Patent ID: 7347874
Filing Date: 2008-03-25
Classification: A61B,A61F,Y10S

Abstract:
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.