Note: Descriptions are shown in the official language in which they were submitted.
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CARTILAGE-PRESERVING KONG BONE HEAD PROSTHESIS
Field of the Invention
The present invention relates to a new type of prosthetic
device, and a method that uses said device in the treatment
of femoral and Numeral neck fractures. More specifically,
the prosthetic device of the invention is capable of being
used to treat long bone neck fractures in procedures
wherein the natural articular cartilage and subchondral
bone of the long bone is preserved.
Background of the Invention
Fractures of the neck of the femur and humerus have always
presented great challenges to orthopedic surgeons and
remain in many ways today the "unsolved fracture" as far as
methods of treatment and the results obtained thereby are
concerned.
Approximately 280,000 hip fractures occurred in the United
States in 1998. The National Osteoporosis Foundation
reported that in 1995, health care expenditures for the
management of osteoporotic hip fractures totaled $8.7
billion, representing 630 of the cost of treating all
osteoporotic fractures, and 430 of the cost of all fracture
care. It is predicted that by the year 2020, the incidence
of hip fractures in the United States will be more than
500,000 new cases per year. It is further predicted that
the cost of treating these patients will rise to $16
billion per year.
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High rates of avascular necrosis and nonunion are common
complications in displaced fractures of the femoral neck
(Garden classification stages 3 and 4). Even when
undisplaced, there is no assurance that a fracture of the
femoral neck may be treated in a satisfactory way. One of
the key reasons for the problematic nature of these
fractures from the therapeutic aspect is that the surgeon
has less control over avascular necrosis, because of the
disturbances to blood flow to the femoral head that occur
following femoral neck fracture.
Femoral neck fractures are usually entirely intracapsular,
and (in common with all intracapsular fractures) the
synovial fluid bathing the fracture may interfere with the
healing process. Furthermore, all healing must be take
place endo-osteally, in view of the fact that the femoral
neck has essentially no periosteal layer. Finally,
angiogenic-inhibiting factors in synovial fluid can also
inhibit fracture repair. All of these factors, together
with the aforementioned precarious blood supply to the
femoral head, result in unpredictable healing and a
subsequent fairly high incidence of nonunions.
Few treatment options are available for the management of
long bone neck fractures. Of these options, the most
commonly employed are:
1. Osteosynthesis - fracture fixation; and
2. Hemiartheoplasty - replacement of the femoral head with
a (normally metal) prosthetic head attached to a monoblock
or modular femoral stem. The most popular types of
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prosthesis used are the Thompson, Austin-Moore, bipolar and
unipolar prostheses. A typical bipolar femoral prosthesis
is shown in Fig. 1.
Many surgeons recommend the second option, that is, the use
of a primary prosthetic replacement for use in the
treatment of elderly by ambulatory patients. While the use
of prostheses may assist in the prevention of nonunion and
avascular necrosis, their use is associated with a number
of other complications.
One of the recognized disadvantages of using a prosthesis
in the management of a fresh femoral neck fracture is the
pain that is produced as a consequence of acetabular
erosion. This complication is often so severe that it has
prompted one expert to comment:
"The sacrifice of the head and neck and replacement
by a metallic foreign substance is not the answer
for the majority of patients; in over half, the
best available material is in the acetabulum, and
its indiscriminate removal should be avoided."
(Salvatore "Campbell's Operative Orthopedics, gtn
edition.)
A further major problem associated with the use of existing
prosthetic devices is the dysfunction that arises from the
mismatch between the acetabulum and the prosthetic head.
Further traumatic complications also arise from the fact
that following implantation of the prosthesis, articulation
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takes place between the hard metal of the prosthetic head
and the much softer acetabular surface.
It is a purpose of the present invention to provide an
improved prosthetic device that may be used in the
treatment of long bone neck fractures.
It is another purpose of the invention to provide a
prosthetic device whose use in the treatment of long bone
neck fractures does not require the loss of either of the
two natural articulating surfaces of the proximal long bone
joint.
It is yet another purpose of the invention to provide a
method of treatment of long bone fractures that allows the
use of an endoprosthesis while preserving the natural
articular surfaces.
It is a further purpose of the invention to provide a
prosthetic device and method that may be used to overcome
the disadvantages and problems associated with prior art
devices and methods.
Further objects and advantages of the present invention
will become apparent as the description proceeds.
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Summary of the Invention
It has now been unexpectedly found that it is possible to
treat fractures of the neck region of the femur and humerus
by means of a surgical method involving the use of a novel
endoprosthesis. The head region of this endoprosthesis is
characterized by being adapted for insertion into a shell-
like cavity comprising the outer layers of the patient's
femoral or humeral head, following removal of most of the
cancellous bone. In this way, the cartilaginous articular
surface of the long bone head, together with the underlying
subchondral bone is preserved, thus retaining the natural
articulating surfaces of the proximal long bone ball-and-
socket joint.
The present invention is thus primarily directed to a long-
bone endoprosthesis comprising an essentially spherical
head region that is connected to a narrowed stem section,
wherein the head region is characterized in having a
roughened outer surface.
In one preferred embodiment of the endoprothesis of the
present invention, the roughened prosthetic head outer
surface has an arithmetic average roughness (Ra) value in
the range of 0.05 um to 500 Vim. More preferably, the Ra
value is between 40 ~Zm and 200 Vim. Most preferably, the Ra
value is 50 Vim. For the purposes of the present invention,
the parameter Ra is defined in accordance with the
International Standards Organization document ISO 468
("Surface Roughness Parameters - their values and general
rules for specifying requirements").
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In another preferred embodiment, the roughened prosthetic
head outer surface is a surface comprising one or more
surface features selected from the group consisting of
indentations, ridges, slots, grooves, pores, dimples and
protuberances. Theses features may be introduced into the
surface of the prosthetic head by any standard procedure
including mold-casting techniques, machine-cutting and (in
the case of small-diameter surface protuberances) grit
blasting techniques. In a particularly preferred
embodiment, the roughened prosthetic head outer surface is
a surface fitted with one or more grooves or slots, as will
be described in more detail hereinbelow.
In the context of the present invention, the term "long-
bone" is used primarily to refer to the femur and humerus.
In one preferred embodiment of the prosthesis of the
invention, the head and neck regions of the prosthesis are
constructed as a one-piece unit, to be referred to
hereinafter as the monoblock embodiment.
In another preferred embodiment, the head and neck regions
are constructed as two separate modular units. In a
particularly preferred embodiment of this aspect of the
invention, the separate head region is a bipolar prosthetic
head.
In another aspect, the present invention is directed to a
long-bone endoprosthetic head comprising an essentially
spherical portion, into the distal side of which is formed
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a recess such that a femoral stem endoprosthesis may be
inserted therein and connected thereto, and wherein said
endoprosthetic head is characterized by having a roughened
outer surface, as defined and described hereinabove.
Thus, in one preferred embodiment of the aforementioned
endoprosthetic head of the present invention, the roughened
prosthetic head outer surface has an arithmetic average
roughness (Ra) value in the range of 0.05 ~m to 500 Vim.
More preferably, the Ra value is between 40 ~m and 200 ~.m.
Most preferably, the Ra value is 50 Vim.
In another preferred embodiment, the roughened prosthetic
head outer surface is a surface comprising one or more
surface features selected from the group consisting of
indentations, ridges, slots, grooves, pores, dimples and
protuberances. In one preferred embodiment of this aspect
of the invention, the average depth or height of the
aforementioned surface features is in the range of 0.05 ~m
to 5000 ~.m. More preferably, the average value is between
400 pm and 2000 Vim. Most preferably, the average height or
depth value is 1000 Vim. In another preferred embodiment,
in the case of slots, grooves and pores, the depth of said
features is in the range of 1 ~m to the maximum thickness
of the material of the prosthetic head surface. In the
case of this maximum depth value, the prosthetic head is
actually perforated by the slots, grooves or pores, such
that a channel is created from the external surface of the
prosthetic head to the inner surface or cavity of said
head.
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_g_
In a further preferred embodiment of the invention, the
aforementioned long-bone endoprosthetic head having a
roughened outer surface is constructed as a bipolar
prosthetic head, having an outer head (with the roughened
outer surface), an intermediate portion adjacent to the
inner surface of said outer head, and an inner head that
articulates with the inner surface of said intermediate
portion.
The present invention also encompasses an endoprosthetic
system comprising a long-bone endoprosthetic head as
disclosed and defined hereinabove, and a femoral stem
endoprosthesis that may be connected thereto.
In a further aspect, the present invention is also directed
to a method for treating fractures of the neck region of a
long-bone in a patient in need of such treatment, wherein
said method comprises the steps of:
a) removing most or all of the cancellous bone from the
head of said long-bone, thereby forming a long-bone head
shell;
b) preparing the long bone canal to accept a prosthetic
stem;
c) inserting, and optionally cementing said prosthetic stem
into said long-bone canal;
d) inserting and cementing a long-bone prosthetic head into
said~long-bone head shell; and
e) reduction of the stem region into the recessed region of
said prosthetic head.
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The present invention is also directed to a method for
treating fractures of the neck region of a long-bone in a
patient in need of such treatment, wherein said method
comprises the steps of:
a) removing the native long-bone head from its natural
location in the body, by the use of a safe technique that
does not cause injury to the cartilage or subchondral bone;
b) preparing the head shell outside the body on the
operative tray;
c) preparing the long bone canal to accept a prosthetic
stem section;
d) inserting the prosthetic stem section with or without
the use of cement;
e) cementing the prosthetic head section to the shell
formed in step (b);
f) reduction of the prepared prosthetic head together with
the attached head shell into the joint of the patient being
treated, and connection of the distal portion of said
prosthetic head to said prosthetic stem section.
The present invention is further directed to a method for
treating fractures of the neck region of a long-bone in a
patient in need of such treatment, wherein said method
comprises the steps of:
a) removing the native long-bone head from its natural
location in the body, by the use of a safe technique that
does not cause injury to the cartilage or subchondral bone;
b) preparing the head shell outside the body on the
operative tray;
c) preparing the long bone canal to accept the stem
section of a monoblock prosthesis;
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d) inserting said monoblock prosthesis stem section into
said long bone canal with or without the use of cement;
e) cementing the head section of said monoblock prosthesis
to the shell formed in step (b);
f) reduction of the prepared monoblock prosthesis head
together with the attached head shell into the joint of the
patient being treated.
The present invention is also directed to another method
for treating fractures of the neck region of a long-bone in
a patient in need of such treatment, wherein said method
comprises the steps of:
a) removing most or all of the cancellous bone from the
head of said long-bone, thereby forming a long-bone head
shell;
b) preparing the long bone canal to accept a prosthetic
stem;
c) inserting, and optionally cementing said prosthetic stem
into said long-bone canal;
d) cementing the outer head of a bipolar prosthesis to the
shell formed in step (a);
e) placing prosthetic stem section trunion into the inner
cavity of the inner prosthetic head;
f) inserting the inner prosthetic head into the inner
cavity of the outer prosthetic head;
g) locking the bipolar head assembly by means of closing
the locking ring.
The present invention is further directed to a method for
treating fractures of the neck region of a long-bone in a
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patient in need of such treatment, wherein said method
comprises the steps of:
a) removing the native long-bone head from its natural
location in the body, by the use of a safe technique that
does not cause injury to the cartilage or subchondral bone;
b) preparing the head shell outside the body on the
operative tray;
c) preparing the long bone canal to accept a prosthetic
stem section;
d) inserting the prosthetic stem section with or without
the use of cement;
e) cementing the outer head of a bipolar prosthesis to the
shell formed in step (b);
f) placing prosthetic stem section trunion into the inner
cavity of the inner prosthetic head;
g) inserting the inner prosthetic head into the inner
cavity of the outer prosthetic head;
h) locking the bipolar head assembly by means of closing
the locking ring;
i) reduction of the prepared prosthetic head together with
the attached head shell into the joint of the patient being
treated.
The present invention is further directed to another method
for treating fractures of the neck region of a long-bone in
a patient in need of such treatment, wherein said method
comprises the steps of:
a) removing the native long-bone head from its natural
location in the body, by the use of a safe technique that
does not cause injury to the cartilage or subchondral bone;
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b) preparing the head shell outside the body on the
operative tray;
c) preparing the long bone canal to accept the stem-inner
section of a monoblock bipolar prosthesis;
d) inserting the prosthetic stem section of the stem-inner
head bipolar monoblock bipolar prosthesis, with or without
the use of cement;
e) cementing the bipolar prosthetic outer head section to
the shell formed in step (b);
f) reduction of the prepared bipolar prosthetic outer head
together with the attached head shell into the joint of the
patient being treated;
g) inserting the bipolar inner head into the internal
cavity of the bipolar outer head;
h) locking the bipolar head assembly by means of closing
the locking ring.
The present invention is further directed to yet another
method for treating fractures of the neck region of a long-
bone in a patient in need of such treatment, wherein said
method comprises the steps of:
a) removing the native long-bone head from its natural
location in the body, by the use of a safe technique that
does not cause injury to the cartilage or subchondral bone;
b) preparing the head shell outside the body on the
operative tray;
c) preparing the long bone canal to accept the stem-inner
section of a monoblock bipolar prosthesis;
d) inserting the prosthetic stem section of the stem-inner
head bipolar monoblock bipolar prosthesis, with or without
the use of cement;
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e) inserting the bipolar inner head into the internal
cavity of the bipolar outer head;
f) locking the bipolar head assembly by means of closing
the locking ring;
g) cementing the shell formed in step (b) onto the bipolar
prosthetic outer head section;
h) reduction of the prepared bipolar prosthetic outer head
together with the attached bipolar prosthesis into the
joint of the patient being treated.
The present invention is also directed to a yet further
method for treating fractures of the neck region of a long-
bone in a patient in need of such treatment, wherein said
method comprises the steps of:
a) removing most or all of the cancellous bone from the
head of said long-bone, thereby forming a long-bone head
shell;
b) preparing the long bone canal to accept the stem-inner
head section of a monoblock bipolar prosthesis;
c) inserting, the prosthetic stem section of the stem-inner
head bipolar monoblock bipolar prosthesis, with or without
the use of cement;
d) inserting the bipolar inner head into the internal
cavity of the bipolar outer head;
e) locking the bipolar head assembly by means of closing
the locking ring;
f) cementing the bipolar prosthetic outer head section to
the shell formed in step (b).
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The above methods of treatment are applicable to the
treatment of fractures of both the femur and the humerus.
All the above and other characteristics and advantages of
the present invention will be further understood from the
following illustrative and non-limitative examples of
preferred embodiments thereof.
Brief Description of the Drawings
Fig. 1 is a photograph of a prior art bipolar femoral
endoprosthesis.
Fig. 2 schematically depicts the prosthetic device of the
present invention.
Fig. 3 is a photographic representation of a prosthetic
device of the present invention after insertion of the head
of the device into the shell of a femoral head, following
removal of most of the cancellous bone.
Fig. 4 is a photograph demonstrating the head of a two-part
prosthetic device according to the present invention
following its insertion into a femoral head shell.
Fig. 5 is a side view of one embodiment of a femoral
endoprosthetic head according to the present invention, in
which the roughened surface is provided by the presence of
both circumferential and longitudinal slots.
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Fig. 6 is an inferior view of the embodiment of the
endoprosthetic head depicted in fig. 5.
Fig. 7 is a superior view of the embodiment of the
endoprosthetic head depicted in figs. 5 and 6, showing the
non-slotted region at the proximal pole of said head.
Fig. 8 is an inferior view of a bipolar prosthetic head
depicting the inner head portion residing within the
internal cavity of the outer head portion.
Fig. 9 is an inferior view of a bipolar prosthetic head
depioting the inner head locked in place in the internal
cavity of the outer head portion by means of a locking
ring.
Detailed Description of Preferred Embodiments
The essential inventive feature of the endoprosthesis of
the invention is the fact that the head region (or at least
a portion thereof) has a roughened, non-polished outer
surface, in order to permit optimal mechanical bonding of
said head region to cement, and by which means to the inner
surface of the femoral or Numeral head shell-like cavity.
This stands in marked contrast to prior art long-bone head
and stem prostheses, whose head regions are characterized
by having a polished surface, the purpose of which is to
replace the natural cartilaginous articular surface of the
natural femoral or Numeral head. The retention of the
natural articular surfaces of the ball-and-socket joints
results in several clinical advantages, including
prevention of acetabular erosion, obviation of the problem
of ball/socket mismatch that is seen with prior art
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approaches, and pain reduction. Many of the above
advantages arise from the fact that the retention of the
anatomical articulating surfaces preserves the natural
clearance between the long bone head and the socket within
the joint. It should be noted that the viability and
integrity of the long bone head articular cartilage is
maintained by virtue of the fact that the nutritional
requirements of this tissue are met by synovial fluid that
bathes said tissue.
A typical femoral endoprosthesis in accordance with the
present invention is schematically illustrated in Fig. 2.
The prosthesis, shown generally as 20 consists essentially
of two sections: the prosthetic head region 21 and the stem
region 22. In the lateral view shown in this figure, it
may be seen that the proximal end 23 of the stem region is
inserted into an elongated recess 24 in said head region.
The femoral head shell 25, comprising the patient's
articular cartilage and associated subchondral bone, is
bonded to the prosthetic head region 21 by means of
biocompatible cement 26. The surface roughness of the
prosthetic head region 21 of the embodiment depicted in
this figure is provided by a series of circumferentially
arranged slots 27. As indicated in the figure, the
biocompatible cement 26 is able to penetrate into said
slots, thus increasing the strength of the bonding between
the prosthetic head region 21 and the femoral head shell
25.
Fig. 3 photographically depicts a prosthesis of the present
invention, generally shown as 30 after assembly of the head
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31 and stem 32 regions. Most of the surface area of head
region 31 is obscured by the femoral head shell 33 that
covers said region.
Fig. 4 photographically depicts the head region of the
prosthesis shown in Fig. 3 (generally shown here as 40)
prior to insertion of the stem region. A small portion of
the roughened outer surface 41 of the head region is shown
extending below the inferior (distal) margin of the femoral
head shell 42. It will be noted that said surface is
perforated by a circular opening 43 into which the stem
region of the prosthesis will be inserted.
In one preferred embodiment of the present invention, the
prosthetic head having the roughened outer surface may be a
bipolar prosthesis. As is well known in the art, bipolar
prostheses for use in the management of long bone neck
fractures comprise the following components:
1. An outer head for articulation with the joint socket
(e.g. acetabular) surface. In the case of the
present invention, the outer head has a roughened
outer surface, in order to permit attachment thereof
to the prepared femoral head, as described herein.
2. An intermediate layer or portion fixed within the
inner cavity of the outer head. Typically, the
intermediate portion is constructed of a material
that is softer than metal (such as polyethylene).
Alternatively, this portion may be constructed of the
same material as the outer head, thereby forming a
single unit therewith. (More details of the
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materials used in the construction of bipolar
prostheses according to the present invention are
given hereinbelow.)
3. An inner head, the outer surface of which movably
articulates with the inner surface of the
aforementioned intermediate portion, and the inner
cavity of which is immovably fixed to the femoral
stem trunion. Fig. 8 illustrates the articulation of
the inner head 81 with the intermediate portion 83
within the inner cavity of the outer head 85.
4. A locking ring, whose function is to retain the inner
head in movable contact with the intermediate portion
within the inner cavity of the outer head. Fig. 9
illustrates (from an inferior aspect) the relative
disposition of the inner head 91 and outer head 95,
following closure of the locking ring 97.
In another preferred embodiment of the present invention,
the prosthetic head having the roughened outer surface may
be part of a bipolar monoblock prosthesis, wherein the
inner head and femoral stem of said prosthesis are provided
as a single integral unit. As in the case of the bipolar
prosthetic head described hereinabove, the inner head of
the monoblock unit is retained in movable contact with the
intermediate layer within the cavity of the outer head and
locked in place with the above-described locking ring.
The endoprostheses of the present invention may be
constructed from cobalt-based alloys (e. g. cobalt-chrome),
titanium, titanium-based alloys, stainless-steel, and
combinations of the above-mentioned metals. In addition,
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the endoprostheses may also comprise components that are
constructed from non-metallic materials such as
biocompatible plastics and polymers, such as polyurethane
and polyethylene, as well as other synthetic biocompatible
materials that are softer than the aforementioned metals,
and hard materials such as ceramics. The aforementioned
lists are intended to exemplify some of the more common
materials, and are not to be considered as limiting.
Various combinations of the different materials mentioned
hereinabove also form part of the scope of the present
invention. Thus, for example, prosthetic heads may be
constructed with a metal trunion in contact with a plastic
body. Another example of the use of a combination of
materials would be the case in which the central bulk of
the prosthetic head is constructed of a metal or metal
alloy, whereas the outer portion (having an external
surface that is cemented to the femoral head shell and an
inner surface that is bonded to said metal or alloy) may be
constructed of a non-metallic, polymeric material.
In the case of a prosthetic head of the invention of a
bipolar construction, the outer head (i.e. the portion
bearing the roughened surface that is cemented to the
femoral head shell) may be constructed of a metal or metal
alloy. Alternatively, the outer head may be constructed of
a ceramic or polymeric material. The intermediate layer
that lines the inside of said outer head is typically
constructed of polyethylene. However, in another
embodiment, this layer may be constructed of the same
material as the outer head, thereby forming a single unit
therewith. The inner head, like the outer head, may be
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constructed of either a metal or of a polymeric or ceramic
material.
Many different combinations of materials may be chosen in
order to obtain prostheses having the desired physical
properties (such as hardness, resilience, elasticity etc.).
The external dimensions of the endoprosthesis of the
present invention are essentially as the same as those of
prior art femoral and Numeral prostheses. Thus, in the
case of a prosthesis of the present invention having a head
region that is essentially spherical in shape, the diameter
of the spherical head is generally in the range of 22 to 40
mm. A preferred head diameter for the femoral head
prosthesis is in the range of 28 to 32 mm. In practice,
however, the head diameter may also be outside of these
preferred ranges, in certain circumstances being as small
as 12 mm or as large as 60 mm. It should be noted,
however, that the prostheses of the present invention are
not limited to those having head regions of spherical
conformation. Rather, prostheses with non-spherical,
mufti-sided head conformations are also included within the
scope of the presently-claimed invention. Preferably, such
mufti-sided head regions have three or more sides. More
preferably, the number of sides present in such
conformations is between four (e. g. square, rectangular
and/or trapezoid) and eight (i.e. octagonal). However,
mufti-sided head geometries of any other type that are
suitable for performing the present invention are also to
be considered as falling within the scope thereof.
Examples of such suitable geometries (in addition to those
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mentioned hereinabove) include, but are not limited to,
regular pyramidal shapes as well as irregular polyhedrons,
star-shaped, "hedgehog-shaped", and so on. In addition,
other head geometries such as conical, frusto-conical and
variations and combinations thereof may also be usefully
employed, and form part of the scope of the present
invention.
It is to be emphasized that, although the external shape
and dimensions of the endoprostheses of the present
invention may be similar to those of corresponding prior
art devices, the presently-claimed devices are
distinguished by having head regions that are unpolished,
and which optionally are further roughened by the presence
of one or more distinctive surface features, as described
hereinabove, and exemplified hereinbelow.
The roughened prosthetic head surface may be produced in
several different ways, by the use of any standard
procedure including mold-casting techniques, machine-
cutting and (in the case of small-diameter surface
protuberances) grit blasting techniques. In a particularly
preferred embodiment, the roughened prosthetic head outer
surface is a surface fitted with one or more slots, as will
be described in more detail in the illustrative example
given hereinbelow.
Many different types of cement may be used to bond the head
of the prosthesis into the head "shell" formed after
removal of most or all of the cancellous bone from the long
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bone head. Examples of suitable cements and glues include
Palacos cement, Simplex, CMW and Cementech.
Surgical method:
The endoprosthesis of the present invention may be used in
the surgical treatment of long-bone neck fractures. The
following procedure is one example of a surgical method
that utilizes the instantly-disclosed prosthesis in the
management of femoral neck fractures:
1. Standard approach to the hip joint.
2. Wide exposure of the hip capsule.
3. Identification of the femoral head fractured margins.
4. Holding the femoral head with a reduction clamp or
similar instrument, with the fracture plane away from the
articular space.
5. Reaming the cancellous bone out of the femoral head
using a high speed bur or any other conventional acetabular
reamer, avoiding rotational forces in the articular space.
6. Retaining a thin layer (2-3 mm) of subchondral bone,
forming (together with the femoral head articular
cartilage) a femoral head "shell".
7. Preparing the femoral canal in the standard way for a
cemented or non-cemented femoral stem.
Either:
8a. Inserting cement into the femoral canal and introducing
the stem into said canal. The stem is held in place within
the femoral canal until polymerization of the cement is
complete.
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Or:
8b. Insertion of the femoral stem into the canal without
the use of cement.
9. Inserting cement inside the femoral head "shell" and
inserting the prosthetic head into said "shell" with
meticulous cooling until cement polymerization is complete.
10. Reduction of the stem trunion into the prosthetic
head.
11. Closure of the capsule.
Other alternative surgical procedures may also be usefully
employed. One example of such an alternative would involve
the dislocation of the femoral head immediately following
its surgical exposure. The head could then be removed from
the body and subjected to essentially the same procedure as
described hereinbefore. These various surgical approaches
may be combined with the use of different types of long-
bone prosthesis including: two-part prostheses, monoblock
prostheses, bipolar prostheses and monoblock bipolar
prostheses. The stages involved in the use of these types
of prosthesis in conjunction with the different types of
surgical procedure described in this section, are disclosed
and defined hereinabove.
The following example is provided for illustrative purposes
and in order to more particularly explain and describe the
present invention. The present invention, however, is not
limited to the particular embodiments disclosed in the
example.
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Example
A rough-surfaced, cartilage-sparing long bone prosthetic
head according to the present invention
In one particularly preferred embodiment of the long-bone
prosthetic head of the present invention, the rough outer
surface is provided by the presence of slots or grooves cut
into said surface. Figs. 5 to 7 illustrate a typical
femoral head endoprosthesis of the present invention, in
which the surface roughness is provided by the presence of
said slots and grooves.
Referring now to fig. 5, it will be noted that the
unpolished stainless steel prosthetic femoral head depicted
therein (shown generally as 50) while generally spherical
in shape, possesses a flattened, truncated base 51 which
contains a circular opening 52 for receiving the proximal
end of an appropriately-sized endoprosthetic femoral stem.
In the embodiment of the femoral head shown in this figure,
the geometric center of femoral head 50 is situated
approximately 11 mm above flattened base 51. The external
diameter of the essentially-spherical head 50 shown in this
example is 32 mm.
The prosthetic femoral head depicted in this figure is
characterized by the presence of two distinct types of
surface feature. Firstly, there is a series of six,
circumferentially-disposed grooves 53, the most inferior
(distal) of which is situated 4.6 mm below a line defining
the "equator" of the essentially spherical head (i.e. the
horizontally disposed circumferential line of greatest
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length, when the prosthetic head is placed vertically such
that the flattened base 51 is situated inferiorly). The
circumferential groove situated immediately adjacent and
superior to the above-described groove is situated at a
distance of 1 mm below said equatorial line. The remaining
four circumferential grooves are situated above said
equatorial line and are separated therefrom (in order from
below to above) by the following distances: 2.6 mm, 6.1 mm,
9.3 mm and 12 mm. The angular separation between each
circumferential groove and its nearest neighbor is five
degrees. Each of said circumferential grooves 53 has a
mean depth of 1 mm. The width of each groove at its outer
end is 1.2 mm, while the width at the inner end thereof
tapers to 0.8 mm.
The second type of distinct surface feature of the
prosthetic head depicted in this figure is a vertically-
disposed slot 54 (of which two such grooves are depicted in
fig. 5.). It will be appreciated from the figure that said
slots are situated along imaginary longitudinal lines, and
are of such a length such that they intersect the three
most superior (proximal) circumferential grooves 53 at an
angle of 90°C. Said vertically-disposed slots are formed by
the use of 5 mm diameter drill that is offered to the
prosthetic head at an angle of 34 degrees in relation to
the geometric center of the spherical head. The upper end
of each slot is located 9 mm from the superior (proximal)
pole of the spherical head, while the lower end thereof is
located 3.5 mm above the above-defined equatorial line. A
total of four such vertically-disposed slots are present in
the prosthetic head, as shown more clearly in Eig. 7,
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wherein said slots are indicated as 71. It will further be
appreciated from this figure that said vertically-disposed
slots are arranged equidistantly from each other.
Fig. 6 schematically depicts the same prosthetic head
(shown generally as 60) as presented in Figs. 5 and 7 in
inferior view (i.e. with the distal surface uppermost). In
this figure, the truncated base 61 is shown to be
perforated by circular opening 62, the purpose of which is
to accept and retain the prosthetic stem section (not
shown). Said opening leads to an internal space that is
essentially conical in shape, the external surface of said
cone having a diameter of 14 mm and the internal base
thereof having a diameter of 12 mm.
While specific embodiments of the invention have been
described for the purpose of illustration, it will be
understood that the invention may be carried out in
practice by skilled persons with many modifications,
variations and adaptations, without departing from its
spirit or exceeding the scope of the claims.
