Understanding the implant performance of magnetically controlled growing spine rods: a review article

Abstract

Purpose Early-Onset Scoliosis (EOS) (defined as a curvature of the spine ≥ 10° with onset before 10 years of age) if not properly treated, can lead to increased morbidity and mortality. Traditionally Growing Rods (TGRs), implants fixated to the spine and extended every 6–8 months by surgery, are considered the gold standard, but Magnetically Controlled Growing Rods (MCGRs) avoid multiple surgeries. While the potential benefit of outpatient distraction procedure with MCGR is huge, concerns still remain about its risks, up to the release of a Medical Device Alert (MDA) by the Medicines and Healthcare Regulatory Agency (MHRA) advising not to implant MCGRs until further notice. The aim of this literature review is to (1) give an overview on the use of MCGRs and (2) identify what is currently understood about the surgical, implant and patient factors associated with the use of MCGRs. Methods Systematic literature review. Results Surgical factors such as use of single rod configuration or incorrect rod contouring might affect early failure of MCGRs. Patient’s older age and higher BMI are correlated with rod slippage. Wear debris and distraction mechanism failure may result from implant design and iteration. Conclusion Despite the complications reported, this technology still offers one of the best solutions to spine surgeons dealing with severe EOS. Lowering the complication rate by identifying risk factors for failure is possible and further studies in this direction are required. Once the risk factors are well described, some of these can be addressed enabling a safer use of MCGRs.

The magnetic field strength and the force distance dependency of the magnetically controlled growing rods used for early onset scoliosis

“…By combining the limited information provided by the manufacturer (Nuvasive Inc.) with the literature 13 , 14 , it is possible to outline the construction of the MCGR, the lengthening mechanism, and the interaction between ERC and MCGR: An internal dipolar magnet mounted on a screw mechanism is brought into rotation, which leads to an extension of the rod that drives the distraction. The rotation is initiated by an interaction with an external rotating magnetic field generated by the ERC.…”

“…A large multicentre study comparing MCGR with TGR reported improvements in quality-of-life measures and concluded that the reduced number of surgeries lessens the psychosocial burden 7 . However, an increasing number of MCGR failure mechanisms have been observed [8][9][10][11] , and approximately 10% of patients undergo unplanned revisions 12 most often because of anchor failure, failure of the distraction mechanism 13,14 , fracture of the internal magnet 15 or a non-functioning MCGR 16 . Titanium wear has raised concerns 17 .…”

Rod Fracture in Magnetically Controlled Growing Spine Rods

“… 2 The aim of these systems is to control curve progression while allowing for spinal growth until the patient has reached their full development potential. 3 Traditional growing rods (TGRs) are constructs fixed to the spine using pedicle screws or hooks that are surgically lengthened every 6 to 8 months. Magnetically controlled growing rods (MCGRs), in contrast, do not need repeated rod distraction surgeries performed when a TGR is implanted, thanks to a magnetic distraction mechanism, which allows for outpatient lengthening procedures.…”

“…Distraction-based systems are usually used to surgically treat the most severe cases 2. The aim of these systems is to control curve progression while allowing for spinal growth until the patient has reached their full development potential 3. Traditional growing rods (TGRs) are constructs fixed to the spine using pedicle screws or hooks that are surgically lengthened every 6 to 8 months.…”

Pin Fracture in Magnetically Controlled Growing Rods: Influence of the Year of Manufacture

“…D ifferent approaches exist in treating EOS depending on its severity and the age of the patient, including observation, casting, and bracing or surgical treatments involving spine implants and fusion of vertebrae. [1][2][3][4] Magnetically controlled growing rods (MCGRs) have been used for the treatment of EOS, requiring elongation every 3 months through an external controller without open surgery, unlike traditional growing rods which need manual lengthening through repeat operations. 5 The only widely commercially available MCGR has been the MAGEC rod (Magnetic Expansion Control, NuVasive Specialised Orthopaedics, San Diego, USA).…”