A cannula assembly adapted to facilitate the percutaneous introduction of surgical instrumentation. In particular, the cannula assembly includes a cannula housing and a cannula member incorporating an restrictor hinge. The restrictor hinge is configured and dimensioned to transition from a first, initial stage in which an initial internal dimension is defined, to a second, expanded stage, such that the proper orientation of any surgical instrument inserted into the cannula may be achieved and a substantially fluid-tight seal may be formed therewith.
