US20080015600A1 - Unicondylar knee implants and insertion methods therefor - Google Patents

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.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• The present application is a continuation of U.S. patent application Ser. No. 11/471,931, filed Jun. 21, 2006, the disclosure of which is hereby incorporated by reference herein. The present application is related to U.S. patent application Ser. No. 11/504,420, filed Aug. 15, 2006, entitled “Unicondylar Knee Implants and Insertion Methods Therefor” and U.S. patent application Ser. No. 11/519,691, filed Sep. 7, 2006, entitled “Unicondylar Knee Implants and Insertion Methods Therefor”, the disclosures of which are hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
• The present invention generally relates to implants and more specifically relates to method and apparatus for preparing bone for receiving an implant.
• The use of prosthetic implants to replace damaged natural joints, or portions of such joints, in the body has become widespread as medical and technological advances have joined to provide improved materials and configurations for prosthetic implants and innovative procedures for implanting these devices. The basic objective of such devices and procedures is to provide a repaired joint of maximum effectiveness, with a minimal intrusion into the body. Component parts of these prosthetic implants are utilized to replace portions of a natural joint which have become damaged, either through injury or disease, and it is usually necessary to remove portions of the natural joint beyond merely the damaged portions in order to enable stable and secure fixation of the component parts to the natural bone. In addition, access to damaged joints is limited and the necessity for reaching the areas to be worked upon can affect the extent of intrusion required to complete an effective implant.
• Improved methods for implanting a prosthetic device are disclosed in commonly assigned U.S. Pat. No. 6,554,838, the disclosure of which is hereby incorporated by reference herein. In certain preferred embodiments of the '838 patent, a method for preparing a seating surface for an implant includes positioning a guide on bone, the guide having a guide slot following a path geometrically similar to the peripheral boundary of the seating surface, inserting a cutting device through the guide slot at any selected location along the path of the guide slot, and translating the cutting device along the guide slot to cut an outline groove in the bone coincident with the peripheral boundary of the seating surface. The guide is removed from the bone, and portions of the bone lying within the area delineated by the outline groove are removed to establish the seating surface. The methods disclosed in the '838 patent provide numerous advantages including minimizing the amount of natural bone that must be removed and attaining accuracy in the delineation of the area, depth and contour configuration of the prepared surfaces of the bone that will receive the implant
• In spite of the above advances, there remains a need for improved methods and apparatus for preparing bone for receiving implants and implanting the prosthetic devices.
SUMMARY OF THE INVENTION
• In certain preferred embodiments of the present invention, 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, flexing the knee joint and measuring a flexion gap between the tibial component seating surface and a posterior region of the femur, and comparing the extension gap 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.
• The method desirably includes the steps of removing a predetermined amount of bone (e.g.6mm) from the posterior region of the femur if the extension gap equals the flexion gap, removing less than the predetermined amount of bone from the posterior region of the 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 the femur if the extension gap is larger than the flexion gap.
• The method also preferably include preparing a femoral component seating surface by removing bone from both the distal end of the femur and the posterior region of the femur, wherein preparation of the distal end of the femur is finalized before preparation of the posterior region of the femur is finalized.
• In certain preferred embodiments, the method includes providing a combination bur template and spacer block including a bur template for guiding removal of bone from the distal end of the femur and a spacer block extending from the lower end of the bur template, and inserting the spacer block into the knee joint. The bur template preferably abuts against the distal end of the femur when the spacer block is fully inserted into the knee joint. The bur template desirably has an upper end, a lower end and a curved inner surface extending between the upper and lower ends thereof, and the spacer block desirably extends from the lower end of the bur template, the 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 the bur template. The trailing end of the spacer block preferably includes an opening with an alignment feature that extends from the trailing end of the spacer block toward the leading end of said spacer block. After insertion of the spacer block into the knee joint, the top surface of the spacer block faces the femur and the bottom surface of the spacer block faces the tibia.
• In certain preferred embodiments of the present invention, the method includes providing a posterior resection guide locator including an alignment rail, and inserting the alignment rail into the opening at the trailing end of the spacer block. The alignment rail is preferably adapted to engage the alignment feature in the opening of the spacer block. The alignment rail desirably has an elongated projection and the alignment feature on the spacer block has an elongated groove that receives the elongated projection.
• The posterior resection guide locator may include an alignment pin guide overlying the alignment rail, whereby the alignment pin guide includes at least one pin opening extending therethrough. The bur template desirably includes a guide rail extending around an outer perimeter thereof and a central opening surrounded by the guide rail.
• The method may also include aligning the at least one pin opening of the alignment pin guide with the central opening when the alignment rail is inserted into the opening of the spacer block, and inserting an alignment pin into the at least one pin opening of the alignment pin guide. The method may include 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 the posterior resection guide over the alignment pin.
• In certain preferred embodiments, the pin opening in the posterior resection guide includes a first set of pin openings and a second set of pin openings that is closer to the upper end of the posterior resection guide than the first set of pin openings. The pin opening may also include a third set of pin openings that is closer to the lower end of the posterior resection guide than the first set of pin openings.
• In another preferred embodiment of the present invention, a method of preparing a knee joint for receiving a unicondylar knee implant 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 method preferably includes comparing the extension gap 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, and providing a combination bur template and spacer block, the 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 the spacer block extending from the lower end of the bur template and having top and bottom surfaces.
• In certain preferred embodiments, the method preferably includes placing a shim on the top surface of the spacer block if the flexion gap is greater than the extension gap, and flexing the knee joint so that the prepared first seating surface at the proximal end of the tibia opposes a posterior region of the femoral condyle. The method desirably includes inserting the spacer block and the shim into the knee joint so that the top surface of the spacer block engages the posterior region of the femoral condyle and the shim over the bottom surface of the spacer block engages the first seating surface at the proximal end of the tibia. While maintaining the spacer block and the shim between the femur and the tibia, the knee joint is extended until the curved surface of the bur template engages a distal region of the femoral condyle. The bur template is preferably anchored to the distal region of the femoral condyle and the bur template is used to guide burring of the distal region of the femoral condyle for preparing a second seating surface on the femur. After the distal region of the femoral condyle is burred, the posterior region of the femoral condyle is resected.
• In other preferred embodiments, a shim is placed over the bottom surface of the said spacer block if the flexion gap is less than the extension gap. In these preferred embodiments, the knee joint is flexed so that the prepared first seating surface at the proximal end of the tibia opposes a posterior region of the femoral condyle, and the spacer block and the shim are inserted into the knee joint so that the shim over the top surface of the spacer block engages the posterior region of the femoral condyle and the bottom surface of the spacer block engages the first seating surface at the proximal end of the tibia. While the shim and the spacer block are maintained between the femur and the tibia, the knee joint is extended until the curved surface of the bur template engages a distal region of the femoral condyle. The bur template is preferably anchored to the distal region of the femoral condyle and the bur template is used to guide burring of the distal region of the femoral condyle for preparing a second seating surface on the femur. After burring the distal region of the femoral condyle, the posterior region of the femoral condyle is resected.
• In still other preferred embodiments of the present invention, if the flexion gap equals the extension gap, the method include flexing the knee joint so that the prepared first seating surface at the proximal end of the tibia opposes a posterior region of the femoral condyle, inserting the combination bur template and spacer block into the knee joint so that the top surface of the spacer block engages the posterior region of the femoral condyle and the bottom surface of the spacer block engages the first seating surface at the proximal end of the tibia. While maintaining the spacer block between the femur and the tibia, the knee joint is preferably extended until the curved surface of the bur template engages a distal region of the femoral condyle. The bur template is preferably anchored to the distal region of the femoral condyle and the bur template is used to guide burring of the distal region of the femoral condyle for preparing a second seating surface on the femur. After burring the distal region of the femoral condyle, the posterior region of the femoral condyle is resected.
• In other preferred embodiments of the present invention, a method of preparing a knee joint for receiving a unicondylar knee implant includes preparing a first seating surface at a proximal end of a tibia such as by resecting the proximal end of the tibia. The method desirably includes providing a combination bur template and spacer block. The bur template and spacer block are preferably integrally connected together. In certain preferred embodiments, the bur template and the spacer block are permanently connected together. The bur template and the spacer block desirably form a single, rigid element. The bur template preferably has 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 the spacer block extends from the lower end of the bur template and has top and bottom surfaces.
• The method desirably includes flexing the knee joint so that the prepared first seating surface at the proximal end of the tibia opposes a posterior region of the femur. The combination bur template and spacer block may be inserted into the knee joint so that the top surface of the spacer block engages the posterior region of the femur and the bottom surface of the spacer block engages the first seating surface at the proximal end of the tibia. While the spacer block is maintained between the femur and the tibia, the knee joint is extended until the curved surface of the bur template engages the femoral condyle of the femur. The bur template may be anchored to the femur, such as by using pins. The bur template is preferably used for guiding burring of the femoral condyle for preparing a second seating surface on the femur. After burring the femoral condyle of the femur, the posterior region of the femur is desirably resected.
• The method may also include determining a distance between the first seating surface on the tibia and the posterior region of the femur, and selecting one of a plurality of combination bur template and spacer blocks for inserting into the knee joint. The spacer block of the selected bur template preferably has a thickness that matches the determined distance between the first seating surface on the tibia and the posterior region of said femur. In certain preferred embodiments, the thickness of the spacer block preferably corresponds to the thickness of a prosthetic device placed in the gap between the first seating surface on the tibia and the posterior region of the femur. The combination bur template and spacer block desirably includes an alignment feature. In certain preferred embodiments, the alignment feature is formed at a trailing end of the spacer block.
• The method may also include inserting an alignment rail of a posterior resection guide locator into the alignment feature formed in the trailing end of the spacer block. The posterior resection guide locator desirably includes at least one pin opening that overlies the alignment rail. When the alignment rail is inserted into the alignment feature formed in the spacer block, the at least one pin opening of the posterior resection guide locator is preferably aligned with an opening of the bur template. A pin may be inserted through the at least one pin opening, through the opening in the bur template and anchored in the femur. In other preferred embodiments, two or more pins are inserted through two or more respective pin openings in the posterior resection guide locator.
• The method may also include disengaging the posterior resection guide locator from engagement with the combination bur template and spacer guide and sliding a posterior resection guide over said at least one pin in said femur.
• In other preferred embodiments of the present invention, a method of preparing seating surfaces in a knee joint for receiving a unicondylar knee implant includes preparing a first seating surface for receiving a tibial component at a proximal end of a tibia, flexing the knee joint so that the first seating surface opposes a posterior region of the femoral condyle, and providing a combination bur template and spacer block. The bur template preferably has a curved surface extending between upper and lower ends thereof and the spacer block desirably extends from the lower end of the bur template. The spacer block is preferably inserted into the knee joint so that the spacer block engages the posterior region of the femoral condyle and the first seating surface on the tibia. While the spacer block is maintained between the femur and the tibia, the knee joint is desirably extended until the curved surface of the bur template engages a distal region of the femoral condyle.
• The method may include using the bur template to guide burring of the distal region of the femoral condyle for preparing a second seating surface for receiving a femoral component. After the second seating surface has been prepared, one or more alignment pins may be anchored in the femoral bone at the second seating surface. The one or more alignment pins anchored in the femoral bone may be used for aligning a posterior resection guide with the posterior region of the femoral condyle. The posterior resection guide preferably has a slot for guiding a cutting instrument. The posterior resection guide is desirably used for resecting the posterior section of the femur.
• In other preferred embodiments of the present invention, a kit for preparing a knee joint for receiving a unicondylar knee implant includes a combination bur template and spacer block having a bur template with an upper end, a lower end and a curved inner surface extending between the upper and lower ends thereof, and a spacer block extending from the lower end of said the template. The spacer block may have 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 the bur template. The trailing end of the spacer block preferably includes an opening with an alignment feature that extends from the trailing end of the spacer block toward the leading end of the spacer block.
• The kit may also include a posterior resection guide locator having an alignment rail insertible into the opening at the trailing end of the spacer block. The alignment rail is preferably adapted to mesh with the alignment feature in the opening of the spacer block. In certain preferred embodiments, the alignment rail has an elongated projection and the alignment feature in the spacer block has an elongated groove that receives the elongated projection. In other preferred embodiments, the alignment rail may have an elongated groove and the alignment feature in the spacer block may have an elongated projection that fits into the groove.
• The posterior resection guide locator preferably includes an alignment pin guide overlying the alignment rail. The alignment pin guide desirably includes at least one pin opening extending therethrough.
• The bur template preferably includes a guide rail extending around an outer perimeter thereof and a central opening surrounded by the guide rail. The at least one pin opening of the alignment guide is preferably aligned with the central opening when the alignment rail is inserted into the opening of the spacer block. An alignment pin is insertible into the at least one pin opening of the alignment guide.
• The kit may also include a posterior resection guide having an upper end, a lower end having an elongated opening for receiving a cutting tool and a pin opening between the upper and lower ends. The pin opening of the posterior resection guide is desirably slidable over the alignment pin. The pin opening may include a first set of pin openings and a second set of pin openings that is closer to the upper end of the posterior resection guide than the first set of pin openings. The pin opening may also include a third set of pin openings that is closer to the lower end of the posterior resection guide than the first set of pin openings. As will be described in more detail below, the different sets of pin openings may be used for adjusting the amount of bone resected from the posterior region of the femoral condyle.
• These and other preferred embodiments of the present invention will be described in more detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIGS. 1A-1J show a method of preparing a knee to receive a unicondylar knee implant, in accordance with certain preferred embodiments of the present invention.
• FIG. 2 shows a tibial resection block and a locking element securable thereto, in accordance with certain preferred embodiments of the present invention.
• FIGS. 3A-3D show the tibial resection block ofFIG. 2 secured to a rod, in accordance with certain preferred embodiments of the present invention.
• FIG. 4 shows a saggital resection alignment guide, in accordance with certain preferred embodiments of the present invention.
• FIGS. 5A-5E show a modular handle, in accordance with certain preferred embodiments of the present invention.
• FIGS. 6A-6H show a combination bur template and spacer block, in accordance with certain preferred embodiments of the present invention.
• FIGS. 7A-7D show a shim engageable with the combination bur template and spacer block shown inFIGS. 6A-6H, in accordance with certain preferred embodiments of the present invention.
• FIGS. 8A-8E show an alignment tower, in accordance with preferred embodiments of the present invention.
• FIGS. 9A-9E show a posterior resection guide locator, in accordance with certain preferred embodiments of the present invention.
• FIGS. 10A-10D show a posterior resection guide, in accordance with certain preferred embodiments of the present invention.
• FIGS. 11A-11C show a posterior resection guide, in accordance with other preferred embodiments of the present invention.
• FIGS. 12A-12F show a femoral trial cutting guide, in accordance with certain preferred embodiments of the present invention.
• FIG. 13A shows a handle attachable to the femoral trial cutting guide ofFIGS. 12A-12F, in accordance with certain preferred embodiments of the present invention.
• FIG. 13B shows a drill passable through an opening in the femoral trial cutting guide ofFIGS. 12A-12F and the handle ofFIG. 13A.
• FIGS. 14A-14E show the handle ofFIG. 13A.
• FIGS. 15A-15D show a punch tower for forming keel openings in tibial bone, in accordance with certain preferred embodiments of the present invention.
• FIGS. 16A-16C show the punch tower shown inFIGS. 15A-15D.
• FIGS. 17A-17D show a chisel for use with the punch tower shown inFIGS. 15A-15D.
• FIGS. 18A-18D show a tamp for use with the punch tower shown inFIGS. 15A-15D.
• FIG. 19 shows a tibial template, in accordance with certain preferred embodiments in the present invention.
• FIG. 20 shows a holder for tibial templates having different sizes, in accordance with certain preferred embodiments of the present invention.
• FIGS. 21A-21E show the tibial template ofFIG. 19.
• FIGS. 22A-22D show a spacer for evaluating flexion and extension gaps, in accordance with certain preferred embodiments of the present invention.
• FIGS. 23-32 show a method of resecting a proximal end of a tibia, in accordance with certain preferred embodiments of the present invention.
• FIGS. 33-37 show a method of aligning the combination bur template and spacer block ofFIGS. 6A-6H in a knee joint, in accordance with certain preferred embodiments of the present invention.
• FIG. 38 shows the bur template/spacer block ofFIGS. 6A-6H secured between a tibia and a femur, in accordance with certain preferred embodiments of the present invention.
• FIGS. 39-43 show a method of resecting a posterior region of a femoral condyle, in accordance with certain preferred embodiments of the present invention.
• FIGS. 44-56 show a method of forming a keel opening at the proximal end of a tibia, in accordance with certain preferred embodiments of the present invention.
• FIGS. 57-59 show a method of making openings for a post and a fin of a femoral component, in accordance with certain preferred embodiments of the present invention.
• FIGS. 60-62 show a prior art bur template.
• FIGS. 63A-63B show the spacer ofFIGS. 22A-22D positioned between an extended knee joint.
• FIGS. 64A-64B show the spacer ofFIGS. 22A-22D positioned between a flexed knee joint.
• FIG. 65 shows a gap balancing table, in accordance with certain preferred embodiments of the present invention.
• FIG. 66 shows a saggittal view of a flexed knee joint with a combination bur template and spacer block inserted into the knee joint.
• FIG. 67 shows a posterior resection guide locator coupled with a combination bur template and spacer block, in accordance with certain preferred embodiments of the present invention.
• FIG. 68 shows the posterior resection guide shown inFIGS. 10A-10D.
• FIG. 69 shows the posterior resection guide shown inFIGS. 11A-11C.
• FIGS. 70A and 70B show a method of aligning a knee implant, in accordance with certain preferred embodiments of the present invention.
• FIG. 71 shows a perspective view of a bur template/spacer block and shim engageable therewith, in accordance with certain preferred embodiments of the present invention.
• FIG. 72 shows a perspective view of a bur template/spacer block and shim engageable therewith, in accordance with another preferred embodiment of the present invention.
• FIGS. 73-76 show a method of inserting a femoral component of a knee implant, in accordance with another preferred embodiment of the present invention.
• FIGS. 77A-77B show a femoral component of a knee implant, in accordance with certain preferred embodiments of the present invention.
• FIGS. 78A-78B show a tibial component of a knee implant, in accordance with certain preferred embodiments of the present invention.
• FIG. 79 shows the femoral component ofFIGS. 77A-77B and the tibial component ofFIGS. 78A-78B implanted in a knee joint.
DETAILED DESCRIPTION
• FIGS. 1A-1J show a method of preparing a knee for receiving an implant, in accordance with certain preferred embodiments of the present invention. In particular preferred embodiments, the method is used for preparing a knee to receive a knee implant such as a unicondylar knee implant. Referring toFIG. 1A, a knee joint100 is located between aproximal end102 of atibia104 and adistal end106 of afemur108. Thedistal end106 of thefemur108 includes adistal condyle110, which is the curved surface on a bone where it forms a joint with another bone. Thefemur108 also has a posterior region of the femoral condyle.
• InFIG. 1A, a tibial resection is performed on theproximal end102 of thetibia104.FIG. 1B shows a saggital resection being performed on theproximal end102 of thetibia104.FIG. 1C shows the positioning and alignment of a combination bur template and spacer block in a knee joint. The combination bur template and spacer block includes a spacer block that is inserted into the knee joint between the femur and the tibia and the bur template that guides burring of the condyle at the distal end of the femur. The bur template and spacer block is aligned withfemur108 using an alignment flag, as will be described in more detail below.FIG. 1D shows the bur template/spacer block after it has been positioned in a knee joint. The bur template includes a rail that surrounds a central opening. The rail preferably guides movement of a burring instrument after the burring instrument is passed through the central opening of the bur template.FIG. 1E shows a posterior resection guide locator assembled with the combination bur template and spacer guide and alignment pins extending through pin openings in the posterior resection guide locator.FIG. 1F shows the alignment pins shown inFIG. 1E being used to align a posterior resection guide for performing a posterior resection of thefemur108.FIG. 1G shows a femoral trial cutting guide used for forming post and fin openings on thecondyle110 located at thedistal end106 of thefemur108.FIGS. 1H-1J show a method of forming a keel opening at theproximal end102 of thetibia104.
• Referring toFIG. 2, in certain preferred embodiments of the present invention, a system for preparing a knee joint for receiving a unicondylar knee implant includes atibial resection block112 having atop surface114, an innercontoured surface116 that is preferably shaped to fit against the proximal end of a tibia and an outercontoured surface118 that is adapted to fit easily within an incision. Thetibial resection block112 has a universal design so that it may be used on the left or right side of the knee, thereby minimizing the number of parts that are required. The tibial resection block is preferably used to perform a tibial resection at a proximal end of a tibia. The tibial resection block desirably includes one ormore holes120 that may receive fasteners such as pins for securing the tibial resection block to bone. One or more of theholes120 may be adapted to secure a tool thereto, as will be described in more detail below. The tibial resection block also preferably includes one ormore openings122 adapted to secure a navigation tracker for properly aligning the tibial resection block relative to the proximal end of a tibia.
• Thetibial resection block112 also preferably includes a C-shapedopening124 engagable with an elongated element such as a rod. After the rod is coupled with the C-shapedopening124, the tibial resection block is designed to slide along the rod for adjusting the location of the tibial resection block relative to the proximal end of the tibia. Thetibial resection block112 may also include a threadedopening126 aligned with the C-shapedopening124. A tighteningscrew128 hasthreads130 that are preferably received within the threadedopening126. The tighteningscrew128 also includes alever132 that may pivot about apivot point134 for enabling greater leverage to be applied to the tightening screw. The pivotable lever also preferably allows thescrew128 and thelever132 to remain below the resection surface.
• Referring toFIGS. 3A-3D, thetibial resection block112 is securable to arod136 having aproximal end138 and a lower end (not shown). The lower end of the rod may be connected to an ankle clamp for stabilizing the rod. Referring toFIG. 3B, therod136 is preferably secured within the C-shapedopening124 of thetibial resection block112, with the inner contouredsurface116 facing the tibia and the outer contouredsurface118 facing away from the tibia. Theproximal end138 of therod136 includes aflange140 having apin opening142 for anchoring the rod to the proximal end of a tibia so as to further enhance the stability of therod136 and thetibial resection block112. Thetibial resection block112 also desirably includes one or morenavigation tracker openings122 for properly aligning the tibial resection block with the surface to be resected.
• Referring toFIGS. 3A,3C and3D, after thetop surface114 of thetibial resection block112 is positioned at a correct height relative to the proximal end of the tibia, thelever132 may be grasped for tightening the tighteningscrew128 so as to lock the position of the tibial resection block relative to therod136.
• Referring toFIG. 3C, in order to more firmly secure the position of thetibial resection block112 relative to the proximal end of the tibia, one or more securing elements such as pins may be passed through theouter openings120. Thecentral openings144 may be used for alignment pins or for securing tools to the tibial resection block, such as securing a stylus to the tibial resection block.
• FIG. 4 shows a saggitalresection alignment guide146 that is securable to thetibial resection block112 shown in FIGS.2 and3A-3D. The saggitalresection alignment guide146 preferably includes amain body148, anelongated rod150 that slides through an opening in the main body and analignment block152 secured to an end of theelongated rod150. Thealignment guide146 also includes adepressible button154 that may be depressed for allowing therod150 to move relative to themain body148. The saggitalresection alignment guide146 may include projections, such as posts or hooks (not shown), that engage one or more of the openings in the tibial resection block shown above inFIG. 2.
• Referring toFIGS. 5A-5E, in certain preferred embodiments of the present invention, amodular handle156 for inserting a combination bur guide and spacer block includes ahandle portion158 having an upper end secured to analignment element160 having aleading end162 and a trailingend164. Theleading end162 of thealignment element160 preferably includes amale projection166 on one lateral side thereof and apin168 on an opposite side thereof.Modular handle156 also includes amale end connector169 projecting from thesecond end164 of thealignment element160. Themodular handle156 also includes adepressible button170 and aspring172 coupled therewith. Thedepressible button170 may be depressed for interacting with thepin168. In one button position, thepin168 is free to move inwardly inpin opening174. When thebutton170 is not depressed, however, the pin is locked outwardly and may not retract within theopening174.
• Referring toFIGS. 6A-6H, in accordance with certain preferred embodiments of the present invention, a bur template/spacer block176 includes abur template portion178 for guiding burring of femoral bone and aspacer block portion180 insertible into a knee joint. Referring toFIGS. 6A and 6E, the bur template/spacer block178 includes aslot182 that defines anouter surface184, aninner surface186 and an apex188. Thebur portion178 includes aninner surface190 and anouter surface192. The inner andouter surfaces190,192 are preferably curved to conform to the condyle at a distal end of a femur. Thespacer portion180 includes atop surface194 and abottom surface196 remote therefrom. Depending upon the gap between the femur and the tibia, a plurality of spacer blocks may be provided having varying thicknesses. In certain preferred embodiments, spacer blocks are available having thicknesses of between 4-14 mm and more preferably 6-12 mm. Referring toFIGS. 6C and 6G, thespacer block portion176 has anopening198 extending from a trailing end of the spacer block toward a leading end of the spacer block. Theopening198 preferably has an elongatedalignment groove200 extending along one side thereof. Referring toFIGS. 6F and 6H, thespacer block portion180 has at least onepost opening202 extending between the top andbottom surfaces194,196. Referring toFIGS. 6A and 6G, theouter rail204 of thebur template portion178 includespin fixation flanges206A,206B. The pin fixation flanges include openings extending therethrough that are adapted to receive securing elements such as pins so that the bur template may be anchored to bone.
• Referring toFIGS. 7A-7D, in accordance with certain preferred embodiments of the present invention, the system includes ashim208 having aposts210 projecting from afirst surface212 thereof. Theshim208 includes opposing sidewalls214A,214B. As will be described in more detail below, the shim may be assembled over either the top surface or the bottom surface of the spacer block portion of the bur template/spacer block shown inFIGS. 6A-6H for adjusting the position of the bur template/spacer block. The shim may also be used for adjusting the thickness of the spacer block. In certain preferred embodiments, more than one shim may be connected with the spacer block.
• Referring toFIGS. 8A-8E, in accordance with certain preferred embodiments of the present invention, the system includes analignment tower216 that may be coupled with the modular handle shown inFIGS. 5A-5E for inserting and aligning the bur template/spacer block in a knee joint. Referring toFIGS. 8A,8B and8E, thealignment tower216 preferably includes ashaft218 having anupper end220 and alower end222. Referring toFIGS. 8A-8E, the alignment tower includes analignment flag224 secured to theupper end220 of theshaft218 and aconnection member226 secured to the lower end of theshaft218. Referring toFIGS. 8A and 8B, thealignment flag224 includes a number ofholes228 extending therethrough that are used for approximating the center of a knee. In certain preferred embodiments, an alignment rod can be passed through one or more of theholes228 in theflag224 for locating or approximating the center of the knee. Referring toFIGS. 8A,8B and8D, theconnection member226 at the lower end includes a C-shapedopening230 having a centrally located well232 and anelongated groove234 extending from opposite sides of thewell232. Thecentral well232 is adapted to fit over themale end connector169 of the modular handle158 (FIGS. 5A-5E).
• Referring toFIGS. 9A-9E, in accordance with certain preferred embodiments of the present invention, the system includes a posteriorresection guide locator236. Referring toFIGS. 9A,9B and9D, the posterior resection guide locator includes analignment rail238 having afirst end240 and asecond end242. Thealignment rail238 also desirably includes a firstlateral surface244 and a secondlateral surface246 extending on opposite sides of thealignment rail238 between the first and second ends240,242 thereof. Thealignment rail238 includes a firstmale projection248 provided adjacent thefirst end240 and a secondmale projection250 provided adjacent thesecond end242. Themale projections248,250 are sized to fit into the elongated alignment groove200 (FIG. 6G) provided at the trailing end of the spacer block. The particularfirst end240 orsecond end242 of therail238 that is inserted into thealignment groove200 may depend upon the type of operation being conducted. For example, thefirst end240 may be inserted in thegroove200 for a LM/RL procedure and thesecond end242 may be inserted in thegroove200 for a RM/LL procedure.
• Referring toFIGS. 9A-9E, the posteriorresection guide locator236 includes asupport element252 and apin guide254 mounted atop thesupport element252. Thepin guide254 preferably includes one or more pin holes256 extending therethrough. As will be described in more detail below, after the posterior resection guide locator is coupled with the elongated alignment groove in the bur template/spacer block shown inFIGS. 6A-6H, the pin holes256 are aligned with the opening in the bur template portion and alignment pins are inserted into bone through thepinholes256. The alignment pins are preferably used to align a posterior resection guide for conducting a posterior resection of the femur, as will be described in more detail below.
• Referring toFIGS. 10A-10D, in accordance with certain preferred embodiments to the present invention, the assembly includes a standardposterior resection guide258 including amain body260 having an upper end withpin holes262 and a lower end with aslot264 extending therethrough. Theslot264 is preferably a captured slot that is bounded on left and right sides thereof by themain body260. As a result, a cutting instrument such as a saw placed into the slot cannot extend beyond the left and right boundaries of the main body. The posterior resection guide also includes aledge266 that projects from one side of theslot264. The combination of theledge266 and the capturedslot264 control movement of a cutting blade so as to accurately control the cut through a posterior region of the femoral condyle. In certain preferred embodiments of the present invention, the standardposterior resection guide258 is sized and configured to remove 6 mm of bone from the posterior region of the femoral condyle, which matches the 6 mm thickness of the femoral component of the implant. The size and configuration of the standard posterior resection guide may be varied so that the amount of bone to be removed matches the thickness of the femoral component.
• FIGS. 11A-11C show aposterior resection guide258′, in accordance with another preferred embodiment of the present invention. Theposterior resection guide258′ is generally similar to the standard posterior resection guide shown inFIGS. 10A-10D, however, it includes three different sets of pin holes. The first set of pin holes268′ is used for performing a standard posterior resection, which in certain preferred embodiments is 6 mm. A second set of pin holes270′ is used when the resection guide must be lowered when performing a posterior resection for reducing the amount of bone removed from the posterior region of the femur. A third set of pin holes272′ is used when the resection guide must be raised when performing a posterior resection for increasing the amount of bone removed from the posterior region of the femur. As will be described in more detail below, it may be necessary to raise or lower theposterior resection guide258′ from a standard resection (e.g. removing 6 mm of bone from the posterior region of the femoral condyle) in order to balance the gap of a knee joint when in an extended position and a flexed position. The posterior resection guide may be raised or lowered so that the gap in extension is equal to the gap in flexion and vice versa. As is well known to those skilled in the art, uneven gaps may result in flexion instability or extension instability.
• Referring toFIGS. 12A-12F, in certain preferred embodiments of the present invention, the system includes a femoraltrial cutting guide274 for preparing the distal end of the femur to receive the femoral component of the implant. The femoraltrial cutting guide274 desirably includes a set of anchoringpins276 projecting from aninner face278 thereof. The cuttingguide274 also desirably includes acentral opening280 extending therethrough and anelongated slot282 that intersects thecentral opening280. The elongated slot preferably extends between upper and lower ends of the cuttingguide274. After the condyle at the distal end of a femur has been burred using the bur template portion of the bur template/spacer block shown above, theinner face278 of the cuttingguide274 is abutted against the burred surface of the femur. Thepins276 are preferably inserted into bone for holding the cutting guide in place. An impactor may be used to advance the anchor pins276 into the bone. A drill may be inserted through thecentral opening280 to form a post opening for an implant peg. In addition, a cutting instrument, such as a saw or cutting blade, may be inserted through theelongated slot282 to form a keel opening for an implant.
• Referring toFIG. 12B, the cuttingguide274 preferably has an outer surface that is curved. The curved outer surface of the cutting guide may be used to perform a range of motion test. After the post and keel openings have been formed, and a range of motion test is completed, the cuttingguide274 may be removed from its attachment to the femoral bone.
• Referring toFIG. 13A, in certain preferred embodiments, the system includes adrill guide286 having afirst end288 with a threadedprojection290 and asecond end292 including a handle. Referring toFIGS. 14A-14E, thedrill guide286 has acentral opening294 extending between thefirst end288 and the second292. Theopening294 includes a reduced diameter area orshelf296 that limits forward movement of a drill. Referring toFIGS. 13A-13B and14C, after the threadedprojection290 of thedrill guide286 is threaded intocentral opening280 of the cuttingguide274, adrill bit298 may be passed through theopening294 of thedrill guide286 until a portion of the drill abuts against theshelf296 for limiting further advancement of thedrill bit298. The drill may be operated for forming a post opening in the femoral bone. The post opening, as will be described in more detail below, is adapted to receive a post of a permanent femoral component of an implant. After the post hole has been formed, thedrill bit298 may be removed from thedrill guide286. Thehandle292 of the drill guide may be grasped to remove the cuttingguide274 from its attachment to the femoral bone. In certain preferred embodiments, thedrill guide286 may be used as an impaction/extraction handle for a trial such as a femoral trial.
• Referring toFIGS. 15A-15D, in accordance with certain preferred embodiments of the present invention, the system includes apunch tower300 for forming keel openings in tibial bone. ReferringFIG. 15A, thepunch tower300 includes amain body302 having aleading end304 and a trailingend306. Thepunch tower300 includes alatch paw308 securable to themain body302. The latch paw includes anopening310 extending therethrough that is adapted to receive apivot pin312 so that the latch paw may be coupled with themain body302 and pivot relative thereto. The latch paw also includes aspring314 that normally urges the latch paw to move downwardly at its hookedfront end316. The punch tower also preferably includes analignment flange318 that may be coupled with a trailingend306 of themain body302. The alignment flange includes one ormore openings320 extending therethrough that are adapted to receive pins for anchoring the punch tower to bone. Thealignment flange318 desirably includes a C-shapedopening322 at an upper end thereof that is adapted to slide over arail324 at the trailingend306 of themain body302. Apin312 is disposed in engagement with thealignment flange318 to secure the alignment flange with themain body302.
• Themain body302 preferably includes a series ofslots326 extending therethrough. The series ofslots326 are adapted for forming different sized keel openings in tibial bone. Referring toFIG. 15A, a first slot126A is used for forming a small keel opening, a second slot126B is used for forming a medium keel opening and a third slot126C used for forming a large keel opening. In other preferred embodiments, more than three slots may be provided.
• Referring toFIGS. 15B and 15C, an underside of themain body302 includes analignment guide328 at theleading end304 thereof. Thealignment guide328 includesmale projections330 extending along opposite sides of the main body.
• Referring toFIG. 16A, theleading end304 of themain body302 is adapted to be coupled with atibial template332 having anelongated opening334. Theelongated opening334 includesfemale grooves336 extending along a longitudinal axis of thetibial template332. Themale projections330 provided at the underside of themain body332 are adapted to slide into thefemale grooves336 in thetibial template332.
• Referring toFIGS. 16A-16C, the assembly includes achisel338 that is insertible into one of theslots326 in the punch tower. The assembly also includes a tamp340 that slides within thechisel338, as will be described in more detail below.FIGS. 16B and 16C show theleading end304 of the punch tower coupled with thetibial template332. As shown inFIG. 16B, thechisel338 and tamp340 are guided along an axis that intersects an axis extending between the leading304 and trailing306 ends of themain body302.
• Referring toFIGS. 17A-17D, thechisel338 preferable includes aleading end342 and a trailingend344. The leading end preferably includes a sharpenedsurface346 that cuts into bone. The trailingend344 desirably includes astriking surface348 so that thechisel338 may be hit with a hammer or mallet. Thesecond end344 includes ahandle350 having ashoulder352 that limits advancement of thechisel338 into the slot of the punch tower. The exact positioning of theshoulder352 may be varied in response to the depth of the bone cut required to be formed in the tibial bone.
• Referring toFIGS. 17C-17D, the chisel includes a C-shapedopening354 extending along the length thereof. The C-shaped opening provides a space for bone to move when the keel opening is being formed. The C-shapedopening354 also provides a space for a tamp, as will be described in more detail below.
• Referring toFIGS. 18A-18D, in accordance with certain preferred embodiments of the present invention, the system includes a tamp340 having aleading end356 and a trailingend358 including ahandle360. Referring toFIG. 18C, thehandle360 includes ashoulder362 that preferably abuts against thestriking surface348 of the chisel338 (FIG. 17A) for limiting advancement of the tamp340. After the chisel has been advanced into bone for forming an outline of the keel opening, the tamp is advanced through the chisel to impact the bone and complete the formation of the keel opening.
• Referring toFIGS. 19 and 21A, thetibial template332 preferably includes acentral opening334 having opposingfemale slots336 extending between aleading end362 and a trailingend364 thereof. The tibial template includes afirst slot366 for receiving a hooked end of a latch paw when the template is used on one side of a knee and asecond slot368 that is also designed to receive the hooked end of a latch paw when the template is flipped over. Thetibial template332 also desirably includes one ormore openings370 extending between top andbottom surfaces372,374 thereof, which are adapted to receive anchor pins for anchoring the tibial template to the proximal end of the tibia.
• FIG. 20 shows aholder380 for holding different sized tibial templates. The holder preferably includes afirst arm382 for holding an extra small or small sizedtibial template332A, asecond arm384 for holding a medium or largesized tibial template332B and athird arm386 for holding an extra largesized tibial template332C. Each arm of theholder380 has an outer end including an opening388 that is the size of a keel opening for the particular implant part to be implanted into bone. Thus, the opening388A in thefirst arm382 is smaller than theopening388B in thesecond arm384 and so on.
• FIGS. 22A-22D show aspacer bar390, in accordance with certain preferred embodiments of the present invention. Thespacer bar390 includes afirst section392 defining a height H₁and asecond section394 defining a height H₂that is greater than H₁. In certain preferred embodiments, the difference between H₁and H₂is preferably the thickness of the implant that is positioned between the posterior condyle and the tibia. The spacer bar includes afirst end396 that is tapered and asecond end398 that is also tapered. As will be described in more detail below, the spacer bar is placed between the distal end of a femur and a proximal end of a tibia to determine spacing between the femur and tibia during extension and flexion of the knee joint. The spacer bar may be used to align a cutting instrument for cutting the posterior region of the femur. As described herein, it is preferable that the gap between the femur and the tibia is the same for both flexion and extension. Thus, the present invention seeks to prepare bone sites and attached implant components to the respective bone sites so that the gap between the femur and tibia is the same in both flexion and extension so as to reduce joint instability and provide for smooth movement between flexion and extension.
• FIGS. 23-32 show a preferred method of preparing a seating surface at a proximal end of a tibia. Referring toFIG. 23, atibial resection block112 is coupled with anelongated rod136. Referring toFIG. 24, theattachment flange140 at theproximal end138 of therod136 is secured to theproximal end102 of thetibia104 using afastener145 such as a pin. A lower end (not shown) of therod136 is preferably secured to thetibia104 such as by using an ankle clamp.
• Referring toFIG. 25, thetibial resection block112 has atop surface114 that defines a cutting plane for theproximal end102 of thetibia104. Astylus141 is preferably coupled with the tibial resection block so as to determine a depth of cut into theproximal end102 of thetibia104. Thetibial resection block112 may slide along therod136 until the desired position of thetop surface114 of theblock112 is determined. At that point, the tighteningscrew128 is tightened for securing the position of thetibial resection block112 along therod136. In other preferred embodiments, the tibial resection block may be coupled with a navigation tracker for aligning thetop surface114 of theblock112 at the appropriate depth for the resection.
• Referring toFIG. 26, anchoring pins143 may be passed through openings in thetibial resection block112 to further stabilize the tibia resection block relative to the tibia. Referring toFIG. 26, asaggital resection guide146 may be moved into abutment against thetibial resection block112.
• Referring toFIG. 27, thesaggital resection guide146 has amain body148 that is abutted against thetibial resection block112. Thedepressible button154 of thesaggital resection guide146 may be depressed to allow movement of thealignment block152 for defining a saggital cutting plane between thealignment block152 and theproximal end138 of therod136. The outer surface of thealignment block152 may be rounded to provide for a perpendicular cut of the bone.
• Referring toFIGS. 28 and 29, asaw149 or other cutting instrument may be used to make a saggital resection of theproximal end102 of thetibia104. Referring toFIG. 30, a second cutting instrument or saw151 may be used to cut theproximal end102 of thetibia104 in a plane defined by thetop surface114 of thetibial resection block112.FIGS. 31 and 32 show theproximal end102 of thetibia104 after the tibial resection if complete. The tibial resection block may then be disengaged from the tibia.
• FIGS. 33-37 show femoral alignment of the bur template/spacer block within the knee joint. Theleading end162 of themodular handle158 shown inFIGS. 5A and 6G is coupled with thefemale opening198 of the bur template/spacer block. Themale projection166 at theleading end162 of themodular handle158 is preferably inserted into theelongated alignment groove200 in theopening198 at the trailing end of thespacer block portion176. A shim may be coupled with the spacer block for adjusting for the gap distance in the knee.
• Referring toFIG. 34, thealignment tower216 shown inFIG. 8A is coupled with themale projection169 of the modular handle158 (FIG. 5A). Themale projection169 of the modular handle is preferably coupled with the well232 at the bottom of thealignment post216. Referring toFIGS. 35-37, thespacer block portion180 of the bur template/spacer block is inserted into the joint between thedistal end106 offemur108 and theproximal end102 oftibia104. An alignment rod is desirably placed in the appropriate hole in thealignment tower216 which is preferably centered on the knee or on thefemur using openings228 in the alignment flag224 (FIG. 8A). Referring toFIG. 37, once thespacer block180 is in place, the tibia is extended until the curvedinner surface190 of the bur template engages the femoral condyle. Once the entire length of the curved inner surface of the bur template engages the femoral condyle, extension of the knee joint may be stopped. At that stage, the bur template is preferably secured from further movement relative to the femur using fasteners such as anchoring pins.
• Referring toFIG. 38, the one or more pins for anchoring the bur template from further movement relative to the femur may be inserted through securingflanges206A,206B. In the particular preferred embodiment shown inFIG. 38, ashim208 is coupled with an underside of the spacer block for adjusting the tension of the bur template/space block in the joint. As will be described in more detail herein, the shim may be used for balancing the gap between the femur and the tibia when the knee joint moves between flexion and extension. A bur (not shown) may be inserted into theslot182 of the bur template/spacer block to prepare the condyle at the distal end of the femur for receiving a femoral component of the implant.
• Referring toFIGS. 9A and 39, thealignment rail238 of the posteriorresection guide locator236 is preferably inserted into the opening at the trailing end of the bur template/spacer guide176. Theprojection248 on thealignment rail238 is preferably inserted into the elongated, alignment groove200 (FIG. 6G) in the spacer block. Referring toFIG. 39, once the alignment rail is inserted into the opening in the spacer block, thepin openings256 of the posteriorresection guide locator236 are preferably in alignment with theslot182 of the bur template/spacer block176. Referring toFIGS. 39 and 40, a pair of alignment pins153 are desirably inserted through the pin openings in the posteriorresection guide locator236 and advanced into the bone at the distal end of the femur. In certain preferred embodiments of the present invention, theguide locator236 is preferably sized and shaped so that the alignment pins153 are attached to the femur at a location that will eventually result in 6 mm of bone being resected from the posterior region of the femur.
• ReferringFIGS. 40 and 41, aposterior resection guide258 is aligned with thefemur108 using the previously anchored alignment pins153. Referring toFIGS. 41 and 42, a posterior resection of the femur is desirably performed by passing a cutting instrument such as asaw155 through theslot264 in theposterior resection guide258. The posterior resection guide is sized and shaped so that it slides over the alignment pins that were previously anchored in the bone using the posterior resection guide locator. The posterior resection guide is preferably sized and shaped so that once it is slid over the alignment pins153, the slot is located so that a predetermined section of bone from the posterior region of the femur is removed. In certain preferred embodiments, the posterior resection guide is sized and shaped so that 6 mm of bone is removed from the posterior region of the femur. As shown inFIG. 43, after the posterior resection of thefemur108 is complete, the posterior resection guide and the alignment pins are removed.
• Referring toFIGS. 44 and 45, atibial template332 may be positioned over the prepared site at theproximal end102 of thetibia104. The surgeon desirably makes a determination of the proper sized tibial template that should be used, which is based upon the area of the prepared site at the proximal end of the tibia. The tibial template is preferably used to prepare the site for receiving a tibial component of an implant.
• Referring toFIGS. 46 and 47, after the proper tibial template has been selected, theleading end304 of thepunch tower300 is coupled with the opening in the tibial template. As described above, the male projections at theleading end304 of thepunch tower300 slide into the female openings in the elongated opening of the tibial template. Thelatch paw308 desirably engages a latch paw groove formed in the top surface of the tibial template for securing the tibial template and the punch tower together.
• Referring toFIGS. 48 and 49, the coupled together tibial template and punch tower are preferably moved into place over the prepared site at the proximal end of the tibia. Referring toFIG. 49, a pin may be used to anchor the tibial template and/or the punch tower to the bone.
• Referring toFIG. 50, addition pins may be passed through theattachment flange318 of the punch tower to further anchor the punch tower to bone.
• Referring toFIGS. 51-53, after the punch tower and tibial template have been anchored to the tibia, thechisel338 is desirably passed through an appropriate slot in the punch tower and hammered in place using a hammer or mallet. As shown inFIG. 51, thepunch tower300 has at least three slots for receiving thechisel338. As noted above, each of the three slots will result in the formation of keel openings having a particular size.FIG. 53 shows thechisel338 after it has been fully advanced in thepunch tower300.
• Referring toFIGS. 54 and 55, the tamp340 is then hammered in place through thechisel338 to complete formation of the keel opening. Referring toFIG. 56, the punch tower is then removed. A keel opening has been formed at the prepared site at the proximal end of the tibia.
• FIG. 57 shows a prepared site at thedistal end106 of thefemur108, which has been prepared by passing a bur through the slot in the bur template/spacer block shown and described above inFIGS. 6A-6H. Referring toFIG. 58, in order to prepare the distal end of the femur for receiving a femoral component of the implant, a femoral trial cutting guide, such as that shown and described above inFIGS. 12A-12F and13A, is abutted against the prepared site. The outer perimeter of the femoraltrial cutting guide274 desirably matches the perimeter of the prepared site previously burred on the femur. The cutting guide is preferably handled by attaching thedrill guide286 to the cutting guide.
• Referring toFIG. 58, after the cutting guide is in place, a drill bit may be passed through an elongated opening in thedrill guide286 to form a post opening for the implant. Referring toFIG. 59, a cutting instrument, such as a saw, may be passed through the elongated slot formed in the cuttingguide274 so as to form an elongated opening for a keel on an implant.
• FIGS. 60-62 show a prior art bur template used to prepare the distal end of a femur for receiving an implant. As is well known to those skilled in the art, the template generally conforms to the shape of an actual implant. Thus, it is important that the template conform to the shape of the distal end of the femur as closely as possible. Referring toFIG. 61, after the posterior region of the femoral condyle has been resected, and while the leg remains flexed, the upper part of the bur template is abutted against the condyle at the distal end of the femur. As shown inFIG. 61, a gap forms between the prepared site at the posterior region of the femur and the template. This may result in a number of problems including a poor fit between the implant and the distal end of the femur, joint instability or the removal of excessive bone from the distal end of the femur in order to fit the implant to the femur bone. Conversely, referring toFIG. 62, if the lower end of the bur template is placed in contact with the prepared site at the posterior region of the femur, the upper part of the bur template is spaced from the condyle of the femur. This may cause a number of problems including a poor fit between the implant and the femur bone, joint instability and/or the removal of excessive bone from the femur in order to fit the implant to the femur bone. In certain preferred embodiments, the present invention seeks to avoid these problems by preparing the site at the distal end of the femur before removing bone from the posterior region of the femur. In other preferred embodiments, the present invention seeks to minimize the amount of bone removed from the posterior region of the femur when balancing the gaps between the femur and the tibia when the joint moves between an extended position and a flexed position.
• FIGS. 63A and 63B show a knee joint in an extended position, after the tibia has been resected but before the femur is resected. A spacer bar, similar to that shown inFIGS. 22A-22D, is placed in the gap between thedistal end106 of thefemur108 and theproximal end102 of thetibia104. The spacer bar is used to measure the distance or gap between the distal end of the femur and the prepared site at the proximal end of the tibia. Referring toFIGS. 64A and 64B, the knee joint is then flexed and the gap between the posterior region of the femur and the prepared site at the proximal end of the tibia is measured. Ideally, the gap between the femur and tibia is the same when the joint is in the extended and flexed positions. For example, in certain instances, the gap when the joint is flexed is 6 mm and the gap when the joint is extended is 6 mm. Often, however, the gap distances change as the joint moves between extended and flexed positions. For example, the flexion gap may be8mm and the extension gap may be 6 mm. Thus, certain preferred embodiments of the present invention seek to balance the gap between the femur and the tibia so that the gap in extension is equal to the gap when the knee is flexed. Unlike prior art methods, certain preferred embodiments of the present invention seek to balance the gaps by taking more or less bone from the posterior region of the femur, rather than by taking additional bone from the distal end of the femur. Moreover, in certain preferred embodiments, the posterior resection of the femur takes place only after the site at the distal end of the femur has been completely prepared. In still other preferred embodiments, although some bone may be removed from the posterior region before the distal end of the bone is burred, the final posterior resection region is not completed until the site at the distal end of the femur is finalized.
• Referring toFIGS. 63A and 63B, the extension gap between the distal end of the femur and the prepared site at the proximal end of the tibia is about 6 millimeters. Referring toFIGS. 64A and 64B, the flexion gap between the posterior region of the femur and the prepared site at the proximal end of the tibia is about 8 millimeters. Thus, the gap is 2 mm larger in flexion than in extension. The present invention seeks to balance the gaps so that the gap in flexion is equal to the gap in extension. In certain preferred embodiments, the present invention balances the gap by decreasing the flexion gap by 2 millimeters, rather than increasing the extension gap by 2 millimeters. As a result, less bone is removed from the femur.
• FIG. 65 shows a gap balancing table that may be used for calculating the amount of bone that is removed from the posterior condyle of the femur. The table may be used by a surgeon for balancing the flexion and extension gaps of a knee joint. As noted above, use of the table preferably minimizes the amount of bone that is removed from the femur. Use of the table also preferably results in proper positioning of the implant parts on the femur and the tibia and smooth movement of the knee joint when moving between the extended and flexed positions. For purposes of clarity, the table uses 6 mm as the preferred gap for a knee joint in both flexion and extension. This chart also assumes that the thickness of the femoral component of the implant is 6 mm. In other preferred embodiments, other thicknesses may be used, e.g. 4 mm, 8 mm, etc. If the initial gap distance is more or less than 6 mm, then more or less bone is removed from the posterior region of the femoral condyle so that the final gap distance in extension is the same as the final gap distance in flexion.
• Referring to the table, the gap distance associated with a tight fit is 4 mm; the gap distance associated with a good fit is 6 mm and the gap distance associated with a loose fit is 8 mm. The table includes a first row that compares a tight extension gap (4 mm) with a tight (4 mm), good (6 mm) and loose (8 mm) flexion gap. If the extension gap and the flexion gap are both tight, then the gap is considered to be in balance and the standard 6 mm of bone is removed from the posterior condyle. If the extension gap is tight (4 mm) and the flexion gap is good (6 mm), then the gaps are not in balance. In order to balance the gaps, 2 mm less bone material is removed from the posterior region of the femoral condyle for a total of 4 mm (6 mm−2 mm=4 mm) of bone being removed. If the extension gap is tight (4 mm) and the flexion gap is loose (8 mm), then the gaps are not in balance and 4 mm less bone material is removed from the posterior region of the femoral condyle for a total of 2 mm (6 mm−4 mm=2 mm) of bone being removed.
• The second row of the gap balancing table is used when the extension gap is good (e.g. 6 mm). If the extension gap is good (6 mm) and the flexion gap is tight (4 mm), then the gaps are not in balance. In order to balance the gaps, 2 mm of additional bone is removed from the posterior region of the femoral condyle for a total of 6 mm (4 mm+2 mm=6 mm) of bone being removed. If the extension gap and the flexion gap are both good, then the gap is considered to be in balance and the standard 6 mm of bone is removed from the posterior region of the femoral condyle. If the extension gap is good (6 mm) and the flexion gap is loose (8 mm), then the gaps are not in balance and 2 mm less bone is removed from the posterior region of the femoral condyle for a total of 6 mm (8 mm−2 mm=6 mm) of bone being removed.
• The third row of the gap balancing table is used when the extension gap is loose (e.g. 8 mm). If the extension gap is loose (8 mm) and the flexion gap is tight (4 mm), then 4 mm of additional bone is removed from the posterior region of the femoral condyle for a total of 8 mm (4 mm+4 mm=8 mm) of bone being removed. If the extension gap is loose (8 mm) and the flexion gap is good (6 mm), then 2 mm of additional bone is removed from the posterior region of the femoral condyle for a total of 8 mm (6 mm+2 mm=8 mm) of bone being removed. If the extension gap is loose (8 mm) and the flexion gap is loose (8 mm), then the gap is balanced and the standard 6 mm (6 mm+0 mm=6 mm) of bone is removed from the posterior region of the femoral condyle and the 8 mm tibial component is preferably used.
• InFIG. 66, the flexion gap is 8 mm and the extension gap is 6 mm so that the flexion gap is 2 mm greater than the extension gap. Thus, a standard 6 mm posterior resection will result in a flexion instability of 2 mm. This is shown inFIG. 66 wherereference line425 designates the cut line for a standard 6 mm posterior resection andline435 is 6 mm away from line425 (the thickness of the femoral component of the implant). When thefemoral component440 is attached to the bone, theouter surface442 is present atline435. However, an 8 mm flexion gap still remains between the proximal end of the tibia (designated by line445) and the outer surface of the implant (designated by line435). Thus, in order to balance the flexion gap with the extension gap, the posterior resection must be lowered by 2 mm so that the outer surface of the implant is lowered by 2 mm. Lowering the femoral component by 2 mm will result in a 6 mm flexion gap and a 6 mm extension gap. As a result, when thefemoral component440 shown inFIG. 66 is attached to the distal end of thefemur108, theouter surface442 of theimplant440 will form a flexion gap of 6 mm.
• Adjusting the posterior resection is shown in conjunction withFIGS. 67-69. Referring toFIG. 67, after the bur template/spacer block has been positioned between the knee joint and pinned to the femur, the alignment rail of the posteriorresection guide locator236 is inserted into the alignment opening of the bur template/spacer block176.Pins153 are then passed through the pin openings of the posterior resection guide locator and into the distal end of the femur bone. As shown inFIGS. 39-40, the posteriorresection guide locator236 is then removed so that only thepins153 remain attached to the bone. Referring toFIGS. 40-43 and68, if the flexion gap matches the extension gap, then the standardposterior resection guide258 may be used to provide a 6 mm posterior resection. The prepared site with the 6 mm posterior resection is shown inFIG. 43.
• If the flexion gap does not match the extension gap, then the posterior resection must be adjusted from the standard 6 mm cut as discussed above with reference to the gap balancing table ofFIG. 65. This may be accomplished by using a secondposterior resection guide258′, shown inFIG. 69, having three sets of pin openings. Although three sets of pin openings are shown, it is contemplated that other preferred embodiments may have four or more sets of pin openings for further modification of the amount of bone removed during a posterior resection. The middle set ofopenings268′ provides for a standard posterior resection of 6 mm of bone. The upper set ofopenings270′ lowers theposterior resection guide258′ by 2 millimeters so that the posterior resection removes 4 mm of bone. In certain preferred embodiments, the upper set ofopenings270′ is used when the flexion gap is greater than the extension gap. Theposterior resection guide258′ also includes a lower set ofopenings272′ that is used when the posterior resection must be raised by 2 mm. The third set ofopenings272′ may be used when the flexion gap is less than the extension gap. In other preferred embodiments, the sets of openings may be 1 mm apart, or another desired distance.
• Referring toFIG. 70A,line425 shows the standard posterior resection of 6 mm of bone.Line435 shows a posterior resection that has been lowered 2 mm so that only 4 mm of bone is removed.Line455 shows the burredsurface455 formed at thefemoral condyle110 at the distal end of thefemur108, with the inner surface of the femoral component of the implant being shown atline442. Due to downward shifting of the femoral component by about 2 mm (preferably after the distal burring is accomplished), a gap may form between the burredsurface455 and theinner surface442 of the femoral component. Referring toFIG. 70B,bone cement460 may be used for filling the gap resulting from the downward shifting of the femoral component.
• In other preferred embodiments of the present invention, the amount of bone removed during the posterior resection may be controlled by coupling a shim with the spacer block portion of the bur template/spacer block. The shim may be coupled with either the top surface of the spacer block or the bottom surface of the spacer block.FIG. 71 shows the bur template/spacer block176 ofFIG. 6A aligned for assembly withshim208 ofFIG. 7A.Shim208 includes apost210 that is insertible in an opening extending throughspacer block180. InFIG. 71, the shim is oriented for assembly with a bottom surface of the spacer block. InFIG. 72, theshim208 is oriented for assembly with a top surface of thespacer block180.
• Referring toFIG. 73, theshim208 having a thickness of 2 mm is assembled with the top surface of thespacer block180. The addition of the 2 mm shim on top of the spacer block lowers the posterior resection by 2 mm. As a result, when the standardposterior resection guide258 ofFIG. 68 is slid over the pins shown inFIG. 40 and the resection conducted, only 4 mm of bone is removed from the posterior region, rather than the standard 6 mm.
• Referring toFIG. 74, when theimplant440 is attached to the prepared site on thefemur108, the gap between theouter surface442 of theimplant440 and the upper prepared surface of thetibia104 is 6 millimeters. This 6 millimeter gap in flexion is the same distance as the 6 mm extension gap.
• FIGS. 75 and 76 show a knee joint having a flexion gap that is less than the extension gap. In order to balance the gaps, the posterior resection must be raised by a particular distance.FIG. 75 shows a standard 6 millimeterposterior resection line470 that may be formed using the standardposterior resection guide258 shown inFIG. 68. When theimplant440 is attached to the distal end of the femur, theouter surface442 of the implant defines atangent line472 that is 4 mm fromline474. In this case, a 2 mm extension instability exists. Correcting this situation requires the posterior resection to be raised 2 mm so that the flexion gap matches the extension gap.
• Referring toFIG. 76, in order to raise the outer surface of the implant 2 mm, the posterior resection line is first raised 2 mm toline471. As a result, when theimplant440 is attached to bone, the flexion gap between theouter surface442 of theimplant part440 and the prepared surface of the tibia is 6 millimeters, which matches the 6 millimeter extension gap.
• After the sites have been prepared at the distal end of the femur and the proximal end of the tibia, a femoral component of the implant is connected with the distal end of the femur and a tibial component of the implant is connected to the proximal end of the tibia. Referring toFIGS. 77A and 77B, thefemoral component440 has anouter surface442 that is preferably curved and aninner surface444. Thefemoral component440 also preferably includes apost446 projecting from theinner surface444 and akeel448 projecting from theinner surface444 thereof. Thefemoral component440 is assembled with the distal end of the femur by abutting theinner surface444 against the femoral bone. Thepost446 and thekeel448 are preferably pressed into openings previously formed in the bone as described above with respect to the femoral trial cutting guide shown inFIGS. 57-59.
• Referring toFIGS. 78A and 78B, the implant includes atibial component482 having atop surface484 adapted to abut against theouter surface442 of the femoral component440 (FIG. 77A). Thetibial component482 includes anunderside486 having akeel488 projecting therefrom. The keel is adapted to be inserted into a keel opening, such as the keel opening shown inFIG. 56.
• Referring toFIG. 79, after final insertion of the implant, theouter surface442 offemoral component440 engages thetop surface484 oftibial component482. The opposing outer surfaces of the two implant parts engage one another as the knee joint moves between a flexed position and an extended position. In certain preferred embodiments, the femoral andtibial components440,482 may be secured using cement. In particular preferred embodiments, the cement is applied over thepost446 andkeel448 of thefemoral component440 shown inFIG. 77A. Cement may also be applied over thebottom surface486 and thekeel488 of thetibial component482 shown inFIG. 78B. The first and second implant parts may be impacted into place just by using a striking instrument such as a hammer, an impactor or a mallet. Any excessive cement present around theimplant parts440,482 is preferably removed.
• Disclosed herein are unicondylar knee implants, surgical instruments and procedures in accordance with certain preferred embodiments of the present invention. It is contemplated, however, that the implants, instruments and procedures may be slightly modified, and/or used in whole or in part and with or without other instruments or procedures, and still fall within the scope of the present invention. Although the present invention may discuss a series of steps in a procedure, the steps can be accomplished in a different order, or be used individually, or in subgroupings of any order, or in conjunction with other methods, without deviating from the scope of the invention.
• While there has been described and illustrated herein embodiments of unicondylar knee implants and insertion methods therefor, it will be apparent to those skilled in the art that variations and modifications are possible without deviating from the broad spirit and principle of the present invention. The present invention shall, therefore, not be limited solely to the specific embodiments disclosed herein and other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims (20)

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 inclaim 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 inclaim 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 inclaim 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 inclaim 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 inclaim 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 inclaim 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 inclaim 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 inclaim 8, wherein the alignment rail is adapted to engage the alignment feature in the opening of said spacer block.

10. The method as claimed inclaim 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 inclaim 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 inclaim 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 inclaim 12, further comprising inserting an alignment pin into the at least one pin opening of said alignment pin guide.

14. The method as claimed inclaim 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 inclaim 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 inclaim 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 inclaim 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 inclaim 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 inclaim 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.

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