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Spinal Lengthening with Magnetically Controlled Growing Rods: Data from the Largest Series of Explanted Devices

Lookup NU author(s): Dr Simon Smith, Goksu Kandemir, Andrew Bowey, Professor Tom Joyce

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Abstract

© 2019 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.Study Design. Laboratory analysis of explanted MAGnetic Expansion Control (MAGEC) rods. Objective. Identify the in vivo lengthening of MAGEC rods Summary of Background Data. Little data is available regarding the lengthening achieved by MAGEC rods. Methods. Cases were identified from the largest series of independently analyzed explanted MAGEC rods. The in vivo growth of rods was determined by the distance between the first 'growth mark' and the actuator. The instrumented spinal lengthening was calculated for each construct. Constructs were considered functional if all rods could lengthen with external remote controller activation and no rods were 'telescoping'. Results. Fifty-five MAGEC constructs (99 rods) from 53 patients treated at 10 centers were included. The mean age at insertion was 8.5 years with rods implanted a mean of 35 months. Sixty rods were suitable for analysis with mean lengthening 21.7mm, 8.9mm/year. Of these 60 rods 3 were maximally distracted. Mean instrumented spinal lengthening for 38 suitable cases was 22.1mm, 8.4mm/year. This was positively correlated with the duration of implantation (r=0.34, p=0.04) but negatively with patient age at insertion (r=-0.35, p=0.03). The rate of instrumented spinal lengthening was negatively correlated with duration of implantation (r=-0.47, p=0.004). Of 55 constructs 34 were non-functional at time of removal with 9 functional and 12 indeterminate. Functional constructs had been implanted significantly less time (20.0 vs. 39.7 months, p<0.001) and lengthened less than those non-functional (12.3mm vs. 23.3mm, p=0.04). Conclusions. This multicenter explant study represents the largest cohort managed with MAGEC rods reported. Rods are very rarely removed having fully lengthened with mean instrumented spinal growth of 22mm over the implant's life. This may be explained by a high rate of lengthening mechanism failure in received rods after around 3 years in vivo. Our findings question the effectiveness of the MAGEC system and mandate urgent comparative clinical studies.Level of Evidence: 4.


Publication metadata

Author(s): Rushton PRP, Smith SL, Kandemir G, Forbes L, Fender D, Bowey AJ, Gibson MJ, Joyce TJ

Publication type: Article

Publication status: Published

Journal: Spine

Year: 2019

Pages: ePub ahead of print

Online publication date: 06/09/2019

Acceptance date: 02/04/2018

ISSN (print): 0362-2436

ISSN (electronic): 1528-1159

Publisher: Lippincott Williams and Wilkins

URL: https://doi.org/10.1097/BRS.000000000000321

DOI: 10.1097/BRS.0000000000003215

PubMed id: 31513114


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