| United States Patent |
4,222,382
|
|
Antonsson
, et al.
|
September 16, 1980
|
Femoral component hip joint prosthesis extractor
Abstract
Extractor for removal of a femoral component of a total or partial hip
joint reconstruction, in which an impact shock is applied directly through
hardware to the extractor which is so shaped that converging jaws secure
the neck of a prosthesis therein and the withdrawal shock is applied
parallel to the stem of the prosthesis.
| Inventors:
|
Antonsson; Erik K. (Vestal, NY);
Flowers; Woodie C. (Auburndale, MA)
|
| Assignee:
|
Massachusetts Institute of Technology (Cambridge, MA)
|
| Appl. No.:
|
006699 |
| Filed:
|
January 26, 1979 |
| Current U.S. Class: |
606/100 |
| Intern'l Class: |
A61B 017/00; A61B 017/18 |
| Field of Search: |
128/303 R,92 EC,92 E,83,92 C,92 CA
3/1.913,1.91
|
References Cited [Referenced By]
U.S. Patent Documents
Other References
Vitallium Surgical Appliances Catalog by Howmet Corp., New York, N. Y.,
1964, p. 76, McReynolds Driver-Extractor Instrument, No. 6869.
|
Primary Examiner: Frinks; Ronald L.
Attorney, Agent or Firm: Smith, Jr.; Arthur A., Shaw; Robert
Claims
What is claimed is:
1. A prosthesis extractor comprising a base portion and a pair of spaced
jaws, the jaws converging toward each other from a widely-spaced region to
closely-spaced region to form an aperture sufficiently large to receive
the head of a prosthesis and tapering so as to grasp the neck of the
prosthesis securely therein, said jaw, being angled with respect to said
base portion to permit the alignment of the stem of the prosthesis with
the direction of applied force on the extractor.
2. Apparatus as claimed in claim 1 that includes an impact device connected
to the prosthesis extractor, said impact device comprising an elongate
portion and an anvil portion to receive impact to dislodge said
prosthesis.
3. Apparatus as claimed in claim 2 wherein the prosthesis extractor is
provided with means to attach the impact device thereto, said means to
attach being secured to the base portion by a joint that permits relative
rotation or pivoting therebetween.
4. Apparatus as claimed in claim 1 wherein the angle between the jaws and
said base portion is in the range from about 30.degree. to 60.degree..
5. Apparatus as claimed in claim 1 wherein the jaws converge at an angle in
the range from about 10.degree. to about 30.degree..
6. Apparatus as claimed in claim 1 wherein said aperture has rounded edges
and terminates in a curved end having a small radius.
7. Apparatus as claimed in claim 1 in which the outside of the jaws which
form the aperture converge in a radius that is small enough not to
interfere with access to the prosthesis head, in vivo.
8. Apparatus as claimed in claim 1 wherein the jaws and the region of
convergence are sufficiently thin that neither interferes with the
extraction.
9. Apparatus as claimed in claim 1 wherein the base portion has an
appropriately threaded portion to attach to an impact device.
10. Apparatus as claimed in claim 1 which is formed of material allowing
sterilization thereof and is sufficiently strong to withstand substantial
impact loads.
11. For removing the femoral component of a hip-joint prosthesis having a
head, a shoulder, with a neck therebetween and a stem, which stem is
elongate and shaped to the conform to the proximal medullary cavity of the
femur within which the prosthesis is implanted, a prosthesis extract
comprising a base portion and a pair of spaced jaws, the jaws converging
toward each other from a widely spaced region to a closely spaced region
to form an opening sufficiently large to receive the head of the
prosthesis and tapering so as to grasp the neck of the prosthesis therein,
said jaws being angled with respect to said base portion to permit
substantial alignment of the jaws with the stem of the prosthesis.
Description
The present invention relates to the surgical procedures involved in the
removal of a femoral component of a total or partial hip joint
reconstruction and, in particular, to extractors for the removal of a
prosthesis which has been cemented with polymethylmethacrylate or the like
into the proximal medullary cavity of the femur.
Current methods used to remove femoral components include that of grasping
the neck of the prosthesis with pliers or a similar instrument and
striking the side of the instrument with a hammer. Such primitive methods
require the surgeon's hands as part of the system and are ineffective in
that the hands absorb a high shock load of the impact of the hammer, and
so transmit a very small part of the shock to the implanted prosthesis.
Removal of an implant in polymethylmethacrylate requires a shock load to
shear the cement at the interface between the implant prosthesis and the
cement. Since the surgeons hands absorb much of the shock, less is
transmitted to the cement, and removal is difficult. This also causes pain
in the surgeon's hands.
It is the object of the invention to provide an effective mechanism for
removal of a prosthesis previously implanted. Another object is to provide
an effective mechanism such that the extraction requires a minimum of
effort, can be performed quickly and is not painful to the operator.
These and still further objects are addressed hereinafter.
The foregoing objects are achieved, generally, in a prosthesis extractor
for removing the femoral component of a hip-joint prosthesis having a
head, a shoulder, with a neck therebetween, and a stem, which stem is
elongate and shaped to the conform to the proximal medullary cavity of the
femur within which the prosthesis is implanted; the prosthesis extractor
has a base portion and a pair of spaced jaws, the jaws converging toward
each other from a widely spaced region to a closely spaced region to form
an opening sufficiently large to receive the head of the prosthesis and
tapering so as to grasp the neck of the prosthesis therein, said jaws
being angled with respect to said base portion to permit substantial
alignment of forces applied by the extractor with the stem of the
prosthesis. The prosthesis extractor, in an operative system, has attached
to it an impact device which, typically, consists of a hammer or weight
slidably disposed upon a shaft which has a stop at the end thereof to
receive impact forces from the hammer. The shaft is attached to the
extractor by a pivot joint that permits compensation for small amounts of
misalignment between the shaft and the stem of the prosthesis--for forces
to be proper, the two should be in alignment.
The invention is hereinafter described with reference to the accompanying
drawing in which:
FIG. 1 is an isometric view of an assembly that includes a prosthesis
extractor of the present invention in an assembly with other elements that
interact therewith and a prosthesis;
FIGS. 2 and 3 are respectively a top isometric view and a side isometric
view of a prosthesis extractor, like the prosthesis extractor in FIG. 1;
FIG. 4 is an elevation view of an assembly like the assembly of FIG. 1 and
a prosthesis; and
FIG. 5 is an isometric view showing the prosthesis extractor shown in FIGS.
2 and 3 and a prosthesis.
Turning now to FIG. 1 there is shown at 101 an assembly or system for
removing the femoral component labeled 100 of a total or partial hip
reconstruction. The typical prosthesis 100 is cemented in a cavity in the
femur, as is well known, and the function of the system 101 is to remove
that prosthesis should trouble arise from the installation. To break the
cement bond, it is necessary that a substantial outward impact shock be
applied to the prosthesis and that shock, to be effective, it has been
found for present purposes, must be one that is substantially aligned with
the stem of the prosthesis.
The system 101 includes a prosthesis extractor 1 which, as best shown in
FIGS. 2 and 5 has a base portion 9 and a pair of spaced jaws 10 and 11
that converge toward each other from a widely-spaced region 12 to a
closely-spaced region 13 to form an aperture 14 sufficiently large to
receive the head labeled 99 of the prosthesis 100 in FIG. 5 and tapering,
as shown, to grasp the neck shown at 98 of the prosthesis securely
therein, the jaws 10 and 11 being angled (at an angle .theta. in FIG. 4)
to the base portion to permit alignment of the stem designated 97 of the
prosthesis with the elements of an impact device to apply the outward
impact force properly.
The impact forces are applied by moving a sliding weight 2 that moves along
a shaft or elongate portion 4 of the impact device up and down in FIG. 1
in the direction of the arrow marked A. Impact is thus effected between
the sliding weight 2 and an end stop or anvil portion 3 of the impact
device secured to the top of the shaft 4. The shaft 4 is attached to the
extractor 1 by a pivotable joint 16 (see the pin labeled 15 in FIG. 1
which permits pivoting of the joint 16) that permits, upon impact,
adjustment of alignment between the shaft 4 and the stem 97 to compensate
for small misalignment therebetween to assure that the impact forces
applied to the prosthesis 100 are properly directed. It has been found by
the inventors that the angle .theta. is in the range from about 30.degree.
to 60.degree.; in the actual extractor shown in FIGS. 2-5, the angle
.theta. is 45.degree.. The jaws 10 and 11 converge in the actual device at
an angle of 25.degree., but a range from about 10.degree. to about
30.degree. is acceptable. The closely-spaced region 13 terminates in a
curved end 17A in FIG. 5 having a small (0.2 inch) inner radius. The
outside of the jaws or legs 10 and 11 converge in a radius that is small
enough not to interfere with access to the prosthesis head 99, in vivo. In
this same matter, the legs and the region of convergence thereof (i.e.,
the curved portion 18 between 17A and 17B in FIG. 5) must be sufficiently
thin enough (.about.3/8 inch) that neither interferes with extraction. The
joint 16 is threaded to accept a threaded shaft 4. The extractor 1 is
formed of stainless steel or some other material which can be sterilized
and which can withstand the large impact forces.
Removal procedure is depicted in FIG. 4 which shows two hands of an
operator who secures the neck of the prosthesis in the tapered portion of
the device and applies the necessary movement of the hammer or weight 2.
The prosthesis extractor 1 eliminates many of the problems of the
previously used mechanisms for removing the femoral component of a
hip-joint prosthesis and provides a relatively simple system, yet one that
applies the necessary shock forces to dislodge such prosthesis. It is a
relatively uncomplicated design, offers easy manipulation, sterlization,
and so forth, and is adapted for use with existing impact-providing
devices.
Further modifications of the invention herein disclosed will occur to
persons skilled in the art and all such modifications are deemed to be
within the spirit and scope of the invention as defined by the appended
claims.
* * * * *