Surgical Instrument Including Housing, A Cutting Accessory That Extends From The Housing And Actuators That Establish The Position Of The Cutting Accessory Relative To The Housing

A system including an instrument adapted to be manually supported and moved by a user. The instrument having a hand-held portion, a drive mechanism movably coupled to the hand-held portion, and a plurality of actuators operatively coupled to the drive mechanism for moving the drive mechanism in at least two degrees of freedom relative to the hand-held portion. The instrument also includes a tracking device for tracking the instrument and a working portion removably coupled to the drive mechanism by a coupling assembly. The system further comprises a navigation system for determining a position of the working portion and a bone to be cut during the medical procedure and a control system in communication with the actuators and configured to control the actuators to actively position the working portion such that the working portion is substantially maintained on a plane.