which is slidably received within cannula shaft 112 as is shown in fig1 obturator 120 is a rigid structure which provides internal support to cannula shaft 112 such that cannula shaft 112 can be received percutaneously shaft 112 can have a cross section which is circular oval racetrack shaped or any other design by holding obturator handle 122 the surgeon is able to advance cannula shaft 112 through the patient 39 s para spinal musculature and dock expandable tip 113 at the patient 39 s annulus as seen in fig1 and 13 expandable tip 113 is comprised of a plurality of petals 114 held together by breakable seals 115 breakable seals 115 can be formed by an elastomeric material with predictable failure segments between the petals in one preferred aspect each of petals 114 has an electrode 116 disposed therein as shown electrodes 116 serve the following important functions first electrodes 116 can be used for electromyography and in particular to sense the presence and relative position of para spinal nerves as cannula shaft 112 is advanced referring to fig1 as can be seen electrodes 116 a 116 b 116 c 116 d 116 e and 116 f are disposed radially about cannula shaft 112 with one electrode disposed in each of petals 114 as has been described electrodes 116 a 116 b 116 c 116 d 116 e and 116 f assist in sensing the presence and location of para spinal nerve 160 as follows the electrodes closest to nerve 160 in this case electrodes 116 b and.