Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS FOR INSTALLING
A FEMORAL COMPONENT
Background and Summary of the Invention
5The present invention relates to a method for
reconstructing a femoral portion of a knee in a total knee
replacement of both the medial and lateral condyles. More
particularly, the present invention relates to a method in
which the femoral component of reconstructed knee presents
both the lateral and medial condyles at substantially the
same distal position as the original natural lateral
condyle to locate the intercondylar notch and distal
patellar groove in a position generally coinciding with the
natural intercondylar notch and distal patellar groove
being replaced.
The proximal/distal placement of the femoral
component in total knee arthroplasty is critical for
duplicating the kinematics of the knee with the
arthroplasty. Several authors have recommended that the
joint line (transverse axis) of the arthroplasty should be
at approximately the same proximal/distal position as the
joint line (transverse axis) of the normal knee. Most
surgical techniques recommend that an amount be resected
off the distal femur roughly equal to the thickness of the
femoral prosthesis, doing so will restore the joint line to
substantially its original position. This is actually too
simplistic an analysis of a complex situation. For
example, sometimes there is wear of the distal condyles and
osteophytes can deform the distal condyles. Thus, the
original cartilage covered surface, which represents the
original distal femoral surface, is usually not available
for referencing at the time of surgery. More importantly,
the average transverse axis (joint line) is tilted 3 with
respect to the mechanical axis of the knee. This is
because the medial femoral condyle is more distally placed
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than the lateral femoral condyle in the normal knee. Most
authorities today recommend that the transverse axis of the
reconstruction be made perpendicular to the mechanical
axis. Thus, the original transverse axis is tilted 3 and
the reconstructed transverse axis is made perpendicular to
the mechanical axis.
In an arthritic valgus knee the medial femoral
condyle is usually much more distally placed than the
lateral femoral condyle due to wear or lateral femoral
condyle hypoplasia. In an arthritic varus knee there has
usually been some wear of the medial femoral condyle, but
in most cases, despite this wear, the medial femoral
condyle is still more distally placed than the lateral
femoral condyle. In both varus and valgus knees the
reference condyle for distal femoral resection is presently
the medial condyle.
The distal femur actually has three different
surfaces for articulation. There is the medial femoral
condyle, the lateral femoral condyle, and the central
portion of the distal femur against which articulates the
patella. The distal femur, obviously, has articulating
against it both the tibia and the patella. The
proximal/distal placement of the patella/femoral joint is
just as important, and perhaps even more important, than
the proximal/distal placement of the tibial/femoral joint.
If a surgeon has an 8 mm thick femoral component
and resects 8 mm off the distal medial femoral condyle, in
almost all knees the surgeon resects several millimeters
less of distal lateral condyle. If the surgeon then
installs an 8 mm femoral component, the knee has a
lengthened lateral femoral condyle and a lengthened
intercondylar notch which defines the patella/femoral joint
line. In other words, the new joint line has been placed
at approximately the level of the original medial femoral
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condyle but has been placed distally with respect to the
original lateral femoral condyle.
This lengthening of the lateral femoral condyle
requires the patella to move more distally with respect to
the femur as the patella moves to the distal aspect of the
femur in the extremes of flexion. This requires more
stretching of the quadriceps mechanism and higher patella
load. This may make the patella more likely to dislocate
and increase the likelihood of subluxation. The higher
patella load may also be the cause of some lateral pain and
may contribute to patella fractures.
In contrast to the above known method, the
present invention reconstructs the distal joint surface of
the knee at approximately the distal level of the original
lateral femoral condyle. One advantage of reconstructing
the knee at the level of the original lateral femoral
condyle is that it gives more room for the tibial
component. The tibial base plate should be adequately
thick for strength and the tibial plastic bearing insert
should be adequately thick for wear considerations. There
is a problem with space in the reconstruction. If a
surgeon lengthens the lateral femoral condyle it aggravates
the space problem. Reconstructing the knee at the level of
the lateral femoral condyle leaves more room for a tibial
component and minimizes the tibial resection level. In
addition, a thicker plastic tibial bearing may be used with
the present invention. As the thickness of the bearing
increases, internal stresses tend to decrease.
The instruments of the present invention resect 3
mm of bone from the intercondylar notch area preferably
using the notch as a reference point. Each femoral
component of the present invention is approximately three
millimeters thick in the patellar groove area, regardless
of the size of the component. Therefore, the distal
patellar groove of the prosthetic femoral component of the
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present invention is anatomically positioned at about the
same distal position as the groove in the normal knee.
Accordingly, the patella must travel only its original
distal excursion distance during normal knee flexion.
Of course, large bones have deeper notches than
small bones since bones are proportionately sized. A
three millimeter depth of resection in the notch area in a
small bone will remove less distal femoral condyle than a
three millimeter depth of resection in the intercondylar
area for a large bone. The present invention provides a
plurality of femoral components having distal femoral
condyles which gradually become thicker with size
proportionally to compensate for the varying amounts of the
distal femoral condyles which are resected.
The present invention preferably uses the
intercondylar notch as a reference point for guiding
resection of the distal end of the femur. The notch
reference is not affected by condyle hypoplasia which can
occur both to the medial and the lateral femoral condyle
and it is typically not affected by wear of an individual
condyle. The notch area is rarely worn, although
occasionally osteophytes do form that need to be resected.
In the valgus knee with a hypoplastic lateral femoral
condyle the notch area is not hypoplastic. The lateral
femoral condyle resection level in such cases gives the
desired lengthening of the lateral femoral condyle in that
type of knee. Referencing the intercondylar notch for
proximal/distal placement of the femoral component
consistently and accurately reconstructs the
patella/femoral joint at its appropriate proximal/distal
level. This results in the tibial/femoral component joint
being reconstructed at also its proper proximal/distal
level but without the problems of severe anatomical
variations and severe bony erosion. The notch reference
point is a more convenient and reliable reference point for
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proximal/distal placement of the femoral component than the
distal femoral condyle reference point.
Another issue which relates to this is the
rotational position of the femoral component. The medial
femoral condyle is larger than the lateral femoral condyle
and for proper femoral rotation, usually a larger piece of
bone needs to be resected off the posterior medial femoral
condyle than the posterior lateral femoral condyle. This
results in a relatively more externally rotated position of
the femoral component with respect to the femur and
provides better patella tracking. The patella tracks
better with this maneuver and is less likely to dislocate
and the knees flex better and are more stable. Fewer
lateral releases are needed and fewer revisional surgeries
are needed for patellar subluxation and dislocation. The
instruments of the present invention have a built-in 3 of
external rotation.
The method and apparatus of the present invention
involves resecting the distal medial and lateral condyles
in a plane generally perpendicular to the mechanical axis
of the femur at a predetermined distance proximal to the
intercondylar notch preferably using the notch as a
reference. Then a femoral component is selected to have a
size and thickness to present both the medial and lateral
condyles at the same general distal position as the
original natural lateral condyle being replaced. This
selecting step involves selecting an appropriate size
femoral component from a group of components having varying
sizes and condyle thicknesses.
The present invention preferably uses the
intercondylar notch as a reference point for distal
condylar resection. However, it is understood that other
reference points can be used in order to reestablish the
patella femoral groove at the same location as the natural
knee and to reestablish the medial and lateral condyles at
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the same general distal position as the original natural
lateral condyle being replaced. The reference points
include the medial condyle and the lateral condyle as well
as the intercondylar notch.
It is not new to use the intercondylar notch as a
reference point for distal condylar resection per se.
Prior art systems have used the notch as a reference point
from which to make the distal condylar resection. For
instance, in one system designed by Buechel & Pappas, the
first resection is a resection of the proximal end of the
tibia to provide a tibia platform. This resection is made
with typical tibial instrumentation. Then, the anterior
and posterior femur condyles are resected independent of
the notch. Then, referencing the intercondylar notch,
Buechel & Pappas resect the distal end of the femur.
Other systems including DePuy's F.I.R.S.T. system
introduced in mid-1980s also use the intercondylar notch as
a reference point for making the distal femoral resection,
but th~is system does not try to reconstruct the natural
lateral condyle being replaced. Also, in DePuy's
F.I.R.S.T. system, the femoral implants were not
proportioned in size and thickness to place both the medial
and lateral condyles of the natural distal position
generally corresponding to the original lateral condyle.
The present invention involves selecting a
femoral component to place both the medial and lateral
condyles at the same level, but at the same level as the
original lateral condyle. The method of the present
invention therefore, is an advancement over the prior art
methods and apparatus because the new method recreates the
lateral condyle joint line versus the medial condyle joint
line. The present invention reestablishes the original
natural distal patellar groove in which the patellar
articulates at the same general position as the natural
distal patellar groove. This improvement places less
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strain, wear and tear on the patellar tendon and
potentially reduces soft tissue releases for proper
tracking of the patellar mechanism.
It is an object of the present invention to
provide a method for reconstructing a femoral portion of a
knee in a total knee replacement of both the medial and
lateral condyles so that the reconstructed knee presents
the lateral and medial condyles at the same general distal
position as the original natural lateral condyle and
locates the intercondylar notch and distal patellar groove
in a position generally coinciding with the natural notch
and groove.
According to one aspect of the present invention,
a method is disclosed for reconstructing a femoral portion
of a knee in a total knee replacement of both the medial
and lateral condyles to locate the intercondylar notch and
distal patellar groove of the reconstructed knee in a
position generally coinciding with the natural
intercondylar notch and distal patellar groove. The method
includes the steps of resecting the distal medial and
lateral condyles to form a resected distal surface,
selecting a femoral component sized to have an
intercondylar notch and distal patellar groove at the same
general distal position as the original natural
intercondylar notch and distal patellar groove being
replaced, and installing the selected femoral component on
the resected distal surface.
In the illustrated embodiment, the plane of the
resected distal surface is generally perpendicular to the
mechanical axis of the femur. The resected distal surface
is spaced apart a predetermined distance proximal from the
intercondylar notch using the intercondylar notch as a
reference. However, other reference points may be used.
The femoral component has a thickness in the area
of a patellar groove substantially equal to said
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predetermined distance so that the distal patellar groove
of the femoral component is positioned at substantially the
natural location of the distal patellar groove. The
selecting step includes the steps of providing a plurality
of femoral components having various anterior/posterior
lengths and increasing distal and posterior condyle
thicknesses as the anterior/posterior length increases and
determining which of the plurality of femoral components
has an appropriate distal and posterior condyle thickness
to approximate the natural distal position of the resected
lateral condyle.
According to another aspect of the present
invention, a method is disclosed for reconstructing a
femoral portion of a knee in a total knee replacement of
both the medial and lateral condyles so that both the
medial and lateral condyles of the reconstructed knee are
located at about the same distal position as the original
natural lateral condyle. The method includes the steps of
resecting the distal medial and lateral condyles to form a
resected distal surface, selecting a femoral component
sized to have both the medial and lateral condyles at the
same general distal position as the original natural
lateral condyle being replaced, and installing the selected
femoral component on the resected distal surface.
The selecting step includes the step of providing
a plurality of femoral components having various
anterior/posterior lengths and increasing distal and
posterior condyle thicknesses as the anterior/posterior
length increases and determining which of the plurality of
femoral components has an appropriate distal and posterior
condyle thickness to approximate the natural distal
position of the resected lateral condyle. The determining
step illustratively includes the step of placing a sizer
assembly on the resected end of the femur to indicate which
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one of the plurality of femoral components is appropriately
sized for the resected femur.
The resected distal surface is spaced apart a
predetermined distance proximal from the intercondylar
notch. The femoral component has a thickness in the area
of a patellar groove substantially equal to said
predetermined distance so that the distal patellar groove
of the femoral component is positioned at substantially the
natural location of the distal patellar groove.
According to yet another aspect of the present
invention, a method is provided for reconstructing a
femoral portion of a knee in a total knee replacement, the
distal end of which has medial and lateral condyles and an
intercondylar notch therebetween defining a distal patellar
groove for the articulation of the patella with the femur
during flexion of the knee. The method includes the steps
of locating and drilling a hole in the intercondylar notch
to access an intermedullary canal of a femur, installing a
femoral alignment guide onto an intermedullary rod, and
inserting the intermedullary rod through said hole toward a
proximal end of the femur. The method also includes the
steps of movinq said femoral alignment guide into contact
with the intercondylar notch of the knee, positioning a
femoral cutting block relative to the alignment guide, and
securing the cutting block to the femur to align a guide
surface of the cutting block at a predetermined proximal
distance from said intercondylar notch. The method further
includes the steps of removing the femoral alignment guide
and rod from the femur, resecting the distal lateral and
medial condyles using the guide surface of the resection
block as a resection reference, and determining an
appropriate size of a femoral component having a size and
condyle thickness which will reconstruct the lateral
condyle and position the distal patellar groove at about
the same distal locations to approximate the anatomy of the
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natural knee being replaced and to position the medial
condyle of the femoral component at the same distal
position as the original lateral condyle.
In the one illustrated method, the step of moving
the femoral alignment guide into contact with the
intercondylar notch of the knee includes the step of
positioning an intercondylar saddle on the alignment guide
in engagement with the intercondylar notch. The step of
positioning the femoral cutting block relative to the
alignment guide includes the step of positioning the
cutting block on an arm of the alignment guide at a
selected position spaced apart from the intercondylar
saddle by predetermined distance so that the femur is
resected a predetermined distance proximal to the
intercondylar notch. The step of determining an
appropriate size of a femoral component includes the step
of placing a sizer assembly on the resected distal end of
the femur to determine an appropriate size femoral
component.
According to still another aspect of the present
invention, an alignment guide is provided for positioning a
saw guide surface of a cutting block at a predetermined
position proximally from an intercondylar notch of a femur
having an intermedullary rod extending along its anatomical
axis. The alignment guide includes a body portion formed
to include an aperture for receiving the rod therethrough,
and an arm coupled to the body for receiving the cutting
block thereon. The alignment guide also includes means for
securing the cutting block to the arm at a predetermined
position relative to the body, and an intercondylar saddle
coupled to the body portion of the alignment guide, the
saddle being configured to engage the intercondylar notch
of the femur to align the cutting block coupled to the arm
of the alignment guide at said predetermined position
proximal to the intercondylar notch.
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The saddle is configured to surround the aperture
for receiving the intermedullary rod. The saddle permits
limited movement of the alignment guide relative to the
intermedullary rod to permit the alignment guide to be
seated at the deepest section of the intercondylar notch.
The saddle includes a first generally U-shaped stop for
engaging the intercondylar notch located above the aperture
a second generally U-shaped stop for engaging the
intercondylar notch located below the aperture.
The alignment guide further includes a calibrated
stop pivotably coupled to the body portion. The calibrated
stop is movable from a first position abutting the arm to
align the guide surface of the cutting block a
predetermined distance from the saddle to establish said
predetermined position relative to the intercondylar notch
to a second position to permit the position of the cutting
block to be adjusted.
According to a further aspect of the present
invention, a sizer assembly is provided for determining the
optimum size femoral component to couple to a resected
distal end of a femur from a group of femoral components
having various sizes and condyle thicknesses. The assembly
includes a body portion including a flat contact surface
for engaging the resected end of the femur, a plurality of
feet coupled to a bottom surface of the body for engaging
posterior femoral condyles to align the body portion with
the resected distal end of the femur, and a stylus assembly
slidably coupled to the body portion. The stylus assembly
includes an arm extending proximally away from the body
portion and a stylus coupled to the arm. The stylus
assembly is movable relative to said body portion until the
stylus engages the anterior femoral cortex. The sizer
assembly also includes means on the stylus assembly and
body portion for indicating the size of femoral component
corresponding to the resected femur based on the position
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of the stylus assembly relative to the body portion. The
sizer assembly further includes means coupled to the stylus
assembly for supporting a drill bushing thereon
corresponding to the size of the femoral component
indicated by the indicating means.
The supporting means aligns the drill bushing
relative to the anterior femoral cortex. The arm the drill
bushing includes first and second apertures for guiding a
drill to bore pilot holes in the resected femur for
securing the femoral component to the resected femur.
According to a still further aspect of the
present invention, an assembly is provided for aligning a
cutting block relative to a resected distal end of a femur.
The assembly includes a body portion having a flat contact
surface for engaging the resected end of the femur, and a
plurality of feet coupled to a bottom surface of the body
for engaging posterior femoral condyles to align the body
portion with the resected distal end of the femur. The
assembly also includes a stylus assembly slidably coupled
to the body portion. The stylus assembly includes an arm
extending proximally away from the body portion and a
stylus coupled to the arm. The stylus assembly is movable
relative to said body portion until the stylus engages the
anterior femoral cortex. The assembly further includes
means coupled to the stylus assembly for aligning a cutting
block on the resected distal end of the femur relative to
the anterior femoral cortex.
According to an additional aspect of the present
invention, a method is provided for reconstructing a
femoral portion of a knee in a total knee replacement, the
distal end of which has medial and lateral condyles and an
intercondylar notch therebetween defining a distal patellar
groove for articulation of the patella with the femur
during flexion of a knee. The method includes the steps of
securing a body portion to the distal end of the knee. The
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body portion is coupled to an intermedullary rod located
within an intermedullary canal of a femur. The method also
includes the steps of coupling a first cutting guide to the
body portion, moving the first cutting guide relative to
S the body portion to align a guide slot of the first cutting
guide at a selected location, resecting an anterior surface
of the femur through the guide slot of the first cutting
guide, and removing the first cutting guide from the body
portion. The method further includes the steps of coupling
a second cutting guide to the body portion, adjusting the
position of the second cutting guide relative to the body
portion to align a guide slot of the second cutting guide a
predetermined distance from the intercondylar notch,
securing the second cutting guide to the resected anterior
lS portion of the femur, and cutting the distal end off the
femur using the guide slot of the second cutting guide as a
reference so that the femur is resected a predetermined
distance proximally from the position of the intercondylar
notch. The method still further includes the step of
determining an appropriate size of a femoral component
having a size and condylar thickness which will reconstruct
the intercondylar notch at about the same distal position
as the natural intercondylar notch.
The step of adjusting the position of the second
cutting guide relative to the body portion includes the
step of aligning a notch formed in the second cutting guide
with the intercondylar notch. The guide slot of the second
cutting guide is spaced said predetermined distance from
the notch.
Additional objects, features, and advantages of
~ the invention will become apparent to those skilled in the
art upon consideration of the following detailed
description of a preferred embodiment exemplifying the best
mode of carrying out the invention as presently perceived.
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Brief Description of the Drawinqs
Fig. 1 is a diagrammatical view illustrating
various joint lines of a knee.
Fig. 2 is a diagrammatical illustration of prior
art methods for replacing the medial and lateral condyles
with a femoral component.
Fig. 3 is a diagrammatical illustration of the
method of the present invention for replacing medial and
lateral condyles with a femoral component.
Fig. 4 is a perspective view illustrating
formation of a pilot hole in the intercondylar notch of a
femur.
Fig. 5 is a perspective view illustrating an
alignment guide and cutting block of the present invention.
Fig. 6 illustrates the alignment guide of
Fig. 5 as it is installed and positioned on the femur.
Fig. 7 is a partial perspective view of an
intercondylar saddle of the alignment guide.
Fig. 8 is a perspective view illustrating the
alignment guide fully seated against the intercondylar
notch of the femur to position the cutting block relative
to the femur.
Fig. 9 is a perspective view illustrating a saw
capture coupled to the resection block for guiding a saw
blade to resect the distal end off the femur.
Fig. 10 is a perspective view illustrating a
sizing apparatus coupled to the resected distal end of
femur for determining an appropriate size femoral component
to install on the end of the femur.
Fig. 11 is a side elevational view of the sizing
apparatus illustrated in Fig. 10.
Fig. 12A-12E are diagrammatical views
illustrating five different sizes of femoral components
which may be selected to install on the distal end of the
femur.
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Fig. 13 is a table illustrating the natural
thickness of lateral condyles on small, medium and large
femurs and illustrating the distal condyle thicknesses for
the various size femoral components of the present
invention.
Fig. 14 is a diagrammatical view illustrating a
femoral component and a drill bushing of the present
invention.
Fig. 15 is a perspective view of a resection
guide and a saw capture for making further resections of
the distal end of the femur.
Fig. 16 is a side elevational view of a second
embodiment of the present invention including a saw capture
assembly for resecting an anterior portion of the femur.
Fig. 17 is an end view of the saw capture
assembly illustrated in Fig. 16.
Fig. 18 is a side elevational view of a cutting
block assembly for guiding a saw blade to resect the distal
end of the femur.
Fig. 19 is a top plan view illustrating the
resection block for aligning the position of resection
plane with the intercondylar notch.
Fig. 20 is a perspective view of the resection
block illustrated in Figs. 18 and 19 with a saw blade
extending through the guide slot to resect the distal end
of the femur.
Detailed DescriPtion of the Drawings
In total knee arthroplasty the goal is to provide
pain free mobility to the patient. This is accomplished by
- resurfacing the tibia, femur, and the patella.
Reconstruction of the knee requires the reestablishment of
two joint lines, the tibial/femoral joint line and the
patella/femoral joint line. Great attention has typically
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been paid to the reconstruction of the tibial/femoral joint
line.
As illustrated in Fig. 1, a knee joint 10 is
established between a distal end 12 of femur 14 and
proximal end 16 of tibia 18. The distal end 12 of femur 14
includes a lateral condyle 20 and a medial condyle 22. The
lateral and medial condyles 20 and 22 articulate against a
superior articulate surface of the tibia 18. Engagement of
the lateral and medial condyles 20 and 22 with the superior
surface of tibia 18 establishes a joint line 24 which is
aligned at about a 3 angle 26 relative to the plane 28
perpendicular to the mechanical axis 30 of tibia 18. Tibia
18 is usually resected about plane 28 during total knee
arthroplasty.
Femur 14 includes a mechanical axis 32 and an
anatomical axis 36 aligned at about a 6 angle 34 relative
to mechanical axis 32. The tibial/femoral joint 24 is
established, provided that the tibia is resected with a 3
of varus slope. Although, currently, most surgeons resect
the proximal tibia at 90 to axis 30 of the tibia 18. This
results in the creation of two joint lines. A surgeon can
recreate the medial joint line 40 or the lateral joint line
38. Instrumentation that references off of the medial
condyle reconstructs the medial condylar joint line 40.
During flexion of the knee, the patella articulates with
the lateral condyle and not the medial condyle.
Reestablishment of the tibial/femoral joint has
typically been accomplished in prior art methods by
instrumentation that references off the distal medial
condyle 22 as illustrated by reference line 42 in Fig. 2.
A fixed amount of bone is resected from the distal medial
condyle 22 corresponding to the thickness of the femoral
component 46 installed distal end 12 of femur 14. Normally
6 to 10 mm is resected as illustrated by resection line 44.
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In prior knee reconstruction methods, a fixed
amount of distal resection is typically made regardless of
the size of the femur. This is because all of the femoral
components have been designed with constant distal and
posterior thicknesses, regardless the size of the implant.
The present invention includes a set of femoral components
having increasing distal and posterior thicknesses as the
size of the implant increases. Anthropometric data
indicates that as the femur increases in the A/P and M/L
dimensions, the size or thickness of the distal and
posterior condyles also increases. The distance from the
distal medial and lateral condyles to the intercondylar
notch increases distally as the A/P dimension of the femur
increases.
Therefore if a constant distal resection is made
regardless of the size of the femur this will result in
excess bone being removed from small knees and in
insufficient bone being removed from large knees. For
small male femurs the thickness of the distal lateral
condyle from the intercondylar is approximately 4 mm and
for large male femurs the thickness is approximately 8.4
mm. A constant distal resection of 8 mm will place the
femoral component in a different location depending upon
the size of the femur. This then results in the shifting
the patella/femoral joint line proximally in small femurs
and distally in large femurs.
By referencing from the medial condyle and
resecting the same amount of bone from the reference line
42, prior art knee reconstruction methods illustrated in
Fig. 2 include a prosthetic femoral component 46 which
approximates the original position of the medial condyle
22. However, such prior art knee reconstruction methods
add condyle thickness to the lateral condyle and add
thickness to the intercondylar notch so that femoral
component 46 extends distally beyond the natural position
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of the lateral condyle and the intercondylar notch. The
natural position of the lateral condyle 20 and the
intercondylar notch 21 are illustrated by the dotted line
in Fig. 2. This extra material in the area of the lateral
condyle and the intercondylar notch increases the distance
that the patella must travel distally with respect to the
femur as the patella moves to the distal aspect of the
femur during extreme reflection. This extra tension can
cause pain and may increase the likelihood of patella
failures.
The new knee construction method of the present
invention is designed to more closely simulate natural
movement of the patella by placing femoral component 54 at
a distal position approximately equal to the distal
position of the lateral condyle 20 as illustrated in
Fig. 3. In addition, the method of the present invention
is designed to place the groove 56 of the femoral component
46 at approximately the same position as the intercondylar
notch 21. The distal end of femur 12 is resected along a
resection line 50 which is located a predetermined distance
illustrated by dimension 52 from the position of the
intercondylar notch. Distance 52 is selected to be equal
to the thickness of the femoral component 54 in the area of
the patellar groove 56. Therefore, when femoral component
54 is positioned on femur 12, the groove 56 of femoral
component 54 is aligned at about the same distal as the
natural intercondylar notch 21.
The method of the present invention does not
replace the total amount of bone resected from the medial
condyle 22. In other words, the medial condyle of femoral
component 54 does not extend as far distally as the natural
- medial condyle 22. The location of natural medial condyle
22 is illustrated by dotted line 22 in Fig. 3.
An advantageous reference point for selecting the
resection line 50 is the intercondylar notch 21 as
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discussed above. However, other reference points may be
used to determine the location of resection line 50.
The instruments of the present invention
reference the intercondylar notch area for proximal/distal
placement of the femoral component. This reference point
for proximal/distal placement is a more reliable one
placing the patella/femoral joint anatomically in every
knee and approximating the new joint line properly at the
level of the smaller lateral distal condyle rather than the
larger and usually more distally placed medial femoral
condyle. This results in more space for the tibial
component thus minimizing the tibial resection and allows
the prosthetic patellar construct to not ha~e to travel
extra distance distally during knee flexion and thus gives
a better range of motion with less problems of patellar
dislocation and subluxation.
One embodiment of the method and apparatus of the
present invention is illustrated in Figs. 4-12.
Preferably, the instruments of the present invention use
the intercondylar notch 21 as a reference point as opposed
to the medial condyle. The intercondylar notch is
typically constant reference point regardless of the
physical size of the femur.
In the present invention, a 3 mm resection of the
intercondylar notch is made on all femurs regardless of
size. The femoral components of the present invention are
all approximately 3 mm thick in the intercondylar notch or
patellar groove region. Thus, by removing 3 mm of bone and
replacing it with 3 mm of metal, a surgeon reestablishes
the distal patella/femoral joint line at substantially its
natural position. This advantageous ;~ improves movement of
the patella during flexion of the knee as discussed above.
The amount of distal condyle resected will vary depending
upon the physical size of the femur. The instruments of
the present invention recreate the natural position of the
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lateral condyle about which the patella articulates with
during flexion of the knee.
According to the first embodiment of the present
invention, the distal end 12 of femur 14 is exposed in a
conventional manner. A surgeon removes any osteophytes
from intercondylar notch 21. In this embodiment of the
invention, the intercondylar notch 21 is used as a
reference point to determine the amount of distal femur
that will be resected. The first step of the method is to
drill and intramedullary (IM) hole in the distal end of
femur 14. A femoral IM initiator drill 60 is used to
create a pilot hole 62. Drill 60 has a stepped up tip 64
to hold the drill 60 at a selected entry point without
"walking". Drill 60 is used only to break through the
proximal cortex and to advance a short distance into the
metaphysis of femur 14. For deep femoral penetration, a
fluted, blunt-tipped femoral IM rod 66 is used.
Pilot hole 60 for IM rod 66 is positioned in the
middle of the intercondylar notch 21 slightly anterior to
the posterior cruciate ligament attachment as illustrated
in Fig. 4. Pilot hole 62 should be in line with the
anatomical axis 36 of femur 14 and should also reference
off the posterior cortex of the medullary canal. Pilot
hole 62 should be large enough so that hole 62 does not
control the attitude of IM rod 66.
Figs. 5-8 illustrated the configuration of the
femoral alignment guide 70 of the present invention.
Alignment guide 70 includes a body portion 71. A 6 distal
femoral cutting block 72 is coupled to alignment guide 70
as illustrated in Fig. 5. An aperture 74 of cutting block
72 is installed over arm 76 of alignment guide 70 until a
guide surface 78 of cutting block 72 abuts a calibrated
stop 80 on alignment guide 70. Cutting block 72 is locked
into place by rotating wing nut 82 45 clockwise so the
eccentric cam 83 engages cutting block 72. Cutting block
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72 is configured to guide resection of distal end 12 of
femur 14 with 6 of valgus inclination that is 3 mm
proximal to intercondylar notch 21. In other words, guide
surface 78 of cutting block 72 is aligned generally
perpendicular to mechanical axis 32 of femur 14. It is
understood that the angle of cutting block 72 may be
changed depending upon the particular knee being
reconstructed.
After cutting block 72 is installed onto
alignment guide 70 and locked into place, a D-shaped
femoral IM rod 66 is inserted through an aperture 84 of
alignment guide 70 with a flat surface facing upwardly. IM
rod is preferably 1 mm smaller than pilot hole 62 to
minimize pressure build-up in the medullary canal and to
allow the isthmus to dictate rod placement. Full seating
of rod 66 is not necessary. The IM rod 66 is slowly
advanced into the distal femur 14. Rod 66 is typically
inserted to about 2/3 of its total length. The blunt tip
of the IM rod 66 passes easily through the hollow shaft of
the femur 14 while minimizing the chances of perforating
the femoral cortex.
After IM rod 66 is inserted into femur 14,
alignment guide 70 is moved along the longitudinal axis of
rod 66 toward femur 14 until an intercondylar saddle 86 of
alignment guide 70 is seated firmly in intercondylar notch
21. Saddle 86 is best illustrated in Figs. 5-7. The
intercondylar saddle 86 includes a generally circular
bearing surface 88 for receiving IM rod 66 therethrough.
Saddle 86 also includes an anterior generally U-shaped stop
90 located above bearing surface 88 and a posterior
generally U-shaped stop 92 located below bearing surface
88. The curvature of generally U-shaped stops 90 and 92
corresponds generally to the curvature of intercondylar
notch 21. Bearing 88 of saddle 86 is slightly larger than
the diameter of IM rod 66 to permit limited movement of
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alignment guide 70 relative to IM rod 66 in the direction
of arrows 93 and 94. This permits generally U-shaped stops
90 and 92 to abut the intercondylar notch despite slight
misalignment of IM rod 66. This ensures that saddle 86 of
alignment guide 70 is seated at the deepest section of
intercondylar notch 21 for referencing resection of femur
14.
Alignment guide 70 positions cutting block 72
above the anterior surface 95 of femur 14 to provide
clearance between the femur 14 and cutting block 72 as
alignment guide 70 slides along rod 66 as illustrated by
dimension 96 in Fig. 6. Calibrated stop 80 positions guide
face 78 of cutting block 72 a predetermined distance from
the front edge of U-shaped stops 90 and 92 of saddle 86 as
illustrated by dimension 98. Illustratively, dimension 98
is about 3 mm which corresponds to the thickness of femoral
components at the intercondylar notch area. Therefore,
guide surface 78 is aligned about 3 mm proximally from the
deepest part of intercondylar notch 21. Because the flat
side of IM rod 66 mates with a spring-loaded plate on
femoral alignment guide 70, approximate rotational
alignment of guide 70 relative to femur 14 can be achieved
using the T-handle 67 of IM rod 66 as a reference. For
additional stability, 1/8 inch (3.175 mm) fixation pins 97
can be inserted into distal holes of visualization bar 99.
If more or less bone resection is desired, the
position of the distal femoral cutting block 72 can be fine
tuned. This is done by rotating wing nut 82, 45 counter
clockwise to the neutral position and moving calibrated
stop upwardly in the direction of arrow 100. Cutting block
72 can then slide proximally or distally on arm 76 of
alignment 70. 2 mm incremental markers are provided on arm
76 for this adjustment. After the predetermined resection
amount is selected, and saddle 86 is seated against
intercondylar notch 21, cutting block 72 is then secured to
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femur 14 using a 1/8 inch (3.175 mm) drill to drill pilot
holes through the center holes in cutting block 72. Two or
more 1/8 inch (3.175 mm) fixation pins 100 are then
extended through the holes in cutting block 72 and seated
into the bone.
Alignment guide 70 is then disengaged from
cutting block 72 by turning wing nut 82 to the neutral
position. IM rod 66 is also removed. The cutting block
then slides down fixation pins 100 until cutting block 72
contacts the anterior femur surface 95.
A surgeon may then verify the varus/valgus
alignment using an external alignment tower (not shown).
Correct alignment is indicated when a proximal end of an
alignment rod of the tower is centered over the head of
femur 14 when a distal end of the tower is positioned on
cutting block 72.
After cutting block 72 is properly positioned, a
saw capture 102 is coupled to cutting block 72 as
illustrated in Fig. 9. Saw capture 102 includes a slot 104
for receiving a saw blade 106 therethrough. Teeth on the
saw blade 106 are typically not offset, allowing the blade
106 to be inserted directly into the saw capture 102,
thereby maximizing the effectiveness of saw capture 102. A
drop of sterile mineral oil on saw blade 106 helps reduce
friction. After the distal lateral and medial condyles 20
and 22 are resected, cutting block 72, fixation pins 100,
and saw capture 102 are removed from femur 14.
As illustrated in Figs. 10 and 11, a sizer
assembly 108 is provided. Because 3 of external rotation
is built into sizer assembly 108, a left and a right are
provided. An appropriate sizer assembly 108 is placed
flush against the resected distal femoral surface 110.
Feet 111 of sizer 108 should be in direct contact with the
posterior femoral condyles 113 of femur 14. Sizer assembly
108 must be centered medially and laterally since it will
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help determine the M/L position of the femoral component
implant. Sizer assembly 108 includes a stylus assembly 112
slidable coupled to a body portion 115. Pressure is
applied to stylus assembly 112 in the direction of arrow
114 until stylus 116 touches in the vicinity of the center
portion of the anterior femoral cortex as best illustrated
in Figs. 10 and 11. The stylus is aligned parallel to the
anatomical axis of femur 14.
After stylus 116 engages anterior femoral cortex,
a surgeon can read the appropriate size femoral component
directly from a calibration gauge 118 based on the relative
position of stylus assembly 112 relative to body portion
115. In the exa~ple illustrated in Fig. 10, the gauge
indicates that a size 3 femoral component should be
selected. If the indicator gauge 118 falls between two
sizes, the smaller size femoral component is typically
selected. This should, however, be determined at the
surgeon's discretion. When the anterior condyle cut is
made for a size 3, the saw will exit at the point where the
stylus touches the femur. After sizer assembly 108 is
~ properly positioned on femur 14, a mallet is used to drive
two captured fixation pins 120 into femur 14 to securely
fix sizer assembly 108 to femur 14. If additional fixation
is required, the sizer assembly 108 also includes anterior
fixation pin holes 122 for receiving pins (not shown)
therethrough.
Figs. 12A-12E illustrate the various sizes of
femoral components available for the surgeon to select
based upon the reading from indicator gauge 118 of sizer
assembly 108. Femoral component 54 illustated in Fig. 12A
corresponds to femoral component size 1. Femoral component
54 illustated in Fig. 12B corresponds to femoral component
size 2. Femoral component 54 illustated in Fig. 12C
corresponds to femoral component size 3. Femoral component
54 illustrated in Fig. 12D corresponds to femoral component
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size 4. Femoral component 54 illustrated in Fig. 12E
corresponds to femoral component size 5. Each femoral
component 54 has a distal condyle thickness illustrated by
dimension 124 and a posterior condyle thickness illustrated
by dimension 126. Dimension 124 is substantially equal to
dimension 126. As the A/P dimension of the femoral
components 54 increase, the thicknesses of the distal
condyle 124 and the posterior condyle 126 also increase.
In other words, the size 2 femoral component illustrated in
Fig. 12B has distal and posterior condyle thicknesses 124
and 126 larger than the distal and posterior condyle
thicknesses 124 and 126 of femoral component 54 having a
size 1 illustrated in Fig. 12A.
Table I illustrated in Fig. 13 discloses the size
variation of femoral components illustrated in Figs. 12A -
12E. The first column of the Table I indicates the natural
lateral condyle thicknesses relative to the intercondylar
notch for small, medium, and large femurs. Small femurs
typically have a lateral condyle which extends about 4 mm
distally from the intercondylar notch. Medium size femurs
typically include lateral condyles which extend about 6 mm
distally from the intercondylar notch. Large femurs
typically include a lateral condyle which extends distally
from the intercondylar notch by about 8.4 mm.
The second column of Table I indicates the distance
from distal position of the natural lateral condyle to the
resected surface 110 of femur 14 taking into account the
3 mm resection of the distal end of femur 14 beyond
intercondylar notch 21. The third column of the Table I
refers to the size of femoral component 54 used in the
present invention. The fourth column of Table I refers to
the distal thicknesses 124 and 126 of the distal and
posterior condyles of the various size femoral components
54. For instance, the size 1 femoral component illustrated
in Fig. 12A has distal and posterior condyle thicknesses
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124 and 126 equal to 6 mm. For the large femoral component
size 5 illustrated in Fig. 12E, the distal and posterior
condyle thicknesses 124 and 126 have increased to 10 mm.
After the appropriate size femoral component 54
is selected, an appropriately sized drill bushing 127 which
corresponds in size to the size of the selected femoral
component is used to drill pilot holes in the resected
distal end 110 of femur 14. As illustrated in Fig. 14,
drill bushing 127 has a width equal to the M/L width of a
corresponding femoral component 54.
Posts 129 are provided on sizer assembly 108 for
receiving a drill bushing 127 thereon. Posts 129 are
aligned at an angle relative to each other and have
different sizes for receiving right side and left side
drill bushings 127. Different size drill bushings 127 are
provided for each different size of femoral component.
After the appropriate size femoral component 54 is
selected, a drill bushing 127 corresponding to that
selected size is inserted over pegs 129 on sizer assembly
108. Sizer assembly 108 must be centered medially and
laterally because it determines the M/L position of femoral
component 54 on femur 14. Holes are drilled through
apertures 128 in drill bushing 127 using drill 130 while
maintaining light finger pressure on stylus assembly 112 in
the direction of arrow 114. The holes formed by drill bit
130 are used to locate the A/P cutting blocks and femoral
component 54. The drill bushing 127 is then removed from
sizer assembly 108. Sizer assembly 108 is removed from
femur 14 using the appropriate end of a slap hammer.
The anterior and posterior femoral condyle
resections and chamfer resections are then made. An A/P
cutting block 132 illustrated in Fig. 15 which corresponds
to the appropriate size femoral component determined
earlier is installed on the resected end 110 of femur 14.
35 Therefore, sizer assembly 108 aligns cutting block 132 on
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resected distal end 110 of femur 14 relative to the
anterior femoral cortex which is engaged by stylus 116.
Drive pegs on the A/P cutting block 132 are inserted into
the predrilled holes using a mallet. If additional
fixation is needed, towel clips or 1/8 inch (3.175 mm) pins
can be inserted into the holes on the side of~cutting block
132. Cutting block 132 must be flush with the distal
femoral cut. Anterior and posterior condyles are then
resected through slot 104 in saw capture 102. The same saw
capture used to resect the distal femur can be used for the
anterior and posterior condyle resections. Chamfer
resections are then made through slots 134 in the A/P
cutting block 132. Cutting block 132 is then removed using
a slap hammer (not shown). An independent anterior chamfer
cutting guide also may be used. After the chamfers are
cut, the distal end of the femur 114 is appropriately sized
to receive the selected femoral component 54 thereon.
Femoral component 54 is then installed out of the resected
distal end of femur 14.
Another embodiment of the present invention is
illustrated in Figs. 16-19. In this embodiment, the
anterior portion 95 of femur 14 is resected first using the
cutting guide assembly 140 illustrated in Fig. 16. Cutting
guide assembly 140 includes a body portion 142 configured
to accept an IM rod 66. Body portion 142 can be rotated on
rod 66 to align body portion 142 at a desired angle
relative to the femur 14. Body portion 142 is rotated
about 3 clockwise or counterclockwise depending on whether
a right or left knee is being resected to provide external
rotation if desired. After body portion 142 is orientated
at the desired position, attachment pins 143 are driven
into femur 14 to secure body portion 142 to femur 14.
A saw capture assembly 144 is slidably coupled to
body portion 142. Specifically, a rod 146 coupled to saw
capture assembly 144 is slidably received within an
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aperture of body portion 142. Therefore, saw capture
assembly 144 moves up and down in the direction of double
headed arrow 148 relative to body portion 142. Saw capture
assembly includes a saw guide 149, an arm portion 150, and
a stylus 152 extending downwardly from arm portion 150.
Saw capture assembly 144 moves relative to femur 14 until
stylus 152 engages the anterior femoral cortex of femur 14.
A knob 154 is then rotated to secure saw capture assembly
144 in the selected position relative to body portion 142.
After saw capture assembly 144 is locked in the desired
position, a saw blade is used to resect anterior portion 95
off femur 14. Guide slot 155 of saw guide 149 aligns the
saw blade in the proper position to resect anterior portion
95 of femur 14.
Saw capture assembly 144 is then removed from
body portion 142. A cutting block assembly 156 illustrated
in Figs. 18 and 19 is then inserted into body portion 142.
Cutting block assembly 156 includes a cutting block 158.
Posts 160 extend from cutting block 158. Posts 160 are
inserted into apertures in a block 162. A post 164 is
coupled to block 162. Post 164 is slidably received within
the aperture of body portion 142 so that the cutting block
assembly 156 can move up and down in the direction of
double headed arrow 166. Cutting block 158 can also move
in the direction of arrow 168 relative to block 162.
As best illustrated in Fig. 19, body portion 142
is aligned at about a 6 angle relative to rod 66. An
aperture formed in body portion 142 is preferably aligned
at the 6 angle. The aperture may be threaded if desired
to receive a threaded rod 66. Therefore, the plane of the
resection surface is aligned substantially perpendicular to
the mechanical axis 32 of femur 14. A surgeon moves
cutting block 158 in the direction of arrow 168 until notch
170 of cutting block 158 is aligned with intercondylar
notch 21 of femur 14. Cutting block 158 includes a first
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saw guide slot 172 which is positioned a predetermined
distance proximally from notch 170 as illustrated by
dimension 174. Dimension 174 is selected to be the
thickness of the femoral component 54 in the area of the
intercondylar notch so that the intercondylar notch and
distal patellar groove are reconstructed at approximately
the same location as the natural intercondylar notch and
distal patellar groove. Preferably, dimension 174 is 3mm
as in the first embodiment of the present invention. A
second saw guide slot 176 is provided in case the surgeon
decides additional resection of femur 14 is needed.
Resection of distal end 12 of femur 14 is best
illustrated in Fig. 20. After cutting block 158 is
properly aligned with intercondylar notch 21, cutting block
158 is secured to femur 14 by captured pins 180.
Additional pins or screws may be used to secure cutting
block 158 to femur 14 if necessary. Rod 66, body portion
142, and block 162 are then removed to permit saw blade 106
to cut the distal end off femur 14 through the previously
aligned saw guide slot 172.
Although the invention has been described in
detail with reference to a certain illustrated preferred
embodiment, variations and modifications exist within the
scope and spirit of the invention as described and defined
in the following claims.
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