US Patent 7399306 Hand-held instruments that access interior body regions

Apparatus and methods provide a tool comprising a trocar and a cannula in which the trocar engages the cannula to form a composite instrument. The trocar includes a handle and a lumen through the trocar and the trocar handle that accommodates passage of a functional instrument, such as a stylet, guidewire, or spinal needle assembly. The cannula includes a handle and is sized and configured to accommodate passage of the trocar. The trocar handle mates with the cannula handle to form a composite handle when the trocar is engaged with the cannula.