An ongoing clinical trial for a Minnesota company's treatment for lower-back pain is going so well that the company, Relievant Medsystems, has opted to halt new enrollments and offer the treatment to everyone in the control group.

Kevin Hykes, chief executive at Relievant, said it is "extremely rare" for a rigorously designed clinical trial like Relievant's Intracept study to be halted early for statistical superiority. "We are thrilled with this result," Hykes said in a news release.

Relievant, which moved its offices from California to Bloomington last year, sells medical devices for a treatment it calls the Intracept procedure. It's an outpatient medical procedure that disables nerves inside painful vertebrae to treat a type of chronic lower-back pain called discogenic pain without fusing the bones or relying on opioid medications.

The procedure involves inserting a narrow ablation catheter into the vertebral bone and emitting radio-frequency energy to destroy part of the basivertebral nerve, which carries pain signals from the top and/or bottom edges of the bone. Although "discogenic" pain is related to the breakdown of the discs between bones, Relievant believes the pain signals happen because of irritation in the ends of the bone caused by breakdown of an adjacent disc. Therefore, severing a nerve in bone can treat pain from a diseased disc.

The system was cleared by the U.S. Food and Drug Administration in 2016 to ablate basivertebral nerves in lower lumbar vertebrae in cases where six months of conservative therapy has not treated the pain effectively and an MRI scan shows signs that the treatment is warranted.

A small early study found that 16 middle-aged patients treated with the Intracept procedure self-reported significant reductions in lower back pain at three months, and the improvements persisted after 12 months.

The larger ongoing Intracept trial has enrolled 104 people out of a planned 150, with one group of patients randomized to get the Intracept procedure and the other group assigned to physician-directed nonsurgical treatments like physical therapy, injections, chiropractic treatments and medications like opioid pills. The study included a "prespecified interim analysis" design that allowed an independent group of physicians to privately analyze the data gathered so far to see if the treatment arm was doing significantly better or significantly worse than the control.

The Intracept patients, it turned out, were doing significantly better.

Pain is difficult to measure because it is so subjective, so studies of pain often use validated patient questionnaire to quantify a person's pain from 0 to 100 on the Oswestry disability index. The 51 patients who got the Intracept procedure in the recent study reported a 25-point reduction in their Oswestry scores at three months, which was 21 points more than reductions in Oswestry scores in the 53-person control group. The full study results are expected to be published in a journal later this year.

Hykes noted that the recent trial was designed to generate "Level 1" clinical evidence, which is considered the most reliable level of evidence in clinical trials.

"Stopping a Level 1 trial early for superiority is an extremely rare event," Hykes said in the release. "This is the second Level 1 study that has demonstrated clinically significant improvement in pain and function … and solidifies the Intracept procedure as a compelling early treatment option for patients with CLBP" or chronic lower back pain.

The single-use components of the system cost about $6,000 per procedure. Each procedure would be expected to cost between $10,000 and $14,000 total, depending on hospital charges, but the patients' expenses would depend on their insurance coverage.

Relievant has its eyes on what it estimates could be a $20 billion market for ablation treatments for discogenic pain. Last year, the company's fifth venture round raised $58 million, on the heels of publication of the smaller study.