Are Magnetically Controlled Growing Rods a Game Changer for Early-Onset Scoliosis?

The debate between magnetically controlled growing rods vs traditional growing rods continued at the 52nd Annual Meeting of the Scoliosis Research Society. With Colin Nnadi, FRCS (Orth) and Laurel C. Blakemore, MD.

“Whether you love them or you hate them, there is good ongoing debate regarding the use of magnetically controlled growing rods for early-onset scoliosis,” said Colin Nnadi, FRCS (Orth) at a pro/con debate held at the Scoliosis Research Society 52nd Annual Meeting & Course September 7th in Philadelphia, PA.

Dr. Nnadi took on the “pro” side of the discussion and outlined several benefits of magnetically controlled growing rods (MCGR) starting with reduced exposure of children to general anesthesia. Dr. Nnadi is a Consultant Spine Surgeon at Oxford University Teaching Hospital.
Young girl giving the "thumbs up" gestureMCGR Reduces Anesthetic Exposure
“With traditional growing rods (TGR), a child who is initially implanted at the age of 6 years will have undergone a minimum of 12 surgeries by the age of 12 years, not including any revision surgeries that may be required,” Dr. Nnadi explained. Studies have demonstrated potential toxic effects of repetitive exposure to general anesthesia during these surgeries on cognitive and psychologic development of children with early-onset scoliosis, including an increased risk for development of attention-deficit/hyperactivity disorder.1,2,3

In fact, the FDA issued a warning in December 2016 that “repeated or lengthy use of general anesthetic and sedation drugs during surgeries or procedures in children younger than 3 years or in pregnant women during their third trimester may affect the development of children’s brains.”4

MCGR Linked to Cost Savings
MCGR offers significant cost savings over TGR rod treatments, Dr. Nnadi explained.5,6 In one study, cost neutrality of MCGR to TGR was achieved over a 6-year period by eliminating the need for repeated TGR surgical lengthenings, and in another study cost, neutrality was achieved at 3 years after the index surgery.7,8

In addition, MCGR reduces the amount of radiation exposure from imaging studies, compared with TGR treatments, Dr. Nnadi said. “In our practice in Oxford, we use the fluoroscopic technique, which requires significantly lower doses of radiation. In other hospitals, ultrasound is used to evaluate distraction distances, almost negating any radiation exposure,” he added.

“Another big advancement is that MCGR have allowed us to think differently about how we manage these patients,” Dr. Nnadi said. “We not only think about surgical and radiologic outcomes, but we also think about growth parameters. Parameters of successful treatment now include change in sitting height, standing height, and weight, which were never used with TGR treatment,” Dr. Nnadi said.

Dr. Nnadi acknowledged several potential problems with MCGR, including pin breaks, metallosis, and infection risk, particularly with revision cases. However, he believes that “these problems are not insurmountable and have occurred with traditional rods.”

Dr. Nnadi concluded that MCGR has revolutionized the treatment of early-onset scoliosis and emphasized that patient selection is paramount in achieving successful outcomes with this treatment. He added that the psychosocial benefits of MCGR include not only fewer hospitalizations and surgeries, but also around improved QOL.

Counterpoint: The “Con” Side of MCGR
While acknowledging that MCGR have been a game-changer for early-onset scoliosis treatment, Laurel C. Blakemore, MD, said during the “con” side of the debate that TGR still have a place in the armamentarium as neurotechnologies are defined and understood. Dr. Blakemore is Chief and Associate Professor of Pediatric Orthopaedics at the University of Florida College of Medicine in Gainesville.

For example, patients may be too small or kyphotic for MCGR to be appropriate, as current actuators require at least 70 mm of “flat space” to be applied. In addition, the Cobb angle may be too high for MCGR, as “we do know that a very high Cobb angle is associated with greater discrepancy between the programmed length with MCGR and the achieved length.”9

Conversion to MCGR May Not Be Advisable in Certain Patients
Also, “it may be too late to apply this technology for some patients,” Dr. Blakemore noted, suggesting that surgeons carefully consider the risks and benefits of converting from TGR to MCGR. Some studies have shown a decrease in length achieved with conversion to MCGR versus primary application of TGR, with one study suggesting that patients lost T1-S1 height at 2 years after conversion to MCGR, Dr. Blakemore said.10,11 In addition, revision surgery is linked to a higher rate of rod breakage and complications, she added.12

Patient factors that may preclude use of MCGR include need for frequent MRI imaging, use of pacemakers, and patient size (eg, patients who are too tall or too deep). Limitations of MCGR include discrepancy between the ultrasound measurement and x-ray measurement of length achieved, Dr. Blakemore said.

“Some studies suggest that x-ray measurement [with MCGR] is actually a little more than the ultrasound estimate of length achieved,” which could lead to lengthening too aggressively over time when relying on ultrasound estimates, Dr. Blakemore said. “Certainly, some radiographic checks probably need to be applied if you are using ultrasound.”
 
Failure of distraction is another possibility with MCGR, and may result from the way the rods are inserted, mechanical problems (eg, development of bone around the actuators), and pin failure (eg, fractures and surface degradation), Dr. Blakemore told the audience.

Finally, the societal issues and costs of treatment should be considered, Dr. Blakemore said. Although there are certainly clear benefits in terms of patient satisfaction and economic burden over the long-term with MCGR, it is not clear what duration is needed to obtain those benefits, Dr. Blakemore noted. “If there is going to be a short duration of need for lengthening, then a magnetic controlled device is probably not cost-effective,” she concluded.

Updated on: 10/04/17
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Measuring Outcomes in the Treatment of Early Onset Scoliosis
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