Medical instruments such as catheter systems and endoscopic systems that exhibit reduced backlash during their operation are disclosed. The reduction of backlash avoids the use of protrusions or fins that can significantly obstruct fluid flow through working channels of the instruments. According to one embodiment, a medical instrument comprises a first member having an inside surface defining a first lumen and a second member extending in the first lumen and having an outside surface cooperating with the inner surface of the first member to define an intermediate longitudinal passage therebetween. One of the inside surface of the first member and the outside surface of the second member is permanently formed to have a sinuous shape defining predisposed locations for contacting the other one of the inner surface of the first member and the outer surface of the second member to reduce backlash during relative longitudinal movement.
