Radially expandable cannula devices, and systems and methods for using them

A cannula device, comprising:

• a first housing defining a first throughbore aligned along a central axis;
• a second housing defining a second throughbore aligned with the first throughbore along the central axis, the second housing moveable in an axial direction along the central axis with respect to the first housing;
• a plurality of elongate members cooperatively defining a passage axially aligned with the first throughbore along the central axis between proximal ends and distal tips of the elongate members;
• and
• a plurality of guide elements on the proximal ends of the elongate members and the first and second housings configured to cooperate such that axial movement of the first housing with respect to the second housing along the central axis causes the proximal ends of the elongate members to move outwardly with respect to the central axis to move away from each other and increase a size of the passage,
• wherein the elongate members are configured such that, as the proximal ends move radially outwardly, if the distal tips are constrained, the elongate members define a tapered shape extending from the proximal ends towards the distal tips.