Learning Curve in Monitoring Magnetically Controlled Growing Rod Distractions With Ultrasound

Increased lengthening frequency does not adversely affect the EOSQ scores in magnetically controlled growing rod surgeries in 133 subjects followed to final fusion

PURPOSE

Magnetically Controlled Growing Rod (MCGR) allows frequent outpatient rod lengthening when treating Early Onset Scoliosis (EOS) patients. But there is lack of expert consensus on the optimal MCGR lengthening interval. EOS 24-Item Questionnaire (EOSQ) is validated for assessing health-related quality of life (HrQOL), family burden, and satisfaction. This is the first study assessing how MCGR lengthening intervals affects patient-perceived outcomes.

METHODS

This is a multicentred cohort study with subjects recruited from 2012 to 2018 and followed till fusion. EOS subjects who underwent MCGR surgeries were grouped into high, medium or low lengthening interval subgroups based on 16 and 20 week cut-offs. Repeated measure analysis was performed on EOSQ's specified 12 domains. EOSQ results were taken: before index surgery, after index surgery, and prior to definitive treatment. Demographic, clinical and radiographic data were included in model adjustment.

RESULTS

133 subjects with mean follow-up of 3.5 (± 1.3) years were included, with 60 males and 73 females; 45 idiopathic, 23 congenital, 38 neuromuscular, and 27 syndromic patients. Mean Cobb angle at surgery was 67° (± 22°) with mean age of 8.3 (± 2.5) years. Between groups, clinical and radiographic parameters were comparable. Higher EOSQ scores in medium lengthening interval subgroup was present in fatigue (p = 0.019), emotion (p = 0.001), and parental impact (p = 0.049) domains, and overall score (p = 0.046). Trendline contrast between subgroups were present in general health (p = 0.006) and physical function (p = 0.025) domains.

CONCLUSION

Patient-perceived outcome improvements appear similar between lengthening interval subgroups. All MCGR lengthening intervals were tolerated by patients and family, with no negative impact observed.

LEVEL OF EVIDENCE

Prognostic Level III.

Longitudinal comparison of direct medical cost, radiological and health-related quality of life treatment outcomes between traditional growing rods and magnetically controlled growing rods from preoperative to maturity

Background

Magnetically controlled growing rods (MCGR) have replaced traditional growing rods (TGR) in the past decade, however, a comparison of their direct costs and treatment outcomes based on real longitudinal data is lacking. This study aims to compare the direct cost and treatment outcomes between TGR and MCGR, whilst incorporating complications, reoperations and changes in health-related quality of life (HRQoL) throughout the entire treatment course.

Methods

Patients with early onset scoliosis (EOS) who underwent initial growing rod surgery between 2003 and 2016 at a tertiary scoliosis clinic were studied with longitudinal data. Accumulated direct medical costs were calculated based on the unit cost of surgeries of each TGR and MCGR, costs incurred for any rod exchange or remedial surgery for post-operative complication. Treatment outcomes were evaluated via: Patient’s HRQoL using SRS-22r questionnaire, and radiological parameters (including major curve correction, spine length gains, spinal balance) throughout the treatment until maturity.

Results

A total of 27 EOS patients (16 MCGR, 11 TGR) were studied. Total direct cost of index surgery for MCGR was HKD$223,108 versus lower cost of HKD$135,184 for TGR (p < 0.001). At 2–3 years post-index surgery, accumulative total direct medical cost of MCGR and TGR became most comparable (TGR:MCGR ratio = 1.010) and had reached neutrality between the two groups since. Radiological parameters had no intergroup differences at maturity. For HRQoL, TGR group had shown the trend of less pain (domain score mean difference: 0.53, p = 0.024) post-index surgery and better self-appearance (domain score mean difference: 1.08, p = 0.017) before fusion. Higher satisfaction with treatment (domain score mean difference: 0.76, p = 0.029) was demonstrated by TGR patients at fusion/maturity. MCGR had negative (r_s = -0.693) versus TGR’s positive (r_s = 0.989) correlations (p < 0.05) of cost and SRS-22r total scores at 2–3 years post-index surgery.

Conclusions

From index surgery to maturity, TGR demonstrated better satisfaction with treatment by patients and comparable overall HRQoL with MCGR during the treatment course, as MCGR did not show apparent benefit despite less surgeries and cost neutrality between the two groups at 2–3 years post-index surgery.

Optimizing Expansion Clinic for Patients With Magnetic Controlled Growth Rods

In 2017, members of the Pediatric Spine Study Group reported that 80% of new growth-friendly implants inserted were magnetically controlled growing rods (MCGRs). MCGRs are usually expanded more often than every 6 months, as was general practice with traditional growth rods. The growing volume of expansion visits is managed variably at different centers. Although there is existing research comparing MCGRs with traditional systems for efficacy and complications, there is limited literature regarding how expansion clinics are managed. This article reviews current practices such as scheduling, expansion verification, billing, and other key parameters for running expansion clinics.

"Law of Temporary Diminishing Distraction Gains": The Phenomenon of Temporary Diminished Distraction Lengths With Magnetically Controlled Growing Rods That Is Reverted With Rod Exchange

STUDY DESIGN

Prospective study.

OBJECTIVES

To study the increasing divergence between targeted and achieved distractions observed with magnetically controlled growing rod (MCGR)lengthening, and the relationship of this reduced rate of achieved lengthening with remaining rod length.

METHODS

Patients with early onset scoliosis (EOS) who underwent MCGRs with minimum 2-year follow-up were consecutively enrolled. Targeted and achieved lengths were compared. Correlation between percentage of lengthening achieved from targeted length was identified with the timing of rod exchanges.

RESULTS

A total of 20 patients fulfilled the inclusion criteria. The mean age at index surgery was 9.5 years and mean postoperative follow-up was 68 ± 28 months. Of these, 8 patients had at least one rod exchange that occurred at 23 ± 4 months. A decrease in rate of achieved lengthening was observed when compared with targeted distractions. The achieved lengthening drops from 86% of targeted length at the first distraction to only 58.8% at the 21st distraction episode for the first set of rods. After rod exchange, the average achieved lengthening went back up to 81.3% of the targeted length but subsequently had a gradual reduction to 35% at the 19th distraction episode.

CONCLUSIONS

We propose a "law of temporary diminishing distraction gains" that MCGR users should be aware of when monitoring rod lengthening. Diminishing distraction length gains is observed as the rod is lengthened and is a phenomenon independent of patient factors. It is only temporary as the rates of achieved lengthening returns to baseline after rod exchange.

Limited trunk motion and posterior pelvic tilting in ambulatory children treated with bilateral rib to pelvis implants for spinal deformity control

In young children, growth-friendly spinal implants with bilateral rib to pelvis fixation are used to control progressive spinal deformity. Whereas curve progression, complications and side-effects have been extensively studied in this patient population, no data are available on gait pattern changes and postural body adjustments. Our study evaluates whether gait pattern changed for ambulatory children treated with bilateral rib to pelvis implants compared to age-matched healthy children. In this small cohort study, gait analysis was performed using spatiotemporal and kinematic parameters of four ambulatory children with severe scoliosis and growth-friendly spinal implants using the bilateral rib to pelvis fixation. Data were statistically analyzed and compared to seven healthy age-matched children. Between both groups, no differences were seen in walking speed, cadence and stride length. The treated patients showed a lower range of motion of the pelvic obliquity and of the trunk obliquity and rotation, but a higher knee flexion. Growth-friendly spinal implants with bilateral rib to pelvis fixation are commonly used in wheelchair children and rarely indicated in ambulatory patients. The presented data show reduced trunk and pelvis motion using this implant construct. These findings help to understand body postural adjustments and add valuable information for families and care providers when considering this surgery. Level of evidence: Therapeutic level IV.

How frequent should the radiographic examination be to monitor magnetically controlled growing rods? A retrospective look two to seven years postoperatively

PURPOSE

Magnetically controlled growing rods (MCGR) allow more frequent outpatient lengthenings to better mimic the physiological growth. The assessment of distractions with radiographs raised concerns regarding ionizing radiation exposure in growing children. The aim was to assess the necessity of radiographs after every lengthening of MCGR.

METHODS

A retrospective analysis of 30 consecutive patients (19F, 11 M) treated in a single institution between 2011 and 2017. Planned radiographs were taken based on a protocol, updated over the years to involve less frequent acquisitions. Unplanned radiographs were obtained after a patient complaint or a significant clinical examination finding. Outcome measures were preoperative and postoperative radiographic measurements, and complications such as proximal and distal junctional kyphosis and failure, rod or actuator breakage, collapse of previously achieved height or failure to lengthen and worsening of deformity.

RESULTS

Mean age at surgery was 7.5 (4-11) years. Mean follow-up was 45 (24-84) months. Mean number of lengthenings and radiographs per patient were 14.4 (8-23), and 13.2 (5-46), respectively. Nine patients (30%) experienced a total of 13 mechanical complications. Almost all complications were detected in unplanned radiographs. The probability of detecting a mechanical complication was significantly lower (p < 0.00001) in planned radiographs.

CONCLUSIONS

Radiographs taken after routine lengthenings of MCGR are not likely to reveal any significant finding, since only 0.9% of planned radiographs displayed a mechanical complication. Exposing growing children to radiation with an intention of checking the MCGR device after every lengthening could not be justified. Obtaining post-lengthening radiographs with a decreased frequency and after a significant complaint or clinical finding may be considered.

Sonography of Magnetically Controlled Growing Rods: A Quality Initiative in the Creation of a Multidisciplinary Clinic

Objective:

The MAGEC (Magnetic Expansion Control) rods were introduced to a medical institution in 2015. The rod expansion procedures were initially evaluated with radiographs. The staff undertook a quality initiative to reduce radiation exposure by utilizing sonography.

Material and Methods:

The radiation dose for a typical visit was measured by examining DICOM imaging data, stored in PACS. Imaging visit time was determined from the difference between times of first radiograph/sonogram before distraction to last radiograph/sonogram after distraction.

Results:

The 21 patients (8 male, 13 female) were an average age of 11.4 ± 2.82 years (age at implant = 7.5 ± 1.94) when evaluated. The average length of time for a radiographic visit was 40.7 ± 20.7 minutes, whereas a sonography visit was 10.7 ± 3.7 minutes. Radiation dose per study visit prior to the introduction of the MAGEC clinic was 0.42 ± 0.39 mSv. Given an ideal patient schedule, the MAGEC clinic could reduce radiation dose by 1.3 to 2.5 mSv annually, with 95% confidence.

Conclusion:

This quality improvement study demonstrated a reduction in radiation exposure and imaging time. The added benefits were providing a successful multidisciplinary imaging clinic and creation of a new exam that aligned with the “ultrasound first” initiative.

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.

Mean 6-Year Follow-up of Magnetically Controlled Growing Rod Patients With Early Onset Scoliosis: A Glimpse of What Happens to Graduates

BACKGROUND

There is no agreement on frequency of distractions of magnetically controlled growing rods (MCGRs) but more frequent and smaller amounts of distractions mimic physiological spine growth. The mid- to long-term follow-up and management at skeletal maturity is unknown.

OBJECTIVE

To analyze patients with mean 6 yr of follow-up and describe the fate of MCGR graduates.

METHODS

Early onset scoliosis (EOS) patients treated with MCGRs with minimum 4 yr of follow-up and/or at graduation were studied. Parameters under study included Cobb angle, spine and instrumented lengths, and rod distraction gains. Relationship between timing of rod exchanges with changes in rate of lengthening was studied.

RESULTS

Ten EOS patients with mean 6.1 yr of follow-up were studied. The greatest Cobb angle correction occurred at the initial implantation surgery and was stable thereafter. Consistent gains in T1-12, T1-S1, and instrumented segment were observed. Rate of lengthening reduced after the first year of use but improved back to initial rates after rod exchange. Seven of the ten patients experienced complications with reoperation rate of 40% for rod distraction failure and proximal foundation problems. Only mild further improvements in all radiological parameters were observed pre- and postfinal surgery. No clinically significant curve progression was observed for rod removal only. All postfinal surgery parameters remained similar at postoperative 2 yr.

CONCLUSION

This study provides an outlook of the end of MCGR treatment. Although this is a fusionless procedure, instrumented segments do experience stiffness limiting further correction and length gain during final surgery whether fusion or rod removal is performed.

The Crooked Rod Sign: A New Radiological Sign to Detect Deformed Threads in the Distraction Mechanism of Magnetically Controlled Growing Rods and a Mode of Distraction Failure

STUDY DESIGN

Case report.

OBJECTIVE

To report a unique mechanical failure of magnetically controlled growing rods (MCGRs) that is related to continuous rod slippage.

SUMMARY OF BACKGROUND DATA

Despite the growing popularity of MCGR in the management of patients with early onset scoliosis, postoperative complications and reoperations are not uncommon. Unique complications or unplanned reoperations are observed in patients with MCGRs that are not seen in traditional growing rods. The complications include rod slippage, mismatch between targeted and achieved distraction length, metallosis, and actuator pin fracture. We have identified an unreported failure mechanism whereby deformed threads occur in the internal distraction mechanism of the MCGR. This phenomenon may indicate increased MCGR internal screw friction and increased distraction resistance. Increased friction and resistance ultimately led to distraction failure and revision surgery.

METHODS

A girl with early onset scoliosis (EOS) was treated by dual MCGRs. She developed proximal junctional kyphosis (PJK) and continuous rod slippage. Distractions in the out-patient clinic and under sedation did not achieve successful rod lengthening. A tell-tale "crooked rod" radiological sign was identified by angulation between the actuator and the extendable portion of the rod.

RESULTS

Rod exchange was performed and she is now 2 years after revision surgery with successful lengthening episodes. Upon review of the extracted MCGR, distraction was not possible even after rod removal and was only resumed after the screw was manually reinserted along its correct threads.

CONCLUSION

Deformed threads is a complication that cannot be reverted without rod removal and exchange. Users should be aware of this potential failure mechanism and proceed to early rod exchange rather than attempting any further distractions.

LEVEL OF EVIDENCE

4.

Does the external remote controller's reading correspond to the actual lengthening in magnetic-controlled growing rods?

PURPOSE

Magnetic-controlled growing rods (MCGRs) are now routinely used in many centres to treat early-onset scoliosis (EOS). MCGR lengthening is done non-invasively by the external remote controller (ERC). Our experience suggests that there may be a discrepancy between the reported rod lengthening on the ERC and the actual rod lengthening. The aim of this study was to investigate this discrepancy.

METHODS

This was a prospective series. Eleven patients who were already undergoing treatment for EOS using MCGRs were included in this study.

RESULTS

One hundred and ninety-two sets of ultrasound readings were obtained (96 episodes of rod lengthening on dual-rod constructs) and compared to their ERC readings. Only 15/192 (7.8%) readings were accurate; 27 readings (14.9%) were false positive; and 8 readings (4.2%) were an underestimation while 142 readings (74.0%) were an overestimation by the ERC. Average over-reporting by the ERC was 5.31 times of the actual/ultrasound reading. When comparing interval radiographs with lengthening obtained on ultrasound, there was a discrepancy with an average overestimation of 1.35 times with ultrasound in our series. There was a significant difference between ERC and USS (p = 0.01) and ERC and XR (p = 0.001). However, there was no significant difference between USS and XR (p > 0.99).

CONCLUSION

The reading on the ERC does not equate to the actual rod lengthening. The authors would recommend that clinicians using the MCGR for the treatment of early-onset scoliosis include pre- and post-extension imaging (radiographs or ultrasound) to confirm extension lengths at each outpatient extension. In centres with ultrasound facilities, we would suggest that patients should have ultrasound to monitor each lengthening after distraction but also 6-month radiographs. These slides can be retrieved under Electronic Supplementary Material.

Use of a distraction-to-stall lengthening procedure in magnetically controlled growing rods: A single-center cohort study

PURPOSE

The objective of this study was to assess the outcome of patients treated with magnetically controlled growing rods (MCGRs) using a standardized distraction procedure with intended distraction-to-stall and to compare the outcomes between idiopathic and nonidiopathic patients.

METHODS

This was a retrospective single-center cohort study. Conversion cases were excluded. Distractions were performed with 2- to 3-month intervals with the intention of distraction-to-stall on both rods. Distraction length was measured on X-rays every 6 months. Spinal height was assessed using T1-T12 and T1-S1 annual increase.

RESULTS

19 patients (eight idiopathic and 11 nonidiopathic) were included. Mean age at surgery was 9.7 ± 1.9 years, and median follow-up was 1.9 years (interquartile range (IQR): 1.3-2.2). Major curve improved from median 76° (IQR: 64-83) preoperatively to 42° (IQR: 32-51) postoperatively ( p < 0.001) corresponding to a curve correction of 43% (IQR: 33-51). Correction was maintained at 1- and 2-year follow-up. Median annual T1-T12 and T1-S1 height increase were 10 mm (IQR: 6-16) and 11 mm (IQR: 7-33), respectively. A total of 159 distraction procedures were performed; 83.5% of these were distracted-to-stall, and 16.5% were stopped due to discomfort. Median rod distraction per procedure was 2.0 mm (IQR: 1.6-2.7) for the concave side and 1.7 mm (IQR: 1.4-2.5) for the convex side. Five patients had implant-related complications. Patients with nonidiopathic etiology were significantly younger and had lower flexibility compared with idiopathic patients ( p ≤ 0.040). However, we found no statistically significant difference in curve correction, spinal height increase, distraction length, or complications between the two groups ( p ≥ 0.109).

CONCLUSION

MCGR effectively corrected the deformity and increased spinal height using a distraction procedure with intended distraction-to-stall. Five of 19 patients had implant-related complications, and we found no difference in the outcomes between idiopathic and nonidiopathic patients.

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

STUDY DESIGN

Cross-sectional study.

OBJECTIVE

To assess the inter- and intraobserver reliability of thoracic, spino-pelvic, and rod lengthening measurements made on biplanar spinal stereoradiography (EOS imaging) in children treated with magnetically controlled growing rod (MCGR).

SUMMARY OF BACKGROUND DATA

MCGR treatment aims to gain spine length while gradually correcting the spinal deformity. Monitoring thoracic and spino-pelvic parameters is crucial for successful management. EOS imaging is widely used for diagnosis and monitoring of children with Early Onset Scoliosis. However, there is a paucity of literature on the reliability of thoracic and spino-pelvic parameters on EOS imaging in children treated with MCGR.

METHODS

Three independent reviewers independently read a random assortment of 20 whole spine posteroanterior and lateral radiographs from patients treated with MCGR. The measurements were repeated 4 weeks after the initial read. The following radiological parameters were measured: Cobb angle of the main and compensatory curves, coronal balance, coronal T1-S1 and T1-T12 length, chest width and depth at T6, pelvic inlet width, MCGR distracted lengths, global kyphosis, proximal and distal junctional angle, lordosis, sagittal balance, pelvic incidence, pelvic tilt and sacral slope. Statistical analysis was performed with paired t test and Cronbach alpha for inter- and intraobserver reliability.

RESULTS

All measurements had good or excellent intra- and interobserver reliability (α>0.8; P < 0.05), except measurements of the proximal junctional angle which showed only poor intra- and interobserver reliability for patients with an upper instrumented vertebra cranial to T4.

CONCLUSION

EOS imaging is reliable for diagnosis and monitoring of children with Early Onset Scoliosis treated with MCGR. EOS imaging is particularly excellent for assessment of MCGR lengthening. Diagnosis and interpretation of early proximal junctional kyphosis within the cervicothoracic junction should be made with caution.

LEVEL OF EVIDENCE

3.

Rod Lengthening With the Magnetically Controlled Growing Rod: Factors Influencing Rod Slippage and Reduced Gains During Distractions

STUDY DESIGN

Prospective study.

OBJECTIVE

To identify the factors that are associated with rod slippage and to study the pattern of achieved length gain with a standard distraction methodology.

SUMMARY OF BACKGROUND DATA

Ability to achieve successful magnetically controlled growing rod (MCGR) distraction is crucial for gradual spine lengthening. Rod slippage has been described as a failure of internal magnet rotation leading to a slippage and an inability to distract the rod. However, its onset, significance, and risk factors are currently unknown. In addition, how this phenomenon pertains to actual distracted lengths is also unknown.

METHODS

A total of 22 patients with MCGR and at least six distraction episodes were prospectively studied. Patients with rod slippage occurring less than six distraction episodes were considered early rod slippage whereas those with more than six episodes or have yet to slip were grouped as late rod slippage. The association of parameters including body habitus, maturity status, age of implantation, total number of distractions, months of distraction from initial implantation, initial and postoperative Cobb angle, T1-T12, T1-S1, T5-T12 kyphosis, curve flexibility, instrumented length, and distance between magnets in dual rods and between the magnets and apex of the curve with early or late onset of rod slippage were studied. Differences between expected and achieved distraction lengths were assessed with reference to rod slippage episodes and rod exchanges to determine any patterns of diminishing returns.

RESULTS

Patients had mean age of 7.1 years at diagnosis with mean follow-up of 49.8 months. A mean 32.4 distractions were performed per patient. Early rod slippage occurred in 14 patients and late rod slippage occurred in eight patients. Increased height, weight, body mass index, older age, increased T1-12 and T1-S1 lengths, and less distance between magnets were significantly associated with early rod slippage. Expected distraction lengths did not translate to achieve distraction lengths and reduced gains were only observed after achieving one-third of the allowable distracted length in the MCGR. Length gains return to baseline after rod exchange.

CONCLUSION

This is the first study to specifically analyze the impact of rod slippage on distraction lengths and the risk factors associated with its onset and frequency. Increased body habitus and reduced distance between internal magnets significantly influenced rod slippage events. Diminishing returns in distracted length gains were only observed after a period of usage.

LEVEL OF EVIDENCE

3.

Traditional growing rod versus magnetically controlled growing rod for treatment of early onset scoliosis: Cost analysis from implantation till skeletal maturity

PURPOSE

To compare the yearly cost involved per patient in the use of magnetically controlled growing rod (MCGR) and traditional growing rods (TGRs) in the treatment of early onset scoliosis (EOS) and to assess the overall cost burden of MCGR with reference to patient and health-care infrastructure.

METHODS

For a hypothetical case of a 5-year-old girl with a diagnosis of EOS, a decision-tree model using TreeAge Software was developed to simulate annual health state transitions and compare the 8-year accumulative direct, indirect, and total cost among the four groups: (1) dual MCGRs with exchange every 2 years, (2) dual MCGRs with exchange every 3 years, (3) TGR with surgical distraction every year, and (4) TGR with surgical distraction every 6 months. Base-case values and ranges of clinical parameters reflecting complication rate after each type of surgical distraction were determined from a review of literature and expert opinion. Government gazette and expert opinion provided cost estimation of growing rods, surgeries, surgical complications, and routine follow-up. Microsimulation of 1000 individuals was conducted to test the variation in total direct costs (in 2016 Hong Kong dollars (HKD)) between individuals, and estimated the standard deviations of total direct costs for each group.

RESULTS

Over the projected treatment period, indirect costs incurred by patients and family were higher for the MCGR as compared to the TGR. However, the total costs incurred by MCGR groups (group 1: HKD164k; group 2: HKD138k) were lower than those incurred by TGR groups (group 3: HKD191k; group 4: HKD290k). Although the accumulative costs of three groups (TGR with distraction every year and MCGR replacing every 2 and 3 years) were approaching each other in the first 2 years after initial implantation, at year 3 the accumulative cost of MCGR exchange every 2 years was HKD36k more than the yearly TGR surgery due to the cost of implant exchange. The cost incurred by both the MCGR groups was less than that incurred by the TGR groups from year 4 to skeletal maturity.

CONCLUSIONS

The use of dual MCGRs, regardless of its 2- or 3-year exchange, was only cost saving and less expensive than the dual TGRs for EOS treatment from the fourth year of continuous treatment. Despite higher patient-related costs during MCGR treatment, it is important to consider the reduced risks and mental burden suffered by these children during repeat surgeries. With improved knowledge of the costs associated with long-term MCGR use, better constructed cost-effectiveness studies can be performed in the future.