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In consultation with academia and the Pharmaceuticals and Medical Devices Agency (PMDA), we have developed guidance for drafting protocols for clinical trials concerning medical devices for the healing of hard-to-heal wounds without ischaemia. The guidance summarises the validity of single-arm trials for hard-to-heal wounds, the definition of hard-to-heal wounds without ischaemia, methods of patient enrolment and clinical endpoints. This review focuses on the logical thinking process that was used when establishing the guidance for improving the efficiency of clinical trials concerning medical devices for hard-to-heal wounds. We particularly focused on the feasibility of conducting single-arm trials and also tried to clarify the definition of hard-to-heal wounds. If the feasibility of randomised control trials is low, conducting single-arm trials should be considered for the benefit of patients. In addition, hard-to-heal wounds were defined as meeting the following two conditions: wounds with a wound area reduction <50% at four weeks despite appropriate standards of care; and wounds which cannot be closed by a relatively simple procedure (for example, suture, skin graft and small flaps). Medical devices for hard-to-heal wound healing are classified into two types: (1) devices for promoting re-epithelialisation; and (2) devices for improving the wound bed. For medical devices for promoting re-epithelialisation, we suggest setting complete wound closure, percent wound area reduction or distance moved by the wound edge as the primary endpoint in single-arm trials for hard-to-heal wounds. For medical devices for improving the wound bed, we suggest setting the period in which wounds can be closed by secondary intention or a simple procedure, such as the primary endpoint. Declaration of interest: The authors have no conflicts of interest directly relevant to the content of this article. The authors' views expressed in the present article do not necessarily reflect the official views of the Pharmaceuticals and Medical Devices Agency. [ABSTRACT FROM AUTHOR]