METHODS

Two representative, ligamentous, scoliotic FEA models were created for this study; one representing TGR and one representing SDS. initial implantation, and up to 18 months of physeal spinal growth were simulated. The SDS model was continuously distracted over this period; the TGR model included two additional distractions following index surgery. Outcomes included differences in rod stress, spinal morphology and iVD stress-shielding.

RESULTS

Maximum postoperative von Mises stress was 249MPa for SDS, and 205MPa for TGR. During the 6-month TGR distraction, TGR rod stress increased over two-fold to a maximum stress of 417MPa, compared to a maximum of 262 MPa in the SDS model at 6-month follow-up. During subsequent follow-up periods, TGR rod stress remained consistently higher than stresses in the SDS model. Additional lengthenings in the TGR model led to a smaller residual curve (16.08) and higher T1-S1 growth (359 mm) at 18-month follow-up compared to the SDS model (26.98, 348 mm). During follow-up, there was less stress-shielding of the IVDs in the SDS model, compared to the TGR model. At 18-month follow-up, upper and lower IVD surfaces of the SDS model were loaded more in compression than their TGR counterparts (mean upper: +112 ± 19N; mean lower: +100 ± 17N).

CONCLUSION

In the present FEA, TGR treatment resulted in slightly larger curve correction compared to SDS, at the expense of increased IVD stress-shielding and a higher risk of rod fractures.

LEVEL OF EVIDENCE

N/A.