A medical instrument assembly including a handle assembly having a first handle portion and a second handle portion proximate the second end, wherein the second handle portion is slidably engaged with the first handle portion. A first localization element is attached to the first handle portion and a second localization element is attached to the second handle portion. A medical instrument is mechanically coupled to the second handle portion and a translation of the second handle portion with respect to the first handle portion causes a coincident and coextensive translation of the medical instrument. The amount of translation of the medical instrument is adapted to be determined by calculating the distance between the first localization element and the second localization element. The first and second localization elements may be electromagnetic sensors which positions may be determined by a navigation system.
