EP2205187A2

EP2205187A2 - Femoral component for a hip prosthesis, and total hip prosthesis comprising same

Info

Publication number: EP2205187A2
Application number: EP08841513A
Authority: EP
Inventors: Levon Doursounian; Pascal Hourtoulle; Philippe Metge
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-10-17
Filing date: 2008-10-16
Publication date: 2010-07-14
Also published as: WO2009053650A2; WO2009053650A3; FR2922436B1; FR2922436A1

Abstract

Femoral component (4) for a hip prosthesis, comprising a distal part (8) intended to be inserted into the medullary cavity (15) of the femur (16) of a patient, and a cervical part (11) which comprises or which can support a neck (12) at the end of which a spherical head (5) is placed or can be placed, characterized in that said distal part (8) and said cervical part (11) are made up of two separate pieces, in that said distal part (8) comprises, at its proximal end (9), an outgrowth forming a pivot (10), and in that said cervical part (11) comprises means for assembling the cervical part (11) on the pivot (10) of the distal part (8), maintaining the possibility of free relative rotation of the cervical part (11) around the pivot (10) after implantation of the prosthesis. Total hip prosthesis of which the femoral component is of the above type.

Description

Femoral hip prosthesis element, and total hip prosthesis comprising it.

The invention relates to orthopedic surgery, and more specifically to the femoral elements of hip prostheses.

Hip prostheses are implants commonly used in human surgery to treat fractures of the upper end of the femur, as well as advanced rheumatic diseases of the hip. They may be femoral only, that is to say have only one element intended to replace the upper end of the femur and provided at its end with a spherical head intended to fit into the natural acetabulum of the acetabulum. patient. They can also be total, that is to say include, in addition to the femoral component, an artificial acetabulum that the surgeon implants in the patient's iliac bone, instead of the natural acetabulum.

The femoral element comprises in the usual way:

a rod of generally rectilinear shape with a section most often oval or parallelepipedic to avoid its rotation in the medullary cavity of the femur; its distal portion is anchored in the femoral diaphysis after a more or less complete resection of the upper end of the femur and a conformation adapted to the medullary cavity of the femur by the surgeon, and which extends at its proximal end by an inclined neck of the femur. an angle of 135 ° (most often, the choice of this value may be different depending on the morphology of the patient) relative to the general orientation of the rod;

and a head of spherical general shape placed at the end of the neck.

Depending on the case, the stem and the head may be two parts of the same monobloc element, or be two initially separated elements, the neck then being terminated by a Morse taper on which the head is placed during the installation of the prosthesis.

A frequent complication of the use of hip prostheses is the possibility of dislocation of the joint. Indeed, the movements of the prosthesis-bearing member are transmitted to the prosthesis, and, in particular, the axial rotation movements of the limb cause axial rotation of the neck of the prosthesis. When rotary movements are important, dislocation of the prosthetic head can occur. This is particularly common in elderly, bedridden or demented patients.

Various configurations of femoral or total prostheses have been developed to limit this risk of dislocation. However, they lead to the realization of relatively complex design prostheses and / or to be finely adapted to the exact morphology of the patient to be really effective.

The object of the invention is to propose a new design of a hip prosthesis femoral element, which considerably reduces the risk of dislocation of the joint, while remaining of a relatively simple and standardized configuration. in order to facilitate its choice and placement by the surgeon.

To this end, the subject of the invention is a hip prosthesis femoral element, comprising a distal portion intended to be inserted into the medullary cavity of a patient's femur, and a cervical part comprising or capable of supporting a cervix at the hip. end of which is placed or can be placed a spherical head, characterized in that said distal portion and said cervical portion are constituted by two separate parts, in that said distal portion has at its proximal end a pivot-forming protrusion, and in that said cervical portion comprises means for assembling the cervical portion on the pivot of the distal portion retaining the possibility of free relative rotation of the cervical portion around the pivot after implantation of the prosthesis.

Said means for assembling the cervical portion on the pivot of the distal portion may comprise a longitudinal perforation formed in the cervical portion and allowing it to fit onto the pivot.

Said pivot may be cylindrical.

The femoral element may include a ring separating the pivot and the cervical portion promoting their sliding during their relative rotations.

It may comprise means preventing or limiting the relative longitudinal sliding of the pivot and the cervical portion.

Said means preventing or limiting the relative longitudinal sliding of the pivot and the cervical portion may be constituted by a cap attached to the proximal end of the pivot. The pivot-shaped outgrowth and the proximal end of the distal portion may have angulation relative to the longitudinal axis of the distal portion.

The pivot can then have an angulation of 5 to 20 ° with respect to the longitudinal axis of the distal portion.

The femoral element may comprise a stud on one of the proximal end of the distal portion and the lower face of the cervical portion and a groove in which is inserted the stud, formed in the other of the proximal end of the distal portion and the underside of the cervical portion.

The invention also relates to a total hip prosthesis, comprising a femoral element and an artificial acetabulum for receiving a spherical head of the femoral component, characterized in that said femoral element is of the above type.

As will be understood, the invention consists in producing the stem of the femoral component of a hip prosthesis in two parts. The first part is the distal part intended to be inserted into the medullary cavity of the femur. It is of a conventional design, except at its proximal end which is constituted by a rotationally symmetrical pivot element. On this pivot is placed, free in rotation around him, the second part of the stem, which is a cervical piece generally comprising:

a central cavity in which the pivot is inserted;

and a neck intended to carry, in a fixed or removable manner as is conventional, the spherical head of the femoral element.

In this way, when the prosthesis carrying member performs an axial rotational movement, this rotation is, as is normal, transmitted to the distal portion of the femoral stem of the prosthesis which is secured to the femur. But if the neck of the prosthesis and the spherical head that it carries resistance during this movement, their own rotation can be interrupted. In contrast, the axial rotational movement of the limb and the distal portion of the femoral stem can continue, since the pivot (and thus the femoral stem) can rotate freely within the cervical part. This prevents dislocation of the joint. The invention is applicable both to total hip prostheses and prostheses limited to the single femoral component. It would also be adaptable to veterinary surgery.

The invention will be better understood on reading the description which follows, given with reference to the following appended figures:

- Figure 1 which shows schematically and axially the right hip of a patient equipped with a total hip prosthesis conventional neutral position of the lower limb;

- Figure 2 shows the same hip as Figure 1, equipped with the same prosthesis, the latter having a primer dislocation;

- Figures 3 and 4 which show schematically in perspective the two parts of a femoral hip prosthesis element according to the invention, in the separated state (Figure 3) and in the assembled state (Figure 4);

- Figure 5 which shows in front of and in section a human femur equipped with a hip prosthesis femoral component according to the invention;

FIGS. 6 and 7 which correspond to FIGS. 1 and 2 in the case where a femoral hip prosthesis element according to the invention is used;

- Figure 8 which shows schematically in longitudinal sectional view another variant of the invention;

- Figure 9 which shows schematically the femoral part of another variant of prosthesis according to the invention.

Figures 1 and 2 very schematically illustrate the manner in which dislocation of the hip can occur with a conventional rigid femoral prosthesis, representative of the prior art that the invention aims to improve.

FIG. 1 represents the articulation, in a neutral position of the lower limb represented by the position of the foot 1 with respect to the pelvic bone 2 in which is placed an artificial acetabulum 3 (in the case where, as shown, an total hip prosthesis). The femoral element 4 conventionally comprises a spherical head 5 inserted in the acetabulum 3 and mounted on the neck 6 rigidly connected to the one-piece rod 7 inserted in the femur of the patient. In this neutral position, the spherical head is well centered inside the acetabulum 3.

Figure 2 shows the same joint after a movement of the lower limb with a strong rotational component. We see that rigidity of the femoral element causes that if it encounters any obstacle during the rotation, by leverage there is the possibility that the head 5 out of its nominal location in the acetabulum 3. This may, in the end result in complete dislocation of the joint.

Figures 3 and 4 show very schematically the general principle of constitution of the stem of a hip prosthesis femoral component 4 according to the invention. This stem consists of two parts initially separated as in FIG.

- A distal portion 8 shown cylindrical in Figures 3 and 4, but may in fact have any conventional form making it suitable for insertion and maintenance in the medullary cavity of the femur; at its proximal end 9, it has a protrusion forming pivot 10, cylindrical in the example shown;

- And a part 11 shown cylindrical in Figures 3 and 4 but can take any external form compatible with its function, which is to form the cervical portion of the femoral element; for this purpose, it has, connected at its proximal end, a neck 12, in the form of a Morse cone in the example shown, and on which is intended to be connected the spherical head 5 (not shown) of the femoral element 4 ; it should be understood that this neck 12 may be integral with the cervical portion 11, or be attached thereto during assembly of the femoral component 4 for greater modularity thereof.

The cervical portion 11 is provided with a central longitudinal perforation 13 allowing the cervical portion 11 to fit onto the pivot 10 of the distal portion 8, with a possibility of relative free rotation, according to the arrow 14, of the cervical portion 11 around the pivot 10. The cervical portion 11 then rests on the proximal flat end 9 (in the example shown) of the distal portion 8. This possibility of a relative free rotation of the cervical portion 11 around the pivot 10 is retained after implantation of the prosthesis.

Figure 5 shows schematically how the femoral element 4 according to the invention can be implanted in the medullary cavity 15 of the femur 16 of a patient, previously prepared by the surgeon in a conventional manner to allow this implantation with or without cement. In the example shown, the distal portion 8 has a substantially cylindro-conical shape, tapered in its portion distal 17, but any other conventional shape for the distal parts of femoral elements would be usable. The upper end 18 of the femur 16 has, in the example shown, been resected only partially, foraging a cavity 19 allowing a relative rotation14 without obstacle of the cervical portion 11 around the pivot 10. Of course , resection of the end 18 more or less important than represented would be possible, at the option of the surgeon, depending in particular on the dimensions of the femoral element 4 and the state of the end 18.

With the conformation of the femoral element 4 according to the invention, it is understood that a rotation of the femur 16 along the arrow 14 is transmitted to the distal portion 8 of the element 4 since it is integral with it, but is not not necessarily transmitted to the cervical portion 11 which can remain motionless, in particular if the movement of the femur 16 could tend to cause the spherical head 5 to come out of the femoral component 4 out of the acetabulum 3, if this head 5 was rigidly connected to the distal portion 8 of the femoral component 4 as is the case in Figures 1 and 2, representative of the prior art.

Figures 6 and 7 correspond to Figures 1 and 2, in the case of the use of a femoral element 4 according to the invention. It is seen that, this time, the rotation of the lower limb carrying the femoral element 4 was carried out without significant displacement of the cervical portion 11, therefore the neck 12 and the head 5 which are integral therewith. This rotation was only reflected by a rotation of the pivot 10 in the perforation 13 of the cervical portion 11. Under these conditions, the head 5 has not made movements that could have made it tend to leave the acetabulum 3, and dislocation of the joint is thus avoided.

The materials that can be used to form the various parts of the femoral component 4 according to the invention are biocompatible materials, in particular ceramics, metals and / or polymers, which can conventionally be used in hip prostheses. The essential point in the context of the invention is that they have, due to their nature and / or the preparation of their surfaces, sufficiently low friction coefficients at the interface between the distal portion 8 and the cervical portion 11 to ensure easy rotation of one relative to the other.

FIG. 8 represents schematically (without the collar 12) a variant of the invention, in which the contact between the pivot 10 and the cervical part 11 is not done directly, but by means of a ring 20, made by exam- polyethylene or a self-lubricating material such as PTFE or graphite. This configuration ensures a very good slip between the pivot 10 and the cervical portion 11 during their relative rotations. It can also be the part that experiences the greatest wear when using the prosthesis, and whose replacement, if it is necessary later in the patient's life, will be easier and less expensive than the replacement of the others. parts 8, 11 of the femoral component 4.

Also, this variant has another improvement (which may be present regardless of the previous) of providing a cap 21 at the end of the pivot 10, fixed by screwing, fitting or any other method. This cap 21 makes it possible to avoid or limit the longitudinal relative movements of the distal portion 8 and of the cervical portion 11 of the femoral component 4 to a very small amplitude. Other means that are functionally equivalent to this cap 21 may to be substituted.

In the examples described and shown, the pivot 10 is of cylindrical shape, but it is obvious that it could take any other form, in particular tronconic, having a symmetry of revolution allowing the relative rotation of the cervical portion 11 around him. It may also be expected that it comprises at its base a spherical cap-shaped portion on which rest the lower portion of the cervical portion 11, which would itself be correspondingly shaped. Such configurations make it possible to strengthen the base of the pivot 10, and thus to limit the risks of shear failure at its level during the use of the prosthesis.

In general, it should be understood that any means allowing the cervical portion 11 to be assembled on a pivot-shaped outgrowth 10 of the proximal end of the distal portion 8 with the possibility of relative free rotation of the two parts 8, 11 after implantation of the prosthesis would be in accordance with the invention.

By way of indication, an example of sizing of a femoral element 4 according to the invention made of chromium-cobalt alloy or stainless steel would be: overall length of the distal portion 8 and its pivot 10: 140 mm, including 35 mm for the pivot 10, this dimension also corresponding substantially to the length of the cervical portion 11;

- Pivot diameter 10: 10 mm;

diameter of the distal portion 8: 25 mm at its portion proximal to the base of the pivot 10, and 12 mm at its distal portion 17;

- outer diameter of the cervical part: 25 mm;

- length of the neck 12 including the Morse taper supporting the spherical head 5: 35 mm.

Also, in an advantageous variant of the invention shown in Figure 9, the pivot 10 and the proximal end 9 have an angulation α relative to the longitudinal axis of the distal portion 8 of the prosthesis. In this way, it is possible to automatically center the cervical portion 11 under the effect of the stresses to which the prosthesis is subjected. This angulation α of the pivot 10 is preferably of the order of 5 to 20 ° with respect to the longitudinal axis of the distal portion 8.

One can also provide as shown in Figure 9 (and this is also valid for the variant of Figures 1 to 8) to have a stud 22 on the proximal end 9 of the distal portion 8 of the prosthesis.

The stud 22, in cooperation with a corresponding groove formed in the lower face of the cervical portion 11 of the prosthesis, acts as a guiding and abutment function during the relative rotation of the distal portion 8 and the cervical portion 11. respective positions of the stud 22 and the groove in which it is inserted could, of course, be reversed with respect to the configuration described and shown.

Claims

A hip prosthesis femoral component (4) having a distal portion (8) for insertion into the medullary cavity (15) of a patient's femur (16) and a cervical portion (11) comprising or capable of supporting a neck (12) at the end of which is placed or can be placed a spherical head (5), characterized in that said distal portion (8) and said cervical portion (11) are constituted by two separate pieces, in that said distal portion (8) has at its proximal end (9) a pivot-shaped outgrowth (10), and in that said cervical portion (11) comprises means for assembling the cervical portion (11) on the pivot (10) of the distal portion (8) retaining the possibility of a relative free rotation of the cervical portion (11) around the pivot (10) after implantation of the prosthesis.

2. Hip prosthesis femoral component (4) according to claim 1, characterized in that said means for assembling the cervical portion (11) on the pivot (10) of the distal portion (8) comprise a longitudinal perforation (13) formed in the cervical portion (11) and allowing its fitting on the pivot (10).

3. hip prosthesis femoral component (4) according to claim 1 or 2, characterized in that said pivot (10) is of cylindrical shape.

4. Femoral component (4) of hip prosthesis according to one of claims 1 to 3, characterized in that it comprises a ring (20) separating the pivot (10) and the cervical portion (11) promoting their sliding during their relative rotations.

5. Femoral element (4) of hip prosthesis according to one of claims 1 to 4, characterized in that it comprises means preventing or limiting the relative longitudinal sliding of the pivot (10) and the cervical portion (11). .

Hip prosthesis femoral component (4) according to claim 5, characterized in that said means preventing or limiting the relative longitudinal sliding of the pivot (10) and the cervical part (11) consist of a cap (21). attached to the proximal end of the pivot (10).

Hip prosthesis femoral component (4) according to one of claims 1 to 6, characterized in that the pivot-shaped protrusion (10) and the proximal end (9) of the distal portion (8) have a angulation with respect to the longitudinal axis of the distal portion (8).

Hip prosthesis femoral component (4) according to claim 7, characterized in that the pivot (10) has an angulation (α) of 5 to 20 ° with respect to the longitudinal axis of the distal portion (8). .

9. Femoral element (4) of hip prosthesis according to one of claims 1 to 8, characterized in that it comprises a stud (22) on one of the proximal end (9) of the distal portion ( 8) and the underside of the cervical portion (11) and a groove in which the stud (22) engages in the other of the proximal end (9) of the distal portion (8) and from the underside of the cervical portion (11).

10. Total hip prosthesis, comprising a femoral component (4) and an artificial cotylate (3) for receiving a spherical head (5) of the femoral component (4), characterized in that said femoral component (4) is of the type according to one of claims 1 to 9.