outer dimension 132 of the dilating element 112 is greater than the inner diameter of the sealing trocar the advancement 412 of the cannula 100 may then be conducted under gas insufflation to improve visualization of the previously formed surgical cavity fig5 a illustrates an embodiment of cannula 100 with a locking mechanism 150 for a detachable dilating element 112 as shown in fig5 b locking mechanism 150 includes a length of screw threads disposed on the surface or outer housing of the cannula 100 at a position near the distal end of the cannula that allows the locked dilating element 112 to be located in a position on the cannula 100 as described previously herein with reference to fig1 3 fig5 c illustrates a cross section of the dilating element 112 having a mating lock or set of screw threads 162 which couples to locking mechanism 150 of fig5 a a bore hole 154 is formed along the horizontal axis of the dilating element 112 and the screw threads are disposed along a portion of the bore hole 154 as a mating lock 162 the dimension 158 of the bore hole 154 is wider than the diameter 136 of the cannula 100 but is small enough to ensure a tight coupling upon inserting the dilating element 112 into the locking mechanism 150 thus in this configuration the dilating element 112 is.