FR2827155A1 - Hip prosthesis femoral shank has pairs of cavities in inner face of metaphysis section - Google Patents

Abstract

The femoral shank (1) of the prosthesis, having a neck extension (3) to receive a head engaging with a cotyloid cup, has a series of cavities (8) about 0.5 mm deep in the inner face (5) of its metaphysis section. The cavities are in pairs, located symmetrically on either side of the inner face's median line, and make contact with the inner cortex of the femur when implanted. The sides of the prosthesis shank have chevronshaped transverse grooves (9) with their points (10) lying on a curved line at a tangent to the axis of the prosthesis neck and the main axis of the shank.

Description

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The invention relates to a new femoral rod for total hip prosthesis.

In known manner, a hip prosthesis basically consists of a femoral stem, intended to be inserted into the medullary canal of the femur of the hip joint considered, and of a prosthetic neck surmounted by a head, making or not an integral part of the rod, and intended to cooperate at its free end with a friction core, most often made of polyethylene, ceramic, or even metal, and itself intended to cooperate with the acetabular cavity of the bone iliac of the hip considered, at the level of which a cup of appropriate shape is previously inserted or put in place.

A large number of hip prostheses are known today and available on the market.

Among the difficulties encountered in the implementation of such prostheses, there are in particular the risks of loosening of the femoral stem. We also quite frequently observe peaks of stress, exerted in particular on the internal cortex of the femur, by the femoral stem, causing intense pain in the prosthetic patient. Such stress peaks are also likely to cause bone changes, risking causing pain for the patient, in addition to defects in the attachment of the rod within the spinal canal.

In order to overcome this last drawback, it has been observed that it is advisable to give the femoral stems the most anatomical profile possible in order to, if not cancel these peaks of stress, at least to lessen their effects.

However, the risks of loosening remain, which can cause significant damage to the joint.

In order to combat these loosening phenomena, different solutions have been proposed. Among these, there is in particular the principle of optimization of the so-called secondary fixation, that is to say the implementation of physical characteristics capable of promoting bone regrowth at the level of the stem proper.

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 Among the solutions conforming to this objective of bone regrowth, it has for example been proposed to coat the rod in whole or in part with hydroxyapathite. It has also been proposed, in order to increase the contact surface, to provide the rod with a number of grooves, generally oriented more or less parallel to the axis of the rod. In doing so, not only does it increase the contact surface of the rod with the bone, but, if necessary, the replacement of the rod is possibly favored when required, without causing excessive damage to the femur.

Although optimizing bone regrowth and therefore secondary fixation, it has been observed that these grooves, called longitudinal grooves, prove to be insufficient in the face of the risks of sinking of the prosthesis, and of its corollary loosening.

Such rod penetrations have crippling consequences, namely first of all the loosening of the rod, capable of causing pain for the patient, as well as irreversible damage within the bone cavity. In addition, they may also induce dislocation phenomena by cam effect.

The object of the present is to propose a femoral stem of the type in question, making it possible both to reduce the risks of loosening, but also to cancel the risks of sinking.

Thus, the invention relates to a femoral stem for hip prosthesis, intended to be buried in the femur to be prosthetic, extending by a prosthetic neck whose end receives a head, intended to cooperate with a friction core , itself received in the acetabular cavity of the iliac bone of the coxofemoral joint considered.

According to the invention, the metaphyseal part of the rod has at its internal face a plurality of hollow orifices. In doing so, not only does it increase the contact surface between the rod and the bone, increasing the reception areas of the newly formed bone, and thus, promoting the secondary fixation mentioned above, but by supporting this orifice hollow against the anterior cortex of the femur, we fight against the phenomena of sinking of the stem that we usually observe.

According to a characteristic of the invention, these hollow orifices are distributed in pairs, symmetrically on either side of the median line of the internal face considered.

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 Furthermore, the distribution of these recesses extends substantially between the central region of the rod up to the upper edge of the rod, and more precisely up to the vicinity of the collar, coming to bear, in known manner, on the Merckel spur, also known as calcar.

In addition, the hollows are in contact with the internal cortex of the femur in the metaphyseal and metaphyso-diaphyseal zone, increasing the reception areas of the newly formed bone, and therefore promoting the anchoring of the internal face of the stem femur.

According to another advantageous characteristic of the invention, the rod has on its lateral faces, that is to say the faces defined as being directed towards the front and towards the back of the patient, grooves oriented substantially transversely with respect to the axes of the stem, respectively longitudinal axis and axis of the prosthetic neck.

sur une ligne courbe venant tangenter respectivement l'axe du col et l'axe de la tige. These transverse grooves can advantageously have a chevron shape, and therefore have an inflection point, all of these inflection points being located

on a curved line tangent respectively to the axis of the neck and the axis of the rod.

ZD According to another characteristic of the invention, the prosthetic neck has a reduced section asymmetrically with respect to the axis of said neck, so as to optimize the deflection of the rod for adduction movements.

Finally, the rod has on its internal and external faces, substantially between the median zone and its lower end, a longitudinal groove, intended to increase the contact surface of the rod with the bone tissue, and therefore optimize the secondary fixation at this level. , thus optimizing the stabilization in rotation of said rod.

The manner in which the invention can be implemented and the advantages which ensue therefrom will emerge more clearly from the example of embodiment which follows, given by way of indication and without limitation in support of the appended figures.

Figure 1 is a schematic perspective view seen from three quarters before the rod according to the invention.

Figure 2 is a perspective view of the rear three quarters of the femoral stem according to the invention.

Figure 3 is a view of the internal face of the rod according to the invention.

Figure 4 is a sagittal view of the rod.

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Figure 5 is a view of the outer face.

Figure 6 is a detail view of the internal face.

Figure 7 is a detail view of prosthetic neck of the rod according to the invention.

Figure 8 is a detail view of the internal face of the rod according to the invention.

Figure 1 shows schematically, as already said, a femoral stem for hip prosthesis according to the invention. This femoral stem (1) is extended at its proximal end by a prosthetic neck (3). In known manner, the prosthetic neck (3), connected to the rod (1) by a zone (2) is intended to protrude from the femur to be prosthetic and comprises, in the present case, a Morse taper, capable of receiving a spherical head, most often made of stainless steel, crome-cobalt alloy, or ceramic, and intended in turn to cooperate with the acetabular cup placed at the level of the coxo-femoral joint, via 'a friction core.

The prosthetic neck (3) has symmetrical lateral flats at its base, allowing an increase in angular travel, thus aiming to limit the risk of contact of the neck with the edge of the acetabulum, and therefore, to reduce the risks of dislocation, but also the phenomena of bimetallism. Such phenomena of bimetallism are well known in the matter and induce inflammation of the tissues in the vicinity of which they occur, detrimental to the comfort of the patient and to the holding of the prosthesis.

According to a characteristic of the invention, the neck (3) has a reduced section asymmetrically, as can be seen in FIG. 7. In fact, the internal face (14) is more machined than the face external (15) of said neck, relative to the axis P of the prosthetic neck.

In doing so, the displacement of the rod is improved for the adduction movements, while retaining a larger section of the neck, limiting the risks of mechanical breakage of said neck. At the same time, the cam effects, which may cause dislocation, are further limited, as well as the risks of bi-metallism, which may result from contact of the neck with the edge of the acetabular cup at which it is intended to s 'insert.

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 According to a characteristic of the invention, the rod (1) has at its internal face (5) a plurality of hollow orifices (8), distributed in the present case in pairs, on either side of the midline of said internal face (5).

These recessed orifices can be better viewed in FIG. 6, representing a detail view of this internal face. They adopt a noticeable form of fish scale.

These recessed orifices have a typical depth of 0.5 mm. However, and advantageously, this profile is not symmetrical, as can be seen in FIG. 8. Indeed, the distance separating the bottom (16) from the hollow of the envelope of the internal face (5) of the rod in the direction of the lower end of the latter is carried out in a relatively gentle slope (17), so as to favor the extraction of the rod if necessary, and as a corollary, to oppose to its depression.

These hollows provide a greater contact surface with the bone, and therefore allow the bone anchoring to be optimized at this level, bone anchoring coming from the internal cortex, against which the internal face (5) of the femoral stem.

This bone regrowth not only makes it possible to reduce the risks of loosening, but also to limit, if not to cancel the risks of sinking of the rod inside the femur, and therefore the risks of loosening which may result therefrom. medium and long term, as well as the risks of dislocation.

According to another characteristic of the invention, these hollows are distributed in pairs, as can be observed, both in FIG. 1 and in FIG. 6.

These pairs of hollow orifices extend between the median zone of the rod and the epiphyseal zone, and in particular up to the vicinity of the collar (4), which comes to bear on the cutting face of the neck of the femur after ablation. of the latter (Merckel spur).

Furthermore, according to another characteristic of the invention, the rod has, always at the level of the internal face (5), a longitudinal groove (11) extending between the median zone and the lower end of the rod, and intended, given the bone regrowth it is likely to promote in this place, to stabilize the rotating rod.

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 According to another characteristic of the invention, the rod also has, at its lateral faces (7), grooves oriented substantially transversely relative to the main axis X of the rod.

sont rectilignes, les rainures immédiatement adjacentes présentent la forme de chevron i (9), présentant un point d'inflexion (10), ainsi qu'on peut bien l'observer sur les figures 1 et 4. Plus précisément, l'ensemble des points d'inflexion des chevrons est localisé sur une même courbe, venant tangenter l'axe P du col prothétique d'une part, et l'axe X de la tige d'autre part. Le rayon de courbure de cette courbe est compris entre 65 et 80 mm en fonction de la taille de la tige. En outre, l'angle des chevrons est voisin de 138 . More specifically, if the grooves at the proximal end of the rod

are rectilinear, the immediately adjacent grooves have the shape of a chevron i (9), having an inflection point (10), as can be seen in FIGS. 1 and 4. More precisely, all of the inflection points of the rafters is located on the same curve, coming to tangent the axis P of the prosthetic neck on the one hand, and the axis X of the rod on the other hand. The radius of curvature of this curve is between 65 and 80 mm depending on the size of the rod. In addition, the angle of the rafters is close to 138.

These chevron grooves (9) have the function of increasing the reception surface of the bone regrowth, and of limiting the risks of loosening of the rod, by development of the contact surface with the bone tissue, as well as of limit the risks of sinking of the rod, taking into account their orientation substantially perpendicular to the direction of the forces undergone by the rod.

Advantageously, the lateral faces (7) of said rod also have, at the level of the lower portion of the rod, longitudinal grooves (12), also participating in the secondary fixation, and this, in a known manner, and participating in the stabilization in rotation of the rod.

Finally, the rod has at the external face (6) a longitudinal groove (13), extending from the lower end of the rod until substantially at the level of the metaphysso-diaphyseal zone. This groove (13) performs substantially the same function as that of the groove (11) formed on the internal face (5).

It is therefore understandable the interest of the femoral stem according to the invention, in so far as while preserving the comfort of the patient, it limits the risks of loosening, as well as the risks of sinking.

Claims (12)

 CLAIMS 1. Femoral stem for hip prosthesis, intended to be buried in the femur to be prosthetic, extended by a prosthetic neck (3), the end of which receives a head, intended to cooperate with a friction core, itself received in the acetabular cavity of the iliac bone of the coxofemoral joint considered, characterized in that the metaphyseal part of the rod has at its internal face (5) a plurality of hollow orifices (8). 2. Femoral stem for hip prosthesis according to claim 1, characterized in that the hollow orifices (8) are distributed in pairs, symmetrically on either side of the midline of the internal face (5). 3. Femoral stem for hip prosthesis according to one of claims 1 and 2, characterized in that the hollow orifices (8), when the stem is in place within the femur, come into contact against the internal cortex of said femur . 4. Femoral stem for hip prosthesis according to one of claims 1 to 3, characterized in that the recesses are substantially distributed between the central region of the stem up to the vicinity of the flange (4) of the stem, coming to take support on the cutting face of the neck of the femur after removal of the latter. 5. Femoral stem for hip prosthesis according to one of claims 1 to 4, characterized in that the depth of the hollow orifices (8) is close to 0.5 millimeter. 6. Femoral stem for hip prosthesis according to one of claims 1 to 5, characterized in that the profile of the hollow orifices (8) is asymmetrical, the

 distance separating the bottom of the hollow of the envelope from the internal face of the rod in Z: D direction of the lower end taking place on a relatively gentle slope. 7. femoral stem for hip prosthesis according to one of claims 1 to 6, characterized in that the prosthetic neck (3) has an asymmetrically reduced section (14,15) relative to the axis P of said neck, so as to optimize the deflection of the rod for adduction movements. <Desc / Clms Page number 8> 8. Femoral stem for hip prosthesis according to one of claims 1 to 7, characterized in that it has on its lateral faces (7), respectively the faces defined as being directed towards the front and towards the back of the patient, grooves (9) oriented substantially transversely to the axes (X, P) of the stem. 9. Femoral stem for hip prosthesis according to claim 8, characterized in that at least part of the transverse grooves (9) have a chevron shape.  10. Femoral stem for hip prosthesis according to claim 9, characterized in that the set of inflection points (10) defined by the rafters is located on a curved line coming respectively to tangent the axis P of the prosthetic neck (3 ) and the main axis X of the rod. 11. Femoral stem for hip prosthesis according to one of claims 1 to 10, characterized in that it has a longitudinal groove (11) on its internal face (5) extending substantially between the median zone and the end. bottom of the rod. 12. Femoral stem for hip prosthesis according to one of claims 1 to 11, characterized in that it has a longitudinal groove (13) on its external face (6), extending substantially between the lower end of the stem and metaphysso-diaphyseal area.