METHOD AND SYSTEM FOR REGISTERING A BONE OF A PATIENT WITH A COMPUTER ASSISTED ORTHOPAEDIC SURGERY SYSTEM

• US 20080154127A1
• Filed: 12/21/2006
• Published: 06/26/2008
• Est. Priority Date: 12/21/2006
• Status: Active Grant

• Current Assignee: Depuy Products Incorporated (Johnson & Johnson)
• Original Assignee: Depuy Products Incorporated (Johnson & Johnson)
• Inventors: DiSilvestro, Mark R., Sherman, Jason T., Woods, Sherrod A.
• Granted Patent: US 8,068,648 B2
• Time in Patent Office: Days
• US Class Current: 600/427
• CPC Class Codes: A61B 2034/102 Modelling of surgical devices, implants or prosthesis
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 2034/2055 Optical tracking systems
• CPC Class Codes: A61B 2034/2068 using pointers, e.g. pointers having reference marks for determining coordinates of body points
• CPC Class Codes: A61B 2034/256 having a database of accessory information, e.g. including context sensitive help or scientific articles
• CPC Class Codes: A61B 2090/364 Correlation of different images or relation of image positions in respect to the body
• CPC Class Codes: A61B 2090/367 creating a 3D dataset from 2D images using position information
• CPC Class Codes: A61B 2090/3954 magnetic, e.g. NMR or MRI
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• CPC Class Codes: G06T 2207/30008 Bone
• CPC Class Codes: G06T 7/30 Determination of transform parameters for the alignment of images, i.e. image registration
• CPC Class Codes: G06V 10/24 Aligning, centring, orientation detection or correction of the image
• CPC Class Codes: G06V 2201/03 Recognition of patterns in medical or anatomical images

Abstract

A method and system for registering a bone of a patient with a computer assisted orthopaedic surgery system includes retrieving an image of the bone having indicia of the position of a magnetic source coupled thereto, determining first data indicative of the position of the magnetic source in a bone coordinate system, determining second data indicative of a correlation between a coordinate system of the image and the bone coordinate system based on the first data; and displaying an image of the bone based on the second data.

Claims

1. A method for registering a bone of a patient with a computer assisted orthopaedic surgery system, the method comprising:

retrieving an image of the bone including indicia of the position of a magnetic source coupled to the bone, the image defining an image coordinate system;

determining a position of a reference array coupled to the bone, the reference array defining a bone coordinate system;

determining first data indicative of the position of the magnetic source in the bone coordinate system;

determining second data indicative of a correlation between the image coordinate system and the bone coordinate system based on the first data; and

displaying an image of the bone in a position determined based on the second data.

2. The method of claim 1, wherein retrieving an image of the bone comprises retrieving a three-dimensional medical image of the bone of the patient.

3. The method of claim 1, wherein coupling a reference array to the bone of the patient comprises coupling a reference array to the bone of the patient selected from the group consisting of a reflective reference array and a radio frequency reference array.

4. The method of claim 1, wherein determining the first data comprises positioning a magnetic sensor array in a magnetic field generated by the magnetic source, the magnetic sensor array defining a magnetic sensor array coordinate system.

5. The method of claim 4, wherein determining the first data comprises measuring a magnetic flux density of the magnetic field at a plurality of points in space with a number of magnetic sensors of the magnetic sensor array.

6. The method of claim 4, wherein determining the first data comprises determining the position of the magnetic source in the magnetic sensor array coordinate system.

7. The method of claim 6, wherein determining the position of the magnetic source in the magnetic sensor array coordinate system comprises:

(i) determining the location of the centroid of a magnet coupled to the bone in the magnetic sensor array coordinate system, and

(ii) determining the direction of a polar axis of the magnet in the magnetic sensor array coordinate system.

8. The method of claim 7, wherein determining the first data comprises:

(i) determining the position of the magnetic sensor array in a global coordinate system defined by a tracking unit of the computer assisted orthopaedic surgery system, and

(ii) determining the position of the bone of the patient in the global coordinate system based on the position of the reference array.

9. The method of claim 8, wherein:

(i) determining the position of the magnetic sensor array in the global coordinate system comprises determining a first transformation matrix, and

(ii) determining the position of the bone of the patient in the global coordinate system comprises determining a second transformation matrix.

10. The method of claim 9, wherein determining first data indicative of the position of the magnetic source in the bone coordinate system comprises:

(i) determining the location of the centroid of the magnet in the bone coordinate system; and

(ii) determining the direction of the polar axis of the magnet in the bone coordinate system.

11. The method of claim 10, wherein the location of the centroid of the magnet is determined using the following equation:

P_B=RT[2]<sup>−

1</sup>*(RT[1]* P_M)

wherein P_B the location of the centroid of the magnet in the bone coordinate system, RT[2] is the second transformation matrix, and RT[1] is the first transformation matrix, and P_M is the location of the centroid of the magnet in the magnetic sensor array coordinate system.

12. The method of claim 10, wherein the direction of the polar axis of the magnetic is determined using the following equation:

D_B=R[2]<sup>−

1</sup>*(R[1]*D_M)

wherein D_B the direction of the polar axis of the magnet in the bone coordinate system, R[2] is the second transformation matrix, and R[1] is the first transformation matrix, and D_M is the direction of the polar axis of the magnet in the magnetic sensor array coordinate system.

13. The method of claim 1, wherein determining the first data indicative of the position of the magnetic source in the bone coordinate system comprises:

(i) determining the location of the centroid of a magnet coupled to the bone in the bone coordinate system; and

(ii) determining the direction of a polar axis of the magnet in the bone coordinate system.

14. The method of claim 1, wherein determining second data indicative of a correlation between the image coordinate system and the bone coordinate system comprises determining a transformation matrix.

15. The method of claim 14, wherein determining the transformation matrix comprises:

(i) estimating a transformation matrix for transforming the image coordinate system to the bone coordinate system,

(ii) transforming the position of the magnetic source from the image coordinate system to the bone coordinate system using the estimated transformation matrix,

(iii) generating third data indicative of the transformed position of the magnetic source,

(iv) calculating a difference between the first data and the third data, and

(v) repeating steps (i)-(iv) until the difference between the first data and the third data is less than a predetermined minimum threshold value.

16. The method of claim 15, wherein calculating a difference between the first data and the third data comprises calculating a sum of the squared difference between the first data and the third data.

17. The method of claim 15, wherein displaying the image of the bone comprises displaying an image of the bone in a location and orientation determined using the estimated transformation matrix.

18. The method of claim 15, wherein the magnetic source comprises a magnet and the first and second data comprise location data indicative of the location of the centroid of the magnet and direction data indicative of the direction of a polar axis of the magnet.

19. A system for registering a bone of a patient to with a computer assisted orthopaedic surgery system, the system comprising:

a first reference array configured to be coupled to the bone of the patient, the first reference array defining a first coordinate system;

a display device;

a processor electrically coupled to the display device; and

a memory device electrically coupled to the processor, the memory device having stored therein a plurality of instructions, which when executed by the processor, cause the processor to;

retrieve an image of the bone including indicia of the position of a magnetic source coupled to the bone, the image defining a second coordinate system;

determine first data indicative of the position of the magnetic source in the first coordinate system;

determine second data indicative of a correlation between the second coordinate system and the first coordinate system based on the first data; and

display an image of the bone on the display device in a position determined based on the second data.

20. The system of claim 19, further comprising a magnetic sensor array having a second reference array coupled thereto, the second reference array defining a third coordinate system, wherein:

to determine first data comprises to determine the position of the magnetic source in the third coordinate system based on data received from the magnetic sensor array.

21. The system of claim 20, wherein to determine first data comprises to transform the position of the magnetic source from the third coordinate system to the first coordinate system.

22. The system of claim 19, wherein to determine first data comprises to:

(i) determine the location of the centroid of a magnet of the magnetic source in the first coordinate system, and

(ii) determine the direction of a polar axis of the magnet in the first coordinate system.

23. The system of claim 19, wherein to determine second data indicative of a correlation between the image coordinate system and the bone coordinate system comprises to determine a transformation matrix.

24. The system of claim 23, wherein to determine a transformation matrix comprises to:

(i) estimate a transformation matrix for transforming the image coordinate system to the bone coordinate system,

(ii) transform the position of the magnetic source from the image coordinate system to the bone coordinate system using the estimated transformation matrix,

(iii) generate third data indicative of the transformed position of the magnetic source,

(iv) calculate a difference between the first data and the third data, and

(v) repeat steps (i)-(iv) until the difference between the first data and the third data is less than a predetermined minimum threshold value.

25. A method for registering a bone of a patient with a computer assisted orthopaedic surgery system, the method comprising:

determining the position of a magnet coupled to the bone in a first coordinate system defined by a magnetic sensor array;

transforming the position of the magnet from the first coordinate system to a second coordinate system defined by a reference array coupled to the bone;

generating first data indicative of the position of the magnet in the second coordinate system;

retrieving an image of the bone having indicia of the position of the magnet, the image defining a third coordinate system;

determining a transformation matrix for transforming the position of the magnet from the third coordinate system to the second coordinate system based on the first data; and

displaying an image of the bone in a location and orientation determined using the transformation matrix.

26. The method of claim 25, wherein determining the position of a magnet coupled to the bone in the first coordinate system comprises:

(i) determining the location of the centroid of the magnet in the first coordinate system, and

(ii) determining the direction of a polar axis of the magnet in the first coordinate system.

27. The method of claim 25, wherein transforming the position of the magnet from the first coordinate system to a second coordinate system comprises:

(i) determining a first matrix defining the position of the magnetic sensor array in a fourth coordinate system defined by the computer assisted orthopaedic surgery system, and

(ii) determining a second matrix defining the position of the bone of the patient in the fourth coordinate system.

28. The method of claim 25, wherein generating first data indicative of the position of the magnet in the second coordinate system comprises:

(i) determining the location of the centroid of the magnet in the second coordinate system, and

(ii) determining the direction of a polar axis of the magnet in the second coordinate system.

29. The method of claim 25, wherein determining a transformation matrix for transforming the position of the magnet from the third coordinate system to the second coordinate system comprises

(i) determining an estimated transformation matrix for transforming the third coordinate system to the second coordinate system,

(ii) transforming the position of the magnetic source from the third coordinate system to the second coordinate system using the estimated transformation matrix,

(iii) generating second data indicative of the transformed position of the magnetic source,

(iv) calculating a difference between the first data and the second data, and

(v) repeating steps (i)-(iv) until the difference between the first data and the second data is less than a predetermined minimum threshold value.

30. The method of claim 29, wherein calculating the difference between the first data and the second data comprises calculating a sum of the squared difference between the first data and the second data.