The ALARP Principle
When a risk cannot be mitigated further without compromising the device's functionality, you must write a Residual Risk Justification.
Clinical Benefit Baseline
The core of this justification is proving that the clinical benefit outweighs the risk. To do this, you must establish a baseline using the "State of the Art". If your device's risk profile is similar to or better than legally marketed alternatives, the risk is generally acceptable.
Literature and State of the Art
Do not use vague statements like "The risk is low." Use quantitative data from clinical literature, complaint databases (like MAUDE), and clinical evaluations to justify your position.
Always document that all possible risk control options were considered and implemented "as far as possible" before accepting the residual risk.