Method for locating the mechanical axis of a femur

• US 20050015022A1
• Filed: 07/15/2003
• Published: 01/20/2005
• Est. Priority Date: 07/15/2003
• Status: Active Grant

• Current Assignee: ORTHOsoft ULC. (Zimmer Biomet Holdings, Inc.)
• Original Assignee: ORTHOsoft Holdings Inc. (Zimmer Biomet Holdings, Inc.)
• Inventors: Richard, Alain, Jansen, Herbert Andre, Brosseau, Eric
• Granted Patent: US 7,427,272 B2
• Time in Patent Office: Days
• US Class Current: 600/587
• CPC Class Codes: A61B 17/154 for preparing bone for knee prosthesis
• CPC Class Codes: A61B 2034/105 Modelling of the patient, e.g. for ligaments or bones
• 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 2034/2072 Reference field transducer attached to an instrument or patient
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• CPC Class Codes: A61B 34/25 User interfaces for surgical systems
• CPC Class Codes: A61B 5/103 Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes A61B5/08 takes precedence; measuring aids for tailors A41H1/00; measuring instruments specially adapted for dentistry A61C19/04
• CPC Class Codes: A61B 5/1127 using markers
• CPC Class Codes: A61B 5/4504 Bones A61B5/4547 takes precedence
• CPC Class Codes: A61B 90/36 Image-producing devices or illumination devices not otherwise provided for
• CPC Class Codes: A61F 2/46 Special tools or methods for implanting or extracting artificial joints, accessories, bone grafts or substitutes, or particular adaptations therefor
• CPC Class Codes: A61F 2/4657 Measuring instruments used for implanting artificial joints for surgical instruments A61B90/06

Abstract

There is described a method for determining a mechanical axis of a femur using a computer aided surgery system having an output device for displaying said mechanical axis, the method comprising: providing a position sensing system having a tracking device capable of registering instantaneous position readings and attaching the tracking device to the femur; locating a center of a femoral head of the femur by moving a proximal end of the femur to a first static position, acquiring a fixed reading of the first static position, repeating the moving and the acquiring for a plurality of static positions; and locating the centre by determining a central point of a pattern formed by the plurality of static positions; digitizing an entrance point of the mechanical axis at a substantially central position of the proximal end of the femur; and joining a line between the entrance point and the center of rotation to form the mechanical axis.

Claims

1. A method for determining a mechanical axis of a femur using a computer aided surgery system having an output device for displaying said mechanical axis, the method comprising:

providing a position sensing system having a tracking device capable of registering instantaneous position readings and attaching said tracking device to said femur;

locating a center of a femoral head of said femur by moving a proximal end of said femur to a first static position, acquiring a fixed reading of said first static position, repeating said moving and said acquiring for a plurality of static positions; and

locating said centre by determining a central point of a pattern formed by said plurality of static positions;

digitizing an entrance point of said mechanical axis at a substantially central position of said proximal end of said femur; and

joining a line between said entrance point and said center of rotation to form said mechanical axis.

2. A method as claimed in claim 1, wherein said position sensing system automatically registers said instantaneous position readings periodically and said acquiring a fixed reading comprises taking an average value of a plurality of said instantaneous position readings to determine said static position.

3. A method as claimed in claim 1, wherein said position sensing system responds to user input to register said instantaneous position readings and said acquiring a fixed reading comprises enabling said position sensing system to register a single instantaneous position reading.

4. A method as claimed in claim 1, wherein said pattern formed by said plurality of static positions is a conical pattern.

5. A method as claimed in claim 1, wherein said plurality of static positions is between 7 and 10.

6. A method as claimed in claim 1, wherein said plurality of static positions is 14.

7. A method as claimed in claim 1, wherein said acquiring a fixed reading comprises determining a position of said proximal end relative to a reference.

8. A method as claimed in claim 7, wherein said reference is a fixed reference placed on a pelvis bone adjacent to said femur.

9. A method as claimed in claim 1, wherein said repeating said moving comprises waiting for a signal from an acquisition system that said fixed reading has been acquired before moving to a next static position.

10. A method as claimed in claim 9, wherein said signal is an audio sound.

11. A method as claimed in claim 1, wherein said repeating said moving comprises moving said proximal end at least 20 mm to a next static position.

12. A method as claimed in claim 1, wherein said digitizing comprises applying an instrument to a surface of said bone such that a point and a normal axis to said point are determined.

13. A method as claimed in claim 1, wherein said substantially central position is determined visually.

14. A method as claimed in claim 1, wherein said bone is a femur, said first end is a femoral head of said femur, and said substantially central position is determined by locating an inter-condylar notch.

15. A method as claimed in claim 14, wherein said inter-condylar notch is located by digitizing a medial and a lateral epicondyle at said second end of said femur, forming an epicondylar axis, and determining a center of said epicondylar axis.