FI87728C - ANORDNING FOER ATT FAESTA EN LEDPROTES - Google Patents

Description

5 87728 Arrangement for attaching a joint prosthesis Anordning för att fästa en ledprotes

The present invention relates to an attachment-improving arrangement for attaching joint prostheses, especially hip joint prostheses, but also shoulder, knee, leg and finger joint prostheses, etc. In particular, the invention relates to an arrangement for attaching a joint prosthesis according to the preamble of claim 1.

Surgical fixation of joint replacements is now commonplace in orthopedic surgery. The difficulties encountered with the surgical technique 15 are generally reasonable, but the more serious problem is - apart from infections and vascular thrombosis - the detachment of one or both parts of the prosthesis. The most common joint repair procedure is the so-called hip joint reconstruction. In 1981, about 5,500 such surgeries were performed in Sweden, and the most common causes are joint disease in the hip-20 joint and joint damage due to bone fractures and other causes, such as deformities due to rheumatic conditions.

; The problem of hip joint repair measures has been studied centrally during the last decades and it has been shed light on e.g.

25 Consensus Conference in Stockholm, 12-14 May 1982. In one Medicinska. The Consensus Statement issued by the Forskningsrädet following this conference recommends the use of prostheses and; material The choice is to use metal in the femur and plastic in the pelvis, and as a routine procedure to attach the prosthesis to the preferred roll for use in cement. 1

It is clear from other sources that Msementin most commonly refers to polymers that are subjected to in situ polymerization. The polymerization temperature can vary depending on the components used, but often often significantly exceeds 47 ° C, which is the temperature limit at which bone tissue can survive without initial tissue damage, followed by so-called film formation.

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Many researchers (Rik Huiskis, Department of Orthopedics, University of Nijmegen, E. Morscher, Department of Orthopedic Surgery, University of Basel, etc.) are of the opinion that the prosthetic material of the femur should be stainless steel, cobalt, chromium or titanium and the pelvis should be plastic. . This combination is advantageous because it results in relatively low friction and low wear. The choice of material is determined not only by the mechanical properties of the material but also by its suitability to body tissues from a biological point of view. Stainless steel has been increasingly abandoned and the greatest interest these days has been in titanium, titanium alloys and cobalt-chromium alloys. Titanium appears to be the most tissue-friendly and corrosion-resistant of the metals tested so far, and titanium has the excellent property of having good resistance to fatigue and (or but) being relatively flexible.

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As the material for the hip joint pit, researchers primarily recommend polyethylene, Delrin, and methyl methacrylate. High-density polyethylene is widely used in hip joint wells because of its excellent friction and wear properties in combination with the above-mentioned metals and because the wear particles cause minimal irritation to the tissues. Delrilni, which has been introduced recently, is harder than polyethylene and is unlikely to have any advantages over the latter material. Other possible materials include ceramic materials that are well woven. This material is capable of resisting corrosion, but is considered unreliable from a mechanical point of view and can cause irritation and infections due to the release of small parts from the surfaces of the ceramic material.

! .. January 30 for attaching portion of the prosthesis, especially a femoral portion of the prosthesis, cement is used, the task is to meet the size of the prosthesis and the bone '· space between the inside of the wall and divide the load as much of the components:: bone as possible. The cementitious materials used so far (plastic adhesive) bind well to metal, but do not tend to maintain a chemical bond with bone tissue. The main function of cement is therefore to form a stabilizing filling between the prosthesis and the bone.

Although the prosthetic materials for articular cavities and articulated balloons are well developed and give satisfactory results in terms of friction between the articular cavity and articular ball, and although materials with suitable elastic properties can be selected, a serious problem remains between the core canal and the attached femur. micro-movements occur in the femoral-10 part prosthesis due to the loads applied to the articular ball due to body weight and movement and due to the fact that the arm is not sufficiently stably attached to the bone tissue in the core canal. Unfortunately, all too often, these micro-movements, which are most significant between the upper and lower ends of the arm, result in the arm 15 coming loose and thus making re-cutting necessary.

It is an object of the present invention to provide an arrangement which provides a secure and permanent attachment of such prosthetic parts made of a material having good tissue-friendly and mechanical properties in connection with bone tissue without the creation of undesirable properties.

: These objects have now been achieved in that the features of the invention are set out in the claims.

25: The invention will be described in more detail below with reference to the accompanying drawing, which shows in longitudinal section a joint prosthesis and an associated femoral prosthesis attached to the femur of the invention. . arrangement.

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The articulated pit prosthesis shown in the drawings consists of a bowl-shaped 'main part 1 and a layer 2 arranged on the concave side of the bowl, which forms the articular surface of the articulated pit prosthesis. The main part 1 of the cup is primarily made by compression molding of metal powder and sintering. 35a metal powder by known powder molding, compression molding and sintering methods so that its concave side has pores to provide a good 4 87728 connection to the layer 2. The well part 1 is preferably made so that its convex upper side against the pelvic bone B is also porous or rough, bone tissue grows better adhering to the surface.

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The layer 2 is preferably positioned so that the well portion 1 is placed in an injection molding means by which the layer 2 is injection molded against the articular ball pattern so as to obtain a good calibration of the articular surface of the well against the articular ball with which it is to co-operate. The material of the layer 2 is preferably selected from one of the initially mentioned plastics or another tissue-friendly plastic whose elasticity and thickness are suitable for distributing the loads normally present in the pelvic joint. Suitable plastics are, for example, plastics of the polyethylene, delrin and methyl methacrylate types.

15 Instead of plastics, it is possible to choose a suitable enamel or ceramic.

The articulated well part 1 can be fastened to the pelvic bone, e.g. by means of pins and screws, by a method known from the connection of plastic well prostheses, but primarily the well part 1 is fastened by a plurality of barbed, needle-friendly metal pins 3 projecting from the convex side of the well part 1.

Primarily, the femoral prosthesis 5 is made in the same way and of the same type of material as the articular well part 1. By manufacturing, pressing and sintering the prosthesis 5 from a metal powder having a suitable particle size - - '· a suitable porous or rough surface is obtained. to bond the type of cement commonly used to attach prosthetic arms to bones. However, a femoral prosthesis can be. . is also manufactured in a conventional manner, in which case also the surface of the shank part 30 must be sufficiently porous or rough to obtain good adhesion to the cementitious material selected for cementation into the bone.

After the manufacture of the prosthesis part 5, this is placed on the bone of the injection molding tool 35, by means of which a layer 7 of a material giving a smooth slippery joint surface similar to the joint surface in the articular prosthesis 1,2 is applied to the articular ball 6. The material to be injection molded onto the articular ball is selected taking into account the injection molded material into the articular pit so as to achieve the best possible combination in terms of both friction and elasticity between the articular pit and the articular ball, e.g. plastic against plastic, enamel against plastic or ceramic against plastic. By injection molding the layer 7 against the design of the articular well and vice versa, a very precise fit is obtained between the articular well and the articular ball. By using this shaping technique in connection with both the joint ball and the joint pit, the very expensive fine machining and polishing used so far can be reduced or eliminated altogether.

However, in the case of the articulation surface combination where the plastic was placed against the metal, it is also possible to apply the metal layer on the articulation ball 15 by evaporation of the metal or possibly by electrolytic or electrochemical addition of metal. However, these methods generally make more precise manufacturing methods necessary in the case of the articulated spherical surface on which the layer 7 is applied, because it is more difficult to achieve the desired accurate shape and dimensional calibration during metal application than by injection molding. It is emphasized that an essential advantage of the described method is that the accuracy requirements can be reduced in the manufacture of the prosthetic parts on which the joint surfaces are to be formed by applying a layer of material.

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In order to attach the arms 8 of the prosthetic parts 5 to the femur, the tried and tested technique is used in part, in which the arm is masked with cement 9, which fills the space between the entire arm 8 and the bone wall 10. Like . . however, it is clear from the introduction to the explanation that this method does not give a completely satisfactory result because detachment between the cement and the bone tissue is a problem. According to the invention, the cementation is therefore supplemented by attaching the cementitious agent to the bone tissue via an element of metallic material which is tissue-friendly and allows the bone tissue to adhere to the element and which is "cement-friendly" so that the conventional cementitious agent used binds to the elements.

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According to the invention, the barbed pins 11 are used as the fastening metal element, which are similar to the pins 3 used for attaching the articular cavity to the pelvic bone. Barbed pins can be inserted into bone tissue e.g.

5 by inserting them from inside the core channel by means of a setting member or by pressing them in with any suitable tool. The attachment of the pins is performed before the prosthetic arm is inserted and before it is cemented into the core channel. The pins need only penetrate the bone tissue and of course should not extend through the wall of the bone 10, but in contrast the pins inside the core channel must have sufficiently large contact surfaces, contact ends or protrusions to obtain a good adhesion of the cementitious material.

Instead of barbed pins, which are preferred, metal screws may be used, which may be screwed in from the outside so as to extend into the core channel cavity for inclusion in and attachment to the cementitious material.

As an alternative to more or less simple pins, pins can be used which are provided with metal plates or strips to which the cementitious material used for cementing the shaft is attached.

It may be advantageous to use pins, screws or the like, wherein: 25 have porous surfaces for good adhesion to the cementitious material and bone. for stable adhesion of tissue to pins, screws, etc.

It is advantageous to form the metal elements 11 so that the cementitious material 9 does not. . not only adheres to the metal elements but also forms a form-bonded adhesion with those parts which are incorporated into the cement.

A sufficiently large number of relatively small pins, screws, etc. must be used: especially in the area of the lower end and neck of the prosthetic arms: so as to obtain a sufficient number of attachment points to effectively form a lock between the cement and the bone wall.

35 7 87728 By using a certain centering of pins, nails, etc. in annular areas at the top of the core channel mainly the articular ball and at the lower end of the shaft, the joint can be centered in these areas and the use of metallic centers can be made unnecessary, often below the shaft. on.

However, the number of such anchorage points must be chosen taking into account that re-cutting may be necessary despite 10 secure anchorages. In re-surgery, of course, the attachment points must be removed to allow the prosthesis to be removed, which argues that there should be as few attachment points as possible. During re-cutting, it may be necessary to drill the joints on the outside to remove the pins 15 or by removing them in some other way. Of course, the fewer they are, the simpler it becomes to remove the anchor points. If the pins are drilled out, the holes should not be larger than that they become closed after re-cutting.

As indicated above, a guide or centering member is often used at the outer (lower) end of the shaft of the femoral prosthesis to hold (center) the shaft in the most correct position possible during fixation cementation.

; In order to implement the idea of stabilizing the prosthesis according to the core channel invention, it is proposed that the guide or centering member be attached at least at the lower end of the prosthesis arm by hooks, pins or the like penetrating the bone wall and made of titanium or titanium-based tissue-friendly material. pins or the like.

It is possible in various ways to effect the penetration of pins or other members which are attached or which are attached as described above. . 35 control or centering member or even the prosthetic arm itself.

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One way is to cut in the pins from the outside to the bone wall and attach the pins to the shaft. Another way is to attach the ring with pins or the circumference of the pins to the bone before the prosthesis is inserted so that the prosthetic arm can then be inserted into the ring or circumference and fitted to it to obtain a very stable attachment without fixation. As another method, although it does not appear promising based on clinical results, it is proposed according to the invention to use an expandable annular member 12 with pins, which is externally expandable and has an embodiment 10, e.g. as substantially shown in the drawing.

The annular member 12 shown is expandable by a bolt 13 which, by a threaded end portion 13 ', engages two internally threaded expansion plates 14 on either side of an expandable inner guide ring 15 arranged in the end portion of the arm 8, a plurality of pins extending radially outward . The bolt extends through a channel drilled through the arm 8 to a point at the upper end portion of the arm at a distance and laterally offset from the hinge ball 6. The bolt 13 20 has a member 17 at its upper end which allows gripping of a tool (not shown).

To move the expansion plates 14 against each other to expand the member 15, one plate has a left-hand thread and the other a right-hand thread 25 and the bolt thread consists of a left-hand thread and a right-hand thread, i.e. the plates 14 and the bolt 13 act as a tightening screw device in the example shown.

. . Instead of the expansion device 12 shown in the drawing, any ... 30 other expandable device known in the art and suitable for the purpose may be used, provided that it stabilizes the arm 8 as described by expanding so that the pin penetrates the bone wall and / or expanding against the inside of the core channel. and relies on it.

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The cylindrical ring-shaped member 15 must be made of a tissue-friendly material such as titanium or a titanium-based material or tissue-friendly plastic. With suitable material selection and designs, it is possible to achieve a certain elasticity to force the expandable member 12 (15) to join the core channel cavities without compromising vibration elimination or at least reducing prosthesis arm vibration in the core channel cavity.

In particular, it should be noted that the expandable annular member and the prosthesis arm 10 can be arranged so that the prosthesis arm can be introduced into the annular member after this expansion into the core channel before the prosthesis is placed. In this case, the prosthetic arm does not need a channel and bolts 13, but a tool is needed that can be inserted through the bone or from the bone end to expand the organ.

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It should be noted that the invention is illustrated only schematically in the drawing, in which e.g. the thicknesses of the cement layer 9 and the layers 2 and 7 formed on the articulated surfaces are chosen mainly for the purpose of clarifying the observation and this also applies to studs acting as fastening elements.

The layer thicknesses and in particular the geometric shapes of the fastening elements can vary and many variations in the shape of the fastening elements are possible. Many combinations of material-25 can also be used in the fastening elements. For example, it is possible to make the fastening elements from • steel or another inexpensive material and to coat the surface with a more biologically suitable material, primarily pure titanium or a titanium-based material, which is highly tissue-permeable and otherwise biologically acceptable.

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However, it must be emphasized that the femoral prosthesis does not have to be made entirely of titanium. On the contrary, such an embodiment is preferred, which consists, for example, of a steel core to which a titanium metal coating has been applied. Also, all metal fastening elements 35 consist primarily of, for example, a steel core with a titanium coating as described above. In addition, it should be noted that the joint prosthesis of the invention can also be made for joints other than femoral joints, knee joints, shoulder joints, etc., and that in addition to the fastening members shown, metal screws coated with a surface layer of titanium can be used. Steel-5 screws with a titanium layer are as fabric-friendly as titanium screws, but are less expensive and, moreover, suitable elasticity is more easily achieved when the material combination is a steel / titanium surface layer. Such screws can also be used to fasten bones together in connection with complex fractures or to strengthen the bone into which the joint prosthesis is placed.

The invention is also not limited to the described way of placing metal fastening elements before cementing the prosthetic arm 8. Namely, it is possible to screw or insert the fastening element 15 outwards through the bone and into the cementitious material. In order to avoid prohibited stresses, a fastening element must be used which is provided with through holes which release the pressurized cement. This setting method can also be carried out after the cementation, but before the cementitious material has hardened.

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Claims (1)

An arrangement for attaching a joint prosthesis, wherein the joint prosthesis has a portion (1,8) to be attached to bone tissue, said arrangement having said portion 5 having a jagged surface and a bone cement layer (9) covering this portion fixedly attached to the portion, characterized in that the arrangement further comprises, for the bone cement layer, fastening elements (3, 11) consisting of or covered with a tissue-friendly material and partially embedded in said cement layer and said cement layer and having sharp parts, corners, edges or the like which protrude out of the layer and penetrate the bone tissue. 12 87728 Anordning för fixering av en ledprotes, som har ett parti (1,8) som skall fixeras vid benvAvnad, vilken anordning har en scrrovlig yta pA 5 NAmnda parti ocet ett skikt (9) av bencement som tAcker detta parti och Ar Fast förankrat dArpA, kAnnetecknad därav, att anord-ningen vidare innefattar fixeringselement (3,11) för bencementskiktet vilka bestAr av eller Ar tAckta med vAvnadsvAnligt material or vilka Ar partiellt inbAddade i nAmnda cementskikt och fast It is therefore possible to use the internal and internal rules.