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

Bow

2020

Global Spine Journal

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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.

Section: Discussionmentioning

confidence: 99%

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

Bow

2020

Global Spine Journal

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Journal of Pediatric Orthopaedics

“…3 Among different growth friendly techniques used for the treatment of EOS, 12 GR are the most popular option with successful results reported by numerous studies. [13][14][15][16] The amount of reported spinal growth achieved by this technique has been far from consistent. 8 To evaluate the true effect of curve severity on lengthenings, we measured the vertebral height change per each instrumented segment during the period between index and final surgeries.…”

Section: Discussionmentioning

confidence: 99%

The Effect of Apical Vertebra Position on Growing Rod Treatment: A Clinical and Finite Element Study

Dursun

Çetik

Güzel

et al. 2022

Background: Growing rods (GRs) is a commonly utilized technique for the management of early-onset scoliosis. The significance of the position of the apical vertebrae relative to the rods is not known. The purpose of this study is to analyze the potential effects of the position of the apical vertebrae in relation to the GRs on deformity control through plain radiographs and finite element analysis (FEA) modeling. Methods: We identified 140 patients treated with GR between 2000 and 2018. Patients who had a congenital vertebral anomaly or <2-year follow-up were excluded. Curve magnitude, traction radiograph under general anesthesia (TRUGA) flexibility, apical rotation, the lengths of T1-12, T1-S1, and the instrumented segments were recorded. Patients were divided into 3 groups according to the apical position on the postoperative radiographs: group 1 (both pedicles are between the rods), group 2 (convex rod is between the apical vertebra pedicles), group 3 (both pedicles are lateral to the convex rod). FEA models were created simulating the 3 groups. Both radiographic and FEA data were analyzed to compare the deformity control and growth in each group. Results: Fifty-eight patients were included in the final analyses (mean age 84 mo; range: 38 to 148). Ten patients (17%) were in group 1, 34 (59%) in group 2, and 14 (24%) in group 3. Difference between TRUGA flexibilities was statistically insignificant. Group 3 was the least successful in terms of both height gain and rotational control. FEA showed a decrease in rotation and displacement for every group, however, the residual rotation and displacement was highest in group 3. Conclusions: Bringing the apex in line with the GR increases the capacity of growth preservation as it results in largest height gain and better deformity control. FEA model demonstrated that distraction alone is inadequate for controlling rotation, and with increasing apical translation, residual rotation after distraction also increases. Level of Evidence: Level III.

J Orthop Surg (Hong Kong)

“…A load of 175N was chosen to replicate the upper body weight of a MCGR EOS patient (mean, 9.5 years) at Queen Mary Hospital, Hong Kong. [38][39][40] A pilot trial with two porcine spines was conducted previously to finalize the testing procedures. The pilot trial demonstrated the spine's condition and strength remained the same after the aforementioned loading protocol, thereby validating the methodology and allowing comparison of data after different distraction magnitudes in the same spine.…”

Section: Biomechanical Testsmentioning

confidence: 99%

A biomechanical study on the effect of lengthening magnitude on spine off-loading in magnetically controlled growing rod surgery: Implications on lengthening frequency

Wong

Nafo

2021

Purpose: To assess whether the magnitude of lengthening in magnetically controlled growing rod (MCGR) surgeries has an immediate or delayed effect on spinal off-loading. Methods: 9 whole porcine spines were instrumented using two standard MCGRs from T9 to L5. Static compression testing using a mechanical testing system (MTS) was performed at three MCGR lengthening stages (0 mm, 2 mm, and 6 mm) in each spine. At each stage, five cycles of compression at 175N with 25 min of relaxation was carried out. Off-loading was derived by comparing the load sustained by the spine with force applied by the MTS to the spine. Micro-CT imaging was subsequently performed. Results: The mean load sustained by the vertebral body before lengthening was 39.69N, and immediately after lengthening was 25.12N and 19.91N at 2 mm and 6 mm lengthening, respectively; decreasing to 10.07N, 8.31N, and 8.17N after 25 minutes of relaxation, at 0 mm, 2 mm, and 6 mm lengthening stages, respectively. There was no significant difference in off-loading between 2 mm and 6 mm lengthening stages, either instantaneously ( p = 0.395) or after viscoelastic relaxation ( p = 0.958). CT images showed fractures/separations at the level of pedicle screws in six spines and in the vertebral body’s growth zone in five spines after 6 mm MCGR lengthening. Conclusion: This study demonstrated MCGRs cause significant off-loading of the spine leading to stress shielding. 6 mm of lengthening caused tissue damage and microfractures in some spines. There was no significant difference in spine off-loading between 2 mm and 6 mm MCGR lengthening, either immediately after lengthening or after viscoelastic relaxation.