Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reissue Patent
1995-01-19
2003-01-07
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reissue Patent
active
RE037964
ABSTRACT:
TECHNICAL FIELD
The invention relates to a femoral prosthesis consisting of a metal rod and a femoral head or ceramic ball, preferably of zirconia, assembled by a conical sleeve fixing. The said femoral head is generally associated with a high density polyethylene (PE) acetabular cup.
STATE OF THE ART
When a total hip prosthesis is implanted, femoral heads are used which have a diameter of usually between 22.22 and 32 mm according to the surgical procedures employed. The materials used for producing the femoral heads are preferably metals such as stainless steel, the alloys Cr-Co-Mo, titanium, etc., or ceramics such as dense sintered alumina. Such a ceramic material offers demonstrated advantages of biocompatibility and a better friction coefficient vis-a-vis the high density PE than the metals. But taking into account its mechanical properties which are indeed high but insufficient its use is confined to large diameter femoral heads greater than or equal to 28 mm and to limited geometrical configurations (essentially a maximum neck gap of 4 mm for femoral heads of 28 mm diameter and of 8 mm for a diameter of 32 mm), in the event of its being desired to implant femoral prostheses consisting of a metal rod which, by a conical sleeve mounting, is attached to an alumina ball.
At the present time, if it is desired to implant prostheses having small diameter femoral heads fixed by a conical sleeve mounting on the femoral rod, then only metals are used with the disadvantages which they offer, particularly of less satisfactory friction properties vis-a-vis the high density PE cup.
Attempts have been made to use dense alumina femoral heads in order to take advantage of its better friction coefficient but taking into account their inadequate mechanical characteristics, such femoral heads cannot be used with a diameter which is smaller than 28 mm and which are assembled by a conical sleeve fitment on the femoral head without running the risk of the said head splitting.
Thus, various arrangements or modifications of the conical sleeve fitment have been proposed to overcome this problem. These arrangements generally consist in introducing a “stress deadener” into the conical sleeve fitment, between the metallic rod and the ceramic head.
It is possible, for example, to quote:
FR 2580170 (Flegeau) the use of an intermediate metal sleeve which by various means (particularly metallisation, brazing . . . ) is rendered rigid with a ceramic cup forming the femoral head, the said sleeve being engaged onto the frustoconical part of the femoral head;
FR 2610514 (Cuilleron) the pouring of a metal into a ceramic cup, providing in this solidified mass a recess in which the end of the femoral head is housed;
FR 2391711 (Sulzer) the use of a plastics sleeve inserted between the ceramic material and the metal.
All these solutions may provide answers to the problem of the mechanical strength of dense alumina femur heads but they are often difficult to use at the time when it is necessary to position the prosthesis and they do not generally satisfy the surgeon.
OBJECT OF THE INVENTION
That is why the applicants have sought to perfect a femoral prosthesis comprising an assembly by direct conical sleeve fitment between a femoral head of ceramic material and of small diameter of not more than 26 mm and a metal femoral rod without the help of intermediate members and/or other associated fixing means such as gluing, brazing, tenon, etc.
Thus, such a prosthesis is not subject to bursting when subjected to intense mechanical stresses, while it is at the same time simple to use and to place in position.
DESCRIPTION OF THE INVENTION
The invention is a femoral prosthesis consisting of a metal rod comprising at one of its ends a male frustoconical portion and a ceramic femoral head comprising at least one frustoconical blind recess, assembled by means of a conical sleeve fitment, characterized by the combination of the following means: the said head is of ceramic material, preferably dense stabilised zirconia, it has a diameter of not more than 26 mm, the total angle at the apex of the frustoconical blind recess used for the conical sleeve fitment is generally greater than 4°, the inlet diameter of the said truncated cone serving for conical sleeve fitment measured at the periphery of the femoral head is comprised between 8 and 14 mm and preferably between 10 and 11 mm.
The zirconia ceramic is obtained by sintering from a mixture of powdered zirconia and a stabilising agent known by a man skilled in the art, such as Y
2
O
3
, MgO, CaO, rare earth oxides . . . or their mixtures, the final content of ZrO
2
being generally greater than 95% (by weight). Either natural sintering is carried out after shaping and pressing cold, or a sintering under load of better still a sintering under isostatic load (HIP=Hot Isostatic Pressing) possibly including a presintering stage without a load.
Thus, a stabilised zirconia ceramic is obtained in the quadratic phase which can be used in accordance with the invention.
The quadratic phase is also known in the art as the tetragonal phase.
It is preferably that it should have at least the following physical properties:
a specific mass in excess of 6 g/cu.cm or 98% of the theoretical density
mean grain size (measured by electron scanning microscope using the method NF A 04102, which corresponds to ASTM E 112/82) less than or equal to 1 micron
flexion breakage modulus 3 points better than 920 MPa (draft French Standards B41G Doc 12, now NF B 41-104, August 1989)
elasticity modulus (ASTM C 674 method) better than 220 GPa
A sintered ceramic of another type, for example oxide, carbide, nitride, may likewise be used according to the invention so long as it has at least the mechanical characteristics of resistance to flexion
, Young's modulus,
and grain size previously indicated for zirconium and obviously so long as it satisfies the biocompatibility conditions required for the present application.
Advantageously, stabilised zirconia parts can be used which are obtained by HIP; for example, they have at least the following characteristics:
specific mass greater than 6 g/cu.cm
mean grain size less than 1 micron
resistance to flexion greater than 1600 MPa
Young's modulus in excess of 220 GPa
.
Similarly, other ceramics may be used which have at least the characteristics of one or other of the two aforementioned series.
The femoral head is generally spherical and has a diameter of at most 26 mm; the invention is particularly interesting for spheres with a diameter of 22.22 mm. The said head comprises at least one frustoconical blind recess the axis of which is preferably radial and the applicants have found that it was preferably necessary to use a total angle at the apex of at least 6° in order to obtain femoral prosthesis with a small diameter head (of at most 26 mm), of sufficiently high strength to be implanted with the minimum risk of breakage. It is generally considered that the femoral head has to be able to withstand a minimum loading of about 30 to 35 kN without damage or breakage. This rupture loading is measured according to the draft French Standards PR.S 90443 of Feb. 10, 1988, now NF S 90-443 of Sep. 28, 1988 in which an increasing force is applied to the femoral head mounted on the metal rod according to the axis of the assembly. A notable increase in solidity is obtained preferably by using an angle of about 10°.
Likewise, it is essential that simultaneously the inlet diameter of the cone should be as defined hereinabove, values in excess of 14 mm being in particular likely to increase significantly the risk of breakage of the femoral head.
The frustoconical blind recess has lateral walls which serve to ensure a self-locking assembly by conical sleeve fitment, being in contact with the walls of a corresponding metal male cone of preferably the same conicity, the said male cone situated at one end of a femoral rod of which the other end is implanted into the femur, is fitted with force and is therefore locked directly in the frustoconical recess.
The said blind
Prats Christian
Vivier Pierre
Ceramiques Techniques Desmarquest
Isabella David J.
Nixon & Peabody LLP
LandOfFree
Femoral prosthesis employing a small ceramic ball does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Femoral prosthesis employing a small ceramic ball, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Femoral prosthesis employing a small ceramic ball will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3016995