Method for repairing focal defects in tissue of a patient

1. A method for repairing focal defects in tissue of a patient using an instrument having a cutting tip and a drive motor for rotating the cutting tip, said method comprising the steps of:

attaching one or more tracking devices to the patient;

placing an access cannula through skin of the patient to provide minimally invasive access to a target volume of material in a bone having a focal defect;

placing the cutting tip into the access cannula;

operating a tracking and control system to establish a virtual boundary that defines the target volume of material, track a position of the cutting tip relative to the virtual boundary, and control movement of the cutting tip;

removing the target volume of material from the bone with the cutting tip while the position of the cutting tip is tracked relative to the virtual boundary so that the cutting tip is maintained in a desired position with respect to the virtual boundary; and

placing an implant into the bone so that an upper surface of the implant is flush with an upper surface of the bone surrounding the implant to repair the focal defect.

2. A method as set forth in claim 1 wherein said step of removing includes milling the target volume of material from the bone to receive the implant.

3. A method as set forth in claim 1 wherein the implant is a plug.

4. A method as set forth in claim 3 wherein the plug includes bone and cartilage.

5. A method as set forth in claim 1 wherein the bone is a femur.

6. A method as set forth in claim 1 including the step of registering the virtual boundary to the patient to track movement of the virtual boundary while removing the target volume of material with the cutting tip.

7. A method as set forth in claim 1 wherein the target volume of material is defined by a depth of cutting and a smooth outer edge.

8. A method as set forth in claim 1 wherein said step of attaching one or more tracking devices to the patient includes attaching a first tracker to the bone.

9. A method as set forth in claim 1 wherein said step of placing the access cannula through the skin of the patient includes placing a guide tube through the skin.

10. A method as set forth in claim 1 including the step of placing a second access cannula through the skin of the patient to provide a second minimally invasive access to the target volume of material.

11. A method as set forth in claim 1 including the step of providing a virtual three-dimensional model of the bone.

12. A method as set forth in claim 1 wherein said step of removing includes reshaping worn area of the bone by the cutting tip.

13. A method as set forth in claim 1 including the step of viewing on a display the position of the cutting tip relative to the virtual boundary.

14. A method as set forth in claim 1 wherein said step of operating the tracking and control system to control movement of the cutting tip includes operating the tracking and control system to

control movement of the cutting tip longitudinally along a rotational axis of the cutting tip so that cutting is substantially maintained within the virtual boundary.

15. A method as set forth in claim 14 wherein said step of operating the tracking and control system to control movement of the cutting tip longitudinally along the rotational axis includes operating the tracking and control system to control longitudinal movement of the cutting tip based on the position of the cutting tip relative to the virtual boundary to substantially maintain the cutting tip within the virtual boundary.

16. A method as set forth in claim 14 wherein said step of operating the tracking and control system to control movement of the cutting tip longitudinally along the rotational axis includes operating the tracking and control system to control extension and retraction of the cutting tip.

17. A method as set forth in claim 14 including the step of viewing on a display the target volume of material to be removed by the cutting tip and material to remain after cutting, wherein the target volume of material to be removed is displayed in a different color than the material to remain after cutting.

18. A method as set forth in claim 1 wherein said step of operating the tracking and control system to control movement of the cutting tip includes operating the tracking and control system to control pitch and yaw movement of the cutting tip based on the position of the cutting tip relative to the virtual boundary to substantially maintain the cutting tip within the virtual boundary.

19. A method as set forth in claim 1 wherein said step of operating the tracking and control system to control movement of the cutting tip includes operating the tracking and control system to control a rotational speed of the cutting tip based on the position of the cutting tip relative to the virtual boundary.