The present invention is directed at minimally invasive systems in which the proximal end portion of the working channel has either zero or a limited range of movement in the lateral direction. A first embodiment has a slidable collar attached to a pair of flanges, wherein movement of the collar is bounded by an annular frame. A second embodiment has a substantially spherical element attached to the tube. A third embodiment has a plurality of caps. A fourth embodiment is adapted for a larger working channel.