Smith & Nephew Ex. 1094
`IPR Petition - USP 7,534,263
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`Jun. 20,2000
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`FIG.
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`PRELIMINARY
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`ANTERIOR
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`CUT
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`POSTERIOR
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`RES ECTION
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`FIG. 4A
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`FINAL
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`ANTERIOR
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`CUT
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`DISTAL
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`RESECTION
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`POSTERIOR
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`CHAMFER
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`FIG. 27
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`FIG.16
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`FIG.17
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`FIG.18
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`FIG.19
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`FIG. 26
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`.
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`ill
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`i
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`FIG. 28
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`FIG. 32
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`100
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`O-250
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`204
`L4. 205
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` __~‘.e.V_-‘RAJ’
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`jurliltlg
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`FIG. 39
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`FIG. 40
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`FIG. 41
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`FIG. 42
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`POSTERIOR
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`ANTERIOR
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`FIG. 46B
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`FIG. 46
`I
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`RT
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`EXT
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`LFT
`EXT
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`RT
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`FLEX
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`LFT
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`FLEX
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`FIG. 47
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`FIG. 46A
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`10.5mm—7mm 7m mm
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`FIG. 48
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`FIG. 49
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`FIG. 53A
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`FIG.55
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`mom
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`B.o_.._
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`1
`METHOD AND APPARATUS FOR LOCATING
`BONE CUTS AT THE DISTAL CONDYLAR
`FEMUR REGION TO RECEIVE A FEMORAL
`PROTHESIS AND TO COORDINATE TIBIAL
`AND PATELLAR RESECTION AND
`REPLACEMENT WITH FEMORAL
`RESECTION AND REPLACEMENT
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation-in-part application to
`U.S. patent application Ser. No. 09/049,781, filed Mar. 27,
`1998 entitled METHOD AND APPARATUS FOR LOCAT-
`ING BONE CUTS AT THE DISTAL FEMORAL
`CONDYLES TO RECEIVE A FEMORAL PROTHESIS,
`AND TO COORDINATE TIBIAL AND PATELLAR
`RESECTION AND REPLACEMENT WITH FEMORAL
`
`RESECTION AND REPLACEMENT, now pending, which
`is a continuation-in-part application to U.S. patent applica-
`tion Ser. No. 08/956,015,
`filed Oct. 22, 1997 entitled
`METHOD AND APPARATUS FOR LOCATING BONE
`CUTS AT THE DISTAL CONDYLAR FEMUR REGION
`TO RECEIVE A FEMORAL PROTHESIS AND PROP-
`ERLY ARTICULATED WITH PATELLAR AND TIBIAL
`
`PROTHESIS, now pending, which is a continuation-in-part
`application to U.S. patent application Ser. No. 08/455,985,
`filed May 31, 1995, entitled METHOD AND APPARATUS
`FOR LOCATING BONE CUTS AT THE DISTAL CONDY-
`LAR FEMUR REGION TO RECEIVE A FEMORAL
`PRDSTHESIS, now U.S. Pat. No. 5,776,137, issued Jul. 7,
`1998, the disclosures of which are incorporated by reference
`herein.
`
`FIELD OF THE INVENTION
`
`The invention relates to methods and apparatus for locat-
`ing bone cuts on the medial and lateral femoral condyles to
`form seating surfaces for a femoral knee prosthesis, and to
`coordinate tibial and patellar resection and replacement with
`femoral resection and replacement.
`The invention further relates to a tool for locating said
`cuts.
`
`BACKGROUND OF THE INVENTION
`
`Over the years, the concepts of designs for the total knee
`arthroplasty have evolved to the point where with few
`exceptions, most are quite comparable in the design of
`femoral, tibial and patellar prostheses.
`Major discrepancies and problems encountered are
`caused by physician error and failure to understand the
`principles of more complex alignment or ligament problems
`to be corrected at surgery. With the more complex alignment
`or “routine” degenerative knee, the major differences are the
`ease and consistency of instrumentation for alignment and
`proper bone cuts allowing proper ligament balance. This
`allows satisfactory motion and stability post operatively.
`The distal femoral cuts must be placed to provide the knee
`prosthesis with a proper fiexion and extension gap, proper
`varus-valgus alignment, proper patellofemoral relationship
`and proper rotation. It is customary to use an intramedullary
`rod placed in a retrograde fashion between the medial and
`lateral femoral condyles just anterior to the intercondylar
`notch to establish a single point of reference for subsequent
`bone cuts. A major problem is in the instrumentation to
`indicate the location of the femoral cuts which relies upon
`the “experience” or “eyeballing” of the surgeon. Over the
`years, two basic instrument system designs have become
`popular.
`
`2
`
`In one design (anterior referencing), the total knee align-
`ment system takes its point of reference from a centrally
`placed rod and careful attention is given to the patellofemo-
`ral joint by using an anteriorly placed feeler gage. The distal
`femoral cut is consistent with the thickness of the prosthesis.
`This instrument system operates on the principle of ana-
`tomic anterior and distal femoral cuts to allow proper
`ligament balancing and stability in extension as well as
`consistent patellofemoral placement on the anterior surface.
`The femur is not notched, and the anterior surface of the
`femoral prosthesis not elevated above the anterior surface of
`the femur. Notching the femur may cause a decrease in
`strength of the distal femur. Elevation of the anterior surface
`of the prosthesis will cause extremely high patellofemoral
`pressures in a joint that seems to be prone to a high rate of
`post-operative failure.
`By establishing the anterior femoral cut as the benchmark
`or datum starting point, however, the anterior referencing
`instruments result in the installation of a knee prosthesis
`which sacrifices consistent stability in fiexion due to the
`formation of a posterior femoral condylar cut that may leave
`the posterior space either too wide or too narrow. This can
`cause instability in fiexion, or restrict fiexion and cause
`increased wear.
`
`The second type of instrument design (posterior
`referencing) is based on the concept that the fiexion and
`extension stability are more important and the patellofemo-
`ral joint is of secondary importance. This system also uses
`an intramedullary rod for referencing. Although I consider
`all three joints as “important”, when a compromise must be
`made,
`the posterior referencing systems compromise the
`patellofemoral joint while the anterior reference systems
`sacrifice stability in fiexion (the posterior tibial femoral
`joint). Both systems allegedly equally address the distal
`tibial-femoral space. Neither consistently addresses the dis-
`tal rotation of the femoral component.
`Neither system tries to preserve the joint line at or near an
`“anatomic” level. By elevating the jointline, the patella is
`distalized. The femur is also shortened. Since the arthritic
`
`knee often has a loss of cartilage, there may be a patella
`infera of 2-3 mm initially. Elevating the distal femoral
`resection beyond this will:
`1) Further alter the patellofemoral relationship.
`2) Change the isometric and rotational balance of the
`MCL and the LCL.
`
`3) Shorten the femur in fiexion and may cause increased
`roll back, anterior lift off, and increased posteromedial
`wear.
`
`4) Elevate the level of tibial resection necessitating a
`major amount of posterior femoral resection to achieve
`a satisfactory fiexion space.
`When performing a unicompartmental knee replacement,
`it is imperative to maintain the jointline. As a consequence,
`it is desirable to maintain a full range of motion.
`SUMMARY OF THE INVENTION
`
`An object of the invention is to provide methods and
`apparatus for locating bone cuts on the medial and lateral
`femoral condyles to form seating surfaces for a femoral knee
`prosthesis, and to coordinate tibial and patellar resection and
`replacement with femoral resection and replacement which
`reliably and anatomically provide:
`1. Consistent distal tibio-femoral stability.
`2. Consistent distal femoral rotation.
`
`3. Consistent placement of the anterior cut flush with the
`anterior surface of the femoral cortex,
`i.e., without
`notching or elevation.
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`4. Consistent placement of the posterior femoral cut such
`that
`the distal and posterior cuts are equal (when
`indicated) allowing for satisfactory extension and flex-
`ion stability and motion.
`The method and apparatus of the invention contemplate
`placement of the anatomic joint line which,
`in extreme
`cases, varies up to the difference between the anterior-
`posterior A-P internal measurements of the size prostheses.
`Based on my knowledge of total knee replacement, personal
`experience with numerous routine total knee replacements,
`numerous more complicated cases consisting of knees with
`flexion deformities and revision surgery, a maximum of a
`few mm proximal or distal displacement of the joint line is
`considerably less harmful than:
`1. A lax flexion gap;
`2. Sloping the proximal tibial cut to accommodate for an
`inconsistent posterior femoral condylar cut;
`Significantly notching the femur anteriorly;
`4-9»
`. Raising the anterior flanges of the prosthesis and thus
`the patellofemoral joint;
`Not allowing full extension;
`Raising the joint line;
`. Tightness in flexion;
`Malrotation; and
`. Patient pain.
`With an understanding of the measurements involved in
`total knee replacement, a new instrument system and meth-
`odology has been developed to allow flexion 120-130
`degrees; to perform less soft tissue releasing; and decrease
`surgical time. Starting with a “normal” knee, the goal should
`be to maintain the anatomic landmarks as close to normal as
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`“-7.°°\‘5-""5"
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`possible. Then, if deformities are present, the procedure can
`be modified to accommodate the situation.
`
`In accordance with the invention, a method is provided for
`forming planar cuts on the medial and lateral condyles of the
`femur to form seating surfaces to receive a femoral knee
`prosthesis, comprising:
`determining a prospective planar cut at the posterior of the
`condyles of the femur at which the distance between
`the anterior surface of the femoral cortex and the
`
`prospective planar cuts is substantially equal to the
`interior dimension of a knee prosthesis to be fitted on
`said femur at the anterior surface and the cut planar
`surface,
`determining the thickness of the posterior lateral or
`medial condyle which will be resected by said prospec-
`tive planar cut,
`cutting the distal ends of the condyles along a plane at
`which the maximum thickness of resection of the more
`
`prominent condyle at said distal end is substantially
`equal to the thickness determined to be resected at the
`posterior medial or lateral condyle by said prospective
`planar cut, and
`cutting the condyles along a plane substantially flush with
`the anterior surface of the femoral cortex, and along
`said prospective planar cut.
`The method further contemplates loosely placing a lon-
`gitudinal intramedullary rod in the femur such that an end of
`the rod projects from the femur, mounting a tool on the
`projecting end of the rod, establishing, by said tool, an
`angular position of said prospective planar cut along a plane
`rotated at an angle of between 0 and 15° with respect to a
`tangential plane at the posterior of the lateral and medial
`condyles about an axis located in said tangential plane.
`In further accordance with the method, the tool is rotated
`with said rod through said angle and a datum or benchmark
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`is established by the rotated rod or by pins installed in the
`condyles on the basis of the rotated position of the tool. A
`cutting guide can be mounted on said tool, to enable the
`distal end of the condyles to be cut along said plane.
`Thereafter, the tool is removed and a second A-P cutting
`guide is mounted on the selected benchmark, i.e., the rod or
`the pins and the posterior and anterior cuts are made. The
`axis about which the plane of the prospective cut is rotated
`is located in said tangential plane at the posterior surfaces of
`the medial and lateral condyles and can be located at either
`of the condyles or at any location therebetween. It is a
`feature of the invention that the tool may remain on the rod
`both for the measurements and for the cutting of the distal
`end of the femur.
`The invention also contemplates that the cutting guide
`supports a means which enables the cutting guide to be
`secured to the condyles during the cutting of the distal ends
`of the condyles.
`The invention further contemplates an apparatus for form-
`ing planar resections on the medial and lateral condyles of
`a femur to form seating surfaces to receive a femoral
`prosthesis and to properly articulate with a tibial and patellar
`prosthesis comprising:
`a caliper feeler and measurement plate to measure for the
`size of the femoral prosthesis to be received, said
`caliper feeler and measurement plate adapted to deter-
`mine a first distance between an anterior surface of the
`
`to a posterior
`femoral cortex and a plane tangent
`surface of the medial and lateral condyles of a femur,
`the caliper feeler referencing the anterior surface of the
`femoral cortex and the measurement plate referencing
`the plane tangent to the posterior surface of the medial
`and lateral condyles;
`a graduated scale to compare the first distance to at least
`two standard femoral prosthesis sizes and to determine
`the smaller of the at least two standard femoral pros-
`thesis sizes;
`a graduated scale to measure a second distance between
`the first distance and the size of the smaller standard
`
`femoral prosthesis size, so that a thickness or thick-
`nesses can be measured to be resected at the posterior
`surface of the medial and lateral condyles of the femur
`by adding the average thickness of the posterior
`condyles of the smaller standard femoral prosthesis and
`the second distance;
`a tool to resect the medial and lateral condyles along a
`plane at the anterior surfaces thereof flush with the
`anterior surface of the femoral cortex; and
`a tool
`to resect distal ends of the medial and lateral
`
`condyles at a resected thickness equal to the average
`thickness of the distal condyles of the smaller standard
`femoral prosthesis plus the second distance.
`The apparatus further contemplates a tool to resect the
`measured thickness at the posterior surface of the medial and
`lateral condyles of the femur.
`The invention also contemplates a method for forming
`planar resections on the medial and lateral condyles of a
`femur to form seating surfaces to receive a femoral pros-
`thesis and to properly articulate with a tibial and patellar
`prosthesis comprises:
`measuring for the size of the femoral prosthesis to be
`received by determining a first distance between an
`anterior surface of the femoral cortex and a plane
`tangent to a posterior surface of the medial and lateral
`condyles of a femur;
`using a graduated scale to compare the first distance to at
`least two standard femoral prosthesis sizes;
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`measuring a second distance between the first distance
`and the size of the smaller standard femoral prosthesis
`size; and
`measuring a thickness or thicknesses to be resected at the
`posterior surface of the medial and lateral condyles of
`the femur,
`the thickness being equal to the average
`thickness of the posterior condyles of the smaller
`standard femoral prosthesis plus the second distance.
`The method further contemplates the steps of resecting
`the medial and lateral condyles along a plane at the anterior
`surfaces thereof substantially flush with the anterior surface
`of the femoral cortex; and
`measuring a thickness or thicknesses to be resected at the
`distal ends of the medial and lateral condyles,
`the
`thickness being equal to the average thickness of the
`distal surface of the smaller standard femoral prosthesis
`plus the second distance, and resecting the distal ends
`of the medial and lateral condyles at
`the measured
`thickness.
`
`Other features and advantages of the present invention
`will become apparent from the following description of the
`invention which refers to the accompanying drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a diagrammatic, lateral view of the femur and
`tibia at a knee joint showing prospective cuts to be made on
`the femur for installation of a femoral prosthesis.
`FIG. 2 is a diagrammatic illustration of the knee joint of
`FIG. 1 seen anteriorly of the joint.
`FIG. 3 is an end view from the distal end of the femur of
`
`the knee joint.
`FIG. 4 is a sectional view of a femoral knee prosthesis
`adapted for placement on the femur after the planar cuts
`have been made on the femur.
`
`FIG. 4a is a side view identifying each of the cuts made
`to the femur.
`FIG. 5 is a side view similar to FIG. 1 in which the tibia
`
`has been turned 90° to expose the distal end of the femur, an
`intramedullary rod has been inserted into the femur and a
`tool placed on the rod, the tool being partly broken away and
`shown in section.
`FIG. 6 is an end view of the tool taken in the direction of
`arrow 6—6 in FIG. 5.
`FIG. 7 is a sectional view taken on line 7—7 in FIG. 6.
`
`FIG. 8 is a broken, perspective view of a lower caliper
`feeler of the tool.
`
`FIG. 9 is similar to FIG. 6 and illustrates a first stage in
`which the rod is angularly rotated by a specific amount.
`FIG. 10 is similar to FIG. 9 in a subsequent stage.
`FIG. 11 is an exploded view showing a cutting guide to be
`installed on the tool.
`
`FIG. 12 is a top, plan view showing the cutting guide
`installed on the tool.
`FIG. 13 illustrates the distal end of the femur after the
`
`distal end has been cut and an AP cutting guide has been
`placed on the rod.
`FIG. 14 is an end view similar to FIG. 6 of a second
`embodiment of the tool.
`FIG. 15 shows the tool of FIG. 14 in a rotated state.
`FIG. 16 is an end view similar to FIG. 6 of a third
`embodiment of the tool.
`FIG. 17 shows the tool of FIG. 16 in a rotated state.
`FIG. 18 is an end view similar to FIG. 6 of a fourth
`embodiment of the tool.
`
`6
`FIG. 19 shows the tool of FIG. 18 in a rotated state.
`FIG. 20 is similar to FIG. 13 but shows a modification
`
`5
`
`adapted to the embodiment of FIGS. 16 and 17.
`FIG. 21 is an end view similar to FIG. 6 of a fifth
`
`embodiment of the tool including an A-P measuring guide.
`FIG. 22 is a side view similar to FIG. 5 of the tool of FIG.
`21 mounted on the distal femur.
`
`FIG. 23 is a top view of the tool of FIG. 21 mounted on
`the distal femur.
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`FIG. 24 is an exploded view of a distal cutting block to be
`installed on the tool of FIG. 21.
`FIG. 25 is a side view of the tool of FIG. 21 mounted on
`
`the femur installed with the distal cutting block.
`FIG. 26 is a top view of the tool of FIG. 25 mounted on
`the femur.
`
`FIG. 27 is an enlarged fragmentary view of the sliding
`scale of the distal cutting block.
`FIG. 28 is a side view of the femur with the distal cutting
`block mounted thereon.
`
`FIG. 29 is a top view of the A-P cutting block mounted on
`the distal femur.
`
`25
`
`FIG. 30 is a view similar to FIG. 13 illustrating the distal
`end of the femur after the distal end has been cut and the A-P
`
`cutting block has been mounted thereon.
`FIG. 31 is a top view of the A-P cutting block mounted on
`the distal end of the femur after the distal end has been cut
`
`30
`
`and the A-P cutting block has been mounted thereon.
`FIG. 32 is a side view of the distal end of a femur after
`
`it has been cut and a preferred prosthesis is ready to be
`mounted thereon.
`
`35
`
`40
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`45
`
`50
`
`55
`
`60
`
`65
`
`FIG. 33 is a front view of the preferred prosthesis to be
`used with the tool of FIG. 21.
`FIG. 34 is an alternative embodiment of the tool of FIG.
`
`22, including posterior clips.
`FIG. 34a is a rear perspective view of a posterior clip of
`FIG. 34.
`
`FIG. 34b is a front perspective view of a posterior clip of
`FIG. 34.
`
`FIG. 35 is a top view of the tool of FIG. 34.
`FIG. 36 is a front view of the tool of FIG. 34.
`FIG. 37 is rear view of the tool of FIG. 34.
`
`FIG. 38 is a top view of the tool of FIG. 34 mounted on
`the femur installed with a distal femoral cutting block and a
`distal femoral resection caliper.
`FIG. 39 is a top view of the femur with the distal femoral
`cutting block mounted thereon.
`FIGS. 40 and 41 are perspective views of distal femoral
`resection calipers for use in right and left femurs.
`FIG. 42 is a front view of a tibial resection guide of the
`present invention mounted on a tibia.
`FIG. 43 is a side view of the tibial resection guide of FIG.
`42.
`
`FIG. 44 is a top view of the tibial resection guide of FIG.
`42.
`
`FIG. 45 is a side view of a tibial external resection guide
`of the present invention mounted on a tibia.
`FIG. 46 is a top view of a spacer of the present invention.
`FIG. 46a is an end view of the top extension portion of the
`spacer of FIG. 46.
`FIG. 46b is an end view of the bottom fiexion top
`extension portion of the spacer of FIG. 46.
`
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`7
`FIG. 47 is a side View of the spacer of FIG. 46.
`FIG. 48 is a front View of the knee space including a
`spacer in flexion.
`FIG. 49 is a front View of the knee space including a
`spacer in extension.
`FIG. 50 is a side View of a tibial reresection guide in
`accordance with the present invention mounted on a tibia.
`FIG. 51 is a front View of the tibial reresection guide of
`FIG. 50.
`
`FIG. 52 is a top View of a tibial reresection guide of FIG.
`50.
`
`FIG. 53 is a partial side View of a patellar clamp including
`a hinge feature in accordance with the present invention.
`FIG. 53a is a partial top View of the hinge feature of the
`patellar clamp of FIG. 53.
`FIG. 54 is an end View of the patellar clamp of FIG. 53
`showing a scale to measure the patella thickness.
`FIG. 55 is a side View of a patellar clamp in accordance
`with the present invention without the hinge feature shown
`reaming a patella.
`FIG. 56 is a top View of the patellar clamp of FIG. 55
`reaming a patella.
`FIG. 57 is a side partially broken away View of a patella
`having a patella insert fitted therein.
`FIG. 58 is a side View of an improved nail in accordance
`with the present invention.
`FIG. 59 is a side View of the tool of FIG. 34 mounted on
`
`a femur installed with a distal femoral cutting block and a
`distal femoral resection caliper of the present invention,
`showing the nail of FIG. 58 being removed from the femur
`in accordance with an improved slap hammer of the present
`invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`When performing a unicompartmental knee replacement,
`it is imperative to maintain the jointline at or near anatomic
`level. As a consequence,
`this maintains a full range of
`motion. The instrument system of the present invention has
`been developed which combines the advantages of anterior
`and posterior referencing systems to maximize motion in a
`reproducible fashion and can easily be incorporated into an
`operative protocol. With the instrument system of the
`present invention, orthopedic surgeons can reconstruct a
`knee and retain “anatomic” landmarks. This makes it pos-
`sible to deal with many of the deformities confronting the
`orthopedic surgeon in an arthritic knee.
`There are three ways that joint surgeons can insert a total
`knee replacement:
`1) Resect the distal femur to accommodate the thickness
`of the femoral prosthesis. Resect the proximal tibia to
`accommodate the thickness of the tibial prosthesis.
`This recreates any lost motion and requires major soft
`tissue releasing. The flexzion and extension resection
`spaces are not coordinated.
`2) Rebuild the “normal” knee by compensating for loss
`articular cartilage and bone in the measurements for
`bony resection; then soft tissue releases can be per-
`formed to accommodate the proper dimensions. This
`places even greater demands on contracted soft tissues.
`Although this may be most anatomically correct, it
`requires such major tissue releases as to make it
`impractical.
`3) Accept bony and articular cartilage loss. Resect the
`amount of bone in flexion and extension to accommo-
`
`10
`
`15
`
`20
`
`25
`
`30
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`35
`
`40
`
`45
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`50
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`55
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`60
`
`65
`
`8
`date full extension and as much flexion as deemed
`necessary. This method relies on a coordinated resec-
`tion of the flexion-extension spacing. It relies on accu-
`rate measurements to allow for the resection of bone
`and minor soft
`tissue release. Within certain
`parameters, this method is preferable and can only be
`possible with better instrumentation, such as the instru-
`mentation of the present invention.
`Referring now to FIG. 1, the drawing diagrammatically
`illustrates the femur 1 and tibia 2 of a knee joint 3. The
`invention is concerned with the placement of planar resec-
`tions or cuts at the distal condylar region 4 of the femur 1 to
`receive a femoral knee prosthesis 5 (FIG. 4). Typically, a
`total knee replacement also requires placing a planar cut at
`the proximal tibia of the tibia 2 to receive a tibial prosthesis,
`not shown. The tibial prosthesis typically consists of a tibial
`baseplate, not shown, that is fitted on the proximal tibia after
`the tibial cut is made, and an articular insert, not shown,
`secured to the baseplate to articulate with the femoral
`prosthesis 5.
`The cut made on the tibia 2 and installation of the tibial
`
`knee prosthesis should be as close to the anatomic level as
`possible and should be substantially parallel to the floor in
`the mediolateral plane. This maintains the joint line at or
`close to anatomic level. Moreover, the angle of the proximal
`tibial resection should correspond to the angle of the distal
`femoral resections 12. For example, the proximal tibia is in
`mild varus and is resected such that the resection in the
`
`to the floor and oriented
`mediolateral plane is parallel
`posteriorly about 3°. Accordingly,
`the cuts made on the
`femoral prosthesis, discussed below, must also take into
`account this 3° mediolateral orientation in order to align the
`femoral prosthesis with the tibial prosthesis as will be
`explained later.
`Assuming normal anatomy, it is also important that the
`resected space medially in extension between the tibia 2 and
`the femur 1 of the knee equals the combined thickness of the
`medial tibial prosthesis and the distal medial femoral pros-
`thesis; that the resected space laterally in extension between
`the tibia 2 and the femur 1 of the knee equals the combined
`thickness of the lateral tibial prosthesis and the distal lateral
`femoral prosthesis;
`that
`the resected space medially in
`flexion between the tibia 2 and the femur 1 of the knee
`
`equals the combined thickness of the medial tibial prosthesis
`and the posterior medial femoral prosthesis; that the resected
`space laterally in flexion between the tibia 2 and the femur
`1 of the knee equals the combined thickness of the lateral
`tibial prosthesis and the posterior lateral femoral prosthesis;
`and that the resected space between the tibia 2 and the femur
`1 of the knee in flexionzn must be equal to or greater than the
`resected space between the tibia 2 and the femur 1 of the
`knee laterally in extension, assuming normal ligament bal-
`ance.
`
`The condylar region 4 of the femur 1 is formed with a
`medial condyle 6 and a lateral condyle 7 separated by an
`intercondylar notch 8. The femur 1 includes a shaft 9
`forming the femoral cortex, the condylar region 4 being at
`the distal end of the shaft 9.
`
`In order to install the femoral knee prosthesis 5 on the
`distal condylar region 4 of the femur 1, three planar cuts are
`made in the condylar region 4 to form seating surfaces for
`the prosthesis 5. These cuts consist of an anterior cut 10, a
`posterior cut 11 and a distal end cut 12. The placement of
`these cuts 10, 11, 12 is crucial to the installation of the
`prosthesis 5 and its effect on the overall function of the
`prosthetic knee joint.
`The invention is based on complying with the following
`conditions.
`
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`9
`1. Forming the planar cut 10 at the anterior surface of the
`femoral condylar region flush with the anterior surface
`13 of the femoral cortex so as to form a continuous
`surface therewith free of formation of either a notch or
`
`elevation at the juncture of cut 10 and surface 13.
`2. Forming the planar cut 11 at the posterior surface of the
`femoral condylar region at: a distance D from planar
`cut 10 equal to the interior dimension S between the
`anterior and posterior mounting surfaces 14, 15 of the
`prosthesis 5. The dimension S is the so-called A-P
`distance of the prosthesis and this distance varies for
`different size prostheses. For example, prosthesis are
`categorized as small, small (+), medium, large, large
`(+) and extra large and the A-P distance increases in
`proportion to the size increase.
`With reference to FIG. 3,
`therein is seen a plane T
`tangential to the medial and lateral condyles at the posterior
`surface 16 of the condylar region. The planar cut 11 is made
`at an angle A, with respect to plane T to angularly align the
`femoral prosthesis with the tibial prosthesis. Normally, the
`angle would be 3° to match the angle of the tibial prosthesis,
`however due to anatomical conditions of the patient such as
`wear of the medial or lateral condyles posteriorly the angle
`A can vary substantially, generally between 0 and 15°. The
`planar cut 11 will result in resection of bone of a thickness
`t1 at the medial condyle 6 and a thickness t3 at the lateral
`condyle. The thickness t3 is usually less than t1 and controls
`the location of planar cut 11 so that a minimum thickness of
`bone is resected at the posterior surfaces of the condyles. In
`this regard, the thickness t3 is established as the difference
`between distance D‘ between the anterior surface 13 of the
`
`femoral cortex and a plane P tangent to the posterior surface
`of the lateral condyle 7 and parallel to planar cut 11 and
`distance D between the anterior surface of the femoral
`
`cortex 13 and planar cut 11.
`The thickness t3 and the location of the prospective planar
`cut 11 therefore can be established based on measurement of
`the distance D and the A/P dimension of the selected size of
`the prosthesis. The size of the prosthesis is determined on the
`basis of the measurement of the distance D‘ and in general,
`the prosthesis size will be selected so that the thickness t3
`falls within a relatively narrow range, generally at least 6
`mm and between 6 and 11 mm. The resected thickness of
`
`bone t1 and t3 at
`generally unequal.
`The distal end cut 12 is made so that
`
`the medial and lateral condyles are
`
`the maximum
`
`thickness t2 of bone resected at the distal end is substantially
`equal to t3, i.e., the maximum thickness t2 of bone resected
`at the more prominent condyle at the distal end (the medial
`condyle 6 in FIG. 2) is equal to the minimum thickness t3 of
`bone resected at the posterior surface.
`Referring now to FIG. 5, in order to establish the precise
`positions of the three planar cuts 10, 11, 12 to be made on
`the femur 1, a referencing or datum system is utilized which
`in the description herein is in the form of an intramedullary
`rod 20 installed in a bore 21 formed in the femur 1. The use
`
`of the intramedullary rod 20 as a benchmark or datum is
`known in the art and is illustrated herein by way of example.
`Other referencing or datum systems can be employed as
`well, for example, utilizing two pins placed in the condyles
`as set distance below the anterior femoral cut to position an
`AP cutting guide thereon. This will be de