(12) United States Patent
`Carignan et al.
`
`I lllll llllllll Ill lllll lllll lllll lllll lllll 111111111111111111111111111111111
`US006712856Bl
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6, 712,856 Bl
`Mar.30,2004
`
`(54) CUSTOM REPLACEMENT DEVICE FOR
`RESURFACING A FEMUR AND METHOD OF
`MAKING THE SAME
`
`(75)
`
`Inventors: Roger Carignan, Ventura, CA (US);
`Clyde R. Pratt, Somis, CA (US)
`
`(73) Assignee: Kinamed, Inc., Camarillo, CA (US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/528,128
`
`(22) Filed:
`
`Mar. 17, 2000
`
`Int. CI.7 ................................................... A61F 2/38
`(51)
`(52) U.S. Cl. .................................................... 623/20.35
`(58) Field of Search ........................... 623/20.35, 20.31,
`623/20.3, 20.32, 21.11, 21.12, 21.14, 20.18,
`20.19, 20.2, 20.21, 20.14, 11.11
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`3,748,662 A * 7/1973 Helfet ..................... 623/20.31
`4,178,641 A * 12/1979 Grundei et al. .......... 623/20.31
`5,123,927 A
`6/1992 Duncan et al.
`5,226,915 A * 7/1993 Bertin ..................... 623/20.15
`1/2001 McDowell
`6,171,340 Bl
`6,197,064 Bl * 3/2001 Haines et al. ............ 623/20.31
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`EP
`FR
`GB
`WO
`
`* 10/1989
`0336861
`0685210 Al * 12/1995
`* 4/1993
`2682589
`2215610
`9/1989
`* 6/1994
`9413214
`
`............. A61F/2/38
`............. A61F/2/38
`............. A61F/2/38
`
`........... A61B/17/16
`
`* cited by examiner
`
`Primary Examiner-Corrine McDermott
`Assistant Examiner-Alvin Stewart
`(74) Attorney, Agent, or Firm-Christopher Darrow;
`Claude I. Nassif; Greenberg Traurig, LLP
`
`(57)
`
`ABSTRACT
`
`A replacement device for resurfacing a joint surface of a
`femur and a method of making and installing such a device
`is provided. The custom replacement device is designed to
`substantially fit the trochlear groove surface, of an indi(cid:173)
`vidual femur. Thereby creating a "customized" replacement
`device for that individual femur and maintaining the original
`kinematics of the joint. The replacement device may be
`defined by four boundary points, and a first and a second
`surface. The first of four points is 3 to 5 mm from the point
`of attachment of the anterior cruciate ligament to the femur.
`The second point is near the bottom edge of the end of the
`natural articulatar cartilage. The third point is at the top ridge
`of the right condyle and the fourth point at the top ridge of
`the left condyle of the femur. The top surface is designed so
`as to maintain centrally directed tracking of the patella
`perpendicular to the plane established by the distal end of the
`femoral condyles and aligned with the center of the femoral
`head.
`
`DE
`
`3305237
`
`2/1983
`
`11 Claims, 6 Drawing Sheets
`
`~200
`
`-1-
`
`Smith & Nephew Ex. 1006
`IPR Petition - USP 7,534,263
`
`

`
`U.S. Patent
`
`Mar. 30, 2004
`
`Sheet 1of6
`
`US 6, 712,856 Bl
`
`FIG. 1
`
`~200
`
`FIG. 2
`
`-2-
`
`

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`U.S. Patent
`
`Mar. 30, 2004
`
`Sheet 2 of 6
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`US 6, 712,856 Bl
`
`FIG. 3
`
`f
`
`t
`
`FIG. 4
`
`_ /7
`
`-3-
`
`

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`U.S. Patent
`
`Mar. 30, 2004
`
`Sheet 3 of 6
`
`US 6, 712,856 Bl
`
`FIG. 6
`
`K
`
`&1
`
`FIG. 9
`
`3
`
`-4-
`
`

`
`U.S. Patent
`
`Mar. 30, 2004
`
`Sheet 4 of 6
`
`US 6, 712,856 Bl
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`22
`
`\
`
`33
`
`FIG. 7
`
`100
`
`FIG. 8
`
`-5-
`
`

`
`U.S. Patent
`
`Mar.30,2004
`
`Sheet 5 of 6
`
`US 6, 712,856 Bl
`
`70
`DIGITIZE EACH OF
`THE PLATES WITH
`THE IMAGE INTO A
`COMPUTER, WITH A
`X&Y REFERENCE
`FOR THE
`REFERENCE ROD ON
`EACH OF THE
`PLATES
`
`72
`
`BASED ON THE
`MARKINGS
`ORGANIZE EACH OF
`THE IMAGES INTO
`THEIR RELATIVE
`POSITIONS AND
`PREDETERMINED
`DISTANCE APART
`FROM EACH OTHER,
`THEREBY FORMING
`AN IMAGE OF THE
`DISTAL END OF THE
`FEMUR
`
`ONCE WEHAVi
`THE IMAGE OF
`THE DISTAL END
`OF THE FEMUR
`DO THE
`FOLLOWING
`
`78
`
`FROM THE
`DIGITIZED
`INfORMA TION, CUT
`OUT A PLASTIC
`PLATE FOR EACH
`LA YER, AND A HOLE
`ATTHEX&Y
`REFERENCE
`
`SCAN THE DISTAL
`END OF THE FEMUR
`IN PREDETERMINED
`INCREMENTS ALONG
`THE LONGITUDINAL
`AXIS OF THE
`FEMUR, WITH A
`REFERENCE ROD
`THERE THROUGH
`
`64
`
`TRANSFER THE
`INCREMENTAL
`SCANNED IMAGES
`ONTO FILMS
`
`66
`
`CUT AND MARK THE
`FILMS SO THAT
`RELATIVE
`POSITIONS OF EACH
`OF THE FILMS CAN
`BE DETERMINED
`
`68
`
`FORM A PLATE FOR
`EACH IMAGE ON
`THE FILM, ALONG
`WITH THE MARKING
`
`FIG. 10
`
`82
`
`ASSEMBLE THE
`PLASTIC PLATES BY
`INSERTING THE
`RECEPTIVE PLATE
`THROUGH A TUBE
`ABOUT THE HOLE
`IN THEX&Y
`REFERENCE, AND
`SPACED
`PREDETERMINED
`DISTANCES APART
`
`84
`
`APPLY FILLER OVER
`THE ASSEMBLED
`PLASTIC PLATES TO
`FORM A MODEL OF
`THE FEMUR
`
`86
`
`FORM A FEMALE
`MOLD FROM THE
`MODEL
`
`-6-
`
`

`
`U.S. Patent
`
`Mar.30,2004
`
`Sheet 6 of 6
`
`US 6, 712,856 Bl
`
`97
`
`103
`
`ON THE UNDERSIDE
`OF THE THIRD
`MOLD, MARK FOR
`PEGS, ASAN
`EXAMPLE, AN
`EQUILATERAL
`TRIANGLE WITH THE
`CENTER HALFWAY
`BETWEEN THE RIGHT
`AND LEFT CONDYLE
`EXTENTS, WHERE
`THE PEGS PROTRUDE
`PERPENDICULARLY
`FROM THE
`UNDERSIDE OF THE
`THIRD MOLD
`
`98
`
`MACHINE THE THIRD
`MOLD TO ALONG
`THE INK BOUNDARY
`AND THE TOP
`SURFACE TO FORM
`AN UNIFORM
`THICKNESS
`RESULTING IN A
`CONCAVE TOP
`SURFACE
`
`101
`
`DRILL HOLES ON
`THE THIRD MOLD
`WHERE IT IS
`MARKED FOR THE
`PIN(S)
`
`92
`
`FROM THE FEMORAL
`MOLD MAKE A
`SECOND MODEL OF
`THE FEMUR
`
`94
`
`ON THE SECOND
`MODEL, USEA
`TRANSFER INK TO
`MARK THE PROFILE
`AROUND THE
`BOUNDARY WHERE
`THE REPLACEMENT
`DEVICE JS TO BE
`PLACED
`
`96
`
`CAST A THIRD MOLD
`(USING MACHINABLE
`MATERIAL, SUCH AS
`PLASTIC GLASS) OFF
`OF THE SECOND
`MODEL AROUND THE
`BOUNDARY MARKED
`OFF, SO THAT THE
`UNDERSIDE OF THE
`THIRD MOLD
`CONTOURS THE
`TROCHLEAR GROOVE
`OF THE FEMUR, AND
`THE BOUNDARY OF
`THE REPLACEMENT
`DEVICE JS ALSO
`INDICATED BY THE
`TRANSFER INK
`
`INSERT PLASTIC
`PIN(S) IN THE
`HOLE(S) OF THE
`THIRD MOLD,
`FORMING A THIRD
`MODEL OFA
`REPLACEMENT
`DEVICE WITH PINS
`
`105
`
`USING THE THIRD
`MODEL WITH THE
`PINS MAKE A
`FOURTH MOLD TO
`MAKEA METAL
`REPLACEMENT
`DEVICE
`
`107
`
`USING THE THIRD
`MODEL BREAK OFF
`THE PINS AND MAKE
`A FIFTH MOLD TO
`MAKEA METAL
`MARKING TEMPLATE
`
`END OF THE
`PROCESS FOR
`MAKING THE
`REPLACEMENT
`DEVICE AND
`THE MARKING
`TEMPLATE
`
`FIG. 11
`
`-7-
`
`

`
`US 6,712,856 Bl
`
`1
`CUSTOM REPLACEMENT DEVICE FOR
`RESURFACING A FEMUR AND METHOD OF
`MAKING THE SAME
`
`BACKGROUND OF THE INVENTION
`
`1. Field of Invention
`The invention relates generally to a replacement device
`for a knee joint, and more particularly, to a device for
`resurfacing the trochlear groove of a femur that is custom(cid:173)
`ized to an individual and to methods for installing and
`making the same.
`2. Description of the Related Art
`The human knee joint primarily includes three parts, 15
`anatomically referred to as the femur (thighbone), the tibia
`(shinbone) and the patella (kneecap). The knee joint is then
`further subdivided into two joints: the patella-femoral joint
`(space between the kneecap and distal anterior surface of the
`thighbone) and the tibia-femoral (space between the thigh- 20
`bone and shinbone).
`During normal bending and straightening of the leg, the
`patella (kneecap) slides over the femur (thighbone) within a
`groove that is located on the front distal surface of the femur.
`This groove is referred to as the trochlear groove. Several 25
`types of abnormalities can occur with the movement of the
`patella over the femur. For example, the patella may dislo(cid:173)
`cate or slip out of place, it may fracture, or develop a
`tracking problem. Normally, the patella tracks, or glides
`within the central region of the trochlear groove. A tracking 30
`problem occurs when the patella no longer remains centered
`within the groove as it glides over the femur. The resulting
`abnormal biomechanics can cause chronic pain in the joint
`and if left untreated, it can lead to degenerative arthritis.
`The distal end of the femur (within which resides the 35
`trochlear groove) is covered with articular cartilage. This
`cartilage functions as a cushion between the femur and the
`tibia. In arthritis of the knee joint, the articular cartilage
`breaks down, either from abnormal wear as mentioned
`above, or from injury, age, congenital predisposition, 40
`inflammatory arthritis, or obesity, etc. When this cartilage
`breaks down, the cushion is lost, resulting in pain, swelling,
`bone spur formation and/or decreased range of motion of the
`knee joint.
`Due to the inability of damaged cartilage to repair itself 45
`after injury, the range of treatment for patients with unicom(cid:173)
`partmental disease involving the patella is limited. The most
`commonly prescribed treatments included soft tissue
`releases and/or realignment of the patellar tendon,
`patellectomy, where the patella is completely removed, or a 50
`total knee replacement with a standardized patello-femoral(cid:173)
`tibial prosthesis. In certain instances none of these proce(cid:173)
`dures may be desirable or effective. For example, the soft
`tissue procedures may not work. A patient having undergone
`a patellectomy is left partially crippled due to the loss of the 55
`kneecap, which served to hold the joint together.
`Additionally, these patients often still suffer from pain due to
`contact of the remaining tendon moving directly over the
`groove. A total knee replacement with a standardized pros(cid:173)
`thesis is also far from ideal because much of the femur bone 60
`must be carved away in order to "fit" the distal surface of the
`femur to the standardized prosthesis. Additionally, the
`patients are often young and are likely to require replace(cid:173)
`ment of the prosthesis. Each revision operation is more
`difficult. Therefore, there still is a need for a better treatment 65
`of patient's with degenerative arthritis of their patella(cid:173)
`femoral joint.
`
`2
`The present invention provides a replacement device that
`is customized to each individual knee joint. Due to the
`"fitting" of the replacement device to the patient's femur,
`instead of the reverse as is the case with standard prosthetic
`5 devices, the patient's original range and force of motion
`(kinematics) through the knee joint is preserved and the
`patient does not suffer from device-related pain. Also
`included is a method for making a customized replacement
`device and a marking template for such a device. Bone stock
`10 removal is limited and functionally is maximized.
`
`BRIEF SUMMARY OF THE INVENTION
`The present invention is directed toward a custom
`replacement device for resurfacing an articulating or joint
`surface of the femur and methods of making and installing
`such a device. This custom replacement device overcomes
`the problems associated with prior knee joint replacement
`devices or prostheses in that it is made specifically to fit the
`trochlear groove surface (surface over which the patella
`slides) of a femur from an individual patient. Thereby
`creating a "customized" replacement device for that indi(cid:173)
`vidual femur.
`The replacement device is substantially defined by four
`outer points and first and second surface areas. The first of
`four points is defined approximately as being 3 to 5 mm
`from the point of attachment of the anterior cruciate liga(cid:173)
`ment to the femur. The second point is defined approxi(cid:173)
`mately at or near the superior edge of the end of the natural
`cartilage. The third point is defined approximately at the top
`ridge of the right condyle. The fourth point is defined
`approximately at the top ridge of the left condyle. The first
`surface area is customized to substantially match the bone
`surface area of the trochlear groove of the femur. The second
`surface area has a tracking path that is approximately
`perpendicular to the end of the condyles of the femur. The
`thickness between the first and second surface areas may be
`approximately between 2 mm and 6 mm. To couple the
`replacement device to the femur, a pin protruding from the
`first surface area may be used to penetrate an opening in the
`femur prepared by a surgeon. Boney ingrowth may secure
`the prosthesis or bone cement may be used.
`The replacement device can also include a customized
`drill guide that is substantially defined by first and second
`surface areas. The first surface area is customized to the
`surface area of the trochlear groove of the femur. The second
`surface area includes a hole that is aligned substantially to
`the pin to assist in drilling the opening into the femur for the
`pin.
`In accordance with one aspect of the present invention,
`these and other objectives are accomplished by providing a
`replacement device having a top surface; a bottom surface;
`the bottom surface substantially formed to match the tro(cid:173)
`chlear groove surface of a femur; and the top surface
`substantially tracking the trochlear groove of the femur.
`In accordance with another aspect of the present
`invention, these objectives are accomplished by providing a
`system for installing a replacement device to a distal end of
`a femur having a trochlear groove surface, comprising: a
`marking template, wherein: the marking template has a back
`side substantially matching the distal end of a femur; and an
`opening through the marking template; a drilling apparatus
`to form a hole on the distal end of the femur assisted by the
`opening in the marking template; and a replacement device,
`wherein: the replacement device has a bottom side substan(cid:173)
`tially matching the distal end of the femur; and a pin
`protruding from the bottom side of the replacement device
`adapted to insert into the hole on the distal end of the femur.
`
`-8-
`
`

`
`3
`In accordance with yet another aspect of the present
`invention, these objectives are accomplished by providing a
`method of making a replacement device, comprising the
`steps of: forming a model of a distal end of a patient's femur;
`forming a first mold from the model, wherein the first mold
`has a bottom side that substantially matches the trochlear
`groove of the patient's femur, wherein the first mold has a
`top side opposite of the bottom side; coupling a peg on a
`predetermined location on the bottom side of the first mold;
`shaping the top side of the mold to substantially track the 10
`trochlear groove of the patient's femur; forming a second
`mold from the first mold; and pouring viscous material into
`the second mold to make a replacement device.
`In accordance with still another aspect of the present
`invention, these objectives are accomplished by providing a
`replacement device having a bottom side that substantially
`matches the trochlear groove of a patient's femur, wherein
`the bottom side of the replacement device has a pin at a
`predetermined location; providing a marking template hav(cid:173)
`ing a back side that substantially matches the trochlear
`groove of the patient's femur, wherein the marking template
`has an opening corresponding to the predetermined location
`of the pin; removing the cartilage from the distal end of the
`femur; positioning the marking template about the femur
`substantially similar to the desired installed position of the
`replacement device; drilling a hole on the distal end of the
`femur though the opening of the marking template; remov(cid:173)
`ing the marking template from the femur; and inserting the
`pin of the replacement device into the hole of the femur to
`install the replacement device on the desired location of the
`femur.
`Alternatively, a method of forming a customized replace(cid:173)
`ment device for a femur will include the steps of duplicating
`the surface of the distal anterior femur from an individual;
`and using the duplicate to form a back surface of the
`customized replacement device and/or a customized mark(cid:173)
`ing template.
`
`15
`
`the
`the
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a perspective view of a femur showing
`patellar side with its trochlear model groove, and
`replacement device adapted to couple to the femur;
`FIG. 2 is a perspective view of a embodiment of the
`present invention illustrating an exemplary replacement
`device coupled to the distal end of a femur;
`FIG. 3 is an another perspective view of the femur with
`the replacement device coupled to the femur;
`FIG. 4 is yet another perspective view of the femur
`associating with a custom marking template having guide
`holes that correspond to the pin on a replacement device,
`residing on the trochlear groove surface of the femur;
`FIG. 5 is a cross-sectional view of the replacement device
`residing on the femur, along the line 5-5 in FIG. 2;
`FIG. 6 is the perspective view of FIG. 4 with a patella
`residing on the trochlear groove surface of the replacement
`device;
`FIG. 7 is an exemplary illustration of a human femur
`attached to a tibia by the anterior and the posterior cruciate 60
`ligaments;
`FIG. 8 is an expanded view of a human knee joint in a
`bent position;
`FIG. 9 is a perspective view showing a patellar face side
`of a human femur and a back side view of a replacement 65
`device prior to placement of the replacement device onto the
`femur;
`
`US 6,712,856 Bl
`
`4
`FIG. 10 is a diagrammatic chart of a method of making a
`mold for constructing a replacement device; and
`FIG. 11 is a diagrammatic chart of a method of making a
`replacement device and a marking template from a femoral
`5 mold.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`This description is not to be taken in a limiting sense, but
`is made merely for the purpose of illustrating the general
`principles of the invention. The section titles and overall
`organization of the present detailed description are for the
`purpose of convenience only and are not intended to limit
`the present invention.
`One of the features of the present invention is to provide
`a replacement device for a patient's knee joint that replicates
`as closely as possible the original kinematics of the patient's
`knee. More particularly, the replacement device substan-
`20 tially replicates patient's actual trochlear tracking pattern of
`the femur to maintain the original articulating movement of
`the knee. To do so, unhealthy articular cartilage is removed
`and replaced with the replacement device, which is custom
`fitted for a patient's femur to maintain as closely as possible
`25 the original articulating movement of the patella about the
`trochlear groove. That is, the replacement device is custom
`fitted so that the underside of the patella articulates about the
`femur approximately two (2) to six (6) mm away, which
`mimics what a patella on a healthy articular cartilage would
`30 articulate from. The above feature may be accomplished by
`providing a trochlear groove that is formed along the
`replacement device that tracts the trochlear groove on the
`femur. Moreover, as further discussed below, the underside
`of the replacement device substantially matches the face of
`35 the femur, to minimize any error in positioning the replace(cid:173)
`ment device about the femur. With this introductory in mind,
`more detailed description of the invention is discussed
`below.
`As illustrated by way of example in FIGS. 2 and 9, one
`40 embodiment of the present invention includes a custom
`replacement device 4 adapted to associate with the distal end
`of a patient's femur 2. FIG. 2 shows a model made of the
`patient's femur in FIG. 9. The model 200 is substantially
`similar to the patient's femur 2 and is used to make the
`45 custom replacement device 4 (as discussed below). The
`surface near the distal end of the femur 2 defines a patellar
`face 5, and along the patellar face is a trochlear groove 3 of
`the femur. FIGS. 7 and 8 show exemplary views of a normal,
`intact knee joint. Referring to FIG. 8, on a healthy knee, the
`50 trochlear groove would be covered with about 5 mm of
`articular cartilage 100. However, if the articular cartilage
`wears down for any reason, the cushion and sliding surface
`that the cartilage provides is lost, resulting in pain, and
`therefore may need to be replaced with the custom replace-
`55 ment device 4.
`One of the advantages with the replacement device 4 is
`that it is custom fitted for a patient's femur so that the
`replacement device 4 replacing the articular cartilage will
`maintain as closely as possible the original kinematics of the
`patient's knee. That is, the replacement device 4 is custom(cid:173)
`ized specifically to fit the patellar face 5 surface and tro(cid:173)
`chlear groove 3 region of the femur 2. In this regard, as
`illustrated in FIGS. 1 and 9, the back surface 6 of the
`replacement device 4 substantially matches the surface area
`of the patellar face 5 of the femur 2. Moreover, the back
`(bottom) surface 6 also matches and fits to the contours of
`the trochlear groove region 3 of the patellar surface 5. The
`
`-9-
`
`

`
`US 6,712,856 Bl
`
`5
`custom replacement device is coupled to the femur through
`one or more hole(s) 202 in the distal end of a human femur.
`The hole(s) 202 can be made by a surgeon and may be
`located so as to reside along the trochlear groove region 3 of
`the human femur 2. As shown in FIG. 5, the replacement 5
`device can be implanted into the femur via a pin 19 inserted
`into the one or more corresponding hole 202, thus resurfac(cid:173)
`ing the patellar face surface of the human femur. The front
`(top) surface 7 of the replacement device is contoured to
`maintain the tracking of the patella centrally within the front 10
`surface during articulation of the patella about the trochlear
`groove (FIG. 2).
`As illustrated by way of example in FIGS. 1 and 2, the
`replacement device 4 may be substantially defined by four
`boundary conditions 8, 10, 12, 14, along with the back 15
`surface 6 and the front surface 7. By way of background, a
`human knee joint includes two cruciate ligaments which are
`located in the center of the knee joint. As shown in FIG. 8,
`these two ligaments, referred to in the art as the anterior
`cruciate ligament (ACL) 22 and the posterior cruciate liga- 20
`ment (PCL) 24, are the primary stabilizing ligaments of the
`knee. The ACL 22 attaches, at its bottom 26, to the tibia 30,
`and, passes obliquely upward to insert 20 into the inner and
`back part 32 of the outer condyle 15 of the femur 2.
`Attachment of the ACL to the femur stabilizes the knee joint 25
`along the rotational axis and prevents the femur from sliding
`backwards on the tibia (or the tibia from sliding forward on
`the femur).
`In one embodiment of the present invention, the distal
`portion of the patellar tongue or first boundary condition of 30
`the replacement device may be designed to not extend far
`back to impinge upon the tibial surface or cartilage of the
`tibia. Therefore, the first boundary condition of a replace(cid:173)
`ment device may be defined to be approximately 3 to 5 mm
`from the point of attachment of the ACL to the patient's 35
`femur. Specifically, as illustrated in FIGS. 3 and 8, the first
`boundary condition 8 may be approximately 3 to 5 mm from
`the point of attachment 20 of the anterior cruciate ligament
`22 to the femur 2. In other words, there is approximately 3
`to 5 mm distance between the patellar tongue region (first 40
`boundary condition) 8 and the attachment 20 of the anterior
`cruciate ligament 22. Alternatively, the first boundary con(cid:173)
`dition of a replacement device 8 is of a sufficient distance
`above the groove 21 where the ACL exits so as not to result
`in impingement upon the tibial surface 33 during function- 45
`ing.
`Referring to FIGS. 1 and 8, the second boundary condi(cid:173)
`tion 10 may be defined approximately at or near the superior
`edge 100 of the end of the natural cartilage 102. As shown
`in FIGS. 3 and 8, the third boundary condition 12 may be
`approximately at the top ridge of the right condyle 104. The
`fourth boundary condition 14 may be approximately at the
`top ridge of the left condyle 106. The four boundary
`conditions 8, 10, 12, 14 and front 6 and back 7 surface, as
`described above, may substantially define the perimeter or 55
`outer edges of the replacement device in approximately an
`oval shape. However, the replacement device need not be
`defined by any one of the four boundary conditions.
`Alternatively, the replacement device may be defined by any
`one of or any combination of the four boundary conditions. 60
`Of course, the perimeter or outer edges of individual
`replacement devices may differ depending on the unique
`anatomic characteristics of an individual patient's femur.
`Besides the four boundary conditions, the back surface 6 is
`customized to match the patellar face 5 of the femur 2 (FIG. 65
`1). Moreover, edges of the replacement device may be
`streamlined to have smooth or rounded edges so that the
`
`6
`replacement device may come in direct contact with the
`bony surface of the femur without etching away at the femur.
`Still further, the streamlined edges prevents tearing or dam-
`aging the soft tissue around the knee.
`As further illustrated in FIGS. 2 and 3, the front surface
`7 is generally concave, which is formed by the inner and
`outer lateral (side) lip regions being raised to contour around
`the third and fourth boundary conditions 12 and 14, respec(cid:173)
`tively. Accordingly, as illustrated by way of example in FIG.
`3, the longitudinal path of the resulting front surface sub(cid:173)
`stantially replicates the actual trochlear groove-tracking
`pattern for a healthy knee generally in two ways. The first
`way is to create a mold that substantially replicates the distal
`end of a patient's femur (as discussed below); and based on
`the geometry of the replicated mold, the patient's trochlear
`groove tracking pattern can be determined off of the mold.
`As illustrated by way of example in FIG. 3, the second way
`is to align the tracking pattern (axis t-t) along the front
`surface area 7 so that it is approximately perpendicular to the
`ends of the condyles 104 & 106 of the femur 2, i.e., and
`aligned with the center of the femoral head (axis f-t); as
`most patients have a tracking pattern that is generally
`perpendicular to the ends of the condyles. Thus, the first
`method can be used to check the alignment of tracking
`pattern calculated by the second method, and vice versa.
`Alternatively, the tracking pattern produced by both meth-
`ods can be combined to produce an average tracking pattern
`of both methods. Either way, the tracking pattern produced
`by both methods will substantially replicate the correct
`trochlear groove-tracking pattern. Without such customiza(cid:173)
`tion of the replacement device, there are too many variations
`amongst patients' knees such that the original kinematics for
`a patient could not be reproduced. In addition, standard
`devices require the removal of large amounts of bone in
`order to make them fit onto the femur. Still further, other
`known or new methods of tracking the patient's trochlear
`groove of the femur may be used.
`As illustrated by way of example in FIG. 6, the tracking
`pattern is generally formed along the base of concave
`surface 313 of the replacement device 4, thereby maintain(cid:173)
`ing the patella 30 centrally within the device 312. Therefore,
`regardless of the direction or angle of movement of the
`patella and tibia (shin bone) along the replacement device,
`the trajectory of the patella will be maintained centrally
`within the intercondyle space and the patella will glide
`smoothly within the central line due to the increased cur-
`vature of the device along its lateral and medial or side lip
`regions. This allows the present invention to use a standard
`dome patellar prosthesis 30 such as the Kinamed, Inc. GEM
`50 Knee System patella, which has a large contact area 34 with
`the device, to distribute the stress applied to the patella and
`the device. So that even if there is a slight misaligninent with
`replicating the trochlear groove of the femur, if at all, there
`is room for error and still full contact across the surface of
`the patella to distribute the load in an optimal manner.
`Accordingly, the patella will repeatedly glide over the front
`surface of the replacement device, reliably, and there is little
`chance, if at all, that the patella will dislocate from the
`tracking surface of the replacement device. In addition, the
`large contact area distribute' s the load and minimizes peak
`contact stress in the polyethylene thus reducing wear debris
`generation.
`In the past, replacement of a diseased knee joint required
`surgical modification of the surface of the femur so as to
`allow a close "fit" of the prosthetic device within the new
`joint. This required extensive removal or carving of the
`cartilage and bone surfaces of the head of the femur in order
`
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`US 6,712,856 Bl
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`7
`to "match" with the back surface of a standardized prosthetic
`device. With the present invention, there is almost no
`removal of original bone and therefore, no loss of requisite
`anatomical structures. Insertion of the replacement device
`requires minimal removal of existing anatomic structures, if
`at all. Therefore, the intent is to remove only the diseased
`portion (the natural cartilage) of the patient's knee joint prior
`to installing the replacement device.
`In a healthy knee joint, the average thickness of the
`articular cartilage 102 at the knee joint is about 4 to 5 min
`(FIG. 8). In other words, there is about 4 to 5 mm of articular
`cartilage covering the femur, so that the patella articulates
`about 4 to 5 mm from the trochlear grove of the femur. In
`the case of unhealthy cartilage, where the replacement
`device is needed, the unhealthy cartilage is removed and 15
`replaced with the replacement device, which has been cus(cid:173)
`tom made for the patient's femur. To replicate as closely as
`possible the original kinematics of the patient's patello(cid:173)
`femoral joint, as illustrated by way of example in FIG. 2
`(and further detailed in FIG. 5), the thickness between the 20
`back 6 and front 7 surface areas of the replacement device
`may vary approximately between 2 mm and 6 mm. In other
`words, the thickness of the custom replacement device may
`be approximately that of the patient's original articular
`cartilage. To further enhance the interaction between the 25
`custom replacement device 4 and the femur 2, a pin 19 may
`be located at a predetermined position along the back
`surface 6 of the replacement device. One or more pin(s) 19
`can protrude from the back surface area to enhance the
`association of the replacement device with the femur. As 30
`illustrated in FIG. 9, the replacement device may have three
`pins that insert into the corresponding holes in the femur, so
`that there will be very little play, if any, once the pins are
`inserted into the holes. Alternatively, other apparatus and
`methods may be used to couple the replacement device to 35
`the femur, for example, a bone ingrowth surface or
`adhesives, including cement, may be applied between the
`replacement device and the femur. Still another alternative
`may be a screw or bolt, where the screw penetrates through
`the opening in the replacement device and into the femur. In 40
`other words, any known or new apparatus or methods may
`be used to couple the replacement device to the femur.
`By way of background, a bone ingrowth surface is a
`surface treatment applied to an implant which is designed to
`allow the patient's bone to attach or ingrow into the 45
`prosthesis, and thereby securing the prosthesis to the bone.
`The surface coating can assume a number of different forms.
`For example, commonly used is a process where a layer is
`physically attached to the prosthesis through titanium
`plasma spraying. Other techniques involve sintering small 50
`beads or mesh to the surface or applying a layer of
`hydroxyapatite may also be used.
`With regard to surgically implanting the replacement
`device, as illustrated in FIG. 4, a customized marking
`template 300 may be provided that is substantially defined 55
`by first (back or bottom) and second (front dr top) surface
`areas 302 and 304, respectively. Like the back surface 6 of
`the replacement device 4, the first surface area 302 of the
`marking template 300 is customized to match the surface
`area of the trochlear groove 5 of the femur so that the 60
`marking template will be positioned properly with the
`femur. The second surface area 304 includes a hole 306 or
`holes (depending upon the number of pins protruding from
`the replacement device) that is in a predetermined position
`to align substantially to the pin on the customized replace- 65
`ment device. Furthermore, the holes or slots 306 of the
`second surface area 304 of the custom marking template,
`
`8
`extend through to the first surface 302 of the custom marking
`templat