A surgical apparatus for positioning within a tissue tract accessing an underlying body cavity adapts to tissue tracts of different widths. The surgical instrument includes a proximal member, a distal member, and a sleeve extending between the proximal member and the distal member and defining a longitudinal passage therein. The proximal member includes an inflatable member that selectively adjusts the radial dimension of the proximal member. A ring member may be separately insertable by a user during a surgical procedure into the space directly adjacent to the radially-inner surface of the inflatable member, so as to selectively provide rigidity to the proximal member.