High Failure Rate for Magnetic Rod System in Scoliosis Surgery

Pauline Anderson

February 14, 2020

A surgical magnetic rod system used to treat scoliosis in children has a high failure rate, necessitating multiple surgeries and causing significant morbidity in these young patients, new research suggests.

The Magnetic Expansion Control (MAGEC) rod system (NuVasive), which was developed to replace traditional rods because of their high failure rate, has itself turned out to have a less than stellar success rate.

Researchers found that the most common complications associated with the MAGEC rod system are failure of the distraction mechanism used to stretch soft tissues to make space for bone growth, as well as rod fracture.

"This rod system fails very often compared to any standard spinal implant," study investigator Aakash Agarwal, PhD, director of research at Spinal Balance Inc and adjunct professor of bioengineering at the University of Toledo, in Ohio, told Medscape Medical News.

The relatively high frequency of such adverse events is of "great concern," said Agarwal, who recommended that neurosurgeons use more gradual distractions to minimize stress on spinal rods.

The study was published online October 19 in Spine Surgery and Related Research.

A Mainstay of Treatment

Scoliosis refers to the lateral curving of the spine, usually in the thoracic or thoracolumbar region. The degree of scoliosis is typically determined with x-rays.

Early-onset scoliosis (EOS) occurs in children younger than 5 years. It occurs more often in boys than girls. Although only about 1 or 2 in 10,000 children develop the condition, it can be severe, sometimes interfering with normal organ development.

Surgical intervention is required when bracing and casting fail to stop progression of the scoliotic curve. The aim of the surgery is to allow growth of the spine and ribcage and to correct and limit the extent of spinal deformity, said Agarwal.

Only children with adequate potential for spine and ribcage growth are candidates for the surgery. The age of eligible patients can vary but is typically up to about age 10 for girls and age 12 or 13 for boys, said Agarwal.

Although other surgical techniques are sometimes used, the distraction-based mechanism has been the mainstay of surgical intervention in EOS for more than a decade, he noted.

"The concept uses distraction, or stretching of the spine, to create additional soft-tissue space between the vertebrae for the bone to gradually grow into," he said.

This has traditionally been achieved by putting two rods – proximally and distally – in each side of the spine. The attachment points of the rods must be repeatedly loosened and pushed apart.

Traditional growth rods are subject to risk of fracture and autofusion, which is stiffening of soft tissues in vertebral segments caused by trauma to the spine with excessive distraction.

Trauma Nightmare

The major problem with traditional growth rods is the need for invasive surgery every 6 to 12 months, said Agarwal.

"The trauma of repeated surgery is a nightmare for both the patients and the surgeons, from increased complications with each subsequent surgery to infections and unplanned surgeries," he said.

This limitation led to the development of the titanium-based MAGEC rods. This noninvasive magnetic distraction system allows the rod to be expanded from outside the body using a remote control.

This approach results in a "drastic reduction" in the number of consecutive surgeries and has the potential to reduce growth rod fracture and autofusion, said Agarwal.

The system also allows for more gradual distractions of the growth rods.

"With the MAGEC system, you can stretch the spine a little bit every week without invasive surgery," said Agarwal.

His own research showed that smaller and more frequent distractions result in much less stress in the rods. He suggests, for example, a distraction of 1.5–2.0 mm every month, rather than 4.5–6.0 mm every 3 months.

In the United States, the MAGEC system is used for all children undergoing distraction-based corrections. But in developing countries, at least 70% of patients still undergo surgery using traditional growth rods, owing to the very high initial cost associated with MAGEC rods, said Agarwal.

He believes traditional rods should not be used at all. In regions where MAGEC rods are unaffordable or inaccessible, surgeons should use alternative surgical techniques, he said.

"Given the variety of surgeon options, use of traditional growth rods isn't justified," he said.

For this new study, Agarwal and his colleagues searched the Manufacturer and User Facility Device Experience (MAUDE) database to identify relevant adverse events. Operated through the US Food and Drug Administration, MAUDE is a voluntary reporting system for adverse events involving medical devices.

Of the 163 reports related to the MAGEC system through June of last year, 129 were for failures of the distraction mechanism, 24 were for rod fracture, and 10 were for other medical complications, such as infection and tissue necrosis.

Bare Minimum

These reports are "just the bare minimum," said Agarwal. "For example, tissue necrosis ― or metalosis due to wear ― is present in almost all cases with MAGEC," but these cases aren't reported because of "absence of clinical symptoms."

Agarwal called these MAGEC-related complications "very worrisome."

"Every single failure of rod fracture or noninvasive distraction mechanism failure in MAGEC leads to another open surgery. And with each surgery, the risk of other complications, such as infection, goes up very significantly," he said.

He added that the failure of the distraction of the growth rods reduces the overall efficacy of the device.

"Newer studies even question if there is a real quality-of-life difference with use of MAGEC rods over the myriad of other options," he said.

He stressed the need for better technical and clinical controls to avoid such adverse events ― for example, more frequent use of minimum distraction.

The researchers also retrieved MAUDE data on the top five failures associated with standard instrumentation used in spinal fusion. These included pedicle screw breakage post surgery (336 reports), set screw damage during surgery (257), rod breakage post surgery (175), interbody cage breakage during surgery (118), and pedicle screw breakage during surgery (75).

The rates of adverse events involving the MAGEC rods, which are used in relatively rare surgical procedures, "seem high" in comparison, said Agarwal.

Commenting for Medscape Medical News, Lee Tan, MD, assistant professor of neurologic surgery, University of California, San Francisco, praised the authors for conducting an "interesting" study on the complications and mode of failure related to MAGEC rods in scoliosis correction using a large database.

"They identified distraction mechanism failure and pedicle screw breakage as the most common device-related complication and standard instrumentation-related complication, respectively," said Tan.

"This is very useful information during patient education and preoperative counseling. It also identifies the areas for improvement and innovation on this important topic. I commend the authors for their excellent work," he said.

The study received no funding. Agarwal has received royalties from and consults for Spinal Balance and is an editorial board member for Clinical Spine Surgery and Spine.

Spine Surg Relat Res. Published online October 20, 2019. Abstract

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