Tensioner-balancer for knee joint

1. A knee gap tensioning apparatus, comprising:

a tensioner-balancer, including:

a baseplate;

a top plate; and

a linkage interconnecting the baseplate and the top plate and operable to move the top plate relative to the bottom plate between retracted and extended positions in response to application of an actuating force, the linkage including:

a first toggle linkage, including:

a lower link having a first end and a second end, the first end pivotally connected to the baseplate;

an upper link having a first end and a second end, the first end pivotally connected to the top plate, wherein the second ends of the first and second links are pivotally connected to each other;

a second toggle linkage, including:

a lower link having a first end and a second end, the first end pivotally connected to the baseplate;

an upper link having a first end and a second end, the first end pivotally connected to the top plate, wherein the second ends of the first and second links are pivotally connected to each other;

a connector linkage interconnecting the first and second toggle linkages;

wherein the links of the linkage comprise parallel pivot axes;

wherein the linkage is configured so as to produce linear movement of the top plate relative to the base plate, in response to a rotational movement of one or more of the links;

wherein the linkage includes an input shaft coupled to the linkage and configured to accept a rotary input about an axis parallel to the parallel pivot axes of the links of the linkage; and

at least one sensor operable to measure a distraction load applied by the tensioner-balancer.

2. The apparatus of claim 1 , wherein the top plate is pivotally connected to the linkage so as to be able to freely pivot about a single mechanical pivot axis to change its angular orientation relative to the base plate.

3. The apparatus of claim 1 , wherein a distraction height of the tensioner-balancer defined as distance between a tibia interface surface of the baseplate and a femoral interface surface of the top plate, in the extended position, is in a range of 8 mm to 20 mm.

4. The apparatus of claim 1 , wherein the at least one sensor is configured to measure an input torque to the tensioner-balancer.

5. The apparatus of claim 1 , wherein the at least one sensor comprises a stress or strain transducer disposed on the top plate.

6. The apparatus of claim 1 , wherein the at least one sensor comprises a stress or strain transducer disposed on at least one of the links.

7. The apparatus of claim 1 , wherein the at least one sensor is configured to measure a distraction load on left and right portions of the top plate separately.

8. The apparatus of claim 7 , wherein the at least one sensor comprises an array of electronic force sensors.

9. The apparatus of claim 1 , further comprising at least one sensor configured to measure a tilt angle of the top plate.

10. The apparatus of claim 9 , wherein the at least one sensor configured to measure a tilt angle of the top plate comprises a rotary position sensor that pivots with the top plate.

11. The apparatus of claim 9 , wherein the at least one sensor configured to measure a tilt angle of the top plate comprises a linkage that moves dependent on the angle of the top plate, independent of a separation distance between the baseplate and the top plate.

12. The apparatus of claim 1 , further comprising: an actuating instrument including an interface complementary to an interface of the tensioner-balancer and a powered mechanism operable to apply the actuating force to the tensioner-balancer.

13. The apparatus of claim 12 , wherein the powered mechanism comprises a motor and a gearbox.

14. The apparatus of claim 13 , wherein the gearbox comprises a multi-stage planetary gearset.