U.S. patent application number 10/766568 was filed with the patent office on 2004-09-30 for bone prosthesis and method of implantation.
Invention is credited to Grimes, James B..
Application Number | 20040193281 10/766568 |
Document ID | / |
Family ID | 36062501 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040193281 |
Kind Code |
A1 |
Grimes, James B. |
September 30, 2004 |
Bone prosthesis and method of implantation
Abstract
A bone prosthesis for implantation at a joint includes a stem
having a tip generally at one end thereof. The stem is sized and
shaped for reception in a bone at the joint such that the tip of
the stem is exposed to locations outside of the bone. The stem has
a passageway extending from a first location on the bone prosthesis
to a second location on the bone prosthesis.
Inventors: |
Grimes, James B.;
(Bakersfield, CA) |
Correspondence
Address: |
SENNIGER POWERS LEAVITT AND ROEDEL
ONE METROPOLITAN SQUARE
16TH FLOOR
ST LOUIS
MO
63102
US
|
Family ID: |
36062501 |
Appl. No.: |
10/766568 |
Filed: |
January 28, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10766568 |
Jan 28, 2004 |
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09913826 |
Aug 20, 2001 |
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Current U.S.
Class: |
623/22.12 ;
606/102; 606/89; 606/93; 623/23.19; 623/23.31 |
Current CPC
Class: |
A61B 2017/320012
20130101; A61B 2090/034 20160201; A61F 2002/30594 20130101; A61F
2002/4677 20130101; A61B 17/15 20130101; A61F 2002/4668 20130101;
A61F 2002/3631 20130101; A61F 2/30767 20130101; A61B 10/02
20130101; A61F 2/3601 20130101; A61F 2002/30726 20130101; A61B
17/74 20130101; A61F 2002/30682 20130101; A61B 17/175 20130101;
A61F 2/4607 20130101; A61B 2090/067 20160201; A61F 2/36 20130101;
A61F 2002/3625 20130101; Y10S 623/908 20130101; A61F 2002/368
20130101; A61F 2/367 20130101; A61F 2220/0033 20130101; A61F 2/3676
20130101; A61F 2310/00023 20130101; A61B 17/1659 20130101; A61F
2230/005 20130101; A61F 2002/30677 20130101; A61B 17/1668 20130101;
A61F 2002/30322 20130101; A61F 2310/00029 20130101; A61F 2002/4635
20130101; A61F 2/4684 20130101; A61F 2002/30171 20130101; A61F
2002/30354 20130101; A61F 2002/3082 20130101; A61F 2002/365
20130101; A61F 2/4657 20130101; A61F 2002/3694 20130101; A61B
17/8875 20130101; A61F 2250/0026 20130101; A61B 17/3472
20130101 |
Class at
Publication: |
623/022.12 ;
623/023.31; 623/023.19; 606/089; 606/093; 606/102 |
International
Class: |
A61F 002/36; A61F
002/46; A61B 017/88 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 19, 1999 |
WO |
PCT/US99/03709 |
Claims
What is claimed is:
1. A bone prosthesis for implantation at a joint, the prosthesis
comprising a stem sized and shaped for implantation in a bone at
the joint such that at least a portion of the stem is received in
the bone and a portion is exposed to locations outside the bone,
the stem having a passageway arranged to vent fluid pressure from a
first location which is subject to elevated fluid pressures when
the joint is in use after implantation of the prosthesis to a
second location for venting fluid from the first location to the
second location thereby to inhibit fluid pressure build up between
bone located at the joint and the prosthesis.
2. A bone prosthesis as set forth in claim 1 wherein the passageway
is arranged to vent joint wear debris from the first location which
is subject to high concentrations of joint wear debris after
implantation of the prosthesis to the second location for venting
joint wear debris from the first location to the second location
thereby to inhibit wear debris build up between bone located at the
joint and the prosthesis.
3. A bone prosthesis as set forth in claim 1 wherein the stem
includes a tip adapted to be received through the bone upon
implantation of the prosthesis, the tip being disposed generally at
the second location and the passageway having an aperture generally
at the tip.
4. A bone prosthesis as set forth in claim 3 wherein the passageway
extends within the stem.
5. A bone prosthesis as set forth in claim 4 wherein the passageway
includes a primary channel extending generally longitudinally of
the stem and secondary channels extending from multiple, spaced
apart openings on the exterior of the stem to the primary
channel.
6. A bone prosthesis as set forth in claim 5 wherein the stem has
side surfaces, the secondary channel openings being located in the
side surfaces so that the secondary channels and the primary
channel are in fluid communication with a prosthesis-bone
interface, the secondary channels extending inwardly from the
openings at angles oblique to the side surfaces.
7. A bone prosthesis as set forth in claim 6 wherein the stem is
sized for transosseous implantation in which the stem extends
through the bone and the tip of the stem is exposed outside of the
bone.
8. A bone prosthesis as set forth in claim 7 wherein the primary
channel opens at the aperture in the tip of the stem, the aperture
and primary channel being sized and shaped to receive an infusion
element for infusing fluid into the channel when the bone
prosthesis is installed in the bone, the fluid passing from the
primary channel to the secondary channels and the prosthesis-bone
interface.
9. A bone prosthesis as set forth in claim 4 for implantation in a
femur at a hip joint, the prosthesis further comprising a collar on
an end of the stem opposite the tip, a neck mounted on the collar
and a ball mounted on the neck, the passageway in the stem opening
at the first location disposed on an upper surface of the
collar.
10. A bone prosthesis as set forth in claim 9 wherein the
passageway constitutes a first passageway, and wherein the stem has
a second passageway in the stem opening on an upper surface of the
collar and extending to the second location.
11. A bone prosthesis as set forth in claim 10 wherein the second
passageway is sized and shaped to receive an instrument
therethrough to provide access to the first location.
12. A bone prosthesis as set forth in claim 11 wherein the second
passageway has no connection to the first passageway.
13. The bone prosthesis of claim 12 wherein the first and second
passageways extend through the stem to separate apertures at the
stem tip.
14. A bone prosthesis for implantation at a joint, the prosthesis
comprising a stem having: a tip generally at one end thereof, and a
collar on an end of the stem opposite the tip, the stem being sized
and shaped for reception in a bone at the joint such that the tip
of the stem is exposed to locations outside of the bone, the stem
having a passageway therein extending from a first location on the
bone prosthesis to a second location on the bone prosthesis.
15. A bone prosthesis as set forth in claim 14 in combination with
an infusion element, wherein the passageway of the bone prosthesis
has an aperture at the second location, the aperture and passageway
being sized and shaped to receive an infusion element for infusing
fluid into the passageway when the bone prosthesis is installed in
the bone.
16. A bone prosthesis as set forth in claim 15 wherein the
passageway comprises a primary channel extending from the aperture
at the second location and secondary channels extending from the
primary channel to openings in the bone prosthesis, the infused
fluid being capable of passing from the primary channel to the
secondary channels and thence out of the secondary channel
openings.
17. A bone prosthesis as set forth in claim 16 wherein the infusion
element has threads formed thereon, and wherein the primary channel
has threads at the aperture adapted to engage the threads of the
infusion element for securing the infusion element in the
aperture.
18. A bone prosthesis as set forth in claim 17 wherein the tip of
the stem is generally at the second location and the primary
channel aperture is located generally at the tip.
19. A bone prosthesis as set forth in claim 15 further in
combination with an infusion port in fluid communication with the
infusion element, the infusion port being adapted for implantation
under the skin for use in repeated infusion of fluid into the
passageway.
20. A method of implanting a femoral head-neck prosthesis in a
femur without the use of cement, the femur having a shaft and a
neck at the upper end of the shaft at the medial side of the femur,
the prosthesis having a longitudinal passageway for venting fluid
pressure from a first location which is subject to elevated fluid
pressures when the joint is in use after implantation of the
prosthesis to a second location for venting fluid from the first
location to the second location thereby to inhibit fluid pressure
build up between bone located at the joint and the prosthesis, the
method comprising the steps of: cutting the neck of the femur to
form a seat on the femur neck; drilling a passage along a line
through the shaft of the femur; and inserting the stem of the
prosthesis in the passage of the femur such that the longitudinal
passageway for venting fluid is not occluded.
21. A method as set forth in claim 20 wherein the step of inserting
the stem comprises driving the stem through the passage until a
distal end of the stem protrudes from the lateral side of the
femur.
22. A method as set forth in claim 21 further comprising, prior to
said step of inserting the stem, the step of attaching a removable
guide on the distal end of the stem to inhibit occlusion of the
longitudinal passageway of the stem during said step of inserting
the stem.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/913,826, filed Aug. 20, 2001, which is a
PCT National of PCT/US99/03709, filed Feb. 19, 1999. The entire
text of both applications is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to femoral prostheses and
methods for their implantation.
[0003] Total hip replacement became a clinical reality for the
first time in November, 1962. The femoral head and neck were
removed, the upper marrow canal of the femur was cleaned out (i.e.,
marrow contents removed), and the metal femoral component was
inserted into the femur. Total hip replacement using a femoral
component or implant is generally successful for the short term
(ten years), however in the long run, deterioration of the bone
occurs and the implant may loosen.
[0004] Bone deterioration adjacent femoral implants is a
multi-factored process which includes at least two elements, strain
deprivation and osteolysis. Bone loss due to strain deprivation (or
what is commonly but incorrectly referred to as "stress shielding")
occurs in association with substantially all conventional
intramedullary femoral components and is caused by the implant
splinting the upper femur, preventing the upper femur from being
subjected to natural bending. My prior application, PCT Application
Serial No. US97/14233, includes features directed to alleviating
splinting osteolysis is a late complication of joint replacement
surgery in which the bone adjacent the implant develops lesions,
either "scooped out" (focal) or diffuse (linear) areas. Osteolysis
is somewhat less common than bone loss due to strain deprivation,
and depends on the type of implant used. Several factors are known
to contribute to osteolysis, including access of joint wear debris
to a joint space JS above the collar of the component and to the
area between the implant and the bone (the implant-bone interface
IB). Joint wear debris carried by the fluid remains in the joint
space JS and becomes concentrated. The synovial lining of the joint
has limited ability to absorb and encapsulate the wear debris,
resulting in osteolysis of the exposed bone. Another factor is
joint fluid pressure in the implant-bone interface IB. The latter
factor commonly occurs in prior art implants because fluid is able
to enter the implant-bone interface IB. As the person walks, high
fluid pressures are generated at the interface and within the bone
cells. Recent research suggests that joint fluid pressure is a
significant factor in osteolysis.
[0005] Although much less common than strain deprivation or
osteolysis, the most disastrous cause of bone deterioration
adjacent a femoral implant is infection. Infection may occur
shortly after the total hip replacement operation (acute
infection), or may occur months or years after the operation (late
infection). Acute infections may be caused by bacterial
contamination of the incision by airborne bacteria or from bacteria
from the patient's skin. Late infections usually are caused by
bacteria going through the patient's circulatory system and lodging
in the bone adjacent the femoral implant.
[0006] Infection adjacent a femoral implant is a serious problem
because of the pain, fever and disability it causes. The bacteria
(or other organisms) cause infection in the bone and soft tissues
around the implant and begin to multiply (osteomyelitis). The
body's attempt to fight the infection tends to damage the bone as
well.
[0007] The diagnosis of deep infection of a total joint replacement
is often delayed because of the inaccessibility of the hip joint
within the body. The diagnosis of infection of a total hip
replacement requires aspiration of joint fluid (inserting a needle
into the joint space JS (FIG. 34) and drawing infected fluid out of
the joint with a syringe) or alternatively, obtaining deep tissue
specimens from the joint. Tissue specimens are obtained by open
surgery at the joint, or, much less commonly, by arthroscopic
surgery (exploration of the joint through small incisions using
fiberoptic telescopes).
[0008] An infection may be present at the implant-bone interface IB
and not manifest itself in the joint fluid (false negative
aspiration). It can be technically difficult to obtain fluid from
the hip joint because of scarring from the previous surgery. The
scar tissue which forms around a femoral implant may also make
arthroscopic visualization of the joint difficult. Surgically
exposing the hip to obtain tissue samples carries with it the pain
and disability of open surgery as well as the risk of introducing
bacteria around the implants.
[0009] Infrequently, the infection can be treated without removing
the implant. The hip joint is surgically exposed and cleaned
(debrided) through removal of dead and infected tissue. However, it
is not possible to clean everywhere around the implant. Moreover,
the interface between the bone and implant is generally
inaccessible, which inhibits the introduction of antibiotics into
the implant-bone interface IB. As shown in FIG. 34, antibiotics
introduced into the joint space JS will generally remain in the
joint space and will not flow down into the implant-bone interface
IB. Intravenous systemic antibiotics are administered for several
weeks or months following surgery. This method of treating an
infection adjacent an implant usually is attempted only on early
infections (less than three or four weeks) and is not always
successful in eradicating the infection.
[0010] More commonly, infection adjacent a femoral prostheses
requires complete removal of the implant and removal of bone cement
(if present). The removal of cemented or non-cemented
intramedullary stem femoral implants will destroy some amount of
bone. In the case of removal of porous ingrowth (non-cemented)
femoral implants, the destruction of bone is extensive. These
components frequently require cutting the upper thigh bone (femur)
in half longitudinally (extended trochanteric osteotomy), cutting
the metal stem in half transversely, and using a hollow coring
drill to remove the lower half of the stem (trephining). The extent
of bone loss associated with removal of total hip replacement
femoral implants is aggravated in cases where pre-existing bone
loss from strain deprivation and osteolysis is present. Once the
implant is removed, the patient is given systemic (intravenous or
oral) antibiotics for two months or more. When there is evidence
that the infection has been cleared, a new total hip replacement is
installed in a second operation. Fixation of the new implant in the
bone is frequently compromised by loss of bone stock.
[0011] In some patients, the joint replacement implants are
permanently left out (Girdlestone procedure). This option is
considered for patients having a weakened immune system, such as
those with diabetes, rheumatoid arthritis or who require steroids.
A Girdlestone procedure is also considered for patients who are too
ill to withstand an additional major operation. With the hip
implant absent, the hip joint tissues contract and the leg becomes
significantly shorter. With no bony or mechanical connection or
support, the hip is unstable and frequently painful. Most patients
require the use of crutches, walker or wheelchair after a
Girdlestone procedure.
[0012] Another problem in the treatment of infection is presented
by the systemic administration of antibiotics, taken orally or
intraveneously. Systemic antibiotics expose the entire body to the
antibiotic. Potential side effects of antibiotics limit the amount
that can be given. Side effects of systemic antibiotics include
allergic reactions, impairment of kidney function, damage to the
nerves which allow hearing and balance, gastrointestinal
complications, and other problems. Additionally, bone has a
relatively poor blood supply compared with other tissues, e.g.,
muscles or internal organs, so that achieving high enough
concentrations of antibodies in the bone to eradicate the bacterial
infection is difficult. The implant, acrylic bone cement (if
present), nonviable bone and scar tissue may also harbor deep
seated bacteria which may again begin to multiply once antibiotics
are discontinued.
[0013] An alternative method of delivering antibiotics to an
infected hip implant employs an antibiotic cement spacer. The
infected hip replacement components are removed and the bone is
thoroughly cleaned of infected tissue. A sterilized stem of a
femoral implant is covered with a layer of acrylic cement which
contains high concentrations of an antibiotic. The stem/antibiotic
cement composite structure is placed in the marrow canal of the
femur. One advantage of this method is the delivery of high local
concentrations of antibiotic directly to the infected tissues. This
may decrease the need for systemic antibiotics with their potential
side effects. Another advantage is the maintenance of the soft
tissue length about the hip which makes the later implantation of a
new hip implant technically easier. One disadvantage of the
antibiotic cement spacer is a significant decline in the antibiotic
levels in the fluid and tissues about the hip after two or three
weeks. Also, the antibiotic spacer is usually put in loosely to
facilitate later removal. The resulting instability of the implant
within the bone may cause pain and prevent full weight bearing.
Moreover, if a spacer is left in for a long time it may be
difficult to remove, which may result in additional bone loss upon
removal.
[0014] A second method of delivering antibiotics directly to the
infected tissues about an infected hip implant site is the infusion
port method. This technique is used after removal of an infected
implant to provide a renewable supply of antibiotics directly to
the infection site. The port method involves placing an infusion
port under the skin away from the infected joint at a location
where it is readily accessible from outside the body. The infusion
port is anchored with sutures to fascia (connective tissue). A
length of tubing from the port is passed under the skin to the site
of infection (e.g., hip, knee, shoulder). After surgically cleaning
the joint and removal of the infected implants, the end of the
tubing is placed in the infected joint. After the operation to
insert the infusion port, a needle is passed through the skin
overlying the port, through a plastic, self-sealing membrane of the
port and into the port. A syringe attached to the needle contains a
solution of antibiotics that is infused through the port and tubing
directly into the joint. The advantage of this method over an
antibiotic spacer technique is that antibiotics can be administered
daily, or more often if necessary. This renewable source of
antibiotics provides extremely high local concentrations of
antibiotics directly to the site of the infection without the side
effects associated with systemic antibiotics. These concentrations
can be maintained indefinitely by repeatedly infusing antibiotics
directly into the joint. A disadvantage of the infusion port method
is that it usually is combined with removal of the implant to
assure that the antibiotic has access to all of the potentially
infected sites at the joint. Referring again to FIG. 34, when
conventional intramedullary stem femoral implants are left in
place, the antibiotics may not be able to reach the interface
between the bone and the implant (or between the cement and the
bone).
SUMMARY OF THE INVENTION
[0015] Among the several objects and features of the present
invention may be noted the provision of a prosthesis and method of
implantation which inhibit bone deterioration; the provision of
such a prosthesis and method which reduces fluid pressure in the
implant-bone interface; the provision of such a prosthesis and
method which transports joint wear debris away from the joint
space; and the provision of such a prosthesis which has a longer
useful life.
[0016] Further objects of the invention include the provision of a
method and apparatus for diagnosing and treating infections
associated with a prosthesis which does not require removal of the
prosthesis; the provision of such a method and apparatus which
achieves high antibiotic levels at the infection site without
affecting the entire system of the patient; and the provision of
such a method that maintains soft tissue length adjacent the
prosthesis.
[0017] Generally, a bone prosthesis for implantation at a joint
comprises a stem sized and shaped for implantation in a bone at the
joint such that at least a portion of the stem is received in the
bone and a portion is exposed to locations outside the bone. The
stem has a passageway arranged to vent fluid from a first location
which is subject to elevated fluid pressures when the joint is in
use after implantation of the prosthesis to a second location for
venting fluid pressure from the first location to the second
location thereby to inhibit fluid pressure build up between bone
located at the joint and the prosthesis.
[0018] In another aspect of the invention, a bone prosthesis for
implantation at a joint includes a stem having a tip generally at
one end thereof. The stem is sized and shaped for reception in a
bone at the joint such that the tip of the stem is exposed to
locations outside of the bone. The stem has a passageway extending
from a first location on the bone prosthesis to a second location
on the bone prosthesis.
[0019] Another aspect of the present invention is a method for
implanting a femoral head-neck prosthesis in a femur without the
use of cement. The femur has a shaft and a neck at the upper end of
the shaft at the medial side of the femur. The prosthesis has a
longitudinal passageway for venting fluid pressure from a first
location which is subject to elevated fluid pressures when the
joint is in use after implantation of the prosthesis to a second
location for venting fluid pressure from the first location to the
second location thereby to inhibit fluid pressure build up between
bone located at the joint and the prosthesis. The method comprises
the steps of cutting the neck of the femur to form a seat on the
femur neck, drilling a passage along a line through the shaft of
the femur and inserting the stem of the prosthesis in the passage
of the femur such that the longitudinal passageway for venting
fluid pressure is not occluded.
[0020] Yet another aspect of the invention is a method of minimally
invasively accessing the femoral head-neck prosthesis which is
transosseously implanted in a femur in a thigh of a patient. The
prosthesis includes a stem having a passageway extending at least
partway through the stem along a longitudinal axis and opening at a
tip of the stem. The passageway is in fluid communication with a
prosthesis-bone interface. The stem is implanted such that the
opening of the passageway in the stem is accessible from a location
external to the femur. The method includes examining the prosthesis
using an X-ray device while simultaneously rotating the femur until
a viewing plane of the X-ray device is generally parallel with the
longitudinal axis of the passageway. An intersection point of the
longitudinal axis of the stem with skin of the thigh is determined.
An incision is made at the intersection point and an instrument is
inserted through the skin generally along the longitudinal axis and
into the opening of the passageway.
[0021] Other objects and features of the present invention will be
in part apparent and in part pointed out hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a fragmentary cross section of an upper femur
showing a femoral head-neck prosthesis of the present invention
implanted in the femur (the prosthesis being shown in full
lines);
[0023] FIG. 1A is a view of an intact femur showing the medial
trabecular stream of the femur and axes of the femur and
prosthesis;
[0024] FIG. 1B is a cross-sectional view through the femoral neck
illustrating the planes of the femur;
[0025] FIGS. 2A-2D illustrate areas of contact between the upper
prosthesis and bone at locations indicated by lines 2A-2A through
2D-2D, respectively;
[0026] FIG. 3 is a cross-section through the splined portion of the
lower stem taken in the plane of line 3-3 of FIG. 1;
[0027] FIGS. 4A-R are schematic views of a lesser preferred
embodiment and a preferred embodiment of a method of implanting the
prosthesis:
[0028] FIG. 4A is a view of the femur showing the axis of the
medial trabecular stream;
[0029] FIG. 4B is a view showing the angle guide and the saw guide
around the femur for femoral neck resection;
[0030] FIG. 4C is a view showing the angle guide, a reamer guide
and a reamer for reaming of the second bore in the femoral
neck;
[0031] FIG. 4D is a view showing the reamer for reaming the second
bore in the femoral neck;
[0032] FIG. 4E is a view showing the angle guide, calcar milling
guide and calcar miller for milling the first bore in the femoral
neck;
[0033] FIG. 4F is a view showing the calcar milling guide and
calcar miller for milling the first bore in the femoral neck with
the angle guide omitted for clarity;
[0034] FIG. 4G is a view showing a drill pin guide, a trocar point
guide pin and a drill point guide pin for drilling through the
lateral femoral cortex;
[0035] FIG. 4H is a view showing the drill point guide pin and a
cannulated cortex drill for drilling through the lateral femoral
cortex;
[0036] FIG. 4I is a view showing the insertion of a calcar planing
guide in the femoral neck;
[0037] FIG. 4J is the view of FIG. 4I, but with the calcar planing
guide removed;
[0038] FIG. 4K is a view showing the calcar planing guide and the
calcar planer for planing of the femoral neck;
[0039] FIG. 4L is a view showing the implantation of the
prosthesis;
[0040] FIG. 4M shows the start of the more preferred implantation
steps and is a view showing the calcar miller for milling the first
bore;
[0041] FIG. 4N is a view showing the angle guide, calcar milling
guide, cannulated pin guide, trocar point guide pin and drill point
guide pin for drilling through the posterolateral femoral
cortex;
[0042] FIG. 4P is a view showing the drill point guide pin and
cannulated cortex drill for drilling through the posterolateral
femoral cortex;
[0043] FIG. 4Q is a view showing the offset reaming guide and
cannulated reamer for reaming the second bore in the femoral
neck;
[0044] FIG. 4R is a view showing the calcar planing guide and
calcar planer for planing of the femoral neck;
[0045] FIG. 4S is a view showing the implanted prosthesis;
[0046] FIG. 5A is a perspective view of the split stem prosthesis
of FIG. 1;
[0047] FIG. 5B is a front elevational view thereof;
[0048] FIG. 5C is a left side elevational view thereof;
[0049] FIG. 5D is a right side elevational view thereof;
[0050] FIG. 5E is a top plan view thereof;
[0051] FIG. 5F is a bottom plan view of the split stem
prosthesis;
[0052] FIG. 5G is a sectional view of the split stem prosthesis
taken in the plane of line 5G-5G in FIG. 5B;
[0053] FIG. 5H is an enlarged bottom end view of the stem of the
split stem prosthesis showing splines on the stem;
[0054] FIG. 6 is a perspective view of a solid stem prosthesis;
[0055] FIG. 7A is a perspective view of an angle guide;
[0056] FIG. 7B is a left side elevational view thereof;
[0057] FIG. 7C is a front elevational view thereof;
[0058] FIG. 8A is a perspective view of a bracket of an angle
guide;
[0059] FIG. 8B is a front elevational view thereof;
[0060] FIG. 8C is a top plan view of a bracket thereof;
[0061] FIG. 8D is a left side elevational view thereof;
[0062] FIG. 9A is a perspective view of an arm of the angle
guide;
[0063] FIG. 9B is a front elevational view thereof;
[0064] FIG. 9C is an enlarged, fragmentary front elevational view
of the left end of the arm;
[0065] FIG. 9D is a top plan view of the arm of the angle
guide;
[0066] FIG. 9E is a left side elevational view thereof;
[0067] FIG. 10A is perspective view of a calcar miller guide;
[0068] FIG. 10B is a front elevational view thereof;
[0069] FIG. 10C is a front elevational view thereof;
[0070] FIG. 10D is a bottom plan view thereof;
[0071] FIG. 11A is a perspective view of a calcar miller;
[0072] FIG. 11B is an elevational view of the calcar miller;
[0073] FIG. 11C is a bottom end view of the calcar miller;
[0074] FIG. 12A is an elevational view of a cannulated pin
guide;
[0075] FIG. 12B is a perspective view of the cannulated pin
guide;
[0076] FIG. 12C is a bottom end view thereof;
[0077] FIG. 12D is a fragmentary, elevational view of the
cannulated pin guide showing the bottom end;
[0078] FIG. 13A is a perspective view of the cannulated cortex
drill;
[0079] FIG. 13B is a front elevational view of a cannulated cortex
drill;
[0080] FIG. 13C is a bottom end view thereof;
[0081] FIG. 13D is a fragmentary front elevational view of a top
end of the cannulated cortex drill;
[0082] FIG. 14A is a front view of the offset reaming guide;
[0083] FIG. 14B is a front elevational view thereof;
[0084] FIG. 14C is a left side elevational view thereof;
[0085] FIG. 14D is a top plan view of the offset reaming guide;
[0086] FIG. 14E is a bottom plan view of the offset reaming
guide;
[0087] FIG. 15A is a perspective view of the cannulated reamer;
[0088] FIG. 15B is an elevational view of a cannulated reamer;
[0089] FIG. 15C is a bottom end view of the cannulated reamer;
[0090] FIG. 15D is an enlarged, fragmentary elevational view of the
cannulated reamer showing an upper end;
[0091] FIG. 16A is a perspective view of a calcar planing
guide;
[0092] FIG. 16B is a left side elevational view thereof;
[0093] FIG. 16C is a top plan view of the calcar planing guide;
[0094] FIG. 16D is a front elevational view of a calcar planing
guide of a second embodiment;
[0095] FIG. 17A is a perspective view thereof;
[0096] FIG. 17B is a front elevational view of a calcar planer;
[0097] FIG. 17C is a bottom end view thereof;
[0098] FIGS. 18A-18Q illustrate a most preferred embodiment of a
method for implanting the prosthesis;
[0099] FIG. 18A is a view of the femur showing the axis of the
medial trabecular stream;
[0100] FIG. 18B is a view showing setting of the angle guide prior
to mounting on the femur;
[0101] FIG. 18C is a view showing the angle guide and the saw guide
around the femur for femoral neck resection;
[0102] FIG. 18D is a view showing an initial reaming step;
[0103] FIG. 18E is the view of FIG. 18D in vertical section with
the angle guide removed;
[0104] FIG. 18F is a view showing sizing the femur for selection of
the appropriate prosthesis;
[0105] FIG. 18G is a view showing a calcar miller milling the first
bore;
[0106] FIG. 18H is a view showing a pin guide and drill point guide
pin for use in drilling through the posterolateral femoral
cortex;
[0107] FIG. 18I is a view showing the drill point guide pin after
removal of the pin guide;
[0108] FIG. 18J shows a cortical drill and sleeve used to drill the
posterolateral femoral cortex;
[0109] FIG. 18K shows the cortical drill as received on the guide
pin after drilling through the posterolateral femoral cortex;
[0110] FIG. 18L is a view showing an offset reaming guide and
cannulated reamer for reaming the second bore in the femoral
neck;
[0111] FIG. 18M is a view showing the calcar planing guide and
calcar planer for planing of the femoral neck;
[0112] FIG. 18N is a view illustrating installation of the
prosthesis employing a removable bullet tip;
[0113] FIG. 18P is a view illustrating an installed prosthesis;
[0114] FIG. 19A is a side elevation of a prosthesis having and a
saw template mounted on the prosthesis for use in seating the
prosthesis;
[0115] FIG. 19B is a fragmentary cross section of an upper portion
of the femur and saw template as shown in FIG. 19A, as seen from a
position generally medial of the femur;
[0116] FIG. 19C is a top plan view of the femur and saw
template;
[0117] FIG. 19D is a section taken in a plane including line
19D-19D of FIG. 19A;
[0118] FIG. 20 is a plot of test results on the prosthesis of the
present invention.
[0119] FIG. 21 is a front elevation of a prosthesis of a fourth
embodiment;
[0120] FIG. 22 is a right side elevation thereof;
[0121] FIG. 23 is a left side elevation thereof;
[0122] FIG. 24 is a top plan view of the prosthesis of the fourth
embodiment;
[0123] FIG. 25 is a bottom plan view thereof;
[0124] FIG. 26 is a front elevation of a prosthesis of a fifth
embodiment;
[0125] FIG. 27 is a right side elevation thereof;
[0126] FIG. 28 is a top plan view thereof;
[0127] FIG. 29 is a front elevation of a prosthesis of a sixth
embodiment;
[0128] FIG. 30 is a right side elevation thereof;
[0129] FIG. 31 is a bottom plan view of the prosthesis of the sixth
embodiment;
[0130] FIG. 32 is a front elevation of a prosthesis of a seventh
embodiment;
[0131] FIG. 33 is a right side elevation thereof;
[0132] FIG. 34 is a schematic, fragmentary cross section of an
upper femur showing a prior art femoral head-neck prosthesis
implanted in the femur (the prosthesis being shown in full
lines);
[0133] FIG. 35 is a schematic, fragmentary cross section of an
upper femur showing a femoral head-neck prosthesis of the present
invention implanted in the femur (the prosthesis being shown in
full lines);
[0134] FIGS. 36A-B illustrate a step in a method for determining
the axis of an implanted prosthesis;
[0135] FIG. 37 is an enlarged fragmentary cross section similar to
FIG. 35 illustrating insertion of a pin in the prosthesis (the
single line to the right of the femur and prosthesis is intended to
represent the surface of the skin of the thigh through which the
pin extends);
[0136] FIGS. 38A-B illustrate insertion of the pin in the
prosthesis using a centering guide (the single line to the left of
the centering guide is intended to represent the femur through
which the prosthesis projects);
[0137] FIG. 39 is an enlarged, schematic perspective view of a
cannulated brush prior to insertion in the prosthesis;
[0138] FIGS. 40A-D illustrate a method of attaching an infusion
assembly to the prosthesis
[0139] FIG. 40A is a perspective view of the infusion assembly and
wrench for installing the assembly;
[0140] FIG. 40B is a perspective view of the infusion assembly and
the threaded passageway of the prosthesis;
[0141] FIG. 40C is a schematic, fragmentary cross section similar
to FIG. 37 illustrating a syringe attached to the infusion
assembly; and
[0142] FIG. 40D is a fragmentary cross section similar to FIG. 37
illustrating the infusion port assembly and a syringe inserted in
the infusion port.
[0143] Corresponding reference characters indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0144] (a) The Femoral Head-Neck Prosthesis
[0145] Referring now to the drawings, and in particular to FIGS. 1,
1A and 1B, a transosseous, non-cemented femoral head-neck
prosthesis of the present invention (indicated generally at 1) is
shown as implanted in a femur F. The femur includes a femoral shaft
S, a femoral head H, neck N and a greater trochanter T at the upper
end of the shaft at the lateral side of the femur. The femur F has
a hard layer of cortical bone C adjacent the surface of the bone,
relatively soft cancellous bone and endosteum (not shown) inside
the femur. The prosthesis 1 is made of cobalt-chrome alloy,
titanium or other suitable material, and has a longitudinal axis
generally indicated at AX-1. As implanted, the prosthesis 1 extends
generally from the resected femoral neck N diagonally across the
medullary canal MC and out (posterolaterally) an opposite side of
the femur. The prosthesis 1 is of the type which is not cemented
into the femur F, but is secured by mechanical interconnection of
the prosthesis with the bone, as described more fully hereinafter.
The prosthesis 1 is constructed so that it is securely held in the
bone from rotation (about its longitudinal axis AX-1) and toggling
(anterior-posterior and medial-lateral) motion, while permitting
axial micromotion to achieve natural bone loading condition thereby
to preserve the bone.
[0146] The prosthesis 1 has a generally spherical ball 3 which is
received in a cup (not shown) implanted in the hip socket (not
shown) to permit movement at the hip joint. Referring now
additionally to FIGS. 5A-5H, the ball 3 is fixedly attached to an
upper portion 5A of a neck 5 of the prosthesis which is received in
a hole (not shown) in the underside of the ball. The neck 5 is
generally cylindrical in shape and includes a lower portion 5B
below the upper portion 5A which is of a smaller diameter than the
upper portion. The lower portion 5B of the neck is mounted on a
collar (generally indicated at 7) of the prosthesis 1 which rests
against the femoral neck N, as shown in FIG. 1, and transmits loads
to the upper femur. As shown, the continuous, circumferential
collar 7 is sized and shaped to extend outward laterally,
anteriorly, medially and posteriorly to cap the medullary canal
MC.
[0147] The collar 7 includes a neck platform 9 on which the neck 5
is mounted, and a curved flange 11 which engages the greater
trochanter T of the femur. The underside of the neck platform 9A
has a slight frustoconical shape and the underside of the flange
11A has the shape of a section of cone. In the preferred
embodiment, the underside 9A of the platform makes an angle of
about 10.degree. with a plane perpendicular to the longitudinal
axis AX-1 of the prosthesis. The shape of the underside 9A and its
close correspondence to the shape of the seat formed on the
resected neck N allow the collar 7 to cap the medullary canal MC
and inhibit migration of debris and fluid into the medullary canal
after implantation of the prosthesis 1. By inhibiting migration of
fluid into the medullary canal, the prosthesis reduces the fluid
pressure at the implant-bone interface and thereby inhibits bone
deterioration. The curved underside 11A of the flange makes an
angle of about 60.degree. with the same plane. Thus, the underside
(9A, 11A) of the collar 7 defines a compound angle. The flatter
neck platform 9 lies on the partially resected femoral neck N, and
the flange 11 rests against the greater trochanter T of the femur.
The greater trochanter is the primary sight of muscle attachment to
the femur F at the hip. The upstanding flange 11 permits the collar
7 to solidly support the prosthesis 1 on cortical bone C on the
upper femur while allowing most of the greater trochanter T to be
preserved. Use of a substantially flat collar (not shown) would
require resection of a substantial portion of the trochanter T to
provide room for the collar. The underside (9A, 11A) of the collar
7 of the present invention engages and is supported by the hard
cortical bone C of the femur.
[0148] In the preferred embodiment, the underside 9A of the neck
platform 9 and underside 11A of the flange 11 are coated with a
porous material (not shown) to facilitate bone growth into the
collar 7 where it rests on the upper end of the femur F. However,
the remaining portions of the collar 7 and all other parts the
prosthesis 1 preferably remain free of porous coating, roughening
or other construction which would encourage bone growth into the
prosthesis. It is to be understood that the use of porous coating
or other structure to facilitate bone ingrowth into the prosthesis
1 may be other than described and still fall within the scope of
the present invention.
[0149] A stem, generally indicated at 13, mounted on the underside
of the collar 7 extends generally downwardly through the femur F.
In the preferred embodiment, the neck 5, collar 7 and stem 13 are
formed as one piece. The longitudinal axis AX-2 of the neck 5 is
parallel to the longitudinal axis of the stem, which is coincident
with the longitudinal axis AX-1 of the prosthesis 1. As installed,
the prosthesis 1 is substantially parallel to an axis AX-5 (FIG.
1A) corresponding to the direction of the normal loading vector of
the hip so that forces from the hip are applied compressively to
the neck 5 which transmits those forces (via the collar 7)
compressively to the femoral neck N. Axial fixation of the
prosthesis 1 in the bone is achieved by bone ingrowth of the upper
femur F into the collar 7. As described more fully hereinafter,
axial fixation of the stem 13, caused by bone ingrowth into the
stem and/or strain hardening of bone engaging the stem, is
prevented by construction of the stem.
[0150] The stem 13 includes an upper portion and a lower portion
(designated generally by reference numerals 15 and 17,
respectively). The radially outwardly facing surfaces of the stem
13 disposed for engaging the interior of the femur F are, broadly,
"fixation surfaces." The lower portion 17 is sized for a close fit
within the femur F, and has longitudinally extending splines 19
(see FIGS. 3 and 5H) which penetrate the bone inside the femur to
secure the prosthesis 1 in the femur. The lower portion 17 has a
longitudinal split 21 to accommodate normal load deflection of the
proximal femur. The splines 19 hold the prosthesis 1 securely
against rotational movement about the longitudinal axis AX-1 of the
prosthesis after implantation, and encourage bone growth between
the splines. However, although the splines 19 resist axial
displacement of the prosthesis 1 relative to the femur F, the
splines do not rigidly fix the prosthesis against axial
micromotion. To provide additional fixation of the prosthesis 1,
splines (not shown) may also be formed on the upper portion 15 of
the stem.
[0151] A more preferred embodiment of a prosthesis 1' is shown in
FIG. 6 has a solid lower stem portion 17'. It is believed that the
solid stem provides for greater accuracy in installation and
prevents axial fixation which potentially might occur through
ingrowth of bone into the slot 21 of the prosthesis 1. A still more
preferred embodiment of a prosthesis 1" is shown in FIGS. 18P and
19 to have a flat underside 9A" of the collar 7".
[0152] The distal end of the lower portion 17 of the stem 13 is cut
on an angle to the longitudinal axis, so that the distal end of the
lower portion is somewhat pointed. Moreover, the distal end of the
lower portion 17 is generally aligned with or parallel to the outer
surface of the femur F on the posterolateral side. The lower
portion 17 preferably extends outwardly from the posterolateral
side of the femur F to inhibit bone growth over the distal end of
the lower portion which would fix the prosthesis 1 in an axial
direction and prevent the natural loading at the upper end of the
femur by the collar 7.
[0153] The upper portion 15 of the stem 13 generally has the shape
of overlapping cylinders near the collar 7 (see FIG. 5G). A first
overlapping cylindrical element of the upper portion is designated
23, and a second overlapping cylindrical element of the upper
portion is designated 25. The first (smaller) cylindrical element
23 is co-axial with the longitudinal axis AX-1 of the prosthesis 1,
while the second (larger) cylindrical element 25 has an axis which
is parallel to the first cylindrical element and radially offset a
distance from the axis AX-1 less than the sum of the radii of the
first and second cylindrical elements. The first cylindrical
element 23 has a diameter greater than the coaxial stem lower
portion 17 of the stem. The diameter of the lower portion 17 is
kept small to minimize the size of the opening formed in the
posterolateral femoral cortex. As an example, if the diameter of
the first element 23 were 15 mm, the diameter of the lower portion
17 would be about 12 mm. The shape of the upper portion 15 is
defined by the portions of the first and second cylindrical
elements 23, 25 which are not overlapping. The offset, eccentric
location of the second element 25 causes the upper portion 15, as
received in the bores B1, B2 to hold the prosthesis against
rotation about axis AX-1. A lower end surface 25A of the second
cylindrical element is cut in a plane which makes an angle of
approximately 30.degree. with respect to the longitudinal axis
AX-1.
[0154] As illustrated by FIGS. 2A-D, the upper portion 15 of the
stem 13 contacts the endosteal neck cortex of the femur F only in
discrete areas around the circumference of the upper portion. The
cross sectional views of the drawings (taken as indicated in FIG.
1) schematically illustrate the regions of engagement of the cortex
and the upper portion 15 of the stem at four distinct locations
along the length of the upper portion. It will be noted that
engagement does occur at three spaced apart locations around the
upper portion 15 so that the upper portion is able to provide good
fixation against both rotation motion of the prosthesis 1 about its
longitudinal axis AX-1 and toggling motion of the prosthesis about
axes perpendicular to the longitudinal axis.
[0155] However, the discrete areas of contact do not rigidly fix
the upper portion 15 of the stem 13 against axial movement relative
to the femur F. The limited area of contact reduces the frictional
interaction of the prosthesis 1 and bone in the endosteal neck
cortex. Moreover, the upper stem portion 15 has smooth exterior
walls which substantially prevent bone from growing into the upper
stem portion thereby to prevent axial fixation of the prosthesis by
bone ingrowth. Thus, the upper stem portion 15 will not prevent
loads from the hip from being applied compressively to the upper
end of the femur F. This more natural loading of the femur induces
more natural straining of the upper femur and prevents
deterioration of the upper femur, which is important to maximizing
the useful life of the implanted prosthesis 1.
[0156] (b) Instruments used to Implant the Prosthesis
[0157] While a number of different instruments may be helpful for
implanting the femoral head-neck prosthesis 1, an angle guide
generally designated at 29 and shown in FIGS. 7A-7C is particularly
adapted to be removably secured to the femoral shaft S for holding
a plurality of cutting, drilling and reaming accessories in
position with respect to the femur F. The angle guide 29 comprises
a bracket 31 (see FIGS. 8A-8D) having a first member 31A adapted to
be removably secured by a suitable clamp (not shown) in
face-to-face engagement with the femoral shaft S. A second member
31B extends outwardly from the first member 31A and includes an
arcuate faceplate 31C. A guide sleeve 33 or outrigger portion (see
FIGS. 9A-9E) is capable of extending at a selected angle upwardly
and outwardly from the bracket 31 at one side of the femoral shaft.
The guide sleeve 33 includes a mounting member 33A attached to the
bracket 31 by a screw 35. The guide sleeve 33 may be angularly
adjusted relative to the bracket 31 by loosening the screw 35 and
turning the guide sleeve on the screw to a selected angular
position. The faceplate 31C carries indicia which are pointed to by
a pointer 37 associated with the mounting member 33A to show the
angle of the guide sleeve. The angle is selected so that the guide
sleeve 33 extends from the bracket 31 along a line substantially
parallel to the previously determined average compression loading
vector (the "normal" direction in which the femur F is loaded,
AX-5) for the femur of the specific patient when the bracket is
attached to the femur. The guide sleeve 33 has a through hole 39
for receiving and holding other instruments in the same angular
position as the guide sleeve.
[0158] As noted above, angle guide 29 is adapted for holding a
variety of different instruments used in implanting the prosthesis
1 of the present invention. One such instrument is a saw guide 41
(see FIG. 4B) which can be detachably mounted in the through hole
39 of the guide sleeve 33 for guiding a saw blade (not shown) to
cut the femoral neck N. The saw guide 41 has a sawcut slot 41A
generally perpendicular to the central longitudinal axis of guide
sleeve 33. The saw guide 41 is slidably adjustable in the through
hole 39 to properly position it with respect to the femoral neck N.
A set screw 43 of the angle guide 29 is provided for securing the
saw guide 41 in adjusted position.
[0159] Referring now to FIGS. 10A-10D a calcar miller guide,
generally indicated at 45, has an outrigger portion 47 receivable
in the through hole 39 of the angle guide 29 for mounting on the
angle guide in the same manner as the saw guide 41. The calcar
miller guide has a guide tube 49 attached to the outrigger portion
47. Calcar miller guide 45 is slidably adjustable along guide
sleeve 33 in the through hole 39 to properly position it with
respect to the femoral neck seat of the femoral neck N. The calcar
miller guide 45 is fixedly held from rotation with respect to the
guide sleeve 33. The position of the calcar miller guide tube 49
over the femoral neck N defines the axis AX-1.
[0160] A number of calcar millers (not shown) are provided having
progressively larger diameters to gradually increase the side of
the hole formed in the femur F. A final calcar miller 51 (FIGS.
11A-11C) is sized to mill the first bore B1 in the medial endosteum
to provide a close fit between the prosthesis 1 and the medial
endosteum.
[0161] A cannulated pin guide 53 (FIGS. 12A-12D) is sized to be
received through the guide tube 49 of the calcar miller guide 45
and to be slidably received in the first bore B1 created by a
calcar miller 51 in the femoral neck N. The cannulated pin guide 53
has a central axial passage 55 to slidably receive a trocar point
guide pin 57 (FIG. 4N) and a drill point guide pin 59 (FIG. 4P).
The trocar point guide pin 57 and the drill point guide pin 59 have
the same diameter, e.g., 3.5 mm.
[0162] A cannulated cortex drill 61 (FIGS. 13A-13D) is sized to be
slidably received over the drill point guide pin 59. The cannulated
cortex drill 61 is sized to drill a bore through the posterolateral
femoral cortex C that is slightly smaller in diameter than the
distal stem of the prosthesis 1 (e.g., 9 mm for a 9.5 mm diameter
prosthesis stem).
[0163] An offset reaming guide, generally indicated at 63 (FIGS.
14A-14E), is sized to be slidably received in the first bore B1.
The offset reaming guide 63 comprises a trunnion 65 and guide
finger 67 mounted on a platform 69, and a distal end section 71.
The distal end section 71 of the offset reaming guide 63 is sized
(14 mm in the illustrated embodiment) to allow passage through the
first bore B1 and has a bullet distal end to facilitate passage
through the first bore. The exterior shape of the platform 69 (as
seen from the ends of the reaming guide 63) is generally that of
non-overlapping surfaces of two axially parallel, radially
overlapping cylinders (see FIGS. 14C and 14E). A larger cylinder
69A of the overlapping cylinders coaxial with the axis of the
distal end section 71 of the reaming guide 63 is larger than that
of a smaller cylinder 69B. The smaller cylinder 69B is cut on a
plane angling downwardly toward the intersection with the larger
cylinder 69A. The largest transverse dimension of the platform 69
is about 15 mm to provide line-to-line fit with the first bore B1.
However, it is to be understood that the transverse dimension of
the platform will vary depending upon the size of the bone.
[0164] The guide finger 67 is disposed parallel to and generally in
registration with the trunnion 65. The guide finger 67 engages the
endosteal wall in the femur F to facilitate holding the trunnion 65
in position as a cannulated reamer 73 (see FIGS. 15A-15D) cuts the
bone. The trunnion 65 is cylindrical and offset about 6 mm from the
central longitudinal axis of the distal end section 71 of the
offset reaming guide 63. The precise offset distance will vary
depending upon the size of the bone in which the prosthesis 1 will
be installed. The trunnion 65 is sized to receive the cannulated
reamer 73 thereon and to permit rotation of the cannulated reamer
on the trunnion for reaming the bone while guiding the reamer along
a line parallel to the axis AX-1 of the first bore B1 formed in the
femur F. The cannulated reamer 73 forms the second bore B2.
[0165] A calcar planing guide, generally indicated at 75, comprises
a stem 77 including an upper portion 77A and a lower portion 77B,
and a trunnion 79 generally coaxial with the stem (FIGS. 16A-16D).
The calcar planing guide 75 has a bullet shaped distal tip to aid
in passage through the first bore B1. The shape of the stem 77 is
generally the same as that of the prosthesis 1 except that the
lower stem portion 77B is smooth (i.e., lacking the splines 19 of
the prosthesis). The upper portion 77A of the stem is received in a
double bore (first B1 and second B2) arrangement formed in the
femur neck. The calcar planing guide 75 fits snugly in the first
and second bores B1, B2 to hold the planing guide from moving
within the femur F. The exterior surface of the stem 77 is smooth
in the embodiment illustrated in FIGS. 16A and 16B.
[0166] However, the calcar planing guide should preferably
correspond closely to the shape of the prosthesis 1. FIG. 16D
illustrates an embodiment of a calcar planing guide 75' in which
the stem 77' has splines 77C' corresponding identically to the
splines 19 of the prosthesis. In the event the prosthesis 1 also
had splines (not shown) on the upper portion 15 of its stem 13,
similar splines (not shown) would be formed on the upper portion
77A' of the planer guide stem 77'. By more precisely matching the
shapes of the stems (13, 77') of the prosthesis 1 and planing guide
75', a greater congruency of the underside (9A, 11A) of the collar
7 and the seat formed on the neck N may be achieved.
[0167] A calcar planer of the present invention (generally
indicated at 81) forms a seat for the collar 7 of the prosthesis 1
on the resected neck N of the femur F (see FIGS. 17A-17C). The
calcar planer 81 comprises a head, generally indicated at 83, and a
shaft 85 extending axially from the head. The calcar planer head
has a central axial passage 87 which receives the trunnion 79 of
the planing guide 75 therein to mount the planer on the planing
guide for rotation relative to the planing guide on the trunnion.
The bottom 89 of the head 83 has the shape of a frustum of a cone.
The angle of the cone to a plane perpendicular to the central
longitudinal axis AX-1 is about 10.degree. when the planer 81 is
mounted on the planer guide 75. The side 91 of the head 83 is also
conical in shape, making an angle of about 60.degree. with the
plane perpendicular to the central longitudinal axis AX-1. The
shape of the head 83 corresponds closely to the shape of the
underside (9A, 11A) of the collar 7.
[0168] In the event the prosthesis 1" having a flat underside 9A"
is to be installed, the bottom 89' of the head 83' of the calcar
planer 81' is also flat. The calcar planer 81' having a flat bottom
89' is illustrated in FIG. 18M. It is believed the use of the flat
bottomed calcar planer 81' and prosthesis 1" increases the chance
of obtaining a very high level of congruency between the prosthesis
and the seat on the neck N formed by the calcar planer.
[0169] (c) Method of Implanting the Prosthesis
[0170] The method of the present invention for implanting the
prosthesis 1 assures close replication of normal loading of the
femur F (i.e., loading prior to implantation of the prosthesis).
One preferred method of the present invention is illustrated in
FIGS. 4A, 4B and 4M-4S. A lesser preferred method is illustrated in
FIGS. 4A-4L. A most preferred method is illustrated in FIGS.
18A-18P. A femoral head-neck prosthesis which fails to replicate
normal loading conditions will change the stress distribution
through the femur F. As mentioned in U.S. Pat. No. 4,998,937,
incorporated herein by reference, according to Wolff's law these
changes in stress distribution eventually cause alterations in the
internal structure of the bone. Those portions subject to a lesser
stress than before are likely to deteriorate and those subject to
greater stress than before are likely to thicken. Excessive
increases in stress over those associated with normal loading may
kill the bone cells if the stress is applied over an extended
period of time. To replicate normal loading, the method of the
present invention aligns the stem 13 of the prosthesis 1 with the
average compression loading vector for the particular femur, which
vector is variable from person to person.
[0171] Referring to FIG. 1A, the human femur F has two externally
visible axes: the axis of the femoral neck AX-4 and the axis of the
femoral shaft AX-3. However, the bone is not loaded along either of
these two visible axes, but rather is loaded through a third axis
(parallel to the average compression loading vector) which is not
externally apparent. In response to compressive loading and the
strain energy density experienced by the femur F, reinforcing lines
of bone, which are called compression trabeculae, form within the
femur. The collection of these reinforcing lines is the compression
trabecular stream TS. The particular collection of compression
trabeculae in the femur neck, as shown in FIG. 1A, is referred to
as the medial trabecular stream TS, and the average direction of
the medial trabecular stream may be referred to as the medial
trabecular stream axis AX-5. Angle .THETA. which axis AX-5 makes
with the central longitudinal axis of the femur shaft AX-3
generally ranges from 140 to 170 degrees. In practice, this angle
is measured from a profile X-ray of the hip between the axis AX-5
and a lateral surface of the femur F (see FIG. 4A). The use of the
medial trabecular stream TS to position the prosthesis 1 is
discussed in U.S. Pat. No. 4,998,937.
[0172] To install the prosthesis 1 in the femur F in accordance
with the method of this invention, the hip joint and the lateral
side of the femur are first surgically exposed. A vertical plane
P-1 through the central longitudinal axis AX-2 of the femoral neck
is typically at an angle of approximately 15 degrees anterior to a
lateral-medial plane P-2 through the central longitudinal axis AX-3
of the femoral shaft, as shown in FIG. 1B. This angle is commonly
referred to as the "anteversion" of the femoral neck. Accordingly,
the angle guide 29 is positioned radially on the femur F such that
the vertical axis of bracket 31 lies in plane P-1 approximately 15
degrees posterior from the lateral-medial plane P-2 (since the
bracket is lateral of axis AX-3 and the femoral neck 7 is medial).
In this position, a vertical plane P-3 through guide sleeve 33
should be parallel to plane P-1. In addition, the angle guide 29 is
positioned proximally-distally on the femur F such that the upper
end of guide sleeve 33 is centered with respect to the base of the
femoral neck, as shown in FIG. 1B. The angle guide 29 is then
clamped on the femoral shaft S by a clamp (not shown). The guide
sleeve 33 is adjusted, by loosening screw 35, relative to the
bracket 31 so that its angle relative to the central axis AX-3 of
the femur shaft S matches the angle .THETA. of the medial
trabecular stream TS. This is accomplished by aligning pointer 37
of the guide sleeve with the appropriate angle indicated on the
faceplate 31C of the bracket 31.
[0173] The saw guide 41 is positioned (proximally-distally) on
guide sleeve 33 such that the sawcut slot 41A is located adjacent
the base of the femoral neck N and generally aligned with the upper
surface of the lateral femoral cortex of the femur F, as shown in
FIG. 4B. In this position, the sawcut slot should be perpendicular
to the medial trabecular stream TS. Set screw 43 is tightened to
firmly attach the saw guide 41 in the guide sleeve 33 of the angle
guide 29.
[0174] With the saw guide 41 in place, the femoral neck N is cut
with an oscillating saw (not shown) by passing the saw through the
sawcut slot 41A to form a cut surface extending from the lateral
femoral cortex at an angle of approximately 60 degrees with respect
to the central longitudinal axis AX-3 of the femoral shaft S. The
saw guide 41 is then removed from the guide sleeve 33, leaving the
angle guide 29 attached to the femoral shaft S in its original
position, and the femoral head H is removed.
[0175] If a total hip replacement (i.e., replacement of the femoral
head H and acetabulum (not shown) is required, the acetabulum
should now be prepared.
[0176] In the first preferred embodiment, as shown in FIGS. 4A, 4B
and 4M-4S, the calcar miller guide 45 is secured to the guide
sleeve 33, which effectively centers the calcar miller guide with
respect to the cut surface of the femoral neck N. The angle guide
29 also aligns the calcar miller guide 45 parallel to the axis
AX-5. A starter hole is drilled into the femoral neck 7.
[0177] A miller (not shown) of relatively small milling diameter is
slidably received in the calcar miller guide 45 to mill the femoral
neck. The femoral neck N is milled by a progression of end and side
cutting millers, with each succeeding miller having a larger
diameter than the preceding miller. The femoral neck N has an inner
lining (or surface) referred to as the endosteum. The final milling
diameter is determined for the individual femur to provide an
appropriate diameter of the first bore B1 adjacent to the medial
endosteum. The calcar miller 51 of the appropriate diameter mills a
bore in the medial endosteum to the final diameter (e.g., 15 mm).
The calcar miller 51 is then removed from the calcar miller guide
45 (FIG. 4M).
[0178] As shown in FIG. 4N, the cannulated pin guide 53 is received
in the calcar miller guide 51 and into the first bore B1 in the
medial endosteum. The trocar point guide pin 57 is received in the
cannulated pin guide axial passage 55 to make a starter mark on the
lateral endosteum. After the starter mark is made, the trocar point
guide pin 57 is removed from the passage 55. The drill point guide
pin 59 is then received in the cannulated pin guide axial passage
55 and is used to drill through the posterolateral femoral cortex
C, forming an oblique hole in the posterolateral femoral cortex.
The drill point guide pin 59 is left in place after drilling the
oblique hole in the cortex, the cannulated pin guide 53 is removed
from the femur F and the calcar miller guide 45 is removed from the
guide sleeve 33 of the angle guide 29.
[0179] As shown in FIG. 4P, the cannulated cortex drill 61 is
received over the drill point guide pin 59 to drill through the
posterolateral femoral cortex C on the same axis as the first bore
B1 milled by the calcar miller 51. Cortex drill 61 drills the
oblique hole to a diameter that is smaller than the first bore B1
formed in the femur F. The cannulated cortex drill 61 and the drill
point guide pin 59 are then removed from the femur 3.
[0180] The offset reaming guide 63 is then placed into the first
bore B1 bullet end first. A first cannulated reamer (not shown) is
received on the trunnion 65 to ream the second bore B2 in the
femoral neck N which is parallel to the first bore B1. A
progression of cannulated reamers (not shown) are used, with each
succeeding reamer having a larger diameter. The final cannulated
reamer 73 reams the second bore B2 to a diameter which achieves
line-to-line contact between the prosthesis 1 and the endosteum
(FIG. 4Q). After the second bore B2 is reamed to a depth to
accommodate the upper stem portion 15 of the prosthesis 1, the
cannulated reamer 73 and the offset reaming guide 63 are removed
from the femur F.
[0181] Referring to FIG. 4R, the calcar planing guide 75 is
inserted into the proximal side of the first bore B1 and through
the oblique hole in the posterolateral cortex C. The central
longitudinal axis of the trunnion 79 and the stem 77 of the calcar
planing guide 75 are collinear with the first bore B1. The calcar
planer 81 is then placed on the trunnion 79 and the surface of the
femoral neck is planed generally perpendicular to the axis (AX-1)
of the first bore B1 while even pressure is applied to the calcar
planer to form a seat for the collar 7 of the prosthesis 1. The
greater trochanter T is substantially preserved by the calcar
planer 81. Only an angled segment of the trochanter T is cut away
providing an angled seat for the flange 11 of the collar 7. In this
way, a secure engagement of the prosthesis 1 on the cortical bone C
of the upper femur is achieved without sacrificing a substantial
portion of the trochanter T (FIG. 1).
[0182] The bottom 89 of the calcar planer 81 is slightly cupped so
that the portion of the seat on the femoral neck N slopes
downwardly toward the axis AX-1. The shape of this portion of the
seat is complimentary to that of the underside 9A of the prosthesis
collar 7. The cup shape of the seat on the femoral neck N helps to
locate the prosthesis 1. Moreover, when the underside of the collar
7 and the seat are congruent, the entire area of the seat engages
the underside (9A, 11A) of the collar 7 and is subjected to loading
by the prosthesis 1. Loading of the bone material of the seat over
the entire area of engagement with the collar surface (9A, 11A)
prevents resorption (withdrawing) of the bone after the prosthesis
1 is implanted. However, although macroscopic congruence is
important, microscopic roughness or porosity of the collar
undersurface (9A, 11A) possibly combined with bioactive or chemical
coating (e.g., calcium phosphate compound) allows an ingrowth of
bone from the seat which facilitates bonding of the collar surface
with the seat. Because the collar undersurface (9A, 11A) achieves
one hundred percent cortical contact and transmits substantially
one hundred percent of the cortical loading, the chemical coating
is used only on the underside of the collar 7 and at no locations
on the stem 13. After planing, the calcar planer 81 and the calcar
planer guide 75 are removed.
[0183] The prosthesis 1 (without the ball 3) is then implanted by
driving the stem 13 into the first bore B1 as shown in FIG. 4S. The
splines 19 of the stem bite into the walls of the first bore B1 and
the stem protrudes slightly through the oblique hole so that
cortical bone does not later grow over the end of the stem. Growth
of bone over the end of the stem 13 would be undesirable since it
would impede the ability of the prosthesis 1 to transmit loads from
the hip to the upper femur. The upper stem portion 15 fits closely
into the first bore B1. The underside 9A of the collar platform 9
is congruent with the portion of the seat which was formed by the
bottom 89 of the calcar planer head 83 and the underside 11A of the
flange 11 is congruent with the portion of the seat on the
trochanter T formed by the side 91 of the calcar planing head.
[0184] Once the prosthesis 1 is implanted, an appropriately sized
ball 3 is then locked onto the neck.
[0185] In a second, lesser preferred embodiment, the procedure is
somewhat modified. Referring to FIGS. 4C and 4D, after the femoral
neck N is resected, a reamer guide 95 (similar in construction to
the calcar miller guide 45) is secured to the guide sleeve 33 of
the angle guide 29, which effectively centers the reamer guide over
the femoral neck N so that the second bore B2 is formed first. As
before, the second bore B2 is formed by a progression of reamers
(not shown), with each succeeding reamer having a larger diameter
than the preceding reamer. The final reamer 97 has a diameter of 21
mm, so that the femoral neck N is reamed to a diameter of 21 mm.
The reamer guide 95 is then removed from the guide sleeve 33,
leaving the angle guide 29 attached.
[0186] A calcar miller guide 99 having a trunnion 101 is attached
to the angle guide 29 and the first bore B1 is formed by milling
with a series of calcar millers including final calcar miller 103
(FIGS. 4E and 4F). The angle guide 29 is removed in FIG. 4F to more
clearly show the calcar miller guide 99. The calcar miller guide 99
is removed from the angle guide 29 and a drill pin guide 105 is
mounted on the angle guide. Referring to FIG. 4G, the upper portion
of the drill pin guide 105 has a double cylinder construction
similar to the upper portion 15 of the prosthesis stem 13 to fit in
the first and second bores, B1 and B2. The angle guide 29 is also
not shown in FIG. 4G. The same trocar pin 57 and drill pin 59 in
the more preferred embodiment are used with the drill pin guide 105
of the lesser preferred embodiment to start the distal hole in the
posterolateral cortex of the femur F. The planing step and
instrumentation are substantially the same as described for the
method of the first more preferred embodiment.
[0187] In a third, most preferred embodiment shown in FIGS.
18A-18P, the procedure and some of the tools are modified. The
initial step (FIG. 18A) of determining the angle of the medial
trabecular stream TS is carried out exactly as described above in
reference to FIG. 4A. Once the angle of the medial trabecular
stream with respect to the central longitudinal axis AX-3 of the
bone is determined, the angle of the guide sleeve 33 of the angle
guide 29 is set as described above. In the most preferred
embodiment, this angle is checked using a protractor device
indicated generally at 101. The protractor device has a stop 103
against which the bracket 31 of the angle guide 29 is placed. A
pivotable arm 105 can be moved, by loosening set screw 107, to the
angle corresponding to the angle of the medial trabecular stream
TS. The arm 105 is fixed by the screw 107 and the guide sleeve 33
should be in face-to-face engagement with the arm. If not, the
sleeve guide 33 is turned until it matches the angle of the arm 105
of the protractor device 101. The larger scale of the protractor
device 101 permits a more accurate setting of the angle guide
29.
[0188] As illustrated in FIG. 18C, the angle guide 29 is attached
to the surgically exposed femur and the saw guide 41 is secured in
the angle guide. The procedure for resecting the femoral head is
the same as described above in reference to FIG. 4B. The saw guide
41 is removed from the angle bracket and replaced with a visual
sighting bar 109 which extends generally upwardly from the guide
sleeve 33 and beyond the resected neck N of the femur. As shown in
FIGS. 18D and 18E, a reamer 111 is then directed by the surgeon
along the angle indicated by the visual sighting bar 109 into the
femur to form an initial hole HO in the femur. The hole HO thus
formed has a longitudinal axis parallel to the medial trabecular
stream TS and with the proper anteversion, both of which are
indicated by the bar 109. The reaming may be carried out using a
reamer 111 and a number of succeeding reamers of increasingly
larger diameter to form the full diameter of the hole. A skilled
surgeon can alternatively form the full diameter of the hole HO
using only the reamer 111. In that event, the surgeon moves the
reamer 11 in progressively larger circles until the full diameter
is reached. The final diameter of the hole HO is dictated by the
size and shape of the femur of the individual patient.
[0189] Sizing of the hole for the best fitting prosthesis is
carried out using proximal femoral sizers 113 such as the sizer
shown in FIG. 18F. The sizer 113 is substantially identical in
shape to the upper portion 15" of the stem 13" of the prosthesis 1"
to be implanted. The sizers range in size. For example the larger
cylindrical portion 113A of the sizer may range in size from 18 to
26 mm in one millimeter increments. The sizers 113 are inserted
into the hole HO parallel to the visual sighting bar 109 (not shown
in FIG. 18F). Progressively larger sizers are fitted into the
proximal femur to determine the dimensions of the largest
prosthesis which will fit in the femur. The surgeon now knows the
size of the prosthesis 1" to be implanted and the exact dimension
of the bores B1, B2 needed to receive the prosthesis. The
prosthesis 1" is selected to be a size larger than the largest
sizer 113 which is able to fit in the hole HO. For example, if the
largest sizer that would fit had a smaller diameter portion of 14.5
mm a prosthesis having a smaller diameter upper stem portion of 15
mm would be used.
[0190] A reamer 115 having a diameter corresponding to the final
diameter (e.g., 15 mm) of the first bore B1 is selected and used to
form the first bore. As shown in FIG. 18G, the reamer is guided
freehand using the visual sighting bar 109. The first bore B1 is
also formed so that at least a portion of the bore is defined by
the endosteum of the medial femoral cortex. Thus, the prosthesis 1"
when installed will engage the hard cortical bone at this location
in the bore B1. In order to drill a hole in the posterolateral
femoral cortex which is precisely parallel to the medial trabecular
stream TS and with the proper anteversion, a series of one piece,
cannulated outrigger pin guides 117 (only one is shown) of
different sizes are provided. The pin guide 117 having a diameter
corresponding to that of the newly formed bore B1 is selected and
inserted into the bore. The outrigger portion of the pin guide 117
is received in the guide sleeve 33 of the angle guide 29 at the
same time it is inserted into the bore B1 for the most precise
alignment of the pin guide. The tapered tip of the guide is
advanced into the first bore B1 until it makes contact with the
endosteum of the lateral femoral cortex.
[0191] A drill guide pin 119 is inserted into the pin guide 117.
The orientation of the guide pin 119 in the femur is checked by
making sure the angle guide 29 is still at the proper angle
parallel to the medial trabecular stream TS and with the proper
anteversion. Moreover, the pin guide 117 is checked to make sure it
is in contact with the endosteal surface of the medial neck cortex.
A drill (not shown) is attached to the guide pin 119, and it is
drilled through the lateral femoral cortex. As shown in FIG. 18I,
the pin guide 117 and the angle bracket 29 are removed from the
femur, leaving on the guide pin 119. The next step is to drill the
transcortical tunnel through the posterolateral femoral cortex. A
cannulated drill 121 is selected which corresponds to the diameter
of the lower portion 17" of the prosthesis 1". For example if the
diameter of the lower portion 17" is to be 9.5 mm, a 9 mm
cannulated drill is selected. As illustrated in FIG. 18J, the
cannulated drill 121 comes with a guide ferrule 123 which is sized
according to the diameter of the bore B1. Thus as shown in FIG.
18K, the guide ferrule 123 helps (along with the guide pin 119) to
align the drill with the longitudinal axis of the bore B1. The
cannulated drill 121 slides over the guide pin 119 with the guide
ferrule 123 received on the drill and the transcortical tunnel is
formed in the posterolateral femoral cortex. Care is taken during
drilling to make sure the ferrule 123 remains against the medial
endosteal cortex.
[0192] The second bore B2 is formed as shown in FIG. 18L, which is
the same procedure as described above in relation to FIG. 4Q.
However, an offset reaming guide 63' is shown in FIG. 18L which has
splines 71A' for more precise orientation of the reaming guide in
the femur.
[0193] As shown in FIG. 18M, the calcar planing guide 75' inserted
into the bores B1, B2 is virtually identical in shape to the
prosthesis 1". The planing guide 75' has splines 77C' on its lower
stem portion 77B' like those of the prosthesis. The calcar planer
81' is received on the trunnion 79' of the planing guide 75' and a
flat seat is formed on the femoral neck N. There is preferably a
very close tolerance between the trunnion 79' and the planer 81' to
avoid wobble as the planer is rotated to form the seat.
[0194] Referring to FIG. 18N the prosthesis 1" is inserted into the
femur using a guide tip 125 which is attached to the end of the
prosthesis. More particularly, the guide tip 125 has a stem (not
shown) which is received in a hole (not shown) in the distal end of
the prosthesis 1". The tip 125 is held by a friction fit in the
hole. The bullet nosed shape of the tip 125 helps to keep the
prosthesis from hanging up on the bone before it passes through the
posterolateral femoral cortex. Once implanted, the tip 125 can be
pulled off of the prosthesis 1" as shown in FIG. 18P. The
prosthesis 1" is checked to make certain that the collar 7" is
fully seated on the seat of the femur neck N, and checked for the
appropriate amount of stem protrusion from the femur.
[0195] FIGS. 19A-19D illustrate an additional step which may be
performed to make absolutely certain that the a collar 7'" of a
prosthesis 1'" of still another embodiment has seated fully against
the femoral neck N. The prosthesis 1'" differs from the prosthesis
1" only in that the underside 11A'" of its flange 11'" is composed
of two intersecting planes. The underside 11A" of the prosthesis
flange 11" has the shape of a conical section. A saw template,
generally indicated at 127, includes a cap 128 capable of fitting
on the neck 5'" of the prosthesis 1111. The cap 128 precisely
locates slots 129 just under the collar 7'" and to the medial side
of the flange 11'".
[0196] A saw (e.g., oscillating saw SW) may then be used to cut
away additional portions of the femoral neck N under the collar
71". The saw template 127 guides the saw SW and a reciprocating saw
(not shown) for making cuts which are closely congruent with the
shape of the underside (9A'", 11A'") of the collar 7'". The planer
shape of the underside 11A'" permits linear cuts to be made (e.g.,
as by the blade B' of the reciprocating saw in FIG. 19D) adjacent
to the flange while achieving a high degree of congruency between
the cut surface and the flange underside. After removal of these
portions, the underside of the collar 7" is irrigated of remaining
debris and the area is checked for completeness of the removal. The
prosthesis 1'" is then driven downwardly (e.g., 1 or 2 mm) after
the portions are removed for a more congruent seating against the
neck N.
[0197] The slots 129 are disposed in a rim 131 of the saw template
127. Referring to FIG. 19D, the rim 131 has a peripheral edge 133
which is shaped so that the distance of the edge to the upper
portion 15'" of the stem 13'" of the prosthesis 1'" is everywhere
constant. The peripheral edge 133 is engaged by stop bolts SB on
blades B of the saw SW to limit the inward travel of the saw blade.
Thus, the shape of the rim 131 assures that the blades B of the saw
SW will not contact the upper portion 15'" of the stem 13".
[0198] It is envisioned that the saw template 127 could be used in
place of the planing guide (75, 75') and calcar planer (81, 81').
The other steps for implantation of the prosthesis 1'" would be the
same as shown in described above for the lesser preferred, more
preferred and most preferred methods. However, there is no planing
of the neck N after the femoral head H is resected to form a seat
for the collar 7'". The prosthesis 1'" is driven into the femur F
until the underside (9A'", 11A'") of the collar 7'" engages the
neck. The saw template 127 is attached to the prosthesis 1'" and
the bone is cut under the collar 7'" to form the seat for the
collar. The saw template 127 may also be used beneficially in the
removal of a previously implanted prosthesis 1'". Bone ingrowth
into the prosthesis 1'" is promoted (as described above) only on
the underside (9A'", 11A'") of the collar 7'". Minimal amounts of
bone would be removed using the saw template 127 to separate the
underside (9A'", 1A'") of the collar 7'" from the femur F.
[0199] (d) Study Regarding Present Invention
[0200] In total hip arthroplasty (THA), intramedullary stem femoral
components decrease strain levels in the proximal femur resulting
in periprosthetic bone loss. This study evaluates the strain
pattern of the femoral stem design of the present invention in
comparison to a normal femur and to conventional femur head-neck
prostheses.
[0201] Attempts to eliminate strain deprivation bone loss in THA by
means of reduced stiffness intramedullary stems have been
unsuccessful (1). A human study of an instrumented femoral
prosthesis found the load trajectory of the hip to fall within a
relatively narrow range of angles (2). An alternative approach to
improve proximal femoral loading is to align the femoral stem
parallel to the average resultant loading vector of the individual
hip. In theory, unimpeded loading of the femoral neck through a
stable interface should generate strain levels equivalent to the
intact femur. To enable unrestricted collar-neck loading, it is
necessary for the implant stem to go through the bone in line with
the resultant vector. The purpose of this study was to determine
the strain distribution of a transosseous THA prosthesis.
[0202] Twelve synthetic femurs were bonded with twelve triaxial
rosette strain gages (e.g., strain gages 109 shown in FIG. 1), five
each along the posteromedial and anterolateral aspect and one each
proximal-anterior and proximal posterior. The femurs were mounted
in a single limb stance jig. Spinal loads of 1068 and 2135 Newtons
were applied with simulated abductor force of 712 and 1423 Newtons
creating a resultant 21.degree. from the femoral shaft axis. Strain
data were acquired with a computerized multi-channel system which
converted the readings to microstrain.
[0203] Prototype cobalt-chrome transosseous femoral stems
constructed according to the principles of the present invention
were installed and loaded under the same conditions as the intact
femurs. The collar was 10.degree. conical and perpendicular to the
stem. The proximal stem consisted of two cylindrical elements 23,
25 of 15 and 21 mm diameter, respectively, and achieved tangential
contact with the endosteal cortex. The distal stem, which was
fluted and 12 mm in diameter, was press-fit through an 11.5 mm hole
in the posterolateral cortex. Two distal stem variations were
tested in each femur: slotted (n=11) and solid (n=12). Radiographs
of each femur were obtained. The angle of implantation varied from
146.degree. to 158.degree. in relation to the lateral shaft
cortex.
[0204] Eight non-cemented and cemented cobalt-chrome intramedullary
stems (Replica, 16.5-LG and Response, 13.5, manufactured by DePuy,
Inc. of Warsaw, Ind.) were installed and tested.
[0205] Analysis of variance was performed on all data.
[0206] Comparable strain patterns were noted at each of the two
loading conditions. The following results are from the higher load
condition. A graphic representation of the results appears as FIG.
18.
[0207] The non-cemented and cemented intramedullary stems resulted
in proximal posteromedial compression strain levels of 42.7.+-.4.6%
(mean.+-.SEM, p=0.0007) and 32.3.+-.2.6% (p=0.0001) compared with
the intact condition.
[0208] The slotted and solid transosseous stems produced proximal
posteromedial compression strain levels of 119.0.+-.7.4% (p=0.36)
and 101.1.+-.16.6% (p=0.66). Compression, tension and shear strain
levels were generally not significantly different from intact
levels. Exceptions included increased tension strain at the most
proximal posteromedial gage with the slotted stem, 128.9.+-.2.7%
(p=0.029). Significantly increased compression strain was noted at
the gage nearest the stem exit site with the slotted and solid
stems (146.1.+-.11.2%, p=0.0096 and 188.6.+-.11.9%, p=0.0006). A
trend was noted of higher proximal strain levels with a more
horizontal angle of implantation, however this was not significant
on linear regression analysis.
[0209] The diminished strain levels noted with the intramedullary
stem femoral components were consistent with those previously
reported (3). Although significant effort has been expended
attempting to resolve the "modulus mismatch" of intramedullary
stems, the results of this study suggest that a trajectory mismatch
may be a more significant factor in strain reduction. The
compression trabeculae of the hip were found to be 10 to 40.degree.
more horizontal than the axis of the femoral shaft (4). The
consequent bending moment on intramedullary stem components impedes
proximal interface loading. The loading trajectory of the hip is
more horizontal than intramedullary stem insertion trajectory
(femoral shaft axis) which creates a bending moment.
[0210] A trajectory matched femoral component (stem aligned with
loading vector) incurs a smaller bending moment and receives a more
axial load transmission. The cylindrical machining and
corresponding stem of this transosseous design seeks to resist
rotation and toggle with proximal and distal cortical
contact/macrointerlock, but accommodates collar-neck interface
compression. Although proximal femoral strain levels were restored
with this prototype, high strain levels near the distal stem would
raise concern for potential thigh pain.
[0211] Within a synthetic femur strain model, transosseous THA
femoral components demonstrated higher proximal femoral strain
levels than intramedullary stems.
[0212] (e) Embodiments for Reducing Fluid Pressure
[0213] Generally, fluid is produced by the joint lining, or
synovium, for lubricating the joint. After implantation of a
prosthesis, pressure in the joint created by walking or other
activity may force the synovial fluid into the implant-bone
interface IB. The unnatural presence of this fluid in the interface
can cause high fluid pressure resulting in damage to the bone, as
described above. Additionally, the presence of joint wear debris,
which is carried by the fluid, in the joint space JS and in the
implant-bone interface causes damage to the bone. The fluid and
joint wear debris is believed to be satisfactorily vented by a bone
prosthesis of a fourth embodiment (indicated generally at 401 and
shown in FIGS. 21-25). As will be further described, fluid and
debris entering into the interface adjacent the upper portion 415
of the stem 413 is forced by the fluid pressure to enter an opening
430 in the periphery of the upper portion, flow through a secondary
channel 435 and a primary channel 414 of the stem and exit at an
aperture 418 in the stem tip external to the bone. The vastus
lateralis VL (muscle tissue) on the outside of the bone absorbs the
fluid and wear debris because of the relatively good blood supply
in the muscle, as compared to the bone. Joint fluid pressure is
thereby reduced at the implant-bone interface IB and osteolysis is
inhibited.
[0214] The prosthesis 401 of this fourth embodiment is generally
constructed as described with reference to prosthesis 1' shown in
FIG. 6. Referring to FIGS. 21-23, the stem 413 further includes a
central longitudinal bore or primary channel 414 for venting fluid
pressure from generally adjacent the upper portion 415 of the stem
413 to an area external to the femur F. The primary channel extends
from near the top of the stem 413 to the aperture 418 in the stem
tip 420 which is positioned external to the bone when the
prosthesis is implanted. Fluid entering the primary channel 414
thereby exits the aperture 418 external to the bone. Preferably,
the primary channel 414 does not extend through the collar 407 in
this embodiment.
[0215] Preferably, the upper portion 415 includes multiple openings
430-434 and secondary channels 435-439 through which fluid flows to
the primary channel. The primary channel 414 and the secondary
channels 435-439 are collectively considered to be a "passageway".
Multiple openings are preferred to effectively vent the fluid
surrounding the upper portion. However, the number of openings
should not be so great as to weaken the stem. The upper portion 415
of the stem 413 also includes splines 440 extending longitudinally
along its periphery. In this embodiment, five secondary channels
and openings are shown but it is within the scope of the invention
to include any number of secondary channels, including only one.
Each secondary channel 435-439 extends from the primary channel to
its associated opening 430-434 in the periphery of the upper
portion 415. The openings 430-434 are positioned at various
elevations on the upper portion 415 and are staggered
circumferentially around the upper portion so that fluid
surrounding the upper portion is effectively vented. The openings
432, 433 are preferably positioned at the lateral side of the
implant and in a groove between adjacent splines. Openings 430, 431
are positioned at opposite sides of the stem 413 at the
intersection of the overlapping cylindrical elements 423, 425. It
is noted that the openings are not positioned immediately adjacent
the collar 407 so that the hard layer of cortical bone C adjacent
the undersurface of the collar does not grow into the openings.
Another opening 434 is positioned at the medial side of the implant
at a lower elevation on the stem than openings 432 and 433. All of
the openings 430-434 and secondary channels 435-439 are drilled at
oblique angles to the outer periphery of the stem. The angles are
chosen to prevent bone from growing into the openings and causing
axial fixation of the prosthesis 401 after implantation in the
femur. As discussed above, such axial fixation is undesirable. It
is believed that this configuration will relieve any high fluid
pressures encountered in the implant-bone interface IB.
[0216] Referring to FIGS. 26-28, a prosthesis 501 of a fifth
embodiment has a primary channel 514 extending from an opening 542
in the upper side of the collar 507 through the collar and downward
the length of the stem 513 to an aperture 518 in the stem tip 520
positioned external to the femur as implanted. The primary channel
514 may include an angle as shown in FIG. 26. The primary channel
514 is effective to vent fluid pressure from the joint space JS
above the collar 507 to an area adjacent the stem tip 520 which is
external to the femur, thereby relieving joint fluid pressure in
the joint space. This may inhibit the occurrence of acetabular
osteolysis.
[0217] Referring to FIGS. 29-31, a prosthesis 601 of a sixth
embodiment includes the features of the fourth and fifth
embodiments in a single prosthesis. That is, the prosthesis 601
includes openings 630-634 in the periphery of the upper portion 615
of the stem 613 and associated secondary channels 635-639 which are
connected to a first primary channel 614 and first aperture 618 at
the stem tip 620 for venting the implant-bone interface IB at the
upper portion. The prosthesis 601 further includes a second primary
channel 616 extending from the upper side of the collar 607 and
downward through the stem 613 to a second aperture 617 at the stem
tip 620 to vent the joint space JS above the collar. In this
embodiment, the second primary channel 616 is not connected to the
first primary channel 614 or to the secondary channels so that the
fluids vented from the upper side of the collar 607 cannot enter
the secondary channels 635-639 and exit at the upper stem.
Likewise, the fluids vented from adjacent the upper portion of the
stem 613 cannot enter the second primary channel and exit at the
upper side of the collar.
[0218] Referring to FIGS. 32-33, a prosthesis 701 of a seventh
embodiment includes the features of the sixth embodiment, except
that only one primary channel 714 is included to vent both the
implant-bone interface IB and the joint space JS upward of the
collar 707. The primary channel 714 extends from an opening 742
(see FIG. 28) in the upper side of the collar 707 and down through
the stem 713 to an aperture 718 at the stem tip 720. As in the
fourth embodiment the secondary channels 735-739 connect to the
primary channel 714. As is apparent, in this seventh embodiment the
fluids vented from the implant-bone interface IB and from the joint
space JS will be intermixed in the primary channel 714 before being
vented at the aperture.
[0219] The method of implanting the prosthesis of the fourth
through seventh embodiments is the same as the method disclosed
above. Preferably, the guide tip 125 is mounted at the tip of the
stem when the prosthesis is inserted, as discussed above with
respect to FIG. 18N. The guide tip prevents the aperture at the
stem tip from becoming occluded as the prosthesis is inserted in
the femur. As described above, the guide tip is removed after the
prosthesis is inserted.
[0220] It is to be understood that the prosthesis of the present
invention may be other than a femoral prosthesis. That is, the
invention of the fourth through seventh embodiments is directed to
venting fluid pressure adjacent a bone prosthesis to relieve fluid
pressure and is not limited to femoral prostheses.
[0221] (f) Embodiment for Diagnosing and Treating Ailments
Associated with the Prosthesis
[0222] The structure of the prostheses of the fourth through
seventh embodiments facilitates improved diagnosis and treatment
methods without removal of the prosthesis. In particular, these
embodiments permit improved diagnosis and treatment of infections
which may occur at the joint around the implant. The present
invention enables improved diagnosis by allowing a needle, brush,
probe or other instrument to be inserted into the primary channel
714 and into the joint space JS. Improved treatment of the
infection is accomplished primarily by introducing medication, such
as an antibiotic solution, upward through the primary channel 714
and secondary channels 735-739 into the implant-bone interface IB
and joint space JS (see FIG. 35). It is to be noted that this is
accomplished by causing medicine to flow upward into the secondary
channels and out the respective openings, in other words, the
medicine flows in the reverse direction of the synovial fluid
vented from the prosthesis. Hereinafter, the primary channel 714
secondary channels 735-739, joint space JS and the implant-bone
interface IB will be referred to collectively as the "joint
region". It is also to be noted that the term "instrument" includes
needles, brushes, pins and arthroscopic probes, among others. While
any of the prostheses of the fourth through seventh embodiments may
be advantageously used with the methods described below, the
prosthesis 701 of the seventh embodiment is illustrated and
discussed. Preferably, the prosthesis 701 is modified to include
internal threads in the primary channel 714 immediately adjacent
the aperture 718.
[0223] In the minimally invasive method of this embodiment, the
patient is first placed under general, regional (spinal or
epidural) or local anesthesia. The patient is placed in the lateral
decubitus position (side-lying position) with the affected hip
facing upward (FIG. 36A). The skin of the thigh region TH is
prepared with antiseptic solution and isolated with sterile
adhesive drapes. Referring to FIG. 36B, a fluoroscope FL and
monitor MO are used to view the stem 713 of the implanted
prosthesis 701 and to locate the axis of the stem. The fluoroscope
FL is a radiographic instrument that provides a real time X-ray
image of the bone and the prosthesis 701 on a video monitor. The
fluoroscope FL is well known to those in the art. The fluoroscope
FL is positioned to view the femur F from the front looking toward
the posterior of the femur (anteroposterior view). The femur F is
internally rotated inward so that the viewing plane of the
fluoroscope FL is approximately parallel to the longitudinal axis
of the stem 713 and the primary channel 714 so that the stem and,
importantly, the portion of the stem protruding from the femur, is
seen in elevation. The femur F is held in this position while a
metal rod (not shown) is placed in front of the thigh TH to locate
the axis of the stem 713. The thigh TH is then palpated to
determine the location of the bone and the position of the
prosthesis. The location for an incision is then determined by
extrapolating the intersection of the axis and the skin evidenced
by the metal rod rearwardly to a position in the plane of the rod
overlying the bone, and a mark is made. Alternatively, the
fluoroscope may be rotated 90 degrees to determine the location of
the bone and the position of the prosthesis. As a second
alternative, a dual plane fluoroscope, which includes two
fluoroscopes operating simultaneously, may be used to view the
prosthesis and femur F in elevation and in plan to determine the
axis and the position of the prosthesis. Also, the patient may be
placed on a "fracture table" in the supine or lateral decubitus
position. The fracture table allows improved access to the legs and
permits the fluoroscope to be more easily rotated around the legs
of the patient. After marking the intersection, a small
(approximately one cm) incision is made in the skin at the
mark.
[0224] Referring to FIG. 37, a straight elongate pin 801 is
inserted in the incision and slid through the underlying tissue
along the axis. The underlying tissue includes subcutaneous fat,
the fascia lata FA, the vastus lateralis VL. Care must be exercised
to avoid the sciatic nerve and other vital structures. The
fluoroscope FL is used to visualize the pin 801 and the prosthesis
701 to help in locating the stem tip 720 and the aperture 718 of
the primary channel 714 located at the stem tip. To ensure
engagement of the pin 801 with the stem tip 720, the pin may be
used to palpate the stem tip. Alternatively, a guide wire (not
shown) may be used in place of the elongate pin 801.
[0225] If the attempt to locate the stem tip 720 and/or place the
pin 801 in the primary channel 714 is unsuccessful, a centering
guide 803 may be used to help guide the pin. Referring to FIGS. 38A
and 38B, the centering guide is an elongate tube having a bore 805
therethrough sized to receive the pin 801 and a trough-shaped end
corresponding to a segment of the cylindrical exterior shape of the
stem 713 at the tip 720. The guide may also include a second bore
(not shown) for inserting a pin into the prosthesis 601 of the
sixth embodiment wherein the stem 613 includes a second primary
channel 616. The pin 801 is removed from the incision and then the
centering guide 803 is inserted into the incision and slid through
the tissue along the axis until the periphery of the stem tip 720
is partially received in the trough-shaped end of the centering
guide. The bore 805 of the centering guide is thereby centered on
the longitudinal axis of the primary channel 714 of the stem 713.
The pin 801 is passed through the bore of the guide and is guided
into the primary channel 714 of the stem 713 because the bore 805
and primary channel are substantially concentric. Once the pin 801
is inserted in the primary channel 714 of the stem 713, the
centering guide 803 is removed from the incision.
[0226] Fluid is drawn from the joint region using an elongate
needle and syringe (not shown). The fluid samples may be used to
confirm the existence of an infection or the fluid may be removed
simply to clean the joint region and prepare the site for
subsequent procedures. The elongate needle is received over the pin
801 and passed into the primary channel 714 of the stem 713. The
pin 801 is removed and a syringe is attached to the end of the
needle outside the thigh TH to draw a vacuum through the joint
region. The tip of the needle may be positioned anywhere along the
length of the primary channel 714 and in the joint space JS to
withdraw fluid therefrom. The tip of the needle may also be
positioned immediately adjacent each of the secondary channels
735-739 to withdraw fluid from each secondary channel. It will be
apparent in regard to the prosthesis 601 that a second needle (not
shown) may be inserted in the second primary channel 616 to access
the joint space JS. Preferably, the internal diameter of the needle
is sufficiently large so that small bits of fibrous tissue may also
be withdrawn through the needle. After fluid removal is complete,
the syringe is removed and the pin 801 is passed through the needle
into the primary channel 714 of the stem 713. The needle is removed
leaving the pin 801 in the primary channel.
[0227] Referring to FIG. 39, a cannulated brush 809 having stiff
bristles is mounted on an elongate shaft 810. The brush 809 is
passed over the pin 801 and into the primary channel 714 and the
joint space JS. The bristles of the brush 809 simultaneously clean
the joint region and collect fibrous tissue specimens from the
joint region. The brush 809 is withdrawn from the primary channel
714 of the stem 713 leaving the pin 801 in the primary channel. The
tissue on the brush bristles are sent for culture of organisms and
histologic examination (microscopic study). A second brush (not
shown) may also be used to enter the secondary channels 735-739 for
cleaning and collecting tissue samples. The second brush preferably
has a smaller diameter than the cannulated brush 809 and has a bent
tip so that it can enter the secondary channels 735-739.
[0228] Arthroscopic viewing of the joint space JS may be
accomplished by inserting an arthroscope (not shown) through the
primary channel 714 of the prosthesis 701 into the joint space JS.
The arthroscope is inserted into the primary channel 714 as
described above in relation to the needle. The arthroscope is
connected to a digital video camera which allows viewing of the
joint space JS and prosthesis 701. Such viewing enables assessment
of the prosthesis 701 for stability of fixation and for wear of the
joint surfaces.
[0229] Referring to FIGS. 40A and 40B, an infusion assembly
includes a threaded connector 815 (broadly, "infusion element") for
insertion in the primary channel 714 of the stem tip 720, a luer
connector 817 and an infusion tube 819 connecting the threaded
connector to the luer connector. The threaded connector 815 is
tubular, has external threads on its periphery sized to engage
threads 719 in the primary channel 714 immediately adjacent the
aperture 718 and fins 820 or protrusions on the periphery of an end
opposite the threads. The infusion tube 819 is received at one end
in the threaded connector 815 and at its opposite end in a first
end of the luer connector 817. The luer connector has a "luer lock"
at a second end opposite the infusion tube 819 for receiving a
syringe or a second tube. An elongate, tubular wrench 821 is
adapted to receive the assembly and to install the threaded
connector 815 in the aperture 718. The wrench 821 has a socket 822
that receives the fins 820 of the threaded connector 815. The
socket 822 has a shape corresponding to the shape of the exterior
of the threaded connector 815 so that when the connector is
received in the socket it is held for conjoint rotation with the
wrench 821. The wrench has finger grips 823 at an end opposite the
socket.
[0230] The infusion assembly is placed in the wrench 821 so that
the threaded end of the threaded connector 815 protrudes from the
socket 822 of the wrench and the infusion tube 819 extends through
the bore of the wrench. The infusion assembly and the wrench 821
are passed over the pin 801 until the threaded connector 815
contacts the aperture 718 of the primary channel 714. The wrench
821 is turned to screw the threaded connector 815 into the threads
of the primary channel 714. If difficulty is encountered in
engaging the threads, the infusion assembly and wrench 821 are
withdrawn from the incision. The cannulated brush 809 is passed
over the pin 801 and the threads 719 of the aperture 718 are again
cleaned of fibrous tissue. The wrench 821 and pin 801 are then
removed leaving the infusion assembly attached to the prosthesis
701.
[0231] Referring to FIG. 40C, bacteria and debris in the joint
region may be flushed out using the infusion assembly. A syringe
830 filled with saline or lactated Ringer's solution is attached to
the luer connector 817 of the infusion assembly. The saline or
Ringer's solution is infused under pressure into the infusion
assembly. The solution passes through the primary channel 714 and
secondary channels 735-739, exiting at the openings 742, 730-34 of
the channels so that the solution washes out the implant-bone
interface IB within the bone and the joint space JS above the
collar, as well as the channels. The solution is thereafter
withdrawn by the syringe. This process is preferably repeated
several times to thoroughly wash out the prosthesis 701,
implant-bone interface IB and joint space JS.
[0232] Sometimes it may be desirable to infuse a contrast medium
(radiographically opaque sterile fluid, or more simply "dye") to
perform an arthrogram. A syringe filled with the contrast medium is
attached to the luer connector 817 and infused into the joint
region. The fluoroscope FL is used to visualize the dye, which
enhances radiographs and gives information regarding the
relationship of the prosthesis 701 and bone. Relevant information
obtained from the arthrogram in cases of infection includes the
extent to which the dye pervades the joint region. The latter
information gives an indication of the extent to which the
antibiotic solution will infuse the joint region. Additionally,
contrast medium injected through the joint region may be used to
radiographically confirm that the infusion assembly is not blocked
and that the connections do not leak. If a leak in the assembly is
detected, the threaded connector 815 can be tightened using the
wrench 821 or, if necessary, the assembly can be removed and
replaced.
[0233] The contrast medium is irrigated from the joint region with
saline through the infusion assembly as described above. An initial
loading dose of antibiotic solution is then infused into the joint
region through the infusion assembly without removal of the
prosthesis. The antibiotic solution passes through the primary
channel 714 and secondary channels 735-739, exiting at the openings
742, 730-34 of the channels and pervading the implant-bone
interface IB within the bone and the joint space JS above the
collar.
[0234] The present invention provides for repeated administration
of antibiotics to the joint. Referring to FIG. 40D, an infusion
port assembly includes an infusion port 833 for infusing liquid
medicine into the joint region on a regular basis. The port 833 has
a self-sealing membrane cover 834 penetrable by a needle for
injecting the medicine. The port 833 is connected via tubing 835 to
the luer connector 817 of the infusion assembly. The port 833 is
placed in a location spaced from the infected area and is anchored
with sutures to fascia lata FA under the skin. The infusion port
833 is located so that it is easily accessed through the skin by a
hypodermic needle. The incision is then closed. The port 833 is
thereafter used, typically once a day, to infuse the joint region
with antibiotic solution that flows through the tubing into the
joint region. The infusion assembly permits extremely high local
concentrations of antibiotics directly to the joint region that
should eradicate the infection and decrease or eliminate the need
for systemic antibiotics. These concentrations can be maintained
indefinitely by repeatedly supplying antibiotics through the port
833. The antibiotic solution is injected into the port 833 using a
syringe 837 with a non-coring (Huber) needle to enter the skin over
the port. "Non-coring" means that the shape of the needle prevents
it from taking a cylindrical core of plastic out of the membrane
834 which would cause leakage through the membrane. Instead, the
non-coring needle cuts a slit through the membrane 834 which seals
when the needle is removed.
[0235] In addition to infusion of antibiotics or contrast dye,
other medications can be infused through the infusion assembly
during surgery or through the port 833 thereafter. For example, one
treatment used for prevention of osteoporosis is a class of
medications termed "bisphosphonates." These medications have been
investigated as a possible treatment for osteolysis in the bone
adjacent total hip replacements. One of these, pamidronate, comes
in a liquid form for intravenous use. Although the invention
provides means of avoiding osteolysis, if osteolysis were to occur,
consideration could be given to the infusion of pamidronate. This
could provide higher local concentrations of the medication where
it is needed. This medication is typically administered every three
or four months when used intravenously.
[0236] If difficulty is encountered with the minimally invasive
method described above, a "mini-open" procedure can be used in
which an incision is made which is large enough to directly
visualize the tip 720 of the stem 713 protruding from the femur F.
Alternatively, the above technique may be combined with an open
procedure, e.g., a procedure in which the entire incision is
utilized to open the joint and change prostheses.
References
[0237] (1) Bobyn, J. D. et al.: CORR 261:196, 1990
[0238] (2) Davy, D. T. et al.: JBJS 70A:45, 1988
[0239] (3) Oh, I. and Harris, W. H.: JBJS 60A:75, 1978
[0240] (4) Clark, J. M. et al.: J Arthr 2:99, 1987
[0241] (5) Schmalzried, T. P. et al.: JBJS 79A:447, 1997
[0242] (6) Harris, W. H. et al.: Instructional Course Lectures AAOS
45:183-185, 1996
[0243] (7) Aspenberg, P. A. et al.: CORR 352:75, 1998
[0244] In view of the above, it will be seen that the several
objects of the invention are achieved and other advantageous
results attained.
[0245] As various changes could be made in the above constructions
without departing from the scope of the invention, it is intended
that all matter contained in the above description or shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
* * * * *