U.S. patent application number 11/593168 was filed with the patent office on 2008-05-08 for method and apparatus for hip femoral resurfacing tooling.
This patent application is currently assigned to Howmedica Osteonics Corp.. Invention is credited to Robert E. Ledger, Patrick Raugel, Peter Tulkis.
Application Number | 20080109085 11/593168 |
Document ID | / |
Family ID | 39360675 |
Filed Date | 2008-05-08 |
United States Patent
Application |
20080109085 |
Kind Code |
A1 |
Tulkis; Peter ; et
al. |
May 8, 2008 |
Method and apparatus for hip femoral resurfacing tooling
Abstract
Tools and methods for implanting hip resurfacing femoral
prostheses along a path defined by the axis of a shaped femoral
head surface are described. The prostheses are stemless partial
ball components having an outer surface shaped to conform to an
acetabular socket and may be a two part design having a mating
sleeve component with an internal bore adapted to receive the
shaped femoral head. The tools and methods are capable of
accurately implanting both one and two piece ball components and
sleeves without requiring the prosthesis to have a central stem or
the preparation of a stem cavity in the femoral head and neck.
Inventors: |
Tulkis; Peter; (Paramus,
NJ) ; Ledger; Robert E.; (River Vale, NJ) ;
Raugel; Patrick; (Ramsey, NJ) |
Correspondence
Address: |
LERNER, DAVID, LITTENBERG,;KRUMHOLZ & MENTLIK
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Assignee: |
Howmedica Osteonics Corp.
Mahwah
NJ
|
Family ID: |
39360675 |
Appl. No.: |
11/593168 |
Filed: |
November 3, 2006 |
Current U.S.
Class: |
623/22.11 |
Current CPC
Class: |
A61B 17/175 20130101;
A61F 2310/00592 20130101; A61F 2002/30011 20130101; A61F 2002/30378
20130101; A61F 2250/0024 20130101; A61F 2310/00413 20130101; A61F
2310/00491 20130101; A61B 17/1637 20130101; A61F 2002/3021
20130101; A61F 2002/30934 20130101; A61F 2002/4677 20130101; A61F
2220/0033 20130101; A61F 2002/4628 20130101; A61F 2310/00544
20130101; A61F 2/30767 20130101; A61F 2/4607 20130101; A61F
2002/30332 20130101; A61F 2310/00407 20130101; A61F 2310/00179
20130101; A61F 2/3603 20130101; A61F 2/4657 20130101; A61F
2002/30738 20130101; A61F 2310/00011 20130101; A61F 2230/0067
20130101; A61F 2002/30217 20130101; A61F 2002/4687 20130101; A61F
2310/00395 20130101; A61F 2002/3605 20130101; A61F 2002/4627
20130101; A61B 17/8897 20130101; A61F 2002/4631 20130101; A61B
17/1668 20130101; A61F 2/4603 20130101 |
Class at
Publication: |
623/22.11 |
International
Class: |
A61F 2/32 20060101
A61F002/32 |
Claims
1. A tool for translating a hollow sleeve prosthesis component
along a femoral head axis to install the sleeve on a prepared
femoral head, the head axis being defined by a datum used to
prepare the femoral head outer surface, the sleeve having a distal
end with an opening into a cavity to engage the outer surface of
the prepared natural femoral head and a proximal end with an
aperture in the proximal end, the tool comprising: a distal sleeve
interface for retaining and releasing the hollow sleeve by
contacting the sleeve outer surface; a guide capable of aligning
the sleeve interface with the femoral head axis when engaged with
the datum and guiding the interface portion to slidingly translate
along the head axis when engaged; and a handle for applying force
to the sleeve interface.
2. The tool as set forth in claim 1 wherein the datum is a guide
wire.
3. The tool as set forth in claim 2 wherein the guide comprises a
bore through the sleeve interface configured to slidingly journal
the guide wire.
4. The tool as set forth in claim 1 wherein the datum is a guide
wire bore.
5. The tool as set forth in claim 4 wherein the guide comprises a
pin extending from the sleeve interface configured to slidingly fit
in the guide wire bore.
6. The tool as set forth in claim 1 wherein at least one surface of
the the sleeve interface is tapered.
7. The tool as set forth in claim 6 wherein the sleeve interface
comprises an extractor assembly that is capable of applying force
to the sleeve to release the sleeve from the tool.
8. The tool as set forth in claim 7 wherein the force is applied
symmetrically about a central axis of the proximal portion of the
sleeve.
9. The tool as set forth in claim 6 wherein at least one surface of
the the sleeve interface is partially cone shaped.
10. A method of installing a femoral sleeve prosthesis to a femoral
head, said method comprising the steps of: a.) preparing the outer
surface of the femoral head about a datum to a predetermined
configuration to create a prepared femoral head having a head axis
defined by the datum; b.) selecting a sleeve prosthesis, the sleeve
having a distal end with an opening into a cavity, the cavity being
sized and configured to engage the outer surface of the prepared
femoral head, and a proximal end having an aperture; c.) inserting
the sleeve into the sleeve interface of a tool and retaining the
sleeve in the sleeve interface, the tool further comprising a guide
capable of aligning the sleeve interface with the head axis when
engaged with the datum and guiding the interface portion to
slidingly translate along the head axis when engaged with the
datum, and a handle for applying force to the interface portion;
d.) engaging the guide of the tool with the datum; e.) applying
force to the tool handle to slidingly translate the tool and sleeve
along the head axis to seat the sleeve cavity on the prepared
femoral head surface; and f.) releasing the sleeve from the sleeve
interface, disengaging the guide from the datum and removing the
tool.
11. The method as set forth in claim 10 wherein the datum is a
guide wire.
12. The method as set forth in claim 11 wherein the guide comprises
a bore through the sleeve interface configured to slidingly journal
the guide wire and the guide is engaged with the guide wire by
positioning the tool to pass the guide wire into the sleeve cavity,
through the sleeve aperture and into the guide bore.
13. The method as set forth in claim 10 wherein the datum is a
guide wire bore.
14. The method as set forth in claim 13 wherein the guide comprises
a pin extending from the sleeve interface and configured to
slidingly fit in the guide wire bore and the guide pin is engaged
with the guide wire bore by passing the guide pin through the
sleeve aperture and cavity when inserting the sleeve into the
sleeve interface and then positioning the tool to place the guide
pin into the guide wire bore.
15. The method as set forth in claim 10 wherein at least one outer
surface of the sleeve is tapered.
16. The method as set forth in claim 15 whereby the sleeve is
released from the sleeve interface by actuating an extractor
assembly that applies force to the sleeve to release the sleeve
from the tool.
17. The method as set forth in claim 16 wherein the force is
applied symmetrically about a central axis of the proximal portion
of the sleeve.
18. The method as set forth in claim 15 wherein at least one
surface of the sleeve interface is partially cone shaped.
19. The method of claim 10 wherein bone cement is applied between
the interior surface of the sleeve and the prepared femoral head
surface prior to seating the sleeve cavity on the prepared femoral
head surface.
20. The method of claim 10 wherein the outside of the sleeve is
solid metal.
21. The method of claim 10, wherein the sleeve is substantially
composed of a metal selected from the group of titanium, titanium
alloys, cobalt chrome alloys, niobium and tantalum.
22. A tool for establishing a secondary datum for translating a
ball prosthesis along a femoral head axis to install the ball on a
prepared femoral head, the head axis being defined by a datum fixed
in the femoral head and used to prepare the femoral head outer
surface, the ball having a distal end with an opening into a cavity
to engage the outer surface of the prepared femoral head, the tool
comprising: an alignment jig comprising a mount, an extension
connected to the mount by at least one joint, and a secondary datum
location feature connected to the extension, the mount being
capable of being mounted to the proximal femur adjacent the
prepared femoral head, and the extension being capable of moving
the secondary datum location feature, when the jig is mounted, to a
position establishing a secondary datum coaxial with the datum and
distant from the datum along the proximal portion of the femoral
head axis.
23. The tool as set forth in claim 22 wherein the alignment jig
extension further comprises at least one movable and lockable
joint.
24. The tool as set forth in claim 23 wherein the alignment jig
extension further comprises providing at least one translational
degree of freedom between said mount and said secondary datum
location feature.
25. The tool as set forth in claim 23 wherein the alignment jig
extension further comprises providing at least two rotational
degrees of freedom between said mount and said secondary datum
location feature.
26. The tool as set forth in claim 23 wherein the alignment jig
extension further comprises providing at least four degrees of
freedom between said mount and said secondary datum location
feature.
27. The tool as set forth in claim 23 wherein the alignment jig
extension further comprises providing at least four degrees of
freedom including at least two rotational degrees of freedom and at
least one translational degrees of freedom between said mount and
said secondary datum location feature.
28. The tool as set forth in claim 22 wherein the alignment jig
further comprises an axial extension, said mount and said axial
extension being connected by at least one movable and lockable
joint providing at least two rotational degrees of freedom to allow
the axial extension to be aligned axially parallel with the
datum.
29. The tool as set forth in claim 26 wherein the alignment jig
extension further comprises a radial extension incorporating said
secondary datum location feature, said radial extension being
capable of rotation about the axis of said axial extension to
radially align with the axis of the datum and radially translate
relative to the axial extension to allow the axial extension to
align said secondary datum location features coaxially with said
datum and establish the secondary datum when the mount is mounted
to the femur and the axial extension is aligned axially parallel
with the datum.
30. The tool as set forth in claim 22 wherein the alignment jig
allows the distance from the prepared femoral head to the secondary
datum location feature to be a sufficient length to allow the
placement of a ball prosthesis centrally between the femoral head
and the secondary datum.
31. The tool as set forth in claim 22 wherein the alignment jig
allows the distance from the prepared femoral head to the secondary
datum location feature to be at least 25 mm.
32. A tool kit for translating a ball prosthesis along a femoral
head axis to install the ball on a prepared femoral head, the head
axis being defined by a datum fixed in the femoral head and used to
prepare the femoral head outer surface, the ball having a distal
end with an opening into a cavity to engage the outer surface of
the prepared natural femoral head, the kit comprising: an alignment
jig capable of being mounted to the proximal femur adjacent the
prepared femoral head, locating on the datum when mounted and
creating a secondary datum coaxial with the datum and proximally
distant from the prepared femoral head along the femoral head axis;
and a prosthesis holding tool having a first distal ball interface
for retaining and releasing a first ball prosthesis of a first
diameter by contacting the first ball outer surface, a proximal
guide capable of aligning the ball interface with the head axis
when engaged with said secondary datum and guiding the ball
interface to slidingly translate along the head axis when engaged,
and a handle for applying force to the ball interface.
33. A kit according to claim 32 further comprising a second
prosthesis holding tool having a distal ball interface for
retaining and releasing a second ball prosthesis of a second
diameter different from said first diameter of said first ball
prosthesis by contacting the second ball outer surface.
34. A method of installing a femoral ball prosthesis to a femoral
head, said method comprising the steps of: a.) preparing the outer
surface of the femoral head about a datum to a predetermined
configuration to create a prepared femoral head having a head axis
defined by the datum; b.) mounting an alignment jig to the proximal
femur adjacent the prepared femoral head, and using the alignment
jig to locate on the datum when mounted and create a secondary
datum coaxial with the datum and proximally distant from the
prepared femoral head along the femoral head axis; c.) selecting a
ball prosthesis, the ball prosthesis having a distal end with an
opening into a cavity, the cavity being sized and configured to
engage the outer surface of the prepared femoral head; d.)
inserting the ball prosthesis into the ball interface of a
prosthesis holding tool and retaining the ball in the ball
interface, the tool further comprising a proximal guide and a
handle; e.) engaging the guide of the prosthesis holding tool with
the secondary datum, the guide, upon engagement, aligning the ball
interface with the head axis; f.) applying force to the tool handle
to slidingly translate the tool and ball prosthesis along the head
axis to seat the ball prosthesis cavity on the prepared femoral
head surface; and g.) releasing the ball prosthesis from the ball
interface, retracting the tool and removing the alignment jig and
the prosthesis holding tool.
35. A tool for establishing a secondary datum for the purpose of
translating a ball prosthesis along a femoral head axis to install
the ball on a prepared femoral head, the head axis being defined by
a datum fixed in the femoral head and used to prepare the femoral
head outer surface, the ball having a distal end with an opening
into a cavity to engage the outer surface of the prepared natural
femoral head, the tool comprising: an axis alignment jig comprising
a proximal datum location feature having an axis, a distal
secondary datum fixture, and an intermediate extension connected to
the datum location feature and the secondary datum fixture, the
datum location feature being capable of mounting to the datum
adjacent the prepared femoral head, locating the location feature
axis co-axially with the head axis and positioning the jig relative
to the datum, the extension being capable of locating the secondary
datum fixture, when the jig is mounted to the datum, to a position
distally remote from the prepared femoral head for establishing a
secondary datum in the proximal femur with an axis intersecting the
femoral head axis, and the secondary datum fixture being capable,
when the jig is mounted to the datum, of providing a guide for
establishing a secondary datum in the proximal femur with an axis
intersecting the femoral head axis.
36. The tool as set forth in claim 30 wherein the datum is a guide
wire.
37. The tool as set forth in claim 31 wherein the proximal datum
location feature comprises a bore through the feature configured to
slidingly journal the guide wire in order to locate the datum and
position the jig relative to the datum.
38. The tool as set forth in claim 30 wherein the datum is a guide
wire bore.
39. The tool as set forth in claim 33 wherein the proximal datum
location feature comprises a pin configured to slidingly fit in the
guide wire bore in order to locate the datum and position the jig
relative to the datum.
40. The tool as set forth in claim 30 wherein the secondary datum
fixture guide is a slot oriented toward the axis of the datum
location feature.
41. The tool as set forth in claim 30 wherein the secondary datum
fixture guide is a bore with an opening oriented perpendicular to
the axis of the datum location feature.
42. A tool for translating a ball prosthesis toward a femoral head
axis to install the ball on a prepared femoral head by locating on
a secondary datum in the proximal femur with an axis intersecting
the femoral head axis, the head axis being defined by a datum fixed
in the femoral head and used to prepare the femoral head outer
surface, the ball having a distal end with an opening into a cavity
to engage the outer surface of the prepared natural femoral head,
the tool comprising: a prosthesis holding tool having a distal ball
interface for retaining and releasing the ball prosthesis by
contacting the ball outer surface, a guide capable of guiding the
ball interface to slidingly translate toward the head axis when
engaged on the secondary datum, an intermediate extension connected
to the ball interface and the guide, and a handle for applying
force to the ball interface.
43. The tool as set forth in claim 37 wherein the guide is a slot
with an opening oriented toward the head axis when engaged on the
secondary datum.
44. A tool kit for translating a ball prosthesis toward a femoral
head axis to install the ball on a prepared femoral head by
creating and locating on a secondary datum in the proximal femur
with an axis intersecting the femoral head axis, the head axis
being defined by a datum fixed in the femoral head and used to
prepare the femoral head outer surface, the ball having an end with
an opening into a cavity to engage the outer surface of the
prepared natural femoral head, the tool kit comprising: an axis
alignment jig comprising a proximal datum location feature having
an axis, a distal secondary datum fixture, and an intermediate
extension connected to the datum location feature and the secondary
datum fixture, the datum location feature being capable of mounting
to the datum adjacent the prepared femoral head, locating the
location feature axis co-axially with the head axis and positioning
the jig relative to the datum, the extension being capable of
locating the secondary datum fixture, when the jig is mounted to
the datum, to a position distally remote from the prepared femoral
head for establishing a secondary datum in the proximal femur with
an axis intersecting the femoral head axis, and the secondary datum
fixture being capable, when the jig is mounted to the datum, of
providing a guide for establishing a secondary datum in the
proximal femur with an axis intersecting the femoral head axis; and
a prosthesis holding tool having a ball interface for retaining and
releasing the ball-prosthesis by contacting the ball outer surface,
a distal guide capable of guiding the ball interface to slidingly
translate toward the head axis when engaged on the secondary datum,
an intermediate extension connected to the ball interface and the
guide, and a handle for applying force to the ball interface.
45. A method of installing a femoral ball prosthesis to a femoral
head, said method comprising the steps of: a.) preparing the outer
surface of the femoral head about a datum to a predetermined
configuration to create a prepared femoral head having a head axis
defined by the datum; b.) mounting an axis alignment jig to the
datum, the axis alignment jig comprising a proximal datum location
feature having an axis, a distal secondary datum fixture, and an
intermediate extension connected to the datum location feature and
the secondary datum fixture, the datum location feature locating
the datum axis and positioning the jig relative to the datum so
that the extension locates the secondary datum fixture to a
position distally remote from the prepared femoral head, the
secondary datum fixture being capable of providing a guide for
establishing a secondary datum in the proximal femur with an axis
intersecting the femoral head axis, c.) installing a secondary
datum, under at least partial guidance from the secondary datum
fixture, to position the secondary datum in the proximal femur so
that the secondary datum has an axis intersecting the femoral head
axis; d.) selecting a ball prosthesis, the ball prosthesis having a
distal end with an opening into a cavity, the cavity being sized
and configured to engage the outer surface of the prepared femoral
head; e.) inserting the ball prosthesis into the ball interface of
a prosthesis holding tool and retaining the ball in the ball
interface, the tool further comprising a distal guide and a handle;
d.) engaging the guide of the tool with the secondary datum, the
guide, upon engagement, aligning the ball interface with the head
axis; e.) applying force to the tool handle to slidingly translate
the tool and ball prosthesis toward the head axis to seat the ball
prosthesis cavity on the prepared femoral head surface; and f.)
releasing the ball prosthesis from the ball interface, and removing
the alignment jig and the prosthesis holding tool.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to systems, kits and
methods for joint prosthesis installation tools. The present
invention includes jigs and methods for installing a stemless ball
component to a prepared femoral head along an axis defined by the
prepared femoral head and jigs for installing a sleeve component
for adapting a ball component to a prepared femoral head along an
axis defined by the prepared femoral head.
[0002] Artificial joint prostheses are widely used today, restoring
joint mobility to patients affected by a variety of conditions,
including degeneration of the joint and bone structure. Typically,
the failed bone structure is replaced with an orthopedic implant
that mimics, as closely as possible, the structure of the natural
bone and performs its functions. The satisfactory performance of
these implants can be affected not only by the design of the
component itself, but also by the surgical positioning of the
implanted component and the long-term fixation of the implant.
Improper placement or positioning of the implant can adversely
affect the goal of satisfactorily restoring the clinical
bio-mechanics of the joint as well as impairing adequate fixation
of the component when implanted.
[0003] Orthopedic implants are constructed from materials that are
stable in biological environments and withstand physical stress
with minimal or controlled deformation. Such materials must possess
strength, resistance to corrosion, biocompatibility, and good wear
properties. Also, the implants include various interacting parts,
which undergo repeated long-term physical stress inside the
body.
[0004] For these reasons, among others, the bone/implant interface
and the connection between various parts of the implant must be
durable and resistant to breakdown. This is especially important
since installation of an orthopedic implant often involves an
extensive and difficult medical procedure, and therefore
replacement or revision of the installed implant is typically
difficult and traumatic.
[0005] The requirements for the useful life of the implant continue
to grow with the increase in human life expectancy. Also, as
implants improve, younger patients are considered as implant
candidates. It is therefore desirable to develop implants that,
while durable in their own right, minimize the difficulty of
replacement
[0006] The strength and longevity of implants in large part depend
on the bone/implant interface. Various methods of connection are
known in the art. For example, a hip joint is a ball-in-socket
joint, and includes a rounded femoral head and a cup-like socket
(acetabular cup) located in the pelvis. The surfaces of the rounded
femoral head and the acetabular cup continually abrade each other
as a person walks. The abrasion, along with normal loading, creates
stress on the hip joint and adjacent bones. If the femoral head or
the acetabular cup is replaced with an implant, this stress must be
well tolerated by the implant's bearing surfaces to prevent implant
failure.
[0007] Depending on the type of bone, the location of the bone
within the body and individual characteristics, bone has a wide
variation in mechanical characteristics. Bone is generally
categorized as trabecular or cancellous bone, which is porous and
has an open cancellated structure, and cortical bone, which is
dense. Considering the femoral bone of the hip joint, FIG. 1 shows
the proximal portion of a femur 1 with the upper portion of the
shaft 3, a neck 5 and a head 7. A shaft axis A-A is aligned with
the shaft 3 and a head axis B-B is generally aligned with the neck
5. The shaft 3 is primarily composed of cortical bone while the
neck 5 and head 7 are primarily composed of trabecular bone with
cortical bone at the surface.
[0008] Implantable joint prostheses have long been used to provide
an artificial hip. When the prosthesis is situated in this
position, significant forces such as axial, bending, and rotational
forces are imparted to the device. Conventional total hip
replacements use an intramedullary stem as part of the femoral
prosthesis. The stem passes into the marrow cavity of the femoral
shaft. These stem type prostheses are very successful but when they
fail the stem can create considerable damage inside the bone. The
implant can move about inside the bone causing the intramedullary
cavity to be damaged. Because a stiff stem transmits the forces
more directly into the femoral shaft, such implants have the
further disadvantage that they can weaken the surrounding bone
nearer to the hip joint due to stress shielding.
[0009] Early designs of femoral prostheses for artificial hips
relied primarily on cemented fixation. These cements, such as
polymethylmethacrylate, are used to anchor the component within the
medullary canal by acting as a grouting agent between the component
and the endosteal (inner) surface of the bone. While this method of
fixation by cement provides immediate fixation and resistance to
the forces encountered, and allows the surgeon to effectively
position the device before the cement sets, it is not without
problems. Over time, the mechanical properties and the adhesive
properties of the bone cement degrade; eventually the forces may
overcome the cement and cause the components to become loose due to
a failure at the cement/bone or cement/stem interface. Alternative
approaches to address the issue of cement failure include both
biological ingrowth and press-fit type stems.
[0010] Stems designed for biological ingrowth typically rely on the
bone itself to grow into a specially prepared surface of the
component, resulting in firmly anchoring the implant within the
medullary canal. A shortfall of this approach is that, in contrast
to components that utilize cement fixation, surfaces designed for
biological ingrowth do not provide for immediate fixation because
it takes time for the bone to grow into the specially prepared
surface. Press-fit stems precisely engineered to fit within a
surgically prepared medullary canal may or may not have specially
prepared surfaces and typically rely on an interference fit of some
portion of the component within the medullary canal of the bone to
achieve stable fixation.
[0011] The need often arises to replace at least a portion of a hip
implant. Prior art designs often require the entire implant to be
replaced even if only a portion of the implant fails. Similarly,
the entire implant may have to be replaced if the implant is intact
but certain conditions surrounding the implant have changed. This
is often due to the implant suffering from a decrease in support
from the adjacent bone due to stress shielding or other negative
effects of the implant on surrounding bone.
[0012] Surgeons have sought a more conservative device than an
implant using an intramedullary stem as part of the femoral
prosthesis. There have been a number of attempts at implants using
short stems or femoral caps without stems and requiring less
extensive surgery. This type of prosthesis is generally known as a
hip resurfacing prosthesis. In the mid-1940's, Judet in France
designed a prosthesis whereby the majority of the femoral head was
removed and a replacement device was fitted with a peg or nail
which passed a short way down the femoral neck. Small movement of
the device against the bone caused friction of the bone and the
bending loads on the peg often caused them to break out underneath
the bony femoral neck. In the mid-1970's, double cup type
arthroplasty was tried. There were several designs: Wagner in
Germany, an Italian Group, Imperial College London and the Tharies
design from Amstutz in California.
[0013] These all removed a fair proportion of the femoral bearing
surface by turning it down to a cylindrical form or hemispherical
form. A metal shell was then fixed with bone cement on the
remaining bony peg. The acetabular cup was conventional. Unlike
normal total hips, however, which have standard femoral head sizes
in the range of 22-32 mm, these double cup arthroplasties have
large bearing surface diameters closer to the original hip,
typically in a range from 40-60 mm. These latter double cup designs
commonly failed either by a crack progressing around the bone
cement between the prosthetic femoral shell and the bone or by a
fracture of the bone across from one side of the prosthetic femoral
component rim to the other.
[0014] Current approaches to femoral head resurfacing can be traced
back to Amstutz in U.S. Pat. No. 4,123,806. In the '806 patent, a
hemispherical cap is cemented to a prepared femoral head while
preserving a substantial portion of the femoral head. In U.S. Pat.
No. 6,156,069, Amstutz shows a femoral head resurfacing implant
having a stem. A similar femoral head resurfacing technique having
a stem called Birmingham Hip Resurfacing has been developed by
McMinn in the United Kingdom.
[0015] These stem-type femoral head resurfacing prostheses consist
of a bearing cap provided with a central pin that guides the
prosthesis during the insertion. The guiding is important because
it ensures that the prosthesis will be seating at the appropriate
orientation planned by the surgeon with regard to the bone. A
consequence of the misalignment of the prosthesis is a sub-optimal
load transfer to the bone that can lead to the failure of the
prosthetic joint. Similar to the problems with the prostheses
having a stem extending into the femoral shaft, a stem-type
resurfacing prostheses requires the surgeon to remove enough bone
in the neck of the femur so that it can host the pin of the
prosthesis and the stem can contribute to stress shielding.
Therefore the stem-type prosthesis is not as bone preserving as a
stemless prosthesis, either in the short term or long term.
[0016] Notwithstanding the problem of guiding a stemless
prosthesis, stemless approaches have been advocated and continue to
be developed. A modular approach to a stemless femoral hip
resurfacing is shown in U.S. Pat. No. 4,846,841 to Oh. In this
approach, a frustro-conical cap is press-fit to a prepared femoral
head. A ball component is then attached to and retained by the cap
using a Morse taper fit. A similar approach is shown in U.S. Pat.
No. 5,258,033 to Lawes and Ling, which shows a ball component
cemented either directly to a prepared head or, additionally,
retained by a press-fit with a frustro-conical cap. A contemporary
approach to stemless femoral head resurfacing is found in co-owned
U.S. patent application Ser. No. 11/478,870 entitled, Femoral Head
Resurfacing.
[0017] All of these more modern hip resurfacing approaches require
that the femoral head be prepared to provide a properly oriented
and shaped bone interface for the implant by shaping the head. The
outer prepared bone interface with the implant is symmetrical
around a prepared head axis B-B passing through and established
with reference to the central region of the femoral neck and is
typically cylindrical or conical but may be a more complex tapering
solid of revolution. The proximal portion of the prepared head can
be a flat surface, tapered, domed, chamfered, or any combination of
these features and is usually performed as a separate resection. If
a stem is used, it may be cylindrical, conical or a more complex
tapering solid of revolution and is typically short compared to a
conventional intramedullary stem. The portion of the bone that
hosts the prosthesis must be shaped so that it matches the shape of
the prosthesis. The size and shape of the bone may fit exactly the
shape and size of the prosthesis or may provide room for cementing
to take place or have an excess of bone in a region to allow
press-fit fixation, depending on the preferred fixation method.
[0018] Because the desired bone shape of the outer implant
interface is symmetrical around an axis, a guide wire or pin
introduced into the femoral head is typically used to establish the
tooling landmark or datum that establishes and defines the prepared
head axis B-B. The guide pin provides an axis of revolution for the
various measuring and cutting tools used in the preparation process
as shown in FIG. 4 and discussed later. When introduced into the
femoral head, the guide wire creates a corresponding bore that also
provides a datum for the axis B-B in the absence of the guide wire.
Based on pre-operative planning, the surgeon initially places the
guide wire, either freehand or using measurement and guidance tools
based on various anatomical reference points on the femur. In order
to place the pin, the pin is driven or inserted in the proximal
surface of the femoral head directed toward the greater trochanter
and approximately down the mid-lateral axis of the femoral neck. A
gauge having an extended stylus that allows measurement of the
position of the pin with respect to the neck is then typically used
to make a preliminary check of the pin position. By revolving the
gauge, the surgeon can evaluate the position of the pin to ensure
that the femoral neck will not be undercut when the cutting tool is
revolved around the pin. If the surgeon is satisfied that the pin
position meets these criteria, the guide wire is used as the axis
of revolution for the shaping cutter or reamer to prepare the head
to receive the implant.
[0019] For a traditional stem-type resurfacing prosthesis, the stem
cavity is used to guide the stem and prosthesis into position.
Thus, a stem-type resurfacing prosthesis has provided an acceptable
method of guiding the prosthesis with respect to the femoral head
axis because the stem cavity approximates the head axis datums and
the stem serves as tooling to guide the prosthesis along an axis
approximating the femoral head axis during installation by engaging
the stem cavity.
[0020] For a stemless prosthesis, the stem and stem cavity do not
exist and the stem cannot serve as tooling to guide the prosthesis.
It is desirable to have tooling and a surgical method for use with
a stemless prosthesis that allows implanting the prosthesis along
the femoral head axis with at least the same accuracy achieved by
stem-type resurfacing prosthesis.
SUMMARY OF THE INVENTION
[0021] It is an object of the present invention to provide a more
successful surface replacement of the femoral portion of a total
hip replacement based on a stemless modular approach to femoral hip
resurfacing by improvements to the tooling and methods used for
implanting the prostheses components.
[0022] According to an aspect of the present invention, a jig or
tool is used to control the direction of the travel and the seating
force vector of a femoral prosthesis component with respect to an
axis previously used to create the outer surface of the resected or
shaped femoral head surface that will mate with the prosthesis
component.
[0023] In a first embodiment of the present invention, a tool and
method for seating the sleeve component of a two-part prosthesis
guides the sleeve on a guide pin or Kirschner wire located in the
head axis used as a datum to create the femoral head resection. The
sleeve inner and outer distal surfaces are typically in the shape
of a truncated cone, but may also incorporate other anti-rotational
or locking features. The inner surface of the sleeve is shaped and
dimensioned to mate with a prepared femoral head. The sleeve
proximal portion has a central hole capable of allowing the guide
pin to pass through it. The tool also has a central cannulated bore
capable of receiving the guide pin and slidingly journaling on the
guide pin to insure that the tool is aligned with the datum
provided by the guide pin. Consequently, the tool and sleeve are
aligned with the femoral head axis while seating the sleeve. The
tool distal portion has holding features that conform to a portion
of the sleeve outer surface and retains the sleeve with suitable
features such as detents. Because of the tapered sleeve exterior
configuration mating with the holding features, the sleeve will
tend to strongly lock with the tool as a result of the force
applied to the tool as the sleeve is seated.
[0024] In order to remove the tool and overcome this locking force
without damaging the bone surface of the prepared femoral head or
breaking the sleeve loose from the femoral head, the tool
incorporates release features, such as an extractor assembly that
forces pins against the sleeve, to release the prosthesis from the
tool.
[0025] In another aspect of the first embodiment, these releasing
features are symmetrical about the tool and femoral head axis in
order to insure that the sleeve is not cocked with respect to the
axis by the releasing action.
[0026] In a further aspect of the first embodiment, a method is
provided for using the prosthesis holding tool of the first
embodiment. The sleeve prosthesis is first attached to the
prosthesis holder. If necessary, bone cement is applied to the
interior surface of the sleeve or to the mating prepared femoral
head surface. The tip of the guide pin is introduced into the hole
of the sleeve and the cannulated bore of the prostheses holder and
the holder is used to drive the sleeve along the axis defined by
the guide pin until the sleeve is mated with the prepared femoral
head. Then sufficient pressure is applied to seat the prosthesis as
required by the selected fixation method. The extractor assembly of
the prosthesis holding tool is next used to release the sleeve and
the prosthesis holding tool can be removed from the guide pin. The
guide pin is then removed from the patient, and a ball component is
seated on the sleeve using a suitable tool.
[0027] In a second embodiment of the invention, a prosthesis
holding tool similar to the first embodiment is adapted to be used
when the guide pin has been removed prior to using the tool. The
prosthesis holder of the second embodiment has a central pin
projecting from the distal prosthesis holding portion to pass
through the hole in the proximal portion of the sleeve and enter
the bore in the prepared femoral head previously occupied by the
guide pin. In other respects, the operation and method of the
second embodiment is the same as the first embodiment except that,
after preparing the femoral head, the guide pin is removed prior to
the step of seating the sleeve.
[0028] In a third embodiment, the invention is used to seat a ball
component rather than a sleeve. In this embodiment, an alignment
jig is temporarily attached to the femoral neck. Initially, a pin
location guide is fitted on the guide pin projecting from the
femoral head which provides a datum. A frame with various
translational and rotational adjustments is connected with the
location guide, and also fastened to the femoral neck. By adjusting
the jig position and locking the various adjusting joints, the
guide pin position and consequently the femoral head axis are
determined and the alignment jig is constrained to align with the
axis. The guide pin is then removed. The partial ball component and
a suitable prosthesis holding tool are then engaged with the
alignment jig to allow the prosthesis and holding tool to be
installed by translating the prosthesis and tool along the head
axis B-B to create a secondary datum.
[0029] The alignment jig of the third embodiment also has the
capability to establish a new axis for the alignment pin if
necessary. Upon determining that the previous axis is
unsatisfactory, the various translational and rotational
adjustments of the jig can be re-adjusted to a new axis location.
Then a pin location guide can be reinstalled and used as a guide to
drive in a new alignment pin that can, in turn, be used for a
secondary re-surfacing of the femoral head. The prosthesis can be
installed on the newly prepared head and the prosthesis installed
along the new axis as described in the previous paragraph.
[0030] In a fourth embodiment, the tooling of the third embodiment
is modified to provide a separate axis alignment jig and prostheses
alignment jig. The axis alignment jig is fitted directly over the
guide pin without the use of a pin location guide to determine the
head axis and is used to install a mount, typically a mounting pin,
on the side of the femoral neck in a predetermined relationship to
the head axis B-B. The axis alignment jig is next removed and then
the guide pin is removed. The prosthesis is installed in the
prosthesis alignment jig and the jig is aligned with the prepared
femoral head axis B-B using the mount on the side of the neck. The
prosthesis alignment jig is then used to install the prosthesis in
a manner similar to the third embodiment.
[0031] It is also an aspect of the invention to provide the various
surgical methods described in connection with the embodiments
above, along with kits incorporating the various tool and jig
components for adapting to differently sized sleeves, ball
components, and other variations typically encountered in
orthopedic replacements of femoral ball components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a cross-sectional side view of the upper portion
of a human femur;
[0033] FIG. 2 is a cross-sectional side view of a two-piece femoral
resurfacing prosthesis showing a sleeve and ball component
installed on a prepared femoral head;
[0034] FIG. 3 is a perspective view of a sleeve and ball component
corresponding to the sleeve and ball component shown in FIG. 2;
[0035] FIG. 4 is a view of a step in the preparation of a femoral
head as shown in FIG. 2, wherein a guide pin has been installed
along a femoral head axis B-B and is used to prepare a femoral head
surface suitable for a prosthesis by revolving a cutter about the
pin;
[0036] FIG. 5 is a perspective view of a prosthesis holding tool
for a sleeve prosthesis according to the first embodiment of the
invention;
[0037] FIGS. 6-10 show perspective views of a sequence of steps in
the method of use according to the first embodiment of the
invention;
[0038] FIGS. 11-12 show the prosthesis holder according to the
second embodiment of the invention and the method of use according
to the second embodiment of the invention;
[0039] FIG. 13 is a perspective view according to the third
embodiment of the invention showing an alignment jig attached to a
femoral neck to install a ball prosthesis on a prepared femoral
head along femoral neck access;
[0040] FIGS. 14-19 show perspective views of a sequence of steps of
a method of using the alignment jig of FIG. 13 including, starting
in FIG. 16, the use of a prosthesis holder guided by the jig to
install the prosthesis; and
[0041] FIGS. 20-26 show a sequence of perspective views according
to a fourth embodiment of the present invention and the method of
use of an alignment jig to determine the position of a secondary
alignment pin on the side of the femoral neck using an alignment
jig and then using a separate prosthesis holder engaged on the
secondary pin to install the ball component prosthesis.
DETAILED DESCRIPTION
[0042] As shown in FIG. 2, a proximal femur as depicted in FIG. 1
has been surgically prepared for the implantation of a stemless
femoral hip resurfacing prosthesis. The preparation consists of a
re-shaping of the femoral head 7, in this instance, as a surface of
revolution about the prepared femoral head axis B-B. The femoral
head 7 has been re-shaped by known surgical techniques as a
prepared femoral head 7', such that the femoral head surface 9 has
been removed, creating a prepared femoral head surface 9'. Arranged
in close contact with the distal portion of the prepared femoral
head surface 9', is a sleeve 10. In turn, a ball component 20 is
fitted over the sleeve 10. The axis B-B passes approximately
through the center of the femoral neck 5, the center of the
prepared femoral head 7', the center of the sleeve 10, the center
of a hole 12 in the sleeve distal end and the center of the ball
component 20. In this instance, a two-part modular prosthesis
having a sleeve component 10 and ball component 20 is depicted on
the prepared femoral head. In some embodiments, a unitary ball
prosthesis 20' (not shown), integrating the features of the sleeve
10 and the ball 20 will also be discussed.
[0043] FIG. 3 shows in an exploded perspective view the prosthesis
of FIG. 2. It can be seen that the sleeve component 10 fits closely
inside at least a portion of the ball component 20. It can further
be seen that the sleeve 10 is generally a tapering solid of
revolution about a central axis having a sleeve cavity which is
configured to interface with the prepared femoral head surface 9'.
In this instance, the distal portion of the sleeve is in the
configuration of a hollow truncated cone. While shown here in the
preferred configuration of a truncated cone, either of the inner or
outer surfaces of the sleeve can define any hollow cylinder or
tapering surfaces such as an ogive or any parabolic surface capable
of being fit over a matched prepared femoral head surface 9'. The
proximal portion 12 can be a different shape of revolution about
the central axis, for example a flat surface, a spherical domed
surface or a chamfered flat surface. When present, the proximal
portion 12 may be closely configured to the prepared femoral head
surface 9' or may have clearance from the prepared femoral head
surface.
[0044] The sleeve 10 may be a solid metallic or ceramic structure
or it may have a tissue ingrowth surface such as a porous inner
surface integrated with or attached to a solid outer layer. The
sleeve may also be porous throughout.
[0045] The ball component 20 has a spherical outer surface that
serves as the bearing for the implant when assembled with a mating
acetabular cup. The ball component 20 has a bore that has an inner
surface allowing it to closely conform to the distal sleeve outer
surface or in the instance of a a one-piece ball prosthesis 20',
the prepared femoral head surface 9'. The body of the ball
component 20 is preferably made of a metallic or ceramic material
similar to those described for the sleeve 10 with the exception
that the material is typically solid throughout and has a suitable
hardness and durability to provide a bearing surface or substrate.
For durability and bearing performance, the ball component 20 may
be coated or have a surface layer of ceramic material. In any
instance, the hemispherical outer surface must function as a
bearing and requires a fine finish. It is also necessary that a
prosthesis holder provide suitable handling of the prosthesis to
prevent damage to the implant bearing surface during
installation.
[0046] FIG. 4 shows the preparation of the prepared femoral head
7', such that the femoral head surface 9 has been removed to create
the distal portion of the prepared femoral surface 9'. The part of
the prosthesis that comes in contact with the bone can be tapered,
domed, chamfered, cylindered or any combination of any of these
features. The portion of the bone that hosts the prosthesis is
shaped so that it matches the shape of the prosthesis. The size and
shape of the bone may fit exactly the shape and size of the
prosthesis or it may provide room for bone cement or provide an
excess of bone in some area to allow press-fit fixation, depending
on the preferred fixation method. The bone shape is typically
symmetrical around a prepared femoral head axis B-B and created by
an appropriately shaped cutter 32 that revolves about a guide pin
30, located in a femoral neck bore 31. As shown, the surface 9',
the cutter 32, the pin 30 and the bore 31 are co-axial with the
axis B-B. The symmetrical axis B-B of the bone is also the axis
along which it is desirable to guide the prosthesis for proper
installation. The cutter 32 may also shape the proximal portion of
the surface 9'.
[0047] FIGS. 5 and 6 depict a prosthesis holding tool 50 according
to an aspect of the first embodiment of the invention for seating
the sleeve component 10 of a two-part prosthesis onto the prepared
femoral head 7' of the femur 1. The tool 50 is cannulated with a
central bore 51 to allow guiding on the guide pin 30 initially used
to prepare the femoral head. The sleeve 10 has a central hole 12 in
the proximal portion to allow the guide pin 30 to pass through it.
The central bore 51 of the tool 50 is capable of receiving the
guide pin 30 and slidingly journaling on the guide pin to insure
that the tool is aligned with the prepared femoral head axis B-B
while seating the sleeve. The tool distal portion has a sleeve
interface 52 for receiving the sleeve 10. The sleeve interface 52
has holding features 54 that conform to a portion of the sleeve
outer surface and retain the sleeve with suitable features such as
detents 55 or tines. Because of the preferred tapered sleeve
exterior configuration wedging with the holding features 54, the
sleeve 10 will tend to strongly lock with the sleeve interface 52
as a result of the force of seating the sleeve 10 on the head 7'.
In order to remove the tool and overcome this locking force without
damaging the bone surface of the prepared femoral head 7' or
breaking the sleeve 10 loose from the femoral head, the tool
incorporates release features, such as an extractor assembly 60
that forces pins 64 against the proximal portion of the sleeve, to
release the sleeve from the tool.
[0048] It is preferred that the releasing features are symmetrical
about the tool and femoral head axis in order to insure that the
sleeve is not cocked with respect to the axis by the releasing
action. As shown on FIG. 6, the pins 64 are centrally connected and
slidingly journalled on the handle 56 of the tool 50 by an
extractor cage 62 in order to ensure that the extractor pins 64
apply force symmetrically about the handle axis and consequently
the femoral head axis B-B in order to ensure that the sleeve 10 is
not cocked during the separation of the tool from the sleeve. A
camming lever 68 drives the extractor cage 62 and consequently the
extractor pins 64 parallel to the axis B-B when actuated. A return
spring 66 is provided to keep the cage 62 positively engaged with
the cam of the lever 68.
[0049] FIGS. 5-10 illustrate the method of using the prosthesis
holding tool 50. The sleeve prosthesis 10 is first inserted into
the sleeve interface 52 and retained by the tines 55 of the
retention prongs 54 located symmetrically about the interface. If
necessary, bone cement is applied to the interior surface of the
sleeve 10 or to the mating prepared femoral head surface 9'. Using
the tool, the sleeve 10 is brought into position to introduce the
proximal end of the tip of the guide pin 30 into the central hole
12 of the sleeve and the cannulated bore 51 of the prostheses
holder 50. The handle 56 of the holder is used by the surgeon to
drive the sleeve 10 along the axis B-B defined by the guide pin
until the sleeve is mated with the prepared femoral head 7' as
shown in FIGS. 5 and 6. Sufficient pressure is applied to seat the
prosthesis as required by the selected fixation method. If
necessary, the tool 50 is held in position while the bone cement
sets. As seen in FIG. 7, the extractor assembly 60 of the
prosthesis holding tool is then actuated by rotating the handle 68
toward the handle 56. As further seen in FIG. 8, this actuation
drives the extractor cage 62 and pins 64 distally against the
proximal portion of the sleeve 10 to overcome the locking force and
detents in order to release the sleeve. The handle 68 is returned
to the initial position, withdrawing the pins 64 by the action of
the spring 64. The prosthesis holding tool 50 can then be removed
from the guide pin 30 as shown in FIG. 9. The guide pin 30 is next
removed from the femoral head 7', as in FIG. 10 and a ball
component 20 may be seated on the sleeve 10 in a subsequent
operation.
[0050] FIGS. 11-12 show a prosthesis holder according to an aspect
of the second embodiment of the invention and a sequence of steps
of the method of use of the second embodiment of the invention. As
depicted in FIG. 11, a prosthesis holding tool 50 similar to the
first embodiment is adapted to be used after removing the guide pin
30 prior to being used. After finishing the preparation of the
femoral head 7, as previously discussed with respect to FIG. 4, the
guide pin 30 is removed from the femoral head 7'.
[0051] In order to guide the tool 50, a central alignment pin 70
projects from the center of the handle 56 in place of the bore 51
previously used to receive the guide pin 30. To place the sleeve 10
in the tool 50, the central alignment pin 70 is first passed
through the hole 12 in the proximal portion of the sleeve and the
sleeve is captured, as in the first embodiment, by the holding
features 54 and detents 55 of the sleeve interface 52. As shown in
FIG. 11, the tool 50 is positioned with the alignment pin 70
aligned with the axis B-B and guided toward the femoral head 7'
until the alignment pin 70 is seated in the bore 31 to slidingly
journal the tool along the axis B-B. In other respects, the tool,
operation and method of the second embodiment is the same as the
first embodiment except that, of course, the guide pin 30 is
already removed prior to seating the sleeve.
[0052] FIGS. 13-19 show tools and methods according to an aspect of
the third embodiment of the invention wherein an alignment jig 80
is attached to a femoral neck 5 to install a ball prosthesis 20' on
a prepared femoral head 7' along a prepared femoral head axis B-B
determined from the guide pin 30. In this embodiment, the invention
is used to seat the ball component 20' rather than the sleeve 10.
The ball component 20' depicted is a one-piece type prosthesis with
a cavity fitting directly on the prepared femoral head 7' although
the aspects of the invention applicable to a one-piece ball
component 20' are also applicable to any modular ball component
such as ball component 20. Fitting a ball component 20' presents
problems because the axis B-B cannot be directly located by the
datums of the previous embodiments, either by guiding on the guide
pin 30 or the bore 31, during the installation of the ball because
the pin must be removed prior to installing the component and the
bore is inaccesible as the head 7' enters the cavity 10. As
depicted in FIGS. 13-19, an alignment jig 80 is used to transfer
the datum for the axis B-B to create a secondary datum at a
position sufficiently distant from the femoral head 7' to allow a
path for the ball component 20 to be installed on the head. A
sequence of steps of the method of using the alignment jig 80 is
illustrated in FIGS. 13-19 including, starting in FIG. 16, the use
of a prosthesis holding tool 50 guided by the jig to install the
prosthesis.
[0053] Turning to FIG. 13, the alignment jig 80 is attached to a
proximal portion of the femur 1, preferably at the femoral neck 5.
The femoral head 7 has been prepared, as previously discussed with
respect to FIG. 4 and the guide pin 30 is temporarily left in
place. The alignment jig 80 is comprised of a femoral mount 81, an
axial extension 82 and a radial extension 84 with a pin location
guide 86 at the proximal end of the extension. The pin location
guide 86 is an aperture having a central axis that can be aligned
to be co-axial with the femoral head axis datum provided by the
guide pin 30 or the bore 31 and consequently with axis B-B. The jig
80 has various clamps, slides and rotational adjustments that
provide sufficient degrees of freedom to allow the pin location
guide 86 to be co-axially positioned with axis B-B. The pin locator
87 has a bore with a central axis. The bore is sized to slidingly
engage on the guide pin 30 projecting from the femoral head and the
locator 87 has an outer surface coaxial with the bore that
slidingly engages the pin location guide 86 to translate the datum
for the axis B-B originally established by the guide pin 30.
Alternatively, the pin locator 87 may also be configured with a
projecting alignment pin, to locate the datum for axis B-B using
the bore 31 in the same manner as the pin 70 of the tool 50 in the
second embodiment of the invention.
[0054] The femoral mount 81 is first attached to the proximal femur
1, preferably at the femoral neck 5. The attachment may be by
friction means using, for example, a hinged clamping mechanism, as
shown, or by set screws or bone screws, care being taken to not
compromise the integrity of the femoral bone at the interface with
the clamp. The mount 81 incorporates a multi-axis adjuster 88
comprising a spherical cavity 88a and a binder bolt 88b. The
spherical cavity 88a engages a split spherical collet 89 and can
apply a clamping force using the binder bolt 88b as shown. The
collet 89, in turn, is slidingly engaged with the axial extension
82 which passes through a central cavity of the collet to provide
an axial adjustment. Consequently, when the adjuster 88 is not
clamped, the spherical interface 88a provides the collet 89 with
three degrees of rotational freedom and allows the axial extension
82 to translate relative to the collet. When clamped, the three
rotational degrees of freedom and the translational degree of
freedom are locked because the binder bolt 88b constricts the
spherical cavity 88a onto the split collet 89, which in turn
constricts the collet onto the axial extension 82. Two of the
rotational degrees of freedom allow the axial extension 82 to be
positioned parallel to the guide pin 30 and axis B-B while the
third degree of freedom allows rotation of the axial extension 82
about its axis.
[0055] The axial extension 82 has a radial adjustment 85 at its
proximal end with a suitable clamping mechanism, such as a set
screw, to slidingly engage the distal portion of the radial
extension 84 and lock the joint when desired.
[0056] As shown in FIG. 14, when the jig 80 is mounted on the
femoral neck 5 and the jig joints are adjusted and locked to allow
the pin locator 87 to engage the pin location guide 86, the datum
provide by the guide pin 10, and consequently the prepared femoral
head axis B-B, are determined and the pin alignment guide 86 is
constrained to align with the axis and bore of the guide. The pin
alignment guide 86 can now be used as a new datum to determine the
axis B-B.
[0057] It will be understood by the person of skill in the art
familiar with mechanism design and kinematics that numerous
configurations of joints, extensions and locking mechanisms will
provide the necessary ability to reestablish the datum of axis B-B
at a point remote from the surface of the femoral head so long as
the necessary degrees of freedom are provided and that the
configuration shown is but exemplary. Examples of similar joints,
extensions and locking mechanisms indicative of the skill in the
art can be found, for example, in a prosthetic checking jig
disclosed in U.S. Pat. No. 6,203,575. It will also be recognized by
the person of skill that it may be desirable to provide additional
redundant rotational and translational axes and appropriate bearing
configurations to improve assembly sequences, flexibility of the
jig and ease of use, for instance by allowing sideways access to
the pin location guide 86. The number of necessary degrees of
freedom in the jig 80 may also be reduced by allowing the mount 81
to be adjusted to various positions relative to the femoral neck 5
in order to provide additional degrees of freedom at the neck
interface. Supplementary tools, such as a checking fixture to
determine that the axial extension 82 is parallel to the guide pin
30 by locating on the guide pin and the extension, may be used to
simplify establishing the new datum. While the use of the pin
locator 87 is a preferred embodiment, an extended pin 30 may be
directly engaged by the pin location guide 86 to determine the
datum.
[0058] Having established a new datum for the axis B-B, the guide
pin 30 is then removed as shown in FIG. 15. In FIG. 16, the partial
ball component 20' and a prosthesis holding tool 50 adapted to
retain a ball component are mounted on the alignment jig 80 to
allow the ball 20' to be installed by translating the prosthesis
and tool along the axis B-B as established by the jig using the new
datum remote from the femoral head.
[0059] The prosthesis holding tool 50 has been modified to retain
and selectably release the ball component 20'. As previously
discussed the ball component 20' has a finely finished bearing
surface that must be suitably handled to protect the finish. In
this example, the ball 20' is gripped by three retention prongs 54,
that are pivotably mounted to an interface body 52. The prongs 54
may be capable of elastic deformation or spring loaded and may be
released by a suitable pivot arm connected to a release button in
the handle 58 as will be understood by a person of skill in the
art. If desired, detents 55 or tines, may be engaged on the planar
portion of the partial ball component 20' to prevent rotation of
the ball as shown in FIG. 16A. The tines 55 project inwardly from
the spherical inner surface of the prongs 54 at the position
corresponding to the planar portion of the partial ball component
20'. In use, the prongs 54 are deflected outward to install the
ball component 20' and capture the ball component when the ball
component is fully seated and the prongs 44 and tines 55 move
inward. The ball 20' may be released by overcoming a spring preload
or deflecting the retention prongs 54 and tines 55 either as a
result of the frictional retention force created by the interface
of the ball cavity with the prepared femoral head surface 9' as the
tool 50 is retracted or by a plunger acting on the ball to eject it
from the tool. Methods of protecting, retaining and releasing a
ball component 20 or 20' are known as disclosed in U.S. Pat. No.
4,542,825; U.S. Pat. No. 5,133,765; U.S. Pat. No. 6,585,771; and
U.S. Published Patent Application No. 2003/0228357.
[0060] The prosthesis holding tool 50 is guided along the axis B-B
by the sliding engagement of the cylindrical tool handle 56 with
the bore of the pin alignment guide 86 that is now used as a new
datum to determine the axis B-B and control the path of the tool
and consequently the ball component along the axis until seated on
the prepared femoral head 7' as shown in FIGS. 17 and 18. In FIG.
18, the ball 20' has been released from the retention prongs 54 and
the tool retracted and subsequently removed as shown in FIG.
19.
[0061] FIGS. 20-26 show a sequence of perspective views according
to a fourth embodiment of the present invention similar to the
third embodiment except that the datum for the axis B-B is not
absolutely determined and the tooling is simplified by the use of a
separate axis alignment jig and prostheses alignment jig. First,
the axis alignment jig 90 is used to determine the position of a
secondary alignment pin on the side of the femoral neck relative to
the axis B-B, then the axis alignment jig is removed and the
prosthesis alignment 100 is engaged on the secondary pin to install
the ball component prosthesis.
[0062] As shown in FIG. 20, the axis alignment jig 90 has, at its
proximal end, a tube with a bore 92 sized to slidingly engage and
journal the guide pin 30. As in the other embodiments, the guide
pin 30 is the datum for the axis B-B of a prepared femoral head 7'.
The jig 90 has an extension having a slotted fitting 96. The jig is
placed with the bore 92 directly over the guide pin to locate the
datum for axis B-B. A mount, typically a mounting pin 94, is then
placed on the side of the femoral neck in a predetermined
relationship to the axis B-B determined by the slot in the fitting
96 as shown in FIG. 21. It can be seen that an axis defined by the
pin 94 will intersect the axis B-B because the slot orients the pin
94 to intersect the axis B-B. Typically, the surgeon places the pin
approximately perpendicular to the axis B-B in a freehand manner,
but a supplemental tool establishing an axis perpendicular to the
axis of the bore 92 for guiding the pin 94 may be mounted proximal
to the slot of fitting 96 to insure that the pin 94 is
perpendicular to the axis B-B by using, for instance, a bore in the
supplemental tool that is perpendicular to the axis when mounted to
the fitting 96 to guide the pin. As shown on FIG. 22, the axis
alignment jig 90 is then removed followed by the guide pin 30.
[0063] The prosthesis alignment jig 100, shown in FIGS. 23 and 24,
is similar to the pin alignment jig 90 except that rather than
having a cylindrical portion with a bore 92 mounted at the proximal
end, a prosthesis holder 102 is mounted to a mount 101. The ball
20' is gripped by three retention prongs 106, that are connected to
an interface body in a manner similar to that described in
connection with the third embodiment. The ball 20' may be captured
or released by deflecting the retention prongs 106, as shown, or by
any of the methods discussed above in connection with the third
embodiment.
[0064] The prosthesis 20' is installed in the prosthesis alignment
jig 100 and the jig 100 is aligned with the femoral head axis using
the mount 94 on the side of the femur as shown in FIG. 25. The
prosthesis alignment jig 100 is then used to install the prosthesis
10 in a manner similar to the third embodiment as shown in FIG. 26.
Subsequently, the retention prongs 106 are released, the jig 100 is
removed, and the pin 94 is removed.
[0065] It is noteworthy that the tools and methods of this aspect
of the fourth embodiment, as described above, allow considerably
more degrees of freedom, such as rotation about the pin 94, for the
path of the jig 100 as the ball 20' is seated. It has been found
that this simplified tooling is sufficient to seat the prosthesis
and provide increased accuracy in the placement of the prosthesis
because the axis of the pin 94 intersects the prepared femoral head
axis B-B and the ball is sufficiently guided toward the head axis
to prevent cocking and allow accurate placement of the prosthesis
20.
[0066] A person of skill in the art will appreciate that the tools
and methods of the fourth embodiment can readily provide increased
control of any of the degrees of translational or rotational
freedom by various methods known in the art. For example, the pin
94 may have flats oriented parallel with the head axis B-B that
slidingly engage with the slots of the fittings 96 of both the jigs
90 and 100 to prevent rotation about the pin axis and keep the jigs
aligned with the head axis. As another example, a pair of stops may
be fixed on the pin 94 at both sides of the fittings 96 to
establish a radial datum that is transferred from the pin jig 90 to
the prosthesis jig 100 to prevent the radial translation or
rotation of the prosthesis jig relative to the pin.
[0067] It is also possible to combine the attributes of the third
and fourth embodiment in a hybrid embodiment to provide control of
additional degrees of freedom while retaining the relative
simplicity of the fourth embodiment. For instance, the pin
alignment jig 90 may be fitted with a joint such as multi-axial
adjuster 88 configured to allow the pin 94 to be clamped by the
collet 89 to lock the position of the jig in alignment with axis
B-B. In this embodiment, the proximal portion of the alignment jig
90 has a fitting allowing the proximal portion to be detached and
replaced with a second proximal portion having the features of the
prosthesis jig 100 and allowing the prosthesis to translate only in
the axis B-B.
[0068] The modular components of tools according to the embodiments
of the invention described above are particularly well suited for
inclusion in a kit that can be used by a surgeon to implant femoral
ball components 20 and 20' of different sizes by providing the
various prosthesis holders of the invention in various sizes
corresponding to the prostheses sizes.
[0069] Unless stated to the contrary, any use of the words such as
"including," "containing," "comprising," "having" and the like,
means "including without limitation" and shall not be construed to
limit any general statement that it follows to the specific or
similar items or matters immediately following it.
[0070] Although the invention herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
invention as defined by the appended claims.
[0071] Although the invention herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *