A medical device for advancement over a guidewire includes a number of lumens therein including a working channel lumen, one or more control wire lumens, and a guidewire lumen. A flexible support within the device includes a number of interlocking elements that resist longitudinal compression, transfer rotational torque, and can bend side to side. The flexible support also includes a slot that is aligned with the guidewire lumen. An outer jacket includes a perforation, slot, slit, or thinned area that is aligned with the slot in the support member and the guidewire lumen in order to allow a device such as a guidewire to be removed from the guidewire lumen and through the support member.