FR2502939A1 - ROD WITH DEVICE FOR ANCHORING A STENT IN OR ON A BONE - Google Patents

Abstract

The invention aims at improving the durability and reliability of an endoprosthetic stem and the anchorage thereof on or in the bone by a novel system. The invention is based on the object of dispensing with the customary bone cement and of directing the forces acting via the endoprosthesis into the bone on the physiological tensile and compressive strength belt sides (6, 7). For this purpose, the invention is characterised in that the endoprosthetic stem is divided into several individual rods (1, 2, 3, 4). As a result, the medullary space is not filled completely, so that nutrition of the bone through the endosteum is partially retained. For connection to the bone the individual rods are provided with a surface structure (9, 10) and are pressed against the bone walls by bone chips and expanding dowels (11, 12, 13). Moreover, firm anchorage is also ensured by an electric stimulator (14) which strengthens the implant bed in the gaps (8, 22, 23) between the rods by electrically induced bone.

Description

 The present invention relates to the stem of a joint prosthesis and the anchoring thereof in or on a bone. Currently, most of the prosthesis stems used are of circular, quadrangular, heath or lemniscate cross section.

In the form of cross section, they constitute a coherent, non-articulated assembly. In addition, the implantation technique in principle comprises two anchoring methods.

 According to the first process, which is the most frequently used, anchoring is carried out by means of the system known as bone cement "(Charnley, Charnîey-Miiller, Weber-Huggler and others systems). Bone cement is, in its type the more often used, a polymethylmetacrylate, as a two-component synthetic material. During polymerization, there occur instantaneously high temperatures, not physiological, which also partially attack the bone and sometimes destroy it. In many places, it It is necessary that the bone cement ensures the transmission of the forces from the prosthesis rod to the bone. This results in a double danger here for the anchoring of the prosthesis. On the one hand, the bone cement which is, in any case , the partner of weakest resistance in the bond between metal bone cement and bone, often undergoes an introduction of blood during the installation by plugging, so that its support capacity is reduced and that it occurs premature ment of a cracking of the cement under the effect of a load. On the other hand, the blade shape or polygonal shape of the cross section implies extremely high shear stresses which cause permanent cracks in the cement and ultimately loosening of the prosthesis anchor in or on the patient's bone. .

 Finally, capillary slits formed between the bone cement, the prosthesis stem and the bone, constitute a favorable ground for the growth of germs which, according to Buchholz, are responsible for deep secondary infections, leading to a relaxation of the anchoring of the prosthesis.

The second product, called "cementless anchoring" must avoid the risks mentioned above. Mention may be made in this connection of prostheses made of ceramic and metal with a profile with supporting ribs or with an appropriate surface structure (from
Mittelmeier, Judet among others). In all these types of cementless prosthesis anchor rods, considerable spikes can occur between the rod and the bone, which result in absorption of the bone and thus relaxation of the bone. anchoring. In addition, it has been known, for half a decade, and according to numerous biomechanical studies (Dornier / Rôhrle and others in particular) that, in the case of prosthesis rods and usual anchorages, the bone is subjected to stresses of a non-physiological character. When the stress is too high or too low, according to Wolff and others, the physiological constitution of the bone is destroyed. A prosthesis stem which transmits force into the bone according to the physiological principle of pressure and traction belts, does not cause tensions comparable to those which occur in healthy bone subjected to loads.

In almost all common prostheses, there is a significant destruction of living bone, caused by the filling of the bone end, required by the construction of the prosthesis itself, which can also lead to loosening of the anchor. According to Rhînelander's micro-angio-graphic studies, the Corticalis effect is mainly maintained by the histological arrangement of the closure of the end of the bone. The latter is also not possible in the case of prosthesis rods with uniform distribution of the load over a large area, when the rod fills the entire free space of the cord.

Consequently, the object of the invention is to
ffi # make a prosthesis rod with anchoring thereof on or in a bone, which does not have the drawbacks mentioned above. More particularly, the anchoring must be able to be carried out without the usual bone cement, and must ensure both a primary fixation and a permanent fixation. It must be biologically compatible, meet the physiological requirements from a biomechanical point of view, both during movement and in the case of a permanent load, and be able to be anchored securely and durably to the bone. It must therefore simply meet the requirements of a low friction arthroplasty.

 For this purpose, the invention is characterized in that the prosthesis rod is constituted by several individual bars which allow the transmission of forces, according to the principle of tension and compression belts, on the physiological face of tension of tension and compression of bone, without completely filling the space of the cord.

 Thanks to the elastic, but stable shape, provided in the upper part of the prosthesis stem, the belt under tension and pressure is favored.

For connection to the bone, the individual bars are provided with a toothing, or another surface structure known in the implantation technique.

Thanks to its direction of action, its shape, and its size, it is ensured that the traction and pressure forces in the prosthesis stem, due to the weight of the body, to a dynamic force, or to the traction of muscles, are applied to the bone, to an extent identical or comparable to the physiological tensions in normal bone.

 For the primary fixation of the prosthesis stem, it is possible to use fixed, elastic or extensible pins or sockets, or similar elements, which press the bars with their teeth, or their surface structure, against the bone, clinging to it. Thanks to their elasticity, the rod bars can largely adapt to the particular shape of the bone in question. In this way, a transmission of forces is ensured over a large area, which avoids a point charge which would cause absorption. In addition, the process of feeding the bone from its tip is not significantly compromised, thanks to the multi-member shape of the stem.

Electrostimulation is also used for the fixed anchoring of the prosthesis rod in the bone. It is known that electrostimulation acts in three phases, namely
In the initial phase, after primary hyperemia and increased vascular irrigation, a bone tissue-forming mesenchyme is formed which leads to angiofibromatosis. This overactivated bone formation zone constitutes the envelope zone.

 In the intermediate phase there is the development of spongy sclerotic bone tissue that forms structure with the start of calcium insertion.

 In the final phase a definitive, lamellar, calcified, oriented bone tissue occurs. Thanks to the special shape and position of the cathode, around which the new bone is formed, the prosthesis stem is surrounded by solid spongy tissue capable of supporting forces. This spongy tissue, caused by electro-stimulation, is crossed by a dense network sufficient to nourish the bone. To promote bone formation and fixation of the prosthesis stem, bone chips are introduced into the spaces between the sockets.

The invention is explained below with the aid of exemplary embodiments with other characteristics, with reference to the appended drawings in which FIG. 1 is a schematic view in side elevation of a stent with rod with elements grouped in beam, intended to replace the hip joint, inserted into the surrounding bone and addition of an electric stimulator for the formation of new bone Figure 2 is a schematic sectional view through the prosthesis stem of Figure 1 and the bone surrounding it in Figure 3 is an elevational view of Figure 1 in the direction of arrow A; Figure 4 is a schematic view of another embodiment of a two-element rod inserted into the surrounding bone Figure 5 is an elevational view in the direction of arrow B in Figure 4, Figure 6 is a section view of the prosthesis stem of FIG. 4 FIG. 7 is a schematic transverse section view of a prosthesis stem according to another embodiment, here comprising three bars and the surrounding bone
Figures 1 and 3 show a new type of prosthesis rod which consists of a bundle of individual bars. The prosthesis rod can be a single cast, or the individual bars (1, 2, 3 and 4 ) can be fixed in a flange 5 (Figure 3) by means of clamping cones or threads or the like. All the parts can be made of metal or of a complex fibrous material. The articulation between the individual bars 1 to 4 ensures the transmission of the forces in the bone, according to the principle of belt under tension and under compression on the physiological sides of tension of tension 6 and of tension of compression 7 (figure 2 ) of the bone. This is favored by the domain 8, to a certain elastic extent, of the bars 1 to 4. For their connection to the bone 6, 7, the bars are provided with a toothing 9, 10, or another structure of surface known in the implantation technique This toothing or surface structure is provided in such a way that it is effective, on the lateral part 6 of the bone, against a tensile load, and on the central part of the bone 7, against a compression load.

 For the primary fixation of the prosthesis, elastic plugs or sleeves 11, 12, 13 are provided, or, as shown in FIG. 4, expandable sleeves 24, which press the teeth 9, 10 from bars 1 to 4 in the wall 6, 7 of the bone and engage the teeth or the surface structure.

 Under the effect of the charge and the electrical stimulation, new bone tissue is formed around the bars 1 to 4. From the stimulator 14, by one or more cables 25, the cathodes 15, 16, 17, 18 are introduced into 1 ì soft space and arranged centrally or in any other appropriate position. The anode 19 is connected by a separate cable 20, to the electrical stimulator 14, and it is fixed, with a clamping connection 21 to the main trochanter. In order to speed up the fixation of the prosthesis, bone fragments are introduced into the zone 8 and into the intermediate spaces 22, 23 between the sockets 11, 12 and 13.

 By way of example, the signal from the stimulator 14 is delivered in a frequency of 38 to 43 Hertz, a connection duration of 30 to 58% and a potential between 300 and 900 millivolts.

 Figure 2 is a cross-sectional view of the beam-like construction of the individual bars 1, 2, 3 and 4. The number and size of the bars, as well as their length, can be selected depending on the shape and diameter of the bone and the load.

The bars are fixed interchangeably in the collar 5 by means of clamping cones or blocking sleeves known in the art.

 In FIGS. 4, 5 and 6, the prosthesis rod is constituted by two bars 1 and 2. The grouping or bundle of the prosthesis rod begins directly at the outlet of the collar 5. As an alternative to the embodiment of FIG. 1 , four expandable sleeves 24 are provided here for pressing the bars 1, 2 against the bone 6, 7. As has been explained in connection with FIG. 1, an elastic zone 8 is provided in the prosthesis stem. The intermediate spaces 22, 23 between the expandable sleeves 24, as well as the upper zone 8 of the bone are filled with bone fragments, to accelerate the incorporation of the rod.

 In FIG. 7 is shown a prosthesis rod composed of three bars 1, 2, 3.

Claims (5)

- CLAIMS  1. Rod with device for anchoring an articulation prosthesis, characterized in that the rod consists of two bars or a bundle of individual anchor bars (1, 2, 3, 4) which form, with a prosthesis collar (5) a single cast part, or which are assembled as interchangeable parts, which can, thanks to their elasticity, adapt to the walls of the bone, and which, for a primary fixation, are pressed against the bone, by means of fixed, elastic, or expandable dowels or sockets (11, 12, 13, 24), or the like, and which are embedded in the bone with teeth (9, 10) or an appropriate surface structure .  2. An anchoring device according to claim 1, characterized in that, to hasten the incorporation of the rod, an electrical stimulation is used in the form of an implanted device (14).  3. Anchoring device according to one of claims 1 and 2, characterized in that several cathodes (15 to 18) are arranged in the bone, and the anode (19) which is connected by a separate cable (20 ) the electric stimulator (14) is fixed in the major trochanter by a clamping cone (21).  4. An anchoring device according to any one of claims 1 to 3, characterized in that the stimulator signal (14) is delivered in a frequency of 38 to 43 Hertz, a connection duration of 30 to 58% and a potential between 300 and 900 millivolts.  5. An anchoring device according to any one of claims 1 to 4, characterized in that the rod itself constitutes the cathode for electro-stimulation.