A trocar is provided having a needle unit. The needle unit has a paracentetic section, which is substantially pyramidal. The paracentetic section has two curved surfaces that diagonally oppose each other. The surfaces are formed by cutting the ridges of the section, which diagonally oppose each other....http://www.google.ca/patents/US6497714?utm_source=gb-gplus-sharePatent US6497714 - Ultrasonic trocar
