Method and device for determining the mechanical axis of a femur

• US 7,331,932 B2
• Filed: 06/11/2003
• Issued: 02/19/2008
• Est. Priority Date: 12/15/2000
• Status: Expired due to Term

• Current Assignee: Aesculap AG (Lonza Group AG)
• Original Assignee: Aesculap AG (Lonza Group AG)
• Inventors: Leitner, Franc
• Primary Examiner(s): Hindenburg; Max
• Assistant Examiner(s): HOEKSTRA, JEFFREY GERBEN
• Application Number:
  US10/460,637
• Publication Number:
  US 20040034313A1
• Time in Patent Office: 1,714 Days
• Field of Search: 600/595, 600/587, 600/592, 600/594
• US Class Current: 600/595
• CPC Class Codes: A61B 17/154 for preparing bone for knee prosthesis
• CPC Class Codes: A61B 2017/00128 related to intensity or progress of surgical action
• 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 2034/2072 Reference field transducer attached to an instrument or patient
• CPC Class Codes: A61B 2090/378 using ultrasound
• 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 5/1114 Tracking parts of the body
• CPC Class Codes: A61B 5/1121 Determining geometric values, e.g. centre of rotation or angular range of movement
• CPC Class Codes: A61B 5/1127 using markers
• CPC Class Codes: A61B 5/4504 Bones A61B5/4547 takes precedence
• CPC Class Codes: A61B 5/4528 Joints A61B5/4533, A61B5/4538 take precedence
• CPC Class Codes: A61B 90/36 Image-producing devices or illumination devices not otherwise provided for
• CPC Class Codes: G01S 15/872 Combination of several systems for attitude determination using inertial means G01C9/00, control of attitude G05D1/49
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 5/163 Determination of attitude using inertial means G01C9/00; control of attitude G05D1/49
• CPC Class Codes: G01S 5/186 Determination of attitude using inertial means G01C9/00; control of attitude G05D1/49

Abstract

In order to avoid the use of a marking element on the pelvic bone in a method for determining the mechanical axis of a femur, with which the femur is moved about the hip joint, the movement of the femur is followed via a navigation system by means of a marking element on the femur, position data of the femur obtained therefrom are stored and the position of the mechanical axis of the femur is calculated relative to the same from the various position data of the femur in various positions, it is suggested that the femur be pivoted from an initial position only through a maximum pivoting angle of 15° in various directions and that the mechanical axis of the femur be calculated from the position data of the surface area thereby covered by the marking element and from the position data of the knee joint otherwise determined. In addition, a device for carrying out this method is described.

Claims

1. Method for determining the mechanical axis of a femur attached to a pelvis via a hip joint, comprising the steps of:

moving the femur about the hip joint,

following the movement of the femur via a navigation system by means of a marking element on the femur that passes over a surface area during said movement,

storing position data of the femur obtained from the navigation system, and

calculating the position of the mechanical axis of the femur from the stored position data of the femur in various positions,

wherein;

the femur is pivoted from an initial position only through a maximum pivoting angle of 15°

in various directions to prevent movement of said pelvis,

the mechanical axis of the femur is calculated from the position data of the surface area passed over by the marking element when the femur is moved and from position data of the knee joint;

only position data corresponding to a pivoting angle less than a predetermined critical angle smaller than the maximum pivoting angle covered by the femur are used for the calculation of the mechanical axis; and

the critical angle is between 4° and

6°

.

2. Method as defined in claim 1, wherein the femur is pivoted only within a maximum pivoting angle of at most 10°

.

3. Method as defined in claim 1, wherein only position data corresponding to a pivoting angle more than a predetermined minimum angle smaller than the critical angle are used for the calculation of the mechanical axis.

4. Method as defined in claim 1, wherein all the stored position data are left out of consideration when the actual pivoting angle of the femur relative to its initial position exceeds the maximum pivoting angle.

5. Method as defined in claim 1, wherein:

the surface area passed over by the marking element when the femur is moved is a partial spherical surface, and

for the calculation of the mechanical axis of the femur from the partial spherical surface a center point of this partial spherical surface is calculated and the mechanical axis is determined by means of a connecting line from this center point to the knee joint.

6. Method as defined in claim 5, comprising:

determining a virtual center point of the partial spherical surface by calculating a plane from the stored position data of the partial spherical surface;

assuming that a vertical line extending through the knee joint and the virtual center point is at a predetermined distance from the calculated plane on the vertical line; and

calculating the mechanical axis of the femur using the position data of the virtual center point and the position data of the partial spherical surface.

7. Method as defined in claim 6, wherein the position data of the partial spherical surface are converted to a uniform pivoting angle relative to the initial position using the position data of the virtual center point so that corrected position data defining a common circle are obtained therefrom and wherein a mid-vertical of this circle is calculated as mechanical axis of the femur.

8. Method as defined in claim 1, wherein a number and distribution of the measured position data are determined in the entire pivoting area and the recording of additional position data is interrupted once a predetermined number and distribution are reached.

9. Method as defined in claim 1, wherein the stored position data are represented graphically in accordance with their spatial distribution in a pivoting area so that it is apparent what number of position data has been stored for which part of a possible pivoting area.

10. Method as defined in claim 9, wherein sections of a graphically represented surface area are marked when a predetermined number of position data is recorded in a corresponding part of the pivoting area of the femur.

11. Method as defined in claim 10, wherein the surface area is an annular surface area subdivided into segments.

12. Method for determining the mechanical axis of a femur attached to a pelvis via a hip joint, comprising the steps of:

moving the femur about the hip joint,

following the movement of the femur via a navigation system by means of a marking element on the femur that passes over a surface area during said movement,

storing position data of the femur obtained from the navigation system, and

calculating the position of the mechanical axis of the femur from the stored position data of the femur in various positions,

wherein;

the femur is pivoted from an initial position only through a maximum pivoting angle of 15°

in various directions to prevent movement of said pelvis,

the mechanical axis of the femur is calculated from the position data of the surface area passed over by the marking element when the femur is moved and from position data of the knee joint;

only position data corresponding to a pivoting angle less than a predetermined critical angle smaller than the maximum pivoting angle covered by the femur are used for the calculation of the mechanical axis;

only position data corresponding to a pivoting angle more than a predetermined minimum angle smaller than the critical angle are used for the calculation of the mechanical axis; and

the minimum angle is more than 3°

.

13. Method as defined in claim 12, wherein the femur is pivoted only within a maximum pivoting angle of at most 10°

.

14. Method as defined in claim 12, wherein all the stored position data are left out of consideration when the actual pivoting angle of the femur relative to its initial position exceeds the maximum pivoting angle.

15. Method as defined in claim 12, wherein:

the surface area passed over by the marking element when the femur is moved is a partial spherical surface, and

for the calculation of the mechanical axis of the femur from the partial spherical surface a center point of this partial spherical surface is calculated and the mechanical axis is determined by means of a connecting line from this center point to the knee joint.

16. Method as defined in claim 15, comprising:

determining a virtual center point of the partial spherical by calculating a plane from the stored position data of the partial spherical surface;

assuming that a vertical line extending through the knee joint and the virtual center point is at a predetermined distance from the calculated plane on the vertical line; and

calculating the mechanical axis of the femur using the position data of the virtual center point and the position data of the partial spherical surface.

17. Method as defined in claim 16, wherein the position data of the partial spherical surface are converted to a uniform pivoting angle relative to the initial position using the position data of the virtual center point so that corrected position data defining a common circle are obtained therefrom and wherein a mid-vertical of this circle is calculated as mechanical axis of the femur.

18. Method as defined in claim 12, wherein a number and distribution of the measured position data are determined in the entire pivoting area and the recording of additional position data is interrupted once a predetermined number and distribution are reached.

19. Method as defined in claim 12, wherein the stored position data are represented graphically in accordance with their spatial distribution in a pivoting area so that it is apparent what number of position data has been stored for which part of a possible pivoting area.

20. Method as defined in claim 18, wherein sections of a graphically represented surface area are marked when a predetermined number of position data is recorded in a corresponding part of the pivoting area of the femur.

21. Method as defined in claim 19, wherein the surface area is an annular surface area subdivided into segments.