Magnetically Controlled Growing Rods: The Experience of Mechanical Failure from a Single Center Consecutive Series of 28 Children with a Minimum Follow-up of 2 Years

Abstract

Study DesignRetrospective observational study of a continuous series of 28 children.PurposeTo determine the mechanical failure rate in our cohort of children treated with magnetically controlled growth rods (MCGRs).Overview of LiteraturePrevious studies report a MCGR mechanical failure rate of 0%–75%.MethodsAll patients with MCGR implantation between 2012 and 2015 were examined and followed up for a minimum of 2 years. A retrospective evaluation of contemporaneously documented clinical findings was conducted, and radiographs were retrospectively examined for mechanical failure. The external remote controller (ERC)-specified length achieved in the clinic was compared to the length measured on subsequent radiographs.ResultsFourteen mechanical failures were identified in 28 children (50%) across a total of 52 rods (24 pairs and four single constructs). Mechanical failures were due to: failure to lengthen under general anesthesia (seven children), actuator pin fracture (four), rod fracture (one), foundation screw failure (one), and ran out of rod length (one). Of the 14 mechanical failures, six were treated with final fusion operations (reflecting limited further growth potential), and eight patients were treated with the intention for further lengthening. We therefore consider these eight patients to represent the true incidence of mechanical failure in our cohort (29%). The difference between the ERC length and radiographic length was found to be identical in 11% cases; 35% were overestimates, and 54% were underestimates. The median underestimate was 2.45 mm whereas the median overestimate was 3.1 mm per distraction episode. In total, 95% of all ERC distractions were within ±10 mm of the radiographic length achieved over a median of nine distraction episodes.ConclusionsOur series is the most comprehensive MCGR series published to date, and we present a mechanical failure rate of 29%. Clinicians should be mindful of the discrepancies between ERC length and radiographic measurements of rod length; other modalities may be more helpful in this regard.

Mechanical Wear Analysis Helps Understand a Mechanism of Failure in Retrieved Magnetically Controlled Growing Rods: A Retrieval Study

“…The MAGEC system has been increasingly used for treating EOS patients due to its non-invasive lengthening. However, unplanned revisions of MAGEC rods due to a failure of the internal mechanism remains a concern of its use [14,15], of which the mechanism is still unclear. This is one of the first studies to analyse retrieved MAGEC rods using high-precision metrological techniques, which has been widely used in retrieval analysis of hip implants [16,17].…”

Mechanical wear analysis helps understand a mechanism of failure in retrieved magnetically controlled growing rods: a retrieval study

“…The MAGEC system has been increasingly used for treating EOS patients due to its non-invasive lengthening. However, unplanned revisions of MAGEC rods due to a failure of the internal mechanism remains a concern of its use [14,15], of which the mechanism is still unclear. This is one of the rst studies to analyse retrieved MAGEC rods using high-precision metrological techniques, which has been widely used in retrieval analysis of hip implants [16,17].…”

<p>Magnetic Controlled Growth Rods in the Treatment of Scoliosis: Safety, Efficacy and Patient Selection</p>

“…38,39,61 Reduced distraction with repeated lengthenings has been described for both TGRs and MAGEC. 62,63 Both constructs have very limited ability to control the rotatory (3-dimensional) component of scoliotic deformity. There are few studies comparing outcomes between TGRs and MAGEC for EOS; 2 studies comparing the thoracic and total spinal height growth between TGRs and MAGEC have reported no significant difference between groups.…”