A trocar assembly includes a trocar housing having a blunt distal end and a proximal end; a blade assembly having a sharp tip and being slideable within the trocar housing between and armed position wherein the sharp tip extends distally beyond the blunt distal end and a relaxed position wherein the sharp tip is withdrawn proximally relative to the armed position; and a trigger member positioned relative to the housing to contact tissue when tissue is cut with the blade assembly in the armed position, and slideable by contact with the tissue to a proximal position which exposes the sharp tip and actuates a lock release member, the trigger member having member having a spring member biasing the trigger member distally so that removal of contact with the tissue allows the spring to move the trigger member distally, and further wherein distal movement of the trigger member with the lock release member activated releases the blade assembly from the armed position and allows the blade assembly to move to the relaxed position.