A UK company’s spinal implants that allegedly moved and eroded in patients, and which are at the centre of legal action, have highlighted potential weaknesses in the way in which some medical devices enter the market, an investigation has revealed.

Documents seen by the Guardian show the plastic discs were approved for sale by the British Standards Institution (BSI) after tests on 30 people over six months

A customised version was also implanted in nine baboons, according to a paper by members of the company’s own scientific advisory board.

The devices, made by the now-defunct Ranier Technology, which was based in Cambridge, are the focus of legal action brought by prosecutors in Germany against a doctor who implanted them, allegedly without first obtaining fully informed patient consent.

Many of the patients who received them are undergoing surgery to have them removed, with doctors finding some had completely disintegrated, according to an investigation coordinated by the International Consortium of Investigative Journalists, involving the Guardian and BBC’s Panorama.

Ranier Technology was granted CE (Conformité Européenne) safety marks for two implants, Cadisc-L and Cadisc-C. The devices were certified by the BSI in 2010 and 2011 respectively, and once approved were marketed to hospitals across Europe.

The firm gained millions of pounds in backing from investors impressed by its work in developing artificial spinal discs, which it said would bring relief and a normal quality of life to patients suffering degenerative disc disease.

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Instead, about half of the patients given the Cadisc-L implants have had to undergo further surgery after the discs apparently disintegrated or moved in their backs, the Implant Files investigation has discovered.

The implants were seemingly beset by problems from the start, according to scientific analysis. The documents seen by the Guardian show that in trials on baboons using a custom-sized version of Cadisc-L the discs had all been put in the wrong place.

A 2009 review of some of the animals noted that “overall six months is a relatively short time to follow an implant up”, but even after that time there appeared “to be worrying changes between the implant and the bone in all but one subject”.

Details of the tests on humans have not been published, but it is known they only ran for six months before the CE mark application, even though the implants were aimed at young patients.

The case raises questions about the different standards applied by regulators around the world.

The documents reveal Ranier Technology chose to seek approval in Europe first because it was easier than doing so in the USA, and that it hoped to use the CE mark to help it get the approval of the US Food and Drug Administration (FDA). “Like Cadisc-L, the regulatory strategy for Cadisc-C is to penetrate Europe first and follow up in the USA … On the whole the regulatory process and required testing tends to be more stringent in the US compared with the EU.”

Regulators in other European countries approved clinical tests, and patients were recruited in Belgium, Germany and the Netherlands.

The investigations ran from October 2009 until June 2010, and by August 2010 the company had a CE mark for Cadisc-L.

The BSI would not comment on Ranier Technology’s application, citing confidentiality requirements.

The documents show the FDA asked for more data to back up the company’s approval application. The regulator was concerned about the misplacement of the device in the baboon study and asked the company to provide “a breakdown of changes made to the device, instrumentation, and surgical technique as a result of ‘lessons learned’”.

Ranier Technology was dissolved this year. The Guardian put a number of questions to the company’s former chief executive Dr Geoffrey Andrews.

In a statement, he said the Cadisc-L devices used in humans were not the ones used in tests on baboons. The baboons were implanted with a much smaller custom-made version of the device.

“For clarification, no Cadisc-L devices were implanted in any animal,” he said. “Ranier spent over eight years and more than £20m in the design, development and testing of Cadisc-L. The research, development and testing involved many top experts from across the world.”

Andrews said the testing complied with the relevant standards and included checks “to replicate long-term usage and which predicted a 40-year service life for Cadisc-L”.

He said clinical tests in patients had gone very well, with good outcomes after the first four years. It was after four patients had to undergo further surgery that the company “decided unilaterally, and as a precaution, to formally withdraw Cadisc-L from the market, which it did on 31 March 2014”.

In Germany, a case against a doctor was filed late last year alleging assault against 53 patients who had the device implanted. He has denied the allegations. There is no action against Ranier Technology.