Smith & Nephew Ex. 1012
`IPR Petition - USP 8,377,129
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`U.S. Patent
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`Jun. 10, 2003
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`C?T
`(SLOT 98')
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`CUT 5
`(SLOT 7O')
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`F|G. 90
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`CUT 6' (SLOT 84')
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`CUT 6/ NOTCH CUT
`(SLOT 83')
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`C?T 2
`(SLOT 96')
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`CUT 4 (SLOT 92")
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`f
`CUT 3 (SLOT 94")
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`(NOTCH CUT)
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`42b."
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`1
`METHOD AND APPARATUS FOR FEMORAL
`RESECTION
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`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application claims priority pursuant to 35 U.S.C. 119
`based upon U.S. Provisional Application Ser. No. 60/036,
`220 filed Jan. 28, 1997, the entire disclosure of which is
`incorporated herein by reference.
`This application further is a continuation-in-part of Inter-
`national Application No. PCT/US98/01655 filed Jan. 27,
`1998, the entire disclosure of which is also incorporated
`herein by reference.
`
`BACKGROUND OF THE INVENTION
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`1. Field of the Invention
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`The present invention relates to an instrument and method
`for shaping a femur preparatory to implanting a knee pros-
`thesis.
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`2. Description of Related Art
`A total knee replacement or prosthesis, substitutes for a
`patient’s arthritic or otherwise dysfunctional natural knee
`joint. The prosthesis offers the patient an alternative treat-
`ment for the chronic pain and discomfort often associated
`with such problems.
`Burstein et al. U.S. Pat. No. 4,298,992 illustrates a popu-
`lar total knee joint prosthesis known as the Insall-Burstein
`(I/B) knee. Such prostheses comprise a femoral component
`attached to the patient’s femur, a tibial component attached
`to the patient’s tibia, and a patellar component attached to
`the patient’s patella. To use this prosthesis, it is necessary to
`shape by resection the patient’s femur, tibia and patella. The
`tibia and patella are shaped by a flat cut. In the case of the
`I/B prosthesis,
`the femoral component requires five cuts
`about
`the periphery of the femur and three cuts in the
`intercondylar notch in the distal end of the femur. These cuts
`conform to complementary portions of the femoral compo-
`nent which engage the bone.
`It
`is important
`that
`these
`femoral cuts be made precisely and located so that
`the
`position of the femoral component and the tibial component
`will closely approximate the positions of their anatomical
`counterparts. Proper positioning of the femoral and tibial
`components is required to insure the patient’s natural ana-
`tomic limb alignment and normal anatomical movement.
`As part of the installation of a knee joint prosthesis, it is
`important to balance the ligaments crossing the joint. Bal-
`ancing the ligaments means performing soft tissue releases,
`as necessary, so as to ensure that when the femur is lifted off
`of the tibia by a force directed along the long axis of the
`tibia, and the tibia is positioned in natural anatomic limb
`alignment, the tension in the medial and lateral ligamentous
`support is nearly equal. In order for the ligamentous tension
`to be nearly equal, the distance between the medial aspect of
`the femur and tibia, and the lateral aspect of the femur and
`tibia must be nearly equal when the tibia is in natural
`anatomic limb alignment. The distance between the femur
`and tibia should also be approximately equal throughout the
`range-of-motion of the tibia from full extension to approxi-
`mately 90 degrees of flexion. The distance between the
`femur and tibia is commonly called “the gap”, and the
`process of lifting the femur, and measuring the distance
`between the femur and tibia is commonly called “checking
`the gap”. Heretofore, gap checking has been done after the
`femur has been shaped and only at full extension, and 90
`degrees flexion. If proper balancing can not be achieved,
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`then it may be necessary to reshape the femur, which is
`obviously undesirable, or to use a more constrained total
`knee design, thus limiting knee motion.
`An object of the invention is to provide an instrument for
`use in shaping the distal surface of a femur preparatory to
`implantation of a knee prosthesis in which the gaps can be
`checked and adjusted prior to shaping the femur. This
`eliminates the need to recut the femur and reduces the time
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`required for surgery. Moreover, since it is easier to check the
`gaps with the invention, it is likely that more surgeons will
`take the time to check the gaps and, therefore, the quality of
`the surgery will improve.
`A further object of the invention is to provide a device for
`shaping the distal surface of a femur preparatory to implant-
`ing a knee prosthesis wherein all of the cuts required to
`shape the femur can be made using a single instrument.
`Yet another object of the present invention, is the ability
`to check the gaps continuously throughout the range-of-
`motion of the knee, not just at full extension and 90 degrees
`flexion, as with conventional devices.
`The most popular types of instruments used to shape the
`femur are intramedullary devices in which a cutting guide is
`positioned at the distal end of the femur relative to a rod
`which is driven into the intramedullary canal of the femur.
`Historically, surgeons have also used extramedullary align-
`ment to orient the instruments to cut the distal femur. The
`
`invention may be used with intramedullary or
`present
`extramedullary alignment techniques.
`SUMMARY OF THE INVENTION
`
`The principal component of the knee instrument accord-
`ing to the invention comprises a gap checking device which
`includes a curved base adapted to engage the distal end of
`the patient’s femur. Aplurality of slots are defined in the gap
`checking device for guiding the cutting instrument used to
`shape the femur. The gap checking device can be referenced
`to the patient’s femur using conventional intramedullary or
`extramedullary locator techniques.
`The thickness of the gap checking device is such that the
`distance between the distal cut in the femur to the distal
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`surface of the gap checking device plus the thickness of a
`shim corresponds in a predetermined way to the thickness of
`the femoral and tibial components of the prosthesis.
`Accordingly, the gaps can be checked with the gap checking
`device after placing the shim on the cut surface of the tibia.
`The shim also protects the cut surface of the tibia to prevent
`bone damage. After the knee has been properly balanced,
`bone cuts are made by passing a cutting instrument through
`the slots in the gap checking device. If necessary, a slot
`extender may be attached to the gap checking device to
`extend or increase the length of the slots.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The foregoing and other features of the present invention
`will be more readily apparent from the following detailed
`description and drawings of illustrative embodiments of the
`invention wherein like reference numbers refer to similar
`
`elements throughout the several views and in which:
`FIG. 1 is an exploded perspective view showing a 5-in-1
`gap checking device and slot extender according to a first
`embodiment of the invention;
`FIG. 2 is an exploded perspective view of a first embodi-
`ment of a gap checking device and intramedullary locating
`device in accordance with the present invention;
`FIG. 3 is a perspective view from the front showing the
`assembled gap checking device and intramedullary locating
`device of FIG. 2;
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`FIG. 4 is a side plan view of the assembled gap checking
`device and intramedullary locating device;
`FIG. 5 is a partial cross-sectional side plan view of the
`assembled gap checking device and slot extender of FIG. 1;
`FIG. 6 is a perspective view of the gap checking device
`of FIG. 1 positioned on the femur bone after the locating
`device has been removed;
`FIGS. 7a through 7d are different views of an alternative
`embodiment of the intramedullary locating device in accor-
`dance with the present invention;
`FIG. 8a is an exploded view of the alternative intramed-
`ullary locating device and an 8-in-1 gap checking device in
`accordance with the present invention;
`FIGS. 8b through 8d are different views of the alternative
`embodiment of the intramedullary locating device of FIGS.
`8a assembled to the 8-in-1 gap checking device;
`FIG. 9a is a side view of a femoral component and the
`8-in-1 gap checking device in accordance with the present
`invention;
`FIG. 9b is a bottom view of the femoral component and
`the 8-in-1 gap checking device of FIG. 9a;
`FIG. 10a is a side-by-side view of the 5-in-1 gap checking
`device in full extension before resection of the distal end of
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`the femur and after resection with the knee prosthesis
`components;
`FIG. 10b is a side-by-side view of the 5-in-1 gap checking
`device in 90 degrees flexion before resection of the distal
`end of the femur and after resection with the knee prosthesis
`components;
`FIG. 10c is a side-by-side view of the 5 -in-1 gap checking
`device at an angular position between full extension and 90
`degrees flexion before resection of the distal end of the
`femur and after resection with the knee prosthesis compo-
`nents;
`
`FIG. 11 is an exploded view of the 8-in-1 gap checking
`device with angle extender attachments in accordance with
`the present invention; and
`FIG. 12 is bottom view of the intramedullary locating
`device of FIGS. 7a—7a' oriented at an angle of 3 degrees in
`a clockwise direction.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`The instrumentation according to the invention includes a
`locating device, a gap checking device and a slot extender.
`A locating device is first used to properly position the gap
`checking device on the distal end of the femur. The surgeon
`uses the gap checking device to balance the ligaments of the
`patient’s knee before any of the femoral cuts are made. Once
`properly positioned, a cutting instrument or blade is guided
`through slots in the gap checking device in order to make the
`appropriate cuts in the femur. Prior to making the cuts, the
`slot extender may be attached to the gap-checking device to
`extend the length of the slots.
`FIG. 1 is a first embodiment of a 5-in-1 gap checking
`device 40‘ and slot extender 80‘
`in accordance with the
`
`present invention. Gap checking device 40‘ has a curved
`base 42‘ forming two bifurcated portions 42a‘ and 42b‘,
`which overlay the femoral condyles.
`As shown in the exploded view in FIG. 11, angle extender
`attachments 42a“, 42b“ may be secured, for example, by
`dovetail or tongue-and-groove, to the free end of the por-
`tions 42a‘, 42b‘, respectively, to extend the base 42‘ around
`the femoral condyles in order to check the balance of the
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`ligaments over a wider angular range, as explained in detail
`below. Outrigger arms 44‘ and 46‘ are immovably attached
`at one end to opposite sides of the base 42‘. One or more
`apertures 900 are defined in the outrigger arms 44‘ and 46‘
`through which pins 108 are inserted to secure the gap
`checking device 40‘ to the femur.
`Aball tip 66‘ is mounted to one end of the curved base 42‘,
`which overlies the femur during the operation. Two bores
`910 are defined through the ball tip 66‘ through which pins
`108 are inserted to secure the gap checking device 40‘, when
`properly positioned, to the femur. As shown most clearly in
`FIGS. 3 and 5, the gap checking device 40‘ includes five
`slots 70‘, 72‘, 74‘, 76‘ and 78‘ which, as explained below,
`guide the blades used to shape the surface of the femur to
`receive the femoral component of the prosthesis.
`Once secured in its proper position,
`the gap checking
`device 40‘ is used to check the balance of the ligaments in
`extension, flexion and any position therebetween prior to
`making any cuts in the femur bone. If the ligaments are not
`properly balanced,
`the surgeon may perform selected
`releases of soft tissue (ligaments, capsule, muscle) to adjust
`the gaps in the conventional manner, while the gap checking
`device is still attached to the femur. In order to be able to
`
`the thickness of the
`check the balance of the ligaments,
`curved base 42‘ and shim 500, which protects the tibia bone,
`should be such that the patient’s femur and tibia will be
`separated by the same distance that they will be separated
`after the femoral and tibial components of the knee pros-
`thesis are in place. FIGS. 10a through 10c show side-by-side
`views of the gap checking device 40‘ and prosthesis com-
`ponents in full extension, 90 degrees flexion, and at an angle
`between full extension and 90 degrees flexion, respectively.
`FIG. 10a shows the femur bone 505, tibia bone 510 and
`prosthesis components including femoral component 525,
`tibial insert 520 and tibial tray 515. The distance denoted
`between the arrows is the same when the gap checking
`device 40‘ is properly positioned on the distal end of the
`femur prior to resection (left hand side of FIG. 10a) as it is
`after resection when the prosthesis components are put in
`place (right hand side of FIG. 10a). In other words, the
`distance from the slot 70‘ (used to make the distal cut in the
`femur bone) at the distal surface of the base 42‘ to the surface
`of the cut tibia bone is the same as the distance from the
`surface of the distal cut of the femur bone to the surface of
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`the cut tibia when the prosthesis components are in place. To
`accommodate different thicknesses of tibial inserts, match-
`ing shims of different thicknesses are provided. The base 42‘
`of the gap checking device 40‘ is therefore configured so that
`the balance of the ligaments may be checked over a con-
`tinuous range-of-motion while the gap checking device 40‘
`is secured to the distal end of the femur and prior to making
`cuts in the femur bone. This is advantageous over conven-
`tional techniques in which the cutting guide must first be
`removed and the prosthesis components placed on the cut
`femur and tibia in order to check the balance of the liga-
`ments. The kinematics of the knee, while the gap checking
`device is secured to the femur and prior to making any cuts,
`will be substantially the same as the kinematics after the
`femoral and tibial components have been implanted,
`because the structure and outer surface of the gap checking
`device 40‘ is matched to the design of the prosthesis com-
`ponents. This way, balancing of the ligaments may be
`checked with the gap checking device while it is secured to
`the femur and before making any cuts to the femur, as if the
`femoral component itself was being tested.
`After the gaps have been checked and the ligaments
`balanced, a slot extender 80‘ (FIG. 1) may be secured, if
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`necessary, to the gap checking device 40‘ to lengthen the
`slots therein. To retain the gap checking device 40‘ and slot
`extender 80‘ together during the shaping operation, a thumb
`screw 150 is inserted through a hole 152 within the slot
`extender 80‘ and into engagement with a threaded bore 154
`on the gap checking device 40‘. As shown in FIG. 5, slot
`extender 80‘ includes slots 90‘, 92‘, 94‘, 96‘ and 98‘, aligned
`with the corresponding slots 70‘, 72‘, 74‘, 76‘ and 78‘ of the
`gap checking device 40‘, thereby lengthening or extending
`the slots through which a cutting blade can be inserted to
`shape the femur. The distal cut is made through slots 70‘ and
`90‘. The posterior cut is made through slots 78‘ and 98‘, and
`the anterior cut
`through slots 72‘ and 92‘. The anterior
`chamfer cut is made through slots 76‘ and 96‘, and the
`posterior chamfer cut is made through slots 74‘ and 94‘. It
`should be noted that the slot extender 80‘ is only used when
`the base is not sufficiently thick so that it is necessary to
`extend the length of the slot.
`The operation of the intramedullary locating device and
`gap checking device 40‘ shown in FIGS. 1-6 is as follows.
`Initially, an intramedullary rod 174 is inserted into the
`intramedullary canal of the femur and then used to align the
`gap checking device. The intramedullary locating device
`used to provide intramedullary alignment, as shown in
`FIGS. 2-4, includes a first member 160 which has a trian-
`gular projection 161 that mates with the recess 77‘ of the gap
`checking device 40‘. Afirst member 160 is secured to the gap
`checking device 40‘ by a screw 164 which engages a
`threaded hole 165 within the recess 77‘. The first member
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`160 is shaped to form parallel tracks 166 and 168 in which
`a slider 170 having a base and an upstanding collar 172
`projecting therefrom is displaceably positioned. The surgeon
`selects from among different upstanding collars 172 dis-
`posed at different angles a, relative to a reference axis
`perpendicular to the horizontal plane defined by the base in
`order to set the varus/valgus orientation angle. In a preferred
`embodiment, a is at an angle between approximately 2
`degrees and approximately 7 degrees relative to a reference
`axis perpendicular to the horizontal plane defined by the
`base. The assembled intramedullary locating device and gap
`checking device 40‘ are placed on to the distal end of the
`femur so that the intramedullary rod 174 passes through the
`upstanding collar 172. Gap checking device 40‘ is properly
`positioned by: (1) displacing the gap checking device 40‘
`along the axis of the intramedullary rod until the distal
`surface of the gap checking device 40‘ rests on the cartilage
`of the distal surface of the femur, (2) displacing the slider
`170 within tracks 166, 168 of the first member 160 until the
`ball tip 66‘ rests on the anterior surface of the femur; and (3)
`rotating the gap checking device 40‘ until the free end of the
`outrigger arms 44‘, 46‘ are substantially aligned with the
`center of the medial and lateral epicondyles, respectively, of
`the femur.
`
`If cartilage destruction is so significant that the outrigger
`arms 44‘, 46‘ do not align with the epicondyles of the knee
`when the distal surface of the gap checking device 40‘ rests
`on the cartilage of the femur, wedges 180 having the shape
`shown in FIGS. 3-5 may be used to fill
`in the space
`therebetween and ensure proper positioning of the gap
`checking device. Each wedge 180 includes a support surface
`182 which is adapted to contact the distal surface of the
`femur when the gap checking device is properly positioned
`on the distal end of the femur. The wedges are preferably
`shaped so as to be supported in slots 76‘ of the gap checking
`device used to perform the anterior chamfer cut.
`Accordingly, the wedges 180 ensure the proper positioning
`of the gap checking device 40‘ so that the distal cut is
`accurately made in the femur.
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`After the gap checking device 40‘ has been properly
`positioned on the femur, the surgeon tamps the pins 108
`through apertures 900, 910 into the epicondyles and the
`anterior surface of the femur, respectively. Once secured in
`its proper position, the surgeon removes the intramedullary
`locating device and rod from the femur, as shown in FIG. 6.
`The gap checking device 40‘ is used to check the balance of
`the ligaments in full extension, approximately 45 degrees
`flexion, and any position therebetween. If the ligaments are
`not properly balanced, the surgeon may perform selected
`releases of soft tissue (ligaments, capsule, muscle) to adjust
`the gaps. If angle extenders 42a“, 42b“ are attached to the
`gap checking device 40‘ the balance of the ligaments in
`extension and flexion may be checked over a wider angular
`range from full extension to approximately 90 degrees
`flexion, and any position therebetween. The length of the
`slots of the gap checking device 40‘ may be extended by
`attaching the slot extender 80‘ to the gap checking device 40‘
`via the thumb screw 150 received in the threaded apertures
`152 and 154. The cutting instrument is then passed through
`the slots of the gap checking device and the slot extender 80‘
`in order to make the cuts in the femur bone.
`
`An alternative embodiment of an intramedullary locating
`device 200 in accordance with the present
`invention is
`shown in FIGS. 7a through 7d. Intramedullary locating
`device 200 includes a first member 205. A second member
`
`210, having a channel defined therein and slidably displace-
`able in the direction indicated by the arrows so that the first
`member 205,
`is received in the channel of the second
`member and secured by a fastener 225. First member 205 is
`secured to the gap checking device 40‘ by a thumb screw 220
`received in the threaded aperture 154. Slider 216 having a
`base 217 and an upstanding collar 215 slides within a track
`of the first member 205. In a preferred embodiment, the
`surgeon selects from among several available sliders each
`with the upstanding collar 215 disposed relative to a refer-
`ence axis perpendicular to the horizontal plane defined by
`the base 217 at different fixed angles (X, preferably at an
`angle between approximately 2 degrees and approximately
`7 degrees, in order to set the varus/valgus orientation angle.
`It is within the intended scope of the invention to set the
`angle (X, as desired. A free end of the second member 210
`terminates in a movable paddle 201a and a fixed paddle
`201b.
`FIGS. 8a—8a' show different embodiments of the alterna-
`
`tive intramedullary locating device of FIGS. 7a—7d
`assembled to an alternative 8-in-1 gap checking device. In a
`preferred embodiment shown in FIG. 8a, movable paddle
`201a is positionable in one of two predetermined settings
`(denoted “R” and “L”), preferably set to approximately 3
`degrees rotation in a clockwise direction or approximately 3
`degrees rotation in a counterclockwise direction, to account
`for external rotation of the femoral component relative to the
`femur for the right versus the left knee. Movable paddle
`201a is secured in place by a fastener 230. By way of
`example, FIG. 12 shows the movable paddle 201a posi-
`tioned such that the locating device 200 is offset 3 degrees
`in a clockwise direction relative to the reference plane
`denoted by the solid line. It should be noted, however, that
`the predetermined angular settings may be specified as
`desired. FIGS. Sb through 8d show the intramedullary
`locating device 200 assembled to the 8-in-1 gap checking
`device 40“.
`
`The features and details of the 8-in-1 gap checking device
`40" are the same as those described above with respect to the
`first embodiment, except for additional slots forming cuts 6
`through 8. FIGS. 9a and 9b show the 8-in-1 gap checking
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`device 40" and the femoral component 300 of the knee
`prosthesis. The solid lines represent the cuts made in the
`distal end of the femur bone by passing the cutting blade or
`instrument through each of the slots defined in the gap
`checking device 40“. The shape of the distal surface of the
`resected femur complements the distal surface of the femo-
`ral component 300. Cuts 1 through 5 shown in FIG. 9a
`correspond to slots 98‘, 96‘, 94‘, 92‘, 90‘, respectively, in FIG.
`5. An additional three cuts 6, 7 and 8, are made in order to
`form a U-shaped notch in the distal end of the femur. Cuts
`7 and 8 are parallel to one another and defined by the
`confronting surfaces of the bifurcated portions 42a‘, 42b‘of
`the base 42‘, as shown in FIG. 9b. Cut 6 connects cuts 7 and
`8 to form a U-shaped notch in the femur. In one embodiment
`slot 83‘ is used to form cut 6. In another embodiment, slot
`84‘ may be used to form an alternate 6‘ cut to connect cuts
`7 and 8, that is deeper than that formed using slot 83‘. This
`alternative slot
`is suitable, for example, during revision
`when using a constrained condylar component. Although a
`single gap checking device 40“ having both slots 83‘ and 84‘
`is shown in FIGS. 8a—9b, since only one slot is used to form
`the 6th cut, it is also contemplated and within the intended
`scope of the invention to use two gap checking devices 40“,
`one having slot 83‘ and the other having slot 84‘, from which
`the surgeon selects one.
`In operation an intramedullary rod is inserted into the
`intramedullary canal of the femur bone. Movable paddle
`201a is set to one of the predetermined positions depending
`on whether the left or right knee is being worked on. The
`intramedullary locating device 200 is secured to the gap
`checking device 40‘ via the thumb screw 220 and the
`assembled device is placed on to the distal end of the femur
`so that the intramedullary rod passes through the collar 215.
`Then the surgeon positions the gap checking device 40‘ by
`(1) displacing the gap checking device 40‘ along the axis of
`the intramedullary rod until the distal surface of the gap
`checking device 40‘ rests on the cartilage of the distal surface
`of the femur; (2) displacing the slider 215 within the tracks
`of the first member 205 until the ball tip 66‘ rests on the
`anterior surface of the femur; and (3) displacing the second
`member 210 relative to the first member 205 and rotating the
`gap checking device 40‘ until the paddles 201a, 201b contact
`the posterior condyles of the femur. As in the first
`embodiment, if necessary, a wedge may be inserted in slot
`76‘ if the distal surface of the gap checking device 40‘ does
`not contact
`the distal end of the femur. Once the gap
`checking device 40‘ is properly aligned it is secured to the
`femur using pins 108 inserted through apertures 900, 910
`and then the intramedullary locating device 200 is removed
`from the femur. A slot extender 80‘ may be attached to the
`gap checking device 40‘, as described in detail above with
`respect to the first embodiment.
`Although the drawings and accompanying description
`only discuss an intramedullary locating technique, the gap
`checking device in accordance with the present invention is
`also suitable for extramedullary locating techniques.
`Thus, while there have been shown, described, and
`pointed out fundamental novel features of the invention as
`applied to a preferred embodiment thereof, it will be under-
`stood that various omissions, substitutions, and changes in
`the form and details of the devices illustrated, and in their
`operation, may be made by those skilled in the art without
`departing from the spirit and scope of the invention. For
`example, it is expressly intended that all combinations of
`those elements and/or steps which perform substantially the
`same function, in substantially the same way, to achieve the
`same results are within the scope of the invention. Substi-
`
`5
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`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`60
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`8
`to
`tutions of elements from one described embodiment
`another are also fully intended and contemplated. It is also
`to be understood that the drawings are not necessarily drawn
`to scale, but that they are merely conceptual in nature. It is
`the intention, therefore, to be limited only as indicated by the
`scope of the claims appended hereto.
`What is claimed:
`1. A method of shaping a femur preparatory to implanting
`a knee prosthesis having respective femoral and tibial
`components, said method comprising the steps of:
`applying a gap checking device to the distal end of the
`femur prior to resection, the thickness of the device
`corresponding in a predetermined way to the thickness
`of said femoral and tibial components;
`checking the gap; and
`shaping the distal end of the femur for the purpose of
`receiving the femoral component of said knee prosthe-
`sis after the gap has been checked.
`2. A method according to claim 1, wherein said gap
`checking device is referenced to epicondyles of the knee.
`3. A method according to claim 1, wherein said shaping
`step comprises passing a cutting device through slots in said
`gap checking device.
`4. A method according to claim 3, further comprising the
`step of fastening a slot extender to said gap checking device.
`5. A method according to claim 4, wherein said shaping
`step comprises passing a cutting device through slots in said
`gap checking device and said slot extender.
`6. A gap checking device for checking ligament balance
`prior to resection of a femur and use in shaping the distal end
`of the femur preparatory to implantation of a knee prosthesis
`which includes femoral and tibial components, comprising:
`a curved base adapted to extend from the anterior of the
`femur around the distal end to the posterior of the femur
`and receive the distal end of the femur prior to resec-
`tion.
`
`7. A gap checking device according to claim 6, wherein
`said base is adapted so as to check ligament balance in any
`position of flexion and extension, while secured to the distal
`end of the femur.
`
`8. A gap checking device according to claim 6, wherein
`said base is adapted so as to check ligament balance in at
`least three positions of flexion, while secured to the distal
`end of the femur.
`
`9. A gap checking device according to claim 6, wherein
`said base has at least one slot defined therein through which
`a cutting device can be passed therethrough to form at least
`one resect in the distal end of the femur.
`
`10. A gap checking device for checking ligament balance
`prior to resection of a femur and use in shaping the distal end
`of a femur preparatory to implantation of femoral and tibial
`components of a knee prosthesis, comprising:
`a curved base adapted to extend from the anterior of the
`femur around the distal end to the posterior of the femur
`and receive the distal end of the femur prior to resec-
`tion; and
`a shim disposed proximate an outer surface of said base,
`said base and shim having a combined predetermined
`thickness so that when said base is secured to the distal
`
`end of the femur the gap separating the femur and tibia
`is maintained substantially equal to the separation when
`the femoral and tibial components are implanted.
`11. A gap checking device for use in shaping the distal end
`of a femur preparatory to implantation of femoral and tibial
`components of a knee prosthesis, comprising:
`a curved base adapted to receive the distal end of the
`femur prior to resection, said base having at least one
`
`

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`US 6,575,980 B1
`
`9
`slot defined in said base and adapted so that a cutting
`device can be passed therethrough to form a distal cut
`in the femur; and
`a shim disposed proximate an outer surface of said base,
`said base and shim having a combined predetermined
`thickness so that when secured to the distal end of the
`
`femur the gap separating the femur and tibia is main-
`tained substantially equal to the separation when the
`femoral and tibial components are implanted.
`12. A method of shaping a femur preparatory to implant-
`ing a knee prosthesis having respective femoral and tibial
`components, said method comprising the steps of:
`applying a gap checking device to the distal end of the
`femur prior to resection;
`checking the gap; and
`shaping the distal end of said femur so as to receive the
`femoral component of said knee prosthesis after the gap
`has been checked.
`
`13. A gap checking device for use in shaping the distal end
`of a femur preparatory to implantation of a knee prosthesis
`including femoral and tibial components, comprising:
`a base having a curved inner surface adapted to fit around
`an uncut distal end of the femur and a curved outer
`
`surface being adapted so that when said base is con-
`nected to the femur, kinematics of the knee are sub-
`stantially the same as kinematics of the implanted
`femoral and tibial components so as to check balancing
`of ligaments while said base is secured to said femur
`prior to resection of said femur.
`14. A gap checking device in accordance with claim 13,
`wherein the kinematics of the knee and the k