U.S. patent number 3,905,047 [Application Number 05/373,959] was granted by the patent office on 1975-09-16 for implantable ceramic bone prosthesis.
This patent grant is currently assigned to John J. Posta, Jr.. Invention is credited to Roger A. Long.
United States Patent |
3,905,047 |
Long |
September 16, 1975 |
Implantable ceramic bone prosthesis
Abstract
The improved bone prosthesis of the invention comprises a
unitary body containing an eutectic of metal pyrophosphate and
refractory oxide. Preferably, the body also contains discrete
particles of refractory oxide bonded together by the eutectic which
serves as a matrix bonder. Moreover, the particles are preferably
of the same refractory oxide, such as alumina, as is present in the
eutectic and are of extended surface area for improved strength.
The pyrophosphate preferably is calcium pyrophosphate so that the
prosthesis is biodegradable. The prosthesis can be prepared, in
accordance with the present method, by forming the eutectic,
preferably a pourable mixture of the particles and the molten
eutectic, and pouring the mixture into and filling a mold of a bone
to be duplicated, solidifying the mold and recovering it from the
mold. The surface of the prosthesis can be texturized, as by acid
etching it, to increase bond ingrowth and/or tissue attachment when
implanted.
Inventors: |
Long; Roger A. (Escondido,
CA) |
Assignee: |
Posta, Jr.; John J.
(Northridge, CA)
|
Family
ID: |
23474635 |
Appl.
No.: |
05/373,959 |
Filed: |
June 27, 1973 |
Current U.S.
Class: |
623/23.56;
501/153; 264/43; 606/76 |
Current CPC
Class: |
A61F
2/30767 (20130101); A61L 27/425 (20130101); A61F
2310/00203 (20130101); A61F 2210/0004 (20130101); A61F
2002/30062 (20130101) |
Current International
Class: |
A61F
2/30 (20060101); A61L 27/42 (20060101); A61L
27/00 (20060101); A61F 2/00 (20060101); A61F
2/02 (20060101); A61F 001/24 () |
Field of
Search: |
;3/1,1.9-1.913
;128/92C,92CA,92R,92G ;32/1A ;106/39.5,55 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Frinks; Ronald L.
Attorney, Agent or Firm: Posta, Jr., Esq.; John J.
Claims
What is claimed and desired to be secured by Letters Patent is:
1. An improved implantable bone prosthesis, said prosthesis
comprising a unitary ceramic body containing a eutectic of metal
pyrophosphate and refractory oxide, wherein said body includes
discrete particles of refractory oxide bonded together by said
eutectic, whereby said eutectic bonds together the discrete
particles of refractory oxide in such a manner that no substantial
degradation of said discrete particles by the eutectic occurs.
2. The improved bone prothesis of claim 1 wherein said particles
are in the form of fibers.
3. The improved bone prosthesis of claim 1 wherein said particles
are in the form of flakes.
4. The improved bone prosthesis of claim 1 wherein said refractory
oxide comprises refractory metal oxide.
5. The improved bone prosthesis of claim 1 wherein said particles
are of the same refractory oxide as that of said eutectic.
6. The improved bone prosthesis of claim 1 wherein said metal
pyrophosphate comprises calcium pyrophosphate, whereby said
prosthesis is biodegradable.
7. The improved bone prosthesis of claim 4 wherein the refractory
oxide in said eutectic comprises alumina.
8. The improved bone prosthesis of claim 4 wherein said particles
comprise alumina.
9. The improved bone prosthesis of claim 6 wherein said eutectic
consists essentially of calcium pyrophosphate and alumina and
wherein said particles consist essentially of alumina.
10. The improved bone prosthesis of claim 9 wherein said particles
are of extended surface area for improved structural strength, and
wherein said eutectic is present in a concentration in excess of
about 80 percent, by weight, of said prosthesis.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to prostheses and more
particularly to implantable bone prostheses and methods of making
the same.
2. Description of Prior Art
A bone prosthesis is an artificial device to replace a missing bone
in the body. For example, a bone may have to be removed surgically
because of extensive injury thereto, e.g., erosion by disease,
crushing by mechanical injury, or the bone may be missing due to a
congenital defect or as a result of an explosion or the like. An
artificial bone or bone portion (prosthesis) can be implanted in
the body to restore the function of the affected body portion and
to provide the necessary cosmetic effect.
Various types of bone prostheses have been employed. In most
instances, an attempt is made to simulate the appearance, i.e.,
size and shape of the missing bone or bone portion for cosmetic
purposes and also to provide a durable structural support. Metal
prostheses have been widely used in the past because of their high
strength. However, the metal used must be carefully selected with
due regard to the possibility of corrosion of the metal by body
fluids and/or a possible "foreign body" reaction, i.e., rejection
of or reaction to the metal by the body because of toxicity or
incompatibility thereto.
More recently, ceramic bone prostheses more compatible with the
body than metals have been used with some success. However, such
prostheses are usually not very durable, being brittle and so are
easily chipped and broken. Moreover, they cannot be rapidly or
easily fabricated as by melting and casting into exact duplicates
of the bone to be replaced, because of very high temperatures
required to melt such ceramics. Instead, other procedures must be
employed which takes considerable time and raise their cost. For
example, the prostheses can be formed by press and sintering
techniques, often with grinding and fitting to size required after
initial fabrication.
It has been found that a close mechanical fit between a prosthesis
replacing all or a portion of a bone and the adjacent living bone
portions when the prosthesis is in place is important in order to
stimulate ingrowth of living bone to bridge the gap with the
prosthesis and bond the prosthesis tightly to the living bone. Such
tight mechanical bonding enables the assembly to function at an
early date in the manner of the original unimpaired bone. In order
to obtain the required fit, the missing bone or bone portion must
be exactly duplicated in situ and then made permanent. Continued
exposure of the impaired area first for bone duplication and then
for prosthesis fitting, normally involves trauma, so that
minimizing the exposure time becomes important in many instances.
As pointed out above, conventional, standard size ceramic
prostheses normally take considerable time to fabricate and do not
meet this requirement.
Accordingly, there is a need for a prosthesis which can be made
economically, easily and rapidly into the exact duplicate of the
bone or bone portion to be replaced and thus reduce exposure time,
while providing good body compatibility and high structural
strength.
It has also been found that growth of living bone into the
prosthesis can be achieved and good mechanical bonding of the
prosthesis to adjacent bony parts and to adjacent connecting tissue
can be accomplished when the surface porosity of the prosthesis is
carefully controlled within certain limits. Metal prostheses
normally are smooth and, therefore, are unsuitable from this
standpoint without substantial texturizing. Ceramic prosthesis
usually also are smooth surfaced and difficult to render porous
while retaining their structural integrity.
Certain investigations have been made concerning the possibility of
forming ceramic prostheses of material which is resorbable by the
body, the prosthesis gradually being replaced by ingrowing bone
until the prosthesis is completely or substantially completely
substituted by living bone. While such materials can, with some
problems, be made porous to stimulate bone ingrowth, they are
structually weak and are further weakened during resorption, so
that total immobilization of the bony area may be required, even if
only minor bone replacement is made, until resorption is complete,
a considerable inconvenience. Mechanical working of a structurally
weak prosthesis may result in its failure. Moreover, it has been
found that movement between the weak prosthesis and adjacent bony
parts inhibits the healing process, impairing bone ingrowth.
Accordingly, there is a need for a biodegradable resorbable type of
prosthesis which provides improved structural integrity during
resorption, which can be made with a surface porosity easily and
without weakening the same and which can easily be fabricated to
exact dimensions for best initial fit of the part to be
replaced.
SUMMARY OF THE INVENTION
The improved bone prosthesis of the present invention and the novel
method of making the same satisfy the foregoing needs. The
prosthesis and method are substantially as set forth in the
Abstract above. Such prosthesis can be made either permanent or
resorbable (biodegradable). Both versions exhibit high structural
strength, good impact resistance, controlled surface porosity and
compatibility with body fluids, and are capable of economically,
rapidly and easily being fabricated by the present method into
exact duplicates of the bones and bone portions to be replaced.
They stimulate rapid bone ingrowth and can provide a source of
material used in formation of living bone. Other advantages are set
forth in the following detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The single FIGURE of the drawings schematically depicts in enlarged
cross section one embodiment of a portion of a prosthesis in
accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As depicted schematically in cross section in the single FIGURE, a
portion of a preferred embodiment of the bone prosthesis of the
invention is shown. Thus, prosthesis 10 is a unitary ceramic body
comprising a matrix 12 of an eutectic within which a plurality of
discrete particles 14 of refractory oxide are embedded and bonded
together. The eutectic is of metal pyrophosphate and refractory
oxide.
The metal pyrophosphate, due to its atomic bonding structure,
imparts great strength to the ceramic material. It is preferred
that calcium pyrophosphate be utilized as the metal pyrophosphate
because it has controlled biodegradability and is completely
compatible with the body. Calcium pyrophosphate has the general
chemical formula Ca.sub.2 P.sub.2 O.sub.7, with a melting point of
1356.degree. C..+-. 2.degree. C. and a stoichiometric composition
of 44.1% CaO and 55.9% P.sub.2 O.sub.5. It has a density of 3.09
g./cc. in the beta or low temperature (=1140.degree. C.) form. An
inversion occurs on heating or cooling of this material and it has
been noted that molten calcium pyrophosphate has a tendency to
supercool and then freeze rapidly to the beta form, which is more
dense than the alpha form.
Calcium pyrophosphate can be made by established chemical
procedures. However, in order to obtain the most pure form for use
in body implants and the like, it is preferred to calcine dicalcium
phosphate at about 900.degree. C. to calcium pyrophosphate as per
the following:
Calcium pyrophosphate can be hydrolyzed slowly to the ortho
monomolecular form, the rate being dependent on pH and temperature,
increasing with acidity and temperature. Calcium pyrophosphate is
biodegradable to the ortho monomolecular form in body fluids,
assisted by P--O--P splitting body enzymes, so that calcium and
phosphate are supplied to the body sera. In turn, the body sera
supply calcium and phosphate back to the implant in the formation
of normal body bone tissue as a replacement for the absorbed
calcium pyrophosphate. It is believed that the living bone building
mineral crystalline apatite is supplied in the body through
hydrolysis of a less basic calcium phosphate salt. Moreover,
residual phosphate salts are known to nucleate apatite. Current
theory indicates that in bone, the apatite crystals are small and
comprise only a part of the total mineral present, a second mineral
being present in the form of a non-crystalline (amorphous) calcium
phosphate. Whatever the exact mechanism for the building of living
bone involved, it is believed that the availability of a ready
supply of calcium and phosphate adjacent to the replacement site
stimulates bone ingrowth and rapid replacement of a biodegradable
bone implant. Calcium pyrophosphate serves as such a source of
supply.
Magnesium pyrophosphate, sodium pyrophosphate and potassium
pyrophosphate can also be used a biodegradable metal
pyrophosphates, but are less preferred separately since they do not
supply calcium for bone building. These pyrophosphates are slowly
soluble in water or acidic media and therefore should only be used
with a biodegradable or non-biodegradable metal pyrophosphate which
is essentially water insoluble, so as to control the rate of
degrading of the prosthesis. Their use in combination with the
calcium pyrophosphate assists in controlling the hydrolysis
reaction.
In the event that it is desired to make the implant
non-biodegradable, then an inert metal pyrophosphate such as
manganese pyrophosphate, titanium pyrophosphate, iron
pyrophosphate, ziconium pyrophosphate or similar inert
pyrophosphate, such as is set forth in U.S. Pat. No. 3,131,073
issued Apr. 28, 1964, can be employed in the present eutectic.
The refractory oxide component of the eutectic preferably comprises
any suitable refractory metal oxide such as alumina, zirconia,
titania, magnesia, chromia or the like which is insoluble in water
and non-toxic to the body. Of the above, it is preferred to use
alumina, since it is very inexpensive, readily available, totally
inert and non-biodegradable, and it is known, from long term
testing, to be completely non-toxic and compatible with the body
and its fluids.
A eutectic of the metal pyrophosphate and refractory oxide is
formed by any suitable procedure, such as by blending the
pyrophosphate with the refractory oxide, both in fine particulate
form, e.g., 200 to 300 mesh, and in the proper proportions. The
mixture is then melted.
The proper proportion of ingredients for the eutectic is that which
just begins to melt and flow at the processing temperature. This
can be determined experimentally by utilizing various
pyrophosphate-refractory oxide mixtures, varying the concentration
of the refractory oxide from mixture to mixture, compacting each
mixture, as by pressing up to 10,000 psi, and then heating the
mixtures, observing which of the samples just begins to flow, as by
rounding of the corners of the sample at the lowest temperature.
The test temperature is then lowered while minor changes are made
in the concentration of refractory oxide in new pressed samples
containing the pyrophosphate. The lowest temperature at which
corner rounding occurs gives a reliable indication of the proper
eutectic composition. Such a procedure is set forth in detail in
U.S. Pat. No. 3,131,073, described above.
In the case of a mixture of, by weight 92.5% manganese
pyrophosphate (Mn.sub.2 P.sub.2 O.sub.7) and 7.5% alumina (Al.sub.2
O.sub.3), the eutectic temperature is 1,987.degree. F., well below
the melting point of the oxide, 3,720.degree. F. It is a
characteristic of the eutectic that it melts well below the melting
point of its refractory oxide component, so that it can be used to
form at lower temperature high strength ceramics. In the case of an
eutectic employing calcium pyrophosphate (87.5% by weight) and
alumina (12.5% by weight), the eutectic temperature is about
2275.degree. F. Such temperature is sufficiently low to permit
melting of the eutectic and casting of the same in high temperature
resistant molds such as graphite, ceramic, or the like, while the
free particles of refractory oxide, e.g., alumina, are
maintained.
The eutectic used in the improved bone prosthesis of the invention
is highly desirable since it imparts great strength to the
prosthesis, acts as a binder for solid particles of refractory
oxide when they are dispersed therein and permits melting and
casting of exact bone duplicates at temperatures sufficiently low
such that conventional molding materials can be used.
Moreover, of considerable importance is the fact that when free
particles of refractory oxide are present in the prosthesis and are
of the same refractory oxide as that in the eutectic, no
substantial degradation of those particles by the eutectic occurs.
In other words, the eutectic represents a saturated solution in
which the free refractory oxide particles are not dissolved during
processing. Accordingly, the concentration and physical structure
of such free particles is preserved in processing, leading to a
precise prediction of the prosthesis strength, and the size and
arrangement of particles, as well as the biodegradability of the
prosthesis.
It will be understood that the free refractory oxide particles can
be eliminated from the prosthesis, but it usually is much preferred
that they be present, since they increase the strength, reduce the
brittleness and decrease the shrinkage of the prosthesis.
Accordingly, in the preferred embodiment of the invention, the
particles are present.
In order to provide proper melting and total bonding of the free
refractory oxide particles together by the eutectic, it is
preferred to use an initial concentration of the refractory oxide
in the eutectic mixture which is very slightly less than that
necessary for complete saturation of the eutectic. Accordingly,
when the liquid eutectic is formed and the free particles of the
refractory oxide are added, a slight melting or dissolving of the
outer surface of the particles occurs, assuring their proper
bonding together in and with the binder-matric of the eutectic.
The particles of refractory oxide filler particles bonded together
by the eutectic usually are of extended surface area, such as high
modulus fibers, flakes, or the like, to improve bending strength or
stiffness of the prosthesis. Preferably, the particles are of
chemically inert refractory metal oxide, such as alumina, zirconia,
titania, magnesia or the like. Most preferably, those particles are
of the same refractory oxide as is present in the eutectic. Thus,
the novel casting method of the invention is impractical to employ
when it is desired to use fibers of lengths in excess of about 1/8
inch. In such instances, either the press and sinter, hot press
technique, or similar fabrication can be used or the fibers can be
formed into bundles, placed in a mold and then eutectic can be
vacuum cast around them.
The novel prosthesis can be fabricated by any suitable method such
as conventional slip casting and cold pressing followed by
sintering or hot pressing. However, it is preferred to employ the
novel method of the present invention, since precisely shaped and
sized prostheses can be made rapidly and economically by the novel
method. Such method is, however, limited to specific compositions
and particle shapes.
In forming the novel prosthesis in accordance with the present
novel method, the eutectic preferably is rendered molten and,
preferably, refractory oxide particles are mixed therewith to form
a pourable mixture, which is then cast into a mold and solidified
therein, as by cooling, after which the mold is separated therefrom
and the finished prosthesis recovered.
The pourable mixture usually contains less than 20% by weight of
oxide filler particles, with the minimum filler oxide concentration
being only that necessary to make a good casting ceramic.
However, when the cold press, slip cast and sintering or hot press
technique is employed, the refractory oxide filler particles may be
present in a substantially greater concentration by weight, for
example, in excess of that of the eutectic binder-matric. Thus, the
filler particles in such instances may be present, for example, in
a concentration of between about 20 and about 75 percent, by weight
of the prosthesis, the eutectic comprising the remainder.
It will be understood that other substances can be added to the
prosthesis for certain purposes, i.e., structural supports, such as
metal sponge or the like, texturizing or pore-forming agents,
eutectic temperature-lowering agents, such as sodium phosphate,
etc. Such substances usually are present in minor concentrations.
In addition, the prosthesis can be made in several parts, e.g., can
be provided with a shell or core of the same or different
material.
It will also be understood that since the novel prosthesis of the
present invention preferably incorporates at least two distinctive
components, that is, the eutectic binder-matric of metal
pyrophosphate and refractory oxide, plus the filler of refractory
oxide particles, it is readily subject to control of the nature,
size and extent of its surface pores. Such pores can facilitate
live bone ingrowth and locking to or replacement of the prosthesis,
and further facilitate the mechanical attachment of adjacent tissue
to the prosthesis.
Surface texturizing of the prosthesis can be accomplished by
selectively surface etching or leaching out, as by acid or the
like, one of the components of the prosthesis, an advantage over
single component ceramics. As shown in the single figure, surface
pores 16 are present in prosthesis 10, the size and extent
depending on the size and shape of filler particles 14 and the
nature of any texturizing treatment applied to exterior of
prosthesis 10. The nature of the filler and binder-matrix is such
that the biodegradability, if any, of the prosthesis 10, as well as
its structural strength, impact resistance, and other factors, can
easily be controlled by careful selection of the pyrophosphate(s)
and the refractory oxide(s) and their relative concentrations, as
well as the size and shape of the filler particles. Accordingly,
the prosthesis has far greater flexibility in physical and chemical
characteristics than conventional ceramic prostheses. Certain
further features of the prosthesis of the present invention and the
present method are illustrated in the following specific
examples:
EXAMPLE I
A missing central portion of a human femur is replaced by a bone
prosthesis implanted between the two existing end portions of the
femur, with a gap therebetween of not in excess of five thousandths
of an inch. The prosthesis almost exactly duplicates the missing
portion of the femur and is prepared by the following
procedure:
A wax impression is made of the missing central portion of the
femur by filling in the gap between the two existing femur portions
and checking the impression against the cavity defined by the
surrounding leg tissue. The wax impression is then removed, a high
temperature resistant ceramic mold is formed there around from a
dip slurry from which the slurry liquid medium is then removed. The
ceramic cast is baked and the wax is then melted, removed from the
mold and the mold is then further hardened by firing.
A pourable mixture of a molten eutectic of calcium pyrophosphate
and alumina with added solid particles of alumina is then formed.
The eutectic has the composition of about 87.5 percent by weight of
calcium pyrophosphate and about 12.5 percent by weight of alumina.
The eutectic comprises 80 percent by weight of the eutectic mixture
with the alumina particles constituting the remainder.
The pourable mixture while at about 2300.degree. F. is poured into
the mold to fill the mold and is then allowed to solidify, after
which the mold is released and the prosthesis recovered. The total
time for forming the impression, manufacture of the mold, and
fabrication of the prosthesis is about 60 minutes. The ceramic
prosthesis is then inserted into the femur gap and fits
substantially perfectly. The surgical opening is then closed and
the femur is immobilized, since the two ends of the femur adjacent
the prosthesis will need time to solidly fuse with the prosthesis.
The prosthesis is biodegradable, its resorption and replacement by
living bone occurring over a time period. The prosthesis is
economical, hard, durable, of controlled biodegradability,
functions very well, cosmetically and structurally knits tightly
with the remainder of the femur and stimulates bone ingrowth and
bone replacement.
In a parallel test, the eutectic alone is used (without filler
oxide) as the pourable mixture and the results are essentially the
same. However, it is noted that the ceramic cast body is slightly
more brittle and shrinkage is slightly greater.
In a parallel test, titania is substituted for the alumina in the
eutectic and as the filler. The eutectic contains about 14 percent
by weight of titania and has a melting point of about 2275.degree.
F. Comparable results are obtained, since the major eutectic
component is biodegradable, while the titania is not, the relative
proportions of each determining the rate of biodegradation. The
product is strong, of controlled surface porosity, and easy and
rapid to make and use.
In an additional parallel test, calcium pyrophosphate eutectic of
the first run is used. It is blended with alumina in a ratio of 40
weight percent eutectic to 60 weight percent alumina, to form a dry
mixture. This mixture is then pressed into a body at 10,000 psi,
and then fired at about 2300.degree. F. for 30 minutes, resulting
in a dense ceramic body which is then ground to the desired size
and shape to provide a hard, biodegradable prosthesis.
EXAMPLE II
The procedure of Example I is followed, except that a
non-biodegradable inert prosthesis is fabricated from a molten
eutectic of 92.5 percent by weight of manganese pyrophosphate and
7.5 percent by weight of alumina in which alumina particles in a
concentration of about 20 percent by weight of the prosthesis are
dispersed. The eutectic has a melting point of about 1987.degree.
F. and comprises the remainder of the prosthesis. A hard, high
structural strength, high impact resistance, chemically inert
prosthesis compatible with the body is provided by the economical
and rapid casting and molding procedure of Example I. Total time of
obtaining the wax impression, making the mold, casting, cooling and
recovering the prosthesis is only about 60 minutes, so that the
procedure permits customized fabrication of bony parts for
substantially immediate emplacement.
In a second parallel run, an eutectic of 87.5 percent by weight of
manganese pyrophosphate and 12.5 percent by weight of titania is
melted at 1910.degree. F. and mixed with titania flakes in a weight
ratio of about 4:1. The molding and casting procedure of Example I
is followed, utilizing a casting temperature of about 1950.degree.
to 2000.degree. F., followed by solidification and recovery of the
desired prosthesis. The prosthesis exhibits the improved properties
described above for the alumina-manganese pyrophosphate product,
including great strength, impact resistance, durability and total
inertness to body fluids.
In a third parallel run, a prosthesis is fabricated using the
components of the second run except the filler, titania flakes, are
added in a weight percentage of about 80 percent to the eutectic
mixture and blended together in a rubber-lined ball mill. The
mixture is then shape pressed into a body at 10,000 psi, and
sintered for 30 minutes at above 1910.degree. F. The body when
cooled is then ground to the desired size and shape to provide a
hard, durable inert prosthesis. The overall processing time is
considerably longer than in the first two runs of this Example, nor
are the dimensions of the prosthesis as accurate as those of the
first two runs, and the cost is higher.
EXAMPLE III
Prostheses identical to those of Example I (first and parallel
second and third runs) are surface texturized by contacting the
prosthesis in each instance with dilute hydrochloric acid at
elevated temperature (about 120.degree. F.) for about 3 minutes,
until the calcium pyrophosphate eutectic at the surface of the
prosthesis has been eroded to an average depth of about 44 microns,
thereby increasing the porosity of that surface and facilitating
live bone growth and/or other tissue thereinto. Accordingly, secure
attachment of the prosthesis to adjacent femur bone portions is
accomplished rapidly and full functioning of the femur is restored
at an early date.
The preceding Examples clearly establish that the bone prosthesis
of the present invention can be controllably biodegradable or made
totally inert to body fluids. It is non-toxic, very strong and
durable with good to high impact strength and can be made very
easily and rapidly by the present method. The prosthesis can be
surface texturized to control its porosity and can be formed in an
exact size and shape for substitution for a missing bone or bone
portion. The type of bones for which the described prosthesis can
be substituted is not limited to the bones described herein, but
are applicable to any desired bone in the body. Likewise, the
prosthesis can be substituted for either part or all of any
particular bone in the body. Likewise, the prosthesis can be
substituted for either part or all of any particular bone in the
body. Constituents of the prosthesis can stimulate bone ingrowth,
due to the calcium and phosphate supplied by the prosthesis to the
body sera. Other advantages are as set forth in the foregoing.
Various modifications and changes can be made in the present
prosthesis and the components and in the present method, its steps,
constituents and parameters. All such changes and modifications as
are within the scope of the appended claims form part of the
present invention.
* * * * *