FR2630907A1 - Screwed cotyle, in particular for prosthesis of the "hip" type - Google Patents

Abstract

The present invention relates to cotyles which are suitable for being implanted in a bone. The cotyle according to the invention, defining the female element of a prosthetic ball joint, which cotyle can be positioned in a hemispherical bone cavity, is essentially characterised in that it comprises a hollow piece 2 defining a container 3 which comprises two adjacent parts 5, 6, respectively defining two outer surfaces of revolution 7, 8 about an axis 9, the first surface 7 being frustoconical with a large base 11 equal to the cross-section of the opening of the cavity, and with a small base 12 equal to a cross-section of the cavity, defined in a plane 10 parallel to the plane of the entrance opening of the cavity, the distance 13 between the large and small bases being less than the depth of the cavity, the second surface taking the form of a spherical cap 8 whose radius of curvature is greater than that of the hemispherical cavity, and, over at least part of the frustoconical surface 7, a thread 20. Application to producing a prosthesis of, for example, the hip type, for implantation in the iliac bone.

Description

Screwed cup, especially for prosthesis
"hip" type
The present invention relates to cementless screw-on acetabular cups for the production of "hip" type prostheses implanted in patients whose articulation between the pelvis and the femur no longer performs its functions, for example following an accident or a disease .

 When a joint "in particular that between the head of the femur and the pelvic bone, no longer functions normally, we try to remedy this defect by the implantation of a hip prosthesis. This prosthesis has two main parts forming a patella by the combination of a female part with a male part, the hollow female part, generally of hemispherical shape,.. being called acetabulum by the technicians, by analogy with the terms of anatomy.

 This acetabulum is capable of receiving the other part of the ball joint constituting the male part of complementary shape, that is to say a spherical head, this second part being integral, in addition, with a lug capable of being fixed in the femur.

 The whole of this technique is well known and all the specialized surgeons practice it commonly, trying to solve the problems which can still exist with regard, in particular, to the implantation of the female part of the patella in the bone of the pool.

 To make this implantation more reliable, several types of cups have been proposed, arranged to be fixed in the bone of the pelvis in different ways. Certain embodiments include, for example, a convex bearing surface which is housed in a complementary cavity made in the bone of the pelvis. This surface has protuberances which, combined with cement, ensure a certain adhesion with the bone. But in fact experience shows that in the long run, through a slow decomposition, the cement dissociates from both the bone and the acetabulum, sometimes even causing degradation of the bone itself. It is therefore necessary to perform relatively frequent surgical procedures to replace the acetabulum in place.

 In an attempt to overcome this drawback, acetabular cups have been produced, the implantation of which does not require cement. The external surface of these acetabular cups has advantageously self-tapping threads and their fixation in the pelvic bone is obtained by first making, in this bone, a hollow housing generally of substantially spherical or hemispherical shape and in which the acetabulum is then introduced by screwing. The bone waste produced by the self-tapping is ejected by lateral slits towards the internal housing of the acetabulum, in this case the female hollow part intended to receive the pad defining the receptacle of the spherical male part of the patella.

 This embodiment makes it possible not to use binding chemicals such as cement, but still has drawbacks, essentially the fact that it does not allow an effective solidification bond between the acetabulum and the bone, for example by osteogenesis .

 The present invention then gave itself the aim of producing a cup for a prosthetic joint of the "hip" type or the like, which can be very easily fixed in the bone of the pelvis, without adding an auxiliary connecting element such as as cement, by promoting good fixing by connection with the bone in which it is intended to be implanted, in particular by the phenomenon of osteogenesis, and which is nevertheless of a structure facilitating its realization, in particular not machining robots .

More specifically, the subject of the present invention is a cup defining the female element of a ball joint of a prosthesis of the hip type or the like, capable of being positioned in a substantially hemispherical bone cavity and comprising a hollow part defining a housing. receptacle, means associated with said housing and unscrewing a pad for receiving the male complementary element of the ball joint, characterized in that said hollow part comprises
two first and second parts respectively defining a first and a second external surface of shape substantially of revolution around the same axis, the two said parts being joined in a plane perpendicular to said axis,
said first surface affecting a frustoconical shape whose large base is substantially equal to the section of the opening of the hemispherical cavity and whose small base is substantially equal to a section of said hemisphere defined in a plane substantially parallel to the plane in which is defines said opening opening of said cavity, the distance between the two said large and small bases being less than the depth of said cavity,
said second surface substantially affecting the shape of a spherical cap whose base section is substantially coincident with the small base of said frustoconical shape and whose radius of curvature is greater than that of said hemispherical cavity, and,
on at least a portion of said frustoconical surface, protruding parts delimiting solid and hollow, said protruding parts being defined so that their vertices are distributed over an envelope occupying a volume greater than that defined by said cavity.

Other characteristics and advantages of the present invention will appear during the following description given with reference to the drawings annexed by way of illustration, but in no way limitative, in which
FIG. 1 represents, seen in section referenced II in FIG. 3, an embodiment of a cup according to the invention,
FIG. 2 represents, seen in section and on a larger scale, a detail of the structure represented in FIG. 1,
FIG. 3 represents, seen in perspective, the embodiment of the cup as illustrated in section, in whole or in part, in FIGS. 1 and 2, and
FIG. 4 represents, seen in section and partly cut away, a acetabulum according to the invention in application to a hip prosthesis.

 It is firstly specified that, the figures representing the same embodiment of an acetabulum or of a prosthesis with the acetabulum, the same references designate the same elements there, whatever the figure on which they appear.

 Figures 1 to 4 show an embodiment of a cup 1 which defines the basic female element of a patella, for example a prosthesis of the hip type or the like, intended to be positioned in a bone cavity 100 substantially hemispherical, as shown in Figure 4. This cup 1 has a hollow part 2 defining a receptacle housing 3 of the male element of a ball joint. To this receptacle housing 3 are associated means defeating a receiving cushion 124 of the complementary element mSle of the ball joint. This pad may be made of a material such as polyethylene and has been more particularly shown in FIG. 4 illustrating an application of the acetabulum according to the invention in a hip prosthesis.

 The hollow part 2 comprises two first 5 and second 6 parts respectively defining a first 7 and a second 8 outer surfaces of substantially rotational shape about the same axis 9, these two parts 5 and 6 being joined in a plane 10 perpendicular to axis 9.

 The first surface 7 has a frustoconical shape whose large base 11 is substantially equal to the section 101 of the opening 102 of the hemispherical cavity 100 in which this acetabulum is intended to be positioned, and whose small base 12 is substantially equal to a section of the hemisphere which is defined in a plane substantially parallel to the plane of the large base 11 and to the plane in which the inlet opening 102 of the cavity is defined, the distance 13 between the two large 11 and small 12 bases being less than the depth 103 of the cavity taken from the plane 104 passing through the inlet opening 102.

 As for the second surface 8, it substantially affects the shape of a spherical cap whose base section 14 is substantially coincident with the small base 12 of the. frustoconical surface 7, but whose radius of curvature is greater than that of the hemispherical cavity 100.

 In addition and advantageously, this second outer surface 8 has a knurled appearance which, as explained below, makes it possible to anchor the acetabulum 1 well in the bone wall of the bottom of the cavity 100, and to prevent it from unscrewing after 'it was placed by self-tapping in this cavity.

 The acetabulum 1 further comprises, in addition to at least a portion of the frustoconical surface 7, projecting portions 15 delimiting depressions and solids 16, 17. The solids 17 are further defined so that their vertices are distributed over a envelope 18 defined in broken lines in FIGS. 1 and 2, comprising sections greater than those of the cavity 100.

 In an advantageous embodiment, these projecting parts consist of a thread 20 forming the thread of a given thread partially shown in FIG. 2 and surround the frustoconical surface 7 so that, as functionally defined above, the edge 19 of the thread 20 is located on a substantially spherical enveloping surface 18 and of a radius greater than that of the hemispherical cavity 100.

 Figure 2 shows, on a larger scale than Figure I, an advantageous embodiment of the net 20 which surrounds the frustoconical surface 7 and whose edge 19 is located on the envelope 18 as defined above.

 This thread is produced in such a way that it takes the form of an asymmetrical profile known as a sawtooth substantially delimited by two faces 21, 22 oblique to a direction 23 parallel to the axis of revolution 9 and oriented with respect to this axis so that the side furthest from the opening 102 of the cavity 100, in this case the face 21, forms with the direction 23 an obtuse angle 24, and the other face, the 22, makes with this same direction an acute angle.

 In addition, as will be explained below, the thread 20 and the part 5 of the part 2 are advantageously cut by notches 30, 31, 32, ... bringing the bottom 16 of the threads into communication with the hollow housing 3, to allow at least partial elimination of the bone waste produced during the self-tapping introduction of the acetabulum 1 into the bone cavity 100.

 The section of these notches defined in a plane substantially perpendicular to the axis of revolution 9 assumes the shape of an asymmetrical trapezium whose large base 33 substantially joins the ends of the edges 19 of the cut thread and whose small base 34 is located at the wall of the recessed housing 3. In addition, the two other sides 35, 36 of this trapezium are concurrent at a point 37 not located on the axis 9, to form a funnel whose opening is formed by the large base 33 In this way, if the rotation around the axis of revolution 9 is oriented in the direction of screwing by tapping of the acetabulum 1 in the bone cavity 100, the average angular position of the large base 33 is ahead of that of the small base 34 and, during the rotation of the acetabulum for its screwing, the funnel shape of these notches allows the grouping and guiding towards the hollow housing 3 of the bone waste produced by the tapping.

 The insertion of the acetabulum into the bone cavity 100 is carried out by means of special tools known in themselves and which can be linked to the acetabulum by means such as notches in which the tools exert on the acetabulum torque forces for the drive in rotation. These notch means are for example constituted by orifices 40, 41, 42, ... advantageously made in the second part 6 of the hollow part 2 and distributed over a circle centered on the axis 9 so as to leave free the center 43 of this part 6 in order to produce a through orifice 44 making it possible to put in communication the space located opposite the spherical surface 8 and the recessed housing 3, for the purpose which will be explained below.

 To set up a cup as described above, we start by making a hemispherical cavity of a given radius in the bone, for example in the iliac bone of the hip. A cup is then chosen so that it has the characteristics described above with regard, in particular, to the large and the small bases 11 and 12 of the frustoconical surface 7 and the radius of curvature of the spherical cap 8. Au by means of a rotary tool whose head cooperates with the orifices 40, 41, 42, ..., the thread 20 is screwed by self-tapping into the wall of the cavity 100 until the large and small bases 11 and 12 are substantially coincident with two sections of the hemispherical cavity perpendicular to its axis and that the large base is coincident with its opening 102.

 Due to the particular structure of the acetabulum, there therefore exists, defined between the two respective edges SO and 51 of the large and the small bases, the internal wall 110 of the cavity 100 defined between the two planes passing respectively through the large and the small bases, and the frustoconical surface 7, a relatively closed annular volume 111 communicating with the housing 3 only by the notches 30, 31, 32, ...

 Similarly, as the spherical cap 8 has a radius of curvature greater than that of the cavity 100, when the acetabulum is screwed and has taken the position defined above, there is then a volume in the form of a spherical segment 112 between the bottom of the cavity 100 and the surface 8, the base of this spherical segment being generally slightly concave.

 Thus, during the self-tapping of the acetabulum by means of the threads 20 biting into the wall of the cavity, there are produced "bone chips 113, -114 which will remain in the two volumes 111, 112, the surplus being eliminated. and ejected by the notches 30, 31, 32, ... and the bottom orifice 44. This waste remaining in these two volumes will promote growth of the bone of the bone wall by the well-known phenomenon of osteogenesis , the same one which allows the bonding of the bones after a fracture. The growth of the bone will completely fill these two volumes 111 and 112 and therefore perfectly secure the acetabulum with the bone and the cost of unscrewing or be torn from the bone into which it was screwed, the threads acting as harpoons because of their orientation relative to the axis of the cavity, this axis being moreover then coincident with the axis 9 of the acetabulum.

 The osteogenesis time is relatively rapid, of a duration similar to that which is necessary to solidify a fracture.

 Of course, after the cup has been put in place, the pad 124 is positioned in the housing 3. This pad intended to receive the head of the male part of the ball joint also makes it possible to close the notches 30-32 and the orifices 40 -44 and therefore to keep the quantity of bone chips necessary for osteogenesis in the two volumes 111 and 112.

 - The head of the male part 200 essentially constituted by a sphere integral with a tab 201 is arranged to complete the positioning of the prosthesis. This latter technique, which is perfectly known in itself, will not be described more fully here.

 Of course, the structure described above of the acetabulum according to the invention consists of different elements which each have their function. However, it is obvious that the production of such an acetabulum can be obtained from a single block, for example a titanium block, essentially by removal of material by means, for example, of a machining robot. .

 However, it is not excluded that, in the case of the use of other materials, it is possible to obtain such an acetabulum by molding, in particular because of the advantageously form of revolution of its different functional parts.

Claims (9)

 1. Cup defining the female element of a ball joint of a prosthesis of the "hip or similar type, suitable for being positioned in a bone cavity (100) substantially hemispherical, and comprising a hollow part (2) defining a receptacle housing (3) and means associated with said housing defeating a cushion for receiving the complementary element m # le- of the ball joint, characterized in that said hollow part comprises  two first (5) and second (6) parts respectively defining a first (7) and a second (8) external surfaces substantially of the shape of revolution around a same axis (9), the two said parts being joined in a plane (10) perpendicular to said axis,  said first surface (7) affecting a frustoconical shape whose large base (ll) is substantially equal to the section of the opening (102) of the hemispherical cavity and whose small base (12) is substantially equal to a section of said hemispherical cavity defined in a plane substantially parallel to the plane in which said entry opening of said cavity is defined, the distance (13) between the two said large (11) and small (12) bases being less than the depth (103) of said cavity,  said second surface (8) substantially affecting the shape of a spherical cap whose base section is substantially coincident with the small base (12) of said frustoconical shape and whose radius of curvature is greater than that of said hemispherical cavity (100 ), and,  on at least a portion of said frustoconical surface (7), protruding parts (15) delimiting recesses and solids (16, 17), said protruding parts being defined so that their vertices (19) are distributed over a envelope (18) occupying a volume greater than that defined by said cavity (100).  2. Cup according to claim 1, characterized in that said protruding parts (15) delimiting hollows and solids (16,17) consist of a net (20) surrounding said frustoconical surface (7), the ready (19) of the net being located on a substantially spherical envelope (18) with a radius greater than that of said hemispherical cavity (100).  3. Cup according to claim 2, characterized in that the profile of said thread (20) has a substantially "sawtooth shape delimited substantially by two faces (21,22) oblique to a direction (23) substantially parallel to the axis of revolution (9), the most distant face (21) of the large base (12) making with said direction an obtuse angle (24), the closest face (22) of said large base making with this direction an acute angle (25).  4. Cup according to one of claims 2 and 3, characterized in that it comprises notches (30,31,32, ...) made in said thread and said first part (5) of said hollow part (2) said notches placing the bottom (16) of the thread (20) in communication with said recessed housing (3).  5. A cup according to claim 4, characterized in that the section of these notches (30-32) defined in a plane substantially perpendicular to the axis of revolution (9) takes the form of an asymmetrical trapezium whose large base (33) substantially joins the ends of the edge portions (19) on the side of the edge (19) of the net (20) and the small base (34) of which is located in said housing (3), the other two sides (35,36) of the trapezoid being concurrent at a point (37) not located on the axis (9) to form a funnel whose opening is constituted by the large base (33), so that, during screwing by tapping the acetabulum (1) in the bone cavity (100), the average angular position of the large base (33) is ahead of that of the small base (34).  6. Cup according to one of the preceding claims, characterized in that it includes notches (40,41,42) capable of receiving tool heads to exert on it forces of rotational torques.  7. A cup according to claim 6, characterized in that said notches are constituted by orifices (40-42) made in the second part (6) of said hollow part (5) and distributed over a circle centered on the axis (9).  8. Cup according to claim 7, characterized in that it comprises at the center of said spherical cap (8) a through orifice (44) connecting the space located opposite said spherical cap and the recessed housing (3).  9. Cup according to one of the preceding claims, characterized in that the outer surface of said spherical cap (8) is knurled.