In vivo joint space measurement device and method

A method of determining a dimension of a joint space in the body of a patient wherein the patient has a joint endoprosthesis that includes a first prosthetic component and a bearing occupying the joint space adjacent the first prosthetic component, the method comprising:

• generating a voltage within the patient's body that has a characteristic that relates to a dimension of the joint space;
• modulating the voltage within the patient's body to produce a transmitter signal;
• transmitting the transmitter signal from within the patient's body to a location outside of the patient's body, wherein the transmitted signal has a characteristic that relates to the characteristic of the voltage;
• determining a dimension of the joint space based on the value of the characteristic of the transmitter signal.

A method of determining a change in a dimension of a joint space in the body of a patient wherein the patient has a joint endoprosthesis that includes a first prosthetic component and a bearing occupying the joint space adjacent the first prosthetic component, the method comprising:

• generating a first signal from one side of the joint space at a first location within the patient's body;
• receiving the first signal on the opposite side of the joint space at a second location within the patient's body;
• producing a voltage within the patient's body, where the magnitude of the voltage depends upon a characteristic of the first signal;
• modulating the voltage within the patient's body to produce a transmitter signal a characteristic of which depends upon the magnitude of the voltage produced;
• transmitting the transmitter signal from within the patient's body to an external location;
• determining the extent of change in a dimension of the joint space based on said characteristic of the transmitter signal.

A joint endoprosthesis system for use in a joint comprising two bones interfacing at a joint articulation in a patient's body, the joint endoprosthesis system comprising:

• a first prosthetic component;
• a second prosthetic component;
• a bearing having a bearing surface to be placed against the first prosthetic component and a second surface facing the second prosthetic component, the interface of the first prosthetic component and the bearing surface of the bearing defining a joint articulation;
• a magnet affixed within one of the prosthetic components;
• a sensor affixed within the other prosthetic component, the sensor being capable of sensing a property of the magnetic field of the magnet and producing a voltage the magnitude of which depends upon the sensed property of the magnetic field;
• and a modulator received within one of the prosthetic components and connected to receive the voltage produced by the sensor, the modulator being capable of producing a signal having a characteristic that varies depending on the voltage received from the sensor and that is capable of being transmitted from within the patient's body to a location outside of the patient's body.

A joint endoprosthesis system for use in a joint comprising two bones interfacing at a joint articulation in a patient's body, the joint endoprosthesis system comprising:

• a first prosthetic component;
• a second prosthetic component;
• a bearing having a bearing surface to be placed against the first prosthetic component and an opposite surface to face the second prosthetic component, the interface of the first prosthetic component and the bearing surface of the bearing defining a joint articulation;
• a magnet affixed to one of the prosthetic components;
• and an external cuff separate from the first prosthetic component, second prosthetic component and bearing, the external cuff including a sensor to be maintained outside of the patient's body, the sensor being capable of sensing a property of the magnetic field of the magnet.