Medical measurement system and method

• US 8,746,062 B2
• Filed: 02/27/2012
• Issued: 06/10/2014
• Est. Priority Date: 06/29/2010
• Status: Active Grant

• Current Assignee: Howmedica Osteonics Corp. (Stryker Corporation)
• Original Assignee: OrthoSensor, Inc (Stryker Corporation)
• Inventors: Stein, Marc, Chase, Andrew U.
• Primary Examiner(s): THOMPSON, JEWEL VERGIE
• Application Number:
  US13/406,494
• Publication Number:
  US 20120157884A1
• Time in Patent Office: 834 Days
• Field of Search: 600/587, 600/437, 600/508
• US Class Current: 73/379.01
• CPC Class Codes: A61B 5/4509 Bone density determination
• CPC Class Codes: A61B 5/4528 Joints A61B5/4533, A61B5/4538 take precedence
• CPC Class Codes: A61B 5/6846 specially adapted to be brought in contact with an internal body part, i.e. invasive

Abstract

A measurement system for measuring a parameter of the muscular-skeletal system is disclosed. The measurement system comprises a capacitor, a signal generator, a digital counter, counter register, a digital clock, a digital timer, and a data register. The sensor of the measurement system is the capacitor. The measurement system generates a repeating signal having a measurement cycle that corresponds to the capacitance of the capacitor. The capacitor comprises more than one capacitor mechanically in series. Electrically, the capacitor comprises more than one capacitor in parallel. In one embodiment, the capacitor includes a dielectric layer comprising polyimide. A force, pressure, or load is applied to the capacitor that elastically compresses the device.

Claims

1. A medical device including a measurement system to measure a parameter comprising:

a sensor configured to couple to the muscular-skeletal system, where the sensor includes;

a compressible capacitor, where the capacitor includes an elastic dielectric;

a signal generator coupled to the capacitor where the signal generator is configured to output a signal corresponding to a capacitance of the capacitor;

a digital counter coupled to the signal generator; and

a digital timer coupled to the signal generator.

2. The medical device of claim 1 where a change in the parameter produces a corresponding change in the capacitor.

3. The medical device of claim 2 where the medical device is configured to apply a force, pressure, or load to the capacitor.

4. The medical device of claim 3 where the medical device is configured to be coupled to a muscular- skeletal system.

5. The measurement system of claim 1 where the signal generator is configured to output a waveform having a measurement cycle corresponding to the capacitance of the capacitor.

6. The measurement system of claim 5 where the signal generator is configured to oscillate.

7. The measurement system of claim 6 where the digital counter is configured to count measurement cycles during the measurement sequence.

8. The measurement system of claim 7 where the measurement sequence ends after the digital counter counts a predetermined count and where the digital timer measures an elapsed time of the measurement sequence.

9. A medical device including a measurement system to measure a parameter comprising:

a capacitor;

a signal generator coupled to the capacitor where the signal generator is configured to output a signal that is repeated, where a time period of the signal corresponds to a capacitance of the capacitor, and where the signal corresponds to a measurement cycle;

a digital counter coupled to the signal generator where the digital counter is configured to count each measurement cycle; and

a digital timer coupled to the signal generator, where a measurement sequence ends after the digital counter counts a predetermined number of measurement cycles and where the digital timer measures an elapsed time of the measurement sequence, where measurement accuracy of the parameter is increased by raising the predetermined count of measurement cycles.

10. The measurement system of claim 9 where the capacitance of the capacitor is substantially constant during the measurement sequence.

11. The measurement system of claim 10 further including a data register coupled to the digital timer to store a number calculated from the predetermined number of measurement cycles and the measured elapsed time of the measurement sequence.

12. A method to measure a force, pressure, or load comprising the steps of:

applying the force, pressure, or load to a capacitor; and

generating a repeating signal where each signal has a measurement cycle that corresponds to a capacitance of the capacitor, where the capacitor is compressible and where the capacitor includes an elastic dielectric.

13. The method of claim 12 further including the steps of:

repeating the signal a predetermined number of times; and

measuring an elapsed time corresponding to the predetermined number of times the signal was repeated.

14. A method to measure a force, pressure, or load comprising the steps of:

applying the force, pressure, or load to a capacitor;

generating a repeating signal where each signal has a measurement cycle that corresponds to a capacitance of the capacitor;

repeating the signal a predetermined number of times;

measuring an elapsed time corresponding to the predetermined number of times the signal was repeated;

maintaining the force, pressure, or load substantially constant during the measurement sequence; and

correlating the elapsed time and the predetermined number of times the signal was repeated to one of a force, pressure, or load measurement.

15. The method of claim 14 further including a step of raising the predetermined number of times the signal is repeated to increase measurement accuracy.

16. A medical sensor system for measuring a parameter comprising:

a sensor configured to couple to the muscular-skeletal system comprising;

multi-layered interconnect, where the interconnect includes alternating conductive and dielectric layers forming at least one capacitor where deformation of at least one of the dielectric layers in response to an applied force changes the capacitance of the capacitor;

and

a signal generator coupled to the at least one capacitor.

17. The system of claim 16 further including:

a digital counter coupled to the signal generator; and

a digital timer coupled to the signal generator where the signal generator is configured to output a repeating waveform corresponding to a capacitance of the capacitor.

18. The system of claim 17 further including a data register where the digital counter is configured to count a predetermined number of measurement cycles, where the digital timer is configured to measure an elapsed time of the predetermined number of measurement cycles, and where the data register is configured to store a number corresponding to the parameter.

19. The system of claim 16 where the capacitor comprises more than one capacitor in mechanically in series.

20. The system of claim 16 where the capacitor comprises more than one capacitor electrically in parallel.