MEMS-BASED METHOD AND SYSTEM FOR TRACKING A FEMORAL FRAME OF REFERENCE

• US 20110218458A1
• Filed: 07/26/2010
• Published: 09/08/2011
• Est. Priority Date: 03/02/2010
• Status: Active Grant

• Current Assignee: ORTHOsoft ULC. (Zimmer Biomet Holdings, Inc.)
• Original Assignee: ORTHOsoft ULC. (Zimmer Biomet Holdings, Inc.)
• Inventors: Falardeau, Bruno, Proulx, Catherine, Valin, Myriam, Deslongchamps, Julie, Amiot, Louis-Philippe
• Granted Patent: US 9,901,405 B2
• Time in Patent Office: Days
• US Class Current: 600/595
• CPC Class Codes: A61B 2034/2048 using an accelerometer or inertia sensor
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis

Abstract

A system for tracking a femoral frame of reference in computer-assisted surgery comprises a sensor unit. The sensor unit is adapted to be secured to the femur. The sensor unit comprises accelerometer and gyroscope sensors that produce orientation data. A processing unit receives gyroscope and accelerometer data. The processing unit comprises a gyroscope-data calculator to provide calculated acceleration data resulting from movements of the femur, an accelerometer-data calculator to calculate measured acceleration data resulting from movements of the femur, and an acceleration comparator to relate an orientation of the sensor unit to the femur to define a femoral frame of reference. The femoral frame of reference is defined from the comparison between the calculated and the measured acceleration data. A sensor orientation interface provides orientation data for the femur from a tracking of the femoral frame of reference. A method for tracking a femoral frame of reference is also provided.

Claims

1. A system for tracking a femoral frame of reference in computer-assisted surgery, comprising:

a sensor unit adapted to be secured to the femur, the sensor unit comprising an accelerometer sensor and a gyroscope sensor both producing orientation data;

a processing unit receiving gyroscope data and accelerometer data and comprising;

a gyroscope-data calculator for providing calculated acceleration data from at least the gyroscope data resulting from movements of the femur;

an accelerometer-data calculator for calculating measured acceleration data from the accelerometer data resulting from movements of the femur; and

an acceleration comparator for relating an orientation of the sensor unit to the femur to define a femoral frame of reference, from the comparison between the calculated acceleration data and the measured acceleration data;

a sensor orientation interface for providing orientation data for the femur from a tracking of the femoral frame of reference.

2. The system according to claim 1, wherein the gyroscope-data calculator provides the calculated acceleration data using estimated trajectory and radius values for the femur.

3. The system according to claim 1, wherein the gyroscope-data calculator provides the calculated acceleration data using an estimate radius value for the femur for deducting centripetal accelerations from the gyroscope data, and using an orientation of the gyroscope sensor for deducting gravity from the accelerometer data.

4. The system according to claim 1, wherein the frame of reference defined by the acceleration comparator is a three-axis femoral coordinate system.

5. The system according to claim 1, wherein the acceleration comparator applies a numerical optimization to said comparison to define the femoral frame of reference.

6. The system according to claim 1, wherein the acceleration comparator calculates at least one of a femur length and a femoral trajectory.

7. The system according to claim 1, further comprising filters in any one of the sensor unit and the processing unit to reduce noise from any one of the gyroscope data and the accelerometer data.

8. A method for tracking a femoral frame of reference with a sensor unit comprising an accelerometer sensor and a gyroscope sensor secured to a femur, comprising:

obtaining gyroscope readings and accelerometer readings resulting from movements of the femur;

calculating acceleration data at least from the gyroscope readings;

measuring acceleration data from the accelerometer readings;

comparing the calculated and the measured acceleration data;

relating an orientation of the sensor unit to the femur using the comparison to define a femoral frame of reference; and

tracking the femoral frame of reference from the gyroscope readings and from the accelerometer readings.

9. The method according to claim 8, wherein calculating acceleration data comprises using estimate values for the trajectory of the femur and the radius of the femur.

10. The method according to claim 8, wherein calculating acceleration data comprises using an estimate value for the radius of the femur for deducting a centripetal acceleration from the gyroscope readings, and obtaining an orientation of the gyroscope to deduct the gravity from the accelerometer readings.

11. The method according to claim 8, wherein relating an orientation comprises performing a numerical optimization using the comparison to obtain an orientation of the sensor unit with respect to the femur.

12. The method according to claim 8, further comprising calculating at least one of a radius of the femur and a trajectory of the femur from the frame of reference.

13. The method according to claim 8, wherein defining the femoral frame of reference comprises defining a three-axis coordinate system.

14. The method according to claim 8, wherein the method is performed on a bone model or cadaver.