A trocar device, comprising a trocar cutting element, a surrounding insulating sheath, and a cannula surrounding the sheath, also includes an arrangement providing a substantially smooth transition between the sheath and cannula at the distal end of the cannula during the insertion of the trocar device...http://www.google.com.au/patents/US5824002?utm_source=gb-gplus-sharePatent US5824002 - Trocar-cannula device
