A trocar assembly includes a trocar housing that defines a working chamber, and a cannula having a proximal end and a distal end, wherein the cannula is coupled to the trocar housing at the proximal end to facilitate communication between the cannula and the working chamber. A plurality of radial support members are arranged at or near the distal end and comprise a plurality of keystones arranged side by side to form a ring within the cannula. Each radial support member extends radially inward toward a centerline of the cannula to center a surgical tool within the cannula and thereby minimize unintended oscillation and vibration of the surgical tool.
