FR2478462A1 - Artificial joint component securing system - uses parallel lugs pressed into holes previously bored in bone with openings in lugs for osseous invasion - Google Patents

Abstract

The securing system uses a number of parallel fixing spikes formed on the component which are a press-fit inside holes of mating shape previously bored (5) in the tissue. The component itself can have a number of apertures accommodating fixing screws cooperating with the lugs. The lugs can be flat, or of part-cylindrical section, with holes formed in them to permit osseous invasion. The lugs can also bave roughened surfaces, typically in the form of screwthreads, instead of holes around which the bone grows.

Description

 The present invention relates to an improvement to joint endoprostheses, such as, for example, prostheses of the hip or knee joint.

Generally, the difficulty which arises for the installation of an articular endoprosthesis is that it is necessary both to fix it in such a solid way that it takes no play and fixes it in such a way that it can be removed without seriously damaging the bone if it deteriorates or is not supported by the body. The prostheses currently existing badly reconcile these two imperatives. #
On the other hand, the prostheses currently existing are divided into two groups: on the one hand surface prostheses and, on the other hand, massive prostheses. In the particular case of hip prostheses, surface prostheses are composed of two cups which fit into each other, one covering the acetabulum, the other covering the head of the femur. consisting of a fairly large part, fixed to the pelvis and comprising a cavity and a femoral part, replacing the head and the neck of the femur, fixed to the femoral shaft, comprising a ball joint cooperating with the aforesaid cavity. These two pieces are fixed one to the pelvis, the other to the femur, either by cement, or by making their external surfaces in such a way that the bone which is reformed interferes inside porosities and / or notches formed on said surfaces.

These two types of prostheses have the following disadvantages
With regard to surface prostheses, fixing the hollow cup to the pelvic bone is difficult to achieve with sufficient solidity to be sure not to move over time; moreover, the contact of the cephalic cup, placed on the head of the femur very often causes necrosis and / or resorption of the bony material of the head and of the part of the neck included under said cup. causes the appearance of a play which renders the prosthesis inoperative and requires its replacement.

With regard to massive prostheses, their disadvantages come from: their considerable volume which constitutes a frequent point of call for an infection; their weight and inertia which affect their fixity in relation to the bone; and finally, the significant difference in their modulus of elasticity compared to that of the bone, which leads to disorders due to poor distribution of forces and pressures.

The present invention proposes to eliminate these various drawbacks.

 According to a first object, the present invention relates to a method of fixing to the bone mass of a piece of articular endoprosthesis consisting of having on said piece, on the one hand a plurality of fixing lugs, parallel, which are forcibly inserted in cavities of corresponding shape drilled beforehand in the bone mass and, on the other hand, orifices allowing the installation of fixing screws.

The legs may be flat, be portions of a cylinder and be pierced with holes in which the newly formed bone will interfere. The fixing lugs can be rods provided with asperities to hang in the bone. In this case, they will preferably be provided on their surface in contact with the bone with a thread. This arrangement allows, when it is desired to remove the prosthesis to cut each rod and once the part has been removed, to extract each rod from the bone mass by unscrewing it.

 According to a second object of the present invention, the articular endoprosthesis is made up of two parts which nest into one another and characterized in that each part of the joint is itself made up of two parts on the one hand, a base fixed to the ground according to the method of fixing described above and, on the other hand, by a sliding surface fixed to the base by any suitable means.

 In the particular case of a hip prosthesis, it is constituted, according to the present invention, on the one hand by a concave cup, constituting a part of a spherical cap in the shape of a crescent, leaving the background of the acetabulum free (or pulvinar) and, on the other hand, by a hemispherical convex part, replacing the working part of the head of the femur, and not the whole, in the zone going to its upper part, of the junction of the head and the neck and, at its lower part, just above the lower blade of the head; these two parts being carried by bases fixed in the bone both by asperity rods forming an integral part of the base and by screws passing through fixing orifices.

By way of nonlimiting example and to facilitate understanding of the invention, there is shown in the accompanying drawings
Figure 1, a schematic view showing a disjointed femoral joint, the femur and the iliac bone being both provided with parts of the prosthesis according to the invention.

Figure 2, a schematic view, in partial section, illustrating the femoral epiphysis prepared to receive the intermediate fixation part.

 Figure 3, a schematic view in partial section illustrating the drilling of parallel holes in the femoral epiphysis prepared according to Figure 2.

 FIG. 4, a view on an enlarged scale with respect to FIGS. 2 and 3 of the convex part mounted on the intermediate fixing part, in section along A-A of FIG. 5.

 Figure 5, a plan view of the intermediate fixing part, the convex part not yet in place.

Figure 6, a perspective view of the concave part
Figure 7, a plan view, on a larger scale, of the concave part of Figure 6
Figure 8, a sectional view along BB of Figure 7.

Figure 9, a sectional view along C-C of Figure 7.

FIG. 10, a plan view of a flexible cap made of a material having good friction qualities, intended to be mounted in the part shown in FIGS. 6 to 9.

Figure 11, a sectional view along A-A of Figure 10.

FIG. 12, a schematic perspective view illustrating an alternative embodiment of the base piece illustrated in FIG. 6.

Figure 13, a sectional view on a larger scale of an alternative embodiment of the part shown in Figure 12.

 Figure 14, a schematic perspective view illustrating the establishment of the sighting tool for determining the milling axis.

Figure 15, a schematic perspective view illustrating the mole of a knee prosthesis, intended to be fixed to the upper end of the tibia.

 Figure 16, a schematic perspective view illustrating the female part of a knee prosthesis, intended to be fixed to the lower end of the femur.

Figure 17, a view from below of the part shown in Figure 16.

 Figure 18, a schematic view of a knee prosthesis in place.

Referring to the drawings and the explanations which follow, it can be seen that the hip prosthesis shown in FIGS. 1 to 13 takes into account all the drawbacks of known prostheses. In particular, it avoids the drawbacks of necrosis and resorption of the head of the femur, because it replaces the part of this head liable to become necrotic and to be reabsorbed as a result of the devascularisation which is caused, in surface prostheses, by placing a spherical cap on this head; this phenomenon being due to the particular characteristics of the blood network of this bone part. It avoids the drawbacks linked to the volume due to its small size; the disadvantages linked to inertia due to its lightness; and finally, because it replaces only the upper cap of the femoral head, it does not modify the flexibility of the femoral metaphysis and diaphysis and, therefore, does not modify the distribution of the stresses on the femur. On the pelvis side, the prosthesis is fixed on the compact bone around the acetabulum cavity and, therefore, is ensured by a solid and durable fixation, without modifying the elasticity of the pelvis.

The convex part is put in place after preparation of the head of the femur, illustrated in Figure 2. As can be seen by examining this figure, the femur is prepared by a section of the head made by making a section inclined at 200 by relative to the horizontal, that is to say 700 relative to the axis of the body, a section which begins at the junction of the head and the neck and ends in the inner pole of the head; then this section is shaped into a spherical cap 1. In the center of this section, a concave hemispherical cap 2 is excavated.

On this section 1 and centered on the hemispherical hollow cap 2, a template or phantom 3 is placed, which makes it possible to drill a plurality of holes parallel to the axis of the section 1 and of the cap 2. In the example shown, seven parallel holes are drilled: a central hole 4 and six holes 5, distributed in a circle, the drilling tools being guided by the parallel bores 6 formed in the phantom 3. Among the six holes 5, three are intended to receive screws and three are intended to receive threaded rods integral with the intermediate piece.

 This intermediate piece, or base, 7 is shown in Figure 4 where we can see that it is circular.

It has on its lower face a boss 7a, of shape and size corresponding exactly to the hollow cap 2 and a hemispherical concave surface 7b, corresponding to the section 1 formed in the head of the femur. It further comprises a central threaded rod 7c, intended to engage in the hole 4 and three threaded rods 7d intended to engage in three of the holes 5 previously drilled. The rods 7c and 7d are an integral part of the base 7 and they are forced into the holes 4 and 5 which have been previously made, which requires that said holes 4 and 5 and said rods 7c and 7d are parallel. The part 7 further comprises three orifices 7e each intended to receive a fixing screw 8, which may be with a spherical head 9. These screws are put in place by screwing in the three other holes 5. This gives extremely fast fixing solid of the intermediate piece 7.

Concentrically to the hemispherical boss 7a, said part 7 has a central bore 10, provided with a thread 11.

 Preferably, the surfaces of the intermediate piece or base 7 in contact with the bone comprise a porous coating in which the neo-formed bone is capable of interfering.

 Bases 7 of different sizes are provided so as to be able to adapt to different sizes of femurs.

 The articular piece 12 is screwed onto the base 7.

This part has an external wall 12a practically constituting half of a sphere, which completely covers the base 7, its internal wall comprising a recess 12b serving as housing for said base 7 and a cylindrical central stud 12c provided with a thread. 13 engaging the thread 11. The articular piece 12 can be made of ceramic, metal, plastic, a carbon material or any material which can constitute a resistant friction surface while being tolerated by the body .

 A damping device 14 can be inserted between the articular piece 12 and the base 7.

 In the example shown, the cavity 2 and the corresponding boss 7a are hemispherical, but it is possible to give the boss 7a a conical, pyramidal, cylindrical or cubic shape, the cavity 2 then having a corresponding shape.

On the other hand, the part 12 can be fixed to the base 7, not by screwing, as has been shown, but by any other suitable fixing means, for example by means of a cement.

The cavity is shown in Figures 6 to 11. Referring to these figures, we see that it is constituted by a support piece (Figures 6 to 9), metallic, having a central part 15, concave, hemispherical, provided with a plurality of lateral fixing lugs 16 and a plurality of fixing lugs 17, which are cylinder portions.

Part 15 is a crescent of a concave spherical cap, with a contour similar to that of the normal articular surface of the iliac bone; between the horns 15a of the crescent is formed a notch 15b corresponding to the background of the acetabulum or pulvinar.

 The legs 16 are placed flat on the surface of the iliac bone and have holes 16a allowing the passage of fixing screws 18. Preferably, as is known, the holes 16a are spherical, as are the heads of the screws 18 .

The legs 17 are engaged in a cylindrical groove 19 previously hollowed out in the iliac bone; it preferably comprises windows 17a into which the newly formed bone will penetrate.

The establishment of the part 15 is made after the acetabular cavity has been previously rid of its cartilage and returned perfectly to spherical shape
The concave internal surface of the part 15 can be made or coated with a material having good friction characteristics, but it is possible, according to an alternative embodiment shown in FIGS. 10 and 11, to adapt a suitable part 19 to it.

 This part 19 is constituted by a spherical cap split with a slot 20, which makes it possible to elastically shrink the part 19 to put it in place, the two edges of the slot 20 being provided with shoulder 20a (FIG. 11) coming from engage part 15 from below in the pulvinar.

A damping material 21 can also be placed between the part 15 and the friction part 19.

 It is also possible to provide in the part 15 a peripheral groove 22 in which a corresponding rib 23 engages, formed on the friction part 19.

 Preferably, the walls of the part 15 in contact with the bone material are provided with a porous coating of the habitable type with neo-formed bone.

 According to an alternative embodiment shown in Figures 12 and 13, the part 15 may be surrounded by a flat rim 16b, provided, on the one hand with the orifices 16a for the passage of the fixing screws 18 and, on the other hand, with a plurality of rods 17a, parallel and provided with a thread. In this case, instead of digging beforehand, in the iliac bone a cylindrical groove 19, it suffices to drill as many parallel holes as there are rods 17a, these holes being of a diameter slightly smaller than that rods 17aZ so that said rods 17a force their way into it (like rods 7c and 7d in holes 4 and 5). It is possible, as shown in FIG. 13, to have other rods 17'a, which are fixed directly to the part 15.

 FIG. 14 represents a guide tool making it possible to materialize the axis XX 'of FIG. 2, according to which the section 1 of the head of the femur must be carried out. It comprises a foot 24 coming to bear against the neck of the femur, a rod 25 bypassing the head of the femur and a guide tube 26.

 Figures 15 to 18 show a knee prosthesis. FIG. 15 shows the male part 30, which has a central protuberance 31, carried by a plate 32, which is integral with a plurality (four in the example shown) of fixing rods 33, similar to rods 7c, 7d and 17a of the examples previously described and placed in the tibia in an identical manner. The protuberance 31 has the shape of a portion of circular sector, flared at the base, and the upper face 31a of which is a portion of cylinder, hollow. Although this is not shown, the plate 32 can include holes allowing screws similar to screws 8 and 18 to be placed.

 FIGS. 16 and 17 show the female part 34, which has a hollow central portion 35, into which the protuberance 31 fits and two curved edges 36, of shape corresponding to the flared junction between the protuberance 31 and the plate 32. To the edges 36 are fixed a plurality (four in the example shown) of fixing rods 37 similar to rods 7, 7d, 17a and 33 and put in place identically to the lower part of the femur. As can be seen in FIG. 17, the hollow central part 35 flares gradually, so that the protuberance 31 is fitted without play, when the knee is in extension and is fitted with a slight lateral play when the knee is bent .

 Figure 18 shows the parts 30 and 34 in place. It is seen that, preferably, the femur and the tibia are prepared so that the two parts are completely embedded therein; we also see that we can add complementary fixing rods 33a and 37a in the center of the parts.

Claims (27)

 1. A method of fixing to the bone mass of articular endoprosthesis pieces consisting of placing on said piece to be fixed a plurality of fixing lugs, parallel, and forcing them into correspondingly shaped cavities previously drilled in said bone mass.  2. A fixing method according to claim 1, according to which there is additionally on the part to be fixed a plurality of orifices intended to receive fixing screws cooperating with said fixing lugs.  3. Method according to one of claims 1 or 2, according to which the legs are planar. 4. Method according to one of claims 1 or 2, according to which the legs are cylinder portions.  5 Method according to one of claims 3 or 4, according to which these tabs are pierced with orifices in which can come to interfere with the neo-formed bone.  6. Method according to one of claims 1 or 2, according to which the fixing lugs are constituted by rods provided with asperities.  7. The method of claim 6, wherein the rods are provided with a thread. 8. Joint endoprosthesis consisting of two stemboRtant parts one inside the other, characterized in that each part of the joint is itself made up of two parts: on the one hand, a base fixed to the mass bone according to any one of claims 1 to 7, and, on the other hand, by a sliding surface fixed to the base by any suitable means.  9. hip prosthesis according to claim 8, comprising a convex articular piece placed on the head of the femur and a concave articular piece placed on the iliac bone, characterized in that it is constituted, on the one hand, by a concave cup (15) constituting a portion of a crescent-shaped spherical cap, leaving the background of the acetabulum (pulvinar) free, this cup being provided, on its rear face, with a plurality of fixing lugs allowing its anchoring in the bone mass and being covered with a sliding surface (19); and, on the other hand, by a hemispherical convex piece (12) replacing the working part of the head of the femur and not the whole in the zone going, at its upper part, from the junction of the head of the femur and the neck and at its lower part, just above the lower pole of the head, this hemispherical part (12) being carried by a base (7) anchored in the bone mass of the femur by a plurality of fixing rods (7c and 7d). 10. Hip prosthesis according to claim 9, in which the base (7) is circular1 has a hemispherical inner face (1) concave, adapting to the surface of the previously prepared bone, provided in its center with a projection (7a) fitting into a corresponding cavity formed in the bone and comprises an upper face provided with means allowing the fixing of the convex articular piece (12).  11. A hip prosthesis according to claim 10, in which the projection (7a) is hemispherical and engages in a cavity (2) also hemispherical.  12. A hip prosthesis according to claim 10, in which the projection (7a) is conical, pyramidal, cylindrical or cubic and engages in a cavity (2) of corresponding shape previously formed in the bone. 13. Prosthesis according to any one of claims 9 to 12, in which the intermediate piece (7) comprises a plurality of orifices (7e) intended to receive fixing screws (8). 14. Prosthesis according to any one of claims 9 to 13, in which the convex articulation part (12) is fixed to the intermediate part by a cement. 15. Prosthesis according to any one of claims 9 to 13, in which the convex articulation piece (12) is screwed onto the intermediate piece by a threaded central stud (12c) penetrating into a threaded bore (10) formed in said fixing part. 16. Prosthesis according to any one of claims 9 to 15, in which the convex articulation part (12) comprises an external wall (12a) having the shape of a hemisphere entirely covering the intermediate fixing part.  17. A prosthesis according to claim 9, in which the concave cup (15) comprises, on the one hand lateral fixing legs (16) bearing against the surface of the iliac bone and, on the other hand, legs fixing (17) which are cylinder portions and which engage in a cylindrical groove (19), previously hollowed out in the bone.  18. The prosthesis according to claim 17, in which the lateral tabs 16 receive screws (18).  19. A prosthesis according to claim 9, in which the cup 15 comprises a flat rim (16b) to which are integrally fixed a plurality of fixing rods (17a), threaded and comprising a plurality of holes (16a) for screws fixing (18).  20. Prosthesis according to claim 21, comprising additional fixing rods (17'e) integral with the rear face of the cup. 21. Prosthesis according to one of claims 17 to 20, in which the concave part is coated with a friction part (19) constituted by a spherical cap provided with a slot (20) having flanges (19a) s' engaging in the indentation of the crescent leaving the pulvinar clear.  22. The prosthesis according to claim 21, in which the friction piece (19) is provided with a peripheral rib (23) engaging in a corresponding peripheral groove (22) of the support piece 15. 23. Prosthesis according to any one of claims 8 to 22, in which a damping material (14 or 21) is interposed between the support part (7 or 15) and the friction part (12 or 19). 24. Prosthesis according to any one of claims 8 to 23, in which the axis of preparation of the head of the femur is materialized by a guide comprising a foot (2 '), bearing against the neck of the femur, a rod ( 25) bypassing the head of the femur and a guide tube (26).  25. Knee prosthesis according to claim 8, comprising a male part (30) anchored to the upper part of the tibia by a plurality of fixation rods (33) and a female part (34) anchored to the lower part of the femur by a plurality of fixing rods (37). 26. A prosthesis according to claim 25, in which each part comprises a flange carrying the fixing rods (33 or 37) and orifices for the passage of complementary fixing screws. 27. Prosthesis according to claims 25 or 26, in which the male part (30) comprises a central protuberance (31) having the shape of a portion of circular sector flared at the base, the upper face (31 a) of which is a portion of hollow cylinder, the female part (34) having a corresponding shape in which the part 31 fits, the central hollow (39 of the part (34) widening progressively towards one of its ends.