Unicondylar knee implants and insertion methods therefor

Abstract

A method of balancing extension and flexion gaps in a knee joint includes preparing a tibial component seating surface at a proximal end of a tibia, extending the knee joint and measuring an extension gap between the tibial component seating surface and a distal end of a femur, and flexing the knee joint and measuring a flexion gap between the tibial component seating surface and a posterior region of the femur. The extension gap is compared with the flexion gap to determine an amount of bone that is to be removed from the posterior region of the femur for balancing the extension gap with the flexion gap.

1 . A method of balancing extension and flexion gaps in a knee joint comprising:
 preparing a tibial component seating surface at a proximal end of a tibia;   extending said knee joint and measuring an extension gap between the tibial component seating surface and a distal end of a femur;   flexing said knee joint and measuring a flexion gap between the tibial component seating surface and a posterior region of said femur;   comparing the extension gap with the flexion gap to determine an amount of bone that is to be removed from the posterior region of said femur for balancing the extension gap with the flexion gap.   
   
   
       2 . The method as claimed in  claim 1 , further comprising:
 removing a predetermined amount of bone from the posterior region of said femur if the extension gap equals the flexion gap;   removing less than the predetermined amount of bone from the posterior region of said femur if the extension gap is smaller than the flexion gap; and   removing more than the predetermined amount of bone from the posterior region of said femur if the extension gap is larger than the flexion gap.   
   
   
       3 . The method as claimed in  claim 2 , further comprising preparing a femoral component seating surface by removing bone from both the distal end of said femur and the posterior region of said femur, wherein preparation of the distal end of said femur is finalized before preparation of the posterior region of said femur is finalized. 
   
   
       4 . The method as claimed in  claim 1 , further comprising:
 providing a combination bur template and spacer block including a bur template for guiding removal of bone from the distal end of said femur and a spacer block extending from the lower end of said bur template; and   inserting said spacer block into said knee joint.   
   
   
       5 . The method as claimed in  claim 4 , wherein said bur template abuts against the distal end of said femur when said spacer block is fully inserted into said knee joint. 
   
   
       6 . The method as claimed in  claim 4 , wherein said bur template has an upper end, a lower end and a curved inner surface extending between the upper and lower ends thereof, and said spacer block extends from the lower end of said bur template, said spacer block having a top surface, a bottom surface, a leading end for insertion into a knee joint and a trailing end spaced from the leading end and adjacent the lower end of said bur template, wherein the trailing end of said spacer block includes an opening with an alignment feature that extends from the trailing end of said spacer block toward the leading end of said spacer block. 
   
   
       7 . The method as claimed in  claim 6 , wherein after insertion of said spacer block into said knee joint the top surface of said spacer block faces said femur and the bottom surface of said spacer block faces said tibia. 
   
   
       8 . The method as claimed in  claim 6 , further comprising:
 providing a posterior resection guide locator including an alignment rail; and   inserting said alignment rail into the opening at the trailing end of said spacer block.   
   
   
       9 . The method as claimed in  claim 8 , wherein the alignment rail is adapted to engage the alignment feature in the opening of said spacer block. 
   
   
       10 . The method as claimed in  claim 9 , wherein the alignment rail comprises an elongated projection and the alignment feature on said spacer block comprises an elongated groove that receives the elongated projection. 
   
   
       11 . The method as claimed in  claim 10 , wherein said posterior resection guide locator includes an alignment pin guide overlying said alignment rail, wherein said alignment pin guide includes at least one pin opening extending therethrough. 
   
   
       12 . The method as claimed in  claim 11 , wherein said bur template includes a guide rail extending around an outer perimeter thereof and a central opening surrounded by the guide rail, the method further comprising aligning said at least one pin opening of said alignment pin guide with the central opening when said alignment rail is inserted into the opening of said spacer block. 
   
   
       13 . The method as claimed in  claim 12 , further comprising inserting an alignment pin into the at least one pin opening of said alignment pin guide. 
   
   
       14 . The method as claimed in  claim 13 , further comprising:
 providing a posterior resection guide including an upper end, a lower end having a surface for guiding a cutting tool and a pin opening between the upper and lower ends; and   sliding the pin opening of said posterior resection guide over the alignment pin.   
   
   
       15 . The method as claimed in  claim 14 , wherein the pin opening includes a first set of pin openings and a second set of pin openings that is closer to the upper end of said posterior resection guide than the first set of pin openings. 
   
   
       16 . The method as claimed in  claim 15 , wherein the pin opening includes a third set of pin openings that is closer to the lower end of said posterior resection guide than the first set of pin openings. 
   
   
       17 . A method of preparing a knee joint for receiving a unicondylar knee implant comprising:
 preparing a tibial component seating surface at a proximal end of a tibia;   extending said knee joint and measuring an extension gap between the tibial component seating surface and a distal end of a femur;   flexing said knee joint and measuring a flexion gap between the tibial component seating surface and a posterior region of said femur;   comparing the extension gap with the flexion gap to determine an amount of bone that is to be removed from the posterior region of said femur for balancing the extension gap with the flexion gap;   providing a combination bur template and spacer block, said bur template having an upper end, a lower end and a curved surface extending between the upper and lower ends thereof that is adapted to conform to a femoral condyle of a femur and said spacer block extending from the lower end of said bur template and having top and bottom surfaces.   
   
   
       18 . The method as claimed in  claim 17 , further comprising placing a shim on the top surface of said spacer block if the flexion gap is greater than the extension gap. 
   
   
       19 . The method as claimed in  claim 18 , further comprising:
 flexing said knee joint so that said prepared first seating surface at the proximal end of said tibia opposes a posterior region of said femoral condyle;   inserting said spacer block and said shim into said knee joint so that the top surface of said spacer block engages the posterior region of said femoral condyle and said shim over the bottom surface of said spacer block engages the first seating surface at the proximal end of said tibia;   while maintaining said spacer block and said shim between said femur and said tibia, extending said knee joint until the curved surface of said bur template engages a distal region of said femoral condyle;   anchoring said bur template to the distal region of said femoral condyle and using said bur template to guide burring of the distal region of said femoral condyle for preparing a second seating surface on said femur;   after burring the distal region of said femoral condyle, resecting the posterior region of said femoral condyle.   
   
   
       20 . The method as claimed in  claim 17 , wherein if the flexion gap equals the extension gap the method further comprises:
 flexing said knee joint so that said prepared first seating surface at the proximal end of said tibia opposes a posterior region of said femoral condyle;   inserting said combination bur template and spacer block into said knee joint so that the top surface of said spacer block engages the posterior region of said femoral condyle and the bottom surface of said spacer block engages the first seating surface at the proximal end of said tibia;   while maintaining said spacer block between said femur and said tibia, extending said knee joint until the curved surface of said bur template engages a distal region of said femoral condyle;   anchoring said bur template to the distal region of said femoral condyle and using said bur template to guide burring of the distal region of said femoral condyle for preparing a second seating surface on said femur;   after burring the distal region of said femoral condyle, resecting the posterior region of said femoral condyle.