United-States Patent [19]
`Woolson
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,841,975
`Jun. 27, 1989
`
`[54] PREOPERATIVE PLANNING OF BONE
`CUTS AND JOINT REPLACEMENT USING
`RADIANT ENERGY SCAN IMAGING
`[75] Inventor:
`Steven T. Woolson, Los Altos, Calif.
`[73] Assignee: Cemax, Inc., Santa Clara, Calif.
`[21] Appl. No.: 38,515
`[22] Filed:
`Apr. 15, 1987
`
`[51] Int. Clx‘ .............................................. .. A61B 6/00
`[52] US. Cl. .................................. .. 128/653; 378/205;
`128/303 B
`[58] Field of Search .......... .. 378/205; 128/630, 303 B,
`128/653, 659
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,941,127 3/1976 Froning ......................... .. 128/303 B
`4,058,114 11/1977 Soldner .... ..
`.. 128/303 B
`4,360,028 7/1982 Barbier et a1. .
`.... .. 128/659
`
`4,436,684 3/1984 White . . . . . . . . .
`
`. . . . .. 264/138
`
`4,440,168
`4,583,538
`
`128/303 B
`4/1984 Warren
`4/1986 Onik .............................. .. 128/303 B
`
`OTHER PUBLICATIONS
`Rutkow et al., “Orthopaedic Operations in The United
`States”, The Journal of Bone and Joint Surgery, ,vol.
`68-A, #5, 6/86, pp. 716-719.
`Insall et al., “The Total Condylar Knee Prosthesis in
`Gonarthrosis”, The Journal of Bone and Joint Surgery,
`vol. 64-A, #5, 6/83, pp. 619-628.
`Lotke et al., “In?uence of Positioning of Prosthesis in
`Total Knee Replacement”, The Journal of Bone and
`Joint Surgery, vol. 59-A, #1, l/77, pp. 77-79.
`Johnson et al., “The Distribution of Load Across the
`Knee, A Comparison of Static and Dynamic Measure
`ments”, The Journal of Bone and Joint Surgery, vol.
`62-B, #3, 8/80, pp. 346-349.
`
`Corcoran, “Medical Electronics”, IEEE Spectrum,
`1/87, pp. 66-68.
`McDonnell Douglas advertisement, “Breadthrough:
`Computer Graphics that Create Model Patients for
`Surgeons”, Businessweek, 6/ 18/ 84.
`“Machine-Made Body Joints”, Science Digest, 6/ 83.
`Love, “Better Bones”, Forbes, 11/21/83, pp. 314, 316.
`“Hospital for Special Surgery Computer Designs Cus
`tomized Joint Replacements”, Orthopedics Today, vol.
`2, No. 12, 12/83, Pp- 3 & 16.
`Primary Examiner-Ruth S. Smith
`Attorney, Agent, or Firm-Cushman, Darby & Cushman
`[57]
`ABSTRACT
`A method is disclosed for the preoperative planning of
`a total knee replacement. Guide tools having guide
`members which are adjustable for placement on se
`lected positions of the femur and tibia are used for locat
`ing the position of desired bone cuts de?ned by a cut
`ting guide surface existing on the guide member. Se
`lected regions of the femur and tibia are scanned by
`computed tomographic techniques to provide images of
`these regions. The respective centers of the femur head,
`distal femur, proximal tibia and distal tibia, or ankle
`joint are determined. The center points are then used to
`de?ne a mechanical axis relative to which selected cuts
`are to be made corresponding to selected prostheses to
`be implanted. The CT scan representations are used to
`measure the desired location of the guide member cut
`ting surface and the respective locations of guide mem
`bers adjacent selected bone positions. These guide
`members are adjusted relative to the cutting surface
`prior to surgery. This provides for precise placement of
`the guide tools during surgery and the making of accu
`rate and precise bone cuts conforming to the selected
`prostheses.
`
`18 Claims, 4 Drawing Sheets
`
`-1-
`
`Smith & Nephew Ex. 1031
`IPR Petition - USP 7,534,263
`
`

`
`US. Patent Jun. 27, 1989
`
`Sheet 1 of 4
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`4,841,975
`
`FIG. 2A
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`FIG. 2B
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`FIG. 5
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`-2-
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`

`
`US. Patent
`Jun. 27, 1989‘
`US. Patent Jun. 27, 1989‘
`
`Sheet 2 of4
`Sheet 2 01'4
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`4,841,975
`4,841,975
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`)~44
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`R
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`FIG. 3B
`FIG. 3B
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`28
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`US. Patent Jun. 27, 1989
`
`Sheet 3 of 4
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`4,841,975
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`58
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`66
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`58
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`4B5
`66
`68
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`FIG. 6B
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`62
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`FIG. 6A
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`-4-
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`US. Patent Jun. 27, 1989 '
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`Sheet 4 0f 4
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`4,841,975
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`-5-
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`1
`
`PREOPERATIVE PLANNING OF BONE CUTS
`AND JOINT REPLACEMENT USING RADIANT
`ENERGY SCAN IMAGING
`
`O
`
`4,841,975
`2
`intramedullary system of femoral component align
`ment;
`2. localization of the center of the femoral head by
`external markers after operative radiographs are
`taken, and correct estimation of the center of the
`distal femur for the external alignment system of
`femoral alignment;
`3. visual estimation of the centers of the proximal tibia
`and of the ankle joint in both the coronal and sagittal
`planes for correct tibial component alignment.
`These alignment techniques may produce error from
`the fact that the surgeon must estimate the correct posi
`tion of all bone landmarks and from inaccuracies in the
`preoperative radiographs of the knee joint. Flexion
`contractures of the knee will cause signi?cant errors in
`the tibiofemoral angle (the angle between the femoral
`anatomical and mechanical axes). Medullary systems
`require accurate placement of the entrance hole for the
`alignment rods since the rod does not tightly fit into the
`medullary canal and may be angled into it if the drill
`hole is placed too far medially or laterally. A consider
`able amount of the operative time in total knee replace
`ment surgery is expended in positioning and attaching
`the alignment instruments and in double-checking their
`placement, which is essential since any system may fail
`and have to be overruled by the experienced eye of the
`surgeon.
`The present invention overcomes the inherent inac
`curateness of the presently used systems by combining
`several steps. Selected regions of the body adjacent a
`bone to be resectioned are scanned with radiant energy
`to obtain representations of the regions for de?ning the
`structure of the speci?c bone and adjacent body re
`gions. From the representations, desired positions of a
`cutting guide relative to the bone are determined. Thus.
`by having these specific features of bone structure iden
`ti?ed and used for determining speci?c placement of the
`cutting guide, accurate and precise placement during
`the surgical procedure is provided.
`Control of the guide surface of a cutting guide which
`de?nes the contour of a desired bone cut is assured
`where the cutting guide includes one or more gauge
`members positionable adjacent a selected position on
`the bone and adjustable relative to the guide surface for
`positioning the guide relative to the bone. These spe
`ci?c settings of the gauge members relative to the guide
`surface are determined from the representations of the
`selected body regions adjacent and including the bone
`having a section to be replaced. In the preferred method
`of the present invention, a joint is replaced and the
`replacing prostheses are aligned relative to axes associ
`ated with each joint-forming bone so that the resulting
`prostheses will have a speci?c alignment relative to
`those axes. By determining the position of the gauge
`member relative to the axis, the position of the cutting
`guide surface is established prior to the surgical proce
`dure, with corresponding precise placement of the
`guide during the procedure.
`It should be noted that CT scan information has been
`used in the past relative to prostheses. For example, in
`an article in Volume 97 (June 1979) of Fortschritte der
`Medizin on page 781-784 entitled “Ein neues Verfahren
`zur Herstellung Alloplastischer Spezilimplantate fur
`den Becken-Teilersatz”, a method of preparing alloplas
`tic implants is described in which a three-dimensional
`model of a patient’s pelvis is constructed by assembling
`Styrofoam sheets made from computer tomography
`
`35
`
`BACKGROUND AND SUMMARY OF THE
`INVENTION
`This invention relates to a method for preoperative
`planning of surgery. More particularly, it pertains to a
`method of preoperative planning of a bone cut and joint
`replacement using radiant energy scan imaging to deter
`mine the position of a bone-cut-de?ning guide relative
`to the bone to be cut.
`The preferred method of the present invention is for
`the replacement of a total knee. This includes the re
`moval of bone sections from the distal femur and proxi
`mal tibia for replacement by a knee joint prosthesis
`associated with each of these bones.
`Total knee replacement is a common orthopaedic
`surgical procedure currently performed over 150,000
`times each year in the US The clinical results of many
`operations are excellent with complete relief of pain,
`improvement in function, restoration of motion, and
`correction of deformity in over 90% of the cases. How
`ever, there are a number of cases in which failures occur
`following the knee replacement. One of the most impor
`tant causes for failure of the procedure is from prosthe
`sis component loosening because of unbalanced loading
`of the tibial component caused by improper knee joint
`alignment. Because of this fact, all total knee implanta
`tion systems attempt to align the reconstructed knee
`joint in the mechanical axis in both the coronal and the
`sagittal planes. If achieved, this results in the placement
`of the total knee prostheses in a common mechanical
`axis which correspondingly is highly likely to produce
`a successful long-term result.
`Reproducing the mechanical axis at surgery is pres
`ently done by one of two different techniques, which
`use either the external bone landmarks at the hip and
`ankle joints or the medullary canal of the femur or a
`combination of these two systems for alignment. Knee
`systems which use the center of the femoral head as a
`landmark for orienting the femoral component require
`an operative radiograph of the hip joint to position an
`external marker for alignment of the femoral cutting
`guide. Intramedullary knee systems require a preopera
`tive radiograph of the femur in order to determine the
`angle between the anatomical and the mechanical axes
`of the femur for proper orientation of the femoral cut
`ting guide. These intramedullary systems require the
`surgeon to estimate the placement of a drill hole into the
`distal femur at a central location in the bone for intro
`duction of a small diameter rod into the medullary canal
`to produce the correct component alignment. The prox
`imal tibia is cut perpendicular to the mechanical axis of
`the tibia by adjusting the tibial cutting guide in relation
`to the knee and ankle joints. Both of these techniques
`necessitate intraoperative visual estimation of the loca
`tion of the midpoints of the distal femur, the proximal
`tibia and the ankle joint by the surgeon. The alignment
`of the components in the sagittal plane is also done by
`visual means or the “eyeball” method.
`In summary, with the present total knee instrument
`systems, correct knee alignment involves the following:
`1. preoperative determination of the angle between the
`anatomical and mechanical axes of the femur from
`the radiographs, and appropriate placement of the
`medullary rod entrance hole in the femur for the
`
`45
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`55
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`-6-
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`

`
`3
`?lms. U.S. Pat. No. 4,436,684 assigned to the same as
`signee as this application, describes using information
`obtained from CT scans to drive a sculpting tool to
`make a corporeal model.
`As will be more apparent hereinafter, with the pres
`ent invention a surgeon’s need to do preoperative plan
`ning from plain radiographs is eliminated. Because there
`is no need to determine the placement or adjustment of
`cutting guides at the time of surgery, fewer instruments
`are necessary and the surgical procedure is simpli?ed
`and shortened. Accurate sizing of the prosthesis compo
`nents is possible by measurement of the axial CT scan
`slices at the level of component placement for each
`bone. The vast majority of all important intraoperative
`decisions are decided preoperatively by this intensive
`and precise planning method. The surgeon has to make
`fewer critical judgment calls during surgery and is able
`to eliminate the constant visual monitoring of the align
`ment instrument. Elimination of these steps markedly
`reduces the operative time of the procedure.
`
`5
`
`25
`
`30
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`Referring now to the accompanying four sheets of
`drawings:
`FIG. 1 is a silhouette view of a femur as viewed in the
`coronal plane;
`FIGS. 2A. 2B are silhouette views of a tibia in coro
`nal and sagittal planes, respectively;
`FIGS. 3A, 3B are silhouette views of a femur and a
`tibia, respectively, identifying bone regions scanned for
`obtaining representations of the bones;
`FIG. 4 is a perspective view of an anterior femoral
`cutting guide in place on a distal femur;
`FIG. 5 is a distal end view of the cutting guide of
`FIG. 4;
`35
`FIGS. 6A, 6B are anterior and lateral views, respec
`tively, of-a femur with a distal femoral cutting guide in
`place;
`FIGS. 7A, 7B are a lateral view and a perspective of
`another cutting guide for making ?nal femoral cuts; and
`40
`FIGS. 8A, 8B show anterior and lateral views, re
`spectively, of a proximal tibial cutting guide in position
`adjacent a tibia showing adjustments and placement of
`the cutting guide for use during a knee replacement
`operation performed according to the present inven
`tion.
`
`4,841,975
`4
`patient has not been moved. Thus, it will be appreciated
`that the points, lines and dimensions discussed herein
`may be obtained either in a manual process using repro
`duced selected 2D images, or by identifying those
`points on an appropriate computer system which then
`can relate the speci?c points selected.
`Referring initially to FIGS. 1, 2A and 2B, selected
`positions on the bones of interest, in this case the femur
`and tibia, are identi?ed. In this instance it is important
`that the knee prostheses be positioned on, and for rela
`tive rotation about, an axis perpendicular to the me
`chanical axis of a femur 10 and a'corresponding tibia 12.
`A mechanical axis 14 extends through the midpoint 16
`of the femur head. Axis 14 also extends through mid
`point 18 of the distal femur. During the knee replace
`ment surgical procedure, it will be necessary to resec
`tion the medial and lateral condyles of the distal femur
`by cutting along a line 20 which is perpendicular to axis
`14.
`The proximal end of tibia 12 will be resectioned along
`a cut plane identi?ed by the dashed line 22 in FIG. 2B.
`The line of this cut must be perpendicular, or slightly
`angled as will be discussed subsequently, relative to a
`mechanical axis 24 of the tibia. Axis 24 is de?ned by the
`midpoint 26 of the proximal tibia and the midpoint 28 of
`the ankle joint.
`The mechanical axes of the femur and tibia in two
`planes can be graphically determined by identi?cation
`of the 3D coordinates derived from the CT image data
`by identi?cation of the positions of the midpoints of the
`femoral head, the distal femur, the proximal tibia and
`the ankle joint in the coronal and sagittal planes. Fur
`ther, the 3D spatial location of the most distal projec
`tions of the medial and lateral femoral condyles 30, 32,
`respectively, are found in the coronal plane image, as
`shown in FIG. 1. The distance from each of these points
`to distal femoral out line 20 is also determined. These
`are represented, respectively, by distances A and B.
`This gives the proportions of bone from the medial and
`lateral condyles which are to be resected to produce a
`distal femoral cut along line 20. As will be seen, the
`plane represented by line 20 in FIG. 1 is also perpendic
`ular to the anterior femoral cortex which, in the sagittal
`plane, is parallel with mechanical axis 14. The remain
`der of the femoral bone cuts, as will be described, are
`customized to the speci?c prosthesis, and ligamentous
`balancing of the new knee joint is done in a routine
`manner.
`As will be seen, the tibial cutting guide includes
`gauge members positioned to contact opposite sides of
`the proximal tibia and, with an allowance for skin
`depth, the lateral and medial ankle protusions. More
`speci?cally, tibial mechanical axis 24 in the coronal and
`sagittal planes, as seen in FIGS. 2A, 2B, is graphically
`depicted and the distances from this line are found to
`the medial cortex (distance C) and to the lateral cortex
`(distance D) of the proximal tibia. Also the distance
`from mechanical axis 24 to the skin surface over the
`medial malleolus (distance E) and to the skin surface
`over the lateral malleoulus (distance F) are determined
`for alignment in the coronal plane. Further, from a
`representation of the tibia in the sagittal plane, the dis
`tance from the axis to the anterior cortex of the proxi
`mal tibia where the tibial cutting guide 34 contacts it
`(distance G) and the distance from the axis to the skin
`surface over the anterior aspect of the distal tibia (dis
`tance H) is determined. Further, the distance along axis
`24 from cut line 22 to the position where distance H is
`
`45
`
`DETAILED DESCRIPTION OF THE
`PREFERRED METHOD
`The preferred method of practicing the present in
`vention is based on exact three-dimensional (3D) data of
`the bone anatomy obtained from computed tomography
`(CT) scans of the knee, hip and ankle joints for a total
`knee replacement. Any point on a CT scan slice can be
`located on the x or horizontal axis (coronal plane) and
`on the y or vertical axis (sagittal plane) as seen on a
`two-dimensional (2D) CT image. Speci?c points may
`be located by scaling or measuring relative to a refer
`ence point on the 2D image. Alternatively, such points
`may be simply identified on a CT scan imaging system,
`such as a CEMAX-IOOO or CEMAX-lSOO system avail
`able from CEMAX, Inc. of Santa Clara, Calif. In such
`system, the image generated from CT scan information
`is identi?ed by movement of a cursor to the speci?c
`point of interest. The system then determines the spatial
`or 3D coordinates associated with that point which then
`may be related to any other point selected which re
`sulted from the same scan procedure, so long as the
`
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`5
`measured, is also determined. This distance is shown as
`distance I.
`Finally, as will be further described subsequently, the
`position of the base of tibial cutting guide 34 from the
`skin surface over the anterior aspect of the distal tibia
`can be varied to control the angle of cut line 22 with
`respect to axis 24. Thus, a distance J must be determined
`for producing the corresponding selected angle.
`In order to obtain the necessary representations or
`images of the regions of the femur and tibia, and associ
`ated body portions, such as the skin around the ankle,
`suitable CT scans are made. Further, since only selected
`regions need be measured, only those regions need to be
`scanned. The CT scan protocol involves independent
`scans of the femur and of the tibia with the patient
`supine and with the knee joint in extension. The femoral
`scan includes a single centimeter-thick scan through the
`center of the femoral head as identi?ed by region 36 of
`FIG. 3A. With the femur held in position, a single 1
`centimeter-thick scan is made through the distal femur,
`in region 38, through the femoral condyles at the mid
`point of the patella. Then 1.5- or Z-milIimeter-thick
`scans are performed through the distal projections of
`both femoral condyles, shown as region 40, so that the
`most detailed information is of the articular surface of
`25
`the femur.
`The patient is repositioned for the scans of the tibia. A
`single centimeter thick scan through the ankle joint
`(region 42) is made and again, without any patient mo
`tion, the proximal articular surface of the tibia is simi
`larly scanned (region 44).
`When an enhanced computerized imaging system is
`used, a magnetic tape copy of the CT image data is
`made for transfer of the data to the imaging system for
`producing the representations of the selected bones.
`From the spatial coordinates in the coronal plane
`derived from the scans of the femoral head and the
`distal femur, a femoral coronal mechanical axis line 14 is
`mapped out on graph paper as illustrated in FIG. 1.
`Distal femoral out line 20 is drawn perpendicular to
`mechanical axis line 14. Measurements of the distances
`from line 20 to the most distal points 30, 32 on the me
`dial and lateral femoral condyles, respectively, are
`taken from the graph. The relative distances for medial
`and lateral condylar bone resection to create a distal
`femoral cut along line 20 are thus known. This bone cut
`is also made perpendicular to the anterior femoral cor
`tex, and therefore, the distal femoral cut need only be
`planned in the coronal plane.
`Planning of the proximal tibial cut is more complex,
`since the reference points for it must be determined in
`two planes preoperatively. The tibial mechanical axis 24
`in the coronal and sagittal planes is determined from the
`coordinates of the centers of the ankle joint (point 28)
`and of the proximal tibia (point 26). The distances from
`this axis to the medial (distance C) and lateral (distance
`D) cortexes of the proximal tibia and to the skin over
`the medial (distance E) and lateral (distance F) malleo
`lus are used for appropriate positioning of the tibial jig
`or cutting guide 34 in the coronal plane. It will be ap
`preciated that any two of these distances are suf?cient
`to align the tibial jig relative to the axis.
`The direction of the proximal tibial cut in the sagittal
`plane will be dependent upon the particular total knee
`prostheses chosen. This cut may be made perpendicular
`to the sagittal mechanical axis, as is shown in FIG. 2B,
`or inclined posteriorly up to 5 or 10 degrees. The dis
`tance from the skin surface over the distal tibial plafond
`
`4,841,975
`6
`to the distal portion of the tibial cutting guide (distance
`J) determines the amount of posterior inclination of the
`tibial cut.
`Using this preoperative planning method, the surgeon
`is able to determine mechanical axes 14, 24 and dis
`tances A-J. These speci?c bone landmarks and dis
`tances correspond for presetting the cutting guides illus
`trated in FIGS. 4»8, which now will be discussed. It
`will be appreciated that the various cutting guide ad
`justments which need to be made are precisely deter
`mined. The gauge members of the guides are adjusted
`corresponding to the determined distances. Thus. when
`these cutting guides are placed in position adjacent the
`bone to be resectioned, precise positioning and align
`ment are achieved.
`In particular, during a surgical procedure, the ?rst
`femoral bone cut is flush with and parallel to the ante
`rior cortex of the femur as illustrated in FIGS. 4 and 5.
`In these ?gures, the position of an anterior cortex cut
`ting guide 46 is shown positioned on the distal end of a
`femur 10. Guide 46 includes a block member 48 which
`is tacked into position against the distal condyles as
`shown in the ?gures. A cutting-surface-de?ning mem
`ber 50 has a slit 52 which is planar and aligned with the
`underside of a foot 54 positionable on the anterior tibial
`cortex. Thus, a saw 56 cutting through slit 52 makes an
`initial anterior femoral cut flush with the anterior femo
`ral cortex, as shown by the dashed lines in FIG. 4. This
`results in a bone surface which is parallel with the ante
`rior femoral cortex which, as discussed previously, is
`parallel with the mechanical axis of the femur.
`As illustrated in FIGS. 6A and 6B, the distal femur
`condylar cuts are then made using a distal femoral cut
`ting guide 58 placed flat on the anterior femur surface
`just cut and pinned into place. The proportion of the
`medial and lateral femoral condylar bone to be resected
`which was determined by the preoperative planning
`system is used to set this instrument. If, for example, this
`proportion is 2:1, or removal of twice the amount of
`medial femoral condylar bone as lateral femoral condy
`lar bone, and the distal thickness of the femoral prosthe
`sis is 8 mm, then the distal femoral cutting guide gauge
`member 60 is correspondingly adjustably positioned on
`an adjustment post 62 relative to a slit 64 de?ning a cut
`surface contour (corresponding to out line 20). Corre
`spondingly, the lateral femoral condyle cut is deter
`mined by positioning a gauge member 66, which ex
`tends down across the face of the condyle, a distance B
`from slit 64, by adjustment along an adjustment post 68.
`With the bottom surface of cutting guide 58 being pla
`nar and perpendicular to slit 64, a cut, identi?ed by line
`70 in FIG. 6B, results which is perpendicular to me
`chanical axis 14.
`The ?nal anterior, posterior and chamfer cuts on the
`femur are made after the proximal tibial cut has been
`made and a trial test of adequate bone resection has been
`made with the knee in extension using trial spacers, as is
`conventionally done. The ?nal distal femoral cuts are
`made with a single conventional cutting guide 72 which
`is ?xed in position on femur 10 by pins which are placed
`in holes drilled in the end of the femur which corre
`spond to the pegs in the actual femoral prosthesis, as
`represented by the use of a drill 74. The resulting cuts
`by saw 56 are illustrated in FIG. 7A.
`FIGS. 8A, 8B illustrate the positioning of tibial cut
`ting guide 34 relative to tibia 12. Cutting guide 34 in
`cludes a telescoping shaft, parallel with axis 24 as
`viewed in FIG. 8A, consisting of a base member 76, an
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`intermediate shaft member 78, and a cut-positioning
`member 80. Each of these three members are adjustable
`relative to the other, as shown. Intermediate member 78
`includes a brace 82 which contacts the anterior cortex
`of the proximal tibia. This position corresponds with the
`location for measuring distance G described with refer
`ence to FIG. 2B. Further, cut-positioning member 80
`has a cross-arm 84 with a slit 86 de?ning the proximal
`tibial cut. Cross-arm 84 includes laterally extending
`adjustment bars 88, 90 to which are adjustably attached
`corresponding gauge members 92 and 94, respectively.
`These gauge members are positioned relative to shaft
`member 80 in accordance with dimensions C and D, as
`described previously. At the end of base shaft member
`76 opposite from intermediate shaft member 78 is a plate
`96 which is adjustable relative to shaft member 76 for
`varying the distance of the associated end 760 of the
`base shaft member from the skin surface over the ante
`rior aspect of the distal tibia, as discussed previously.
`End 76a is also referred to herein as a gauge member.
`Thus, plate 96 is adjustable for positioning the end 760
`a distance J from the skin surface.
`Mounted on base shaft member 76 adjacent end 760 is
`a lateral adjustment bar 98 which extends to each side of
`shaft member 76, as shown in FIG. 8A. Each end of bar
`98 has an ankle‘ joint gauge member. A gauge member
`100 is positioned a distance E for placement on the skin
`over the medial malleolus. The other gauge member 102
`is positioned a distance F from the longitudinal axis of
`shaft member 76 for placement on the skin over the
`lateral malleolus. Thus, the adjustments of the various
`gauge members as well as the length of the shaft mem
`bers result in cutting slit 86 being aligned perpendicular
`to mechanical axis 24. Thus, cutting guide 34 is aligned
`precisely relative to the tibia.
`The p_osterior inclination of the tibial bone cut is
`determined by the design requirements of the particular
`prosthesis. Adjustable plate 96 on shaft end 76a, as has
`been discussed, is set at a distance which will result in
`the desired posterior inclination of the angle of proximal
`tibial bone cut de?ned by slit 86. It is suf?cient, to align
`tibial out line 22 below the most de?cient tibial plateau
`as determined by the CT scan representations. Cutting
`guide 34 is then stabilized in the proximal tibia by pins
`45
`shown in dashed lines in brace 82. The bone cut is made
`along out line 22 by passing a saw 56 through slit 86.
`The posterior cruciate ligament may be removed or
`spared according to the surgeon‘s preference. After
`making the tibial and the distal femoral bone cuts, a trial
`tibial component and trial femoral spacer is inserted into
`the joint space to test the adequacy of bone resection
`with the knee in extension, as is conventionally done. If
`this space is inadequate, further resection of the distal
`femur is possible before the remaining femoral bone cuts
`are made.
`The remainder of the surgical procedure is carried
`out as usual. The patella is prepared, trial components
`are inserted, and soft-tissue balancing is done by varying
`the thickness of the tibial component or by ligamentous
`release procedures. The actual prostheses are selected
`and implanted.
`It is seen that this preoperative CT planning method
`produces distal femoral and proximal tibial bone cuts
`which are perpendicular to the coronal mechanical axis
`without intraoperative localization of the femoral head
`or other external bone landmarks. Positioning of align
`ment instruments in relation to the-hip joint or femoral
`
`40
`
`8
`medullary canal at surgery is not needed, since all land
`marks for these bone cuts are at the knee and ankle joint.
`The above discussion is directed speci?cally to a
`preferred method of practicing the invention. However,
`it will be appreciated that the method has general appli
`cability to any bone resectioning in which the bone cuts
`are de?ned by a cutting guide surface of a guide mem
`ber placeable adjacent the bone for guiding the resec
`tioning. Thus, while a preferred method of practicing
`the invention has been described, it will be understood
`by those skilled in the art that various changes may be
`made without departing from the spirit and scope of the
`invention as de?ned by the claims and their equivalents.
`What is claimed is:
`1. A method of preoperative planning of surgical cuts
`of a selected bone in a body using a cutting guide having
`a guide surface de?ning the contour of a desired bone
`cut and a gauge member having a predetermined posi
`tion relative to the guide surface and positionable adja
`cent a selected postion on the bone, comprising:
`selecting regions of the body in which the selected
`bone is located to be used in determining a desired
`positioning of the cutting guide relative to the bone
`during cutting;
`subjecting the selected body regions to radiant en~
`ergy to produce radiant energy responses that are
`characteristic of the body and the selected bone
`and are detectable externally of the body;
`detecting produced radiant energy responses to ob
`tain representations of the selected body regions,
`including representations of the corresponding
`regions of the individual bone; and
`determining from the representations a selected posi
`tion of the gauge member relative to the bone so
`that when the gauge member is placed adjacent the
`selected position on the bone, the guide surface is in
`the selected position relative to the bone.
`2. A method according to claim 1 wherein the gauge
`member is adjustable relative to the guide surface for
`positioning the guide surface relative to the bone, said
`determining from the representations further including
`adjusting the gauge member relative to the bone so that
`when the gauge member is placed adjacent the selected
`position on the bone, the guide surface is in the selected
`position relative to the bone;
`said method further including adjusting the position
`of the gauge member relative to the guide surface
`corresponding to the determined position so that
`the guide surface is in the selected position when
`the cutting guide is placed adjacent the bone.
`3. A method according to claim 2 usable when a
`surgical cut is desired having a selected orientation
`relative to a de?nable axis associated with the bone and
`the cutting guide has a plurality of gauge members;
`said selecting including selecting regions of the bone
`relative to which the position of the axis can be
`determined;
`said determining further including determining the
`desired positions of the gauge members relative to
`the bone appropriate for positioning the guide sur
`face in the desired position relative to the axis; and
`said adjusting including adjusting the position of the
`gauge members relative to the guide surfaces cor
`responding to the determined positions so that the
`guide surfaces are positioned relative to the axis
`when positioned with the gauge members adjacent
`the bone.
`
`-9-
`
`

`
`4,841,975
`4. A method according to claim 3 which further in
`cludes producing three-dimensional coordinates corre
`sponding to portions of th