Apparatus and method of ligament balancing and component fit check in total knee arthroplasty

Apparatus for determining the kinematics of a large joint undergoing arthroplasty, for comparing the kinematics of the joint with trial prosthetic joint components fitted to resected bone surfaces of the joint with the kinematics of a normal joint, and for providing the surgeon with information allowing the balancing of the ligaments of the joint with a prosthesis joint in place, said apparatus including a plurality of optical targets mounted on said trial joint replacement components fitted to the resected bone surfaces of the joint, the position and orientation of each of said targets being known with respect to its respective said trial component such that by knowing the position and orientation of said targets of said respective trial components the position and orientation of said trial components is known, one or more video cameras, said one or more cameras being positioned with respect to said joint such that as the joint is flexed, extended and rotated by the surgeon said targets are within the field of view of said one or more cameras, said one or more cameras obtaining a series of images of the optical targets as the joint is flexed, extended, and rotated, a computer responsive to the images of the targets for determining the position and orientation of the targets and hence of the trial components with respect to said one or more cameras, said computer determining the position and orientation of said trial components with respect to one another as the knee is flexed, extended and rotated thereby enabling the determination of the kinematics of the joint, said computer comparing the kinematics of the observed joint with the kinematics of a normal joint and determining, based on anomalies of the observed joint relative to the normal joint, which ligaments must be relaxed or contracted so that with the prosthesis joint installed the ligaments are balanced, said computer displaying suggestions to the surgeon for relaxing or contracting specific ligaments so that the ligaments may be balanced.

Apparatus for determining the kinematics of prosthesis joint components relative to one another and relative to a normal joint during joint replacement surgery to aid the surgeon in fitting joint components to the resected bones of the joint undergoing surgery and to aid the surgeon in balancing the ligaments of the joint after a prosthesis joint has been installed, said apparatus comprising:

• a. a first set of optical targets mounted to a first trial joint component fitted to a first resected bone of the joint, said first set of optical targets being in a predetermined geometrical relationship with respect to said first trial joint component;
• b. a second set of optical targets mounted to a second trial joint component fitted to a second resected bone of the joint, said second set of optical targets being in a predetermined geometrical position with respect to said second trial joint component;
• c. a video camera disposed to receive images of said first optical targets and said second optical targets, said video camera having a field of view, said first and second sets of targets being within said field of view as the joint is flexed, extended and rotated;
• d. a computer operatively connected to said camera, said computer being responsive to the images of said first and second sets of targets to determine values of the position and orientation of said trial joint replacement components in space and with respect to one another and to determine the kinematics of the trial joint components relative to one another as the joint is extended, flexed and rotated;
• and
• e. said computer displaying information to the surgeon relating to the balancing of the ligaments of the joint.

A method of balancing the ligaments of the knee during total knee arthroplasty comprising the steps of:

• a. resecting the distal end of the femur so as to receive a femoral prosthesis implant;
• b. resecting the proximal end of the tibia so as to receive a tibial prosthesis implant:
• c. fitting trial implant components to the resected ends of the femur and tibia, said trial components having a plurality of optical targets affixed thereto with the location of the targets for each trial component being known;
• d. manipulating the extremity in flexion, extension and rotation;
• e. viewing said optical targets on said trial components with an video camera as said extremity is manipulated;
• f. determining the position and orientation of the targets with respect to said camera;
• g. determining the position and orientation of said trial components with respect to one another so that the kinematics of the trial components relative to one another may be determined;
• h. identifying anomalies between the observed kinematics of the trial components as the extremity is manipulated which result from an unbalance of the ligaments of the knee;
• and
• i. suggesting to the surgeon which of the ligaments of the knee should be adjusted either by relaxing or contracting such ligaments such that upon installation of the prosthesis components the ligaments of the knee are balanced.