Determining a range of motion of an artificial knee joint

A non-transitory computer readable medium on which is stored software which, when implemented by a processor of a medical navigation system, causes the processor to perform steps of:

• determining, by the processor of the medical navigation system, for one or more flexion angles of a knee joint of a patient:
• a first relative position of a tibia and a femur of the patient when the knee joint is under varus stress;
• and
• a second relative position of the tibia and the femur when the knee joint is under valgus stress;
• wherein the first and second relative positions are further determined when lateral and medial ligaments of the knee joint are stretched to their maximum lengths, respectively;
• determining, by the processor of the medical navigation system, a range of motion including the first and second relative positions;
• and
• outputting, by the processor of the medical navigation system, to a user the range of motion for each of the one or more flexion angles.

A system to assist in knee arthroplasty, the system comprising:

• a device that determines for one or more flexion angles of a knee joint of a patient:
• a first relative position of a tibia and a femur of the patient when the knee joint is under varus stress;
• and
• a second relative position of the tibia and the femur when the knee joint is under valgus stress;
• wherein the device further determines the first and second relative positions when lateral and medial ligaments of the knee joint are stretched to their maximum lengths, respectively;
• and
• a medical navigation system comprising:
• a processor that determines a range of motion including the first and second relative positions;
• and
• a display which displays the range of motion for each of the one or more flexion angles.

A method to assist in knee arthroplasty using a medical navigation system, the method comprising:

• determining for one or more flexion angles of a knee joint of a patient:
• a first relative position of a tibia and a femur of the patient when the knee joint is under varus stress;
• and
• a second relative position of the tibia and the femur when the knee joint is under valgus stress;
• generating, by the medical navigation system, one or more transformation matrices representing one or more of the first or second relative positions;
• determining, by the medical navigation system, a range of motion including the first and second relative positions using the one or more transformation matrices;
• and
• outputting, by the medical navigation system, to a user the range of motion for each of the one or more flexion angles.

A non-transitory computer readable medium on which is stored software which, when implemented by a processor of a medical navigation system, causes the processor to perform steps of:

• determining, by the processor of the medical navigation system, for one or more flexion angles of a knee joint of a patient:
• a first relative position of a tibia and a femur of the patient when the knee joint is under varus stress;
• and
• a second relative position of the tibia and the femur when the knee joint is under valgus stress;
• wherein the first and second relative positions represent maximum varus and valgus angles, respectively;
• determining, by the processor of the medical navigation system, the maximum varus and valgus angles using a surface model of the femur in which at least one of a lateral condyle or a medial condyle of the femur is modelled;
• determining, by the processor of the medical navigation system, a range of motion including the first and second relative positions;
• outputting, by the processor of the medical navigation system, to a user the range of motion for each of the one or more flexion angles.

A non-transitory computer readable medium on which is stored software which, when implemented by a processor of a medical navigation system, causes the processor to perform steps of:

• determining, by the processor of the medical navigation system, for one or more flexion angles of a knee joint of a patient:
• a first relative position of a tibia and a femur of the patient when the knee joint is under varus stress;
• and
• a second relative position of the tibia and the femur when the knee joint is under valgus stress;
• generating a first length of the lateral ligament or a second length of the medial ligament from one or more transformation matrices;
• determining, by the processor of the medical navigation system, a range of motion including the first and second relative positions using the one or more transformational matrices;
• outputting, by the processor of the medical navigation system, to a user the range of motion for each of the one or more flexion angles.

A system to assist in knee arthroplasty, the system comprising:

• a device that determines for one or more flexion angles of a knee joint of a patient:
• a first relative position of a tibia and a femur of the patient when the knee joint is under varus stress;
• and
• a second relative position of the tibia and the femur when the knee joint is under valgus stress;
• wherein the device further determines first and second fully stretched lengths of lateral and medial ligaments, respectively, perpendicular to a tibial cutting plane;
• and
• a medical navigation system comprising:
• a processor that determines a range of motion including the first and second relative positions;
• and
• a display which displays the range of motion for each of the one or more flexion angles.