In vivo joint implant cycle counter

1. A joint endoprosthesis system to be implanted in a patient, the system comprising:

a first prosthetic component having a bone engaging surface to be affixed to one bone of the joint and an articulation surface;

a second prosthetic component having a bone-engaging surface to be affixed to the other bone of the joint and a second surface spaced from the bone-engaging surface;

the first and second prosthetic components being capable of relative articulation;

an electromagnetic field source affixed directly to one of the prosthetic components, the electromagnetic field source having a pole in a fixed position and orientation with respect to the prosthetic component to which it is affixed and a maximum magnetic field strength in a fixed orientation with respect to the prosthetic component to which it is affixed;

a sensor having characteristics allowing it to generate a signal each time the magnetic field strength at the sensor exceeds a predetermined threshold and to refrain from generating a signal when the magnetic field strength at the sensor falls below the predetermined threshold, the sensor being affixed directly to the other prosthetic component and being in a fixed position with respect to the bone-engaging surface of the prosthetic component to which it is directly affixed; and

a counter electrically connected to the sensor for storing the number of signals generated by the sensor, the counter being affixed directly to one of the first and second prosthetic components for implantation with the prosthetic component;

wherein the electromagnetic field source and sensor are positioned and oriented so that the electromagnetic field strength at the sensor is above the threshold of the sensor when the first and second prosthetic components are articulated in one orientation and so that the electromagnetic field strength falls below the threshold of the sensor when the first and second prosthetic components are articulated in a plurality of orientations.

2. The joint endoprosthesis system of claim 1 wherein the sensor comprises a transducer.

3. The joint endoprosthesis system of claim 1 further comprising a first power source for supplying continuous power to the counter.

4. The joint endoprosthesis system of claim 1 further comprising a transmitter for transmitting data related to the number of signals stored.

5. The joint endoprosthesis system of claim 4 further comprising:

a first power source for supplying continuous power to the counter; and

a second power source for selectively supplying power to the transmitter.

6. A joint endoprosthesis system comprising:

a first prosthetic component to be affixed to one bone of the joint, the first prosthetic component having a non-articulating surface and a recess in the non-articulating surface;

a second prosthetic component to be affixed to the other bone of the joint, the second prosthetic component having a non-articulating surface and a recess in the non-articulating surface;

a bearing to be carried by one of the prosthetic components and positioned between the first and second prosthetic components;

an electromagnetic field source;

a sensor for generating a signal each time the bones are in a predetermined position, the sensor being permanently affixed directly to one of the prosthetic components;

a counter electrically connected to the sensor for storing the incremental number of signals generated by the sensor, the counter being permanently affixed directly to one of the first and second prosthetic components;

a transmitter electrically connected to the counter for selectively transmitting a signal having a characteristic related to the incremental count recorded by the counter, the transmitter being permanently affixed directly to one of the first and second prosthetic components;

a first power source electrically connected to the counter for supplying continuous power to the counter; and

a second power source electrically connected to the transmitter for selectively supplying power to the transmitter;

wherein the electromagnetic field source is received and sealed in the recess of one of the prosthetic components and the sensor, counter and first power source are received and sealed in the recess of the other prosthetic component.

7. The joint endoprosthesis system of claim 6 wherein the sensor comprises a switch.

8. The joint endoprosthesis of claim 7 wherein the sensor comprises a Hall effect switch and the electromagnetic field source comprises a permanent magnet.

9. The joint endoprosthesis of claim 6 wherein the first prosthetic component comprises a distal femoral component and the second prosthetic component comprises a proximal tibial component.

10. The joint endoprosthesis system of claim 6 wherein the first power source and the second power source are affixed to the second prosthetic component.

11. A method of monitoring use of a joint endoprosthesis system implanted within the body of a patient, wherein the joint endoprosthesis system includes a first prosthetic component affixed to one bone of the joint of the patient and a second prosthetic component affixed to another bone of the joint of the patient, wherein at least one of the prosthetic components includes a sensor, a counter and a transmitter and wherein the other prosthetic component includes an electromagnetic field source, and wherein the first and second prosthetic components are movable through a plurality of positions, the method comprising the steps of:

generating a signal each time the first and second prosthetic components are in a predetermined position;

storing an incremental count of the number of signals generated, wherein the count is stored in the counter within the patient's body;

converting the incremental count stored into a transmittable signal, wherein the count is converted within the patient's body;

transmitting the transmittable signal to a Position outside of the patient's body; and

determining the incremental count outside of the patient's body.