Does the external remote controller\u2019s reading correspond to the actual lengthening in magnetic-controlled growing rods?

Kar Hao Teoh,Stuart H James,Kausik Mukherjee,Sridhar Kamath,Sashin Ahuja,Paul R Davies,Alwyn Jones,John Howes,Abdul Nazeer Moideen

doi:10.1007/s00586-020-06335-5

Kar Hao Teoh, Stuart H James + Show 7 more

Open Access

https://doi.org/10.1007/s00586-020-06335-5

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Abstract

PurposeMagnetic-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.MethodsThis was a prospective series. Eleven patients who were already undergoing treatment for EOS using MCGRs were included in this study.ResultsOne 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).ConclusionThe 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.Graphic abstractThese slides can be retrieved under Electronic Supplementary Material.

Highlights

Early-onset scoliosis (EOS) is an abnormal curvature of the spine diagnosed before the age of ten
This study suggests that the external remote controller is highly inaccurate at reporting the actual extension achieved and consistently over reports the length of extension of the growing rod
We found that ultrasound tends to overestimate the achieved length as measured by radiographs

Summary

Introduction

Early-onset scoliosis (EOS) is an abnormal curvature of the spine diagnosed before the age of ten. Following failure of non-operative treatment, surgical treatment is usually the only option as these curves are generally progressive. Growth sparing spinal surgery is usually preferred as it allows correction of the curve while maintaining growth of the spinal column until the child is close to skeletal maturity when a final spinal fusion operation can be performed. In June 2014, the National Institute for Health and Care Excellence (NICE) in the UK approved the use of magneticcontrolled growing rods (MCGRs) in EOS on the basis of efficacy and cost-effectiveness [1]. Prior to the introduction of magnetic-controlled growing rods (MCGRs), one of the main options for growth sparing spinal surgery was conventional growing rods. Conventional growing rods normally require 6-month operations to lengthen the rods under general anaesthesia throughout childhood and is associated with high complication rates, e.g. wound infections [2, 3]

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