FR2629337A1 - Device for intra-osseus sealing of a prosthesis element - Google Patents

Abstract

The present invention relates to a device for intra-osseus sealing of a prosthesis element, in particular for a joint prosthesis, comprising at least one part 1 termed the stem which is intended to be inserted into a cavity 9 made in the bone 8, and to be immobilised therein. According to the invention, the stem 1 is at least partially surrounded over its part which is inserted into the bone cavity 9 by a flexible covering 4 forming a deformable leaktight chamber around the said part, with, emerging in the said chamber, a channel 7 made in the stem and emerging at its other end beyond the limit of insertion into the bone cavity; after forming the cavity 9 in the bone 8, a plug 10 is placed in the medullary canal, the stem 1 is inserted into this cavity and the prosthesis is prepositioned by injecting under pressure, through the channel 7, into the leaktight chamber defined by the covering 4, a product which can set at a low temperature with a delay of a few minutes. The invention is applicable to the fitting of prostheses, in particular hip prostheses.

Description

Device for intraosseous sealing of a prosthesis element.

The present invention relates more particularly to the field of joint prostheses and in particular hip prostheses but it can be applied in all cases where a prosthetic element or the like must be inserted into a cavity made in a bone and be sealed in said cavity. In joint prostheses at least one element of the prosthesis must be sealed in the bone leading to said joint. This is so if, in the hip prosthesis, the femoral prosthesis which has a tail which must be sealed in a cavity made in the medullary canal of the femoral shaft, the head of this femoral prosthesis hinging on the acetabular prosthesis fixed on the pelvis.

In the most common known techniques for hip prosthesis, the tail of the femoral prosthesis is fixed in the femoral shaft either by cementing, the tail being embedded in a mass of cement lining the cavity cut in the end of the femur, either by friction, the tail having a rough surface and being forcibly engaged in the medullary canal of the femoral barrel according to the so-called self-locking technique. Some techniques combine self-locking by form fitting, with sometimes a mechanical system increasing the surface pressure against the bone of the elements constituting the tail, and cementing.

The self-locking technique requires precise machining of the cavity made in the femoral barrel and, despite the precautions taken and the possible addition of mechanical clamping mechanisms, the contact between the prosthesis tail and the bone remains low and around 15%. In practice, the regeneration of bone tissue improves over time the connection between the prosthesis and the bone. However, when the rehabilitation is too important, it becomes practically impossible to remove, if necessary, the prosthesis without breaking the femur. In addition, because of the many anatomical types of femurs, the practice of the self-locking technique requires providing series of prostheses whose size varies gradually.

To give the possibility of adaptation of the rod to the medullary canal of the femur, it has been proposed, in FR-A-2,485,367, to have segments of elastic elastomeric material between two parts of the rod, in particular between the core rod and rigid spacers forming peripheral supports against the internal surface of the bone. Maintaining the rod in place is however only ensured by the elastic compression force of the elastomer segments so that the prosthesis retains, until the regeneration of the bone, a certain mobility.

Fixing by cementing also poses many problems because of the short setting or polymerization time of the cement which is of the order of a few minutes. Within this period, the surgeon must fill the cavity and place the prosthesis, ensuring it the correct final position. Other drawbacks are medical such as the drop in blood pressure which is frequently observed and can lead to a state of shock very detrimental to the patient or embolism. The setting of the cement is accompanied by a very significant rise in the local temperature which burns the surrounding bone tissue causing its devitalization. Finally, in the event that it becomes necessary to change the prosthesis as a result of its loosening or appearance of an infection, it is extremely difficult to remove the cement which becomes very hard and there is a risk of bone fracture during the loosening operation.

The present invention aims to remedy these drawbacks and it relates to a prosthesis element, in particular for articular prosthesis, comprising at least one part called tail intended to be inserted into a cavity cut in the bone and to be immobilized therein. , characterized in that the tail is at least partially surrounded on its part inserted into the bone cavity by a flexible envelope forming a deformable sealed chamber around said part, with, opening into said chamber, a channel formed in the tail and opening out its other end beyond the insertion limit into the bone cavity.

For its implementation, after making the cavity in the bone, the tail is inserted into this cavity and the prosthesis is prepositioned by closing the medullary canal with a plug beyond the penetration limit of the prosthesis tail. then injected under pressure, through the injection channel, into the sealed chamber delimited by the envelope, a product capable of setting at low temperature with a delay of a few minutes. The prosthesis element is then positioned precisely and the hand holds in position until the product is completely set. The pressure of injection of the product into the deformable waterproof envelope surrounding the tail tightly applies the external surface of the latter against the wall of the cavity whose roughness it marries, which ensures perfect anchoring of the prosthesis element in the cavity Controlling the injection pressure, on the other hand, limits the pressure stresses exerted inside the bone. Preferably and according to another characteristic, the surface of the part of the tail which is surrounded by the envelope is at least partially furnished with asperities and in particular frosted by electrolysis to increase the contact surface between the tail of the prosthesis and the injected product having set and improve their joining.

The envelope preferably has the shape of a hood which is threaded onto the tail and secured to the neck of the latter by gluing, vulcanization or mechanical crimping. This hood is made of a bio-compatible material and in particular of latex. The surface also
Both inside and outside of the hood is frosted by acid attack or otherwise to increase the adhesion between said surface and the injected product, on the one hand, and the bone, on the other hand.

The material injected under pressure is preferably a mixture of copolymerizable liquid resins of the type used in dental prosthesis for relining the cavities. Said material acting as a shim and not by its own mechanical strength, it is preferable to choose a material which, in the polymerized state, retains a certain brittleness allowing the destruction of the mass, without risk of bone fracture , in case the prosthesis needs to be changed.

 The injection of the product consisting of two copolymerizable liquid resins is carried out by a flexible tube connected to the channel produced in the tail by a non-return valve, this flexible tube being connected at its other end by a mixing connector to the syringes of injection each containing one of the copolymer resins.

The dosage of the copolymer resins which determines the time after which the injected mass sets by copolymerizing can be adjusted by choice of the sections of the syringes and the injection pressure by the pressures exerted on the pistons of the syringes. The end of the polymerization is detected by taking the mixture in the flexible injection tube.

The invention will be described in more detail below in the form of an exemplary embodiment with reference to the accompanying drawings # in which:
Figure 1 is a side elevational view with cutaway
partial ment of a femoral prosthesis; Figure 2 is a
profile view of the top of the prosthesis and Figure 3 illus
be the placement of the prosthesis.

The invention is described in its application to a femoral prosthesis made of a biocompatible metal such as titanium, stainless steel, chromium-cobalt alloy, vitallium, etc. The reference 1 designates the tail which has the general shape in usual wedge, the reference 2 the collar constituted by an overflowing plate inclined at approximately 16 on the horizontal and 3 the end piece for receiving the patella whose axis says cervicodiaphyseal angle makes an angle between 120 and 140 with the axis of the tail. The faces of the tail 1 of the prosthesis are etched by electrolysis in order to increase the surface and improve the bonding with the sealing copolymer.

In accordance with the invention the envelope 4 in the form of a hood, is made of latex by blowing with its surfaces etched with acid to increase the coefficient of adhesion of the external surface to the bone tissue and of the internal surface with the co-polymer. Said hood is threaded onto the tail 1 and it is tightly fixed at 5 to the neck of the prosthesis by bonding, vulcanization or the like. A connection 6 is provided on the upper face of the flange 2, this connection extending by two V-shaped channels 7 opening into the upper part of the lateral faces of the tail below the area 5 for fixing the hood 4.

The prosthesis is placed in a femoral barrel 8 in which a cavity 9 has been dug by first placing a plug 10 at the bottom of said cavity beyond the position reached by the end of the tail of the prosthesis . The tail 1 covered by the hood 4 is then placed in the cavity 9. The plug 10 8 a Opposes the creep, towards the medullary canal, of the hood 4 under the effect of the pressure of the injected copolymerizable liquid mixture between the tail 1 and the hood 4. The injection is carried out by a fitting 12 with non-return valve fixed on the fitting 6, this fitting 12 being joined by a flexible tube 13 to a mixer fitting 14 on which the nozzles are adapted of two syringes 15 and 16. The pistons of the two syringes are controlled by a single plunger 17 on which acts, for example, an electric syringe pump, not shown, fitted with a pressure controller.

The syringes 15 and 16 are previously filled with liquid products which are copolymerized by simple mixing. These liquid products will for example be the resins marketed under the brand "SI
LAR "by the company 3M, the setting time of which varies between approximately 1 minute 30 and 3 minutes depending on the proportion chosen for the two resins. The two resins mix in the fitting 14 and are injected through the pipe 13, the fittings 12 and 6 and the channels 7 in the space between the tail 1 and the hood 4 which inflates to come to bear against the wall of the cavity 9 under a pressure which is regulated by the force exerted on the plunger 17 of the syringes.

 The mass 18 of resin injected then polymerizes to give a rigid mass which ensures the final blocking of the prosthesis. The setting of the copolymer is controlled by the hardening of the flexible pipe 13 which becomes rigid and which is detached from the prosthesis.

If necessary, the prosthesis can be removed by removing the polymer constituting the molding 18 by drilling or fragmentation with scissors struck according to conventional techniques.

Claims (7)

Claims 1. Device for the intraosseous sealing of a prosthesis element, in particular for articular prosthesis, comprising at least one part called tail (1) intended to be inserted in a cavity (9) cut in the bone (8) and to be immobilized there, characterized in that the tail (1) is surrounded at least partially on its part inserted into the bone cavity (9) by a flexible envelope (4) forming a deformable sealed chamber around said part, with, opening in said chamber, a channel (7) formed in the tail and opening at its other end beyond the limit of insertion into the bone cavity. 2. Device according to claim I, characterized in that the surface of the part of the tail (1) which is surrounded by the envelope (4) is at least partially provided with roughness and in particular frosted by electrolysis to increase the surface contact between the tail (1) of the prosthesis and the injected product having set (18) and improve their connection. 3. Device according to any one of claims 1 and 2, characterized in that the envelope has the shape of a hood (4) which is threaded on the tail (1) and-integral with the neck of the latter ( 5) by bonding, vulcanization or mechanical crimping. 4. Device according to claim 3, characterized in that the hood (4) is made of latex, the interior and exterior surfaces of the hood being etched by acid attack. 5. Device according to any one of claims 1 to 4, characterized in that it is combined with a obturator or plug (10) capable of closing the medullary canal beyond the position reached by the end of the tail (1) of the prosthesis to close the cavity and limit the expansion of the envelope (4) under the pressure of injection into it of a product capable of setting at low temperature with a delay of a few minutes .  6. Device according to claim 5, characterized in that the product capable of 'setting at low temperature is a mixture of copolymerizable liquid resins of the type used in dental prosthesis for relining the cavities. 7. Device for implementing the device according to any one of claims 1 to 6, characterized in that it comprises a flexible tube (13> connected to the channel (7) produced in the tail (1) by a valve non-return (12), this flexible tube (13) being connected at its other end by a mixing connector (14) to the injection syringes (15-16) each containing one of the copolymer resins.