U.S. patent application number 12/609465 was filed with the patent office on 2010-05-06 for method of resecting a femoral head for implantation of a femoral neck fixation prosthesis.
This patent application is currently assigned to HOWMEDICA OSTEONICS CORP.. Invention is credited to Theodore Crofford.
Application Number | 20100114101 12/609465 |
Document ID | / |
Family ID | 28794142 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100114101 |
Kind Code |
A1 |
Crofford; Theodore |
May 6, 2010 |
METHOD OF RESECTING A FEMORAL HEAD FOR IMPLANTATION OF A FEMORAL
NECK FIXATION PROSTHESIS
Abstract
A femoral neck fixation prosthesis and method of using same
which reduces bone loss and the avoids the other shortcomings of
the prior art by allowing the fixation of a stable femoral head
replacement while reducing the amount of the femur which must be
reamed for the insertion of the prosthesis. The preferred
embodiment provides that the femoral head is attached to a fixation
prosthesis, which extends coaxially through the canal of the
femoral neck, into the femur, and is then attached to the opposite
lateral wall of the femur. In this manner, the prosthesis serves to
imitate the original structure of the femoral neck. No other
support members, either crosspins or arms extending into the length
of the femur, are required.
Inventors: |
Crofford; Theodore; (Fort
Worth, TX) |
Correspondence
Address: |
LERNER, DAVID, LITTENBERG,;KRUMHOLZ & MENTLIK
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Assignee: |
HOWMEDICA OSTEONICS CORP.
Mahwah
NJ
|
Family ID: |
28794142 |
Appl. No.: |
12/609465 |
Filed: |
October 30, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10914749 |
Aug 9, 2004 |
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12609465 |
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10779353 |
Feb 14, 2004 |
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10914749 |
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10228907 |
Aug 27, 2002 |
6695883 |
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10779353 |
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60371837 |
Apr 11, 2002 |
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Current U.S.
Class: |
606/89 |
Current CPC
Class: |
A61F 2230/0023 20130101;
A61F 2002/3631 20130101; A61F 2220/0033 20130101; A61F 2310/00023
20130101; A61F 2002/30827 20130101; A61F 2/30767 20130101; A61F
2002/30535 20130101; A61F 2002/30332 20130101; A61F 2220/0041
20130101; A61F 2230/0069 20130101; A61F 2002/30616 20130101; A61F
2310/00029 20130101; A61B 17/8665 20130101; A61F 2002/3079
20130101; A61F 2250/0058 20130101; A61F 2002/30339 20130101; A61F
2002/30224 20130101; A61F 2002/3055 20130101; A61F 2002/4658
20130101; A61F 2002/30968 20130101; A61F 2002/30774 20130101; A61F
2002/30113 20130101; A61B 17/742 20130101; A61F 2002/365 20130101;
A61F 2002/4635 20130101; A61F 2002/3611 20130101; A61F 2002/30797
20130101; A61F 2230/0006 20130101; A61B 17/8695 20130101; A61F
2002/30156 20130101; A61B 17/74 20130101; A61F 2002/30329 20130101;
A61F 2002/30433 20130101; A61B 17/175 20130101; A61F 2002/4631
20130101; A61F 2/3601 20130101; A61F 2/4657 20130101; A61F 2/4607
20130101; A61F 2220/0025 20130101; A61F 2002/30604 20130101 |
Class at
Publication: |
606/89 |
International
Class: |
A61B 17/58 20060101
A61B017/58 |
Claims
1. A method of resecting a femoral head from a femur having a
femoral neck, the method comprising the steps of: positioning a
locator shaft adjacent an exterior surface of the femoral head and
substantially parallel to a longitudinal axis of the femoral neck;
positioning a pin locator guide having at least two holes along the
locator shaft; inserting a pin through each of the at least two of
the holes in the pin locator guide and into the femoral head; and
resecting the femoral head by aligning a cutting guide relative to
the pins in the femoral head.
2. A method according to claim 1, wherein a locator plane formed by
the pins is parallel to a cutting plane at which the femoral head
is resected.
3. A method according to claim 1, wherein: a locator plane formed
by the pins is parallel to a cutting plane at which the femoral
head is resected; and the cutting plane is perpendicular to the
longitudinal axis of the femoral neck.
4. A method according to claim 1, wherein the step of positioning a
locator shaft further comprises the steps of: providing a femoral
neck clamp having a superior clamping member, an inferior clamping
member, and a locator shaft guide member connected to at least one
of the superior clamping member and the inferior clamping member;
and clamping the femoral neck clamp around the femoral neck at an
isthmus of the femoral neck such that the superior clamping member
is adjacent a superior region of the femoral neck, the inferior
clamping member is adjacent an inferior region of the femoral neck,
and a longitudinal axis of the locator shaft guide member is
substantially parallel to the longitudinal axis of the femoral
neck.
5. A method of resecting a femoral head from a femur having a
femoral neck, the method comprising the steps of: locating an
isthmus plane at an isthmus of the femoral neck; fixing the
orientation of a cutting plane based on the isthmus plane; and
resecting the femoral head at the cutting plane.
6. A method according to claim 5, wherein the step of fixing the
orientation of the cutting plane further comprises the steps of:
inserting at least two pins into the femoral head.
7. A method according to claim 6, wherein the pins are positioned
along a line parallel to the isthmus plane.
8. A femoral neck clamp for locating a cutting plane on a femur for
resecting a femoral head of the femur, the femoral neck clamp
comprising: a superior clamping member; an inferior clamping member
adjustably connected to the superior clamping member; a locator
shaft guide hole connected to at least one of the superior clamping
member and the inferior clamping member; and wherein the locator
shaft guide hole is oriented substantially parallel to a
longitudinal axis of the femoral neck when the femoral neck clamp
is positioned at an isthmus of the femoral neck such that the
superior clamping member is adjacent a superior region of the
femoral neck and the inferior clamping member is adjacent an
inferior region of the femoral neck.
9. A femoral neck clamp according to claim 8, wherein the superior
clamping member includes an arcuate region to contact an
antero-superior ridge on the femoral neck.
10. A femoral neck clamp according to claim 8, wherein the inferior
clamping member is V-shaped to cradle the inferior region of the
femoral neck.
11. A femoral neck clamp according to claim 8, wherein: the
superior clamping member includes an arcuate region to contact an
antero-superior femoral neck; and the inferior clamping member is
V-shaped to cradle the inferior region of the femoral neck.
12. A femoral neck clamp according to claim 8, wherein the inferior
clamping member further comprises: a proximal clasp aligned with
the superior clamping member; and a distal clasp rotatably
connected to the proximal clasp.
13. A femoral neck clamp according to claim 12, wherein the distal
clasp provides anti-rotational stability for the femoral neck clamp
when secured around the femoral neck.
14. A femoral neck clamp according to claim 12, wherein a
connecting member is used to rotatably connect the proximal clasp
to the distal clasp.
15. A femoral neck clamp according to claim 12, further comprising:
a connecting member pivotally connected to the proximal clasp and
rigidly connected to the distal clasp; and a torsion spring
operably connected to the connecting member and the proximal clasp
to bias the distal clasp toward the femoral neck.
16. A femoral neck clamp according to claim 12, further comprising:
a connecting member rigidly connected to the proximal clasp and
rigidly connected to the distal clasp; and wherein the connecting
member is made from a flexible material to bias the distal clasp
toward the femoral neck.
17. A femoral neck clamp according to claim 16, wherein the
connecting member is made from spring steel.
18. A femoral neck clamp according to claim 12, further comprising:
a connecting member pivotally connected to the proximal clasp and
rigidly connected to the distal clasp; and a fastener connected
between the connecting member and the proximal clasp to lock a
rotational position of the distal clasp relative to the proximal
clasp.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of and claims
priority to U.S. patent application Ser. No. 10/779,353, filed Feb.
14, 2004, which is a continuation of U.S. patent application Ser.
No. 10/228,907, filed Aug. 27, 2002, now U.S. Pat. No. 6,695,883,
which claims priority to U.S. Provisional Application No.
60/371,837, filed Apr. 11, 2002. Priority is claimed to all of the
above-mentioned applications and patents, and each application and
patent is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention The present application relates
generally to hip prostheses and more specifically to an improved
method of implanting a femoral neck fixation prosthesis in the
femoral neck.
[0003] 2. Description of Related Art
[0004] A widely used design for replacement of the proximal portion
of a femur employs an elongate, often curved, shaft that extends
into the medullary canal of the femur. This design has the tendency
to place unnatural stresses on the femur, which lead to pain and
the consequent curtailment of activity for the patient. Further,
present techniques can lead to proximal bone loss and call for the
resection of the majority of the femoral neck. Current designs also
call for fixing the prosthesis in the proximal third of the femur.
The useful life of an intramedullary implant is often less than the
expected life span of a young patient.
[0005] Previously known prostheses for replacing a femoral head
that do not extend into the medullary canal have been mechanically
complex or have proven troublesome in actual use. Huggler, U.S.
Pat. No. 4,129,903 and Grimes, U.S. Pat. No. 4,795,473 are examples
of prosthetic implants having a side plate attached to the exterior
lateral side of the femur opposite the femoral head. Screws are
used to secure the plate to the femur and one or more holes are
drilled into the femur for securing the plate to the bone. The
additional holes and the stresses at the site of fixation are
believed to cause trauma to the bone.
[0006] Masini, U.S. Pat. No. 5,571,203 discloses a device having a
shaft that extends through a resected portion of the proximal
femur, positioned co-axially relative to the longitudinal axis of
the femur. The device is secured by a screw or similar locking
device that extends into the femur from the lateral side, just
below the greater trochanter. It is believed that the natural
forces applied to the prosthesis during normal hip motion result in
the application of shear forces to the greater trochanter. The
shear forces can be harmful to the greater trochanter and can
permit micro-movement of the prosthesis on the unsecured side.
[0007] A conventional method for implanting the above types of
femoral head implants is described in Campbell's Operative
Orthopaedics, (Mosby, 7th ed., 1987) and typically includes making
a large incision in the patient's lateral side at the hip joint and
through the skin and muscle, dislocating the hip and then sawing
off the femoral head. This method is considered invasive because of
the need to dislocate the hip and cut through muscle surrounding
the hip joint. Invasive procedures increase the trauma to the
patient, the potential for complications, recovery time and the
cost.
[0008] Replacement of the proximal portion of the femur is
sometimes necessary due to degenerative bone disorders or trauma to
otherwise healthy bone caused by accidental injury. In the latter
instance it is desirable to replace the traumatized portion of the
bone without causing further trauma to healthy bone. There is a
need, therefore, for an implant that replaces a traumatized portion
of the femur, but also significantly minimizes stress to the
remaining healthy bone and that can be implanted by a method that
is less invasive.
[0009] There are several other significant problems and issues
relating to hip arthroplasty. One problem is encountered with the
young, active patient. Younger patients are more likely to have
failure of their primary arthroplasty both due to increased demand
on the mechanical construct, and from a pure life expectancy
standpoint. It follows that they are more likely to require a
revision and a second revision, which may lead to a catastrophic
bone loss situation.
[0010] Another problem relates to instability of the hip following
implantation of the prosthesis. This problem still occurs at the
same rate that it did 50 years ago. Larger femoral heads may
decrease the incidence, but no other significant technical changes
have occurred to effect the incidence of this serious
complication.
[0011] Still another problem is related to bone loss in patients
receiving hip prostheses. The overwhelming majority of present
successful femoral prostheses achieve fixation at least as far
distal as the proximal femoral metaphysis. When these prostheses
fail, the next step usually involves diaphyseal fixation, often
with a large diameter, stiff stem.
[0012] Leg length inequality is another problem associated with hip
arthroplasty. An average lengthening of the leg of 1 centimeter is
common. Lengthening is sometimes accepted for the sake of improved
stability; however, leg length inequality has been reported as the
primary reason why surgeons are sued after hip arthroplasty.
[0013] Finally, another problem associated with hip arthroplasty is
surgical morbidity. The surgery usually involves significant blood
loss, body fluid alterations, and pain. Shortly, the surgery is a
big operation that hurts. It should be the goal of every
compassionate surgeon to minimize these issues. If the operation
can be made smaller, with less blood loss and less pain without
diminishing long term results, every effort should be made to do
so.
[0014] It would therefore be desirable to provide a femoral neck
prosthesis and method for implanting the prosthesis that overcomes
these significant disadvantages.
BRIEF SUMMARY OF THE INVENTION
[0015] It is therefore one object of the present invention to
provide an improved apparatus and method for hip replacements.
[0016] It is another object of the present invention to provide an
improved and less-invasive prosthesis and implantation method that
replaces the femoral head while retaining a substantially intact
femoral neck.
[0017] The foregoing objects are achieved as is now described. A
femoral neck fixation prosthesis and method of implanting the
prosthesis according to the principles of the present invention,
reduce bone loss and avoid the other shortcomings of the prior art
by allowing the fixation of a stable femoral head replacement while
reducing the amount of the femur that must be removed and reamed
for the insertion of the prosthesis. The preferred embodiment
provides that the femoral head is attached to a fixation
prosthesis, which extends coaxially through the central canal of
the femoral neck, into the femur, and is then attached to the
opposite lateral wall of the femur. In this manner, the prosthesis
serves to imitate the original structure of the femoral neck. No
other support members, either crosspins or arms extending into the
length of the femur, are required.
[0018] The above as well as additional objectives, features, and
advantages of the present invention will become apparent in the
following detailed written description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates a schematic of an anterior view of a
prosthesis in accordance with the principles of the present
invention;
[0020] FIGS. 2A-2H depict a schematic of the cross-section at
various levels of the body of a prosthesis in accordance with the
present invention;
[0021] FIG. 3 illustrates joining members used with a prosthesis in
accordance with the present invention;
[0022] FIG. 4 depicts a centering guide for placement of a starting
pin in accordance with the present invention;
[0023] FIG. 5 illustrates how the center of rotation of the femoral
head can be reproduced in accordance with the present
invention;
[0024] FIG. 6 depicts a prosthesis in accordance with the
principles of the present invention;
[0025] FIG. 7 illustrates a prosthesis in accordance with the
principles of the present invention;
[0026] FIG. 8 depicts a posterior view of a human femur having a
femoral head and a femoral neck;
[0027] FIG. 9 illustrates multiple cross-sectional views of the
femoral head and femoral neck of FIG. 8 taken at A-A, B-B, and
C-C;
[0028] FIG. 10 depicts a perspective view of a femoral neck clamp
according to the principles of the present invention positioned at
an isthmus of the femoral neck of FIG. 8;
[0029] FIG. 11 illustrates a perspective view of the femoral neck
clamp of FIG. 10;
[0030] FIG. 12 depicts a posterior view of a human femur with the
femoral neck clamp of FIG. 10 shown installed at an isthmus of the
femoral neck, the handle members of the femoral neck clamp being
omitted for clarity;
[0031] FIG. 13 illustrates a cross-sectional distal view of the
femur and femoral neck clamp of FIG. 12 taken at XIII-XIII;
[0032] FIG. 13A-13C depict alternative shapes of an inferior
clamping member of the femoral neck clamp of FIG. 13;
[0033] FIG. 14 illustrates a posterior view of the femur and
femoral neck clamp having superior and inferior clamping members,
the inferior clamping member having a proximal clasp attached to a
distal clasp by a connecting member according to principles of the
present invention;
[0034] FIG. 15 depicts a posterior view of a femur and femoral neck
clamp similar to those of FIG. 14, the femoral neck clamp having an
alternative connecting member according to the principles of the
present invention;
[0035] FIG. 16 illustrates a posterior view of a femur and femoral
neck clamp similar to those of FIG. 14, the femoral neck clamp
having an alternative connecting member according to the principles
of the present invention;
[0036] FIG. 17 depicts a side view of a femoral neck clamp
according to the principles of the present invention;
[0037] FIG. 18 illustrates a side view of a femoral neck clamp
according to the principles of the present invention;
[0038] FIG. 19 depicts a posterior view of a human femur having a
femoral neck clamp attached to a femoral neck of the femur, a
locator shaft connected to the femoral neck clamp, and a pin
locator guide slidingly received on the locator shaft;
[0039] FIG. 20 illustrates a perspective view of a human femur
having a cutting guide positioned on pins placed in the femoral
head using the pin locator guide of FIG. 19;
[0040] FIG. 20A depicts a method of resecting a femoral head
according to the principles of the present invention;
[0041] FIG. 21 illustrates a perspective view of a starter guide
according to the principles of the present invention and a human
femur having the femoral head of the femur resected;
[0042] FIG. 22 depicts a posterior view of a human leg, including a
human femur, and a drilling guide according to the principles of
the present invention for preparing the femur for implantation of a
femoral neck prosthesis;
[0043] FIG. 23 illustrates a side view of the drilling guide of
FIG. 22;
[0044] FIG. 23A depicts a method of preparing a femur for
implantation of a prosthesis according to the principles of the
present invention;
[0045] FIG. 24 illustrates a posterior view of a femoral neck liner
and a reamer path protector according to the principles of the
present invention, the femoral neck liner being positioned within a
femoral neck, and the reamer path protector being threadingly
received by the femoral neck liner;
[0046] FIG. 25 depicts a side view of the reamer path protector and
femoral neck liner of FIG. 23;
[0047] FIG. 25A illustrates a method of preparing an acetabulum
according to the principles of the present invention; and
[0048] FIG. 26 depicts a method of implanting a prosthesis in a
femur according to the principles of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0049] In the following detailed description of the preferred
embodiments, reference is made to the accompanying drawings, which
form a part hereof and in which is shown by way of illustration
specific preferred embodiments in which the invention may be
practiced. These embodiments are described in sufficient detail to
enable those skilled in the art to practice the invention, and it
is understood that other embodiments may be utilized and that
logical mechanical, structural, and chemical changes may be made
without departing from the spirit or scope of the invention. To
avoid detail not necessary to enable those skilled in the art to
practice the invention, the description may omit certain
information known to those skilled in the art. The following
detailed description is, therefore, not to be taken in a limiting
sense, and the scope of the present invention is defined only by
the appended claims.
[0050] The present invention provides a femoral neck fixation
prosthesis and a method of implanting the prosthesis which reduces
bone loss and avoids the other shortcomings of the prior art by
allowing the fixation of a stable femoral head replacement while
reducing the amount of the femur, that must be removed and reamed
for the insertion of the prosthesis. The preferred embodiment
provides that the femoral head is attached to a fixation
prosthesis, which extends coaxially through the central canal of
the femoral neck, into the femur, and is then attached to the
opposite lateral wall of the femur. In this manner, the prosthesis
serves to imitate the original structure of the femoral head while
substantially retaining the natural femoral neck. No other support
members, either crosspins or arms extending into the length of the
femur, are required.
[0051] A femoral neck fixation prosthesis in accordance with the
principles of the present invention is designed to achieve fixation
in the femoral neck with or without cement. Therefore, revision of
the disclosed femoral neck fixation prosthesis would essentially
become the complexity of a present day primary hip arthroplasty for
the femoral component. The improved femoral neck fixation
prosthesis would require an operation equivalent to a primary
arthroplasty on the femoral side. Therefore it would be ideal for
the younger patient, but would also be recommended for the older
patients with accommodating anatomy.
[0052] The innovative method for implanting the femoral neck
fixation prosthesis would allow less muscular dissection, and the
capsule can be repaired anteriorly at the end of the procedure. The
disclosed femoral neck fixation prosthesis is designed to be used
with larger diameter femoral heads. The combination of these
factors would significantly improve stability of the hip. The goal
is to minimize the need for hip position precautions
postoperatively.
[0053] One advantage of the preferred embodiment is that less bone
would be resected initially using the femoral neck fixation
prosthesis, and the stress would be transferred to the bone in the
femoral neck. The metaphysis and the diaphysis of the proximal
femur would be minimally disturbed. Only the femoral head itself
will be resected.
[0054] Another advantage of the preferred embodiment, is that the
femoral neck length and offset would be accurately measured and
reproduced when using the femoral neck fixation prosthesis. Leg
length inequality due to hip arthroplasty could be minimized, and
muscle mechanics could be accurately restored.
[0055] Further, an operation using the femoral neck fixation
prosthesis would be less invasive with less blood loss, less post
operative pain, and less perioperative morbidity than an operation
that employs the vast majority of commonly used prostheses.
[0056] The economic implications of a shorter hospital stay, fewer
blood transfusions, and fewer medical complications are
significant.
[0057] A femoral neck fixation prosthesis according to the
principles of the present invention is shown in FIG. 1, wherein
femur 100 is shown with femoral neck 105, joining member 115, and
prosthetic head 110.
[0058] An uncemented porous coated femoral prosthesis body 125 with
a modular head 110 and joining member 115 is provided. The metal
used is preferably either titanium or chrome-cobalt based, and can
be any metal commonly used in hip prosthesis construction. The
modulus of elasticity of such a short segment will be of less
significance than in a standard femoral stem. The coating is
preferably either sintered beads or plasma sprayed, depending on
the type of metal used for the body of the prosthesis.
[0059] The body 125 of the prosthesis will preferably be available
in various diameters, approximately every 1-1.5 mm. The length of
the prosthesis will preferably be chosen from one or two lengths,
approximately 30 mm. Most of the fixation and ingrowth of the bone
to the prosthesis will occur in the first 10-20 mm.
[0060] As described in more detail below, fixation to the femur
will be achieved by reaming the femoral neck 105 to accommodate a
cylindrical porous coated sleeve body 125, which is supported by a
proximal collar and given distal stability with a compression screw
120 through the lateral wall of the femur just distal to the
greater tuberosity (location 140). Reaming will be progressive
until the cortex of the femoral neck is encountered. A femoral
component 1/2 mm greater than the last diameter reamed will then be
selected.
[0061] After insertion, the long axis of the body of the component
body 125 will coincide with a longitudinal axis in the preoperative
femur 100 corresponding to an imaginary line connecting the center
of the femoral neck 105 with the center of the femoral head 110.
Resection of the femoral head will be measured such that the center
of rotation of the femoral head 110 can be measured and reproduced.
The femoral neck 105 will be reamed with a planar reamer that fits
in the reamed canal of the femoral neck 105 to establish a flat
surface. The proximal body 125 of the prosthesis will have the
female end of a morse taper to allow the attachment of the joining
member 115.
[0062] A compression screw 120 passes through the center of the
body of the prosthesis. This screw attaches to a barrel nut 130 in
the lateral wall of the femur at point 140 and preferably has a
hexagonal head. The screw 120 is preferably smooth in the segment
within the body of the prosthesis and has threads on the distal
end. The tunnel through the body of the prosthesis forms a snug fit
around the smooth portion of the screw 120. The barrel nut 130 is
preferably angled to be flush with the lateral side of the femur at
point 140. The head of the screw 120 is preferably located in the
base of the morse taper in the body 125 of the femoral component.
This screw 120 adds stability to the construct by giving
antero-posterior and varus-valgus stability to the body 125 of the
prosthesis and by compressing the prosthesis on the neck 105 of the
femur 100. These screws will be available in various lengths.
[0063] It is important to note that this innovative design allows
the prosthesis to be installed and used without requiring any other
fastener on the femur. In particular, the preferred embodiment does
not require any additional screws or other fasteners to be placed
in the femur, and does not require any sort of support plate on the
lateral wall of the femur.
[0064] Male-male morse taper joining member 115 acts as a joining
portion in connecting the body 125 of the prosthesis to the femoral
head 110. Adjustments in joining member length will occur in this
segment with several lengths of joining member segments available
for each femoral body and femoral head. The joining member segment
needed to exactly reproduce the center of rotation of the femoral
head will be known based on the amount of bone resected. In this
embodiment, the joining member 115 has male morse tapers 135 on
each side, and will have a variable-length section in between the
morse tapers to fit the specific patient.
[0065] The femoral head 110 will have a female morse taper to
connect to the joining member 115. Femoral heads 110 will be of
various diameters depending on the acetabulum, and several
exemplary sizes are shown in FIG. 1. Ideally, larger femoral head
diameters (e.g., 36 mm to 50 mm) are used to both improve stability
and prevent impingement of the neck on the acetabular rim. The
femoral head 110 is preferably polished chrome-cobalt, as the
industry standard, but other materials can be used.
[0066] In another embodiment of the present invention, a
de-rotation component is added to reduce the likelihood of the
rotation of the prosthesis within the femoral neck. This can be
accomplished with a pin or stem with grooves or slots that passes
through the lateral cortex into the body of the prosthesis. This
would then be compressed with a screw, which would be put through
the head end of the body of the prosthesis into the stem.
[0067] It should be clear that the femoral neck fixation prostheses
described herein can be used with or without cement.
[0068] FIGS. 2A-2C show several cross-sectional views of the
cylindrical porous coated body 225 of the prosthesis of the
preferred embodiment. FIG. 2A shows a longitudinal cross-section of
the body 225. In this view, a collar 248 at the proximal end of the
body 225 is illustrated, as is the female morse taper cavity 246,
which is fit to receive the joining member. The collar 248 is
configured to abut the proximal end of the resected femoral neck.
Communicating with cavity 246 is tubular channel 247 which will
receive the compression screw. Below the collar 248, the exterior
of the body 225 has a porous coated layer 249.
[0069] While the preferred embodiment has a substantially circular
cross-section, as shown in FIGS. 2A-2C, the body member 225 can
also be configured with a triangular (FIG. 2E), scalloped (FIG.
2F), oval (FIG. 2H), or fluted (FIG. 2G) cross-section.
[0070] FIG. 2B shows a lateral cross-section of body 225 as cut
across line B of FIG. 2A. In FIG. 2B, the cavity 246 is shown, and
the proximal collar 248 is also illustrated.
[0071] FIG. 2C shows a lateral cross-section of body 225 as cut
across line C of FIG. 2A. In FIG. 2C, channel 247 for the
compression screw is shown passing through the center of body 225.
On the exterior of body 225 is shown the porous coated layer 249. A
cross-section across line D of FIG. 2A is the same as described for
line C of that FIG.
[0072] FIG. 3 shows joining members 316/317/318 of various sizes,
which can be used for patients with differing requirements. Each
joining member 316/317/318 has a morse taper on each end, and a
variable-length straight section connecting the morse tapers.
[0073] FIG. 4 depicts the centering guide for placement of the
starting pin in accordance with the principles of the present
invention. In this FIG., femoral neck gripping clamp 405 is to grip
and hold the femoral neck after the femoral head centering device
410 has been placed over the patient's femoral head.
[0074] The femoral neck gripping clamp 405 is expanded or
contracted using adjustment piece 420, which operates gears 415.
Cannulated rod 425, which is connected to femoral head centering
device 410, allows pin insertion into the cannula at 435.
[0075] Free nut 430 is used to tighten the femoral head centering
device 410. The centering guide shown in FIG. 4 is preferably made
of a stiff metal, and can also be used as a retractor to expose the
femoral head.
[0076] FIG. 5 depicts how the center of rotation of the femoral
head can be reproduced in accordance with a preferred embodiment of
the present invention. First, distance A from the head to the
lateral cortex is measured. After the femoral head is removed,
distance B, from the cut surface to the lateral cortex, is
measured. The diameter D of the femoral head is also measured. When
these measurements are known, distance C is calculated using the
formula
C=(A-D/2)-B
[0077] Distance C then represents the distance from the cut surface
of the femoral neck that the prosthetic femoral head
center-of-rotation should be placed in order to reproduce the
pre-operative femoral head center-of-rotation.
[0078] In another embodiment shown in FIG. 6, compression screw
620, preferably with washer 645, is inserted through the lateral
wall of the femur at location 640 and screwed into the body 625 of
the femoral component. This simplifies the barrel nut portion of
the design shown in FIG. 1. It would require that the screw 620 be
of various lengths that would engage the body 625 of the prosthesis
without reaching the depth of the hole in the femoral prosthesis.
The body of the prosthesis would preferably be longer, using
optional extension 650 to provide enough length so that the
compression screw will be stable within the body of the
prosthesis.
[0079] The remainder of FIG. 6 is similar to FIG. 1. In this FIG.,
femur 600 is shown with femoral neck 605, joining member 615, and
prosthetic head 610.
[0080] This embodiment provides an uncemented porous coated femoral
prosthesis body 625 with a modular head 610 and joining member 615.
The body 625 of the prosthesis include threads 655 for receiving
screw 620.
[0081] As described in more detail below, fixation to the femur
will be achieved by reaming the femoral neck 605 to accommodate a
cylindrical porous coated sleeve body 625, which is supported by a
proximal collar and given distal stability with a compression screw
620 through the lateral wall of the femur just distal to the
greater tuberosity (location 640).
[0082] After insertion, the long axis of the body of the component
body 625 will coincide with a longitudinal axis in the preoperative
femur 600 corresponding to an imaginary line connecting the center
of the femoral neck 605 with the center of the femoral head 610.
Resection of the femoral head will be measured such that the center
of rotation of the femoral head 610 can be measured and reproduced
as discussed with reference to FIG. 5. The femoral neck 605 will be
reamed with a flat reamer that fits in the reamed canal of the
femoral neck 605 to establish a flat surface. The proximal body 625
of the prosthesis will have the female end of a morse taper to
allow the attachment of the femoral neck 615.
[0083] Compression screw 620 passes through the center of the body
of the prosthesis. The screw 620 is preferably smooth in the
segment within the body of the prosthesis and has threads on the
proximal end, for engaging threads 655. The tunnel through the body
of the prosthesis forms a snug fit around the smooth portion of the
screw 620. Screw 620 adds stability to the construct by giving
antero-posterior and varus-valgus stability to the body 625 of the
prosthesis and by compressing the prosthesis on the neck 605 of the
femur 600. These screws will be available in various lengths.
[0084] Male-male morse taper joining member 615 connects the body
625 of the prosthesis to the femoral head 610. Adjustments in
joining member neck length will occur in this segment with several
lengths of joining member segments available for each femoral body
and femoral head. The joining member segment needed to exactly
reproduce the center of rotation of the femoral head will be known
based on the amount of bone resected.
[0085] The femoral head 610 will have a female morse taper to
connect to the joining member 615. Femoral heads 610 will be of
various diameters depending on the acetabulum. Ideally larger
femoral head diameters (e.g., 36 mm to 60 mm) are used to both
improve stability and prevent impingement of the neck on the
acetabular rim. The femoral head 610 is preferably polished
chrome-cobalt, as the industry standard, but other materials can be
used.
[0086] FIG. 7 shows a preferred embodiment of the femoral neck
fixation prosthesis of the present invention. If the compression
screw 720, with washer 745, is inserted through the lateral wall of
the femur at 740, the length of the body 725 of the prosthesis may
not be long enough to provide adequate stability for the
compression screw 720. In order to provide this stability for the
compression screw, a fixed length joining member 760 on the body of
the prosthesis would be necessary to act as a joining member,
abandoning the modular joining member (115 in FIG. 1). The varied
lengths required on the joining member would be incorporated into
the femoral head either with separate individual lengths for each
head diameter (2 to 3 for each diameter femoral head) or by using
an interposing piece of metal to provide additional neck length.
The latter is done with several femoral components available on the
market today.
[0087] The femoral neck fixation prosthesis is implanted by first
preparing the femur for reception of the prosthesis. Referring to
FIG. 8, several orientations and anatomical features relative to a
femur 811 should first be defined to more easily understand the
process of preparing the femur and implanting the prosthesis. As
used herein, the term "medial" shall mean "pertaining to the
middle," while the term "lateral" shall mean "pertaining to the
side." The femur 811 includes a medial side 813 and a lateral side
815. The term "proximal" shall mean "nearest the point of
attachment, center of the body, or point of reference," while the
term "distal" shall mean "the opposite of proximal, or farthest
from the center, from a medial line, or from the trunk." The terms
proximal and distal are generally used to convey positional or
directional information relative to a particular feature, so it
would not be entirely proper to refer to a proximal "side" of the
femur or a distal "side" of the femur. However, these terms can be
demonstrated by comparing some of the basic anatomy of the femur.
Femur 811 includes a femoral head 821, a femoral neck 823, a shaft
825, a greater trochanter 827, and a lesser trochanter 829. Since
the femoral head 811 serves as a point of attachment when it is
received by the acetabulum (not shown), the femoral head 821 is
located proximal to the femoral neck 823 and the shaft 825. The
shaft 825 is located distal to both the femoral neck 823 and the
femoral head 821. As used herein the term "superior" shall mean
"higher than or situated above something else," while the term
"inferior" shall mean "beneath or lower." The term "anterior" shall
mean "before or in front of" and shall generally refer to the
ventral or abdominal side of the body. The trem "posterior" shall
mean "toward the rear" and shall generally refer to the back or
dorsal side of the body. A posterior side 831 of the femur 811 is
shown in FIG. 8, while the anterior side is hidden from view in
FIG. 8.
[0088] A longitudinal axis 845 of the femoral neck is difficult to
precisely define because the geometry of the femoral neck 823 is
usually not perfectly cylindrical. Theoretically speaking, if the
femoral neck 823 were sectioned along its length at a finite number
of cross-sectional planes (e.g. B-B and C-C in FIG. 8), and the
center of each cross-section were determined, the line passing
through the center of rotation of the femoral head (described
previously with reference to FIG. 5) and passing through an average
of the centers of the cross-sections would likely represent the
longitudinal axis 845 of the femoral neck 823. In reality, it is
difficult to locate the center of each cross-section of the femoral
neck 823. It is also difficult to locate the plane at which each
cross-section would be taken. Theoretically, each cross-section is
located at a plane perpendicular to the longitudinal axis 845, but
this presents a somewhat circular method for determining the
orientation of the cross-sectional planes and the longitudinal axis
845.
[0089] One method for determining the proper orientation of the
cross-sectional planes would be to envision an isthmus 849 of the
femoral neck 823. The isthmus 849 is the narrowest point on the
femoral neck 823 when viewed from the anterior or posterior side of
the femur 811. Visualization of the posterior side 831 of the femur
811 allows a lateral line to be constructed across the femoral neck
823 at the isthmus 849. In FIG. 8, the line at section C-C
represents an isthmus plane 851, which is a cross-sectional plane
extending through the femur in an antero-posterior direction. The
visualization of this plane at the isthmus 849 of the femoral neck
823 allows a close approximation of a plane that would be
perpendicular to the longitudinal axis 845 of the femur 811. Other
cross-sectional planes visualized through the femoral neck 823
would be parallel to the isthmus plane at the isthmus 849.
[0090] In practice, the femoral neck 823 is not actually cut at
each of the cross-sectional planes discussed above. Rather, the
visualization of these planes is helpful in determining,
theoretically, where the longitudinal axis 845 of the femoral neck
823 would lie. It would be sufficient to define the longitudinal
axis 845 as the line passing through the center of rotation of the
femoral head 821 and the center of the femoral neck 823 at the
isthmus 849. However, as previously mentioned, it would also be
appropriate and perhaps more accurate to define the longitudinal
axis 845 as the line passing through the center of rotation of the
femoral head 821 and the average of the centers of the femoral neck
823 taken at several cross-sections, all of which are parallel to
the isthmus plane 851. It should also be noted that for some
patients, the center of rotation of the femoral head may not
necessarily coincide with the longitudinal axis 845.
[0091] Referring to FIG. 9, the visualization of the "center" of
the femoral neck is not necessarily simple due to the varying
geometry of the femoral neck 823. For example, a cross-section
taken at A-A in a region of transition between the femoral head 821
and the femoral neck 823 is approximately round. However, the
cross-sectional shapes of the femoral neck 823 taken at B-B and C-C
are not perfectly round, and instead have various protrusions and
other anatomical features that make it difficult to locate the
center point of the cross-section. A cross-section from a more
proximal portion of the femoral neck 823 is illustrated at B-B and
demonstrates that this portion of the neck is somewhat circular in
shape. Cross-section C-C at the isthmus 849 of the femoral neck 823
illustrates several prominent features that cause the femoral neck
823 to deviate from a perfectly round shape. The features of the
femoral neck at C-C include an antero-superior ridge 850 and a
postero-inferior ridge 855. The antero-superior ridge 850 is a
pronounced feature of the femoral neck 823 at this part of the
femoral neck 823 and joins the greater trochanter 827 in a region
distal to the isthmus 849. The postero-inferior ridge 855 is less
pronounced and joins the lesser trochanter 829 in a region distal
to the isthmus 849. The femoral neck 823 includes a relatively flat
superior surface 857, while an inferior surface 859 is more
rounded. These anatomical features of any particular femur will
vary slightly and could vary greatly from person to person.
[0092] Referring still to FIGS. 8 and 9, the center of any given
cross-section will be at the mean geometric center for any
particular cross-section. When several cross-sections are
visualized along the femoral neck 823, the mean geometric centers
of all the cross-sections may not be aligned such that the centers
can be connected by a line. In this particular instance, a line
representing longitudinal axis 845 could be drawn through the
center of rotation of the femoral head and through the plurality of
cross-sectional centers so as to minimize deviation with respect to
the plurality of cross-sectional centers. If the femoral head is
misshapen, the longitudinal axis 845 may be considered only with
respect to the cross-sectional centers and not the center of
rotation of the femoral head.
[0093] Alternatively, the center of each cross-section could be
located based on the shape of the cancellous bone at that
cross-section. Since the prosthesis according to the principles of
the present invention is to be implanted within the cancellous
bone, it may be more appropriate to define the center of the
femoral neck 823 based on the shape and location of the cancellous
bone. The center of each cross-section would be the point at which
a circle circumscribed around the point would most fully contact
the surrounding cortex.
[0094] The "location" and/or "visualization" of the longitudinal
axis 845 of the femoral neck 823 is theoretical and is discussed to
more easily explain how the femoral neck fixation prosthesis is
oriented and implanted within the femur 811. It is not necessarily
required that the longitudinal axis 845 be found prior to
implanting the prosthesis; however, it is important to note that in
most cases, the femoral neck fixation prosthesis will be installed
in the femur such that a longitudinal axis of the prosthesis is
substantially coaxial to the longitudinal axis 845 of the femoral
neck 823 as described above. This implantation could be
accomplished by using non-invasive techniques such as X-rays or
magnetic resonance imaging (MRI) to visualize and locate the
longitudinal axis 845 of the femoral head 823, but in most
instances, the prosthesis will be implanted using specialized tools
that properly orient the prosthesis based on anatomical landmarks
on the femoral neck. We believe that the use of these tools and
anatomical landmarks will closely align the prosthesis with the
longitudinal axis of the femoral neck, thereby obviating the need
for calculating or identifying the longitudinal axis during the
procedure.
[0095] It will be appreciated by those of ordinary skill in the art
that certain femoral anatomical variations among patients may
result in the prosthesis being implanted such that the longitudinal
axis of the prosthesis is not coaxial to the longitudinal axis 845
of the femoral neck 823. In fact, the implantation of the
prosthesis in some patients could result in the longitudinal axis
of the prosthesis being located as much as 5 to 10 degrees from the
longitudinal axis 845 of the femoral neck 823.
[0096] Implantation of the femoral neck fixation prosthesis is
accomplished by resecting the femoral head 821, reaming at least
one passage through the femoral neck, reaming the acetabulum, and
implanting the femoral neck fixation prosthesis into the reamed
passage. Access to the femoral head and femoral neck is
accomplished by making a small incision in the gluteus maximus to
expose the hip joint. The femoral head 821 is dislocated from the
acetabulum in a manner similar to that employed in current hip
arthroplasty procedures. The leg of the patient is then internally
rotated (i.e. rotated such that the toe of the patient's foot are
rotated toward a medial plane of the body) to expose the femoral
head and neck through the incision. Following exposure, the femoral
head may be resected as explained below from the internally rotated
position. The remaining procedures (i.e. reaming the passages,
reaming the acetabulum, and implanting the femoral neck fixation
prosthesis) are performed as described below with the patient's leg
in either the internally-rotated position or in a neutral position
(i.e. non-rotated position). The procedures for preparing the femur
and implanting the prosthesis could alternatively be accomplished
by rotating the patient's leg externally if the location of the
initial incision were moved.
[0097] Referring to FIGS. 10-13, a femoral neck clamp 1011
according to principles of the present invention assists in
locating the cutting plane at which the femoral head 821 is to be
resected. The femoral neck clamp 1011 does this by locating the
isthmus 849 of the femoral neck 823 by grasping anatomical
landmarks on the femoral neck, such as the antero-superior ridge
850 and the inferior region of the femoral neck 823. Again, the
isthmus 849 defines a line that is substantially perpendicular to
the longitudinal axis 845 of the femoral neck 823.
[0098] The femoral neck clamp 1011 includes an inferior clamping
member 1013 and a superior clamping member 1015. A locator shaft
guide member 1021 includes a cylindrical passage 1023 and is
attached to either the inferior clamping member 1013 or the
superior clamping member 1015. The superior clamping member 1015
preferably includes an arcuate region 1025 for securely gripping
the antero-superior ridge 850 (see FIG. 9) of the femoral neck 823;
however, the superior clamping member 1015 could be substantially
flat with no arcuate region. The inferior clamping member 1013
preferably includes a proximal clasp 1031 and a distal clasp 1033
that are connected by a connecting member 1035. The inferior
clamping member 1013 cradles the inferior region of the femoral
neck 823 with preferably at least two points of contact occurring
between the femoral neck 823 and each of the proximal and distal
clasps 1031, 1033. It is important to note that while it is
preferred that the shape of the proximal and distal clasps 1031,
1033 is V-shaped, the shape could be hemi-circular (see FIG. 13A),
square (see FIG. 13B), polygonal (see FIG. 13C), or any other shape
that provides adequate contact with the femoral neck 823. While the
preferred embodiment includes the presence of a proximal and distal
clasp, the inferior clamping member 1013 may include only one clasp
that is preferably aligned with the superior clamping member 1015
to locate the isthmus 849 of the femoral neck 823.
[0099] Referring still to FIGS. 10 and 11, the femoral neck clamp
1011 preferably includes a handle portion 1041 having a pair of
handle members 1043 biased apart by a spring member 1045. The
spring member 1045 is preferably made from sheets of spring steel
and shaped to hold the handle members 1043 apart in an open
position. However, the spring member 1045 could be any device used
to apply such a force, including without limitation a helical
spring, a leaf spring, or a resilient bushing. A pair of rods 1047
is rigidly attached to one of the handle members, and each rod 1047
passes through an aperture 1049 in the other handle member 1043.
Since the handle members 1043 are not pivotally attached, the rods
1047 assist in guiding the movement of the handle members 1043
relative to one another. By applying a force to each handle member
1043 directed toward the other handle members 1043 (i.e. by
squeezing the handle members 1043), a surgeon can decrease the
distance between the inferior and superior clamping members 1013,
1015 in order to position the clamping members securely around the
femoral neck. When the squeezing force applied to the handle
members 1043 is released or relaxed, the spring member 1045 pushes
the handle members 1043 apart, thereby returning the femoral neck
clamp 1011 to the open position. The configuration of the handle
members 1043, rods 1047, and spring member 1045 allow the inferior
and superior clamping members 1013, 1015 to move in translational,
parallel fashion relative to one another when the handle members
1043 are squeezed. Since rotation of the handle members 1043
relative to one another is avoided, the inferior and superior
clamping members 1013, 1015 are allowed to more effectively grip
the appropriate anatomical features of the femoral neck 823. A
locking member 1051 may be attached to the handle portion 1041 to
lock the inferior and superior clamping members 1013, 1015 once
positioned around the femoral neck 823. The locking member 1051
shown in FIG. 11 is pivotally attached to one of the handle members
1043 and is rotatably positionable to engage a plurality of teeth
1053 on at least one of the rods 1047. In FIG. 11, two locking
members 1051 are shown.
[0100] The femoral neck clamp 1011 is used to locate the isthmus
plane 851, which is represented by a line in FIG. 12 at the isthmus
849 of the femoral neck 823. To find the isthmus plane 851, the
inferior and superior clamping members 1013, 1015 are first
positioned on inferior and superior sides of the femoral neck 823,
respectively, with the superior clamping member 1015 and the
proximal clasp 1031 visually aligned with an area of the femoral
neck 823 that appears to be the isthmus 849. As the handle members
1043 are squeezed, the superior clamping member 1015 and the
proximal clasp 1031 grip the femoral neck 823 in the area of the
isthmus 849. Further squeezing of the handle members 1043 and
gentle side-to-side manipulation of the femoral neck clamp 1011 in
a direction approximately parallel to the longitudinal axis 845 of
the femoral neck 823 allows the superior clamping member 1015 and
the proximal clasp 1031 to settle at the isthmus 849 of the femoral
neck 823. Further alignment of the femoral neck clamp 1011 is
ensured by the distal clasp 1033, which prevents the femoral neck
clamp 1011 from rotating about the line representing isthmus plane
851 in FIG. 12. The distal clasp 1033 accomplishes this by
providing a second point of contact for the inferior clamping
member 1013 in the inferior region of the femoral neck 823.
Preventing rotation of the femoral neck clamp 1011 about the line
representing isthmus plane 851 in FIG. 12 could also be
accomplished by having an inferior clamping member 1013 that
included a single clasp with a wider area of contact on the
inferior region of the femoral neck 823. However, widening either
the inferior clamping member 1013 or the superior clamping member
1015 too much will decrease the ability of the femoral neck clamp
1011 to find the isthmus 849 since the inferior and superior
clamping members 1013, 1015 will be unable to properly settle into
the concave portions of the femoral neck 823 as illustrated in FIG.
12.
[0101] Both the inferior and superior clamping members 1013, 1015
take advantage of anatomical landmarks present on the femoral neck
823 to locate the isthmus 849 and the isthmus plane 851, which is
typically substantially perpendicular to the longitudinal axis 845
of the femoral neck 823. As previously mentioned, the superior
clamping member 1015 primarily contacts and, depending on whether
it includes an arcuate region 1025, cradles the antero-superior
ridge 850 (see FIG. 13). The inferior clamping member 1013,
including the proximal and distal clasps 1031, 1033, preferably is
formed in one of the shapes previously described (see FIGS. 13-13C)
to cradle the postero-inferior ridge 855 and other portions of the
inferior region of the femoral neck 823. The distal clasp 1033 of
the inferior clamping member 1013 provides stability to the femoral
neck clamp 1011 to prevent rotation of the femoral neck clamp 1011
about the line representing isthmus plane 851 in FIG. 12. The
distal clasp 1033 is preferably not directly connected to either
handle member 1043, but rather is connected to proximal clasp 1031
by the connecting member 1035, which allows rotation of the distal
clasp 1033 relative to the proximal clasp 1031. By connecting the
distal clasp 1033 to the proximal clasp 1031 (as opposed to the
handle members 1043), the application of force through the handle
members 1043 is directed primarily to the superior clamping member
1015 and the proximal clasp 1031. This allows the superior clamping
member 1015 and the proximal clasp 1031 to more easily locate the
isthmus 849 of the femoral neck 823, while the distal clasp 1033
maintains rotational stability of the femoral neck clamp 1011
without causing the superior clamping member 1015 and the proximal
clasp 1031 to shift positions along the femoral neck 823.
[0102] Referring to FIGS. 14-16 in the drawings, several different
variations of the connecting member 1035 are shown, each of which
would be suitable to allow rotation of the distal clasp 1033. In
FIG. 14, a connecting member 1411 is rigidly connected to the
distal clasp 1033 and pivotally connected to the proximal clasp
1031. A torsion spring (not shown) is operably connected to the
proximal clasp 1031 and the connecting member 1411 to bias the
distal clasp 1033 toward the femoral neck 823 in a
counter-clockwise direction (with respect to the view shown in FIG.
14). In FIG. 15, a connecting member 1511 is rigidly connected to
both the proximal and distal clasps 1031, 1033. The connecting
member 1511 is preferably made from a resilient material such as
spring steel that allows rotation of the distal clasp 1033 relative
to the proximal clasp 1031, but provides sufficient force to the
distal clasp 1033 to firmly contact the femoral neck 823. In FIG.
16, a connecting member 1611 is rigidly attached to the distal
clasp 1031 and is pivotally attached to the proximal clasp 1031.
The connecting member includes a slot 1615; and a fastener 1617,
preferably a screw, a bolt, or a locking pin, is received through
the slot 1615 and is attached to the proximal clasp 1031. The
fastener 1617 allows rotation of the distal clasp 1033 to be
selectively chosen. After rotating the distal clasp 1033 enough to
firmly contact the femoral neck 823, the fastener can be tightened
or locked in place to prevent further rotation of the distal clasp
1033 relative to the proximal clasp 1031.
[0103] Referring again to FIGS. 10-12, the locator shaft guide
member 1021 of the femoral neck clamp 1011 is connected to the
superior clamping member 1015 or the handle member 1043 adjacent
the superior clamping member 1015. The locator shaft guide member
1021 is oriented such that the cylindrical passage 1023 of the
locator shaft guide member 1021 is substantially parallel to the
longitudinal axis 845 of the femoral neck 823 when the femoral neck
clamp 1011 is finally positioned at the isthmus 849. Typically, the
locator shaft guide member 1021 will be rigidly connected to the
superior clamping member 1015 because the anatomy of most femurs is
such that the positioning of femoral neck clamp 1011 at the isthmus
849 will provide automatic, parallel alignment of the locator shaft
guide member 1021 relative to the longitudinal axis 845 of the
femoral neck 823. However, it is conceivable that certain
anatomical features of some femurs may prevent proper alignment of
the locator shaft guide member 1021, so the locator shaft guide
member 1021 may be adjustably mounted to the superior clamping
member 1015 to allow for rotational adjustment and visual alignment
of the locator shaft guide member 1021 relative to the longitudinal
axis 845.
[0104] Referring to FIG. 17, a femoral neck clamp 1711 according to
the principles of the present invention includes an inferior
clamping member 1713 and a superior clamping member 1715 similar to
those of femoral neck clamp 1011. Femoral neck clamp 1711 includes
a parallelogram, four-bar-linkage mechanism 1721 to provide
translational movement (as opposed to rotational movement) of the
inferior clamping member 1713 relative to the superior clamping
member 1715. Linkage mechanism 1721 includes an inferior handle
member 1743 pivotally connected to a superior handle member 1745.
Superior handle member 1745 is pivotally connected at one end to a
coupler link 1747 that is rigidly connected to the superior
clamping member 1715. A side link 1751 is pivotally connected at
one end to the coupler link 1747 and at another end to the inferior
handle member 1743. The side link 1751 and the portion of the
superior handle member 1745 extending between the inferior handle
member 1743 and the coupler link 1747 are preferably parallel and
equal in length. The coupler link 1747 and the portion of the
inferior handle member 1743 extending between the superior handle
member 1745 and the side link 1751 are preferably parallel and
equal in length. A torsion spring 1753, or other spring mechanism,
may be operably connected to the inferior handle member 1743 and
superior handle member 1745 to bias the handle members 1743, 1745,
and thus the inferior and superior clamping members 1713, 1715,
apart. A locking member 1755 may be pivotally attached to an end of
either the inferior or superior handle members 1743, 1745.
Preferably, the locking member 1755 includes a plurality of teeth
1759 adapted to engage the other handle member 1743, 1745 and thus
lock the inferior clamping member 1713 relative to the superior
clamping member 1715. A locator shaft guide member 1765 is
connected to either the inferior clamping member 1713 or the
superior clamping member 1715 similar to locator shaft guide member
1021 of FIG. 12. Alternatively, the locator shaft guide member 1765
could be connected to coupler link 1747, inferior handle member
1743, or superior handle member 1745 near the inferior and superior
clamping members 1713, 1715.
[0105] Referring to FIG. 18, a femoral neck clamp 1811 according to
the principles of the present invention includes an inferior
clamping member 1813 and a superior clamping member 1815 similar to
those of femoral neck clamp 1011. Femoral neck clamp 1811 further
includes an inferior handle member 1843 pivotally connected to a
superior handle member 1845. A torsion spring 1853, or other spring
mechanism, may be operably connected to the inferior handle member
1843 and superior handle member 1845 to bias the handle members
1843, 1845, and thus the inferior and superior clamping members
1813, 1815, apart. A locking member 1855 may be pivotally attached
to an end of either the inferior or superior handle members 1843,
1845. Preferably, the locking member 1855 includes a plurality of
teeth 1859 adapted to engage the other handle member 1843, 1845 and
thus lock the inferior clamping member 1813 relative to the
superior clamping member 1815. A locator shaft guide member 1865 is
connected to either the inferior clamping member 1813 or the
superior clamping member 1815 similar to locator shaft guide member
1013 of FIG. 12.
[0106] Referring to FIG. 19, the femoral neck clamp 1011 (could
also be femoral neck clamp 1711 or 1811) has been positioned around
the femoral neck 823 at the isthmus 849 such that the superior
clamping member 1015 and the proximal clasp 1031 of the inferior
clamping member 1013 are aligned with the isthmus plane 851. The
distal clasp 1033 also engages the femoral neck 823 to prevent
rotation of the femoral neck clamp 1011 about the line representing
isthmus plane 851. Following positioning of the femoral neck clamp
1011 at the isthmus 849, the locator shaft guide member 1021 is
automatically aligned such that a longitudinal axis of the
cylindrical passage 1023 of the locator shaft guide member 1021 is
oriented at an angle of approximately ninety (90) degrees to the
isthmus plane 851.
[0107] A locator shaft 1911 is positioned within the cylindrical
passage 1023 of the locator shaft guide member 1021 after the
femoral neck clamp 1011 has been positioned at the isthmus 849 of
the femoral neck 823. A base plate 1915 is rigidly connected to an
end of the locator shaft 1911 such that following insertion of the
locator shaft 1911 in the cylindrical passage 1023, the locator
shaft 1911 can be advanced in a distal/lateral direction until the
base plate 1915 abuts the femoral head 821. Indicia 1921 in the
form of ruled demarcations is printed along the locator shaft 1911
for accurately positioning a pin locator guide 1925, which is
slidingly received on the locator shaft 1911. Pin locator guide
1925 preferably includes at least two spaced apart holes 1931 that
may be located on one side of the locator shaft 1911, or as
illustrated in FIG. 19, may be located on opposite sides of the
locator shaft 1911. Holes 1931 are positioned on the pin locator
guide 1925 such that a line connecting the center of the holes 1931
is preferably parallel to the isthmus plane 851.
[0108] Referring to FIGS. 19 and 20, by slidably positioning the
pin locator guide 1925 along the locator shaft 1911 a selectable
distance from the proximal end of the femoral head 821, pins 2011
can be inserted through the holes 1931 on the pin locator guide
1925. The placement of the pins 2011 in the femoral head 821 fixes
the previously determined orientation of the isthmus plane 851,
which allows the femoral neck clamp 1011 to be removed from the
femur. In FIG. 20, a cutting guide 2021 includes a pair of holes
2027 that are spaced apart the same distance as the holes on the
pin locator guide 1925. The cutting guide 2021 is placed over the
pins 2011 such that the pins 2011 are received by the holes 2027. A
cutting slot 2025 is positioned on the cutting guide 2021 such that
it is oriented substantially parallel to a line connecting the
centers of the two holes 2027. When installed on the pins 2011 as
shown in FIG. 20, the cutting guide 2021 places the cutting slot
2025 a known distance from the pins 2011 to allow resection of the
femoral head 821 along a cutting plane (not shown) that is
substantially parallel to the isthmus plane 851. The femoral head
821 is resected from the femur 811 by inserting a cutting blade or
other cutting tool through the cutting slot 2025 and cutting
through that portion of the femur 811.
[0109] As mentioned previously, the locator shaft 1911 includes
indicia 1921 in the form of ruled demarcations that are spaced
apart precise distances. These demarcations can be used to
precisely locate the cutting plane relative to the proximal end of
the femoral head 821. The amount of resection that will be
performed depends on several factors. A prosthetic femoral head
will be chosen to match the measured diameter of the patient's
native femoral head. This is done to insure that the center of
rotation is closely matched by the prosthesis and that the length
of the patient's leg is not significantly lengthened or shortened.
Based on the diameter chosen for the prosthetic femoral head, a
height of the prosthetic femoral head (measured along longitudinal
axis 845) will be known. This height equates to the amount of bone
resected from the proximal end of the native femoral head 823.
Since the distance between the holes 2027 on the cutting guide 2021
and the cutting slot 2025 is known, the pin locator guide 1925 can
be accurately positioned along the locator shaft 1911 using the
indicia 1921 to place the pin locator guide 1925 according to the
amount of bone that needs to be resected. The placement of the pins
2011 using the pin locator guide 1925 then allows the cutting slot
2025 to be accurately positioned at the correct location to remove
the correct length of bone.
[0110] It will be apparent to one of ordinary skill in the art that
the cutting guide 2021 of the present invention could be combined
with the femoral neck clamp 1011 to eliminate the need for a
locator shaft 1911 and a pin locator guide 1925. The combination
clamp and cutting guide would allow the clamp to be positioned at
the isthmus 849 of the femoral neck 823 as previously described,
but would provide a slot or other guide to allow resection of the
femoral head along a cutting plane substantially parallel to the
isthmus plane 851. The slot or guide would be adjustable relative
to the isthmus plane 851 to allow a measured amount of bone to be
resected from the femur 811. A cutting guide that aligns the
cutting plane a measured distance from the isthmus plane 851 would
be particularly useful in the event that the femoral head is
missing, deformed, substantially misshapen, or broken. Measurements
could be performed preoperatively using radiographic measurement
techniques (e.g. X-ray).
[0111] Referring to FIG. 20A, a method of resecting a femoral head
from a femur having a femoral neck 2051 is illustrated. The first
step at 2055 includes positioning a locator shaft adjacent an
exterior surface of the femoral head and substantially parallel to
a longitudinal axis of the femoral neck. At step 2059 a pin locator
guide having a least two holes is positioned along the locator
shaft. At step 2063 a pin is inserted through each of the two holes
in the pin locator guide and into the femoral head. The femoral
head is resected by aligning a cutting guide relative to the pins
at step 2065.
[0112] Following resection of the femoral head 821, a proximal neck
surface 2111 is exposed that is substantially parallel to the
isthmus plane 851. Progressive reaming and drilling of the femoral
neck 823 is needed to prepare passages between the proximal neck
surface 2111 and the lateral side 815 of the femur 821. With the
patient's leg still in an internally rotated position (or
alternatively in an externally rotated position), a starter guide
2121 having a positioning portion 2125 and a guide portion 2127 is
placed against the proximal neck surface 2111 such that the surface
of the positioning portion 2125 opposite the guide portion 2127
mates with the proximal neck surface 2111. The starter guide 2121
further includes a guide passage 2131 that passes through both the
guide portion 2127 and the positioning portion 2125 such that a
longitudinal axis of the guide passage 2131 is substantially
perpendicular to the proximal neck surface 2111 when the starter
guide 2121 is placed against the proximal neck surface 2111. A
starter passage, or main passage, or primary passage 2141
(represented in FIG. 21 by dashed lines) is formed in the femoral
neck 823 from the proximal neck surface 2111 by first drilling a
small hole 2145 using a drill bit or other boring tool placed in
the guide passage 2131. The starter passage is preferably drilled
only partially into the femoral neck, and not through the lateral
side 815 of the femur. When placing the starter guide 2121 and
drilling the hole 2145, it is preferred to visualize the
approximate center of the femoral neck on the proximal neck surface
2111 so that the hole 2145 is approximately centered within the
femoral neck 823.
[0113] After drilling the hole 2145, the starter guide 2121 is
removed from the proximal neck surface 2111, and the femoral neck
823 is progressively reamed until the hole 2145 extends to the
cortical bone of the femoral neck 823, thereby forming the starter
passage 2141. In practice, depending on the anatomical shape of the
patient's femoral neck 823, it may only be possible to form the
starter passage 2141 to contact the cortical bone at two points of
contact. It is of course preferable to maximize the number of
contacts of the cortical bone, and in most instances, it will be
possible to contact the cortical bone in at least three locations
without significantly decreasing the wall thickness of the cortex
in any location, The starter passage 2141 is reamed to a depth that
is preferably equal to the longitudinal length of the body 125,
625, 725 (see FIGS. 1, 6 and 7) of the femoral neck prosthesis. The
final diameter of the starter passage 2141, which is determined by
how much reaming is needed to contact the cortical bone, will be
slightly less than the chosen diameter of the body 125, 625, 725 of
the prosthesis.
[0114] The method for forming the starter passage 2141 described
above is largely based on visualization of the center of the
femoral neck and formation of a hole 2145. In an alternative
embodiment, a guide may be placed flush against the proximal neck
surface 2111 to orient a reamer at a ninety (90) degree angle to
the proximal neck surface 2111 and center the reamer relative to
the longitudinal axis of the femoral neck. The neck is sequentially
reamed until the starter passage 2141 extends to the cortex. In
another embodiment, a guide pin may be inserted into the femoral
neck substantially parallel to the longitudinal axis of the femoral
neck. The pin may be placed based on visualization or guided into
place with a guide that is fixed relative to the femoral neck. The
guide pin would be used to direct sequential reaming of the starter
passage 2141.
[0115] Referring to FIGS. 22 and 23, a drilling guide 2211 having
an anchor member 2215 rigidly connected by a connecting member 2217
to an alignment sleeve 2219 is used to drill a distal passage, or
fastener passage, or secondary passage 2221 (represented in FIG. 22
by dashed lines) from the lateral side 815 of the femur 811. The
alignment sleeve 2219 includes an alignment passage 2225 for
receiving a drill bit or other boring tool. The connecting member
2217 may be C-shaped and connects the anchor member 2215 to the
alignment sleeve 2219 such that a longitudinal axis of the
alignment passage 2225 is coaxial to the longitudinal axis of the
anchor member 2215, both of which are coaxial to a longitudinal
axis 2227 of the drilling guide 2211. The anchor member 2215 is
cylindrical and sized to fit within the starter passage 2141. The
anchor member 2215 could be interchangeable to allow different
diameters to be used to properly fit within the starter passage
2141 of a particular patient. Alternatively, the anchor member 2215
could be tapered to allow a snug fit within starter passages 2141
of several different diameters. The anchor member 2215 may also
include a collar 2231 for further stabilizing the drilling guide
2211 against the proximal neck surface 2111 when inserted into the
starter passage 2141.
[0116] After positioning the anchor member 2215 within the starter
passage 2141, the alignment sleeve 2219 is located on the lateral
side 815 of the femur 811. The patient's skin and other soft tissue
2233 are located between the alignment sleeve 2219 and the femur
821. The leg of the patient is then rotated to a neutral position,
and an incision 2235 is made through the soft tissue of the patient
in the vicinity of the alignment sleeve 2219. A drilling bit 2241
or other boring tool is inserted through the alignment passage 2225
of the alignment sleeve 2219 for drilling the distal passage 2221
to join the starter passage 2141. Because the alignment sleeve 2219
is coaxial to the anchor member 2215 and because the anchor member
2215 is securely positioned within the starter passage 2141, the
distal passage 2221 is easily formed coaxial to the starter passage
2221.
[0117] As shown in FIG. 22, the distal passage 2221 is typically
smaller in diameter than the starter passage 2141, since the distal
passage 2221 will receive the fastener 120, 620, 720 (see FIGS. 1,
6, and 7) for securing to the body 126, 625, 725 of the femoral
neck fixation prosthesis.
[0118] The primary reason for using a drilling guide 2211 to
complete drilling through the femur is that it is less desirable to
drill a hole completely through the femur from the proximal neck
surface 2111 toward the lateral side 815 of the femur 811. When
drilling from the proximal neck surface 2111, the patient's leg
would be in the internally rotated position. It is not as safe to
drill through the lateral side 815 of the femur 811 when the leg is
internally rotated because the drill bit may contact and sever
vital anatomy, such as the femoral artery or other vessels and
nerves, upon exiting the femur 811. Since use of the drilling guide
2211 allows the leg to be rotated back to the neutral position,
drilling can proceed from the lateral side 815 of the femur 811
without fear of contacting vital anatomy.
[0119] Referring to FIG. 23A, a method of preparing a femur for
implantation of a femoral neck fixation prosthesis 2321 includes
two steps. The first step at 2325 includes first forming a main
passage in the femoral neck from a medial side of the femur
substantially coaxial to a longitudinal axis of a femoral neck. The
second step at 2329 includes second forming a secondary passage
from a lateral side of the femur that is coaxial to and joins the
main passage.
[0120] Although the preparation of the femur for implantation of
the prosthesis includes forming two separate passages from
different sides of the femur, the starter and distal passages could
be formed from the same side of the femur. Following the formation
of the starter passage 2141, a guide may be placed within the
starter passage 2141 to guide drilling of the distal passage 2221
from the proximal side of the femoral neck 823. Since the leg of
the patient would likely be in an internally rotated position
during this drilling procedure, care would be taken to only
slightly penetrate the cortex on the lateral side of the femur 821.
This would help avoid major arteries and nerves in the patient's
leg. After forming both the starter and distal passages 2141, 2221
from the medial side of the femur, the drilling guide 2211 could be
used to place the fastener 120, 620, 720 in the femur during the
implantation of the femoral neck prosthesis, which is described in
more detail below.
[0121] After forming both the starter passage 2141 and the distal
passage 2221, the femur 811 is capable of receiving the femoral
neck fixation prosthesis. However, prior to implantation of the
prosthesis, it may be desirable to prepare the acetabulum for
receipt of an acetabular component (not shown) that will mate with
the head of the femoral neck fixation prosthesis. The starter and
distal passages 2141, 2221 may be used to guide the preparation of
the acetabulum, which initially involves reaming.
[0122] Referring to FIGS. 24 and 25, a reamer path protector 2411
includes an insertion end 2415 and a handle end 2419. The insertion
end preferably includes a plurality of threads 2421, while the
handle end 2419 includes a hand guard 2425. A passage 2427 passes
through the reamer path protector 2411. A femoral neck liner 2431
is also provided and includes a main body 2435 having a passage
2437 and a collar 2439. The passage 2437 includes internal threads
2441 at an end of the main body 2335 opposite collar 2339.
[0123] In operation, the reamer path protector 2411 is inserted
from the lateral side 815 of the femur 811 and into the distal
passage 2221. The femoral neck liner 2431 is inserted from the
proximal neck surface 2111 into the starter passage 2141 until the
collar 2439 mates with the proximal neck surface 2111. The femoral
neck liner 2431 is sized in diameter the same as or slightly less
than the diameter of the starter passage 2141. As is the case with
the anchor member 2215 (see FIG. 22) discussed previously, the
femoral neck liner 2431 could be provided in different sizes to fit
variously sized starter passages 2141, or the femoral neck liner
2431 could be tapered. After inserting the femoral neck liner 2431,
the reamer path protector 2411 is advanced further into the distal
passage 2221 until it contacts the femoral neck liner 2431. The
reamer path protector 2411 is then rotated to engage the threads
2421 with internal threads 2441. The attachment mechanism between
the reamer path protector 2411 and the femoral neck liner 2431 is
not required to be accomplished by a threaded connection. The
connection could be formed by any mechanism that would allow the
components to be easily disassembled following reaming of the
acetabulum.
[0124] When the reamer path protector 2411 is securely fastened to
the femoral neck liner 2431, a sufficient portion of the reamer
path protector 2411 remains extending outside of the femur 811 to
allow gripping by the surgeon or other person who will ream the
acetabulum. The reamer path protector 2411 is therefore gripped in
this area, and a reamer shaft 2451 is inserted through the passage
2427 and the passage 2437 to connect to a reamer head 2453 near the
proximal neck surface 2111. The acetabulum is then reamed by
rotating the patient's leg into a neutral position and applying
power to rotate the reamer shaft 2451 and reamer head 2453 from the
lateral side 815 of the femur 811. Some internal rotation of the
femur 811 may also be necessary depending on the position of the
femur 811 relative to flexion/extension and abduction/adduction.
The acetabulum is progressively reamed until enough material has
been removed to accommodate the acetabular component of the
prosthesis. By reaming the acetabulum through the distal and
starter passages 2221, 2141 formed in the femur 811, a highly
effective reaming process is accomplished. Since the patient's leg
is positioned in the neutral position during the reaming process,
and since the reamer head 2353 is connected to the reamer shaft
2451 along the same axis as that about which the head and body of
the prosthesis will be oriented, the acetabulum can be efficiently
reamed to closely match the shape of the head of the
prosthesis.
[0125] Following the reaming process, the reamer head 2453 is
removed from the reamer shaft 2451, and the reamer shaft 2451 is
removed from the femoral neck liner 2431 and the reamer path
protector 2411. An impactor shaft (not shown) may be inserted into
the reamer path protector 2411 and the femoral neck liner 2431
similar to the original insertion of the reamer shaft 2451. The
impactor shaft is releasably connected to an impactor head (not
shown) near the proximal neck surface 2111. The impactor shaft and
impactor head are used to apply force to and seat the acetabular
component of the prosthesis in the reamed acetabulum. After the
acetabular component is firmly seated, the impactor shaft, impactor
head, femoral neck liner 2431, and the reamer path protector 2411
are disassembled and removed from the femur 811
[0126] Referring to FIG. 25A, a method for preparing an acetabulum
for receiving a head of a femoral prosthesis 2521 is illustrated. A
first step 2525 includes forming a primary passage within the femur
substantially coaxial to a longitudinal axis of the femoral neck.
At step 2529, a secondary passage is formed from a lateral side of
the femur that joins and is coaxial to the primary passage. Step
2531 includes inserting a reamer path protector having a reamer
passage within the secondary passage. A reamer shaft is inserted
through the reamer passage at step 2535. A reamer head is attached
to the reamer shaft at step 2539, and the acetabulum is reamed at
step 2541.
[0127] The femoral neck fixation prosthesis is implanted into the
femur 811 by inserting the body 125, 625, 725 of the prosthesis
into the starter passage 2141. Preferably, the diameter of the body
125, 625, 725 is sized slightly larger than the diameter of the
starter passage 2141 such that a secure fit within the starter
passage 2141 is obtained when the body 125, 625, 725 is driven into
the starter passage 2141. The starter passage 2141 is deep enough
to accommodate the body 125, 625, 725 of the prosthesis and allow
the collar of the body 125, 625, 725 to mate with the proximal neck
surface 2111.
[0128] The fastener 120, 620, 720 is then inserted into the distal
passage 2221 from the lateral side 815 of the femur 811. To
properly feed the fastener 120, 620, 720 through the soft tissue
2233 (see FIG. 22) of the patient's leg and into the distal passage
2221, a small diameter pin can be used to locate and mark the
passage when the leg is in the neutral position. The fastener 120,
620, 720, which may be canullated (i.e. having a passage down the
center of the shaft), can then be placed onto the pin and fed into
the distal passage 2221. The fastener 120, 620, 720 is advanced
into the distal passage 2221 until it contacts the body 125, 625,
725 of the prosthesis, at which time the fastener 120, 620, 720 is
threadingly connected to the body 125, 625, 725 to secure the body
within the femur 811. The head 110, 610, 710 of the prosthesis is
then installed on the morse taper 115, 615, 760 of the prosthesis
be impacting the head of the prosthesis.
[0129] Referring to FIG. 26, a method of implanting a prosthesis in
a femur 2611 according the principles of the present invention is
illustrated. At step 2615 a main passage is formed in the femoral
neck from a medial side of the femur substantially coaxial to a
longitudinal axis of the femoral neck. At step 2619 a fastener
passage is formed from a lateral side of the femur that is coaxial
to and joins the main passage. Step 2623 includes providing a
femoral neck prosthesis having a body member connected to a head
member. At step 2627 a portion of the body member is inserted in
the main passage. A fastener is inserted into the fastener passage
at step 2633. At step 2637 the fastener is connected to the body
member to secure the femoral neck prosthesis within the femur.
[0130] As will be recognized by those skilled in the art, the
innovative concepts described in the present application can be
modified and varied over a tremendous range of applications, and
accordingly the scope of patented subject matter is not limited by
any of the specific exemplary teachings given.
[0131] While the invention has been particularly shown and
described with reference to a preferred embodiment, it will be
understood by those skilled in the art that various changes in form
and detail may be made therein without departing from the spirit
and scope of the invention.
* * * * *