Abstract: Apparatus and associated methods relate to a flexible extrusion having a number of radially extending members configured for slidable insertion into a lumen of a surgical catheter shaft. In an illustrative example, the extrusion may have a flexible wall and define an interior insert lumen extending along the longitudinal axis from a proximal end to a distal end. Each of the radially extending members may have a distal engaging surface. When the extrusion is slidably inserted, for example, into the lumen of the catheter shaft, the distal engaging surface of each of the plurality of radial extending members may slidably engage an interior surface of the catheter shaft. In some examples, the inserted extrusion may define an annular distribution of longitudinally extending channels between a proximal and a distal end of the catheter. The slidable construction may advantageously simplify assembly, for example. The channels may offer end-to-end communication.