Knee flexion and extension gap tensioning and measuring method

1. A method for balancing extension and flexion gaps between the tibia and the femur of a knee joint, comprising:

making a tibial cut along the first cutting plane to cut away a proximal portion of the tibia, and making a distal femoral cut along a second cutting plane to cut away a distal portion of the femur, such that an extension gap is defined between the first and second cutting planes;

positioning the knee joint in extension and inserting a gap tensioner into the extension gap, the gap tensioner including:

a baseplate;

a top plate;

a linkage interconnecting the baseplate and the top plate and operable to move the gap tensioner between retracted and extended positions; and

wherein the top plate is pivotally connected to the linkage so as to be able to freely pivot about a pivot axis;

actuating the linkage to move the gap tensioner towards the extended position, so as to urge the tibia and the femur apart and apply tension to the medial and lateral collateral ligaments of the knee joint; and

determining an adjustment required to bring the first and second cutting planes into a desired angular orientation relative to each other;

positioning the knee joint in flexion, thereby defining a flexion gap between the femur and the tibia;

positioning the gap tensioner into the flexion gap and actuating the linkage to move the gap tensioner towards the extended position, so as to urge the tibia and the femur apart and apply tension to the medial and lateral collateral ligaments of the knee joint; and

determining a third cutting plane to be used for a posterior cut on the femur which will result in the first and third cutting planes being substantially parallel in at least one axis;

removing the gap tensioner; and

making the posterior cut along the third cutting plane.

2. The method of claim 1 further comprising selectively augmenting or releasing at least one of the medial and lateral collateral ligaments.

3. The method of claim 2 wherein the selective augmentation or release occurs prior to determining the third cutting plane.

4. The method of claim 1 further comprising using the gap tensioner to make real-time measurements of gap distance, angle, and separating force during ligament tension augmentation or reduction.

5. The method of claim 1 wherein the second cutting plane is altered by making at least one bone resection cut.

6. The method of claim 1 wherein the patella and patellar tendon of the knee joint are disposed in a normal anatomical position.

7. The method of 1 further comprising the addition of an implantable tensile member to augment a tensile force between the femur and tibia.

8. The method of claim 7 wherein the step of determining the third cutting plane is carried out by:

connecting a marking attachment to the gap tensioner, the marking attachment including a marking implement positioned to define a line parallel to the first cutting plane; and

using the marking implement to make one or more marks on the femur.

9. The method of claim 8 further comprising attaching a cutter guide block to the femur in a predetermined position relative to the marks made by the marking implement, wherein the cutter guide block includes a posterior cut guide surface having a predetermined angular alignment relative to the first cutting plane.

10. A method of measuring alignment of a human knee joint which includes a femur bone, a tibia bone, a patella bone, a patellar tendon, and ligaments, wherein the ligaments and patellar tendon are under anatomical tension to connect the femur and tibia together, creating a load-bearing articulating joint; the method comprising:

providing a gap tensioning apparatus including:

a gap tensioner including:

a baseplate;

a top plate;

a linkage interconnecting the baseplate and the top plate and operable to move the gap tensioner between retracted and extended positions; and

wherein the top plate is pivotally connected to the linkage so as to be able to freely pivot about a pivot axis;

inserting the gap tensioner between the tibia and the femur, with the gap tensioner in the retracted position;

actuating the linkage to move the gap tensioner towards the extended position, so as to urge the tibia and the femur apart and apply tension to the medial and lateral collateral ligaments of the knee joint;

associating at least two tracking markers with the knee joint;

providing an electronic receiving device, wherein the receiving device is operable in combination with the tracking markers to determine a position and orientation of each of the tracking markers relative to the electronic receiving device;

moving the knee joint through at least a portion of its range of motion;

while moving the knee joint, collecting position data from the tracking markers; and

processing the collected position data to compute an origin of motion of the knee joint.

11. The method of claim 10 further comprising carrying out a surgical correction of the knee joint with reference to the computed origin of motion.

12. The method of claim 11 wherein the origin of motion is an instantaneous axis of rotation of the knee joint, and the surgical correction comprises implanting an end of a tensile member with reference to the computed origin of motion.

13. The method of claim 10 further comprising:

moving the knee joint to flexion;

moving the leg laterally so as to produce rotation thereof; and

wherein the origin of motion is an axis passing through the talus joint and the femoral head.

14. The method of claim 13 wherein at least one of the tracking markers comprises a C-shaped clip coupled to a talus joint.

15. The method of claim 10 further comprising measuring a relative position of the tracking markers to determine a varus/valgus angle of the knee joint.

16. The method of claim 10 wherein one of the tracking markers is contained in the gap tensioner.

17. The method of claim 10 wherein one of the tracking marks is contained in an actuating instrument coupled to the gap tensioner.