FR2615726A1 - Prosthetic fixation element with anchoring stud - Google Patents

Abstract

The fixation element comprises a support 2, and at least one anchoring stud 3 joined to the support. The stud has a blind hole 36, 37, 38 and longitudinal slots 39F delimiting anchoring lips 39L. Preferably, the hole is tapped in order to receive a screw which exerts a calibrated pressure against the bottom 38 of the hole in order to separate the lips and anchor them to the wall of a drill hole in the bone to be fitted with the prosthesis. The anchoring takes place preferably without surgical cement and is reinforced by crevices on the lips, such as circular fluting 33. The shape of the support 2 can be adapted to the prosthesis. The fixation element may be a knee prosthesis tibial base or a hemispherical hip prosthesis acetabulum.

Description

 prosthetic fixing element with anchoring stud.

 The present invention relates to a prosthetic fixing element comprising a support and at least one anchoring stud linked to the support. It relates in particular to improvements to studs for anchoring a base or an acetabulum of an orthopedic prosthesis for patellar knee joint, or hip coxofemoral for example.

 Currently, the fixing of such an element is carried out, with or without surgical cement, by means of studs, also called nipples, offering circular peripheral lamellae with rectangular longitudinal section.

 The impact of the studs in corresponding bone pilot holes is obtained by force pushing so as to block both in axial translation and in rotation the studs in the pilot holes.

 The thrust cannot be easily dosed according to the rigidity of the prosthetic bone varying with the individuals which can cause a weakening of the bone, even a crumbling of the bone and the bony cracks. In addition, although the anchoring of the studs, in particular without cement, is suitable for operating manipulations during implantation of the prosthesis, the anchoring of the stud may prove to be discontinuous or insufficient after the operation due to the efforts in particular of traction. and against which the studs are subjected by the articulated movements of the prosthesis. These stresses can lead to instability of the studs and to their loosening, leading to a new surgical operation.

 The present invention aims to improve the final anchoring of studs of a prosthetic fixing element, by avoiding any embrittlement of the prosthetic bone by a precise adjustment of the contact forces between the studs and the walls of the bone pilot holes.

 To this end, a prosthetic fixing element is characterized by an anchoring stud shaped into a socket having. a blind hole and longitudinal slots, said slots delimiting radially expandable anchoring lips.

 According to a preferred embodiment, the expansion of the anchoring lips is obtained by means of a screw screwed in abutment against the bottom of the hole in the stud, which hole is partly tapped. The penetration depth of the screw in the hole is thus easily measurable and adjustable, and consequently the spacing of the yeasts and the contact forces between them and the wall of the bone pilot hole receiving the stud are evaluated with accuracy based on bone strength. In addition, the stud before expansion of the lips is introduced into the pilot hole substantially by force, or even by gentle sliding, which prevents weakening of the prosthetic bone.

 According to another aspect of the invention, the external surface of the anchoring lips comprises small crevices formed between circular or helical grooves, or between serrations or between discrete polygonal points, which makes it possible to increase the anchoring of the stud in the bone, especially when this anchor does not use surgical cement.

 As will be seen below, the shape of the support is adapted according to the type of orthopedic prosthesis. Depending on operational constraints and manufacturing, the support and the anchoring stud can be linked by welding, or by screwing the stud in a tapped hole in the support, or by a screw, with a head preferably embedded in the support, screwed into a tapped hole in the stud, or may constitute a single piece from molding. The choice of the material of the support and the pad, such as metal or plastic possibly reinforced with carbon fibers, glass or aramid, results in particular from the importance of the efforts and contacts to which the support and the pad will be subjected.

Other advantages and characteristics of the invention will appear more clearly on reading the following description of several preferred embodiments of the invention with reference to the corresponding appended drawings in which
- Fig. 1 is an exploded perspective view of a prosthesis of
knee containing a base according to the invention:
- Fig. 2 is a side view of a fastening element according to
the invention, to constitute one knee prosthesis base of FIG.

1;
- Fig. 3 is a top view of a flat support of the base:
- Fig. 4 is a sectional view taken along the line IV-IV
of Fig. 3 of the knee prosthesis base;
- Fig 5 is a vertical view in axial half-section of a stud
tap anchor, welded to the flat support of the knee prosthesis base;
- Fig. 6 is a view in axial half-section of the anchoring stud alone;
- Figs. 7 and 8 are top and bottom views of the stud
anchor respectively;
- Figs. 9 and 10 are longitudinal and top views of a
screw-needle screw screwable and can be accommodated in the stud;
- Fig. 11 is an axial half-section view of a centering pivot
on the support;
- Fig. 12 is a side view of another fastener
according to the invention, to constitute a cup or a cup cup of
hip prosthesis; and
- Fig. 13 is an axial sectional view taken along the line
XII-XII of Fig. 12, of a hip prosthesis acetabulum in which a
external cup is constituted by a fixing element according to
the invention.

According to the embodiment illustrated in FIG. 1, a fixing element
according to the invention constitutes a femoral base 1 of a total prosthesis
knee. The base l is metallic and essentially comprises a
support plate 2, here in the form of a crescent, two anchoring studs
identical expanders 3 and a centering pivot 4. As shown in
Figs. 2, 3 and 4, the anchoring pads are arranged symmetrically by
relative to a central anteroposterior transverse axis IV-IV of the #plate 2 and are projecting under the underside 20 of the plate 2. The
pivot 4 is centered on the axis IV-IV and protruding on the upper face 21
from plate 2.

 The underside of the plate 20 is intended to be applied to a resection plane formed on the head of a -tibia to be prosthetic, simultaneously with the penetration of the two anchoring studs 3 into pre-punched holes. or pilot holes, in the tibial head. The upper face of the plate 21 is suitable for receiving a plate PL also with a crescent profile LU, preferably of plastic material such as polyethylene.

The PL plate is underlying a set of articulated and convex ROT femoral support pieces constituting the prosthetic patellar joint proper. The convex parts are linked to the condylar surfaces and to the trochlea of the corresponding femur. The patellar plateau PL has a lower face which is complementary to the upper face 21. In particular, a centering hole TR and lower notches EN are provided in the PL plate so that it is fixed on the support plate 2 by centering around the pivot 4 and fitting between two pairs of anterior and posterior stops, 22A and 22P protruding at the edge of the upper face 21 of the plate 2, as shown in Fig. 1.

 With reference to Figs. 5 and 6, an anchoring pad 3 according to the invention is a tapped and split cylindrical socket.

 Seen from the outside, as shown on the left in Figs. 5 and 6, the stud 3 comprises in the upper part, a smooth cylindrical collar 30, then a frustoconical shoulder 31 separated from the collar 30 by a circular clearance 32, and six circular frustoconical grooves 33, or alternatively helical, superimposed axially under the shoulder 31, and in the lower part, a smooth short cylindrical guide pin 34 terminated by a chamfered end 35.

 The flange 30 has a diameter less than that of the shoulder 31, typically less than 1 mm, so that. when the collar is threaded into a corresponding hole 23 in the plate 2 and from below the face 20, as shown in FIG. 5, the shoulder 31 abuts against the face 20. The height of the flange 30 and the clearance 32 exceeds by one or two tenths of a millimeter the thickness of the plate to allow the flange 30 to be welded to the upper face 21 of -plate 2.

According to another variant, the collar 30 is secured to the plate 2 by an annular clip partially embedded in a groove in the hole 23 and partially engaging in a circular groove in the collar 30.

 The grooves 31 are truncated cones having a large base at the top, on the side of the shoulder. The large diameter of the grooves exceeds by 1 to 2 mm the diameter of the guide stud 34 in order to facilitate penetration of the stud into the perforated hole in the tibia. Indeed, the diameter of the stud 34 is equal to or substantially less than that of the pre-punched hole, and consequently, during the penetration of the stud into the bone by progressive thrust exerted by an adequate tool, the stud 34 guides the stud in the perforated hole and the grooves penetrate at least partially into the bone wall of the perforated hole, or ripe on this wall, without causing bone burst. Typically an angulation o of the grooves 33 relative to a diametral plane of the stud of the order of 60 to 80 is suitable to allow a substantially forced penetration of the stud into the bone without bone bursting.

 As shown in section, right in Figs. 5 and 6, the stud 3 has a blind cylindrical axial hole. A threaded portion 36 of the axial hole extends from the flange 32 to about the penultimate lower groove. A smooth portion 37 of the axial hole extends between the penultimate lower groove and the guide pin 34, The smooth portion 37 has a diameter equal to the diameter of the top of the threads of the tapped portion and is terminated by a bottom in conical tank 38. The bottom 38 is substantially parallel to the chamfered end 35, and has an apex angle of the order of 90 '.

 As appears in particular in Figs. 7 and 8, the pad 3 comprises long longitudinal slots 39F extending downward from the underside of the shoulder 31. The slots 39F are distributed circularly around the axis of the pad and are at least two in number . According to the illustrated embodiment, four slots 39F are diametrically opposed, two by two. Thus, the slots 39F share Most of the stud containing the grooves 33 and underlying the shoulder 31 in four longitudinal anchoring lips 39L with cross section substantially in a quarter of a circle.

 The anchoring lips 39L and the slots 39F allow, thanks to the inherent elasticity of the metallic material constituting the stud 3, decreases and increases in the cross section of said major part of the stud.

 The introduction of the stud into the perforated hole in the bone confers a slight approximation of the lips 39L towards the axis. of the stud and a reduction in the cross section of the slots 39F following the friction of the grooves 33 against the wall of the hole. Crumbling of the wall of the hole is thus avoided. The proper bending of the 39L lifts tending to spread them radially may be sufficient for the final anchoring of the stud in the osseous pilot hole.

 However, this anchoring can be improved by increasing the spacing of the lips and the penetration of the grooves 33 in the bone.

Thus after housing of the stud in the perforated hole of the bone, the lips 39L are moved away from the axis of the stud and the slots 39F are widened by means of a needle screw 5 by progressive bending of the body of the stud from shoulder 31.

 According to other embodiments, the anchoring of the stud can be achieved, in place of the screw, by a rod having a tapped lower end screwed into the tapped hole, or a smooth lower end sliding in the hole of the stud which can be entirely smooth, the rod being moved back and forth by means of a specific ancillary apparatus, including for example a small compressor.

 Referring to Figs. 9 and 10, the screw 5 is a headless screw with a pointed end and is substantially complementary to the axial hole 36-37-38 of the stud 3. The screw 5 has a threaded upper section 50 with hexagon socket 51 for screwing in the threaded section 36, and a smooth lower section 52 having a diameter substantially smaller than that of the smooth hole section 37. The screw 5 is terminated by a pointed end 53 having an angle at the top of the order of 90 *. The total length of the screw sections 51 and 52 is less than that of the stud hole sections 36 and 37 so that the screw can be embedded in the stud 3 and therefore does not hinder the subsequent laying of the plate PL on the plate 2.

 The length of the smooth section of screw 52 is greater than that of the smooth section of hole 37 which allows, after insertion of the stud 3 in the perforated hole of the tibia and application of the plate 2 against the tibial resection plane, to screw the screw 5 in the block 3 until the end of the screw 53 exerts radial pressures on the conical bottom 38 of the hole in the block. These radial pressures cause a widening of the slots 39F and a separation of the lips 39L, by bending at the level of the upper ends of the lips. The widening and spacing are more pronounced at the lower ends of the slots and of the lips and are progressive by a metered screwing of the screw simultaneous with a sliding of the tip 53 against the bottom of the hole 38. The spacing of the lips results in penetration of the sharp edges of the large bases of the grooves 33 which is progressive in the bone wall of the tibial hole and by a pushing and a superficial compaction of the bone material between the grooves, - without causing any harmful microlesion around the wall of the perforated hole. The lips 39L are thus anchored in the bone material, and block the stud 3 both in rotation and in translation. Depending on the depth of the penetration of the screw 5 into the hole 34-35-36, the bending of the lips 39L can be permanent and irreversible and consequently the screw 5 can be removed. Any crevices at the level of the small bases of the grooves 33 will then be filled by bone growth.

 The final implantation of the two studs 3 as described above thus makes it possible to offer a base 1 perfectly secured to the tibia preferably without the addition of surgical cement, and therefore capable of receiving the assembly of the patellar parts, and in particular the patellar plate centered and embedded on the face 21 of the plate 2.

 With reference to FIG. 11, the centering pivot 4 is a solid cylindrical metallic element comprising a cylindrical smooth lower section 40, a cylindrical smooth upper section 41 having a diameter significantly greater than that of the section 40 and forming therewith a circular shoulder 42, and a tapered upper end 43 offering in the lower part, a large base in the form of a small biconical flange 44, or cylindrical with clearance, overlying the section 41.

 The lower section 40 is housed with clearance in a centering hole 24 made in the plate 2, in order to facilitate welding between the cylindrical surface of the section 40 and the cylindrical wall of the hole 24.

According to another variant, the section 40 is a threaded section to be screwed into the hole 24 which is tapped. The thickness of the plate 2 is at least equal to the height of the section 40 so that it does not project from the lower face 20, when the shoulder 42 of the pivot 4 abuts against the upper face 21 for fixing the stud to the plaque.

 The upper section 41 has a diameter substantially equal to that of the centering hole TE of the plate PL already mentioned, and a height less than the hole TE when the latter is blind and contains a circlip to cooperate with the flange 44, or else substantially equal to the thickness of the plate when the hole in the plate is transverse. In addition, the centering pivot 4 has at least one diametrical upper slot 45 and according to the illustrated embodiment, two perpendicular and diametrical slots 45 extending to the top of the shoulder 42. The plate PL is then made integral in translation axial to the pivot 4 with the plate 2, by engaging the hole TE of the plate on the chamfered end 43, and by pushing the plate towards the face 21 of the plate 2. This last push produces a narrowing of the slots 45 during the crossing of the collar 44 in the hole of the plate, then a return of the slots 45 to their initial width when the plate abuts against the face 21 and the section 41 is completely contained in the centering hole of the plate.

The flange 44 thus prevents any escape of the plate PL relative to the base 1, and the plate is locked in rotation around the pivot thanks to the interlocking of the four notches EX under the underside of the plate with the stops 22A and 22P in plate border 2.

 Although the invention has been described with reference to a particular knee prosthesis, modifications can be envisaged within the scope of the subject of the present patent application defined in the annex.

 The fastening element, such as base 1, can be in one piece, that is to say all the parts 2, 3 and 4 can come directly from mold # age in order to avoid adjustment and welding operations. . According to other variants, the flange 30 of the anchoring studs 3 can be threaded so as to be screwed into tapped holes 23 in the support plate 2; due to the presence of two studs, there is no risk of unscrewing after implantation. In addition, the fixing element may be made of metallic material, such as an alloy, in particular for casting, based on cobalt, titanium alloy or steel, or else of resistant plastic material, such as polyethylene. In all cases, the material of the element can be reinforced by fibers embedded in carbon, glass, aramid or the like. The surface condition of the fixing element, or at least that of the face bottom of the plate and of the anchoring studs can be made rough or porous by means of a shot peening, or a coating by projection of plasma or deposit of hydroxyapatite.

 The fastening element may include one or more than two parallel or non-parallel, identical or different anchoring pads. In particular, for each fixing stud, the grooves can be replaced by other surface crevices, such as those formed between serrations, or between sharp, discrete points, such as diamond-shaped or polygonal-based points. The end 53 of a screw 5 and the end 38 of the hole in an anchorage stud 3 can be respectively convex and concave, for example in the form of a spherical cap or a drop of tallow.

 A fixing element according to the invention can be used whenever it is necessary to firmly implant a support by studs, also called pins or lugs, in a bone. The support can be a ball joint prosthesis base, as described above, optionally provided with a long tibial pin, and / or incidentally with pins. However, the support may be a fastening element having a flat, curved, or more generally curvilinear support for receiving a load relative to other articulation prostheses, such as elbow, shoulder or hip prostheses.

 For example, the fixing element constitutes a acetabulum or an external element of an acetabulum to cover a spherical head of a prosthesis, such as a hip prosthesis. The support has the form of a spherical cap partially covering the spherical head of the hip prosthesis and supporting two anchoring studs according to the invention and possibly spikes to be implanted in the iliac bone.

 According to the embodiment illustrated in Figs. 12 and 13, the acetabulum la is composed of a semi-spherical metal cup Sa having two studs or pins 3a according to the invention, and an internal semi-spherical NO core made of plastic, such as polyethylene. The two studs 3a are implanted in two holes of the iliac bone and anchored in these thanks to the expansion of their lips 39La resulting from the screwing of corresponding needle screws. The external surface of the cup Sa has coaxial circular grooves 25 and is preferably covered with hydroxyapatite in order to present crevices for bone growth.

The NO core is nested concentrically under the cup 2a and bonded thereto, the external surface of the core being practically complementary to the internal surface of the cup. The base of the cup may also include, as is known, holes for the passage of pins or fixing screws
Finally according to other embodiments, the support and an anchoring pad can be separable and assembled by means of a needle screw having a head housed in a countersink or countersinking made at the upper mouth of the corresponding hole 23 in the support, the assembly being carried out after implantation of the stud, which makes it possible to measure the force of application of the support against the corresponding surface of the bone.

Claims (24)

R E V E N D I C A T I O E S.  1 - Prosthetic fixing element (1) comprising a support (2) and at least one anchoring stud (3) linked to the support, characterized in that the anchoring stud (3) is shaped into a socket having a hole blind (36, 37, 38) and longitudinal slots (39F), said slots delimiting radially expandable anchoring lips (39L).  2 - prosthetic fixing element according to Aa claim 1, characterized in that the external surface of the anchoring lips (39L) comprises circular or helical grooves (33).  3 - prosthetic fastening element according to claim 2, characterized in that the grooves (33) have a frustoconical profile forming an angle (a) of about 60 to 80 with a diametral plane to the stud.  4 - prosthetic fastening element according to claim 1, characterized in that the external surface of the anchoring lips (39L) comprises serrations of points, preferably polygonal.  5 - prosthetic fastening element according to any one of claims 1 to 4, characterized in that the stud (3) comprises a guide stud (34), preferably with a chamfered end (35), having a diameter less than external diameter of the major part of the whole of the anchoring lips (39L).  6 - prosthetic fastening element according to any one of claims 1 to 5, characterized in that the blind hole (36, 37, 38) has a threaded portion C36) to receive a screw (5) whose screwing in abutment against the bottom (38) of the hole causes the spacing of the anchoring lips (39L).  7 - prosthetic fixing element according to claim 6, characterized in that the screw (5) has a smooth end (52) having an end (53) substantially complementary to the bottom (38) of the hole (36, 37, 38) of the stud (3), and preferably the smooth end (52) being cone-shaped, spherical cap or drop of tallow.  8 - prosthetic fastening element according to claim 6 or 7, characterized in that the screw (5) is a headless screw having a length less than that of the hole (36, 37, 38) of the stud, or a screw with head accommodating in a counterbore or a countersink in a hole (23) in the support (2).  9 - prosthetic fastening element according to any one of claims 1 to 8, characterized in that the anchoring stud (3) has one end (30) at the mouth of the blind hole  (36, 37, 38), accommodable in a hole (23) of said support (2), and linked to the latter preferably by welding, or by screwing, or by clips.  10 - prosthetic fastening element according to claim 9, characterized in that said housing end (30) of the stud (3) has a height at most equal to that of the hole (23) of said support (2) so that the stud does not protrude on one face (21) of the support (2) opposite the major part (33, 34) of the protruding stud on the other face (20) of the support.  11 - Prosthetic fastening element according to any one of claims 1 to 10, characterized in that the support (2) and the anchoring stud (3) constitute a single piece coming from molding.  12 - prosthetic fastening element according to any one of claims 1 to 11, characterized in that the support is a flat plate (2), or curvilinear, or spherical (2a).  13 - prosthetic fastening element according to any one of claims 1 to 12, characterized in that it comprises at least two or more anchoring studs (3; 3a).  14 - prosthetic fastening element according to any one of claims 1 to 13, characterized in that the support (2) and / or the anchoring stud (3) are made of metal or plastic, optionally reinforced with fibers of carbon, glass, aramid or the like.  15 - Fixing element 'prosthetic according to any one of claims 1 to 14, characterized in that the support (2) and / or the anchoring stud (3) offer an external surface at least partly rough preferably by covering a shot or hydroxyapatite.  16 - prosthetic fastening element according to any one of claims 1 to 15, characterized in that the support is a  flat plate (2), preferably with a crescent outline, to constitute  a base (1) for a ball joint prosthesis.  17 - Prosthetic fastening element according to the claim  16, characterized in that the support (2) offers an upper face <21)  opposite the anchoring stud (3), complementary to a lower face  a plate (PL) of the patella prosthesis intended to support the patellar  prosthetics (ROT).  18 - Prosthetic fastening element according to claim  17, characterized in that the support (2) comprises at the edge of the face  upper (21) of the stops (22A, 22P) recessed in notches  (EN) of the platform (PL).  19 - Prosthetic fastening element according to claim 17  or 18, characterized in that it comprises a centering pivot (4) linked to the  support (2) and projecting on the upper face (21) of the support to be  housed in a hole (TR) in the plate (PL).  20 - prosthetic fastening element according to claim  19, characterized in that the centering pivot (4) has a  collar (44), preferably biconical, located above the upper face (21) of the support (2) at a distance substantially equal to or  less than the thickness of the patellar plateau, and at least one slot  longitudinal (45) slitting the collar (44).  21 - prosthetic fastening element according to claim 19  or 20, characterized in that the centering pivot <4) is built-in  partially in a hole (24) in the support (2) and linked to it by  preferably by welding or screwing.  22 - Prosthetic fastening element according to any one  of claims 1 to 15, characterized in that the support is a  semi-spherical cap to form a cup (la) covering the head  spherical of a prosthesis in particular of hip.  23 - Prosthetic fastening element according to any one  of claims 1 to 15, characterized in that the support is a  semi-spherical cap to form an outer cup (2a) of a  cup (la) covering the spherical head of a prosthesis including  hip via a semi-spherical core (NO). concentric and linked to the cup, said core preferably being made of plastic.  24 - prosthetic fastening element according to claim 22 or 23, characterized in that the external surface of the support has crevices, preferably such as circular grooves (25).