JPH0447577B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a prosthetic device or a prosthetic component, and more specifically, the present invention relates to a prosthetic device or a prosthetic component, and more specifically, the present invention relates to a prosthetic device or a prosthetic component, and more specifically, a uniform layer of bone cement is formed between the bone cement and the bone by using a protruding spacer. The present invention relates to a transplant member capable of holding. In particular, the present invention
The present invention relates to an acetabular cup using such a spacer.

[Prior art]

Implants for replacing damaged or deteriorating parts of bone are known. Such implants are often fixed to bone using bone cement. An acetabular cup is a typical example of such an implant. This acetabular cup is used when both parts of the ball and socket joint require replacement. That is, the femoral head is replaced with a correspondingly shaped spherical member, and the acetabular cup is used as a concave member for receiving this spherical member.

In order to securely fix the acetabular cup to the bone, it is preferable to form a uniform and flat cement layer over the entire surface of the acetabular cup facing the bone. Various types of spacers are used to prevent the cup from hitting the acetabulum when it is fixed with cement.

When a spacer is not used, a layer of cement is applied to the acetabular bone and the cup is then placed in place on the bone cement. but,
This method may result in uneven distribution of the cement as the cup is pressed into place on the cement. For example, cement tends to be squeezed out around the edges of the cup, resulting in a very thin cement distribution near the center of the cup and a much thicker distribution near the edges. the result,
Cup fixation becomes weak.

To address this issue, U.S. Patent No. 4285071
No. 1, which teaches the use of multiple spacers in the acetabular cup. These spacers provide a means for controlling the thickness of the cement layer formed between the cup and its spine. Each spacer includes a standoff and a sharp wire extending outwardly from the standoff. Each of these spacers is attached to the bone by threading a wire into the bone. A layer of bone cement is then formed thereon and an acetabular cup is placed against the outermost surface of each standoff. The spacer standoff is made of acrylic bone cement. The surface of the polymerized acrylic bone cement forming the separator undergoes a polymerization reaction with the acrylic bone cement when the acrylic bone cement layer is applied. The nature of the joint formed between the acrylic bone cement layer and the separator prevents stress concentrations at the joint surfaces. The disadvantage of this spacer is that the surgeon must attach each spacer to the spine. This not only wastes time, but also causes errors in the positioning of the spacers with respect to each other and with the acetabular cup placed over the spacers. Also,
Even after repolymerization, sharp "thumbtack"-like wires remain.

British patent application no. GB2080118A discloses an acetabular cup made of plastic material. The outer surface of the cup includes a plurality of studs made of the same material as the rest of the cup. The stud may be integral with the cup, or may be inserted into and embedded in the cup. The stud functions as a spacer to facilitate the formation of a substantially constant thickness of bone cement between the cup and the acetabulum. Spacers, such as the plastic spacer of this British patent, are not incorporated into the cement, but instead partition the cement. In addition, plastic spacers
It also causes stress build-up in the surrounding bone cement.

Other conventional acetabular cups include the ES-32 cup sold by Biomet. The cup includes a plurality of protruding spacers to help form a uniformly thick layer of bone cement and avoid thick and thin sections of the bone cement. This spacer is integrally molded with the polyethylene cup. The cup is reinforced with a metal backing cap to eliminate possible deformation and consequent fracture of the cement due to excessive cold flow. This metal cap has
An opening is provided for the spacer to protrude. As with the spacer in the UK patent application mentioned above, the ES-32 plastic spacer is
It does not become incorporated into the bone cement and instead has a tendency to compartmentalize the cement and also tends to create stress build-up in the surrounding cement.

[Problem to be solved by the invention]

An object of the present invention is to provide an acetabular cup equipped with a plastic spacer reinforced with a metal backing member, in which the spacer can be reliably bonded to the outer surface of the backing member and integrally bonded to the bone cement layer. The purpose is to make it possible to join.

[Means to solve the problem]

In order to solve the above problems, the present invention comprises an acetabular cup made of an inner member made of ultra-high molecular weight polyethylene and an outer shell made of metal. At least a portion of the surface of the outer shell is made porous, and a plurality of spacers are formed on the porous surface so as to protrude by a predetermined distance. This spacer is at least partially formed of an acrylic material.

The method of the present invention for manufacturing such an acetabular cup includes forming a porous surface on at least a part of the outer surface of a cup-shaped metal member, forming a spacer of an appropriate shape from an acrylic material, The spacer is firmly adhered to the porous surface by applying the spacer to a predetermined position on the porous surface and melting the material of the spacer, allowing it to flow into the porous surface and solidifying.

[Action and effect]

According to the present invention, since the spacer is bonded to the porous portion formed on the surface of the metallic outer shell, the bond between the spacer and the outer shell becomes strong. Also,
Since the spacer is formed of an acrylic material and the acetabular cup is bonded to the trabecular bone using acrylic bone cement, a polymerization reaction occurs between the acrylic material of the spacer and the acrylic material of the trabecular bone, and the spacer and the bone No discontinuous sections are formed between the cement and the cement, and the bond between the two becomes strong.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Referring first to FIGS. 1, 2, 3 and 5, the acetabular cup 1 shown in these figures has an internal abutment surface 10 and an external surface 20. An inclined surface 35 is formed at the edge of the internal joint surface 10, and a rim 30 is formed following the inclined surface 35.

A plurality of spacers 40 are provided to protrude outward from the exterior surface 20. Spacer 40 typically has a uniform thickness and width, and may be formed in any suitable shape or desired thickness.
In the examples shown in FIGS. 1, 2, and 4-9, the protruding portion of the spacer 40 is substantially cylindrical in shape. If such small cylindrical spacers 40 are used, it is preferred that at least three spacers 40 be appropriately spaced on the external surface 20. This is to ensure that a uniform distance is maintained between the external surface 20 and the spine when the cup 1 is attached to the spine. Any configuration can be used for the spacer 40. 1st
The figures and FIG. 2 show a cup 1 with four spacers 40. FIG. In the example of FIG. 4, eight spacers 40 are evenly spaced along the exterior surface 20.

FIG. 5 shows an acetabular cup consisting of an inner member 28 and a metal shell 21 disposed outside of the inner member 28. This member 28 is made of ultra-high molecular weight polyethylene. The metal shell 21 can be made of a variety of materials, such as titanium, cobalt-chromium, high grade stainless steel, or metal/plastic composites. Conventional manufacturing methods can be used to form the inner member 28 and the outer metal shell 21.

The exterior surface 20 has a thin layer of perforated metal beads as shown in FIGS. 1, 2, 4, and 5. In the illustrated example, a bead-free portion 2 is provided on the external surface 20.
2 and a bead portion 24 are formed. Portions of the external surface 20 may be covered with a thin layer of porous metal beads to form the bead portions 24, or the entire surface of the external surface 20 may be covered with a bead surface. The porous bead surface described in detail in US Pat. No. 3,605,123 can be used. However, other means of forming a porous surface may be used. This porous bead surface allows for a strong fixation between the bone cement applied during surgery and the external surface 20 of the cup 1.

Spacer 40 is comprised of an acrylic material, such as a polymer or copolymer of polymethyl methacrylate, or other comparable material. Various methods can be used to form this spacer. For example, a commercially available bone cement prepolymer/monomer mixture may be used and the mixture then poured into a suitable mold or cavity. Alternatively, the spacer is formed by injection molding a polymethyl methacrylate polymer using an injection mold without using a prepolymer/monomer mixture. Methods of molding polymers are known in the art, and thus any suitable method can be used to mold the desired shape of the spacer. An alternative method is to purchase preformed acrylic rod and trim it to the desired length.

In a particularly advantageous embodiment of the invention shown in FIG. A bonding surface is formed therebetween. It is known to use ultrasonic welding to bond one polymer to another or to insert metal inserts into polymers. In this case, the ultrasonic energy is approximately 20000Hz
through a transmission mechanism, i.e. an ultrasonic horn,
It is delivered to the part to be welded or molded, ie the spacer in this case. This process can be stated as follows. Namely: 1) Energy is transferred to the interface between the horn and the spacer. 2) Energy is transferred through the spacer. and 3) concentrate on the plane between the two parts to be welded, namely the spacer and the outer shell. Such energy concentration is caused by point or line contact between the two parts, namely the spacer and the outer surface 20 of the outer shell 21. The subsequent release of energy, ie the vibrations, heats the surface between the spacer and the shell. The temperature at this time rises to a level where the polymer softens and sometimes melts. The resulting softening causes the acrylic material of the spacer to become viscoelastic and flow into and around the gaps of the metal shell 21.

(In the case of two polymers, such as an acrylic spacer welded to a polyethylene cup without a metal shell, as in Figure 6, the melts mix at the molecular level.) The time is approximately 1 to 2 seconds. Maintain pressure without vibration to cool and solidify the polymer.

In the following, the outer surface 20 of the metal outer shell 21 of the acetabular cup 1 as shown in FIGS. 1-2 and 4-5 will be described.
The preferred method used to bond the acrylic spacer 40 to the porous bead 24 in FIG. This process is as follows. That is, 1) Place cup 1 on the fixture. 2) Spacer 4
0 is attached to the porous bead portion 2 of the cup 1 by means of a fitting.
4. Press it to the desired position. 3) Touch the horn of the ultrasound machine to the wide bottom area of the spacer 40. 4) When ultrasonic energy is applied, the contact point between the acrylic spacer 40 and the needle-like body of the porous bead portion 24 formed on the outer surface 20 of the metal outer shell 21 of the cup becomes the energy release point. 5) The polymer melts and flows into the porous surface. and,
6) When the ultrasonic energy is stopped and the pressure is continued to be applied, the polymer in the spacer 40 hardens, thereby ensuring that the spacer adheres to the porous bead portion 24 of the metal shell 21.

There are other suitable methods for bonding the spacer 40 to the metal shell 21, which can be used as follows. That is, 1) softening the end of the spacer 40 by immersing it in a solvent;
This softened spacer is then pushed into the porous bead 24 of the metal shell 21. 2) Melt the end of the spacer 40 by contacting it with a heated surface and force it rapidly into the porous bead 24 of the metal shell 21; 3) Molding spacer 40 onto the cup directly from a prepolymer-monomer mixture such as is used in current bone cement preparation. 4) With a mold for injection molding the acetabular cup 1,
Spacer 40 is injection molded directly onto metal shell 21 . 5) Any combination of the above methods is used to embed the polymer into the porous bead 24 of the metal shell 21 to form a hard spacer of an appropriate shape. Further, instead of the porous bead portion 24, the metal outer shell 21 may have a rough surface, for example, an embossed pattern surface.

The external surface 20 may be coated with a thin layer of polymethyl methacrylate (PMMA) film (not shown), which serves to enhance the adhesive effect between the bone cement used during the surgery and the external surface 20 of the cup 1. good. U.S. Patent Nos. 4,281,420, 4,336,618 and
No. 4,365,359 discloses an example of a thin film of PMMA body applied to the portion of the external surface of the acetabular cup for contacting the spine. As previously mentioned, this layer may optionally cover portions or the entire exterior surface of the cup.

The cup 1 according to the invention has a spacer 40 made of acrylic material. This cup 1 is directly cemented intraoperatively to a layer of fresh acrylic bone cement that has already been applied to the acetabulum. The cup 1 is manually pushed to a predetermined position where it is felt that the spacer 40 rests on the acetabulum, which is the supporting bone. The already polymerized acrylic spacer 40 then undergoes a polymerization reaction again with this new acrylic cement layer, thereby forming a new joint. This joint is likely to occur with spacer elements made of metal or plastic.
This has the effect of eliminating stress concentration at the joint surface.
As described above, the present invention eliminates the troublesome work of replacing spacers made of acrylic material one by one, and also eliminates the need for the wire pins described in US Pat. No. 4,285,071.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an acetabular cup according to the present invention, FIG. 2 is a plan view of the acetabular cup of FIG.
Figure 3 is a bottom view of the acetabular cup in Figure 1;
5 is a plan view of an alternative embodiment of an acetabular cup according to the present invention, and FIG. 5 is a side sectional view taken along line 5--5 of FIG. 1... Prosthetic device (acetabular cup), 20... External surface, 40... Spacer.

Claims (1)

[Scope of Claims] 1. Consisting of an inner member made of ultra-high molecular polyethylene and an outer shell made of metal, at least a part of the surface of the outer shell is porous, and a part protrudes from the porous surface by a predetermined distance. Multiple spacers are glued to
An acetabular cup for fixation to a trabecular bone with an acrylic bone cement, characterized in that at least a portion of the spacer is made of an acrylic material. 2. The acetabular cup according to claim 1, wherein the spacer is entirely made of acrylic. 3. An acetabular cup according to claim 1 or 2, wherein the acrylic material is polymethyl methacrylate. 4. The acetabular cup according to any one of claims 1 to 3, wherein the spacer is adhesively fixed to the porous surface by ultrasonic melting. 5. An acetabular cup according to any one of claims 1 to 4, wherein the porous surface is formed by blasting of metal particles. 6. The spacer has a substantially uniform height so that when the cup is attached to the spine, a uniform gap for filling with bone cement is formed between the cup and the spine. An acetabular cup according to any one of claims 1 to 5. 7 A method for manufacturing an acetabular cup having a plurality of spacers made of acrylic material on the surface and lined with metal, the method comprising: (a) providing a porous surface on at least part of the outer surface of the cup-shaped metal member; (b) forming a suitably shaped spacer from an acrylic material; (c) applying the spacer to a predetermined position on the porous surface to melt the spacer material and causing it to flow into the porous surface; , by solidifying
A method of manufacturing an acetabular cup, comprising firmly adhering the spacer to the porous surface. 8. The acetabular cup of claim 7, wherein the melting of the spacer material during the step of bonding the spacer to the porous surface is carried out by ultrasound. 9 A method for manufacturing an acetabular cup having a plurality of acrylic material spacers on the surface and lined with metal, the method comprising: (a) providing a porous surface on at least a portion of the outer surface of the cup-shaped metal member; (b) placing the cup-shaped metal member in a holding device; (c) molding an acrylic material into a suitable shape as a spacer; and (d) placing the molded acrylic material into the spacer on the porous surface. (e) bringing the horn of an ultrasonic generator into contact with the spacer-shaped acrylic material; (f) applying ultrasonic energy; and (g) causing the acrylic material to (h) terminating the ultrasonic energy to solidify the molten acrylic material between a spacer comprised of the acrylic material and the porous surface; (i) For all spacers to be bonded, adhere to (d) above.
A method for manufacturing an acetabular cup, characterized by repeating steps (h).