U.S. patent application number 10/779353 was filed with the patent office on 2004-08-19 for femoral neck fixation prosthesis.
Invention is credited to Crofford, Theodore W..
Application Number | 20040162621 10/779353 |
Document ID | / |
Family ID | 28794142 |
Filed Date | 2004-08-19 |
United States Patent
Application |
20040162621 |
Kind Code |
A1 |
Crofford, Theodore W. |
August 19, 2004 |
Femoral neck fixation prosthesis
Abstract
A femoral neck fixation prosthesis and method of using same
which reduces bone loss and the avoids the other shortcomings of
the prior art by allowing the fixation of a stable femoral head
replacement while reducing the amount of the femur which must be
reamed for the insertion of the prosthesis. The preferred
embodiment provides that the femoral head is attached to a fixation
prosthesis which extends coaxially through the canal of the femoral
neck, into the femur, and is then attached to the opposite lateral
wall of the femur. In this manner, the prosthesis serves to imitate
the original structure of the femoral neck. No other support
members, either crosspins or arms extending into the length of the
femur, are required.
Inventors: |
Crofford, Theodore W.; (Fort
Worth, TX) |
Correspondence
Address: |
PATTON BOGGS
1660 LINCOLN ST
SUITE 2050
DENVER
CO
80264
US
|
Family ID: |
28794142 |
Appl. No.: |
10/779353 |
Filed: |
February 14, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10779353 |
Feb 14, 2004 |
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10228907 |
Aug 27, 2002 |
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6695883 |
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60371837 |
Apr 11, 2002 |
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Current U.S.
Class: |
623/22.43 ;
606/104; 623/22.12; 623/23.27 |
Current CPC
Class: |
A61F 2002/30113
20130101; A61B 17/8695 20130101; A61F 2002/4658 20130101; A61F
2002/30604 20130101; A61F 2002/3631 20130101; A61F 2002/365
20130101; A61F 2002/30339 20130101; A61F 2/4607 20130101; A61F
2002/4631 20130101; A61B 17/8665 20130101; A61F 2002/30827
20130101; A61B 17/74 20130101; A61F 2002/30332 20130101; A61F
2002/4635 20130101; A61F 2220/0025 20130101; A61F 2/30767 20130101;
A61F 2002/30433 20130101; A61F 2220/0041 20130101; A61B 17/175
20130101; A61F 2002/3055 20130101; A61F 2230/0023 20130101; A61F
2250/0058 20130101; A61F 2310/00023 20130101; A61F 2002/30968
20130101; A61F 2310/00029 20130101; A61F 2/4657 20130101; A61F
2002/30329 20130101; A61F 2002/3079 20130101; A61F 2002/30797
20130101; A61F 2002/3611 20130101; A61F 2220/0033 20130101; A61F
2002/30156 20130101; A61F 2002/30774 20130101; A61F 2230/0069
20130101; A61F 2/3601 20130101; A61F 2002/30535 20130101; A61F
2002/30224 20130101; A61F 2002/30616 20130101; A61F 2230/0006
20130101; A61B 17/742 20130101 |
Class at
Publication: |
623/022.43 ;
623/023.27; 623/022.12; 606/104 |
International
Class: |
A61F 002/36; A61F
002/46 |
Claims
What is claimed is:
1. An implant for replacing the proximal portion of a femur having
a substantially intact natural femoral neck and a lateral side
opposite the femoral neck, the implant comprising: a solid body
member having a longitudinal axis, a distal end, and a proximal
end, being configured for positioning, in use, in the natural
femoral neck; a head member having a distal end and a proximal
substantially-spherical portion configured for positioning in a
natural or prosthetic hip socket; a joining member positioned
between the distal end of the head member and the proximal end of
the body member; and a fastener for insertion, in use, between the
distal end of the body member and the exterior of the lateral side
of the femur, substantially in line with the longitudinal axis of
the solid body member, wherein no other fasteners pass within or
through the femur.
2. The implant of claim 1, wherein the solid body member has a
length for positioning, in use, in the natural femoral neck without
passage of the distal end through the lateral side of the
femur.
3. The implant of claim 1, wherein the body member comprises a
collar positioned at the proximal end of the body member and
configured for abutting contact, in use, with a proximal surface of
the resected femoral neck.
4. The implant of claim 1 wherein the body member, the head member,
and the joining member are integrally attached.
5. The implant of claim 1 wherein the body member and the joining
member are an integral unit.
6. The implant of claim 1 wherein the joining member comprises at
least one morse-tapered portion.
7. The implant of claim 1 wherein the joining member comprises a
first morse-tapered portion which extends into a cavity in the head
member and a second morse-tapered portion which extends into a
cavity in the solid body member, both of the morse-tapered portions
extending in substantial coaxial alignment relative to the
longitudinal axis of the body member.
8. The implant of claim 1 wherein the body member, the head member,
and the joining member are separable modular components.
9. The implant recited in claim 1 wherein the fastener comprises a
barrel nut located at the exterior lateral side of the femur and a
compression screw extending between the solid body member and the
barrel nut.
10. The implant recited in claim 1 wherein the fastener comprises
compression screw extending between the exterior lateral side of
the femur and the solid body member.
11. The implant of claim 1 further comprising a first surface
coating on at least a portion of the body member for promoting bone
ingrowth into the coating following implantation.
12. The implant of claim 1, wherein the distal end of the solid
body member is configured to connect with the fastener.
13. The implant of claim 1 further comprising a body extension
member which extends from the distal end of the solid body member
at least partially along the fastener, and which is in substantial
coaxial alignment relative to the longitudinal axis of the body
member.
14. The implant of claim 1 wherein at least a portion of the body
member is triangular in cross section.
15. The implant of claim 1 wherein at least a portion of the body
member is fluted in cross section.
16. The implant of claim 1 wherein at least a portion of the body
member is scalloped in cross section.
17. The implant of claim 1 wherein at least a portion of the body
member is substantially circular in cross section.
18. The implant of claim 1 wherein at least a portion of the body
member is oval in cross section.
19. The implant of claim 1 wherein no additional support member is
attached to the lateral side of the femur.
Description
CROSS-REFERENECE TO OTHER APPLICATION
[0001] This application claims priority from U.S. Provisional
Application 60/371,837, filed Apr. 11, 2002 (MM/DD/YYYY), which is
hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present application relates to an improved apparatus and
method for hip replacements, and more specifically to a
less-invasive prosthetic which replaces the femoral head while
retaining the natural femoral neck.
DESCRIPTION OF THE RELATED ART
[0003] A widely used design for replacement of the proximal portion
of a femur employs an elongate, often curved, shaft that extends
into the medullary canal of the femur. This design has the tendency
to place unnatural stresses on the femur which lead to pain and the
consequent curtailment of activity for the patient. Further,
present techniques can lead to proximal bone loss and call for the
resection of the majority of the femoral neck. Current designs also
call for fixing the prosthesis in the proximal third of the femur.
The useful life of an intramedullary implant is often less than the
expected life span of a young patient.
[0004] Previously known prostheses for replacing a femoral head
that do not extend into the medullary canal have been mechanically
complex or have proven troublesome in actual use. Huggler, U.S.
Pat. No. 4,129,903 and Grimes, U.S. Pat. No. 4,795,473 are examples
of prosthetic implants having a side plate attached to the exterior
lateral side of the femur opposite the femoral head. Screws are
used to secure the plate to the femur and one or more holes are
drilled into the femur for securing the plate to the bone. The
additional holes and the stresses at the site of fixation are
believed to cause trauma to the bone.
[0005] Masini, U.S. Pat. No. 5,571,203 discloses a device having a
shaft that extends through a resected portion of the proximal
femur, positioned co-axially relative to the longitudinal axis of
the femur. The device is secured by a screw or similar locking
device that extends into the femur from the lateral side, just
below the greater trochanter. It is believed that the natural
forces applied to the prosthesis during normal hip motion result in
the application of shear forces to the greater trochanter. The
shear forces can be harmful to the greater trochanter and can
permit micro-movement of the prosthesis on the unsecured side.
[0006] A conventional method for implanting the above types of
femoral head implants is described in Campbell's Operative
Orthopaedics, (Mosby, 7th ed., 1987) and typically includes making
a large incision in the patient's lateral side at the hip joint and
through the skin and muscle, dislocating the hip and then sawing
off the femoral head. This method is considered invasive because of
the need to dislocate the hip and cut through muscle surrounding
the hip joint. Invasive procedures increase the trauma to the
patient, the potential for complications, recovery time and the
cost.
[0007] Replacement of the proximal portion of the femur is
sometimes necessary due to degenerative bone disorders or trauma to
otherwise healthy bone caused by accidental injury. In the latter
instance it is desirable to replace the traumatized portion of the
bone without causing further trauma to healthy bone. There is a
need, therefore, for an implant that replaces a traumatized portion
of the femur, but also significantly minimizes stress to the
remaining healthy bone and that can be implanted by a method that
is less invasive.
[0008] There are several other significant remaining problems and
issues relating to hip arthroplasty. They include:
[0009] The Young, Active Patient: Younger patients are more likely
to have failure of their primary arthroplasty both due to increased
demand on the mechanical construct, and from a pure life expectancy
standpoint. It follows that they are more likely to require a
revision and a second revision, which may lead to a catastrophic
bone loss situation.
[0010] Instability: This problem still occurs at the same rate that
it did 50 years ago. Larger femoral heads may decrease the
incidence, but no other significant technical changes have occurred
to effect the incidence of this serious complication.
[0011] Bone Loss: The overwhelming majority of present successful
femoral prosthesis achieves fixation at least as far distal as the
proximal femoral metaphysis. When these prosthesis fail, the next
step usually involves diaphyseal, fixation, often with a large
diameter stiff stem.
[0012] Leg Length Inequality: Leg length inequality after hip
arthroplasty has always been a problem and an average lengthening
of the leg of 1 centimeter is common. Lengthening is sometimes
accepted for the sake of improved stability. Leg length inequality
has been reported as the number one reason why surgeons are sued
after hip arthroplasty
[0013] Surgical Morbidity: Hip arthroplasty usually involves
significant blood loss, body fluid alterations and pain. Shortly,
it's a big operation that hurts. It should be the goal of every
compassionate surgeon to minimize these issues. If the operation
can be made smaller, with less blood loss and less pain without
diminishing long term results, every effort should be made to do
so.
[0014] It would therefore be desirable to provide a femoral next
prosthetic apparatus that overcomes these significant
disadvantages.
SUMMARY OF THE INVENTION
[0015] It is therefore one object of the present invention to
provide an improved apparatus and method for hip replacements.
[0016] It is another object of the present invention to provide an
improved and less-invasive prosthetic which replaces the femoral
head while retaining a substantially intact femoral neck.
[0017] The foregoing objects are achieved as is now described. The
preferred embodiment provides a femoral neck fixation prosthesis
and method of using same which reduces bone loss and the avoids the
other shortcomings of the prior art by allowing the fixation of a
stable femoral head replacement while reducing the amount of the
femur which must be reamed for the insertion of the prosthesis. The
preferred embodiment provides that the femoral head is attached to
a fixation prosthesis which extends coaxially through the central
canal of the femoral neck, into the femur, and is then attached to
the opposite lateral wall of the femur. In this manner, the
prosthesis serves to imitate the original structure of the femoral
neck. No other support members, either crosspins or arms extending
into the length of the femur, are required.
[0018] The above as well as additional objectives, features, and
advantages of the present invention will become apparent in the
following detailed written description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The novel features believed characteristic of the invention
are set forth in the appended claims. The invention itself however,
as well as a preferred mode of use, further objects and advantages
thereof, will best be understood by reference to the following
detailed description of illustrative sample embodiments when read
in conjunction with the accompanying drawings, wherein:
[0020] FIG. 1 depicts a schematic of an anterior view of a
prosthesis in accordance with a preferred embodiment of the present
invention;
[0021] FIG. 2 shows a schematic of the cross section at various
levels of the body of a prosthesis in accordance with a preferred
embodiment of the present invention;
[0022] FIG. 3 depicts a schematic of the femoral necks of a
prosthesis in accordance with a preferred embodiment of the present
invention;
[0023] FIG. 4 depicts the centering guide for placement of the
starting pin in accordance with a preferred embodiment of the
present invention;
[0024] FIG. 5 depicts how the center of rotation of the femoral
head can be reproduced in accordance with a preferred embodiment of
the present invention;
[0025] FIG. 6 depicts a prosthesis in accordance with an alternate
embodiment of the present invention; and
[0026] FIG. 7 depicts a prosthesis in accordance with an alternate
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The numerous innovative teachings of the present application
will be described with particular reference to the presently
preferred embodiment (by way of example, and not of
limitation).
[0028] The preferred embodiment provides a femoral neck fixation
prosthesis and method of using same which reduces bone loss and the
avoids the other shortcomings of the prior art by allowing the
fixation of a stable femoral head replacement while reducing the
amount of the femur which must be removed and reamed for the
insertion of the prosthesis. The preferred embodiment provides that
the femoral head is attached to a fixation prosthesis which extends
coaxially through the central canal of the femoral neck, into the
femur, and is then attached to the opposite lateral wall of the
femur. In this manner, the prosthesis serves to imitate the
original structure of the femoral head while substantially
retaining the natural femoral neck. No other support members,
either crosspins or arms extending into the length of the femur,
are required.
[0029] A femoral neck fixation prosthesis in accordance with the
preferred embodiments is designed to achieve fixation in the
isthmus of the femoral neck with or without cement. Therefore,
revision of the disclosed femoral neck fixation prosthesis would
essentially become the complexity of a present day primary hip
arthroplasty for the femoral component. The improved femoral neck
fixation prosthesis would require an operation equivalent to a
primary arthroplasty on the femoral side. Therefore it would be
ideal for the younger patient, but would also be recommended for
the older patients with accommodating anatomy.
[0030] The innovative method for implanting the femoral neck
fixation prosthesis would allow less muscular dissection, and the
capsule can be repaired anteriorly at the end of the procedure. The
disclosed femoral neck fixation prosthesis is designed to be used
with larger diameter femoral heads. The combination of these
factors would significantly improve stability of the hip. The goal
is to minimize the need for hip position precautions
postoperatively.
[0031] One advantage of the preferred embodiment is that less bone
would be resected initially using the femoral neck fixation
prosthesis, and the stress would be transferred to the bone in the
femoral neck. The metaphysis and the diaphysis of the proximal
femur would be minimally disturbed. Only the femoral head itself
will be resected.
[0032] Another advantage of the preferred embodiment, is that the
femoral neck length and offset would be accurately measured and
reproduced when using the femoral neck fixation prosthesis. Leg
length inequality due to hip arthroplasty could be minimized and
muscle mechanics could be accurately restored.
[0033] Further, an operation using the femoral neck fixation
prosthesis would be less invasive with less blood loss, less post
operative pain, and less perioperative morbidity than the an
operation that employs the vast majority of commonly used
prosthesis. The economic implications of a shorter hospital stay,
fewer blood transfusions, and fewer medical complications are
significant.
[0034] The preferred embodiment of the present invention is shown
in FIG. 1, wherein femur 100 is shown with femoral neck 105,
joining member 115, and prosthetic head 110.
[0035] The preferred embodiment provides an uncemented porous
coated femoral prosthesis body 125 with a modular head 110 and
joining member 115. The metal used is preferably either titanium or
chrome-cobalt based, and can be any metal commonly used in hip
prosthesis construction. The modulus of elasticity of such a short
segment will be of less significance than in a standard femoral
stem. The coating is preferably either sintered beads or plasma
sprayed, depending on the type of metal used for the body of the
prosthesis.
[0036] The body 125 of the prosthesis will preferably be available
in various diameters, approximately every 1-1.5 mm. The length of
the prosthesis will preferably be chosen from one or two lengths,
approximately 30 mm. Most of the fixation and ingrowth of the bone
to the prosthesis will occur in the first 10-20 mm.
[0037] Fixation to the femur will be achieved by reaming the
femoral neck 105 to accommodate a cylindrical porous coated sleeve
body 125, which is supported by a proximal collar and given distal
stability with a compression screw 120 through the lateral wall of
the femur just distal to the greater tuberosity (location 140).
Reaming will be progressive until the cortex of the femoral neck is
encountered. A femoral component 1/2 mm greater than the last
diameter reamed will then be selected.
[0038] After insertion, the long axis of the body of the component
body 125 will coincide with the axis made in the preoperative femur
100 by an imaginary line connecting the center of the femoral neck
105 with the center of the femoral head 110. Resection of the
femoral head will be measured such that the center of rotation of
the femoral head 110 can be measured and reproduced. The femoral
neck 105 will be reamed with a flat reamer that fits in the reamed
canal of the femoral neck 105 to establish a flat surface. The
proximal body 125 of the prosthesis will have the female end of a
morse taper to allow the attachment of the joining member 115.
[0039] A compression screw 120 passes through the center of the
body of the prosthesis. This screw attaches to a barrel nut 130 in
the lateral wall of the femur at point 140 and preferably has a
hexagonal head. The screw 120 is preferably smooth in the segment
within the body of the prosthesis and has threads on the distal
end. The tunnel through the body of the prosthesis forms a snug fit
around the smooth portion of the screw 120. The barrel nut 130 is
preferably angled to be flush with the lateral side of the femur at
point 140. The head of the screw 120 is preferably located in the
base of the morse taper in the body 125 of the femoral component.
This screw 120 adds stability to the construct by giving
antero-posterior and varus-valgus stability to the body 125 of the
prosthesis and by compressing the prosthesis on the neck 105 of the
femur 100. These screws will be available in various lengths.
[0040] It is important to note that this innovative design allows
the prosthesis to be installed and used without requiring any other
fastener on the femur. In particular, the preferred embodiment does
not require any additional screws or other fasteners to be placed
in the femur, and does not require any sort of support plate on the
lateral wall of the femur.
[0041] Male-male morse taper joining member 115 acts as a joining
portion in connecting the body 125 of the prosthesis to the femoral
head 110. Adjustments in joining member length will occur in this
segment with several lengths of joining member segments available
for each femoral body and femoral head. The joining member segment
needed to exactly reproduce the center of rotation of the femoral
head will be known based on the amount of bone resected. In this
embodiment, the joining member 115 has male more tapers 135 on each
side, and will have a variable-length section in between the morse
tapers to fit the specific patient.
[0042] The femoral head 110 will have a female morse taper to
connect to the joining member 115. Femoral heads 110 will be of
various diameters depending on the acetabulum, and several
exemplary sizes are shown in FIG. 1. Ideally larger femoral head
diameters (e.g., 36 mm to 50 mm) are used to both improve stability
and prevent impingement of the neck on the acetabular rim. The
femoral head 110 is preferably polished chrome-cobalt, as the
industry standard, but other materials can be used.
[0043] In another embodiment of the present invention, a
de-rotation component is added to reduce the likelihood of the
rotation of the prosthesis within the femoral neck. This can be
accomplished with a pin or stem with grooves or slots that passes
through the lateral cortex into the body of the prosthesis. This
would then be compressed with a screw which would be put through
the head end of the body of the prosthesis into the stem.
[0044] It should be clear that the prosthesis of the preferred
embodiments can be used with or without a cement.
[0045] FIGS. 2A-2C shows several cross-section views of the
cylindrical porous coated body 225 of the prosthesis of the
preferred embodiment. FIG. 2A shows a longitudinal cross-section of
the body 225. In this view, a collar 248 at the proximal end of the
body 225 is illustrated, as is the female morse taper cavity 246
which is fit to receive the joining member. The collar 248 is
configured to abut the proximal end of the resected femoral neck.
Communicating with cavity 246 is tubular channel 247 which will
receive the compression screw. Below the collar 248, the exterior
of the body 225 has a porous coated layer 249.
[0046] While the preferred embodiment has a substantially circular
cross-section, as shown in FIGS. 2A-2C, the body member 225 can
also be configured with a triangular, scalloped, or fluted
cross-section.
[0047] FIG. 2B shows a lateral cross-section of body 225 as cut
across line B of FIG. 2A. In FIG. 2B, the cavity 246 is shown, and
the proximal collar 248 is also illustrated.
[0048] FIG. 2C shows a lateral cross-section of body 225 as cut
across line C of FIG. 2A. In FIG. 2C, channel 247 for the
compression screw is shown passing through the center of body 225.
On the exterior of body 225 is shown the porous coated layer 249. A
cross-section across line D of FIG. 2A is the same as described for
line C of that figure.
[0049] FIG. 3 shows joining members 316/317/318 of various sizes,
which can be used for patients with differing requirements. Each
joining member 316/317/318 has a morse taper on each end, and a
variable-length straight section connecting the morse tapers.
[0050] FIG. 4 depicts the centering guide for placement of the
starting pin in accordance with a preferred embodiment of the
present invention. In this figure, femoral neck gripping clamp 405
is to grip and hold the femoral neck after the femoral head
centering device 410 has been placed over the patient's femoral
head.
[0051] The femoral neck gripping clamp 405 is expanded or
contracted using adjustment piece 420, which operates gears 415.
Cannulated rod 425, which is connected to femoral head centering
device 410, allows pin insertion into the cannula at 435.
[0052] Free nut 430 is used to tighten the femoral head centering
device 410. The centering guide shown in FIG. 4 is preferably made
of a stiff metal, and can also be used as a retractor to expose the
femoral head.
[0053] FIG. 5 depicts how the center of rotation of the femoral
head can be reproduced in accordance with a preferred embodiment of
the present invention. First, distance A from the head to the
lateral cortex is measured. After the femoral head is removed,
distance B, from the cut surface to the lateral cortex, is
measured. The diameter D of the femoral head is also measured. When
these measurements are known, distance C is calculated using the
formula
C=(A-D/2)-B
[0054] Distance C then represents the distance from the cut surface
of the femoral neck that the prosthetic femoral head
center-of-rotation should be placed in order to reproduce the
pre-operative femoral head center-of-rotation.
[0055] In an alternate embodiment shown in FIG. 6, compression
screw 620, preferably with washer 645, is inserted through the
lateral wall of the femur at location 640 and screwed into the body
625 of the femoral component. This simplifies the barrel nut
portion of the design shown in FIG. 1. It would require that the
screw 620 be of various lengths that would engage the body 625 of
the prosthesis without reaching the depth of the hole in the
femoral prosthesis. The body of the prosthesis would preferably be
longer, using optional extension 650 to provide enough length so
that the compression screw will be stable within the body of the
prosthesis.
[0056] The remainder of FIG. 6 is similar to FIG. 1. In this
figure, femur 600 is shown with femoral neck 605, joining member
615, and prosthetic head 610.
[0057] This embodiment provides an uncemented porous coated femoral
prosthesis body 625 with a modular head 610 and joining member 615.
The body 625 of the prosthesis include threads 655 for receiving
screw 620.
[0058] Fixation to the femur will be achieved by reaming the
femoral neck 605 to accommodate a cylindrical porous coated sleeve
body 625, which is supported by a proximal collar and given distal
stability with a compression screw 620 through the lateral wall of
the femur just distal to the greater tuberosity (location 640).
[0059] After insertion, the long axis of the body of the component
body 625 will coincide with the axis made in the preoperative femur
600 by an imaginary line connecting the center of the femoral neck
605 with the center of the femoral head 610. Resection of the
femoral head will be measured such that the center of rotation of
the femoral head 610 can be measured and reproduced as discussed
with reference to FIG. 5. The femoral neck 605 will be reamed with
a flat reamer that fits in the reamed canal of the femoral neck 605
to establish a flat surface. The proximal body 625 of the
prosthesis will have the female end of a morse taper to allow the
attachment of the femoral neck 615.
[0060] Compression screw 620 passes through the center of the body
of the prosthesis. The screw 620 is preferably smooth in the
segment within the body of the prosthesis and has threads on the
proximal end, for engaging threads 655. The tunnel through the body
of the prosthesis forms a snug fit around the smooth portion of the
screw 620. Screw 620 adds stability to the construct by giving
antero-posterior and varus-valgus stability to the body 625 of the
prosthesis and by compressing the prosthesis on the neck 605 of the
femur 600. These screws will be available in various lengths.
[0061] Male-male morse taper joining member 615 connects the body
625 of the prosthesis to the femoral head 610. Adjustments in
joining member neck length will occur in this segment with several
lengths of joining member segments available for each femoral body
and femoral head. The joining member segment needed to exactly
reproduce the center of rotation of the femoral head will be known
based on the amount of bone resected.
[0062] The femoral head 610 will have a female morse taper to
connect to the joining member 615. Femoral heads 610 will be of
various diameters depending on the acetabulum. Ideally larger
femoral head diameters (e.g., 36 mm to 60 mm) are used to both
improve stability and prevent impingement of the neck on the
acetabular rim. The femoral head 610 is preferably polished
chrome-cobalt, as the industry standard, but other materials can be
used.
[0063] FIG. 7 shows yet another alternate embodiment of the present
invention. If the compression screw 720, with washer 745, is
inserted through the lateral wall of the femur at 740, the length
of the body 725 of the prosthesis may not be long enough to provide
adequate stability for the compression screw 720. In order to
provide this stability for the compression screw, a fixed length
joining member 760 on the body of the prosthesis would be necessary
to act as a joining member, abandoning the modular joining member
(115 in FIG. 1). The varied lengths required on the joining member
would be incorporated into the femoral head either with separate
individual lengths for each head diameter (2 to 3 for each diameter
femoral head) or by using an interposing piece of metal to provide
additional neck length. The latter is done with several femoral
components available on the market today.
[0064] Modifications and Variations
[0065] As will be recognized by those skilled in the art, the
innovative concepts described in the present application can be
modified and varied over a tremendous range of applications, and
accordingly the scope of patented subject matter is not limited by
any of the specific exemplary teachings given.
[0066] While the invention has been particularly shown and
described with reference to a preferred embodiment, it will be
understood by those skilled in the art that various changes in form
and detail may be made therein without departing from the spirit
and scope of the invention.
[0067] None of the description in the present application should be
read as implying that any particular element, step, or function is
an essential element which must be included in the claim scope: THE
SCOPE OF PATENTED SUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED
CLAIMS. Moreover, none of these claims are intended to invoke
paragraph six of 35 USC .sctn.112 unless the exact words "means
for" are followed by a participle.
* * * * *