Telemetric tibial tray

• US 20050010302A1
• Filed: 03/31/2004
• Published: 01/13/2005
• Est. Priority Date: 07/11/2003
• Status: Active Grant

• Current Assignee: Depuy Products Incorporated (Johnson & Johnson)
• Original Assignee: Depuy Products Incorporated (Johnson & Johnson)
• Inventors: Dietz, Terry, Tomaszewski, Paul, Slamin, John E., Matthews, Frank D., Hastings, Bob, DiSilvestro, Mark, Petrella, Tony
• Granted Patent: US 7,470,288 B2
• Time in Patent Office: Days
• US Class Current: 623/20.210
• CPC Class Codes: A61B 2090/064 for measuring force, pressure or mechanical tension
• CPC Class Codes: A61B 2562/02 Details of sensors specially adapted for in-vivo measurements
• CPC Class Codes: A61B 5/076 Permanent implantations telemetry using implanted circuitry A61B5/0031; implanted stimulators for therapy A61N1/3605, A61N1/362, A61N1/372
• CPC Class Codes: A61B 5/4528 Joints A61B5/4533, A61B5/4538 take precedence
• CPC Class Codes: A61B 90/06 Measuring instruments not otherwise provided for
• CPC Class Codes: A61F 2/38 for elbows or knees
• CPC Class Codes: A61F 2/3859 Femoral components
• CPC Class Codes: A61F 2/389 Tibial components A61F2/3868 takes precedence
• CPC Class Codes: A61F 2002/30133 kidney-shaped or bean-shaped
• CPC Class Codes: A61F 2002/3067 for data transfer
• CPC Class Codes: A61F 2002/30878 with non-sharp protrusions, for instance contacting the bone for anchoring, e.g. keels, pegs, pins, posts, shanks, stems, struts
• CPC Class Codes: A61F 2002/30892 parallel
• CPC Class Codes: A61F 2002/4666 for measuring force, pressure or mechanical tension
• CPC Class Codes: A61F 2230/0015 Kidney-shaped, e.g. bean-shaped
• CPC Class Codes: A61F 2250/0002 for data transfer

Abstract

A telemetric tibial tray includes a lower plate that defines a plurality of cylindrical transducer cavities having circular load diaphragms. An upper plate is attached to the lower plate through support posts projecting from the load diaphragms. The support posts have a circular cross-section and a diameter of about 5.0 mm. The lower plate further defines wiring channels communicating between the transducer cavities and a central cavity housing the circuit board for the telemetric tray. The wiring channels are arranged at a 45 degree angle relative to the sagittal plane of the knee joint in order to reduce the effects of the wiring channel intersection on the strain sensitivity of the tray. Each transducer cavity includes a radial strain gage array with four pairs of radially aligned strain gages, each pair aligned at a 45 degree angle relative to the sagittal plane of the knee joint. Each pair of strain gages includes an inner gage positioned at the point of maximum positive micro-strain across the diaphragm when loaded, and an outer gage positioned at the point of maximum negative micro-strain, to thereby increase the differential strain measured by the gages and increase the strain sensitivity of the tibial tray.

Claims

1. In a telemetric knee prosthesis adapted to measure forces transmitted across the knee joint, the knee prosthesis having a femoral component, a tibial bearing member in articulating contact with the femoral component, a tibia engaging member and a tibial tray engaged to the tibial bearing member and the tibia engaging member, the tibial tray comprising:

an upper plate having a portion configured for engaging the tibial bearing member;

a lower plate having a portion configured for engaging the tibia engaging member, said lower plate spaced apart from said upper plate and defining a plurality of cavities opening away from said upper plate, each of said cavities including a diaphragm adapted to flex when subjected to a load normal to the diaphragm;

a plurality of support posts, each connected between said upper plate and said diaphragm of a corresponding one of said cavities, wherein said support posts are circular in cross-section; and

a force sensing element disposed within each of said plurality of cavities and operable to produce an output signal in response to flexing of said diaphragm.

2. The tibial tray of claim 1, wherein said support posts each have a diameter of about 5.0 mm.

3. The tibial tray of claim 1, wherein said support posts each have a diameter that is about ⅓

the diameter of the corresponding cavity.

4. In a telemetric knee prosthesis adapted to measure forces transmitted across the knee joint, the knee prosthesis having a femoral component, a tibial bearing member in articulating contact with the femoral component, a tibia engaging member and a tibial tray engaged to the tibial bearing member and the tibia engaging member, the tibial tray comprising:

an upper plate having a portion configured for engaging the tibial bearing member;

a lower plate having a portion configured for engaging the tibia engaging member, said lower plate spaced apart from said upper plate and defining a plurality of cavities opening away from said upper plate, each of said cavities including a diaphragm adapted to flex when subjected to a load normal to the diaphragm;

a plurality of support posts, each connected between said upper plate and said diaphragm of a corresponding one of said cavities; and

a force sensing element disposed within each of said plurality of cavities and operable to produce an output signal in response to flexing of said diaphragm, said force sensing element including four pairs of radially aligned strain gages, the strain gages of each pair arranged to measure differential strain in a radial direction,

wherein said lower plate defines a plane parallel to the sagittal plane of the knee joint when the knee prosthesis is implanted therein, and

wherein each of said pairs of strain gages is aligned in a radial plane that is at about 45 degrees relative to said parallel plane.

5. In a telemetric knee prosthesis adapted to measure forces transmitted across the knee joint, the knee prosthesis having a femoral component, a tibial bearing member in articulating contact with the femoral component, a tibia engaging member and a tibial tray engaged to the tibial bearing member and the tibia engaging member, the tibial tray comprising:

an upper plate having a portion configured for engaging the tibial bearing member;

a lower plate having a portion configured for engaging the tibia engaging member, said lower plate spaced apart from said upper plate and defining a plurality of cavities opening away from said upper plate, each of said cavities including a diaphragm adapted to flex when subjected to a load normal to the diaphragm, said lower plate further defining a central cavity disposed between said plurality of cavities and a plurality of wiring channels, each communicating between a corresponding one of said plurality of cavities and said central cavity;

a plurality of support posts, each connected between said upper plate and said diaphragm of a corresponding one of said cavities;

a force sensing element disposed within each of said plurality of cavities and operable to produce an output signal in response to flexing of said diaphragm;

a circuit element disposed in said central cavity for processing said output signal from said force sensing element in each of said plurality of cavities; and

wiring electrically connecting each force sensing element in said plurality of cavities to said circuit element to transmit said output signal, said wiring disposed in a corresponding one of said plurality of wiring channels,

wherein said lower plate defines a plane parallel to the sagittal plane of the knee joint when the knee prosthesis is implanted therein, and

wherein each of said plurality of wiring channels is aligned at about 45 degrees relative to said parallel plane.

6. In a telemetric knee prosthesis adapted to measure forces transmitted across the knee joint, the knee prosthesis having a femoral component, a tibial bearing member in articulating contact with the femoral component, a tibia engaging member and a tibial tray engaged to the tibial bearing member and the tibia engaging member, the tibial tray comprising:

an upper plate having a portion configured for engaging the tibial bearing member;

a lower plate having a portion configured for engaging the tibia engaging member, said lower plate spaced apart from said upper plate and defining a plurality of cylindrical cavities opening away from said upper plate, each of said cavities including a circular diaphragm adapted to flex when subjected to a load normal to the diaphragm and an outer wall;

a plurality of support posts, each connected between said upper plate and said diaphragm of a corresponding one of said cavities; and

a force sensing element disposed within each of said plurality of cavities and operable to produce an output signal in response to flexing of said diaphragm, said force sensing element including four pairs of radially aligned strain gages, the strain gages of each pair arranged to measure differential strain in a radial direction and includes an inner gage mounted on said diaphragm adjacent the center of said circular diaphragm and an outer gage mounted on said diaphragm immediately adjacent said outer wall of said cylindrical cavity.

7. The tibial tray of claim 6, wherein said inner gage is mounted on said diaphragm at a radius of about 2.5 mm from the center of said circular diaphragm.

8. The tibial tray of claim 6, wherein said circular diaphragm exhibits a micro-strain behavior under load that produces a maximum magnitude at a radial location from the center of said circular diaphragm, and further wherein said inner gage is positioned to span said maximum magnitude radial location.

9. The tibial tray of claim 6, wherein said circular diaphragm exhibits a micro-strain behavior under load that produces a zero-crossing point between the center of said circular diaphragm and said outer wall of said cylindrical cavity, and further wherein said outer gage is positioned between said zero-crossing point and said outer wall.

10. The tibial tray of claim 9, wherein said circular diaphragm exhibits a micro-strain behavior under load that produces a negative maximum magnitude at a radial location between said zero-crossing point and said outer wall, and further wherein said outer gage is positioned to span said negative maximum magnitude radial location.

11. The tibial tray of claim 9, wherein said circular diaphragm further exhibits a micro-strain behavior under load that produces a positive maximum magnitude at a radial location from the center of said circular diaphragm, and further wherein said inner gage is positioned to span said positive maximum magnitude radial location.

12. In a telemetric knee prosthesis adapted to measure forces transmitted across the knee joint, the knee prosthesis having a femoral component, a tibial bearing member in articulating contact with the femoral component, a tibia engaging member and a tibial tray engaged to the tibial bearing member and the tibia engaging member, the tibial tray comprising:

an upper plate having a portion configured for engaging the tibial bearing member;

a lower plate having a portion configured for engaging the tibia engaging member, said lower plate spaced apart from said upper plate and defining a plurality of cavities opening away from said upper plate, each of said cavities including a diaphragm adapted to flex when subjected to a load normal to the diaphragm, said lower plate further defining a central cavity disposed between said plurality of cavities and a plurality of wiring channels, each communicating between a corresponding one of said plurality of cavities and said central cavity;

a plurality of support posts, each connected between said upper plate and said diaphragm of a corresponding one of said cavities;

a force sensing element disposed within each of said plurality of cavities and operable to produce an output signal in response to flexing of said diaphragm said force sensing element including four pairs of radially aligned strain gages, the strain gages of each pair arranged to measure differential strain in a radial direction;

a circuit element disposed in said central cavity for processing said output signal from said force sensing element in each of said plurality of cavities; and

wiring electrically connecting each force sensing element in said plurality of cavities to said circuit element to transmit said output signal, said wiring disposed in a corresponding one of said plurality of wiring channels,

wherein none of said four pairs of radially aligned strain gages is aligned with said wiring channel communicating with said corresponding one of said plurality of cavities.

13. The tibial tray of claim 12, wherein said four pairs of radially aligned strain gages are aligned at an angle of about 45 degrees or 135 degrees relative to said wiring channel.