1. A surgical navigation system comprising: a first inertial sensor that measures its own motion without an external reference and in response thereto provides data relating to a position and an orientation of said first inertial sensor, said first inertial sensor being configured to attach to a patient's body; a sensor processor that receives said data from said first inertial sensor and using said data calculates the position of said first inertial sensor and the orientation of said first inertial sensor in a common coordinate system that defines position and orientation coordinates relative to an initial position and an initial orientation of the first inertial sensor; a mapping processor that stores in memory an initial location of a point on the patient's body and determines a location of said point on the patient's body in the common coordinate system based on the position and orientation of said first inertial sensor after the patient's body has moved, wherein the mapping processor computes from the determined location of said point on the patient's body, a point display element that represents a graphical depiction of the location of said point on the patient's body in the common coordinate system; and a display in communication with the mapping processor, the display comprising a graphical user interface that receives the point display element from the mapping processor and displays the point display element to provide a graphical depiction of the determined location of said point on the patient's body relative to a planned surgical cut, thereby providing feedback as to an alignment of the patient's body with the planned surgical cut.