Ulllt?d States Patent [19]
`Schuster
`
`US
`OO5735277A
`[11] Patent Number:
`[45] Date of Patent:
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`5,735,277
`Apr. 7, 1998
`
`[54] METHOD OF PRODUCING AN
`ENDOPROSTHESIS As A JOINT
`SUBSTITUTE FOR KNEE-JOINTS
`
`4,976,737 1711990 Rake‘
`5,370,692 12/1994 Fink et a1. .............................. .. 623/16
`FOREIGN PATENT DOCUMENTS
`
`[76} Inventor: Luis Schuster. Ringstr. 15. D 86911
`Riederau. Germany
`
`,
`[21] Appl' No" 530529
`
`2/1988 European Pat. 011'. .
`0 255 797
`32 13 434 4/1982 Germany .
`3417 609 11/1985 Germany .
`35 22 196 2/1986 Germany .
`36 26 549 211988 Germany .
`
`Sep. 20, 1995
`[22] Filed:
`[30]
`Forelgn Apphcanon Pmmty Data
`Sep. 27, 1994 [DE]
`Germany ........................ .. 44 34 539.9
`
`OTHER PUBLICATIONS
`“MG II Total Knee System Surgical Technique Using Zim
`mer® Intramedullary Instrumentation.” Introduction. p. l.
`
`[51] rm, (:1.6 ...................................................... .. A61]! 6/00
`U-S. Cl. ................................... ..
`
`623/20
`[58] Field of Search ............................ .. 128/653.1. 653.2;
`623/16‘ 18‘ 20‘ 66
`
`[56]
`
`.
`References Clted
`U_S_ PATENT DOCUMENTS
`_
`
`""""""""""""""""" "
`45501490 3/1987 Figgie, m I
`4,658,808
`4/1987 Link
`4,759,350
`7/1988 Dunn‘etal. .
`
`Prim,” Emme,_Ruth S_ Smith
`Attorney, Agent, or Fim1_R3m5[ & Prestia
`
`ABSTRACT
`[57]
`In a process of producing an endoprosthesis as a joint
`replacement especially for knee joints. a reference image for
`determining contour diiferences on the femur and the tibia.
`which are obtained by comparing a corrected preoperative
`image of the damaged knee joint with a postoperative image.
`is used as the basis for preparing corresponding femoral and
`tibial components of the endoprosthesls.
`
`7 Claims, N0 Drawings
`
`-1-
`
`Smith & Nephew Ex. 1013
`IPR Petition - USP 9,295,482
`
`

`
`1
`METHOD OF PRODUCING AN
`ENDOPROSTIIESIS AS A JOINT
`SUBSTITUTE FOR KNEE-JOINTS
`
`BACKGROUND OF THE INVENTION
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`5.735.277
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`2
`implantation of such an endoprosthesis as a joint replace
`ment for knee joints.
`
`The present invention pertains to a process of producing
`an endoprosthesis as a joint replacement for knee joints.
`wherein the production of the prosthesis utilizes information
`from a surgical intervention on the femur. the tibia. and the
`patella of a damaged knee joint.
`The surgical intervention on a knee joint is taken into
`consideration by the attending physician when the patient
`complains about severe pains in the knee and disability as a
`consequence of. e.g.. rheumatoid arthritis or other joint
`diseases. The surgical intervention takes place convention
`ally in a plurality of steps. which are adapted exclusively to
`the shape of individual joint moldings. which are manufac
`tured industrially in di?erent graduated sizes and which are
`ultimately fastened to milled surfaces mainly of the anterior
`femoral condyle. of the distal femur. of the proximal tibia.
`and of the patella in such a way that a vertical alignment is
`achieved with such components in relation to an axis which
`is obtained. e. g.. by means of a preoperative X-ray image
`and an intramedullary pin alignment system for the straight
`line connecting the center of the hip. the knee and the
`malleolus. An illustrative representation of such a surgical
`procedure can be found. e.g.. in prospectus No. 9'7-5110- 102
`20 MA of the ?rm of Zimmer. Inc.. 1989 edition. entitled
`"MG 11 TOTAL KNEE SYSTEM SURGICAL TECH
`NIQUE" as well as in US. Pat. No. 4.759.350. in which a
`corresponding intramedullary pin system is described.
`Not only is the implantation of such three-part knee joint
`endoprostheses very expensive. but. taking into account the
`often great differences in the patients’ growth. only an
`approximate restoration of the conditions of a healthy knee
`joint is achieved at best. Therefore. complications also occur
`frequently; they can be attributed to the mechanics of the
`implanted prosthesis components. and thus they lead. e.g.. to
`an anterior knee joint pain syndrome. which is caused by
`incorrect gliding of the patella. with a nonphysiological
`loading of the femur-patella gliding joint Irritations also
`frequently develop. occasionally with considerable hyper
`trophy of the joint mucosa and pronounced effusions in the
`knee joint as a consequence of a massive abrasion of the
`implanted prosthesis parts. some of which consist of poly
`ethylene and will then lead to unfavorable gliding behavior
`with this material if such abrasion becomes excessive or
`loosening of the bone anchoring of the components of the
`prosthesis occurs. which is usually performed by means of
`pins and a screw connection and often with cementing.
`When such complications are determined. it is frequently
`necessary to implant a new endoprosthesis. in which case
`new problems arise. e.g.. concerning the creation of a
`changed support for the components of a new prosthesis.
`with the requirement of a resection of additional bone parts.
`
`DESCRIPTION OF THE INVENTION
`This object is accomplished with a process of producing
`an endoprosthesis as a joint replacement especially for knee
`joints by making use of the following steps:
`1. A preoperative image of the patient’s damaged knee
`joint is prepared. The preparation of such an image may
`be performed by computed tomography. i.e.. a tomo
`graphic method. or preferably by nuclear magnetic
`resonance tomography. because it makes possible an
`especially sharp de?nition of the joint contour by
`representing the cartilaginous tissue and other soft parts
`of the damaged knee joints. so that correspondingly
`optimal preconditions are also created for the surgical
`intervention.
`2. The surgical intervention is performed on the femur. the
`tibia. and the patella of the damaged knee joint subse
`quent to the preparation of such a preoperative image.
`Basically only the complete removal of the non-load
`bearing bone and additionally the removal of only an
`absolute minimum of the adjacent healthy bone at least
`on the femur and the tibia have to be performed during
`this surgical intervention. so that a resection surface
`which is ideal for a subsequent cementing of the
`corresponding femoral or tibial component of the
`endoprosthesis to be implanted is obtained on the bone.
`3. When the surgical intervention has been concluded. a
`corresponding postoperative image of the knee joint is
`prepared. again either by computed tomography or
`preferably by nuclear magnetic resonance tomography.
`4. Subsequent to this surgical intervention or already
`subsequent to the preparation of the preoperative image
`of the damaged knee joint. a correction of this preop
`erative image is then performed. attempting to
`approach the conditions occurring in a healthy knee
`joint with this correction. This correction of the pre
`operative image may be performed either manually on
`this preoperative image itself. in which case the more
`or less ideal contours of at least the femur and of the
`tibia. which lead to a correspondingly optimal physi
`ological joint contour of the knee joint for the joint
`surfaces provided with the endoprosthesis implanted
`later. are consequently followed with the correction.
`This correction of the preoperative image may there
`fore also be brought about. as an alternative. on the
`basis of an image which is. to the extent possible. a
`mirror image of a healthy knee joint opposite the
`damaged knee joint. based on the assumption that the
`two knee joints of a patient have identical shape and
`that the most favorable conditions for the implantation
`of the endoprosthesis can indeed be created for the
`damaged knee joint by such a comparison of a damaged
`knee joint with a healthy knee joint. It is also
`conceivable. in principle. to perform the correction of
`the preoperative image by a comparison with images of
`knee joints which were taken under comparable
`conditions. and the knee joints have joint surfaces of
`the femur. tibia and patella which are comparable with
`the damaged knee joint.
`5. The preoperative image thus corrected is then com
`pared with the postoperative image prepared subse
`quent to the surgical intervention in order to determine
`the di?erences between the two images. The conditions
`on the contours of the femur and tibia are of special
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`SUMMARY OF THE INVENTION
`The basic object of the present invention is therefore to
`provide a process of producing an endoprosthesis as a joint
`replacement especially for knee joints. which helps mini
`mize the complications which can be observed in the case of
`the conventional implantation of such endoprostheses. e.g..
`the nonphysiological loading of the joint. the problem of a
`su?icient possibility of anchoring especially of the femoral
`and tibial components of the prosthesis. and the avoidance
`of an excessive loss of bone primarily at the time of the ?rst
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`5 .735_.277
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`interest in this connection. because the difference in the
`size of these contours is the basis for the subsequent
`preparation of corresponding femoral and tibial com
`ponents of the endoprosthesis.
`6. As was indicated above. the last process step of
`producing an endoprosthesis as a joint replacement for
`knee joints thus pertains to the preparation of at least
`femoral and tibial components. which corresponds to
`the difference in the size of the surfaces which were
`imaged for the corrected preoperative conditions on the
`femur and the tibia. the difference being detemiined
`with the reference image. The preparation of such
`femoral and tibial components of an endoprosthesis.
`which is subsequently to be implanted. is carried out.
`e.g.. by digitizing the reference image which deter
`mines the differences between the corrected preopera
`tive image and the postoperative image and subse
`quently using it for preparing the components on a
`machine according to a copying process.
`As a result of the process of producing an endoprosthesis
`as a joint replacement for knee joints. components are
`obtained which thus have the contours of the healthy knee
`joint or lead at most to slightly different joint contours.
`which are adapted to the current bone-soft tissue conditions
`and are at the same time correspondingly ideally adapted
`physiologically. and whose successful implantation will then
`depend more or less only on the quality of the anchoring of
`the components. Since a major risk of mechanical loosening
`can hardly be expected in the case of the implantation of
`such nearly ideal joint replacement components. cementless
`anchoring of the components on the femur and the tibia is
`suitable for their anchoring. and the surgical intervention on
`the damaged knee joint can already be accomplished—with
`respect to the individual adaptation of the joint conditions in
`a patient—concerning the additional removal of healthy
`bone. besides the complete removal of no longer load
`bearing bone. such that physiologically satisfactory anchor
`ing of the components of the endoprosthesis is achieved for
`the implantation.
`If necessary. the preparation of an endoprosthesis also
`includes. of course. the preparation of a component. which
`is used for the patella of the damaged knee joint. The process
`can also be used for a surgical intervention on other joints.
`e.g.. the ankle joint. if comparable conditions can be pre
`sumed
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`I claim:
`1. A method of producing an endoprosthesis as a joint
`replacement for knee joints comprising:
`preparing a preoperative tomographic image of the dam
`aged knee joint;
`preparing a healthy knee joint tomographic image by
`approximating the contours of at least the femoral bone
`and the tibia of the damaged knee joint to those of a
`healthy knee joint;
`preparing a postoperative tomographic image of the dam
`aged knee joint;
`comparing and determining the differences between: (1)
`the contours of at least the femoral bone and of the tibia
`of the healthy knee joint tomographic image; and (2)
`the contours of at least the femoral bone and of the tibia
`of the postoperative tomographic image of the damaged
`knee joint. to prepare a tomographic reference image
`representing said differences; and
`preparing at least a femoral component and a tibial
`component of an endoprosthesis based on the tomo
`graphic reference image.
`2. The method of claim 1. wherein all of said tomographic
`images are prepared by a computed tomography.
`3. The method of claim 1. wherein all of said tomographic
`images are prepared by a nuclear spin resonance tomogra
`phy.
`4. The method of claim 1. wherein the step of preparing
`said healthy lmee joint tomographic image comprises manu
`ally altering said preoperative tomographic image.
`5. The method of claim 1. wherein the step of preparing
`said healthy knee joint tomographic image includes prepar
`ing a mirror image of a healthy knee joint of the patient.
`6. The method of claim 1. wherein the step of preparing
`said healthy knee joint tomographic image includes identi
`fying an image of a healthy knee joint having contours of at
`least the femoral bone and the tibia comparable to the
`contours of the preoperative image of the damaged knee
`joint.
`‘ 7. The method of claim 1. wherein the step of preparing
`at least a femoral component and a tibial component of an
`endoprosthesis includes digitizing the refmence image and
`using said digitized reference image to prepare said femoral
`component and said tibial component according to a copying
`process.
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