U.S. patent number 3,905,777 [Application Number 05/436,850] was granted by the patent office on 1975-09-16 for composite and porous metallic members which can be used for bone prosthesis.
This patent grant is currently assigned to Comptoir Lyon-Alemand-Louyot. Invention is credited to Roger Lacroix.
United States Patent |
3,905,777 |
Lacroix |
September 16, 1975 |
Composite and porous metallic members which can be used for bone
prosthesis
Abstract
A prosthesis comprises a metal member of for example titanium or
tantalum and includes a solid core or substrate and a covering of
perforated metal of a porous nature. The perforations are
preferably arranged in the foil so that when laminated the complete
covering has pores of irregular shape. This irregularity assists in
the keying of bone substance to the prosthesis. The minimum pore
transverse dimension is 50 microns. A method is also described
which involves dipping the member into a suspension of the hydride
of the member of the core and subsequently heating the core at high
temperature.
Inventors: |
Lacroix; Roger (Suresnes,
FR) |
Assignee: |
Comptoir Lyon-Alemand-Louyot
(Paris, FR)
|
Family
ID: |
9114127 |
Appl.
No.: |
05/436,850 |
Filed: |
January 28, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Jan 31, 1973 [FR] |
|
|
73.03415 |
|
Current U.S.
Class: |
428/550; 428/555;
428/607; 428/661; 606/76; 428/608; 428/926; 428/596 |
Current CPC
Class: |
A61F
2/30907 (20130101); A61L 27/56 (20130101); A61L
27/04 (20130101); C08K 3/08 (20130101); C08K
3/12 (20130101); A61L 27/306 (20130101); A61F
2/28 (20130101); B22F 7/002 (20130101); A61F
2230/0023 (20130101); A61F 2310/00131 (20130101); A61F
2002/3429 (20130101); Y10T 428/12042 (20150115); Y10T
428/12444 (20150115); A61F 2002/3631 (20130101); A61F
2/3094 (20130101); A61F 2/3662 (20130101); A61F
2310/00407 (20130101); A61F 2002/30912 (20130101); Y10T
428/12812 (20150115); A61F 2002/30112 (20130101); A61F
2230/0004 (20130101); A61F 2310/00544 (20130101); A61F
2002/30156 (20130101); Y10S 428/926 (20130101); Y10T
428/12076 (20150115); A61F 2230/0026 (20130101); A61F
2002/30929 (20130101); A61F 2002/30451 (20130101); A61F
2220/0058 (20130101); A61F 2310/00023 (20130101); Y10T
428/12361 (20150115); Y10T 428/12438 (20150115); A61F
2002/30158 (20130101) |
Current International
Class: |
A61F
2/30 (20060101); A61L 27/04 (20060101); A61L
27/00 (20060101); A61L 27/56 (20060101); A61L
27/30 (20060101); B22F 7/00 (20060101); A61F
2/00 (20060101); A61F 2/32 (20060101); A61F
2/34 (20060101); A61F 2/36 (20060101); B21D
039/00 () |
Field of
Search: |
;29/191,191.2,191.4,183.5 ;3/1,17,19 ;128/92C,92CA |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rutledge; L. Dewayne
Assistant Examiner: Crutchfield; O. F.
Attorney, Agent or Firm: Millen, Raptes & White
Claims
I claim:
1. A composite metallic member comprising
a core, and
a porous covering welded to the core, said covering having a
thickness between 5 and 50% of the maximum transverse dimension of
the core and said covering comprising
a plurality of layers of foil, the foil having a thickness between
0.05 and 0.5mm. and having perforations, the covering being formed
by welding the foil layers so that the perforations together form
passages of which the minimum transverse dimension is at least 50
microns.
2. A member according to claim 1, wherein the metal of the core and
covering is selected from the group titanium, tantalum, alloys of
titanium, alloys of tantalum and Vitallium, the latter being an
alloy, on a percent by weight basis, of: 25.5-30 Cr, 5-7 Mo, up to
0.35 C, up to 1.0 Mn, up to 1.0 Si, up to 2.0 Fe, up to 3.75 Ni,
with the balance being Co.
3. A member according to claim 1 wherein the said passages are
irregular.
4. A member according to claim 1 wherein the foil takes the form of
expanded metal.
5. A member according to claim 1, wherein the covering is in the
form of a sheet of annealed foil formed into a laminate.
6. A member according to claim 1, comprising fine particles of the
same metal as the core and covering welded to the surface of the
covering and having a diameter less than 10 microns.
7. A member according to claim 1 wherein the thickness of said
covering is between 10 and 25% of the maximum transverse distance
of the core.
8. A member according to claim 1 wherein the foil is wire mesh.
9. A member according to claim 1 wherein each layer of foil has a
thickness of 0.1 to 0.25 millimeters.
10. A member according to claim 1 wherein the metal of the core and
covering is titanium.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to composite and porous metallic
members which can be used for bone prosthesis and also relates to
methods of their manufacture. Such metallic members are termed
implants.
2. Summary of the Prior Art
It has been proposed to use for certain types of implants,
titanium, tantalum, and alloys with a cobalt base and in particular
the alloy chrome-cobalt-molybdenum, known under the trade name
"Vitallium" (According to Weisman, Annals of the New York Academy
of Science, Vol. 146, article 1, pages 80-95, Jan. 8, 1968,
Vitallium is an alloy, on a percent by weight basis, of: 25.5-30
Cr, 5-7 Mo, up to 0.35 C, up to 1.0 Mn, up to 1.0 Si, up to 2.0 Fe,
up to 3.75 Ni, with the balance being Co.) One of the main problems
to resolve was the bonding of the implants to the bone
substance.
The following four solutions to this problem have already been
proposed:
1. Force fit into the medullary canal of the bone an anchoring
device or the prosthesis device itself.
This solution has several disadvantages which have caused it to be
abandoned:
A. the effective contact surface between the bone and the implant
is small. The joint is thus insecure;
B. the radial constraints exerted on the bone are dangerous or
damaging to the integrity of the latter. They are concentrated at a
small number of contact points because of the difficulty which
arises in adjusting exactly the metallic part to the canal in which
it must be implanted;
C. the bone, when submitted to a permanent stress, reacts in such a
manner that it tends to reduce this stress. This reaction is the
result of the rheological properties of the bone material which
undergoes an extrusion and an actual biological change. The result
is, in the more or less long term, the loosening of the
implant.
2. Securing of the implant in the bone with the aid of screws or
pins. Clinical experience has shown that in the long term this mode
of fixing loses its rigidity probably as a result of similar
changes to those which have been referred to above.
3. Bonding of the implant by a plastic methacrylic resin which
hardens by polymerization. The metallic part is provided with
extensions or keying means which are introduced into the natural or
into artificial cavities of the bone. These cavities are filled
with the plastic resin. After the hardening it ensures the required
fixing by bonding.
This technique is used to a large extent. It has enabled
substantial progress in the repair of necks of femurs which have
been broken and hip joints which have been damaged by arthritis.
The methacrylic resin is not however always tolerated completely by
the organism and may give rise to detachment which cannot be
repaired.
4. A recent method consists in using porous metallic implants or
composite metallic implants including a nucleus, core, or substrate
of solid metal and a porous coating or layer which adheres to the
surface of the core or substrate and which covers it at least
partially. The pores of the coating are for the most part open
pores, that is to say communicating with the exterior. The implant
being placed in contact with the bone substance, the bone substance
itself grows into the pores. There is thus produced in a few weeks
a true biological anchorage of the implant.
The porous body or the porous layer is formed by small discrete
particles of metal welded together and for a proportion of them to
the substrate or core. These welded connections only occupy limited
space so that between the particles free spaces are left which
provide the desired porosity. These particles may be cylindrical or
spherical.
The cylindrical particles are formed by fragments of extruded wire
of small diameter. The spherical particles may be made by the
procedure known in the industry by the term atomization. Now,
titanium like tantalum is an extremely reactive metal at high
temperature, so much so that its atomization presents problems
which can only be resolved by the use of exceptional means in
costly installations with handling and maintenance which requires
great care. The extrusion of Vitallium into fine wire gives rise to
problems which are almost insurmountable.
Moreover, the contact between the spherical or cylindrical
particles before the welding operation is reduced to a point or to
a line. It is thus necessary that the operation of welding should
itself give rise to the growth of a contact surface of larger size
when filaments or atomized powders are sued. This welding can only
be effected by roasting, that is to say, by thermal treatment at
elevated temperature, about 1200.degree.C in the case of Vitallium,
1100.degree.C in the case of titanium. At these temperatures
diffusion phenomena in the solid phase give rise to the joining of
the elements in contact by the growth of joining surfaces from the
contact points. These phenomenon are slow and growth of the contact
areas slows up when the connecting or joining surfaces increase. It
is necessary therefore to rely on excessive thermal treatment times
in practice if it is desired that the connecting surfaces of the
spheres to the core should be equal for example to a large circle
or proportion of these spheres. As micro-photographs reveal,
sections of the porous body or of the composite body connecting
surfaces between particles or between particles and the core are
very small and these impair the integrity of the bonds between the
bone and the metal.
SUMMARY OF THE INVENTION
According to the present invention there is provided a composite
metallic member comprising a core, and a porous covering welded to
the core, said covering having a thickness between 5 and 50% of the
maximum transverse dimension of the core and said covering
comprising a plurality of layers of foil, the foil having a
thickness between 0.05 and 0.5 mm. and having perforations, the
covering being formed by welding the foil layers so that the
perforations together form passages of which the minimum transverse
dimension is at least 50 microns.
In order properly to explain the basis of the invention as well as
the advantages which it provides in relation to known methods, it
is desirable first of all to list the qualities which should be
possessed by a metallic porous prosthesis or a prosthesis having a
porous outer layer.
It is essential first of all that the metal of the particles should
be the same as that of the core in the case of composite implants.
Without this, corrosion of electrolytic origin may be produced.
With biological liquids which contain in solution ionized elements,
the two different metals form an electrical cell.
The pores must be open and form passages of microscopic size into
which the bone substance can grow up to the compact core. Closed
pores, that is to say pores which do not open to an accessible
surface at the bone reduce the integrity of the bond between the
bone and the metal and are thus to be avoided as far as
possible.
So that the bone cells can invade the pores, it is necessary that
the latter should have an opening of at least 50 microns across.
Only considerations of mechanical rigidity can impose an upper
limit to the size of the opening of the pores. Depending on
conditions it may reach or even exceed 400 microns.
From what has been stated above, the length of the passages
perpendicular to the surface of the core is equal to the thickness
of the porous layer. It is larger in general if the passages are
tortuous or otherwise irregular.
The bond must be integral and it is this requirement for integrity
to be maintained over very long periods that it has been necessary
to define the optimum values for the thickness of the porous layer,
of the shape, the dimensions, the number and the distribution of
the pores.
During their use a prostheses, the implants according to the
invention are subjected to two kinds of forces of which the line of
action are perpendicular; shearing forces and tension forces.
The shearing forces acting parallel to the direction of the
longitudinal axis of the core create complementary compressive
stresses. It is necessary that these stresses, exerted on the
material of the bone, should not give rise in the interior of this
material to a deleterious change comparable to that which has
limited the fixing methods for the implant by force fit in the
medullary canal or by the intermediary of pins and screws. It is
thus necessary that the surfaces on which the compressive forces
are exerted under the action of a given imposed force should be
sufficiently large so that the complementary stresses should remain
low. As a result, it is necessary that the connecting surface
between the metal and bone should be adequate and that the
thickness of the porous layer should also be adequate. Each implant
constitutes a specific case. The dimensions of the bone and as a
result of the prosthesis being adapted to the forces to be resisted
and, in practice, the thickness of the porous layer should be
between 5 and 50% of the diameter of the core or substrate, and
preferably between 10 and 25%.
The bond of the bone and metal may be subjected to tension forces
in a direction perpendicular to the longitudinal axis of the core.
In this case, the porous covering in accordance with the invention
will not generate any resistance to the separation of the two
elements, bone and metal, where the passages present in the
interior of the porous covering are straight and perpendicular to
the longitudinal axis of the core. It follows that if the passages
are tortuous, the porous covering ensures an improved connection
between the bone and the implant.
The porous covering is constituted by several layers of metallic
foil, preferably of very light gauge, pierced by numerous apertures
and welded to one another as well as to the core or substrate. The
metallic foils are pierced by perforation method with raising of
the material and/or stamping, or by expanding to form a mesh. It is
also possible to use mesh formed by weaving wire. The perforations
occupy a sufficient fraction of the surface of each foil so that by
superposing said foils the whole portions of one will not block the
apertures of the other. On the contrary, the perforations by their
superimposition constitute capillary passages or ducts of tortuous
or labyrinth nature which reach to the surface of the core as well
as to the free surface of the composite body. The perforated
metallic foils must be sufficiently supple and malleable so that
they can take-up the shape of the surface of the core or
substrate.
In order to achieve the required flexibility, the laminated sheets
used as starting material must have a thickness less than about 0.5
millimetres. In the case of titanium, it is difficult, by
laminating, to go below 0.05 millimeters. Metallic foils of 0.1 to
0.25 millimeter thickness are therefore preferably selected.
Similarly in order to achieve the desired flexibility and moreover
so that the metal should be readily deformable, metal in the
annealed state is preferably used.
The perforations are defined by their shape, their dimensions and
their distribution. In general, manufacturers provide these data in
the form of drawings. They add to this the fraction of the space
cut away by the apertures which they denote by the term
"transparence."
The resistance to fracture should be mainly considered at the level
of the junction between the core and the perforated covering. This
resistance is proportional to the surface welded. The highest
forces which can be applied to a human bone are those which may be
applied to the neck of a femur. These forces are estimated to be
six times the weight of the individual up to a maximum value of 600
kg; these forces cause in the narrowest zone of the neck of the
femur a maximum stress of the order of 3 kg/mm.sup.2. The fracture
load of the metals or the alloys used is substantially in excess of
this value (in the case of titanium it is of the order of 30
kg/mm.sup.2) and it will be apparent that the fracture will not
arise in this part of the prosthesis.
It is moreover, necessary to avoid all permanent deformation of the
metal, in other words, it is necessary to avoid applying to the
metal a stress which reaches its elastic limit. In the case of
titanium, the elastic limit is 20 kg/mm.sup.2. The surface of
welding should thus be in excess of 600/20 = 30mm.sup.2. If the
metal employed initially has a transparence of 50% and if, the
welding having been poorly carried out, the welded proportion
represents only 20% of the metallic surface, it will be apparent
that it is sufficient to cover with welded expanded metal, a
surface of the compact core of ##EQU1##
In example 2, given below, it will be apparent that this value is
in fact very substantially exceeded.
Other advantages of implants according to the invention in
comparison with prosthesis previously known are, in particular, as
follows:
The perforated or expanded sheets are current industrial products
fabricated in a large variety of shapes and dimensions and sizes of
perforations, of length, spaces which separate two successive
perforations, of thicknesses of the initial sheet which it is
possible to change after perforation, if it is required, by
operations such as laminating.
The techniques of powder metallurgy do not enable the use of
particles all of the same size and to orientate them with perfect
regularity. The dimensions of the pores which can be obtained are
always distributed at random; at best one can determine only
certain limits. The perforations in the sheets used in accordance
with the invention are all substantially identical and are
distributed with exact regularity. The perforated or expanded
sheets thus enable the complete avoidance of closed pores and
enable the production of pores of relatively high uniformity.
The techniques of powder metallurgy necessitate the employment of
compression molds, of presses, of vacuum ovens or ovens operating
at atmospheric pressure controlled for treatments of long duration.
In contrast, the operation of welding sheets may be carried out
with equipment which is little different from that used with dental
prosthesis. The perforated sheets may, moreover, be readily shaped
by conventional brazing operations, by stamping or swaging likewise
similarly to the prostheses used in dental work.
The surfaces of the weld joint may have sizes as large as is
required.
The invention relates also to another type of improved implant
characterized in that the external surface of the porous covering
of an implant carries fine particles of the same metal as the
implant, of a diameter less than 10 microns and welded to this
surface.
These particles provide anchorages and supplementary contact points
along the external surface of the porous covering and thus reduce
the shear stresses exerted on the said surface.
The invention also relates to a method of manufacturing the
improved implants characterized in that an implant in accordance
with the invention is plunged into a suspension constituted by a
mixture of ethyl cellulose, ethyl glycol and particles of metallic
hydride of a diameter of less than 10 microns, the implant is
withdrawn from the suspension and the excess of particles removed
and the implant is treated for about 2 hours at high temperature
under a pressure of approximately 15mn (millimicrons), viz,
15.times. 10.sup..sup.-6 mm of mercury.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic section of an implant in accordance with
the invention;
FIGS. 2a, 2b, 2c, 2d, 2e and 2f illustrate Example 1 which relates
to an implant in accordance with the invention for use in an animal
experiment;
FIGS. 3a and 3b illustrate a second example as used in the repair
of the neck of a human femur by an implant in accordance with the
invention; and
FIGS. 4a and 4b illustrate the third example relating to the repair
of the acetabulum of a human hip.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 an implant 1 is illustrated formed from a core
2 and a porous covering 3 constituted by metallic foils 4 of a
light gauge and which are superposed on one another. The bone 5
grows into the pores of this porous covering 3. The implant is
subjected to shear forces F.sub.c and to tension forces
F.sub.t.
EXAMPLE 1
This example relates to the manufacture of an implant of titanium
for use in an experiment on an animal.
FIG. 2a is a sketch of the implant to be manufactured, and the
implant includes a drawn rod 7 partially covered with a porous
covering 8. FIG. 2b is a view to a much enlarged scale of expanded
metal forming the porous covering 8. FIG. 2c is a section on the
line x-y of expanded metal used to build up the covering.
The method is commenced by taking a drawn rod of titanium of 3.17mm
diameter and a sheet of expanded titanium. Before being expanded
this sheet has a thickness of 0.1mm. After expansion the mesh has
the form of lozenges of which the larger diagonal measurement is
1.45mm. The width of the remaining strips is 0.12mm. The optical
transparency is 52%. The thickness overall of the sheet, after the
expansion which causes a certain distortion of the strips, is
0.2mm.
To construct the member, the drawn rod and the expanded metal are
first of all carefully degreased. The expanded titanium is cut into
a strip of 12.7mm width. The drawn rod 7 is clamped in the chuck 6
of a lathe as shown in FIG. 2d, then welding is initiated at one
end of the strip of expanded titanium 10 following a generating
line of the cylindrical envelope of the screw. The lather is then
turned slowly by hand, while exerting a substantial tension on the
strip 9 of expanded metal which is rolled around the drawn rod 7.
Welds 11 are effected on lines as designated in FIG. 2e. When the
thickness required is obtained and the last line of welds is
effected (FIG. 2f), the member is withdrawn from the lathe and the
part formed by the rolled on mesh which has been secured to the
rod, is plunged into a suspension of titanium hydride powder having
the following composition:
Titanium hydride 30 parts by weight Ethyl cellulose in a solution
of 4% in terpinol 30 parts by weight Ethyl glycol 10 parts by
weight.
The member is withdrawn from suspension tapped to remove the excess
of the latter, dried and then treated for 2 hours at 1,100.degree.C
under a pressure of 15.times. 10.sup..sup.-6 mm of mercury. The
completed rod is then cut to the required size.
EXAMPLE 2
This example relates to the repair of the neck of a human
femur.
FIG. 3b is a section on a line A--A of FIG. 3a.
In these two figures, it is seen that the core 12 of forged
titanium is covered with a porous part 13. The porous part is
produced by cutting up elements of expanded titanium to give the
following dimensions:
large diagonal of the pattern of the base 0.75mm.
width of the joining threads 0.12mm.
initial thickness of the sheet 0.10mm.
overall thickness of the expanded metal 0.20mm.
transparence 40%.
Strips of this titanium are cut which are welded to the core or
substrate. Eight layers are used which give rise to a thickness of
about 1.5mm. and the surface of the substrate of the porous layer
is about 40 cm.sup.2
EXAMPLE 3
This example relates to the repair of the acetabulum of a human
hip.
FIG. 4a is a perspective view of the prosthesis and FIG. 4b is a
section on the line A--A of FIG. 4a.
In these two figures a hemispherical core 14 is covered with a
porous covering 15. Broken lines in FIG. 4a indicate a prosthesis
for the neck of the femur. The same expanded titanium is used as in
the preceding Example. Discs are cut and made hemispherical by
pressing. These part-spheres are laid on the convex part of the
core to which they are spot welded. The covering is then
impregnated with a suspension of titanium hydride of the same
composition as that of Example 2, but has been crushed or
pulverized until all the particles of titanium hydride have a
diameter at the most equal to 10 microns.
After drying the prosthesis is treated in a vacuum of 15.times.
10.sup..sup.-6 mm at 1,100.degree.C.
It is possible to provide the concavity with a porous layer in
order to key a plastics material having lubricant properties.
* * * * *