BackgroundWithin the field of plastic surgery, free tissue transfer is common practice for knee and lower leg defects. Usually, after such free flap reconstruction, patients undergo a dangling protocol in the postoperative phase. A dangling protocol is designed to gradually subject the free flap to increased venous pressure resulting from gravitational forces. Worldwide there are multiple variations of dangling protocols. However, there is no evidence available in the literature that supports the use of a dangling protocol.MethodsThis is a multicenter randomized controlled trial that includes patients with a free flap lower leg reconstruction. The primary outcome is to assess whether a no-dangling protocol is not inferior to a dangling protocol, in terms of proportion of partial flap loss, 6 months after surgery. Secondary objectives are to identify differences in major and minor complications, length of stay, and costs, and to objectify blood gaseous changes during dangling. Furthermore, at 2 years we will assess difference in physical function, infection rates, and osseous union rates.DiscussionThe primary outcome of this study will give a more decisive answer to the question of whether a dangling protocol is necessary after a free flap reconstruction of the lower leg. The secondary outcomes of this study will provide a better insight into the physical functions, infection rates, and union rates in these patients.Trial registrationCentral Committee on Research Involving Human Subjects (CCMO), NL63146.041.17. Registered on 11 July 2018. Netherlands Trial Register, NTR7545. Registered on 10 October 2018.