A safety penetrating instrument for penetrating an anatomical cavity wall to gain access to an anatomical cavity includes a cannula, a penetrating member disposed in the cannula and movable relative to the cannula between a penetrating position where the tissue penetrating distal end of the penetrating...http://www.google.ca/patents/US5713870?utm_source=gb-gplus-sharePatent US5713870 - Retractable safety penetrating instrument with laterally extendable spring strip 
