ES2538013A1 - Shock absorbing system for knee and hip prosthesis (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Damping system for knee and hip prosthesis. Currently, knee and hip prostheses continue to maintain the design and materials of 30 years ago, modifying slightly roughness and design. However, to date in society has increased both the life expectancy and the number of incidences in arthroplasty at an increasingly younger age. Therefore, it is necessary to create new prostheses with shock absorbing effect or characteristic stresses, both maximum and routine, modifying the polyethylene component. With this, we intend to minimize the wear of the material due to fatigue, thanks to the energy absorption capacity of the development component, lengthening the patient's revision surgery of his prosthesis. For this purpose, it has been foreseen that the insert (1) incorporates one or more interior recesses (2-2'-2 '' - 2 '' '- 2iv -2v -2vi) as a cushioning element, which may be partially or completely filled with a biocompatible polymeric cushioning material. (Machine-translation by Google Translate, not legally binding)

Description

OB.! ETO FROM I TO INVENTION

The present invention relates to a damping system for joint prostheses, specifically for knee and hip prostheses.

The object of the invention is to improve the distribution of the stresses transmitted on the articular surface corresponding to the knee and hip joint prostheses, minimizing stress peaks and, therefore, the resistance against wear of the material.

BACKGROUND FOR THE INVENTION

Currently, the polymeric material used in the manufacture of knee and hip prostheses presents a series of limitations associated with phenomena of frailty, wear and tear.

20 another series of complications that force them to be replaced over time, which gives them a limited service life. One of the main problems associated with conventional arthroplasties practiced today is the wear of the polyethylene component. Problems related to the presence of particles generated by mechanical wear that usually lead to processes of

25 osteolysis, more than enough reason to subject a patient to a new surgery due to the malfunction of the arthroplasty. In addition, its application in younger and more active patients makes it necessary to develop materials with greater durability for the manufacture of joint implants.

30 Wear is a factor that affects the durability of implants and their fixations. Wear occurs in all artificial joints and there is loss of material in the joint during use due to the friction of polymer metal and deterioration that occurs in all joints. In some patients, the presence of these wear particles has an adverse local effect that can influence the clinical response and shorten the life of the implant.

5 The wear of polyethylene (UHMWPE - Ultra High Molecular Weight Polyethylene), the most commonly used polymer in joints based on ceramic-polymer or metal-polymer pairs, is the result of alterations that may occur in the material as a result of degradation chemical and mechanical to which it is subjected during its intended use. Its weakness to the resistance of breakage stress, as well as wear of the articular surface,

The first limitation for the life of a joint prosthesis is considered.

Within the main wear mechanisms of polyethylene in general conditions

and referring to what is the whole of the prosthesis, is the adhesion. This mechanism

it occurs when the accessory force is stronger than the performance force of the material and

A small piece of it is dragged from one surface and "hooked" to the other, mainly due to the poor absorption of said accessory force by polyethylene. Another wear mechanism is the fatigue of the polyethylene material, which affects the subsurface that allows the surface to break, causing delamination and breakage, also due to a poor absorption of the forces involved in joint mechanics.

20 Different articles advise advancing in the design of these prostheses advising improvements in the reduction of loads in polyethylene or the use of prosthetic models with increased joint congruence.

25 The failure of total knee and hip arthroplasties due to the wear of interposition polyethylene, associated or not associated with periprosthetic osteolysis, is one of the problems that has generated the greatest interest in the global orthopedic community in recent years. The great benefit that patients and society obtain from these arthroplasties is limited, in the medium and long term, by wear that forces the prosthetic replacement after the failure of the

30 implant

The most used polymeric material in orthopedic implants is UHMWPE. Cross-linked UHMWPE is also used

Applications: acetabular insert in hip prostheses; tibial insert, patellar or patellar component in knee prosthesis.

Advantages: Impact resistance, excellent biocompatibility and great resistance to fatigue.

Disadvantages: UHMWPE: Sensitive to oxidation and wear. UHMWPE of crosslinked links: Although it manages to reduce wear, it is susceptible to cracking and has worse mechanical properties. In general, poor absorption of impact energy associated with patient movement.

Although the wear of these interfaces is a concern in knee and hip prostheses that use UHMWPE components and metal alloys, the vast majority of the wear particles produced are made of polyethylene, derived from the frictional joint movement of the joint with the metal component

The most widely used articulated pair is still a metal alloy against ultra-high molecular weight polyethylene (UHMWPE).

Efforts to improve polyethylene wear characteristics have included carbon fiber additives, hot-pressing and crosslinking.

The microstructure of UHMWPE is that of a viscoelastic solid with two phases, consisting of crystalline domains embedded in an amorphous matrix. The large length of the ultra high molecular weight polyethylene chains makes it difficult to arrange the crystalline layers of your molecules, limiting the amount of crystalline material. Thus, the resulting product basically consists of lamellae of 10 to 50 IJm thick and 1 to 50 IJm of

lOin the components

Length with interposed amorphous material. There are molecules that bridge the crystalline domains as a bridge, providing better voltage transfer and greater physical resistance, but usually, the percentage of crystalline domain of a UHMWPE implant ranges between 58 and 70%, depending on the type of resin used ; the rest is made up of the amorphous matrix. The improvement in both the design and the material of this component is of great importance in reducing the problems associated with this type of arthroplasty.

The mechanisms of plastic deformation are related to the processes of wear

Polymeric prostheses used in arthroplasty, while fracture and fatigue mechanisms are directly associated with the elastic limit and maximum tension. Most of the damage that appears on deformation and wear surfaces is linked to the plastic behavior and the elastic limit of the UHMWPE.

The mechanical properties of UHMWPE provide us with important data to evaluate its behavior and the possible combinations of material or design of the component that are likely to be studied. It is also known the different resins created in different conditions, degree of crosslinking, heat treatments and sterilization process, existing in relation to the improvement of the material. However, a combination of materials or the redesign of the component, no work has been found today. All UHMWPE materials used in implants must conform to international standards (ISO), which reflect the valid ranges for the elastic limit, Young's modulus, rupture stress, ductility and impact resistance. These aspects are those that are of interest mainly to improve as a source of origin of the joint wear mechanism.

The technological challenges are in the improvement of the biomechanical behavior of the complete prosthesis, through two ways:

-

Geometric optimization (introducing alternatives regarding the design concept).

-

Using a combination of biomaterials in the polymer component (being able to

be obtained by different production processes, such as extrusion, sintering,

mechanized or others), which allows a better damping of its internal structure, as well

as less wear in the area of contact with the mobile part of the prosthesis.

These two ways can be implemented individually or in a complementary way, in order to improve the damping capacity, reducing the average stresses, and providing greater wear resistance, reducing the individual pressures on the surface of the articular component by increasing the congruence surface.

DESCRIPTION OF I TO INVENTION

The damping system for joint prostheses object of the invention is based on modifying the polymer component used in the prosthesis, currently UHMWPE, in order to reduce the stresses to which the material is subjected and, thus, minimize material wear due to fatigue, thanks to the energy absorption capacity of the development component, lengthening the life of the prosthesis and thus reducing the revision surgery rate.

The invention consists in the incorporation of a damping system in the current knee and hip prosthetic systems, although it could be subsequently implemented to any type of joint prosthesis subjected to compression loads.

For this, and based on an articular prosthesis obtained in any polymeric material, such as polyethylene, the invention focuses its characteristics on the fact that said element has at least one chamber or void by means of which it is possible to optimize the damping effects of the prosthesis.

These chambers may optionally be empty, or partially or completely filled with another polymeric material with different mechanical properties, so that the UHMWPE has a variable composition profile with standard polymer zones and specifically studied areas formed by a modified structure of the same, or another, polymer with different properties. This polymer can be incorporated by different processes. The chamber or emptying is placed in the insert strategically to the optimization of the process of pressure reduction in the areas of greater congruence between the metallic and polymeric components. These areas, with or without filling of polymeric material of different properties, are those that provide the damping effect, helping

reduce both the average stresses and expand the contact area on the articular surface, reducing contact pressures and thereby wear.

DESCRIPTION OF I OS Pl811 lOS

To complement the description that will then be made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical implementation thereof, a set of drawings is attached as an integral part of said description. where, for illustrative and non-limiting purposes, the following has been represented:

Figure 1.- Shows a perspective view of a polymeric knee joint prosthesis insert made in accordance with the prosthetic damping system object of the present invention.

Figure 2.- Shows a plan view of the insert, on which two reference axes have been represented, the antero-posterior axis (AP) and the mid-lateral axis (ML)

Figures 3a and 3b.-They show paths in profile and perspective in section according to the line of cut AA of Figure 2, corresponding to a first variant embodiment in which the insert incorporates a hollow out of the bottom shaped elliptical and with rounding radii to minimize stress, emptying that can optionally be filled with a damping material. The emptying is extensible to a free geometry, either elliptical, circular or rectangular and of variable dimension within the component.

Figures 4a and 4b.-They show paths in profile and perspective in section according to the line AA of Figure 2, corresponding to a second variant embodiment in which the insert incorporates a recess in the form of a groove of width constant, emptying that can optionally be filled with a damping material.

Figures 5a and 5b.-They show paths in profile and perspective in section according to the line of cut AA of Figure 2, corresponding to a third variant embodiment in which the insert incorporates a reticulated emptying with holes in both axes from

reference, emptying that can optionally be filled with a damping material. The geometry of emptying is extensible to any geometry and arrangement of the holes.

Figures 6a and 6b.-They show paths in profile and perspective in section according to the line AA of Figure 2, corresponding to a fourth variant embodiment in which the insert incorporates a recess based on holes arranged parallel to the AP axis, emptying that can optionally be filled with a damping material. The geometry of emptying is extensible to any geometry and arrangement of the holes.

Figures 7a and 7b.-They show paths in profile and perspective in section according to the line AA of Figure 2, corresponding to a fifth variant embodiment in which the insert incorporates a recess based on parallel cylindrical holes to the ML axis, emptying that can optionally be filled with a damping material. The geometry of emptying is extensible to any geometry and arrangement of the holes.

Figures 8a and 8b.-They show paths in profile and perspective in section according to the cut line AA of Figure 2, corresponding to a sixth variant embodiment in which the insert incorporates a recess similar to that of Figure 3 , but in which the emptying has curvature in the AP and ML axes, emptying that can optionally be filled with a damping material.

Figures 9a and 9b.-They show paths in profile and perspective in section according to the line AA of Figure 2, corresponding to a seventh variant embodiment in which the insert incorporates an elliptical geometry chamber, extensible to any geometry This chamber can become emptied by its opening in any direction of the insert.

Figure 10.- Shows a view in front section along the ML axis of the variant shown in Figure 3.

Figure 11.-Shows, finally, a bottom view of the assembly of the previous figure.

Figures 12a and 12b.-Show a plan view and elevation section of a polymeric hip joint prosthesis insert (acetabular insert), on which the reference axes, the anteroposterior axis (AP) have been represented. mid-lateral axis (ML) and cranio-caudal axis (CC). In the figures, the dotted line represents the area in which the cushion system for prostheses object of the present invention can be realized.

PREFERENTIAL REALIZATION PE 1 TO INJECTION

As can be seen in the aforementioned figures, and in particular in relation to figures 1 and 2, there is shown a polymeric tibial insert, which can indistinctly materialize in a conventional insert or in the insert object of the invention, since The external geometry of the device is exactly the same, being obtained from a single piece body (1), of polymeric nature, such as polyethylene, although it could be obtained in other materials.

Well, in accordance with the essence of the invention, it is envisioned that the single-piece insert or body (1) incorporates hollows or chambers (2_2'_2 "_2" '_ iv_2v_2v,) specially designed to improve the damping of this body in normal operation, emptying (2_2'_2 "_2" '_ iv_2v_2v,), which may optionally be filled with a damping material (3), of a different nature than that of the single piece body (1). The filler polymer can be obtained by sintering, injection of other materials or any other productive process (such as extrusion, machining, etc.)

Any polymeric material in its different forms of presentation (powder, pellet, bar, etc.) that, combined with the polymeric material (UHMWPE, PEEK or similar) of the single piece body, confers the insert with greater damping and impact absorption properties, Through a smaller elastic module, it is capable of being used as a filling material for the chamber.

More specifically, and as can be seen in Figures 3A and 38, in a first embodiment of the invention, the insert incorporates a recess (2) for its lower part, of elliptical geometry, whose height can be variable.

As previously mentioned, and according to figures 9 and 10, the recesses (2) can be filled with a damping material, presenting its rounded upper edge to minimize tensions at the interface, so that a structure is achieved combined, so that the UHMWPE has a variable composition profile with standard polymer zones and specifically studied areas formed by a modified structure of the same polymer with different mechanical properties, with the modified polymer zones providing the damping effect, helping to reduce the average tensions as well as to expand the contact area on the articular surface, reducing contact pressures and, with it, wear.

According to a second variant of practical embodiment, the one shown in Figures 4a and 4b, the emptying (2 ') of the insert can take the form of a groove of constant width, emptying that can optionally be filled with a damping material, which may be the variable emptying thickness, as well as presenting a medial elliptical shape with respect to the ML axis. In the case of incorporating said cushioning material occupying said emptying, special care will be taken with rounding radii to minimize tensions at the interface.

Optionally, and although it is not represented in the figures, this type of emptying could be extended until it is flush with the external surface of the prosthesis, preferably on its front face in accordance with the AP axis.

According to a third variant of practical embodiment, the one shown in Figures 5a and 5b, the emptying (2 ") of the insert can be realized in a reticulated emptying with holes in both reference axes AP and ML, being able to be of the diameter and separation between the variable holes, emptying that can optionally be filled with a damping material.

According to a fourth variant of practical realization. the one shown in figures 6a and 6b the emptying (2 "') of the insert is realized by means of holes arranged parallel to the AP axis, whose diameter and separation can be variable, emptying that can optionally be filled with a damping material.

In the fifth variant of practical embodiment, the one shown in Figures 7a and 7b has provided that the emptying (2Iv) is obtained based on cylindrical holes parallel to the ML axis, whose separation and diameter can be variable, emptying that can optionally remain filling of a buffer material.

In the sixth variant of practical embodiment, the one shown in Figures 8a and 8b is provided that the insert incorporates a recess (2v) similar to that of Figure 3, but in which the recess has curvature in the AP and ML axes, emptying that can optionally be filled with a material with different elastic modulus than the material of the articular polymer component.

Finally, in Figures 9a and 9b a seventh variant embodiment is shown in which the insert incorporates a chamber (2v1) of elliptical geometry, extensible to a free geometry. This chamber can become emptied by its opening in any direction of the insert.

In the same way, specifically in relation to Figures 12a and 12b, there is shown a polymeric bilateral aceta insert (hip prosthesis), which can interchangeably materialize in a conventional insert or in the insert object of the invention, since that the external geometry of the device is exactly the same, being obtained from a single piece body (1), of a polymeric nature, such as polyethylene, although it could be obtained in other materials.

In accordance with the essence of the invention, it is envisioned that the single-piece insert or body (1) can incorporate hollows or chambers analogous to those exposed for the knee prosthesis (2_2'_2 "_2 '' '_ i v_2v_2v,) which are specially designed to improve the cushioning of this acetabular insert in its normal operation.The dumps can be optionally filled with a damping material (3), of a different nature from that of the single piece body (1). Filler polymer can be obtained by sintering, injection of other materials or any other productive process.

Claims (6)

18 ._ Cushioning system for knee and hip joint prostheses, which being constituted from a main body or insert (1) of polymeric nature, such as 5 polyethylene, PEEK or the like, is characterized in that it defines at least one emptying or chamber (2_2'_2 "_2" '_iv_2v_2v1), capable of being filled with another material less rigid than the first, as a damping element. 28 ._ Cushioning system for knee and hip prostheses, according to claim 18, 10 characterized in that the chamber or emptying (2_2'_2 "_2" '_ iv_2v_2v1) is capable of being partially or totally filled with a biocompatible polymeric buffer material. 38 ._ Damping system for knee and hip prostheses, according to claims 18, and 28, characterized in that the insert incorporates a recess (2) for its lower part, susceptible 15 to adopt different configurations, such as elliptical, circular or quadrangular, or the like, with rounded edges. 48 ._ Damping system for knee and hip prostheses, according to claims 18, and 28, characterized in that the insert incorporates a recess (2 ') that takes the form of a 20 through groove on the ML axis. 58 ._ Cushioning system for knee and hip prostheses, according to claim 48, characterized in that the emptying (2 ') has an elliptical medial shape with respect to the axis medium-lateral, extensible to another elliptical, circular or quadrangular geometry. 25 68._ Damping system for knee and hip prostheses, according to claim 48, characterized in that the recess (2 ') extends until it is flush with the external surface of the prosthesis, preferably on its front face in accordance with its AP axis . 30 78 ._ Cushioning system for knee and hip prostheses, according to claims 18, and 28, characterized in that the insert incorporates a recessed recess (2 ") with holes, which can be regular or irregular and of different size. sa._ Damping system for knee and hip prostheses, according to claims 1 a, and 2a, characterized in that the insert incorporates a recess (2 "'- i V) based on holes that they can be interns, blind holes, or chambers inside the insert. 5 ga._ Damping system for knee and hip prostheses, according to claims 1a, and 2a, characterized in that the insert, which incorporates a recess (2v) at its bottom, has curvature in the anterior posterior and middle lateral axes. 1Qa._ Damping system for knee and hip prostheses, according to claims 1a, 10 and 2a, characterized in that the insert incorporates a chamber (2v1), preferably of elliptical geometry, capable of becoming emptied by its opening in any direction of the insert.