U.S. patent application number 09/829427 was filed with the patent office on 2001-12-13 for modular hip implant with shock absorption system.
Invention is credited to Goli, Anil Kumar, Subba Rao, Goli Venkata.
Application Number | 20010051831 09/829427 |
Document ID | / |
Family ID | 26832521 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010051831 |
Kind Code |
A1 |
Subba Rao, Goli Venkata ; et
al. |
December 13, 2001 |
Modular hip implant with shock absorption system
Abstract
A modular hip implant that can be custom fit to an individual
patient, including a shock absorption system that absorbs
compressive stresses that are imparted to the implant. The size of
the femoral ball member, size of the femoral stem, femoral neck
length, and tension in the shock absorption system are all
individually adjustable parameters, depending on the particular
patient. A unique coupling member houses a modular spring mechanism
that serves as the shock absorber. The coupling member is received
into the ball member to an adjustable depth, the adjustment of
which varies the length of the femoral neck. The length of the
femoral neck can be adjusted during surgery without requiring
additional parts.
Inventors: |
Subba Rao, Goli Venkata;
(Terre Haute, IN) ; Goli, Anil Kumar; (Terre
Haute, IN) |
Correspondence
Address: |
Dr. G.V. Subba Rao, M.D., F.R.C.S
Midwest Orthopedic Clinic
153 E. Halt Drive
Terre Haute
IN
47802
US
|
Family ID: |
26832521 |
Appl. No.: |
09/829427 |
Filed: |
April 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09829427 |
Apr 9, 2001 |
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09474282 |
Dec 29, 1999 |
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09474282 |
Dec 29, 1999 |
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09134632 |
Aug 14, 1998 |
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Current U.S.
Class: |
623/22.42 ;
623/23.44 |
Current CPC
Class: |
A61F 2002/30774
20130101; A61F 2002/30566 20130101; A61F 2/3609 20130101; A61F
2310/00023 20130101; A61F 2310/00179 20130101; A61F 2/4607
20130101; A61F 2002/30604 20130101; A61F 2002/30433 20130101; A61F
2002/30805 20130101; A61F 2002/30507 20130101; A61F 2250/0064
20130101; A61F 2230/0023 20130101; A61F 2/3662 20130101; A61F
2250/0012 20130101; A61F 2220/0025 20130101; A61F 2002/30329
20130101; A61F 2002/3625 20130101; A61F 2002/30886 20130101; A61F
2002/30235 20130101; A61F 2220/0058 20130101; A61F 2002/365
20130101; A61F 2220/0041 20130101; A61F 2/36 20130101; A61F
2002/30154 20130101; A61F 2/30744 20130101; A61F 2002/30795
20130101; A61F 2002/368 20130101; A61F 2002/30563 20130101; A61F
2002/30474 20130101; A61F 2002/3055 20130101; A61F 2002/30372
20130101; A61F 2/30767 20130101; A61F 2220/0033 20130101; A61F
2002/30014 20130101; A61F 2002/30616 20130101; A61F 2/367 20130101;
A61F 2/30942 20130101; A61F 2002/30546 20130101; A61F 2002/30354
20130101; A61F 2002/30451 20130101; A61F 2310/00017 20130101; A61F
2002/30797 20130101; A61F 2230/0069 20130101; A61F 2310/00029
20130101; A61F 2002/3611 20130101; A61F 2002/3631 20130101; A61F
2002/30948 20130101; A61F 2002/30405 20130101; A61F 2002/4631
20130101; A61F 2002/4619 20130101; A61F 2002/30156 20130101; A61F
2230/0021 20130101; A61F 2250/0018 20130101 |
Class at
Publication: |
623/22.42 ;
623/23.44 |
International
Class: |
A61F 002/32; A61F
002/30 |
Claims
What is claimed is:
1. A modular hip prosthesis, comprising a ball member having an
outer surface adapted to cooperate with an acetabular socket and
further comprising a threaded bore to fit into a coupling member. A
femoral stem having a shank adapted to be inserted and secured into
a medullary cavity of a femur bone, said femoral stem having a neck
at the proximal end comprising a threaded bore thereof, said neck
connected to a coupling member via a spring mechanism attached to
the said bore in the neck. A spring mechanism disposed intermediate
said coupling member and said neck member, said spring mechanism
providing cushioning movement and shock absorption between said
acetabular socket and said ball member via the coupling member.
Said spring mechanism detachably connected to said neck member and
to the coupling member, thereof said coupling member detachably
connected to the ball member.
2. The modular hip prosthesis of claim 1, further comprising: a
coupling member housing said spring mechanism, the connection of
said ball member to said spring mechanism being through said
coupling member, said coupling member received in said threaded
bore of the ball member to an adjustable depth, adjustment of said
depth causing corresponding adjustment of the distance said neck
extends from said ball member.
3. The modular hip prosthesis of claim 2, wherein said threaded
bore in the ball member and the coupling member comprise
corresponding threads, said coupling member being threadingly
received in said threaded bore.
4. The modular hip prosthesis of claim 2, wherein said spring
mechanism includes a first connector at a first end thereof
connecting said neck member to said spring mechanism. The first
connector threadingly connected to said neck member.
5. The modular hip prosthesis of claim 4, wherein said spring
mechanism includes a second connector at a second end thereof
connecting said spring mechanism to said coupling member.
6. The modular hip prosthesis of claim 3, wherein said coupling
member and said bore in the ball member include corresponding
threads, said coupling member threadingly received into said bore
to an adjustable depth, adjustment of said depth causing
corresponding adjustment of the distance said neck extends from
said ball member.
7. The modular hip prosthesis of claim 6, wherein said coupling
member comprises a substantially hollow insert having a
substantially smooth inner-surface, said neck member slidingly
engages said inner smooth surface during said cushion movement and
shock absorption to prevent stress and strain in the hip joint and
in the prosthesis.
8. The modular hip prosthesis of claim 5, wherein said spring
mechanism is threadingly connected to said coupling member wherein
both components are detachable and attachable by the surgeon should
it become necessary during a surgical procedure.
9. The modular hip prosthesis of claim 8, wherein said spring
mechanism is threadingly connected to to said neck member wherein
both components are detachable and attachable by the surgeon should
it become necessary during a surgical procedure.
10. A method of custom-fitting the modular hip prosthesis
comprising the following steps: Selecting a femoral component with
a threaded opening formed in the femoral neck member. Attaching the
neck of the femoral component to a coupling member by means of a
spring mechanism, which is detachabale if desired by the surgeon
during a surgical procedure for any modifications necessary.
Selecting a ball member comprising a threaded bore and afixing the
ball member over the coupling member by using threaded means by
screwing method by the surgeons hands, to a determined depth to
adjust neck length. Both components are detachable and attachable
by the surgeon during a surgical procedure for any modifications,
should it become necessary.
11. The modular hip prosthesis of claim 10, further comprising
installing a versatile spring mechanism to allow a coupling member
attached to the ball member to slide over the neck member.
12. The modular hip prosthesis of claim 11, further comprising
selecting the spring mechanism having spring elements of different
stiffnesses, lengths, removable and reattachable to custom fit a
prosthesis between a coupling member and a neck member.
13. The modular hip prosthesis of claim 1, wherein the ball member,
the coupling member, the femoral stem and the neck, the spring
mechanism are fabricated from selected materials from titanium
alloys, vitallium, stainless steel, nylon, plastic, ceramic or
other suitable combination thereof, suitable for human
implantation.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates in general to an orthopaedic
hip implant, and in particular to `Modular Hip Prosthesis` that can
be custom fit a patient. The present invention also relates to an
implant having a versatile spring mechanism, a coupling member, and
a ball member, which are attachable and detachable by the surgeon
before the surgical procedure, during the surgical procedure, or
during a postoperative revision surgery should it become
necessary.
[0002] Prosthetic implants for the replacement of a portion of a
patient's hip joint are well known, and are typically available as
a two to three component systems. The femoral stem component
includes a shank at its distal end which extends into the canal of
the femur bone and is fixed therein using bone cement or other
means known in the art. At the proximal end of the femoral stem is
a neck which typically terminates in a spherical ball that is
adapted to cooperate with the patient's acetabulum or a prosthetic
acetabular cup fixed into the patient's acetabulum. The ball, neck
and femoral stem are typically formed in one piece from suitable
material. The acetabular cup is typically formed as metal cup or
bowl and optionally, can be provided with a plastic insert that is
fixed therein to enhance the sliding engagement between the ball
and the acetabular cup.
[0003] Conventional one-piece femoral component designs are
available in different sizes, but they do not allow enough
flexibility for variations in individual parameters of the
patient's anatomy. Parameters such as femoral neck length, femoral
shank length and diameter, and femoral head size can vary
independently of one another. For example, the length of the
femoral neck can vary independently of the size of the femoral head
or length of the medullary canal. It can thus be difficult to find
a suitably fitting implant when selecting the implant from the
different sizes available as one-piece femoral components.
[0004] To address this problem, modular implant systems are known.
For example: U.S. Pat. No. 4,938,773 to Strand discloses a femoral
stem which can be fitted with interchangeable, different size
femoral neck portions. Such a system is undesirably limited by the
availability of different size components. Further, a large
quantity of different size components must be produced and stocked
to ensure that all patients can be fitted.
[0005] Similarly, U.S. Pat. No. 5,507,830 to Demane et al discloses
a modular hip prosthesis, which includes a plurality of different
size tubular sleeves that can be attached to cylindrically shaped
stem of the femoral component, thereby allowing the surgeon to
extend the femoral stem length as necessary. Also disclosed are
interchageable frustroconically shaped extension sleeves for the
extension of the neck length of the prosthesis. Removable pads are
provided for attachment to the mid-section of the prosthesis for
cross-sectional configuration thereof. Again such a system is
limited by the availability of the implant kit and various tools.
Demane et al, did not disclose a spring or cushion mechanism,
Demane et al, did not disclose a coupling member and the threaded
method of neck length adjustment using the ball member and the
coupling member.
[0006] Lawes et al, U.S. Pat. No. 5,258,033 discloses a hip implant
consisting of a femoral component that has an outer surface shaped
to conform to an acetabular socket and has an internal bore adapted
to receive a femoral head. The head of the femoral bone has been
shaped and dimentioned to provide a spigot to enter the bore and be
locked in place by a cement mantle between the bone and the walls
of the bore. A spacer is included which creates a void to allow the
components to move further over the spigot and relock should the
cement creep or because of any movement in the bone after assembly.
The spacer is included for preventing cement from reaching the
bottom of the bore. Lawes et al, U.S. Pat. No. 5,258,033 do not
allow enough flexibility for variations in the femoral neck lengths
for variations in individual patients hip anatomy. Lawes et al also
do not disclose a spring or cushion mechanism to prevent shock or
stress at the hip joint or to the prosthesis to prevent related
complications.
[0007] Amino et al U.S. Pat. No. 5,362,311 discloses a method of
custom-fitting modular hip prosthesis in which a tapered hole of a
ceramic stem head to be fixed, a truncated conical sleeve having a
thickness of 50 .mu.m to 5.0 mm is compressedly held between a wall
surface of the tapered hole and an outer circumferential surface of
the tapered cone such that they are taperedly engage with each
other, whereby the length of the stem neck can be optionally
changed. Again such a system is undesirably limited by having
different truncated conical sleeves of different thicknesses. Also
Amino et al do not disclose a spring or cushion mechanism to absorb
shock or a versatile neck length adjustment method.
[0008] U.S. Pat. No. 5,389,107 to Nassar et al discloses a hip
prosthetic implant, having an elongate element that extends
coaxially from the ball section of the femur component. The
elongate element slidably extends into a chamber formed by a
tubular insert that is secured in the femur. Contained at the
bottom of the chamber is a spring against which the elongate
element abuts, thereby providing shock absorption. A pin member
extends from the bottom of the chamber and slidably fits into a
bore formed in the elongate element. A second spring is disposed
between the pin and the bottom of the bore to provide further shock
absorption. U.S. Pat. No. 5,389,107, the invention is limited in
scope for the surgeon and the patient, did not disclose adjustable
neck length of the prosthesis, did not disclose versatile
attachable or detachable head or a spring mechanism, attachable or
detachable coupling member.
[0009] SU 171883-A1, discloses a modular hip implant that includes
a spiral spring that has its ends rigidly mounted to the bottom of
the recess of the head and is rigidly attached to the smooth end
face of the neck. The threaded end of the neck is screwed into the
threaded canal of the base and fixed. The base has a threaded canal
under the neck, a lock nut in the form of a threaded washer with a
hexahedral opening. The possibility of correcting the neck length
is achieved by using special keys and lock nut. The invention
discloses a plastic stopper, a special syringe, a biologically
inert plastic paste or bone cement. The invention is limited in
scope, particularly the prosthetic head can not be separated from
from the neck, since the spring member is rigidly afixed and bonded
between these two components. The invention is not versatile in
case of need, for spare parts removable and replacement during
primary or revision surgery for head or spring or neck members.
Bone and tough scar tissue may grow into the plastic stoper, into
the lock nut, into the base channel and into the hexagonal opening
of the neck member, and may cause considerable difficulty during
revision surgery for the removal of head and neck members using the
special keys. Spare parts replacement can not be done and the whole
modular prosthesis needs to be removed in such a situation and the
surgery can become difficult, this may lead to increased morbidity
to the patients. Also special keys with handle and lock nut are
required for neck length adjustment, using the threaded aperture in
the base, which maneuver can be fiddling and trouble-some in the
blood stained, deep , wet operative field.
[0010] Another problem with artificial hip prosthesis is that
countless compressive stresses are transmitted thereto from daily
activities such as walking, running, exercising, sitting and
standing. These compressive stresses can often result in the
loosening of the prosthesis, acetabular erosion, protrusion of the
prosthetic head into the acetabulum or pelvic bone, dislocation of
the prosthetic head from the socket or cup, chronic pain and
suffering of the patient.
[0011] What is needed is an improved modular hip prosthesis that
provide neck length adjustments, spring mechanism for cushion
effect and shock absorption to prevent complications. Also what is
needed is modular prosthesis whose parts can be easily adjusted or
replaced with surgeons hands or with simple tools. Also cut down
the costs to medicare or to the patients with less inventory of
instruments, less operating time, and a versatile prosthesis
modular in nature with adjustable, removable and also replaceble
parts by the surgeon hands.
SUMMARY OF THE INVENTION
[0012] The present invention provides a modular hip implant that
can be custom fit to an individual patient and that includes a
shock absorption system that absorbs compressive stresses that are
imparted to the implant.
[0013] In one form thereof, the present invention provides a
modular hip prosthesis. The hip prosthesis comprises a ball member
having an outer surface adapted to cooperate with an acetabular
socket and a femoral stem having a shank adapted to be inserted and
secured into a medullary cavity of a femur. The femoral stem has a
neck at a proximal end thereof which is connected to the ball
member. A spring mechanism is disposed intermediate the ball member
and the neck, and provides cushioning movement between the femoral
stem and the ball member. The spring mechanism is detachably
connected to the neck and detachably connected to the ball
member.
[0014] In a preferred form, the modular hip prosthesis further
comprises a bore disposed in the ball member. A coupling member
houses the spring mechanism, and the connection of the ball member
to the spring mechanism is through the coupling member. The
coupling member is received in the bore to an adjustable depth,
adjustment of which causes corresponding adjustment of the distance
the neck extends from the ball member. More preferably, the bore
and the coupling member comprise corresponding threads, the
coupling member being threadingly received in the bore. Still more
preferably, the spring mechanism includes a first connector at a
first end thereof connecting the neck to the spring mechanism. The
first connector and the neck include complementary threads, such
that the first connector is threadingly connected to the neck. The
spring mechanism includes a second connector at a second end
thereof connecting the spring mechanism to the coupling member.
[0015] In another form thereof, the present invention provides a
method of custom fitting a hip prosthesis to an individual patient.
In this method, a ball member is selected from a plurality of
different size ball members, depending upon the size of the
acetabular socket into which the ball member is to be inserted. A
femoral component is selected from a plurality of different size
femoral components, and the neck of the selected femoral component
is attached to a coupling member. A depth that the coupling member
is to be inserted into the selected ball member is determined. Such
depth corresponds to an individual patient. The coupling member is
installed into the ball member to the determined depth.
[0016] In a preferred form of the inventive method, a spring
mechanism is installed in the prosthesis to allow cushioning
movement of the neck of the selected femoral component relative to
the ball member. More preferably, the spring mechanism is selected
from a plurality of spring mechanisms having spring elements of
different spring constants or stiffnesses. The spring stiffness can
be calibrated to the weight of the patient. Further, the length of
the neck can be adjusted intraoperatively to compensate for errors
in neck length obtained from preoperative imaging techniques.
[0017] One advantage of the present invention is that the spring
mechanism absorbs much of the compressive stresses imparted to the
implant during daily activities such as walking, running and
exercising. Because the spring mechanism contracts and expands to
absorb load bearing, shock and compressive stresses imparted to the
hip joint during weight bearing and mobilization, the implant is
less likely to loosen, and the useful life of the implant is
therefore lengthened. The spring mechanism also reduces other
complications, such as dislocation of the femoral stem from the
acetabulum, acetabular damage and erosion, and protrusion of the
femoral ball member into the acetabulum and pelvis during a sudden
jarring event, such as a fall.
[0018] Another advantage of the present invention is that the
spring mechanism is a modular component such that a spring element
having a specific stiffness can be selected.
[0019] Another advantage of the present invention is that the
length of the femoral neck can be changed without adding or
interchanging parts, unlike the above-described prior art implants
which require a plurality of interchangeable parts. Instead, the
present invention employs a single coupling member that can be
installed in the ball member to a depth which corresponds to the
desired length of the femoral neck.
[0020] Yet another advantage of the present invention is that the
length of the femoral neck can be adjusted intraoperatively. While
pre-operative imaging techniques can be used to determine the
appropriate length of the femoral neck, such techniques are often
only an approximation of actual surgical conditions. With the
present invention. adjustments to the length of the femoral neck
can be made during surgery by adjusting the depth to which the
coupling member is inserted into the ball member so that an exact
preoperative neck length need not be entirely relied upon.
BRIEF DESCRIPTION OF DRAWINGS
[0021] The above-mentioned and other features and advantages of
this invention, and the manner of attaining them, will become more
apparent and the invention will be better understood by reference
to the following description of embodiments of the invention taken
in conjunction with the accompanying drawings, wherein:
[0022] FIG. 1 is an exploded side sectional view of a modular hip
implant incorporating the present invention;
[0023] FIG. 2 is side sectional view of the modular hip implant of
FIG. 1;
[0024] FIG. 3A is a fragmentary sectional view illustrating the
femoral neck of a femoral stem component;
[0025] FIG. 3B is a sectional view illustrating a spring mechanism
incorporating the present invention;
[0026] FIG. 3C is a sectional view illustrating a coupling member
incorporating the present invention;
[0027] FIG. 3D is a sectional view illustrating a ball member
incorporating the present invention;
[0028] FIG. 4A is a sectional view illustrating the femoral neck
extending from the ball member a first distance;
[0029] FIG. 4B is a sectional view illustrating the femoral neck of
FIG. 4A extending from the ball member a second distance less than
the first distance; and
[0030] FIGS. 5A-5E are sectional views illustrating alternate
embodiments of the spring mechanism in accordance with the present
invention.
[0031] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplification set forth
herein illustrates preferred embodiments of the invention, in
several forms, and such exemplifications are not to be construed as
limiting the scope of the invention in any manner.
DETAILED DESCRIPTION
[0032] FIGS. 1 and 2 show a modular hip implant 20 including a
femoral ball member 22 having an outer surface 24 adapted to
cooperate with an acetabular socket (not shown) or a prosthetic
acetabular cup (not shown) as is known in the art. Coupling member
26 forms a tubular threaded insert which is threadingly received in
threaded bore 28 of ball member 22. A spring mechanism 30 includes
a spring element 32, shown in FIGS. 1 and 2 as a coiled spring
having connectors 34 and 36 at opposite ends thereof. Connector 34
is received in a threaded opening 38 formed in femoral neck 40 of
femoral stem 42. Connector 36 abuts against cap 44 of coupling
member 26 and is secured thereto by means of a screw 46 received
through threaded aperture 48 in cap 44 and threaded aperture 50
formed in connector 36.
[0033] Femoral stem 42 includes a shank 52 adapted to be inserted
into a medullary cavity 54 (FIG. 2) of a patient by means of bone
cement or other fixation means known in the art. Femoral stem 42
includes a circular hole 56 adapted for a medical instrument to be
hooked thereto to remove the prosthesis should such become
necessary during a surgical procedure. Triangular shaped
fenestration 58 is provided to allow bone and scar tissue to grow
therein and thereby prevent loosening or rotation of femoral stem
42. More than one fenestration can be provided, as is known in the
art. Square shaped notch 60 is provided to accommodate an impactor
or other suitable surgical instrument for implanting shank 52 into
cavity 54. Femoral stem 42 includes a flange 62 that abuts femur
bone portion 64 (FIG. 2) and prevents shank 52 from migrating
downward into cavity 54 of femur 55.
[0034] With reference to FIGS. 1-4, spring mechanism 30 includes a
threaded connector 34, shown in FIGS. 4A and 4B as a threaded plug
fixed to an end of spring element 32. The end of spring element 32
can be welded to or embedded within plug connector 34. The other
end of spring element 32 can also be welded to or embedded within
disk-shaped connector 36. Connector 34 is threadingly received into
threaded opening 38 and, at the other end of spring mechanism 30,
disk-shaped connector 36 is secured to cap 44 by means of screw
46.
[0035] It can be appreciated that the connection of neck 40 to
coupling member 26 and thus to ball member 22 is through spring
mechanism 30, which is disposed intermediate ball member 22 and
neck 40. Similarly, the connection of spring mechanism 30 to ball
member 22 is through coupling member 26. It can be also be
appreciated that spring mechanism 30 is removable from coupling
member 26 and thus from modular hip implant 20. Thus, hip implant
20 provides the flexibility of accepting a spring mechanism having
different spring constants, or stiffnesses, if desired. Such may be
desirable depending on the age, weight and activity level of the
patient.
[0036] The spring mechanism is designed to absorb shock and
vibrations produced by daily activities such as walking, running,
exercising, and even simple load-bearing activities such as sitting
and standing. Because the spring mechanism absorbs some of the
shock and vibrations imparted to the implant, it is less likely
that such shock and compressive stresses will cause the implant to
loosen or fracture over a period of time. Further, because the
stiffness of the spring can be pre-selected, its cushioning effect
can be adjusted for an individual patient. For example, a spring
element 32 that is too stiff will frustrate the load-sharing
purpose of the implant. On the other hand, if the spring element is
not stiff enough, the implant will experience too much movement.
With the present invention, the stiffness of the spring can be
selected to provide the appropriate cushioning effect.
[0037] As shown in FIG. 1, coupling member 26 is formed as a
substantially hollow, tubular insert having an open distal end to
receive neck 40. Neck 40 has an outer surface 66 that corresponds
to a substantially smooth inner surface 68 of coupling member 26
such that neck 40 slidably engages coupling member 22. Various
low-friction, bio-compatible coatings can be applied to the two
surfaces 66, 68. Preferably, the two mating surfaces are
cylindrical, although other complementary shapes are contemplated.
At least half and preferably two-thirds of neck 40 should be housed
within coupling member 26 to adequately secure neck 40 to coupling
member 26. The spring mechanism and the sliding engagement between
surfaces 66 and 68 combine to provide a cushioning movement between
neck 40 and ball member 22.
[0038] With reference to FIGS. 4A and 4B, one of the features of
modular hip implant 20 is that the extent to which neck 40 extends
from ball member 22 is an adjustable parameter, depending on
characteristics of the individual patient. That is, coupling member
22, to which neck 40 of stem 42 is removably attached, can be
screwed into bore 28 to a depth that corresponds to the desired
extension distance of neck 40 from ball member 22. Thus, the
present invention avoids the necessity of interchangeable sleeves
of different sizes to produce different length necks. Instead, a
continuous range of neck lengths are made possible with a single
coupling member 26. For example, the configuration shown in FIG. 4A
can accommodate a patient needing a larger femoral neck length
whereas the configuration in FIG. 4B may accommodate a person
needing a shorter femoral neck length. Further, it is possible with
the present invention to adjust the femoral neck length at the time
of surgery, which might be desirable, for example, when
preoperative data used to establish femoral neck length are
inaccurate.
[0039] Alternate embodiments of the spring mechanisms are possible.
For example, as shown in FIG. 5A, spring mechanism 130 can include
spring element 132 having threaded connectors 134 and 136 at
opposite ends thereof. Coupling member 126 has a portion of its
interior formed with a thread 144 which threadingly engages threads
146 formed on connector 136. This arrangement provides an
additional means to adjust the length that neck 140 extends from
the ball member because the relative position of connector 136 can
be varied by the extent to which it is screwed into coupling member
126.
[0040] As shown in FIG. 5B, neck 240 can be formed with a threaded
fastener 238 which screws into a threaded aperture 248 formed in
connector 236. Spring element 232 is fixed to connector 236 at one
end and is fixed to cap 244 of coupling member 226 at its other
end.
[0041] As shown in FIG. 5C, neck 340 can be formed with a threaded
fastener 338 which screws into a threaded aperture 348 disposed in
connector 336. Spring element 332 can be formed of a compressible
and elastic material such as silicone, closed gel foam, rubber or
the like. Sufficient elastic material is placed in the cavity 380
such that connector 336 is biased against stop 382 which can be
formed as an annular ridge or as a crimped portion on the inside of
coupling member 326 as shown.
[0042] FIG. 5D illustrates an embodiment similar to the embodiment
described with reference to FIGS. 1-4, except that cap 444 of
coupling member is formed with an internally threaded bore 448 that
receives threaded fastener 446 extending from connector 436. On the
other end of spring element 432 is attached a threaded connector
434 that screws into bore 438 formed in neck 440.
[0043] FIG. 5E illustrates an embodiment wherein spring mechanism
530 is fixed within coupling member 526. An end of spring element
532 is fixed to cap 544 of coupling member 526. As with other
embodiments described above, threaded connector 534 is received in
bore 538 formed in neck 540.
[0044] FIG. 5F illustrates an embodiment wherein spring mechanism
630 includes a piston-cylinder spring element 632 connected at one
end to connector 634 and connected at its other end to connector
636. Spring mechanism 630 is detachably connected to coupling
member 626 by means of screw 646 that passes through aperture 648
and is threadingly received in threaded opening 650. Connector 634
is received in threaded bore 638 formed in neck 640.
[0045] The advantages of the modular features of the present
invention can be better understood with reference to a description
of custom fitting a modular hip implant to an individual patient.
Ball member 22 can be selecting from a plurality of different size
ball members, depending upon the size of the acetabular socket into
which the ball member is to be inserted. The acetabular socket can
be the patient's acetabulum or a prosthetic acetabular cup that is
fixed into the patient's pelvic bone. The femoral stem component 42
is selected from a plurality of different size femoral stems. The
femoral stems may vary, among other parameters, by length and/or
diameter of the femoral shank, angle of femoral neck with respect
to the femoral shank, and length and/or diameter of femoral
neck.
[0046] A spring mechanism 30 is selected for the individual patient
and installed into the coupling member 26. The stiffness of spring
element 32 can be chosen based upon various patient factors, such
as weight and activity level. With reference to FIG. 1, connector
36 is placed against cap 44 such that apertures 48 and 50 are
aligned. Screw 46 is then threadingly advanced through the
apertures, thereby securing spring mechanism 30 to coupling member
26. Femoral stem 42 is connected to spring mechanism 30 and thus
coupling member 26 by aligning connector 34 with bore 38 and
turning coupling member 26 such that connector 34 is screwed into
bore 38.
[0047] After coupling member 26 is secured to stem 42 as just
described, coupling member 26 is inserted into bore 28 of the
selected ball member to a specific depth. Based upon patient data
such as computer assisted tomography images (CAT scans). magnetic
resonance imaging (MRI) and the like, the appropriate length of the
patient's femoral neck can be determined preoperatively and then
correlated to determine the corresponding depth to which coupling
member 26 should be inserted into ball member 22. Advantageously,
if the length of the neck as determined preoperatively does not
exactly match the actual length needed as determined during
surgery, the length of the neck can be adjusted during surgery by
turning the ball member 22 relative to coupling member 26.
[0048] While this invention has been described as having an
exemplary design, the present invention may be further modified
within the spirit and scope of this disclosure. This application is
therefore intended to cover any variations, uses, or adaptations of
the invention using its general principles. Further, this
application is intended to cover such departures from the present
disclosure as come within known or customary practice in the art to
which this invention pertains.
[0049] This invention of modular hip prosthesis is used in the
following manner:
[0050] The hip joint area is opened up using the standard surgical
approach, the femoral head and neck of the patient is dislocated
from the acetabular cavity. The femoral head and neck bones are cut
away and removed from the operative field.
[0051] The medullary canal (54) Of the femur bone (55) is cleaned
and reamed and a channel is made in the femur medullary canal for
the insertion of the prosthetic stem (42).
[0052] The modular hip prosthesis (20) that is custom made as in
FIG. 2 , containing the ball member (22), the coupling member (26)
the spring mechanism (30), the neck (40), and the stem member(42)
is selected for the surgical procedure.
[0053] The prosthetic stem (42) is fixed into the medullary canal
(54) of the femur bone (55) in such a way the flange (62) rests on
the proximal end of (64) femur bone (55).
[0054] The desired neck (40) length adjustment can be made during
the surgical procedure by the surgeon, wherein the ball member (22)
is threaded to an adjustable depth by screwing method using the
surgeon's hands, wherein the coupling member (26) threadingly
received into the threaded bore (28) of the ball member (22). To
adjust the neck length,no special keys or tools or instruments are
necessary.
[0055] After the prosthetic neck length adjustment is made, the
ball member (22) is reduced into the acetabular cavity.
[0056] The surgical wound is closed.
* * * * *