The present invention provides a device (10) suitable for insertion between vertebral portions and having a first, collapsed, position and a second, extended, position, wherein the device comprises upper and lower supports (18, 20) and side supports (22, 24) pivotally connected thereto and in which one of said side supports includes a reaction surface (34) against which, in operation, an actuation member (36) acts so as to cause opening of said device.