FR2896984A1 - Hip prosthesis for human body, has insert comprising lateral face including base with diameter larger than that of ring`s base, where axial pressure is exerted on insert to enlarge slit for laterally expanding ring against acetabulum`s wall - Google Patents

Abstract

The prosthesis (PR) has a ring (1) inserted into an acetabulum (4) and including a conical inner face (5) with a small base (6). An insert (8) has a base (9) and a conical outer lateral face (10) comprising a small base (11) with a diameter larger than that of the base (6). Difference between the diameters determines a height of driving course of the insert so that the base (9) stops with the acetabulum`s base. An axial pressure is exerted on the insert to reduce the height to zero and enlarge a lateral slit (2) of the ring for laterally expanding the ring against an acetabulum`s wall. An independent claim is also included for a method of pre-mounting a prosthesis outside a human body.

Description

The present invention relates to an acetabular prosthesis. She

  is particularly, but not exclusively, applicable to the cementless placement of a hip prosthesis.

  In general, alteration of the hip joint has several causes such as cartilage wear, osteoarthritis, rheumatic disease, necrosis ...

  This alteration can lead to pain of increasing intensity, various localization and stiffness. A hip prosthesis is a cure for this alteration.

  The hip joint is composed of two parts: the acetabulum, articular part of the pelvis and the upper end of the femur, the head and the cervix. 25 It is these parts that are replaced during the installation of a hip prosthesis respectively on the one hand by a cup having externally a globally hemispherical surface and internally a concave housing and, on the other hand, by a femoral ball and a rod.

  There are two main techniques for fixing such prostheses: by means of a surgical cement such as an acrylic polymer, by axial impact, hard-rubbing depression and stabilization by holding pressure and then secondary bone regrowth, the contact zone. the bone and the prosthesis being treated for this purpose. Before placing a prosthesis in a bone, the surgeon must prepare the medullary cavity of this bone so as to give it a shape complementary to that of the prosthesis.

  However, regarding the acetabulum, the thickness of the bone is not always sufficient to allow a borehole by milling a circular cavity having a radius which will allow a known cup to come into contact with the bone on a bone. portion of surface large enough to ensure a good implementation. In this case, the conventional prostheses fixed by impact can be reinforced by screws which have the disadvantage of removing bone material thus weakening the bone.

  The object of the invention is to solve these disadvantages by proposing a prosthesis that makes it possible to exert a holding pressure that is both axial and lateral.

  For this purpose, it proposes an acetabular prosthesis comprising two parts: a ring comprising a lateral slot, this ring having an outer face substantially complementary to that of the acetabulum cavity and a frustoconical inner face comprising a small base and a large base; this ring fitting into the cavity, an insert having a bottom of shape substantially complementary to that of the bottom of the acetabulum cavity and a frustoconical outer side face, of conicity substantially equal to that of the frustoconical inner face of the ring, said frustoconical outer side face having a small base of diameter substantially greater than that of the small base of the ring, the difference between the diameters of the small bases determining a height corresponding to the insertion stroke of the insert so that its bottom comes into abutment with the bottom of the cavity, axial pressure to reduce to -3- z ro said height thereby causing a widening of the slot of the ring and a lateral expansion of the ring against the wall of the cavity.

  The operation is as follows: The small base of the insert is brought into abutment against the frustoconical inner face of the ring, the frustoconical inner face of the ring and the frustoconical outer side face of the insert being parallel. The difference between the diameters of the small bases determines a height corresponding to the insertion stroke of the insert so that its bottom comes into abutment, possibly under pressure, with the bottom of the cavity. An axial pressure is then exerted on the insert to reduce to zero said height and cause expansion of the slot of the ring and thus a lateral expansion of the ring against the wall of the cavity.

  It should be noted that the ring and the insert may be introduced separately and successively into the acetabular cavity or be pre-assembled respecting the principle of lateral expansion of the ring.

  Once the lateral expansion achieved, the small bases can be located in the same plane. According to one variant, the small bases may not be located in the same plane.

  Of course, the acetabular cavity can be milled to the diameter of the ring.

  The inner face of the insert may receive a piece forming a housing adapted to receive a femoral ball.

  Said part may be metal or polyethylene or ceramic.

  According to a variant, the inner face of the insert may form a housing, for example spherical, adapted to receive a femoral ball. -4The frustoconical outer side face of the insert may comprise a thread complementary to a tapping located on the inner face of the ring. Locking means after screwing the insert into the ring may be provided.

  The frustoconical outer side face of the insert may comprise notches.

  The frustoconical inner face of the ring may comprise notches, complementary or not, notches located on the frustoconical outer side face of the insert.

  The materials used for the ring and the insert may be identical or different. The ring may be essentially metallic or not. The insert may be essentially metallic or not. The metals used may be, for example, stainless steel or titanium.

  The prosthesis according to the invention may be at least partially covered with a material such as hydroxyapatite and / or have a surface state allowing a construction by bone regrowth (osteoinduction).

  According to a first advantage, the prosthesis according to the invention may allow contact under pressure on the entire cavity.

  According to a second advantage, because of the axial and lateral orientation of the pressure forces, the prosthesis according to the invention can be fixed firmly even when the radius of the cavity is small.

  Embodiments of the invention will be described hereinafter, by way of nonlimiting examples, with reference to the accompanying drawings in which: Figure 1 is a cross section of a prosthesis according to the invention; Figure 2 is a view in the front plane of Figure 1;

  Figures 3a to 3c are schematic representations of the operation of the prosthesis of Figures 1 and 2; Figure 4 is a view in the frontal plane of a second prosthesis according to the invention.

  The example of prosthesis PR illustrated in FIGS. 1, 2 and 3a to 3c comprises two parts: a ring 1 having a lateral slot 2, this ring having an outer face 3 substantially complementary to that of the acetabular cavity 4, for example spherical and a frustoconical inner face 5 comprising a small base 6 and a large base 7, this ring fitting into the cavity 4, an insert 8 having a bottom 9 of shape substantially complementary to that of the bottom of the acetabular cavity, for example spherical, and a frustoconical outer lateral surface 10 of conicity substantially equal to that of the frustoconical inner face 5 of the ring 1, said lateral face 10 having a small base 11 and a large base 12 of diameters substantially greater than those respectively of the small base 6 and the large base 7 of the ring 1 the difference between the diameters of the small bases 6, 11 determining a height h corresponding to the stroke of depressing the insert 8 so that its bottom 9 abuts with the bottom of the cavity 4, an axial pressure to reduce to zero said height h thus causing an enlargement of the slot 2 of the ring and a lateral expansion of the ring 1 against the wall of the cavity. The operation of the prosthesis PR is illustrated schematically in FIGS. 3a to 3c:

  The ring 1 is placed in the acetabulum cavity 4, its small base 6 abutting in said cavity 4 (FIG. 3a). The small base 11 of the insert 8 is brought into abutment against the inner face 5 of the ring, the inner face 5 of the ring and the outer lateral face 10 of the insert being parallel (Figure 3b). The difference between the diameters of the small bases 6, 11 determines a height h 10 corresponding to the insertion stroke of the insert 8 so that its bottom 9 comes into abutment under pressure, with the bottom of the cavity 4. A pressure axial (arrow A) is then exerted by impact on the insert 8 to reduce to zero the height h and cause the pressure contact of the bottom 9 with the bottom of the cavity 4 and an enlargement of the slot 2 of the ring and thus a lateral expansion (Arrows B) of the ring 1 against the wall of the cavity (Figure 3c).

  Once the lateral expansion has been achieved, the small bases 6, 11 of the insert and the ring are situated in the same plane P. Given the dimensions of the ring and the insert in this example, the large bases 7, 12 of the insert and the ring are also in the same plane.

  Thus, the prosthesis PR according to the invention is fixed by hard friction on the bone, with a pressure contact which is exerted both axially (arrow A) and laterally (arrows B).

  According to one variant, notches on the frustoconical inner face 5 of the ring and / or on the inner face of the lateral face 10 of the insert may be provided in order to reinforce the pressure contact acting axially.

  The example of prosthesis PR 'illustrated in FIG. 4 comprises two parts: a ring 13 having a lateral slot 14, this ring having an outer face 15 substantially complementary to that of the acetabular cavity 4, for example spherical, and a tapered internal frustoconical face 16 comprising a small base 17 and a large base 18, this ring fitting into the cavity 4, an insert 19 having a bottom 20 of shape substantially complementary to that of the bottom of the acetabular cavity, for example spherical and a tapered frustoconical outer side face 21 of conicity substantially equal to that of the tapered inner face threaded 16 of the ring 1, said side face 21 having a small base 22 and a large base 23 of diameters substantially greater than those respectively of the small base 17 and the large base 18 of the ring 1, the difference between the diameters of the small bases 17, 22 determining a height h 'corresponding to the insertion stroke of the insert 19 so that its bottom 20 abuts with the bottom of the cavity 4, an axial pressure to reduce to zero said height h' thus causing a widening of the slot 14 of the ring and a lateral expansion of the ring 13 against the wall of the cavity.

  The operation is substantially similar to that illustrated in FIGS. 3a to 3c:

  The ring 13 is put in place by a slight impact in the acetabulum cavity 4 so that it is not mobile, its small base 17 abutting against said cavity. The small base 22 of the insert is brought into abutment against the inner face of the ring, the inner face 16 of the ring and the outer lateral face 21 of the insert being parallel. The difference between the diameters of the small bases 17, 22 determines the height h 'not shown corresponding to the insertion stroke of the insert 19 so that its bottom 20 comes into abutment under pressure, with the bottom of the cavity 4 This height h 'is brought back to zero (arrow E) by screwing the insert 19 in the ring 13 in a fraction of a turn along the arrow C which causes a pressure contact with the bottom of the cavity and an enlargement of the slot 14 of the ring thus causing a lateral expansion (Arrows D) of the ring 13 against the wall of the cavity.

  More precisely, once the lateral expansion has been achieved, the small bases 17, 22 of the insert and the ring are situated in the same plane.

  The invention is not limited to the examples described above. Various modifications can be envisaged without departing from the scope of the invention. For example, the impact can be achieved by protecting a prosthesis according to the invention with a martyr.

  The prosthesis according to the invention may be at least partially covered with a material and / or have a surface state allowing construction by osteoinduction.

  More specifically, the outer face 3, 15 of the ring and the bottom 9, 20 of the insert may be covered with at least partially covered with a material such as hydroxyapatite and / or have a surface state allowing a construction by bone regrowth (osteoinduction). 10

Claims (9)

claims   1. Cotyloid prosthesis, characterized in that it comprises two parts: a ring (1, 13) having a lateral slot (2, 14), said ring having an outer face (3, 15) substantially complementary to that of the cavity acetabulum (4) and a frustoconical inner face (5, 16) comprising a small base (6, 17) and a large base (7, 18), this ring (1, 13) fitting into the cavity (4), an insert (8, 19) having a bottom (9, 20) of a shape substantially complementary to that of the bottom of the acetabular cavity (4) and a frustoconical outer lateral face (10, 21) of conicity substantially equal to that of the frustoconical inner face (5, 16) of the ring (1, 13), said frustoconical outer lateral face (10, 21) having a small base (11, 22) of diameter substantially greater than that of the small base (6, 17). ) of the ring (1, 13), the difference between the diameters of the small bases (6, 11, 17, 22), determining a height (h) corres laying on the insertion stroke (8, 19) so that its bottom (9, 20) abuts with the bottom of the cavity (4), an axial pressure to reduce to zero said height (h) thereby causing an enlargement of the slot (2, 14) of the ring (1, 13) and a lateral expansion (B, D) of the ring (1, 13) against the wall of the cavity (4).   2. Prosthesis according to claim 1, characterized in that the inner face of the insert (8, 19) is shaped to receive a piece forming a housing adapted to receive a femoral ball.   3. Prosthesis according to claim 1, characterized in that the inner face of the insert (8, 19) forms a housing adapted to receive a femoral ball. 9-10-   4. Prosthesis according to claim 1, characterized in that the frustoconical outer side face (10, 21) of the insert (8, 19) has a thread complementary to a tapping located on the frustoconical inner face (5, 16). of the ring (1, 13).   5. Prosthesis according to claim 1, characterized in that the frustoconical outer side face (10, 21) of the insert (8, 19) comprises notches. 10   6. Prosthesis according to claim 1, characterized in that the frustoconical inner face (5, 16) of the ring has notches, complementary or not, notches located on the frustoconical outer side face (10, 21) of the insert. (8, 19). 15   7. Prosthesis according to claim 1, characterized in that the ring (1, 13) and / or the insert (8, 19) are metallic.   8. Prosthesis according to claim 1, characterized in that it is at least partially covered with a suitable material and / or has a surface state allowing construction by osteoinduction.   9. A method of pre-assembly outside the human body of a prosthesis according to claim 1, characterized in that it comprises the following steps: the small base (11, 22) of the insert is brought into abutment against the frustoconical inner face (5, 16) of the ring, the frustoconical inner face (5, 16) of the ring and the frustoconical outer lateral face (10, 21) of the insert being parallel, the distance between the diameters of the small bases (6, 11, 17, 22) determines a height (h) corresponding to the insertion stroke of the insert (8, 19), an axial pressure is then exerted on the insert (8, 19). ) to reduce said height to zero and cause expansion of the slot (2, 14) of the ring and thus a lateral expansion (B, D) of the ring.