High failure rate of the magnetic rod system in scoliosis surgery

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A magnetic rod surgical system used to treat scoliosis in children has a high failure rate, which requires multiple surgeries and causes significant morbidity in these young patients, recent research suggests.
The Magnetic Expansion Control Rod (MAGEC) (NuVasive) system, which was developed to replace traditional rods due to its high failure rate, proved to have a lower success rate than the stellar one.

The researchers found that the most common complications associated with the MAGEC rod system are the failure of the distraction mechanism used to stretch soft tissues to make room for bone growth, as well as rod fracture.
"This rod system fails very often compared to any standard spinal implant," study researcher Aakash Agarwal, PhD, director of research at Spinal Balance Inc and associate professor of bioengineering at the University of Toledo, told Medscape Medical News. in Ohio.

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 bars.

The study was published online October 19 in Spine Surgery and Related Research.
A pillar of treatment
Scoliosis refers to the lateral curvature of the spine, usually in the thoracic or thoracolumbar region. The degree of scoliosis is usually determined with X-rays.

Early onset scoliosis (EOS) occurs in children younger than 5 years. It occurs more often in boys than in girls. Although only about 1 or 2 in 10,000 children develop the condition, it can be serious and sometimes interfere with normal organ development.
Surgical intervention is required when bracing and plaster do not stop the progression of the scoliotic curve. The goal of the surgery is to allow the growth of the spine and rib cage and correct and limit the extent of spinal deformity, Agarwal said.
Only children with adequate potential for growth of the spine and rib cage are candidates for surgery. The age of eligible patients may vary, but it is generally about 10 years for girls and 12 or 13 years for boys, Agarwal said.
Although other surgical techniques are sometimes used, the distraction-based mechanism has been the pillar 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 so that the bone grows gradually," he said.

This has traditionally been achieved by placing two rods, proximally and distally, on each side of the spine. The fixing points of the rods should be loosened and separated repeatedly.

Traditional growth bars are subject to risk of fracture and self-fusion, which is the hardening of soft tissues in the vertebral segments caused by trauma to the spine with excessive distraction.

Trauma Nightmare
The biggest problem with traditional growth bars is the need for invasive surgery every 6 to 12 months, Agarwal said.

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

This limitation led to the development of titanium-based MAGEC rods. This non-invasive magnetic distraction system allows the rod to expand from the outside of the body through a remote control.

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

The system also allows more gradual distractions of the growth bars.

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

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

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

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

"Given the variety of surgeon options, the use of traditional growth bars is not justified," he said.

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

Of the 163 reports related to the MAGEC system until June of last year, 129 were due to failures in the distraction mechanism, 24 were due to a fractured rod and 10 were due to other medical complications, such as infection and tissue necrosis.

The minimum
These reports are "the minimum," said Agarwal. "For example, tissue necrosis, or metalosis due to wear, is present in almost all cases with MAGEC," but these cases are not reported due to the "absence of clinical symptoms."

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

"Each rod fracture failure or non-invasive distraction mechanism failure in MAGEC leads to another open surgery. And with each surgery, the risk of other complications, such as infection, increases significantly," he said.

He added that the failure of the distraction of the growth bars reduces the overall effectiveness of the device.

"The most recent studies even question whether there is a real difference in quality of life with the 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, the most frequent use of minimal distraction.

The researchers also retrieved MAUDE data on the five major failures associated with the standard instrumentation used in spinal fusion. These included the breakage of the pedicle screw after surgery (336 reports), the damage of the fixation screw during surgery (257), the breakage of the bar after surgery (175), the rupture of the interbody fusion cage during surgery. surgery (118) and pedicle screw rupture during surgery (75).

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

Commenting on Medscape Medical News, Lee Tan, MD, assistant professor of neurological surgery, University of California, San Francisco, praised the authors for conducting an "interesting" study on the complications and failure mode associated with MAGEC bars in the Scoliosis correction using a large database

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

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

The study received no funds. Agarwal has received royalties and inquiries from Spinal Balance and is a member of the editorial board of Clinical Spine Surgery and Spine.

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

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