EP3930633A1

EP3930633A1 - Range of articular implant systems with double mobility

Info

Publication number: EP3930633A1
Application number: EP20710242.7A
Authority: EP
Inventors: Daniel Noyer; Philippe Bauchu; Alain Cypres; Arnaud Fiquet; Christophe Roy; Olivier Bonnard; Philippe Girardin; Bertrand SEUTIN; Gualter VAZ; Philip John Roberts
Original assignee: Giles
Current assignee: Giles
Priority date: 2019-03-01
Filing date: 2020-02-18
Publication date: 2022-01-05
Also published as: FR3093285A1; US20200276021A1; FR3093285B1; WO2020178494A1; US11951011B2

Abstract

In this range of articular implant systems, the implant is of the type comprising: - an anchoring chamber (1) in one of the elements of the articulation (2) being considered, defining a smooth internal cavity which is substantially hemispherical; - an insert (3) which is movable within the internal cavity of the anchoring chamber (1) and the smooth external surface of which is intended to cooperate via a ball and socket joint with the internal cavity of the anchoring chamber (1), and in turn defining a smooth internal cavity which is substantially hemispherical; - a head or ball (4) which is fixedly joined to a second element of the articulation, which is spherical and which is intended to be received in the internal cavity of the movable insert (3) and to constitute a second ball and socket joint. The ratio of the internal diameter of the internal cavity of the anchoring chamber to the internal diameter of the internal cavity of the movable insert is constant for all the elements of the range, whatever the diameter of the ball (4) selected.

Description

RANGE OF DOUBLE JOINT IMPLANT SYSTEMS

MOBILITY

FIELD OF THE INVENTION

The present invention relates to the field of joint implants, in particular with dual mobility, and aimed at replacing the bone joints of substantially hemispherical geometry of the human or animal body.

It relates more specifically, but not limited to the hip joint.

PRIOR STATE OF THE ART

In the field of total hip prostheses, the so-called dual mobility principle has been known for many years, i.e. the rotation of a spherical head or ball, fixed on a prosthetic rod inserted into the femur within a core or movable insert, captured by the constriction with which said movable insert is provided, joint described generally as constituting the small joint, the movable insert being most often made of high density polyethylene. Said insert is itself also mobile in rotation in a cup or acetabulum anchored in the acetabular cavity of the pelvis, generally called the large joint. These two joints, large and small, are called dual mobility. The small joint is used in low amplitude movements and the large joint comes into action when the femoral neck of the prosthetic stem comes into contact with said constriction of the movable insert during large amplitude movements. This contact is described in the literature as being the third joint, often the most fragile.

This double mobility made it possible to significantly reduce the dislocations of the joint thus prosthesis. Such a prosthesis has, for example, been described in document LR 2 710 836. If, undoubtedly, the implementation of such dual mobility hip prostheses has, on the one hand, reduced the number of dislocations of the joints thus prosthesis, and on the other hand, increased their lifespan, experience shows that 'however, there remain a certain number of cases in which these dislocation phenomena always appear, or even that blockages of the mobile insert, by multiple factors, within the anchoring cup, resulting from cooperation between the different cooperative surfaces between the constituent elements of such prostheses lead to prosthetic failure.

In practice, the orthopedic surgeon faced with the need to proceed with the placement of a total hip prosthesis, has a range of implants, typically made up of:

^■ a series of anchoring cups, the external diameter of which varies discretely and incrementally, in order to adapt to the different acetabular cavities, the standard thickness of which is generally between 2 and 4 millimeters;

^■ two or three sizes of ball or joint head, but generally with a diameter of 22 and 28 millimeters, intended, as already said, to come to be fixed on the prosthetic rod inserted in the femur;

^■ and finally a series of mobile inserts, taking into account the external diameter of the ball and the variation in the internal diameter of the internal cavity of the anchoring cup.

In other words, in such a range, first of all the surgeon must choose the suitable mobile insert taking into account the chosen anchoring cup, as well as the diameter of the chosen ball. From a purely physical point of view, it is observed that the more the diameter of the respective contacting surfaces increases, the more the friction torque increases. As a result, more wear is generated at the level of the large joint, i.e. between the movable insert and the internal cavity of the anchoring cup, than at the level of the small joint, i.e. 'That is to say between the head or ball and the internal cavity of the mobile insert, on equivalent amplitudes of movement. In fact, notwithstanding the improved quality of the materials used, wear debris is generated which may lead to osteolysis which can lead to prosthetic failure. Another problem is inherent in the thickness of the mobile insert. In fact, if this thickness is too small, the ball or head which receives it is liable to cause the insert to break due to the stresses that the latter receives, typically by creep for example. As a corollary, if the thickness is too great, one is penalized at the level of the large articulation, that is to say the cooperation between the external surface of the insert and the internal cavity of the anchoring cup. In fact, the greater the external diameter of the insert, the greater its starting torque, linked to the friction torque of the surfaces involved and the mass of this mobile insert, which results in a contact of greater energy at the shrinkage of the mobile insert which can be detrimental in the long term and often observed.

Finally, cases of blockage of the large joint have also been observed, in particular by peri-prosthetic fibrosis or osteophytes.

The object of the present invention is to provide a range of joint implant systems which significantly overcome these various drawbacks.

DISCLOSURE OF THE INVENTION

To this end, the invention relates to a range of joint implant systems, said implant being of the type comprising:

^■ an anchoring cup in one of the elements of the joint in question, defining a smooth internal cavity of substantially hemispherical shape;

^■ an insert movable within the internal cavity of the anchoring cup, whose smooth outer surface is intended to cooperate by ball bonding with the internal cavity of the anchoring cup and in turn defining an inner cavity smooth, substantially hemispherical in shape;

^■ a head or bead, integral with a second element of the joint, spherical in shape, intended to be received in the internal cavity of the movable insert, and constitute a second ball joint. According to the invention, the ratio of the internal diameter of the internal cavity of the anchoring cup to the internal diameter of the internal cavity of the mobile insert, for all the elements of the range, is constant.

In other words, the ratio of the areas of the small joint to the large joint is constant for a chosen ball diameter. In fact, the respective diameters and surfaces are linked to each other by the classical and well-known relations of the calculation of a sphere, particularly truncated, with regard to the insert.

From which it follows that, whatever the chosen parameter (diameter or area), the constant character of the respective ratios is retained.

In other words, the practicing surgeon determines, after the patient's acetabulum has been reamed, the external diameter of the appropriate anchoring cup, in particular in order to conserve as much bone capital as possible. This determined anchoring cup will have a thickness such that it respects the aforementioned constant dimensional ratio, so as to reduce the friction torque of the large joint, and consequently further reduce the phenomena of dislocation, in addition to the phenomena of wear liable to to lead, as indicated above, to blockage of the joint and other risks of prosthetic failure mentioned above.

Advantageously, this ratio is between 1.1 and 3.

BRIEF DESCRIPTION OF THE FIGURES

Other characteristics and advantages of the invention will emerge clearly from the description which is given below, by way of indication and in no way limiting, with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation illustrating a dual mobility joint implant according to the prior art.

FIG. 2 is a series of sagittal sections of a range of articular implants in accordance with the invention, mainly illustrating the variation in the thickness, in particular of the outer cup. DETAILED DESCRIPTION OF THE INVENTION

As already indicated, Figure 1 shows the block diagram of a dual mobility joint implant according to the prior art.

Basically, this implant consists first of all of an anchoring cup (1), in the shape of a cap, intended to be fixed within a first element of a joint to be prosthesis (2), and for example , the acetabular cavity of a patient's pelvis as part of a hip prosthesis.

This anchoring cup is made of a rigid biocompatible material, for example of metal such as one-piece chromium-cobalt, or a chromium-cobalt composite with an added thickness of trabecular titanium, for example in order to lighten it. This anchoring cup defines an internal cavity of substantially hemispherical shape, defining a first internal surface (SI) of articulation.

This internal cavity of the anchoring cup is intended to cooperate and receive a mobile insert (3), also made of biocompatible material, and typically of high density polyethylene. This movable insert (3) also of substantially hemispherical shape, is therefore intended to be received in the internal cavity of the anchoring cup (1) to form a first ball joint called large joint. The external diameter of this movable insert (3) is therefore, except for the clearance, substantially equal to the internal diameter of the internal cavity of the anchoring cup (1).

This movable insert (3) also comprises an internal cavity, also of substantially hemispherical shape, and defining a second articulation surface (S2), called small articulation, said internal cavity being intended to receive and cooperate with a head or ball (4 ) of spherical shape, secured to another element of the prosthesis joint, in this case, to a femoral rod (5), inserted into the medullary cavity of the femur of the joint in question.

Conventionally, this ball (4) is mounted on a Morse taper located at the end of the neck (7) of the femoral stem (5), in a known manner. The femoral stem is typically made made of a rigid biocompatible material such as titanium, cobalt-chromium, stainless steel, etc.

In doing so, a possible double rotational movement is created according to a double ball joint connection, respectively of the movable insert (3) relative to the anchoring cup (1), and of the ball (4) relative to the mobile insert (3).

Advantageously, and to optimize the movement of the joint, and as a corollary to limit dislocation phenomena, the base of the movable insert is of flared shape defining a constriction (6), able to cooperate with the frustoconical shape of the neck (7) located at the upper end of the rod (5).

In a known manner, the dimensions of the anchoring cup (1) are inherent, on the one hand, to the joint considered, with the primary objective of conserving the patient's bone stock, and on the other hand, to the constraints that 'she is meant to endure. Conventionally in the case of a hip joint implant, the outer diameter of the anchoring cups of a range typically varies between 44 and 74 millimeters in 2 millimeter increments.

The thickness of the anchoring cup of the implants of the prior art is constant in a standard range, and therefore depending on the growth of the external diameter thereof, the articular surface (SI), that is to say of the internal surface of the internal cavity of the anchoring cup, is impacted according to this growth, as is the thickness of the mobile insert. Due to the increase in the thickness of the insert, the articulation surface (SI) increases, and therefore the frictional torque at this level increases; It follows that the wear of the prosthesis at this level also increases for large amplitude movements.

In the same spirit, two sizes of articular balls (4) are conventionally retained, for a hip prosthesis, respectively a diameter of 22 and 28 mm.

It is inferred that, as indicated above, with the implants of the prior art, in order to take account of the variation in the diameter of the anchoring cup (1), and of the diameter standard of the ball (4), the size of the movable insert will vary, and more precisely its external diameter, in contact with the articulation surface SI, de facto increasing its thickness.

According to the present invention, once the external diameter of the anchoring cup has been determined by the surgeon, which is a function of the state of the patient's acetabulum after milling and of the desired maximum conservation of bone stock, within the same range of such joint implants, the choice of insert is naturally deduced, and consequently that of the ball. More practically, for external diameters of the anchoring cup typically between 52 and 74 millimeters, a ball 28 millimeters in diameter will be preferred for the sake of limiting the friction torque at the surface (SI). Once this ball has been selected, there is no more choice as to the insert, the latter being unique for a ball of determined diameter. On the other hand, and taking into account this uniqueness, the choice of the anchoring cup in terms of thickness is dictated by the constant ratio sought from the invention of the internal diameter of the internal cavity of the anchoring cup, and in the species of the surface of the joint (SI), on the internal diameter of the mobile implant, and therefore in this case (S2), and typically between 1.1 and 3, advantageously close to 1.6 .

On the other hand, for external diameters of the anchoring cup less than 52 millimeters, a ball of 22 millimeters in diameter will be favored, then determining the choice of the second insert in the range of implants, the internal cavity of which is adapted to this diameter. ball. Here again, the choice of the anchoring cup in terms of thickness is directly inherent in this insert, again to respect the constant ratio of the invention.

In the example described of implants for a hip prosthesis, and according to the invention, the range considered comprises only two balls, respectively of diameter 22 or 28 millimeters, and corollary two movable inserts, depending on the diameter of the ball adopted.

In other words, taking into account, on the one hand, the mobile insert selected (itself dependent only on the diameter of the ball chosen), and on the other hand, the external diameter of the anchoring cup, determined by the acetabular environment observed by the surgeon, the latter is able to choose the most suitable anchoring cup for the desired result while respecting the ratio in accordance with the invention.

In this case, FIG. 2 shows a series of views in sagittal section of different cup / movable insert pairs in accordance with the invention, in which it can be observed that for a given movable insert, in this case suitable for a 28-millimeter diameter ball, the thickness of the anchoring cup increases with the increase in its external diameter, in order to respect the constancy of the ratio of diameters, respectively internal of the anchoring cup and internal of the insert. In other words, if the range of balls (4) is composed of 2 sizes, typically with a diameter of 22 millimeters and a diameter of 28 millimeters for a hip, there are for the range of inserts (3) only two sizes corresponding respectively to the sizes of the balls (4). In fact, we can observe in Figure 2, from left to right six anchor cups whose external diameter varies from 52 to 62 millimeters in discrete increments of 2 millimeters, and corollary, a single movable insert, suitable for a 28 millimeter ball.

The situation is strictly similar for anchor cups, the external diameter of which varies from 44 to 50 millimeters, with the difference that the diameter of the ball is this time of 22 millimeters, and that consequently, the insert placed implementation is adapted to this diameter of the ball.

With respect to such a ratio, the present invention aims to further significantly reduce the few prosthetic failures of dual mobility implants of the prior art. In fact, reducing the starting torque differential in the joint between the small and the large joint results in:

^■ on the one hand, the fact that when the prosthetic neck of the rod comes into contact with the mobile insert in the large deflections, the large articulation requires less energy to be put into action and therefore proves to be less damaging to the shrinkage of the mobile insert which is the weak point of dual mobility implants, and

^■ on the other hand, the external surface of the mobile insert is optimized so that, even in anchoring cups of large external diameter, the external surface of said mobile insert remains constant and reduced, thus limiting wear debris can lead to osteolysis and therefore prosthetic failure; the literature shows that the number of particles emitted in a hip joint depends, among other things, on said external surface of the mobile insert. As a corollary, due to the reduction in these friction torques, the wear phenomena, which inevitably appear notwithstanding the use of material of high hardness, are also reduced, thus leading to a reduction in debris, and therefore optimizing over time. the duration of such joint implants. One can therefore see the advantage of the present invention which, in addition to reducing the phenomena of dislocation on the one hand, and the genesis of debris on the other hand, economically makes it possible to reduce the number of elements belonging to a range joint implants, and logistically the reduction of stocks. In addition, from a patient safety point of view, the simplification of the number of joint implants avoids a number of operating errors, such as resulting from labeling errors or size compatibility errors between the mobile insert and the cup. anchor.

Claims

1. Range of joint implant systems, said implant being of the type comprising:

^■ an anchoring cup (1) in one of the elements of the joint (2) considered, defining a smooth internal cavity of substantially hemispherical shape;

^■ an insert (3), movable within the internal cavity of the anchoring cup (1), and the smooth outer surface of which is intended to cooperate by ball joint with the internal cavity of the anchoring cup (1) , and in turn defining a smooth internal cavity of substantially hemispherical shape;

^■ a head or ball (4), secured to a second element of the joint, of spherical shape, intended to be received in the internal cavity of the movable insert (3), and to form a second ball joint,

characterized in that the ratio of the internal diameter of the internal cavity of the anchoring cup (1) to the internal diameter of the internal cavity of the mobile insert (3), for all the elements of the range, is constant , whatever the diameter of the ball (4) selected.

2. Range of joint implant systems according to claim 1, characterized in that the ratio is between 1.1 and 3, advantageously close to 1.6.

3. Range of joint implant system according to claim 1 or 2, characterized in that the thickness of the mobile insert G remains constant for a given ball size, regardless of the anchoring cup used.

4. Range of joint implant systems according to claims 1 to 3, characterized in that the movable insert (3) comprises at its base a constriction (6) intended to cooperate with the second element of the joint .