When the interface fails: a patient-safety hazard hidden by the assumption of human error

Medical-device safety surveillance is organized around two failure types: a device that malfunctions and a clinician who errs. A third category, harm arising at the interface between two individually compliant devices used in combination, fits neither model and is poorly captured. As combination and procedure-pack care becomes ubiquitous, the safety significance of this blind spot grows.

This article examines why interface failure evades vigilance and incident-reporting systems, using the syringe-cannula junction in intraocular surgery as a documented exemplar. Evidence was identified through searches of PubMed/MEDLINE and Google Scholar (database inception to July 2026), the US FDA MAUDE adverse-event database, and professional-body safety publications, and comprises surveys, case series, health-economic and litigation analyses, and the small-bore connector (ISO 80369) standards literature. It argues that misattribution to human error is the principal mechanism of under-reporting and traces the resulting cost to patients and staff.

Interface failure is a distinct and legitimate object of safety attention that current systems do not see. Progress depends less on new devices than on whether surveillance acquires a reporting category for combination failure, pursues buried signals through trend analysis, and brings standards attention to high-consequence junctions.