The safety and performance of Magnetically Controlled Growth Rods for treatment of Early Onset Scoliosis

Reshma Tilwani and authors from the Royal National Orthopaedic Hospital and Great Ormond Street Hospital for Children discuss their latest work on the analysis of MAGEC spine rods 

Early Onset Scoliosis (EOS)

Early Onset Scoliosis (EOS) is a condition that involves the malrotation of the spine in skeletally immature paediatric patients less than 10 years of age [1], with an estimated prevalence of 1-2 per 10,000 births [2]. If left untreated, this may hinder not only the growth of the patient, but also dangerously affect the development of the thoracic cage and influence lung function, which may subsequently result in cardiorespiratory issues and possibly death [3, 4]. Depending on the severity of the scoliosis and the age of the patient, the condition can be treated either non-surgically, with the use of casting and bracing, or surgically, with the use of spine implants [5, 6]. The latter involves incorporation of either traditional growth rods (TGRs), which normally require a small incision to be made each time the rod is lengthened or magnetically controlled growth rods (MCGRs), which are distracted with the use of an external magnet. TGRs are however associated with numerous drawbacks such as the need for surgery every six months post implantation, in order to distract the rod, which can contribute to an increase in surgical complications by 24 per cent and psychological issues with the associated costs to the NHS [7, 8, 9].  

MAGnetic Expansion Control (MAGEC) Rod 

The MAGEC rod (NuVasive), a design of MCGRs, has been used for the past decade in the UK for the treatment of EOS. These have increased in popularity due to its unique feature of being the least invasive technique in the treatment of high degree of scoliosis for both primary surgeries and transition operations from traditional growth rods [4, 9-14].  MAGEC rods have been implanted in more than 3000 patients worldwide. While in the patient, MAGEC rods can be distracted non-invasively, with the use of an external remote controller (external magnet), while the patient is conscious in an outpatient’s clinic. The distraction of each rod takes approximately 40s and the entire process is usually repeated every 3-6 months [12, 2].    

Limitations of MAGEC Rods 

Early clinical results are promising with fewer complications than patients with traditional growth rods [13, 15]. However, one third have still reported complications. Recent studies have reported cases of unplanned early implant revision reaching up to 22 per cent of the total number of revision cases [16]. These unplanned early revisions were suggested to be as a result of failure of the internal lengthening mechanism either due to pin fracture, secondary to corrosion of the internal mechanism or off-axis loading of the spinal rod [16-19].  

Retrieval Analysis of MAGEC Rods

Performance of MAGEC rods remains controversial and was the topic of discussion of a recent BBC Panorama episode [20] and a large series of media reports centred around the “Implant Files” published by a team of investigative journalists [21]. As with all implant failures, the mechanisms of failures are multifactorial and often a combination of surgeon, implant and patient (SIP) factors. So far, retrieval studies of MAGEC rods have suggested two mechanisms of failure. The first being corrosion of the internal lengthening mechanism due to fluid ingress, subsequently leading to fracture of the actuator pin [Figures 1 and 2] and the second, off-axis loading and bending of the extending bar component, provoking internal friction and wear of the implant [Figure 3; 22, 23]. 

Retrieval analysis of failed MAGEC rods [Figure 4], as well as well functioning rods, together with comparison against clinical and imaging data can help us untangle the predominant mechanism of failure of these rods through identifying the possible SIP factors associated with them, such as positioning of the spinal rod during implantation, frequency of distraction of the rod and effects on the Cobb angle. To-date, there have only been four retrieval studies investigating the performance of MAGEC rods.

The London Implant Retrieval Centre (LIRC) is an independent implant retrieval centre based at the Royal National Orthopaedic Hospital (RNOH), London, helping patients, surgeons and manufacturers better understand how spine, hip and knee implants perform in the body, with the use of state-of-the-art equipment. Since 2007, the centre has collected more than 9,000 components (spine, hip and knee) from 29 countries and published 130 full journal articles with 200 co-authors and more than 1,500 citations. 

The LIRC has been recently become a global centre for the collection and analysis of retrieved MAGEC rods; this work is supported by NuVasive. This study will assist monitoring of the success/failure of this device, especially with respect to the modifications to the rod that were made since the identification of corrosion and pin breakage. It will also help clinicians to determine optimal fixation point type and quantity; curves in which a high level of failure could be anticipated; the length of thoracic spinal growth achievable; improvement in respiratory function; timing and extent of growth rod lengthening. All these factors are important factors to determine the success and/or failure of this technique in a challenging cohort of patients. Analysis of retrieved implants is an important aspect of this assessment and we urge surgeons to contribute their retrieved rods to this study.

Surgeons can contact the LIRC (www.LIRC.co.uk) to contribute implants to the study.  

References:

1. Gillingham BL, Fan RA, Akbarnia BA (2006) Early onset idio- pathic scoliosis. J Am Acad Orthop Surg 14(2):101–112.
2. Metkar, U., Kurra, S., Quinzi, D., Albanese, S. and Lavelle, W. (2017). Magnetically controlled growing rods for scoliosis surgery. Expert Review of Medical Devices, 14(2), pp.117-126.
3. Campbell RM, Smith MD, Mayes TC, Mangos JA, Willey- Courand DB, Kose N et al (2003) The characteristics of thoracic insufficiency syndrome associated with fused ribs and congenital scoliosis. J Bone Jt Surg Am 85(3):399–408. 
4. Akbarnia, B.A., Marks, D.S., Boachie-Adjei, O., Thompson, A.G. and Asher, M.A., 2005. Dual growing rod technique for the treatment of progressive early-onset scoliosis: a multicenter study. Spine, 30(17S), pp.S46-S57.
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8. Bess, S, Akbarnia, BA, Thompson, GH. Complications of growing-rod treatment for early-onset scoliosis: analysis of one hundred and forty patients. J Bone Joint Surg Am 2010; 92: 2533–2543. 
9. Cheung, K.M.C., Cheung, J.P.Y., Samartzis, D., Mak, K.C., Wong, Y.W., Cheung, W.Y., Akbarnia, B.A. and Luk, K.D.K., 2012. Magnetically controlled growing rods for severe spinal curvature in young children: a prospective case series. The Lancet, 379(9830), pp.1967-1974.
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12. Hickey B, Towriss C, Baxter G, Yasso S, James S, Jones A et al (2014) Early experience of MAGEC magnetic growing rods in the treatment of early onset scoliosis. Eur Spine J 23(1):61–65.  
13. Jenks M, Craig J, Higgins J, Willits I, Barata T, Wood H et al (2014) The MAGEC system for spinal lengthening in children with scoliosis: a NICE Medical Technology Guidance. Appl Health Econ Health Policy 12(6):587–599. 
14. Keskinen H, Helenius I, Nnadi C, Cheung K, Ferguson J, Mundis G, Pawelek J, Akbarnia BA (2016) Preliminary comparison of primary and conversion surgery with magnetically controlled growing rods in children with early onset scoliosis. Eur Spine J 25(10):3294–3300.  
15. MAGEC Rods – British Scoliosis Society (2018).
16. Annual Meeting of the British Scoliosis Society (2016). 
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19. Akazawa T, Minami S, Takahashi K, Kotani T, Hanawa T, Moriya H (2005) Corrosion of spinal implants retrieved from patients with scoliosis. J Orthop Sci 10(2):200–205. 
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21. Icijorg. 2019. ICIJ. [Online]. [19 February 2019]. Available from: https://www.icij.org/investigations/implant-files/     
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23. Joyce, T., Smith, S., Rushton, P., Bowey, A. and Gibson, M. (2018). Analysis of Explanted Magnetically Controlled Growing Rods From Seven UK Spinal Centers. SPINE, 43(1), pp.E16-E22.

Authors

Reshma K. Tilwani¹, Claudia T. S. Maldonado², Harry S. Hothi^1,2, Stewart K. Tucker³, Masood Shafafy⁴, Johann Henckel¹, Alister J. Hart^1,2  

1. The Royal National Orthopaedic Hospital, Stanmore,
   UK  
2. Institute of Orthopaedics and Musculoskeletal Science, Royal National Orthopaedic Hospital, University College London, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK 
3. Great Ormond Street Hospital for Children, London, UK
4. The Centre for Spinal Studies and Surgeries, Queen’s Medical Centre, Nottingham, UK