A stability assembly for a trocar cannula includes a conical stability member, a base, and a cannula retention member. The base has a passage defining an inner surface, and a constriction in the passage. The cannula retention member is rotatable within the passage, and advancement of the cannula retention member over the constriction reduces the inner diameter of the passage to restrain a cannula in the passage. Various latch mechanisms including interface surfaces on the base and the cannula retention member can be used in the stability assembly to secure the stability assembly around a cannula. Various conical stability members can be used in the stability assembly.