A safety trocar penetrating instrument particularly useful in least invasive surgery includes a portal sleeve, a trocar disposed in the portal sleeve and having a sharp, solid, angled tissue penetrating distal end and a safety shield disposed in the portal sleeve and receiving the trocar, the safety...http://www.google.co.uk/patents/US5730755?utm_source=gb-gplus-sharePatent US5730755 - Safety trocar penetrating instrument with mating safety shield nub and trocar depression 
