NL8302178A - METHOD AND TOOLS FOR MAKING A PROSTHESIS - Google Patents

Abstract

The process, for producing a prosthesis intended to be anchored in part of the skeleton of the human or animal body, consists in forming a cavity (2) in the part of the skeleton (1) concerned, in taking an impression of the cavity formed and in producing, by reproduction, at least one part of the prosthesis from the said impression; means used for taking the impression, and a device comprising means for reading the contours of the impression and means for producing the prosthesis on the basis of the data obtained. <IMAGE>

Description

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Method and tools for making a prosthesis.

The invention relates to the making of prostheses, and more particularly implantable prostheses, to be anchored in a skeletal part of the human or animal body.

Implantable prostheses are well known and widely used to replace hip, knee, or shoulder joints, in whole or in part. In addition, the anchoring should be such that the remaining skeleton parts do not tear or break and that a strong bond is ensured for a long time.

Various methods exist for anchoring a prosthesis to a skeletal part such as a bone segment.

In either of these methods, the "stem" of the prosthesis is forcefully punched into the medullary cavity of the bone, creating a forced firm bond. Disadvantages are that the bone can break or tear during impact and also that the bond can be lost over time, causing the prosthesis to become loose. In other methods, the stem of the prosthesis is slid into a pre-formed cavity in the bone segment, which cavity is sufficiently spacious to allow easy insertion. Subsequently, the prosthesis (already by mechanical means such as screws, (b). With chemical means such as a fast-setting "cement" based on polymethyl methacrylate, or (cl using a porous mass which promotes bone tissue growth). Bone Confirmed These methods are satisfactory, but still have drawbacks, such as the fact that screws can loosen over time and the application of a porous mass to the surface of a prosthesis is a relatively laborious operation. "cement" makes the prosthesis difficult to center in the hollow of the bone, while in some places an interruption of the cement layer can occur, resulting in an uneven load transfer from prosthesis to bone. therefore, there is still a need for an improved method of anchoring the prosthesis in a skeleton-5 part.

Tests which led to the invention have shown that good adhesion of the prosthesis to a bone segment can also be obtained without the use of mechanical, chemical or porous means, if a prosthetic stem is slid into a pre-formed cavity in the bone segment, which is precisely "tailor-made", so that a close fit can be achieved without exertion of impact forces and thus a good and even fit of the prosthesis against the bone.

The object of the invention is therefore to obviate the drawbacks of the known anchoring methods for prostheses, and to indicate ways along which the prosthesis, or at least the part of it to be anchored, can be made such that this part, when retracted, into a pre-formed cavity in bone or other skeletal part will fit snugly into that cavity.

In the first place, the invention provides a method for making a prosthesis, intended to be anchored in a skeletal part of the human or animal body, which method is characterized in that a cavity is formed in the relevant skeleton part of the cavity formed makes an impression, and copies the obtained impression into a suitable prosthesis material to obtain at least part of the desired prosthesis.

In this way, a "custom" prosthesis can be made very simply and in a relatively short time, which can then be slid into the formed cavity of the skeleton part to obtain an anchoring by close fitting.

The formation of a cavity in a skeletal part is known per se and can be done in the usual manner, for instance by clearing out the medullary cavity thereof.

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The impression can be advantageously effected by placing a bag of non-adhesive foil material in the formed cavity, against the wall thereof, filling the pouch introduced into the cavity with a cold-setting molding compound, let it harden, and take the bag with the hardened molding compound out of the cavity.

This method is simple, takes little time and results in a manageable and tactile print that can be easily processed further.

Copying the impression can advantageously be effected by scanning the contours of the impression, transferring the probing data to material processing means for controlling it, and processing a rough preform of prosthetic material with the material processing means so controlled for obtaining the desired copy. These operations can also take place in a short time, so that as a result the desired prosthesis or at least the fastening part thereof is quickly available.

To make the impression in the manner described, only simple aids are required, in particular a bag of non-adhesive foil material, a cold-curing molding compound in the form of a two-component system, and means for introducing such a mass. Copying the impression requires a device characterized by means for scanning the contours of the impression, means for processing a rough preform of prosthetic material and means for transferring the touch data to the material processing means control thereof. The invention also extends to these aids and this device.

The invention is further illustrated by the drawings, which show some embodiments of the method, the aids and the device by way of example, focused on making a part of a hip prosthesis.

Pig. 1 schematically shows a first embodiment of making an impression. of a cavity in an 8302178 ar ft -4-botsegraent.

Pig. 2 and 3 schematically show a second embodiment for making such an impression, in two successive stages.

FIG. 4 shows an aid to be used in the embodiments of FIG. 1 and FIGS. 2-3 in the form of a bag of non-adhesive film material.

Fig. 5 shows an intermediate print obtained with the embodiment of FIGS. 2 and 3.

FIG. 6 and 7 show an embodiment of copying this intermediate to obtain the desired prosthesis in two successive stages.

Fig. 1 shows a segment of a hip bone (femur 1), which is part of a human or animal body and in which a part of a hip prosthesis must be attached. In this hip bone a cavity 2 is first formed by clearing the medullary cavity Then a pocket 3 of non-adhesive foil material is placed in the cavity 2, such that the open top end 4 thereof protrudes outside the hipbone 1. In the pocket a spray tube 5 is placed, which is connected to a cold-setting molding compound filled cylinder 6. All these parts and auxiliaries have been sterilized beforehand The molding compound in the cylinder 6 is injected into the bag 3 by means of pressure means (for example a spray gun), which are not shown in the drawing, according to the level of the molding compound 7 in the bag rises, the spray tube 5 is pulled up with the cylinder 6 until the bag is completely filled with molding material, after which the tube 5 and the cylinder 6 are heated and the molding compound 7 is allowed to set in situ, which takes about 4-5 minutes. After the molding compound has hardened, the bag 3 with contents can be effortlessly removed from the cavity 2 of the bone and an impression of the cavity 2 is obtained.

Fig. 2 and 3 show a more preferred embodiment, which incidentally rests on the same principle as the embodiment of Fig. 1. They again see an 8302178 * -5 segment of a hipbone 1 with a cavity 2 formed therein by clearing the medullary cavity. This hipbone forms part of a living human or animal body. A pocket 3 of non-adhesive foil-5 material is placed in the cavity 2 such that the open top end 4 of the pocket protrudes beyond the bone. A stopper 8 of rubber-elastic material is placed on the bottom of the bag, in which a metal centering rod fits, which extends over the entire length of the bag beyond the open top end 4 thereof. A spray tube 5 is then placed in the bag and connected to a cylinder with molding compound (not shown), after which the molding material from the cylinder is injected into the bag via the tube 5.

The spray tube 5 is gradually pulled up as the level of the molding compound 7 in the bag 3 rises. When the bag is completely filled with molding compound, the spray tube 5 is removed and a stopper 10 is attached to the centering rod 9, which presses the molding compound and presses it partly to the side. A round prosthesis head 11 20 with a neck portion 12 is attached to this stop 10 and the plug 10 is fitted in such a way that the head 11 assumes the correct position with respect to the hipbone 1, i.e. in the right direction. The molding compound 7 is then allowed to set, which takes about 4-5 minutes.

After the hardening, the bag 3 with contents can be effortlessly removed from the cavity 2 and an impression of this cavity is obtained.

Various variants are possible on the embodiment of Figs. 2 and 3. Thus, the spray tube 5 can also be placed coaxially around the centering rod 9. Furthermore, the plug 10 can also be placed in the upper end of the bag 3 before filling with molding material, after which the spray tube 5 is pushed through a bore in the plug 10 and the bag 3 is filled with molding material.

FIG. 4 shows an embodiment of the bag of non-adhesive film material to be used in the methods of FIG. 1 and FIG. 2-3. This bag 3 tapers here from the open top end 4 to the closed 8302178 bottom end 13.

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Fig. 5 shows the result of the method of FIGS. 2-3, namely an intermediate which is an imprint of the cavity 2 from the hip-bone segment 1. Thereby the bag of non-adhesive foil material has been removed.

The intermediate 14 mainly consists of a body or stem 15 of hardened molding material, with a stopper 8 of rubber-elastic material on one end and a prosthesis head 11 with neck 12 on the other end. The centering rod 9, 10 passing from the rubber stopper 8 the body 15 extends, protrudes at one end and can further serve as a rotary axis for this intermediate.

Fig. 6 and 7 schematically indicate how an end product, namely a part of a prosthesis, can be formed from the intermediate product of FIG.

In Fig. 6, the intermediate 14 with its ends (plug 8 and centering rod 9) is rotatably mounted in the trunnions 16, 16 of a scanning device 17. A probe 18 is movable horizontally and vertically (according to arrows A and B). mounted in the framework of the device 17. When the intermediate 14 is rotated about its axis by means of the trunnions 16, 16, the probe 18 will scan the contours of this intermediate, or at least of the body 15 thereof. The scan data 25 is converted into numerical values in a converter 20 and recorded on a paper tape 21 leaving the converter in the direction of the arrow C.

Fig. 7 shows the next stage of the method, namely the actual formation of the prosthesis. 30 A rough preform 22 of prosthetic material, with a head 23 and a body or stem 24, is rotatably mounted in turning pins 27, 27 of a machine tool 28 using a centering rod 26. A grinding stone or other machining tool is available via a part 30 mounted horizontally as vertically (according to arrows D and E) in the frame of the device 28 and can be rotated by a motor 31. The device further comprises a converter 32, by means of which the numerical values of a paper tape 21 entered in accordance with the arrow F can be converted into control signals for the grinding stone 29. As the rough preform 22 is rotated via the trunnions 27, 21 and the punched belt 21 is fed into the converter 32, the grinding wheel will make a movement along the surface of the body 24 and process it into a body 25 with exactly the same contours as the body 15 from the intermediate 14 scanned according to Fig. 6 . Thus, a prosthetic portion is obtained which is an exact copy of the intermediate 14.

Various variants are of course possible on the two-stage method of Figs. 6 and 7. For example, the devices of FIGS. 6 and 7 may be combined, if desired, with the transducers 20, 32 and the punched belt 21 combined into a single device, the data collected by the probe 18 being sent directly to the grinding wheel 29 to control it. transferred.

In carrying out the complete process according to the invention, one needs on the one hand some simple means for making a print, such as a bag of non-adhesive foil material, raw materials for a cold-setting molding compound and means for introducing this mass in the pouch, and, on the other hand, a device for copying the print according to FIGS. 6 and 7. The former tools are discussed in more detail below.

The bag of non-adhesive film material must not adhere to a skeleton part, and preferably also not to the hardened molding compound. Furthermore, this box must be sterilizable, for instance with the aid of steam. Polyethylene has worked well as the material for the bag, although other thermoplastic polymers could also be used. If desired, a more elastic film material can also be used. The shape can be tapered, such as in Figure 4, or cylindrical. Of course, the bottom end 13 must always be closed.

The molding compound must be pourable or sprayable on the one hand and fast-curing at ambient temperature 8302178 * -8- on the other, while it must also be sterilizable, for example with steam. Well satisfied here has a silicone elastomer based on polydimethylsiloxane, which is supplied as a tarring component system with a hardener (peroxide plus 5 usual accelerator). The hardener should be added shortly before use and homogeneously mixed with the silicone to ensure even curing. Optionally, the mass can be diluted with a liquid silicone.

After curing, the molding material will form a cohesive body with sufficient hardness to withstand the scanning by a probe. The surrounding bag 3 of non-adhesive film material can be removed, as in Fig. 5, but in the case where the bag consists of elastic material, it can also remain on the intermediate product without any problem.

The plug 8 usually consists of rubber-elastic material, while the plug 10 with the prosthesis head 11 can consist of any material and the centering rod 20 is made of metal. All these parts must of course be sterilized.

The operations for making an impression can be performed in an operating room, while the copy operations can be performed elsewhere.

However, in view of the relatively short duration of the operations, it is also possible to have the copying operations take place in a room a short distance from the operating room.

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Claims (11)

Method for making a prosthesis, intended to be anchored in a skeletal part of the human or animal body, characterized in that: - a cavity is formed in the skeletal part concerned, 5. an impression is made of the cavity formed and copy the resulting impression into a suitable prosthesis material to obtain at least a portion of the desired prosthesis. 2. Method according to claim 1, characterized in that the impression is made by: - placing a bag of non-adhesive foil material in the formed cavity, against the wall thereof, - the bag inserted in the cavity fill with a cold-curing molding compound, 15. allowing the molding compound to harden, and - removing the bag with the hardened molding compound from the cavity. Method according to claim 2, characterized in that the bag of non-adhesive foil material 20 consists of polyethylene. Method according to claim 2, characterized in that the bag of non-adhesive foil material consists of an elastic material. 5. Method according to claim 2, characterized in that the bag of non-adhesive foil material has a tapered shape. Method according to claim 2, characterized in that the bag is removed from the cavity after the molding compound has hardened and after it has been removed. Process according to claim 2, characterized in that the cold-curing molding compound consists of a two-component system based on a hard-hair poly-siloxane elastomer. 8. Method according to claim 1, characterized in that the copying of the print is effected by: - scanning the contours of the print, - - transferring the touch data to material processing means 8302178 -10- Η 'means of control thereof, and to process a rough prosthesis material preform with the thus controlled material processing means to obtain the desired copy. Method according to claim 8, characterized in that the touch data is first transferred to a recording medium, for example a punched tape, and then from this recording medium to the material processing means. Auxiliaries for use in making the impression according to claim 2, characterized by: - a bag of non-adhesive foil material, - a retention hardening molding material in the form of a two-component system, 15. means for introducing the cold-curing molding compound. 11. Device for use in the method of claim 8, characterized by: - means for scanning the contours of the impression, - means for processing a rough preform of prosthetic material, - means for transferring the tactile data to the material processing means for controlling them. 8302178