FDA warning letter says a swapped machine learning model needed a new 510(k)

MedDevice Startups Staff · Oct 7 · 3 min read · Via AuntMinnie

FDA issued a warning letter dated September 1 to O.N. Diagnostics over version 3.0.0 of VirtuOst VFA, software that grades vertebral fractures on spine CT. The cleared version sits under K171435. FDA called the device adulterated under section 501(f)(1)(B) and misbranded under 502(o), and cited 21 CFR 807.81(a)(3)(i) for the missing premarket notification.

The agency named three changes, each of which it said would independently require clearance. The company swapped in a new machine learning model for vertebral landmarking. It moved the software from a desktop application to a web architecture. It migrated the underlying technology platform, which required revalidating the codebase and its third-party components.

FDA quoted the company's own inspection statement that the web transition had expanded its vulnerability to cyberattacks. The letter also cites quality system and medical device reporting problems, and follows a March 2026 inspection. FDA asked the company to stop commercial distribution of 3.0.0.

O.N. Diagnostics says it is finishing verification and validation on a revised version that strips out the machine learning functionality, with updated cybersecurity controls and documentation. A predetermined change control plan filed before the retrain would have covered the model swap and neither of the other two changes.

Questions & Answers

Why did FDA send O.N. Diagnostics a warning letter?

FDA's September 1, 2026 warning letter says O.N. Diagnostics distributed VirtuOst VFA version 3.0.0 without a new 510(k). FDA identified three changes, each of which would independently require premarket notification, and asked the company to stop commercial distribution of that version.

Does changing a machine learning model require a new 510(k)?

In the O.N. Diagnostics case, FDA said yes. The agency said replacing the machine learning model that identifies vertebral landmarks could significantly affect safety or effectiveness, because a model trained on different data or built on a different architecture can behave differently across patient populations and scanners.

What is VirtuOst VFA?

VirtuOst VFA is O.N. Diagnostics software that analyzes spine CT scans to detect and grade vertebral fractures in osteoporosis care. The cleared version was authorized under 510(k) K171435. The company says the product remains available through its existing in-house service.

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