MAGnetic Expansion Control (MAGEC) growing rod internal fracture – a pictorial review of an important mechanism of device failure

Purpose MAGEC rods are increasingly used to stabilise scoliosis in growing paediatric patients in order to avoid the need for repeated surgery. The purpose of this educational poster is to illustrate subtle and easy to miss fractures of the internal mechanism of the MAGEC rod, which often require surgical attention. Identification of these avoids delays to treatment and allows appropriate surgical planning to take place before further complications arise.

What is the MAGEC system? A magnetically controlled spinal bracing and distraction system used in children over 2 years old with early onset scoliosis (EOS). As the child grows, the system allows for distractions (lengthenings) to take place in outpatient clinic approximately every 3 months, without the need for sedation or analgesia. The system has been shown to prevent the progression of scoliosis and avoid repeated surgery which would ordinarily be required for conventional growth rods. Once the child has fully grown, the system is removed and replaced by a static spinal fixation device. Why are we seeing more MAGEC systems? The MAGEC system has been recommended by NICE since 20141 with the major benefit of avoiding repeat surgeries for growth rod lengthening, which means a reduction in hospital stays and surgical complications, and overall improved quality of life. It is also offers a cost saving from 3 years after insertion by approximately £12,0002. What does the MAGEC system consist of? 1 or 2 titanium growth rods with a distraction element containing a cylindrical magnet + wand locator + an external remote control for non-invasive lengthening. There is also a manual distractor to test the implant pre-insertion. (a)3 (b)4 (c) Figure 1: The MAGEC system (NuVasive). The system consists of one or two growth rods fixed to the spine (a)3 with internal magnets and distractor rod (b)4. The magnet and distraction rod should be scrutinised on plain film for complications (c), with special attention paid to the join between the main distraction rod and distraction rod head, which is situated immediately adjacent to the magnet housing.

Why is this important for Radiologists? Conventional rod complications are well documented and can normally be easily demonstrated on plain film. However, the complex internal mechanism in the MAGEC devices is more subtle on plain film. Missing an internal fracture (the most common cause of failure) can lead to unnecessarily delayed or inappropriate treatment.

Case Examples We present a case series from our institution whereby the internal distraction rod of the MAGEC system has fractured. These are visible on plain film, but subtle and easy to miss for the uninitiated. Case 1 (Fig 2) (a) Normal appearance of MAGEC system growth rods on a AP thoracolumbar radiographs. (b) Fracture of the internal rod 6 months later seen as a defect immediately inferior to the head of the distraction rod.

a b Case 2 (Fig 3) Bilateral distraction rod fractures. (a) demonstrates likely left internal fracture and a suspicious right internal fracture. This was confirmed when imaged 6 months later when the distraction interval had increased (b).

a b

Case 3 (Fig 4) Demonstrating the importance of scrutinising the metalwork in two views. (a) AP thoracolumbar radiograph with apparently normal appearing metalwork. (b) lateral projection of the same patient which demonstrates an internal distractor rod fracture.

a b

Case 4 (Fig 5)

Fractures of the internal and main left MAGEC rod seen on different projections. (a) demonstrates a fracture of the internal rod in the left MAGEC rod. (b) lateral projection allowing a better appreciation of the left sided inferior rod fracture, just superior to the site of insertion in the pedicles.

a b

Conclusion With the rise in use of these devices, general radiologists will be asked to report plain films of children who have had MAGEC devices inserted. Most general radiologists will know how to look at metalwork and identify loosening and fractures, however the review of MAGEC rods will be new to most. As always, two views are valuable and the use of magnification for subtle fractures can also be helpful. Always check just inferior to the head of the internal rod. All of our cases demonstrated a fracture in this location.

R Meshaka1 (BSc, MBChB) L Ramsay2 (BM, PGCert, FRCR) J Russell3 (BSc MBChB) M Easty2 (MBBS BSc MRCP FRCR)

Case 5 (Fig 6) This final case illustrates the importance of paying careful attention to the area of weakness below the head of the internal rod; this area can look normal on the full view and may require magnification to see a fracture. (a) AP and lateral views where the fracture could be easily missed. (b) AP and lateral views magnified with clear internal rod fracture just below the head of the internal rod.

Aa b

References 1. National Institute for Health and Care Excellence. The MAGEC system for spinal lengthening in children with scoliosis (MTG18). 2014. Available at

https://www.nice.org.uk/guidance/mtg18. Accessed on 21st August 2019. 2. Craig J, Jenks M, Willits I et al (Newcastle upon Tyne Hospitals and York Health Economics Consortium). MAGEC system for spinal lengthening in children with early onset

scoliosis, November 2013. 3. Image from NuVasive medical devices. Pediatric scoliosis patient brochure. 2018. Available at https://www.nuvasive.com/wp-content/uploads/2018/09/Pediatric-Scoliosis-

Patient-Brochure.pdf. Accessed on 28th August 2019. 4. Image from Pediatrics Nationwide. Magnetic growing rods help patients who have early-onset scoliosis avoid repeated surgeries. 2016. Available at

https://pediatricsnationwide.org/2016/04/28/remote-control-treatment/. Accessed on 28th August 2019.

Magnet housing

Distraction rod head

Distraction rod

1. Department of Radiology, University College London Hospital NHS Foundation Trust

2. Department of Radiology, Great Ormond Street Hospital NHS Foundation Trust

3. Department of Radiology, Royal Free London NHS Foundation Trust