U.S. patent number RE39,301 [Application Number 08/698,781] was granted by the patent office on 2006-09-19 for method for resecting the knee using a resection guide and provisional prosthetic component.
This patent grant is currently assigned to Zimmer, Inc.. Invention is credited to Kim C. Bertin.
United States Patent |
RE39,301 |
Bertin |
September 19, 2006 |
Method for resecting the knee using a resection guide and
provisional prosthetic component
Abstract
A method and apparatus for knee replacement surgery wherein a
femoral provisional component is provided which corresponds to a
permanent component to be implanted in a human and which includes
means for establishing the correct fit and position of such a
component, prior to its implantation, in relation to the soft
tissues of the knee before final resection of the anterior femoral
surface. The provisional component further includes cutting guide
means for such anterior surface resection such that accurate cuts
may be made with the provisional component in place. The method
involves preparing the distal femoral surface using the femoral
intramedullary canal as a constant reference point for posterior
and distal cutting guides followed by locating the provisional
component by means of a provisional intramedullary stem so that the
relationship with the soft tissues of the knee may be accurately
established.
Inventors: |
Bertin; Kim C. (Salt Lake City,
UT) |
Assignee: |
Zimmer, Inc. (Warsaw,
IN)
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Family
ID: |
25339838 |
Appl.
No.: |
08/698,781 |
Filed: |
August 16, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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07862953 |
Apr 3, 1992 |
5258032 |
|
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Reissue of: |
08021039 |
Feb 23, 1993 |
05458645 |
Oct 17, 1995 |
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Current U.S.
Class: |
606/88; 128/898;
606/86R; 623/20.14 |
Current CPC
Class: |
A61B
17/155 (20130101); A61F 2/3859 (20130101); A61F
2/4684 (20130101); A61F 2002/30405 (20130101); A61F
2002/30594 (20130101); A61F 2002/30672 (20130101); A61F
2002/30736 (20130101); A61F 2002/30797 (20130101); A61F
2220/0025 (20130101) |
Current International
Class: |
A61B
17/00 (20060101); A61B 19/00 (20060101); A61F
2/38 (20060101) |
Field of
Search: |
;623/16,18,20,66
;606/80,86,87,88,89 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Isabella; David
Attorney, Agent or Firm: Russell; M. Reid
Parent Case Text
.[.This is a division of application Ser. No. 07/862,953 filed Apr.
3, 1992 now abandoned..]. .Iadd.This application is a reissue of
application Ser. No. 08/021,039, now U.S. Pat. No. 5,458,645, which
is a divisional of application Ser. No. 07/862,953, filed Apr. 3,
1992, now U.S. Pat. No. 5,258,032..Iaddend.
Claims
What is claimed is:
1. A method of knee joint arthroplasty .[.comprising preparing a
distal femur to accept a femoral component in knee replacement
surgery wherein the femoral intramedullary canal is used as the
reference point for all resection cuts.]. comprising the steps of:
.[.i. incrementally reaming the intramedullary canal out to
cortical bone with a reamer means; ii. leaving said reamer means in
place and attaching thereto a distal cutting guide; iii. resetting
medial and lateral distal surfaces of said femur along said distal
cutting guide; iv. replacing said distal cutting guide with a
posterior cutting guide and resetting medial and lateral posterior
condylar surfaces of said femur along said posterior cutting
guide;.]. .[.v.]. .Iadd.i.Iaddend.. .[.removing said posterior
cutting guide and reamer, attaching a provisional intramedullary
stem.]. .Iadd.attaching .Iaddend.to a provisional femoral component
.Iadd.to a distal femur surface what has been preliminarily
resected.Iaddend., .Iadd.which .Iaddend.said provisional femoral
component .[.including an anterior.]. .Iadd.includes a
.Iaddend.cutting guide formed therein and an outer surface
.[.replicating.]. .Iadd.that replicates .Iaddend.the size of a
permanent femoral component.[., and inserting said stem into said
intramedullary canal.]. ; .[.vi.]. .Iadd.ii.Iaddend.. evaluating
flexion/extension gaps of the knee and patella tracking relative to
said provisional femoral component and establishing correct gaps
and soft tissue balance of said knee relative to the anatomical
size of said knee; .[.vii.]. .Iadd.iii.Iaddend.. resetting .[.an
anterior surface of.]. said femur .Iadd.surface .Iaddend.along said
.[.anterior.]. cutting guide of said provisional femoral component;
and .[.viii.]. .Iadd.iv.Iaddend.. removing said .[.provisional stem
and.]. provisional .Iadd.femoral .Iaddend.component and
.[.inserting.]. .Iadd.replacing it with .Iaddend.a permanent
femoral component .[.corresponding.]. .Iadd.that corresponds
.Iaddend.to said provisional component.
2. The method of claim 1 wherein said provisional femoral component
comprises an anterior flange, first and second posterior condylar
flanges and an intermediate distal femoral joint portion, said
flanges and distal femoral joint portion being formed as a single
element having a continuous joint surface around its outer
perimeter.
3. The method of claim 2 wherein said provisional femoral component
further comprises said anterior resection cutting guide, said guide
comprising means relative to said anterior flange for guiding a
bone saw in resection of said anterior femoral surface.
4. The method of claim 3 wherein said guide means relative to said
anterior flange comprises at least one slot formed in and through
said provisional femoral component posteriorly of said anterior
flange and extending inward from an edge thereof to a point
adjacent a center line of said component, said slot having an angle
relative to said component corresponding to that of an anterior
flange of a permanent femoral knee joint prosthesis component.
5. The method of claim 2 further comprising adjusting said
flexion/extension gaps and thereby the position of said provisional
component by interposing provisional augment means between said
component and said femur.
6. The method of claim 5 wherein said provisional augment means
comprise distal and posterior portions having an angular
relationship corresponding to that of said posterior condylar
flanges and said intermediate distal femoral joint portion.
7. The method of claim 6 wherein said provisional augment means are
temporarily interposable between said component and said femur and
may be removed therefrom and permanently adhered to a permanent
implant component.
8. The method of claim 1 wherein resection cuts made to said distal
femur have constant angular characteristics relative to said
intramedullary canal irrespective of the anatomical size of the
knee on which said arthroplasty is conducted.
9. The method of claim 8 wherein resection cuts are determined by
geometric constants defining the construction of a set of permanent
femoral components from which said permanent component
corresponding to said provisional component is selected.
10. A method of knee joint arthroplasty for revision surgery of a
human knee wherein resection of a distal femur preparatory to
implantation of a femoral component employs the femoral
intramedullary canal as the reference point for all resection cuts,
comprising: i. removing an existing femoral component; .[.ii.
fitting a cutting guide means to said femur by a means extending
into said femoral intramedullary canal and first resetting medial
and lateral distal surfaces of said femur and medial and lateral
posterior condylar surfaces of said femur;.]. .[.iii.].
.Iadd.ii.Iaddend.. .[.removing said cutting guide means and.].
fitting a provisional femoral knee component .Iadd.onto
.Iaddend..[.to.]. said .Iadd.distal .Iaddend.femur
.Iadd.surface.Iaddend., said provisional component having .[.an
anterior.]. .Iadd.a .Iaddend.cutting guide means formed therein and
an outer surface .[.replicating.]. .Iadd.that replicates
.Iaddend.the size of a permanent femoral component.[., and wherein
said provisional component comprises an intramedullary stem which
is inserted into said intramedullary canal.]. ; .[.iv. evaluating
and adjusting flexion and extension gaps of the knee and patella
tracking relative to said provisional femoral component and
establishing correct gaps and soft tissue balance of said knee
relative to the anatomical size of said knee followed by.].
.Iadd.iii. .Iaddend.resecting .[.an anterior.]. .Iadd.the
.Iaddend.surface of said .Iadd.distal .Iaddend.femur along said
.[.anterior.]. cutting guide; .[.v.]. .Iadd.iv.Iaddend.. removing
said provisional .Iadd.femoral knee .Iaddend.component and
inserting a permanent femoral component corresponding to said
provisional component.[.; wherein, said anterior resection of said
femur comprises an anterior flange cut and an anterior chamfer cut,
said cuts having constant angular characteristics relative to said
intramedullary canal irrespective of the anatomical size of the
knee on which said arthroplasty is performed.]. .
11. The method of claim 10 wherein said provisional femoral
component comprises an anterior flange, first and second posterior
condylar flanges and an intermediate distal femoral joint portion,
said flanges and distal femoral joint portion being formed as a
single element having a continuous joint surface around its outer
perimeter.
12. The method of claim 11 wherein said constant angular
characteristics of said anterior resection cuts correspond to and
are determined by a stem/anterior flange distance and a
stem/anterior cortex angle which are constant for all sizes of
provisional components.
13. A method of preparing a distal femur to accept a femoral
component in knee replacement surgery wherein the femoral
intramedullary canal is used as the reference point for all
resection cuts, the method comprising the steps of: .[.i. fitting a
first cutting guide means to said distal femur by a means extending
into said intramedullary canal and performing a first resection of
the medial and lateral distal surfaces of said femur and the medial
and lateral condylar surfaces of said femur; ii. removing said
first cutting guide means;.]. .[.iii.]. .Iadd.i.Iaddend..
.[.providing.]. .Iadd.fitting .Iaddend.a provisional .Iadd.femoral
.Iaddend.component .[.for connection.]. to .[.said resected.].
.Iadd.a distal .Iaddend.femur .[.to measure the correct size of a
permanent component to use with the resected femur,.].
.Iadd.surface that has been preliminarily resected, .Iaddend.said
provisional component including an inner surface .Iadd.that is
.Iaddend.engageable with .[.the.]. .Iadd.said .Iaddend.resected
.Iadd.distal .Iaddend.femur .Iadd.surface .Iaddend.and .Iadd.has
.Iaddend.an outer surface .[.replicating.]. .Iadd.that replicates
.Iaddend.the size of .[.the.]. .Iadd.said .Iaddend.permanent
.Iadd.femoral .Iaddend.component, .[.and.]. .Iadd.that includes
.Iaddend.at least one slot extending from .[.the.]. .Iadd.said
provisional component .Iaddend.outer surface to receive a cutting
tool for further resection of .[.the.]. .Iadd.said .Iaddend.distal
femur .Iadd.surface .Iaddend.to prepare .[.the.]. .Iadd.said distal
.Iaddend.femur .Iadd.surface .Iaddend.for connection with said
permanent .Iadd.femoral .Iaddend.component; .[.iv.].
.Iadd.ii.Iaddend.. fitting said provisional .Iadd.femoral
.Iaddend.component to said .Iadd.further .Iaddend.resected
.Iadd.distal .Iaddend.femur .Iadd.surface.Iaddend., evaluating and
adjusting flexion and extension of the knee and patella tracking
relative to said provisional .Iadd.femoral .Iaddend.component, and
performing a second resection of said distal femur using said at
least one slot of said provisional .Iadd.femoral .Iaddend.component
as a guide means.Iadd.; and .Iaddend. .[.v.]. .Iadd.iii.Iaddend..
removing said provisional .Iadd.femoral .Iaddend.component and
insetting .Iadd.in its place .Iaddend.a permanent .Iadd.femoral
.Iaddend.component corresponding to said provisional .Iadd.femoral
.Iaddend.component.
14. The method of claim 13 wherein said second resection comprises
resection of the anterior surface of the distal femur and is
performed at angles having constant characteristics relative to
said intramedullary canal irrespective of the anatomical size of
the knee on which said knee replacement is performed.
15. The method of claim 14 wherein said provisional component
comprises an anterior flange, first and second posterior condylar
flanges and an intermediate distal femoral joint portion, said
flanges and distal femoral joint portion being formed as a single
element having a continuous joint surface around its outer
perimeter.
16. The method of claim 15 wherein said constant angular
characteristics of said anterior resection cuts correspond to and
are determined by a stem/anterior flange distance and a
stem/anterior cortex angle which are constant for all sizes of
provisional components.
17. The method of claim 15 wherein said at least one slot of said
provisional component is located posteriorly of said anterior
flange and extends inward from an edge thereof to a point adjacent
a center line of said component, said slot having an angle relative
to said component corresponding to that of an anterior flange of
said femoral component.
18. The method of claim 17 wherein said provisional component
comprises a further slot located posteriorly of said at least one
slot and at an angle relative to said at least one slot whereby
resection of said distal femur through said further slot produces a
chamber on said distal femur.
Description
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for a knee
joint prosthes is and surgical procedure. More particularly
concerning the proper fitting of the femoral component of a total
knee revision prosthesis, the procedure for performing revision
surgery and apparatus used therein.
BACKGROUND OF THE INVENTION
The present invention relates to a provisional knee prosthesis and
resection guide component together with a surgical procedure
designed for use as a system in revision surgery of previously
performed knee arthroplasties. It may also find utility in an
initial knee replacement procedure.
Revision surgery is performed to correct failures of previously
implanted knee prostheses. These failures occur for a number of
reasons including malposition, loosening of the prosthesis,
infection or dislocation. Such categories are not necessarily
mutually exclusive since infection may cause a loosening of the
prosthesis which, in turn, might cause dislocation.
When a prosthesis must be removed and a revision prosthesis
inserted, it is often the case that additional bone must be removed
in order to stabilize the new prosthesis. When this occurs, the
interior portion of the femoral component of the prosthesis must be
augmented to add additional thickness to compensate for the bone
that has been removed. In addition, the revision cuts that remove
the extra bone must be made correctly relative to the revision
prosthesis for accurate positioning in relation to a tibial
component and the soft tissues of the knee joint. Such cuts are
made with the aid of guides positioned relative to the ends of the
femur and tibia.
It is preferable to perform revision in a single surgical
procedure. Also, it is desirable to be able to test the fit and
operation of the prosthesis relative to the rest of the knee,
particularly the patella and the soft tissues, prior to or at the
same time as the revision cuts are made in the end of the femur.
Indeed, with regard to patellar tracking, it is preferable to
ensure a proper fit before the final anterior cuts are made to the
distal femur.
The apparatus and method of this invention are intended to be used
in conjunction with the revision prosthesis system of applicant's
co-pending application which is based around a constant geometry of
the anterior flange, the distal prosthesis and the intramedullary
stem of the component and uses the intramedullary canal of the
femur as a reference point. Accordingly, the present invention is
similarly based around the intramedullary canal of the femur as a
reference point for all of the bone cuts.
DESCRIPTION OF THE PRIOR ART
Tibial resection for implantation of the tibial component of an
initial knee prosthesis or revision is relatively straight-forward
as it essentially only requires surface treatment of the proximal
end of the tibia. In such treatments, cutting guides are normally
positioned relative to the intramedullary canal of the tibia by
attaching the guides to the intramedullary reamer or to an
alignment rod placed within the reamed canal. Such devices are
shown in U.S. Pat. Nos. 4,952,213 to Bowman, et al., and 5,002,545
to Whiteside, et al.
In contract, however, prior apparatus and methods for performing
the comparable resection of the distal femur have included both
intramedullary and extramedullary positionable guide means, often
both, frequently requiring accurate adjustment for the individual
circumstances. The intramedullary positioned guide means have been
traditionally used only for the distal and posterior resection of
the femur leaving the anterior cuts to be made with extramedullary
positioned means.
Such intramedullary positionable distal and posterior cut guide
means are represented by U.S. Pat. Nos. 4,703,751 to Pohl and
4,935,023 to Whiteside, et al. The Pohl patent presents a guide
means for resection of the distal surface, which guide is
positionable on a jig which is removably connected to an
intramedullary rod. The jig allows the cutting guide to be
angularly pivoted relative to the center line of the femur.
Whiteside, et al., present a shaping guide also removably
attachable to an intramedullary rod and having an adjustable
positioning means together with guides for the shaping of only one
condyle in preparation for the implantation of a unicondylar
prosthesis.
It is known for anterior surface resection guides to be
positionable relative to an intramedullary rod, for example U.S.
Pat. No. 4,474,177 to Whiteside presents an apparatus for shaping
the distal femoral surface wherein a plurality of shaping
instruments or guides are selectively positionable on an
intramedullary rod for use in guiding a saw blade during the
procedure. However, what the prior art lacks is an apparatus and
method whereby all cuts can be made from the common reference point
of the intramedullary canal of the femur and whereby the
positioning and size of a femoral component may be checked relative
to the soft tissues and the track of the patella prior to making
the final resection of the anterior surfaces. In the case of
Whiteside, the cuts are made first then the guides are removed
before any test fittings can be conducted. If the cuts are made in
the wrong place or to the wrong degree, then the surfaces must be
modified by further resection, bone grafts or bone cement to get a
proper fit of the implant.
SUMMARY OF THE INVENTION
The present invention provides a provisional component which allows
the selected size of a prospective implant to be test fit with
respect to the distal and posterior resections of the femur and the
soft tissues of the knee joint before making the final resection of
the anterior surface of the femur. It also provides a guide means
as an integral part of the provisional component for making those
final cuts to the anterior surface. Furthermore, it provides a
means whereby the relative spacing of the extension and flexion
gaps in the knee joint may be tested using the provisional
component with prospective augments or trial pieces, when
necessary, in place following which the provisional component
itself serves as the guide for making the final surface cuts thus
ensuring that the resected femur and ultimate permanent prosthesis
will result in a properly balanced knee.
The augments, which are modular and therefore independently
changeable, allow adjustment of the anterior/posterior box size as
well as the distal positioning of the provisional component. Such
distal positioning is crucial for obtaining correct soft tissue
balance in the knee during trial reduction before final anterior
resection and implantation of the permanent prosthesis. Modular
augments and pretesting of the knee with the provisional component
of the present invention also enable the surgeon to ensure a close
contact fit of the prosthesis with the resected bone surface
whereby a greater degree of adhesion may be obtained through bone
ingrowth or less bone cement need be used.
The provisional component is constructed to emulate the permanent
implant while being temporarily placed in the joint space. Such a
permanent implant system is described by my copending application
Ser. No. 07/862,954 filed Apr. 3, 1992. It includes the anterior
and posterior condylar flanges as well as the intermediate distal
portion of the joint surface. An intramedullary stem is provided
or, alternatively, the provisional may be adapted for attachment to
an intramedullary rod or reamer placed in the femoral
intramedullary canal. Provision is also made for the provisional
component to temporarily accept distal and posterior augments for
proper spacing so that the final anterior surface cuts will be
accurately made. With regard to those cuts, the provisional
component includes bone saw guides positioned through the body of
the component relative to the anterior flange for the correct
location and angular position of the chamfer and anterior surface
cuts necessary to fit a final permanent implant.
It is therefor an object of this invention to provide a combination
knee prosthesis provisional apparatus and resection guide for use
in knee replacement surgery whereby resection and test fitting of
femoral prostheses may be easily and reliably achieved.
It is a further object of this invention to provide a means whereby
the spacing of extension and flexion gaps of the knee may be tested
and evaluated during the process of replacement surgery prior to
final resection and prosthesis implantation.
It is a still further object to provide a means whereby the
resection of the distal femur is made on the basis of a reference
point common to all resection cuts slid implant sizes.
It is an even further object to provide a combination knee
prosthesis provisional apparatus and resection guide which emulates
a permanent femoral implant component.
Further objects and advantages will become evident to those of
skill in the art from the following drawings and description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an oblique view of a standard femoral component of a knee
revision prosthesis.
FIG. 2 is a view of a knee joint in full extension.
FIG. 3 is a view of a knee joint in full flexion.
FIG. 4 is an oblique view of the femoral component provisional and
resection guide apparatus of the present invention.
FIG. 5 is a composite view of the femoral component provisional and
resection guide apparatus of the present invention illustrating its
component parts.
FIG. 6 is a cross section of a partially prepared femur
illustrating the femoral component provisional and resection guide
in place prior to making anterior flange and chamfer cuts on the
femur.
FIG. 7 is a posterior elevation view of the femoral component
provisional and resection guide apparatus of FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
The femoral component revision prosthesis of FIG. 1 is similar to
that employed in most knee prosthetics in that it comprises an
anterior flange 1, a pair of posterior condylar flanges 2 and 3, a
distal femur contacting surface 4, an intramedullary locating and
anchor shaft 5 and a distal joint surface 6 corresponding to the
natural distal femoral surface of the human knee with condylar
surfaces 7 and 8 for cooperation with the corresponding end of a
tibia and means for patellar tracking along the arc of the joint
surface of the anterior flange 1 and between the distal condylar
surfaces 7 and 8. Femoral component prostheses of this general type
have been used for some time in knee reconstruction and have been
made available in a range of sizes to accommodate patients having
different skeletal and joint sizes. Such components have required
that the distal end of the femur be resected to the specific size
of the individual component, necessitating careful shaving of the
bone by the surgeon and multiple fittings of the prosthesis before
the procedure is finished. Alternatively, a wide array of augments
attachable to the distal femur contacting surface 4 of the
component have been necessary to ensure a proper fit of the correct
size component to a patient's femur.
For an initial femoral implant, it is generally not as difficult to
obtain a correct fit of the proper size component; although the
problem can occur where there is a great deal of diseased bone that
must be removed before the implant is fitted. Such instances then
become similar to those encountered in revision surgery where it is
necessary to remove existing bone along with the original implant
either due to infection or physical breakdown of the previously
prepared distal femur. In these cases the size of the bone
supporting the implant is reduced but it is still desired to
maintain the size of the original joint in order to obtain proper
anatomical characteristics of support and function for the patient.
For example, a patient having an anatomical knee size of six may,
following resection of the femur, have a distal femoral surface
corresponding to that for a size four and a half knee. In order to
maintain the proper anatomical characteristics for that knee it is
desirable that the implanted component be a size six. However,
adapting a larger size implant to a smaller size bone has presented
difficulties which, to date, have been solved by the use of custom
made implants or multiple augments.
Prior devices and methods have required measuring the size of the
bone and then cutting it to fit one specific size of prosthesis.
This allows a good fit to be obtained between the prosthesis and
the bone but may not provide a good fit with the soft tissues and
the patella. In revision surgery, the flexion space of the knee,
ie., that space between the posterior edge of the prepared distal
femur and the prepared proximal tibia when the knee is fully bent
as shown by space B in FIG. 3, is often greater than the extension
space, ie., that space between the distal femur and proximal tibia
when the knee is fully extended, as shown by space A in FIG. 2. For
proper working of the knee joint the tension between the distal
femur and the proximal tibia should be the same whether the knee is
in flexion or extension. However, it is often the case in revision
surgery that resection of the distal femur is uneven resulting in
irregularities in the spacing of the flexion and extension gaps
which, in turn, produces uneven tension across the knee. The
present apparatus and method allow testing of the knee action with
the provisional component, which corresponds to the permanent
implant, in order to ensure that the flexion and extension gaps are
even for proper working of the knee before final resection cuts are
made to the anterior surface of the femur and to ensure a close
contact fit with the resected bone surface. The femoral components
of applicant's copending application and the method and apparatus
of this invention are based around the intramedullary canal as a
constant point of reference as well as a constant geometry of the
components in a set with regard to the relationship between the
intramedullary stem and the anterior flange of the components. This
makes adjustment and placement of femoral components during surgery
easier since it eliminates at least one variable from the
procedure. Since the relationship between the intramedullary stem
and the anterior flange is constant, the anterior resection cuts
must be properly placed relative to the intramedullary canal as
well as relative to the posterior and distal cuts in order to
obtain a properly workable knee joint. The apparatus and method of
this invention provide the means whereby this is achieved.
FIGS. 2 and 3 illustrate the relationships of femoral 9 and tibial
10 components in a knee joint at full extension and full flexion
respectively. Under optimum conditions, the extension gap A and the
flexion gap B should be equal for a properly functioning and stable
knee. This relationship between the femur 11 and tibia 12 is
important to get the knee implant components to interface properly
with the soft tissues of the joint and to achieve a proper soft
tissue balance within the knee. The size of the femoral revision
component usually increases relative to the centerline through the
fixation stem 5 with the posterior portion 6 being increased to
tighten the flexion space B. However, this often affects the other
relationships within the knee and upsets the soft tissue balance.
In the present invention the distal and posterior adjustments are
made with the addition of augments between the femoral component 9
and the respective cuts made to the femur 11. Furthermore, since
the inventions herein and in applicant's copending application are
based around the intramedullary canal and the anterior flange as
constants, it is important that the anterior resection be identical
and properly placed. Accordingly, the provisional component of FIG.
4 provides a means whereby the knee joint may be tested for proper
fit and function prior to resection of the anterior femur and
whereby that resection may be accomplished while the provisional
component is in place, thereby ensuring that the anterior cuts are
made in the correct place relative to all other aspects of the
joint replacement components.
FIGS. 4 and 7 illustrate the combination femoral provisional
component and anterior resection guide 20 of the invention which
comprises a femoral component similar to that shown in FIG. 1. The
provisional 20 comprises an anterior flange 21, posterior condylar
flanges 22 and 23, a distal femur contacting surface 24 and a
distal joint surface 26 which corresponds to the natural distal
femoral surface of the human knee with condylar surfaces 27 and 28.
Between the distal femur contacting surface 24 and the inner
surface 21a of anterior flange 21 is chamfer 29 which will
correspond to a chamfer cut made to the distal femur during
resection procedures to be described later. Located medially on the
distal femur contacting surface 24 adjacent chamfer 29 is the
fixation point 25 for an intramedullary stem, rod or reamer by
which the provisional component 20 is affixed to a femur in proper
relation to the intramedullary canal reference point. Any suitable
means for connection of the intramedullary location means may be
used such as threads, 25a as shown, press fit, detents, or the
like.
The provisional component of this invention, as well as the
revision prosthesis of applicant's co-pending application, have a
constant relationship between the center line of the stem, or stem
fixation point, and the anterior cornea of the femur for all sizes
of the component. This relationship provides a constant angle
between the stem and the cortex, represented by the inner surface
of the anterior flange, as well as a fixed distance therebetween
which is the same regardless of the anatomical sizes of the
provisional components to be available in a system.
The joint surface 26 is continuous and extends around the outer
periphery of the component 20 to include the outer surface 21b of
the anterior flange 21 as well as the outer surfaces of the
posterior condylar flanges 22 and 23 and the distal femoral joint
portion. Similarly, inasmuch as the component emulates the joint
surface of a natural distal femur, the condylar surfaces 27 and 28
continue around the periphery of the component as part of the joint
surface 26 thereby providing distal, medial and lateral condylar
surfaces between which will be located a track area or groove 26a
for travel of the patella as the knee joint flexes. Such travel is
shown in FIGS. 2 and 3 by the relative positions of the patella 9a.
This structure of the provisional component enables it to be placed
in the joint space following resection of the distal and posterior
femur. Preferably, the resection of the posterior and distal
surfaces of the medial and lateral condyles is kept to the least
amount necessary. In addition, each condyle is preferably resected
independently of the other and separate augments are selected for
test fitting the provisional component and for final implantation
of the a femoral implant component. These cuts may be standardized
relative to the anatomical characteristics of an average range of
knee sizes for a population or they may be made on the basis of
each individual case. The function of the knee may then be checked
as well as the relationship of the provisional to the soft tissues
of the joint. Although the correct size provisional component and,
thereby, the prosthesis will usually be determined before surgery,
it may be necessary, following initial resection, to upsize to the
next larger component in order to tighten the flexion and extension
gaps. The present invention facilitates this process by permitting
the sizes to be tested before the final prosthesis is implanted.
Once correct working of the joint is established, including
balancing of the soft tissues, the anterior chamfer and anterior
flange resection may be accomplished without removing the
provisional component thereby ensuring that these cuts are made in
the correct locations relative to the intramedullary canal and at
the correct angles relative to the intramedullary stem.
It is important that the anterior flange cut be made last, after
the posterior and distal cuts and after correct working of the
joint and soft tissue balance has been established. Because the
system of revision for which the provisional component of this
invention is intended uses the intramedullary canal of the femur as
a reference point, the angle established between a reamer or
intramedullary shaft and the anterior flange of an implant is
constant through all sizes of such implants. Therefore, if the
anterior flange cut is made before the posterior and distal cuts
and before the extension and flexion gaps are stabilized, the
constant relationship will be lost once those cuts are made and
stabilization of the knee and soft tissue balance will be much more
difficult to achieve. Thus, the correct order for the procedure is
to first resect the distal and posterior femoral surfaces with the
cutting guides therefor positioned relative to the reamer used to
prepare the intramedullary canal. Following this, the provisional
component is inserted, using either the reamer or a separate
intramedullary shaft for positioning, and the fit and balance of
the knee are determined before finally making the anterior flange
cuts.
To accomplish this, the provisional component 20 is provided with
cutting guides 30 and 31. These guides 30 and 31 comprise slots in
the body of the provisional component 20 with guide 30 at the
correct angle and location for the anterior flange resection cut
while guide 31 is at the correct angle and location for the
anterior chamfer resection cut. Each guide actually comprises two
slots placed on either side of the intramedullary stem fixation
point 25 and extending from the edge of the component 20 inward
toward the longitudinal center line 35 of the component to a point
adjacent the intramedullary stem fixation point 25. The slots
further extend completely through the component 20 from the joint
surface 26 to the femoral contact surface 24 with the two slots of
each guide 30 and 31 being necessarily located on the same relative
plane through the component 20. Clearly, cutting guides 30 and 31
do not extend completely across component 20 from edge to edge in
order to maintain the component as a complete unit. Also, the
cutting is primarily conducted on the condylar surfaces of the
femur which will provide a guide for any final dressing of the
intervening mid surface.
FIG. 5 illustrates the primary components of the provisional
apparatus and resection guide of the present invention while FIG. 6
shows their position in relationship to the distal end of a femur.
The entire apparatus comprises the provisional component 20
described above, an intramedullary stem 32 affixable to fixation
point 25 on the provisional component 20, and a combined
distal/posterior augment 33 preferably temporarily affixable to the
femoral contact surface 24 of provisional component 20.
Alternatively, augment 33 may comprise separate distal and
posterior pieces to allow greater variation and accommodate wider
ranges of differences between the individual condyles of the knee.
Anterior flange resection guide 30 and anterior chamfer resection
guide 31 are shown in phantom. The inner surface 21a of anterior
flange 21 is relieved to allow it to fit on the end of the femur 11
prior to anterior resection, as shown in FIG. 6. However, the joint
surface 21b of the anterior flange 21 when the component 20 is in
place will properly correspond to the location of the same joint
surface of a permanent component so that action of the joint with
the provisional component 20 in place will mimic joint action
following implantation of the permanent component. This
relationship is important since the provisional component 20 is
used to test for proper alignment of the knee joint and soft tissue
balance, and to establish proper tracking of the patella 9a.
As shown in FIGS. 4, 5, 6 and 7, the position of anterior resection
cutting guide 30 does not coincide with the relieved inner surface
21a of anterior flange 21. Rather, the position and angle of guide
30 corresponds to the requirement for the anterior femur contacting
surface of the permanent component to be implanted and its
relationship to the constant reference point of the intramedullary
canal. Thus, the angle of guide 30 relative to the axis of
intramedullary stem 32 will preferably correspond to that of the
anterior flange and intramedullary stem of the femoral components
of applicant's copending application.
Augments 33 provide buildup for the resected areas of the distal
and posterior condyles of the femur 11 in order to maintain the
correct anatomical relationships of the knee joint between the
joint surface 26 of the provisional component 20 and the
corresponding surface of a tibial component 10. The size of the
augments 33 is based on the resection cuts made to the femur for
the particular size of permanent component to be used. Where such
cuts are standardized, there will be an equally standardized set of
augments. Alternatively, where the cuts are made on a case by case
basis, a wider variety of augment sizes will be available. The
augments 33 may be provided with the provisional component 20 or
they may be those provided with the permanent component in which
case they will be temporarily attachable to the provisional
component so that they may be removed and permanently mounted on
the permanent component prior to its implantation. As shown in
FIGS. 5 and 6, the one piece augments 33 have a substantial L-shape
corresponding to the interior shape of the provisional component 20
at the distal/posterior portion. As such, the augments 33 comprise
a distal portion 33a and a posterior portion 33b. Alternatively,
the augments may be provided as separate distal and posterior
portions corresponding to portions 33a and 33b. Due to the nature
of the resection of the distal femur and the fact that the
extension and flexion gaps, A and B in FIGS. 2 and 3 respectively,
usually are different following resection, the distal and posterior
portions of the augments are usually of different thicknesses.
These thicknesses are determined by the resection cuts made to the
distal femur relative to the size of the femoral component to be
implanted. The provisional component of this invention allows the
selection of augments 33 to be tested for accuracy in establishing
the extension and flexion gaps. In addition, the provisional
component and the temporary placement of the augments therewith
permits the establishment of the proper position of the patella 9a
relative to the joint line. As shown in FIG. 2, the joint line 34
passes through the joint at a point tangential to the femoral
component 9 and the tibial component 10. The position of the
patella 9a relative to this line is given as C and will depend on
the particular anatomical size of a knee. This position is variable
by changing the augment 33 to one having a different distal
thickness 33a thus altering both the extension gap A and the
patella position C. Similarly, changing the augment 33 to one
having a different posterior thickness 33b will alter the flexion
gap B. In instances where it becomes necessary to upsize to the
next size provisional component and prosthesis, appropriately sized
augments will be employed to ensure that the flexion and extension
gaps are properly established for even tension across the knee. In
this manner an accurate relationship of the provisional component
20 to the hard and soft tissues of the knee joint may be
established before the final resection of the anterior femur is
performed. In addition the necessary augments 33 to be used with a
permanent implant component are selected and can then be attached
to the permanent implant component.
In the surgical procedure employed with this apparatus the proximal
tibia is prepared by incrementally reaming the tibial
intramedullary canal out to cortical bone, leaving the reamer in
place as a point of reference for a tibial cutter, resecting the
proximal tibia and applying provisional components for the tibial
portion of the knee joint. Following this, the distal femur is
prepared using the above described apparatus. Alternatively, the
femur may be prepared first followed by the preparation of the
tibia.
For preparation of the distal femur, the femoral intramedullary
canal is first reamed incrementally to cortical bone. The canal, as
stated, is the constant reference point for the resection of the
distal femur. The reamer may be left in place or a provisional stem
or similar intramedullary rod may be inserted on which distal and
posterior cutters are mounted for resection of the distal and
posterior surfaces of the femur. These cuts will be made based on
the condition of the bone and on the permanent prosthesis to be
implanted but will preferably be made according to a standard
established by the prosthesis system being used. The individual
condyles of the posterior and distal surfaces may be resected to
different levels and brought up to the same level by the use of
augments.
Following the posterior and distal resection, the femoral
provisional component is put in place to test the positions of the
selected prosthesis and the tissues of the knee joint. If the
provisional stem was used as the support for the posterior and
distal cutters then the provisional component may be substituted
for those cutters otherwise it is preferable that the cutter
support be removed from the intramedullary canal, the provisional
stem attached to the provisional component and that assembly put in
place. Augments may be attached as needed to establish the correct
joint characteristics or a different size provisional component may
be tried. Since all sizes of provisionals have the same
stem/anterior flange distance and the same stem/anterior cortex
angle, those characteristics and the resulting position of the
anterior flange cuts will be the same regardless of the size
provisional used. Once all such characteristics have been
established, the provisional component and its included anterior
resection guides are used for the final anterior chamfer and
anterior flange cuts following which the provisional component,
stem and augments are removed and the permanent implant component
inserted.
The foregoing description sets forth the preferred form of the
apparatus of this invention and the method for its use. However,
other modifications and variations will become apparent to those
having skill in the art from an examination of that description and
the accompanying drawings. Therefore, other variations of the
present invention may be made which fall within the scope of the
appended claims even though such variations were not specifically
discussed.
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