Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR REMOVING
PRE-PLACED PROSTHETIC JOINTS AND
PREPARING FOR THEIR REPLACEMENT
ENT
The present invention relates to the replacement
received.
Revision surgery for the replacement of a failed
joint requires that both the prosthetic appliance and
35 the mantle holding it in place within the bone cavity
be removed. The old prosthetic device is usually
easily removed using a slap-hammer, since its surface
of pre-placed prosthetic joints and, more particularly,
is concerned with a method and apparatus for removing
the cement mantle used to secure the pre-placed joint
Title of the Invention
Background of the Invention
in place. In its more particular aspects, the
invention is concerned with such a 3nethod and apparatus
for removing the cement mantle to secure the ball of a
prosthetic hip joint to the patient's femur.
Prosthetic hip and knee joints have become
relatively commonplace. Unfortunately, however, there
has also been a progressive rise in the incidence of
the nonseptic failure of such joints which necessitates
revision surgery to affect their replacement. The
leading cause of the nonseptic failure of hip joints is
the loosening of the femoral side of the prosthetic
appliance. This is generally the result of loosening
of the cement securing mantle for the appliance from
the cavity in the femur within whic3~ the mantle is
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PATENT
is smooth and separable from the underlying cement
mantle. The the cement mantle, however, is tightly
adherent to the surrounding bone and generally remains
so adhered, even after the prosthetic device is
removed. Removal of the adhered cement mantle is
presently performed by progressively chipping the
mantle away using a hammer and chisel. This method is
tedious and the possibility of the chisel going past
the mantle and fracturing the underlying bone is
present. Other methods of removing the cement mantle,
using powered drilling and boring devices, are
similarly tedious and dangerous to the bone.
Prior revision surgery for the replacement of
prosthetic hip joints also often includes a
trochanteric osteotomy to remove the greater
trochanter. Although this exposes the cement mantle
and makes it easier to work upon, it generally does not
eliminate the necessity for chipping the mantle away
with a hammer and chisel to affect its removal.
Summary of the Invention
Methylmethacrylate cement is the most accepted
type of cement used to secure prosthetic joint
appliances to bone. This cement is supplied to the
surgeon packaged in two sterile companents. One
component is a liquid methyl methacrylate monomer and
the other is a finely divided powder mixture of
polymethyl methacrylate, methyl meti~acrylate-styrene-
copolymer. At the time of use, the powder and liquid
are mixed, resulting in the exothermic polymeric
formation of a soft pliable dough-like mass. As the
reaction progresses, within a few minutes a hard
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cement-like complex is formed. It is this complex which forms
the cement mantle which the present invention is designed to
remove.
Old hardened methylmethacrylate cement is capable of
being partially dissolved and softened by the application of
new like fluid cement thereto. The resulting composite of old
and new cement cures into an integral bonded composite,
generally within about ten minutes. Although the present
invention relies upon this characteristic of
methylmethacrylate cement, it may find equal application to
other cements, so long as an adequate bond is provided between
the old and new cement.
In the method of the present invention, a mass of
new fluid methylmethacrylate cement is placed in intimate
contact with the hardened mantle of old methylmethacrylate
cement desired to be removed. A pulling appliance is then
embedded within the fluid cement and the mass of cement is
permitted to cure and harden, thus forming a bond between the
appliance and the mantle of old cement. Tension is then
applied to the pulling mantle to pull the appliance and bonded
mantle from the bone.
The invention provides an improved pulling appliance
for embedment in a mass of fluid cement received within a
cavity, said appliance comprising: (a) a rigid post of
generally rectilinear configuration; (b) a helical screw
thread formed around and extending over a portion of the
length of said post, said thread terminating short of said
distal end of the post; and (c) a non-threaded cylindrical
extension formed on said post between the distal end thereof
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and the portion upon which the screw thread is formed, said
extension being of reduced diameter as compared said portion
and extending axially therefrom. The proximal end of
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PATENT
the post is provided with means to secure a slap-hammer
thereto.
The unobviousness of the present invention becomes
particularly apparent when it is appreciated that the
concept of adding cement to a mantle desired to be
removed is abhorrent to normal removal practice. The
normal practice is only to remove material, as for
example by chipping it away. The thought of adding new
material naturally engenders the concern that it will
aggravate the situation by increasing the mass of
material which must be removed and making it less
accessible to conventional removal instruments.
A principle object of the present invention is to
provide an improved method and apparatus for removing a
cement mantle from adhered condition within a bone
cavity.
Another object of the invention is to provide such
a method and apparatus which enables the mantle to be
removed intact, as a unit.
Still another object of the invention is to
provide such a method and apparatus which avoids the
necessity of chipping away at the mantle to effect its
removal.
Another and more general object of the invention
is to provide such a method and apparatus which enables
the removal of the mantle quickly and efficiently,
with a minimum of trauma to the patient being treated.
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A further general object of the invention is to
provide such a method and apparatus which minimizes the
risk of damage to the bone from which the mantle is
being removed.
These and other objects will become more apparent
from the following detailed description and
accompanying drawings.
Brief Description of the Drawing
Fig. 1 is a perspective ~riew illustrating the kit
of equipment used to practice the method of the
invention, including the pulling post;
Fig. 2 is a cross-sectional elevational view of
the upper femur of a leg with the femoral component of
a prosthetic hip joint secured therein, and a dashed
line showing the step of removing the greater
trochanter from the femur:
Fig. 3 is a cross-sectional elevational view
similar to Fig. 2, illustrating the step of removing
the femoral component of the prosthetic hip joint from
the cement mantle within the femur:
Fig. 4 is a cross-sectional elevational view
similar to Fig. 3, illustrating the step of using a
rotary brush to abrade the cavity left in the cement
mantle by removal of the femoral component of the hip
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A ENT
Fig. 5 is a cross-sectional elevational view
similar to Fig. 4, illustrating the step of irrigating
the cavity within the cement mantle;
Fig. 6 is a cross-sectional elevational view
similar to Fig. 5, illustrating the step of measuring
the cavity in the cement mantle:
Fig. 7 is a cross-sectional elevational view
similar to Fig. 6, illustrating the step of filling the
cavity in the cement mantle with fluid cement;
Fig. 8 is a cross-sectional elevational view
similar to Fig. 7, illustrating the step of placing the
pulling tool within the fluid cement;
Fig. 8A is a cross-sectional elevational view
similar to Fig. 8, with parts thereof broken away,
illustrating the stop which may be used to limit the
degree to which the pulling tool is extended into the
cavity in the cement mantle;
Fig. 9 is a cross-sectional elevational view
similar to Fig. 8, illustrating the step of using a
slap-hammer to apply tension to the cement mantle
through the pulling tool; and,
Fig. 10 is a cross-sectional elevational view
similar to Fig. 9, illustrating the step of removing
the cement mantle from the femur, as a unit.
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Description of the Preferred Embodiments
The kit shown in Fig. 1 includes the following
components: injection gun 10 having a cement cartridge
12 secured thereto; rotary drill 14 having a
longitudinally extending circumferential brush 16
secured in the chuck thereof; distal brush 18 adapted
to be secured to the chuck of the drill 14 in place of
the brush 16; irrigation syringe 20; slap-hammer 22
having a cylindrical shaft 24 with a stop 26 on the
distal end thereof, a screw threaded socket 28 in the
proximal end thereof, and an annual weight 30 slidably
received thereon for abutting engagement with the stop
26; a ball clamp 32 having a screw threaded shaft 34
secured thereto by an articulated joint 36, said shaft
being designed for threaded engagement in the socket 28
of the slap-hammer 22; a cement restrictor plug 38
fabricated of an elastomeric material and having an
injector passage 40 and a vent passage 42 (see Fig. 7)
extending therethrough, said vent passage having a flap
valve 44 thereover; a depth gauge 46: a pulling
appliance 48; and, a stop collar 50.
Except for the pulling appliance 48 and the stop
collar 50, all of the instruments in the kit are
conventional. The pulling appliance and collar are
especially designed for use in the method of the
present invention. While the cement cartridge 12 is
conventional, it is specifically chosen to have a
narrow snout 52 for insertion into the cavity of the
cement mantle intended to be removed.
The pulling appliance 48 has a length and cross
section sufficient to enable it to be extended to the
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ENT
bottom of the cavity in the mantle in which it is
intended to be used, without imparting lateral forces
to the wall of the cavity. Ideally, its outside
diameter closely mimics, but is slightly less than,
that of the femoral component which formed the cavity.
The appliance may be fabricated of any suitable high
tensile strength corrosion-resistant material, such as
stainless steel. -
The pulling appliance provides,a rigid post of
generally rectilinear configuration having a distal end
54 and a proximal end 56. An elongated tapered section
58 is formed on the post between ids proximal and
distal ends and has a helical screw thread 60 formed
therearound. As may be seen from Figs. 8 and 9, both
the section 38 and thread 60 taper so as to converge
toward the distal end 54 of the post. The proximal end
56 provides a screw threaded shaft for receipt in the
socket 28 of the slap-hammer 22. The distal end 54 is
axially aligned with the proximal end 56 and of a
cylindrical reduced diameter crass-section, as compared
to that of the tapered section 38. As can be seen from
Figs. 8 and 9, the distal end sezves as a stop to limit
the degree to which the pulling instrument may
penetrate the cavity in the cement mantle. Its reduced
cross-section assures that space is provided
therearound for. receipt of flu_3 cement, as will become
more apparent from the following description of the
method.
The stop collar 50 is propflrtioned for slidable
receipt over the pulling appliance 48 and is provided
with a set screw 62 extensible therethrough into
engagement with the post of the appliance. Thus, the
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collar may be slid along the length of the appliance
and locked thereto at any desired position.
Figs. 2 through 10 sequentially illustrate the
steps of the method in removing the femoral component
64 of a hip joint and the cement mantle 66 therefor
from the femur 68. It should be appreciated that as
shown in Fig. 2 femoral component 64 has been secured
to the femur 68 through the cement mantle 66 in
conventional manner. The problem to be solved by the
present invention is the removal of the component and
mantle so that the joint can be renewed.
Fig. 2 shows the preparatory step of removing the
trochanter 70 of the femur. The dashed line in Fig. 2
designates the saw line for the trochanteric osteotomy
used to remove the trochanter. This line is chosen so
as to intersect the mantle 66, while at the same time
leaving a sufficient bone interface so that the
trochanter may be reattached to the femur. So removing
the trochanter increases access to the mantle 66 and
aids in assuring that pulling of the mantle from the
femur will not damage the bone structure.
Fig. 3 shows the step of pulling the femoral
component 64 from the mantle 66. For this purpose, the
ball clamp 32 is secured to the component and the slap-
hammer 22 is attached to the clamp through means of
the articulated joint 36. Once the clamp and hammer
are so connected, the position of the hammer is
adjusted so that its axis is generally parallel to the
axis of the femoral component extension, designated 72.
The weight 30 is then slid along the slap hammer to
impact with the stop 26, thus applying impact tension
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to the femoral component and pulling it from the mantle
66, as indicated by the arrow lines in Fig. 3. Removal
of the femoral component from the mantle leaves a
cement cavity, designated 74 therein.
Figs. 4 and 5 show the steps of abrading and
cleaning the interior of the cavity 74. As shown in
Fig. 4, the cavity is being circumferentially brushed
by the brush 16 connected to the drill 14. Fig. 5
shows the cavity being irrigated by the syringe 20.
Although not illustrated, it should be appreciated that
the distal end of the cavity may be additionally
brushed by attaching the distal brush 18 to the drill
14 and extending the brush to the bottom of the cavity.
After irrigation, the cavity may be dried by swabbing
or blowing.
Fig. 6 shows the step of using the gauge 46 to
measure the depth of the cavity 74. The depth
measurement thus achieved is transposed to the pulling
appliance 48 so that it may serve as a guide to limit
the degree to which the appliance is later inserted
into the cavity. This transposition may be by either
marking the pulling instrument to indicate the
measurement, or securing the stop collar 50 to the
instrument by means of the set screw 62 (see Fig. 8A).
Regardless of how the transposition is achieved, the
purpose is the same, namely to assure that the pulling
instrument will not be forced into the bottom of the
mantle 66.
Fig. 7 shows the step of placing the plug 38 in
the open proximal end of the mantle 66 and injecting
fluid cement into the cavity 74 by means of the snout
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52. The mass of fluid cement so injected into the
cavity is designated by the numeral 76. In the
preferred embodiment, the fluid cement corresponds to
that from which the mantle was originally fabricated
and functions to soften and partially dissolve the
mantle. For example, if methylmethachrylate cement is
used for both the mantle and the fluid mass, such
dissolution and softening will occur. As the fluid
cement is injected into the cavity 74, air is vented
through the vent hole 42. Upon filling of the cavity,
continued injection of cement functions to apply upward
pressure to the snout 52 and 'the snout is slowly
withdrawn, thus forming a void-free mass of cement
within the cavity.
Fig. 8 shows the step of inserting the pulling
appliance 48 into the cement mass 76 while the mass is
still in a fluid state. This is achieved by screwing
the threads of the instrument through the passage 40
and into the mass to the point where the distal end 54
engages the bottom of the cavity 74. The point of such
engagement may be determined both by feel and by the
previous measurement transposed to the pulling
appliance from the depth gauge 46. The screwing of the
appliance 48 into the fluid mass of cement is carried
out in a relatively slow controlled fashion so as to
avoid the creation of voids within the mass. This
poses no particular problem, since it takes
approximately ten minutes for the mass to cure to a
hardened state.
Fig. 9 shows the mass of cement 66 after it has
cured to a hardened integral state with the mantle 66
and bonded to the pulling appliance 48. As there
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shown, the slap-hammer is threadably secured to the
proximal end of the appliance.
Fig. 10 shows the final step wherein the slap
hammer 22 is used to apply impact tension to the
pulling instrument, thus pulling the instrument and the
mantle bonded thereto from the femur, as a unit. This
step leaves the original bone cavity, designated 78,
within the femur in a clean state. Thereafter, a new
prosthetic joint may be cemented into the bone cavity.
Conclusion
While a preferred embodiment of the invention has
been illustrated and described, it should be understood
that the invention is not limited to this embodiment.
For example, it is anticipated that the invention may
find use in the removal of a cement mantle in other
than a joint replacement application and that it may be
used in replacing joints other than hip joints.
