Impliant (Princeton, New Jersey) has received FDA approval to restart enrollment of up to 450 patients in a pivotal trial of its TOPS System, a total posterior arthroplasty device designed to treat spinal stenosis with or without facet arthrosis and spondylolisthesis. What's unique about device is that it will allow patients to regain motion, Impliant says.

Impliant voluntarily suspended enrollment in the study in September 2007 following a device-related failure (one patient failure out of 149 implantations). An investigation determined that device misalignment, coupled with excessive shear loading, caused the failure. Impliant said it has since made design and manufacturing changes to the internal components of TOPS that allow it to better withstand high shear loads and misalignment while not affecting its range of motion.

"This particular patient developed some symptoms — an audible noise from the device, a squeaking noise," President/CEO Todd Potokar told Biomedical Business & Technology. "We had never experienced that before. It's the first patient we had to revise. We elected to be very cautious about that revision and we hired an independent expert who has dealt with hip/knee retrievals to lead an investigation. Essentially we found that the device had seen some misalignment of the articulating element."

Impliant then modified TOPS without changing the basic working elements or the way it functioned. "We made it more forgiving so the alignment is not so dependent on the surgeon," he said.

"The key thing in the whole process is that we believe that we acted very responsibly," Potokar said. "It's unusual to stop a study after one patient failure but we had a lot of support from our investigators and we kept open communications with the FDA. We took a product that was very good and made it better."

TOPS is designed to stabilize, but not fuse, the L3-4 or L4-5 vertebral level to alleviate pain stemming from spinal stenosis with or without degenerative facet arthrosis and spondylolisthesis. Following a laminectomy and medial facetectomy, the device is affixed to the spine via four pedicle screws using a standard posterior surgical approach.

Potokar estimates that TOPS could benefit more than 500,000 patients worldwide undergoing spinal fusion surgery each year.

Spinal stenosis occurs mostly in people older than 50 and is often caused by osteoarthritis, but some younger people with a spine injury or a narrow spinal canal are also at risk. Symptoms can include pain in the neck or back, numbness, weakness or pain in the arms or legs, and foot problems. Treatments include medications, physical therapy, braces and surgery.

"There's really no product like TOPS on the market today," Potokar said. "The goal of fusion is that, when you have a patient with spinal stenosis and a significant neural compromise that causes pain or weakness, you remove a lot of bony elements to alleviate the pain. Spinal fusion surgery has about a 55% to 90% success rate. Our product is geared toward motion preservation. We want to allow the surgeon to stabilize a patient in the same manner as fusion, but allow for motion to be restored."

Although patient enrollment and treatment timing at 21 sites will vary, Potokar projects FDA approval of TOPS in 2012. Patients will be followed for a minimum of two years, although TOPS is expected to last a lifetime, particularly since most patients receiving the device are older.

Impliant currently has "some very supportive investors who have bridged the company through this period," Potokar said. "But we'll seek to raise more funds this summer."