FDA panel to consider PMA application of spinal implant

An illustration of the Superion Interspinous Spacer System--Courtesy of Vertiflex

The FDA's orthopedic advisory panel will investigate the agency's concerns about fractures to the back of the spine resulting from the investigational VertiFlex Superion Interspinous Spacer (ISS) as it deliberates on Feb. 20 whether to recommend the device's PMA application for FDA approval.

The FDA is not required to follow the outside experts' acceptance or rejection of the device stemming from the body's vote on the device's safety, effectiveness and risk-benefit profile, but usually does. The meeting was originally scheduled for December, but the FDA rescheduled it for an undisclosed reason.

The ISS is intended to treat skeletally mature subjects "suffering from pain, numbness, and/or cramping in the legs … secondary to a diagnosis of moderate lumbar spinal stenosis," according to the FDA's executive summary of the device's PMA application. The proposed indication is for "those patients with impaired physical function who experience relief in flexion from symptoms of leg/buttock/groin pain, numbness, and/or cramping, with or without back pain."

The ISS met its primary clinical endpoint of a noninferior success rate compared to Medtronic's ($MDT) similar X-Stop Spacer interspinous implant. At 24 months the ISS had a success rate of 52.7% compared to the X-Stop's 50.2%. Both devices offer an alternative to invasive spinal fusion surgery, which has fallen out of favor among insurers, who suspect it is overperformed.

While the ISS met its overarching goal, the FDA noted the more granular data showing that 8.5% of X-Stop patients in the clinical trial (or 17 out of 201) had a spinous process fracture, compared to 16.3% (or 31 out of 190) of ISS patients. A spinous process protrudes from the back of each vertebra and is an attachment point for muscles and ligaments that move and stabilize the vertebrae. The ISS is implanted in between adjacent spinous processes of neighboring lumbar vertebrae, located in the lower, weight-bearing portion of the spinal column.

The FDA says VertiFlex has submitted data showing that patients with the fractures are often asymptomatic and they are therefore of no clinical significance. The FDA is skeptical of the claim, saying in the executive summary it "is reasonable to consider that a fracture involving the spinous process at the operative level would impact the effectiveness of the device," and is "unclear" whether that data is adequate to assess the fractures' clinical significance.

In addition to the usual three voting questions, 5 device-specific questions will be posed to the panel of outside experts that offer insight into the FDA's thinking. The questions are about the clinical significance of the spinous process fractures and whether they were adequately identified using simple radiographs instead of CT scans. The panelists will also be asked to comment on the clinical endpoint of noninferiority to the X-Stop and recent medical literature in the field, as well as possible postmarket studies if the device is approved.

VertiFlex already sells the 510(k)-cleared Totalis Direct Decompression System to perform minimally invasive direct decompressions of the lumbar spine.

- read the meeting literature

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