Method of estimating soft tissue balance for knee arthroplasty

A method of performing an arthroplasty procedure on a patient's knee joint of a leg, the knee joint including a femur, a tibia, and soft tissue, the method comprising the steps of:

• obtaining preoperatively a first image of the knee joint in an unloaded state and a second image of the knee joint in a loaded state, the unloaded state including no weight being applied to the tibia by the leg of the patient being laid down, and the loaded state including weight being applied to the tibia, the first image and the second image being at least one of MRI, CT and X-ray of the knee joint;
• measuring preoperatively at least a distance between at least a first tibial anatomic feature and a first femoral anatomic feature of the knee joint in the first image;
• measuring preoperatively at least a distance between at least the first tibial anatomic feature and the first femoral anatomic feature in the second image;
• evaluating preoperatively a difference by comparing with image processing of a computer at least the measured distances of the first image and the second image, the difference being representative of laxity of the knee joint;
• and
• designing preoperatively a digital model of a patient-specific cut guide that is contoured three-dimensionally to fit against one of the femur and the tibia and configured to guide a cutting tool to a desired resection depth based on the laxity of the knee joint evaluated during the evaluating step, the patient-specific cut guide adapted to be used to resect at least one of the femur and the tibia with the cutting tool guided by the patient-specific cut guide and into one of the femur and the tibia.