System and method for monitoring offset during navigation-assisted surgery

1. A method of navigating a surgical instrument having a variable speed motor relative to a bone, the method using a navigation system including a localizer having a localizer coordinate system, an instrument tracker coupled to the surgical instrument, a patient tracker coupled to a bone, and a controller in communication with the navigation system, the controller controlling the surgical instrument, the method comprising:

registering, with the localizer, the patient tracker in the localizer coordinate system, defining a bone location of the bone relative to the localizer coordinate system;

registering, with the localizer, the instrument tracker in the localizer coordinate system, defining an instrument location of an instrument tool tip relative to the localizer coordinate system;

defining a motor operation for the instrument when the instrument tool tip is not in contact with the bone;

monitoring, with the controller, motor operation of the instrument during a medical procedure;

monitoring, with the navigation system, a position of the instrument tool tip relative to the bone to determine when the instrument tool tip is in contact with the bone in the localizer coordinate system;

comparing the motor operation to the monitored position of the instrument tool tip;

determining an error condition when the monitored position of the instrument tool tip is in contact with the bone in the localizer coordinate system and the monitored motor operation equals the defined motor operation for the instrument when the instrument tool tip is not in contact with the bone; and

triggering an action when an error condition is determined.

2. The method of claim 1 , wherein defining the motor operation for the instrument when the tool tip is not in contact with the bone comprises defining a threshold value for power, voltage, current, or combinations thereof, when the motor is operated while the instrument tool tip is not in contact with the bone.

3. The method of claim 1 , further comprising defining a second motor operation for the instrument when the instrument tool tip is in contact with the bone; determining a second error condition when the monitored position of the instrument tool tip is not in contact with the bone in the localizer coordinate system and the monitored motor operation equals the second defined motor operation for the instrument when the instrument tool tip is in contact with the bone; and triggering a second action when the second error condition is determined.

4. The method of claim 3 , wherein triggering one of an action or a second action comprises one of sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting off power to the surgical instrument, or combinations thereof.

5. A method of navigating a surgical instrument having a variable speed motor using a navigation system including a localizer having a localizer coordinate system, an instrument tracker coupled to the surgical instrument, a patient tracker coupled to a bone, and a controller in communication with the navigation system and providing power to the surgical instrument, the method comprising:

registering, with the localizer, the patient tracker in the localizer coordinate system, defining a bone location of the bone relative to the localizer coordinate system;

registering, with the localizer, the instrument tracker in the localizer coordinate system, defining an instrument location of an instrument tool tip relative to the localizer coordinate system;

defining a first motor operation of the surgical instrument operating while not in contact with the bone;

monitoring, with the controller, a motor operation of the surgical instrument during a medical procedure;

monitoring, with the navigation system, a position of the instrument tool tip relative to the bone in the localizer coordinate system;

comparing the monitored motor operation to the defined first motor operation;

determining a contact time between the instrument tool tip and the bone when the monitored motor operation deviates from the defined first motor operation;

determining, with the navigation system at the contact time, a tool-to-bone offset as a distance between the instrument tool tip and a surface of the bone in the localizer coordinate system; and

triggering an action when the tool-to-bone offset exceeds a predefined magnitude.

6. The method of claim 5 , wherein triggering an action comprises one of sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting off power to the surgical instrument, or combinations thereof.

7. The method of claim 5 , wherein the predefined magnitude is 0.5 millimeters.

8. The method of claim 5 , further comprising displaying, on a display device, the determined tool-to-bone offset.

9. The method of claim 8 , wherein monitoring the position of the instrument tool tip relative to the bone comprises tracking the instrument location of the instrument tool tip and the bone location of the bone during the medical procedure; the method further comprising detecting, with the navigation system, each occurrence during the medical procedure of the monitored position of the instrument tool tip being in contact with the surface of the bone and logging a series of tool-to-bone offset values determined during the medical procedure upon each occurrence.

10. The method of claim 9 , further comprising displaying, on a display device, the series of tool-to-bone offset values as one of a serially updating value, a chart of tool-to-bone offsets over time, or combinations thereof.

11. The method of claim 8 , further comprising defining a first level magnitude and a second level magnitude, wherein the step of displaying the determined tool-to-bone offset comprises displaying the determined tool-to-bone offset in a first color when the determined tool-to-bone offset is less than the first level magnitude; displaying the determined tool-to-bone offset in a second color, different from the first color, when the determined tool-to-bone offset is between the first level and the second level magnitude; and displaying the determined tool-to-bone offset in a third color, different from the first and the second colors, when the determined tool-to-bone offset is greater than the second level magnitude.

12. The method of claim 11 , further comprising defining a third level magnitude, and disabling power from the controller to the surgical instrument when the determined tool-to-bone offset is greater than the third level magnitude.

13. The method of claim 5 , further comprising prompting a user to enter a value for the predefined magnitude.

14. The method of claim 5 , wherein triggering an action comprises prompting a user to update a model of the bone, and wherein updating the model of the bone comprises contacting a resected surface of the bone with the instrument tool tip while power is disabled from the controller to the surgical instrument.

15. A method of operating a surgical system during a surgical operation to verify a tracking registration, the surgical system including a navigation system including a localizer having a localizer coordinate system, an instrument tracker coupled to a surgical instrument, the surgical instrument including a tool tip, a patient tracker coupled to a patient's anatomy, and a control console in communication with the localizer, the control console in communication with data representing the surgical instrument and data representing the patient's anatomy, the method comprising:

tracking, with the navigation system, the surgical instrument and the anatomy and storing, with the control console, first data representing the tracked surgical instrument and second data representing the tracked anatomy in a common coordinate system;

determining the tool tip is within a predefined proximity to the tracked anatomy based on the first data representing the tracked surgical instrument and second data representing the tracked anatomy;

determining the tool tip does not depart the predefined proximity by more than a predefined magnitude over a predefined duration;

determining an offset distance based on the first data representing the tracked surgical instrument and the second data representing the tracked anatomy;

comparing the offset distance to a predefined threshold; and

triggering an action when the offset distance is greater than the predefined threshold.

16. The method of claim 15 , further comprising prompting a user to verify a tracking registration by one of displaying a prompt on a display; sounding an audible alert; generating a haptic sensation; or combinations thereof.

17. The method of claim 15 , wherein determining the tool tip is within a predefined proximity to the tracked anatomy includes defining a surface area of the anatomy not to be resected, and determining the tool tip is within a predefined proximity to the defined surface area.

18. The method of claim 15 , wherein the offset distance is defined as a magnitude of minimum separation between the tool tip and the tracked anatomy in the common coordinate system, or as a magnitude of greatest overlap between the tool tip and the tracked anatomy in the common coordinate system.

19. The method of claim 15 , wherein determining the tool tip is within a predefined proximity to the tracked anatomy includes the surgical instrument positioned at a first pose with respect to the tracked anatomy, the surgical instrument defining a first proximal point of the tool tip and wherein determining the offset distance includes determining a first offset distance;

the method further comprising determining the tool tip is within a predefined proximity to the tracked anatomy including the surgical instrument positioned at a second pose with respect to the tracked anatomy, the surgical instrument defining a second proximal point of the tool tip and wherein determining the offset distance includes determining a second offset distance; and wherein comparing the offset distance to a predefined threshold includes comparing the first offset distance to the predefined threshold, and comparing the second offset distance to the predefined threshold, and wherein triggering an action includes initiating an action when the first offset distance, the second offset distance, or both the first and second offset distances are greater than the predefined threshold.

20. The method of claim 19 , wherein the surgical instrument includes an elongated aspect terminating at the tool tip, the elongated aspect defining a longitudinal axis extending substantially parallel to the elongated aspect; and wherein the second proximal point is at least 90° from the first proximal point relative to a rotation about the longitudinal axis.

21. The method of claim 19 , wherein the surgical instrument includes the tool tip having a spherical aspect defining a centerpoint, wherein the second proximal point is at least 90° away from the first proximal point relative to a rotation about the centerpoint.

22. The method of claim 15 , wherein triggering an action includes one of sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting off power to the surgical instrument or combinations thereof.

23. The method of claim 15 , wherein the predefined threshold includes a first predefined threshold, and a second predefined threshold, and wherein triggering an action includes triggering a first action when the offset distance is greater than the first predefined threshold but less than the second predefined threshold, and triggering a second action when the offset distance is greater than the second predefined threshold, wherein the first action includes one of sounding a first audible alert, displaying a first visual alert, activating a first tactile alert or combinations thereof, and wherein the second action includes one of sounding a second audible alert, displaying a second visual alert, activating a second tactile alert or combinations thereof.

24. A method of providing navigation guidance for a surgical procedure using a navigation system, the navigation system comprising a localizer, the method comprising:

registering a patient's anatomy in a common coordinate system, the patient's anatomy including at least a first bone and a second bone;

registering a surgical instrument in the common coordinate system, the surgical instrument comprising a tool tip;

tracking the patient's anatomy and the surgical instrument with the navigation system during operation of the surgical instrument on the first bone of the patient's anatomy;

determining the tool tip is within a predefined proximity to the second bone;

determining the tool tip does not depart the predefined proximity by more than a predefined magnitude over a predefined duration;

determining an offset distance based on the tracked position of the surgical instrument and the second bone;

comparing the offset distance to a predefined threshold;

triggering an action when the offset distance is greater than the predefined threshold; and

tracking the patient's anatomy and the surgical instrument with the navigation system during operation of the surgical instrument on the second bone of the patient's anatomy.