When medical device maker Medtronic pulled its popular but fracture-prone Sprint Fidelis defibrillator leads from the market a decade ago, a cascade of complaints involving tens of thousands of the skinny wire devices soon followed.

The leads, which allow an implanted defibrillator to shock the heart and prevent sudden cardiac death, were the subject of more than 36,900 individual reports of problems, ranging from delivery of unneeded shocks (2,898 reports) to fractures in the wires (22,093). But those reports were not known to the public, until this week.

The public is getting a clearer view of the risk profile that Medtronic developed regarding its problem-plagued devices, following a report Monday by Kaiser Health News that uncovered the trove of nearly 37,000 previously undisclosed patient complaints in the Food and Drug Administration’s public-facing database of device problems, MAUDE.

Although the Minnesota-based med-tech manufacturer pulled the devices from hospital stockrooms, it didn’t recommend surgically removing the devices from people’s chests because the risks from removal appeared to outweigh the risks of leaving the devices in place.

On Tuesday, Medtronic spokesman Jeffrey Trauring said the company has issued regular reports to the medical community since 2007 disclosing the latest failure rates for the leads, based on adverse event reports, device registry data and independent studies. An FDA spokeswoman issued a similar comment Tuesday, noting that Medtronic’s product performance reports have been published twice annually for more than 15 years.

At issue is the use of an obscure but controversial loophole in federal law. It says that although device makers must report device malfunctions and situations of serious patient harm and death to the FDA’s public MAUDE database, the agency has the power to confidentially grant device companies the ability to file summaries of adverse event reports in secret.

This has been done when the reports were judged redundant because the problems were well-characterized, though critics say device companies might also have financial incentives to file such reports in private.

The summaries are technically still public information, available through a monthslong Freedom of Information Act process, but only when someone learns a summary exists. Information on summary reports has long been redacted from public MAUDE reports, though the Star Tribune in 2016 convinced the FDA to un-redact filings covering hundreds of thousands of events, including more than 1,000 previously unknown post-surgical problems involving experimental applications of Medtronic’s Infuse bone-growth product.

Subsequent investigations showed Medtronic was one of the most prolific users of the summary-reporting system, with more than 46 individual summaries approved between 2007 and 2015, covering some 6,399 events. But even this did not reveal the summary of 36,900 individual reports describing more than 50,000 problems associated with Sprint Fidelis leads.

In March, then-FDA Commissioner Dr. Scott Gottlieb announced that the agency would make old summary reports available to the public. (Gottlieb stepped down in May.) FDA officials have said the agency plans to fully phase out the program called “alternative summary reporting” later this year, though it’s not clear whether other forms of summary reporting will continue.

Medtronic says individual adverse event reports like the 36,900 reports on the Sprint Fidelis are not as meaningful as the information intended for physicians contained in its corporate product performance reports. The latest such report is 204 pages long and contains four pages summarizing how many Sprint Fidelis leads were sold, how many are still in the field, and how many have been returned to the company for product analysis on specific types of failures like wire fractures.

About 74% of the 186,698 Model 6949 Sprint Fidelis leads registered in the U.S. remained in use 10½ years after Medtronic voluntarily pulled them from the market, the report says.

The report contains no narrative information on individual patients or injuries, nor details like how the devices were programmed by the doctor, whether the patient had other health problems, or whether the patient died.

“The impetus for manufacturers to do summary reports is because they don’t have to provide as much information, and the information they provide is not made public,” said former FDA official Madris Tomes, who today runs a service called Device Events, which scrutinizes FDA adverse event reports.

The filing of a narrative adverse event report in MAUDE doesn’t mean anyone legally determined that a device led directly to the reported problem.

Worldwide, Medtronic shipped more than 260,000 Sprint Fidelis leads between 2004 and 2007. One of the device’s key selling points was its thin profile, significant because a lead rests inside a blood vessel leading to the heart, and it is not a simple wire. A defibrillator lead transmits physiological data from the heart to the device, and then sends electricity back to the heart, depending on whether the readings say the heart needs mild pulses for pacemaking or sharp shocks for defibrillating.

In March 2007, Medtronic reported receiving reports of fractures in the thin leads, which can cause a defibrillator to fail to deliver therapy, or administer shocks that are not needed. Studies estimated that the recall cost Medicare more than $287 million.

On Tuesday, Trauring pushed back on the idea that information about problems with the Sprint Fidelis leads had been kept from the public.

“The Sprint Fidelis lead has been the most scrutinized, studied and reported on defibrillator lead in the history of our industry. To suggest that the FDA and Medtronic somehow conspired to hide data on this product … is completely untrue and unsubstantiated,” Trauring wrote. “When malfunctions do occur, we make every effort to inform regulators, the health care community and the public in a timely, transparent and compliant manner, and we are confident that we have done so and continue to do so with Sprint Fidelis.”