Reliability of Rod Lengthening, Thoracic, and Spino-Pelvic Measurements on Biplanar Stereoradiography in Patients Treated With Magnetically Controlled Growing Rods

Evaluation of the lengthening of the magnetically controlled growing rods in juvenile and early-onset scoliosis

INTRODUCTION

The treatment of early onset scoliosis (EOS) has seen significant advancements, particularly with the introduction of magnetically controlled growing rods (MCGR). However, a discrepancy between reported and actual rod lengthening during treatment has raised concerns.

HYPOTHESIS

This retrospective study aims to investigate the disparity between reported and actual lengthening of MCGR and to identify factors contributing to the failure of the lengthening process.

MATERIAL AND METHODS

Radiographs of the whole spine taken immediately before and after surgery were used for measurements. Documented rod lengthening read from the external remote controller (ERC) was used for analysis. The distraction procedure was classified as failed when the quotient of the measured distraction of MCGR actuators on radiographs and the declared lengthening of the rods using the ERC device was less than 0.3.

RESULTS

Analysis of fifty patients with idiopathic and neuromuscular scoliosis revealed a diminishing discrepancy between ERC-reported lengthening and radiographic measurements after the sixth distraction (p < 0.05), with noticeable failures occurring after the eighth procedure (quotient of mm X-ray/mm ERC of less than 0.3). The bending of MCGRs played a crucial role, with a higher failure rate observed on the convex side of the spinal curve (p = 0.045). Additionally, postoperative thoracic kyphosis (TK) demonstrated a potential association with distraction failure, suggesting altered spinal alignment might affect the efficacy of MCGR treatment.

DISCUSSION

The study emphasizes the importance of precise MCGR bending and vigilant monitoring, especially on the convex side of the spinal curve. We discovered a notable difference between expected and real rod lengthenings, especially after multiple procedures. This emphasizes the importance of closely monitoring MCGR treatments for accurate scoliosis management in young patients.

LEVEL OF EVIDENCE

IV; retrospective study.

Supine correction index as a predictor for brace outcome in adolescent idiopathic scoliosis

Aims

The aim of this study was to assess the ability of morphological spinal parameters to predict the outcome of bracing in patients with adolescent idiopathic scoliosis (AIS) and to establish a novel supine correction index (SCI) for guiding bracing treatment.

Methods

Patients with AIS to be treated by bracing were prospectively recruited between December 2016 and 2018, and were followed until brace removal. In all, 207 patients with a mean age at recruitment of 12.8 years (SD 1.2) were enrolled. Cobb angles, supine flexibility, and the rate of in-brace correction were measured and used to predict curve progression at the end of follow-up. The SCI was defined as the ratio between correction rate and flexibility. Receiver operating characteristic (ROC) curve analysis was carried out to assess the optimal thresholds for flexibility, correction rate, and SCI in predicting a higher risk of progression, defined by a change in Cobb angle of ≥ 5° or the need for surgery.

Results

The baseline Cobb angles were similar (p = 0.374) in patients whose curves progressed (32.7° (SD 10.7)) and in those whose curves remained stable (31.4° (SD 6.1)). High supine flexibility (odds ratio (OR) 0.947 (95% CI 0.910 to 0.984); p = 0.006) and correction rate (OR 0.926 (95% CI 0.890 to 0.964); p < 0.001) predicted a lower incidence of progression after adjusting for Cobb angle, Risser sign, curve type, menarche status, distal radius and ulna grading, and brace compliance. ROC curve analysis identified a cut-off of 18.1% for flexibility (sensitivity 0.682, specificity 0.704) and a cut-off of 28.8% for correction rate (sensitivity 0.773, specificity 0.691) in predicting a lower risk of curve progression. A SCI of greater than 1.21 predicted a lower risk of progression (OR 0.4 (95% CI 0.251 to 0.955); sensitivity 0.583, specificity 0.591; p = 0.036).

Conclusion

A higher supine flexibility (18.1%) and correction rate (28.8%), and a SCI of greater than 1.21 predicted a lower risk of progression. These novel parameters can be used as a guide to optimize the outcome of bracing.

Cite this article: Bone Joint J 2022;104-B(4):495–503.

Inter- and intrarater reliability of measuring lengthening of magnetically controlled growing rods on digital radiographs

PURPOSE

The aim of this study was to determine inter- and intraobserver reliability of delta rod extension, and total rod length measured on digital x-rays in patients with early onset scoliosis (EOS) treated with magnetically controlled growing rods (MCGR). For the last decade, patients with EOS have been treated with MCGR. Replacement of MCGR relies heavily on the measurement done at every lengthening session. Only a few studies have looked at inter- and intraobserver reliability of rod lengthening, and none have used the delta extension before.

METHODS

202 radiographs presented in random order were rated and measured twice with at least a 14-day interval and differing order of the radiographs. The measuring was done at both rods. All x-rays came from 15 patients diagnosed with EOS and treated with MCGR from 2009 until 2019. The total extension length and the delta extension (the difference in total extension length between two lengthening in succession) were measured, and the intraclass correlation coefficient (ICC) calculated for both measurements RESULTS: Intrarater ICC scores varied from moderate to good, but non-significantly. Interrater reliability increased significantly from moderate (ICC 0.72 [0.68; 0.76] and 0.73 [0.69; 0.77] to excellent (ICC 0.91 [0.88; 0.93] and 0.97 [0.96: 0.98]), when examining delta extension every sixth instead of every second month.

CONCLUSION

Measuring rod lengthening on x-rays can be done every 6 months, with an ample reliability. The ICC's for the delta extension with 2-3 months interval were only moderately precise, compared to the near perfect ICC's for the total extension length.

Magnetically controlled growing rods in early onset scoliosis: radiological results, outcome, and complications in a series of 22 patients

INTRODUCTION

Magnetically controlled growing rods (MCGR) for the surgical treatment of early onset scoliosis (EOS) allow non-invasive outpatient based distractions during spinal growth. The purpose of this study is to present the results of a single center case series of 22 patients, evaluate the effect of MCGR treatment on the development of spino-pelvic parameters during growth, and report initial outcomes after end of treatment.

MATERIALS AND METHODS

Prospectively collected data of 22 EOS patients with MCGR treatment has been analyzed. The following radiological parameters were measured before index surgery, after index surgery, 1 year after index surgery, and at last follow-up: Cobb angle of the major curves, thoracic kyphosis (TK), lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS). Mean age at index surgery was 9.5 years (range: 4-14 years). Mean length of follow-up was 47.6 months (range: 25-121 months). Etiology of diagnosis was idiopathic in 14 patients, associated with neurofibromatosis in 2 patients, and neuromuscular or syndromic in 6 patients.

RESULTS

Mean Cobb angle of the major curve was 57° preoperatively and 29° at last follow-up (p < 0.0005). Mean TK was 20.1° preoperatively and 20° at last follow-up (p > 0.05). Mean LL was 52.8° preoperatively and 53.2° at last follow-up (p > 0.05). Mean PI was 43.2° preoperatively and 46.3° at last follow-up (p > 0.05). Mean PT was 4.1° preoperatively and 5.8° at last follow-up (p > 0.05). Mean SS was 39.2° preoperatively and 41.7° at last follow-up (p > 0.05). 14 patients finished treatment: nine received final fusion and five received rod removal without fusion. Twelve complications occurred: one deep wound infection, six patients developed proximal junctional kyphosis (PJK), one rod fracture, two rods failed to distract, one deformity progressed after rod removal and required spinal fusion, and one patient developed autofusion of the spine prior to end of treatment.

CONCLUSION

MCGR treatment is able to control deformity progression. Complication rate was 54.5%. Sagittal balance was not altered and treatment does not seem to have a negative impact on the development of spino-pelvic parameters during growth. Optimal end of treatment for the individual patient still has to be defined.

Analysis of 280 Magnetically Controlled Growing Rod Lengthenings Comparing External Remote Control Readouts and Radiographic Measurements: Impact of Patient and Deformity Factors

BACKGROUND

This study aimed to assess the accuracy of the external remote control (ERC) digital readout to the radiographic measurement of magnetically controlled growing rod (MCGR) actuators undergoing lengthenings/expansions and to analyze the impact of patient and spinal deformity factors on the accuracy of the ERC digital readout.

METHODS

Single-surgeon database at 2 tertiary-care pediatric hospitals identified early-onset scoliosis patients with MCGR constructs. There were 14 males and 16 females with a minimum of 2 lengthenings included in the analysis. ERC readouts at each lengthening were recorded.

RESULTS

Sixty-six MCGR actuators were assessed in 30 patients which underwent 280 lengthenings (mean of 5.7 lengthenings). At individual lengthening sessions the ERC and radiographic measurements were correlated (r = 0.69, P<0.001). The summed radiographic measurements averaged 15% less than the summed ERC readouts (SD = 19%). The difference between the sum of radiographic measurements and ERCs was positively correlated with subsequent lengthenings (r = 0.94, P = 0.015). The accuracy of the ERC did not improve with increased grouped sessions (r = -0.54, P = 0.388) with no difference between the group with 2 and the group with ≥5 lengthenings (P = 0.670). In patients with dual rods, the difference was correlated between rods (r = 0.66, P<0.001) and the distraction of each rod was not significantly different from the other (P = 0.124). Patient weight correlated with the difference between the radiographs and ERC readouts (r = 0.27, P = 0.032). In patients with multiple grouped lengthenings, increased weight was positively correlated with an increase in measurement difference (mean r = 0.972).

CONCLUSIONS

Summed radiographic measurements during lengthening sessions averaged 15% less than the summed ERC readouts. The accuracy of radiographic measurements did not increase when sessions were grouped together (2 vs. ≥5). There was no difference in the ERC accuracy over lengthening sessions early versus late. Patient weight, but not body mass index, was positively correlated with the discrepancy between the ERC and radiographic measures.

LEVEL OF EVIDENCE

Level III.

Systematic investigation of metallosis associated with magnetically controlled growing rod implantation for early-onset scoliosis

AIMS

To investigate metallosis in patients with magnetically controlled growing rods (MCGRs) and characterize the metal particle profile of the tissues surrounding the rod.

METHODS

This was a prospective observational study of patients with early onset scoliosis (EOS) treated with MCGRs and undergoing rod exchange who were consecutively recruited between February 2019 and January 2020. Ten patients were recruited (mean age 12 years (SD 1.3); 2 M:8 F). The configurations of the MCGR were studied to reveal the distraction mechanisms, with crucial rod parts being the distractable piston rod and the magnetically driven rotor inside the barrel of the MCGR. Metal-on-metal contact in the form of ring-like wear marks on the piston was found on the distracted portion of the piston immediately outside the barrel opening (BO) through which the piston rod distracts. Biopsies of paraspinal muscles and control tissue samples were taken over and away from the wear marks, respectively. Spectral analyses of the rod alloy and biopsies were performed to reveal the metal constituents and concentrations. Histological analyses of the biopsies were performed with haematoxylin and eosin staining.

RESULTS

Titanium (Ti), vanadium (V), and neodymium (Nd) concentrations in the biopsies taken near the wear marks were found to be significantly higher than those in the control tissue samples. Significantly increased Nd concentrations were also found in the tissues near the barrel of the MCGR. Chronic inflammation was revealed by the histological studies with fibrosis and macrophage infiltration. Black particles were present within the macrophages in the fibrotic tissues.

CONCLUSION

Ti and V were generated mainly at the BO due to metal-on-metal contact, whereas the Nd from the rotor of the MCGR is likely released from the BO during distraction sessions. Phagocytotic immune cells with black particles inside raise concern regarding the long-term implications of metallosis. Cite this article: Bone Joint J 2020;102-B(10):1375-1383.

Level of Experience Does Not Influence the Accuracy of Radiographic and Ultrasound Measurements of Magnetically Controlled Growing Rod Distractions

BACKGROUND

Magnetically controlled growing rods (MCGR) have become a popular surgical option for the treatment of early-onset scoliosis. Both radiographs and ultrasound are currently used to measure the amount of length achieved when MCGRs are distracted. Previous studies have investigated the intraobserver and interobserver reliability of radiographic and ultrasound measurements of MCGR distraction. Some authors have reported that there is a "learning curve" in measuring MCGR lengthening with ultrasound, suggesting that new users require several months of experience before they can accurately perform the measurements. The goal of this study was to determine whether surgical experience of the rater is associated with the accuracy of radiographic and ultrasound measurements of MCGR distraction.

METHODS

Six raters evaluated 29 deidentified radiographs and 30 ultrasound images from early-onset scoliosis patients with MCGR. Raters had varying levels of experience, ranging from a senior fellowship-trained pediatric orthopaedic surgeon to a junior orthopaedic surgery resident. Raters measured the amount of rod distraction in 2 sessions spaced 2 weeks apart. All raters were provided with a document demonstrating the radiographic and ultrasound measurement techniques before the first round of measurements. Intraclass correlation coefficients were calculated.

RESULTS

Excellent intraobserver and interobserver agreement was achieved for both radiographic and ultrasound measurements of MCGR distraction. Subanalysis based on experience level showed that excellent intraobserver agreement was maintained with no evidence of decreased reliability in raters with less experience.

CONCLUSIONS

Excellent intraobserver and interobserver agreement was obtained with radiographic and ultrasound measurements of MCGR distraction, regardless of the experience level of the rater. Posting a document with the radiographic and ultrasound measurement techniques in the orthopaedic surgery clinic, and perhaps also the radiology reading room may help avoid inaccurate measurements of distraction length secondary to a learning curve.

LEVEL OF EVIDENCE

Level III-diagnostic.

Current status of the magnetically controlled growing rod in treatment of early-onset scoliosis: What we know after a decade of experience

The magnetically controlled growing rod (MCGR) has had approximately 10 years of clinical experience worldwide. Clinical effectiveness to control early-onset scoliosis is consistent even at final surgery. MCGRs have significantly lower relative percentage of infection or wound complications as compared to traditional growing rods. Most common complications include foundation failure and failure of distraction. Contouring of the rod especially at the proximal segment while accommodating for the straight actuator remains a difficult task and its failure may lead to proximal junctional kyphosis. Unique complications of MCGR include clunking, temporary diminishing distraction gains, and metallosis. Temporary reductions in distraction gains are observed as the MCGR lengthens but return to normal baseline distraction gains after rod exchange. Lack of standardization for rod configuration, distraction strategies and decisions of whether to keep the rods in situ, remove without fusion surgery or to perform spinal fusion at skeletal maturity will require further study.

The effect of magnetically controlled growing rods on three-dimensional changes in deformity correction

STUDY DESIGN

Prospective radiographic study.

OBJECTIVES

To determine the three-dimensional (3D) changes in deformity correction with magnetically controlled growing rod (MCGR) distractions. MCGRs can achieve similar coronal plane correction as traditional growing rods. The changes in the sagittal and axial planes are unknown and should be studied as these factors reflect potential for proximal junctional kyphosis and rotational deformity. Frequent MCGR distractions may potentially improve axial plane deformities to the same extent as coronal and sagittal plane deformities.

METHODS

Early onset scoliosis (EOS) patients who underwent dual MCGRs with minimum 2-year follow-up were included in this study. 3D reconstructions of 6-monthly biplanar images were used to study changes in coronal, sagittal and axial planes. Changes in growth parameters (body height and arm span) were scaled to changes in coronal Cobb angles, sagittal profile (T1-12, T4-12, L1-L5, L1-S1), and rotational profile at the proximal thoracic, main thoracic and lumbar curves, and pelvic parameters (sagittal pelvic tilt, lateral pelvic tilt and pelvis rotation).

RESULTS

A total of 10 EOS patients were studied. The mean age at index surgery was 8.2 ± 3.0 years and mean postoperative follow-up of 34.3 ± 9.5 months. Six patients had rod exchange at mean 29.5 ± 11.8 months after initial implantation. Despite consistent gains in body height and arm span, the main changes in coronal and rotational profiles only occurred at the initial rod implantation surgery with only small changes occurring with subsequent follow-ups. Patients with higher preoperative proximal junctional angles had flattening of the sagittal plane occurring at initial surgery with early rebound. No changes in pelvic parameters were observed.

CONCLUSIONS

The 3D changes with MCGR are mainly observed with initial rod implantation and no significant changes are observed with distractions. The MCGR can prevent deformity progression in the axial plane.

LEVEL OF EVIDENCE

IV.

Vertebral Growth Around Distal Instrumented Vertebra in Patients With Early-Onset Scoliosis Who Underwent Traditional Dual Growing Rod Treatment

STUDY DESIGN

Retrospective radiographic study.

OBJECTIVE

To investigate the growth of the vertebrae around distal instrumented vertebra (DIV) in patients with early-onset scoliosis (EOS) who underwent dual growing rod (DGR) treatment.

SUMMARY OF BACKGROUND DATA

Previous studies indicated that DGR was likely to preserve or even stimulate the spinal growth. However, report pertaining to the effect of growing rod on the growth of individual vertebral body is rare.

METHODS

The EOS patients treated with DGR who had at least four lengthenings and 5-year follow-up were enrolled. Spine radiographs at index surgery and final follow-up were reviewed. The height, width, and depth of vertebral body from DIV-2 to DIV+2, and the height of the adjacent intervertebral space (IVS) were measured. The percentage of growth was calculated.

RESULTS

Thirty-one patients (mean age, 6.2 ± 2.5 years old) met the inclusion criteria, 74.2% (23/31) of whom were female. The average follow-up was 6.2 years (range, 5.0-10.4 yr). The measured vertebrae were divided into DIV group (n = 65), DIV- group (DIV-1 and DIV-2, n = 60), and DIV+ group (DIV+1 and DIV+2, n = 47). There were 33, 90, and 78 measured IVSs in DIV, DIV-, and DIV+ group, respectively. The total percentage growth of vertebral height was significantly higher in DIV- group than that in DIV and DIV+ groups (56.6 ± 20.3% vs. 45.6 ± 18.0% and 42.7 ± 16.2%, respectively, P ≤ 0.001). The vertebrae in DIV- group also had the highest annual height growth rate (8.7 ± 2.6% vs. 7.0 ± 2.4% and 6.6 ± 2.0%, respectively, P ≤ 0.001). A significant decrease of IVS height was observed in DIV- and DIV groups (P ≤ 0.001).

CONCLUSION

Traditional DGR with periodical distraction stimulated the longitudinal growth of the two segments immediately above DIV in patients with EOS. DGR technique had a negative effect on the development of intervertebral discs within distracted levels.

LEVEL OF EVIDENCE

3.