FR2788429A1 - Hip prosthesis femoral shank assembly has conical socket for shank close to outer edge of metaphysis component to allow for adjustment - Google Patents

Abstract

The prosthesis consists of a metaphysis component (2) with a neck (5) for a spherical head and a conical socket (7) for the tapering end (16) of a shank (3) fixed in place by a screw (11). The socket (7) is located towards the outer edge of the metaphysis component, leaving a wall 1 - 2 mm thick for a large part of its circumference, permitting a slight elastic deformation when an effort is applied to it. The free end of the shank's conical section (16) has a splined portion (17) which engages with a matching toothed cavity (9) adjoining the upper end of the socket.

Description

The present invention relates to a set of parts for the constitution

  a hip prosthesis femoral rod, in particular a so-called "recovery" or <reconstruction "rod, that is to say a rod intended to be implanted in replacement of a rod previously placed and in case of more or less degraded bone. A femoral stem of a hip prosthesis comprises, as is known, a tapered part intended to be engaged in the medullary canal of the bone and to be fixed thereto, and a neck on the end of which a spherical head can be mounted, this head being intended to be received in

  the corresponding cavity of an acetabular implant.

  The morphologies of the hip joints can vary significantly from one patient to another, and it is frequently necessary to adjust the orientation of the stem neck relative to the cavity receiving the spherical head, to ensure the most faithful reproduction. possible to

i 5 the natural joint.

  First-line monoblock implants can be more or less pivoted in the medullary canal to achieve said orientation,

  their tapered diaphyseal parts having relatively limited lengths.

  However, this pivoting is not possible with recovery or reconstruction rods given the curved shape of the diaphyseal parts of

  these, corresponding to the anatomical shape of the femur.

  It was designed to produce a femoral stem for anatomical recovery or reconstruction, consisting of two parts intended to be assembled, namely - a tapered diaphyseal part, comprising a cone with a slight slope projecting from its proximal part, this cone being pierced a tapped hole opening into its upper face, and - a metaphyseal part, having a conical cavity with a slight slope arranged in its distal part, this cavity being suitable for receiving with cone the cone of the diaphyseal part; this wedging allows the assembly of the two parts according to different relative angular positions in order to orient the neck adequately relative to the femur according to the specific morphology of the patient; the metaphyseal part is also pierced with a hole for the installation of a screw coming to engage in the tapped hole of the diaphyseal part to ensure a

  final assembly of the two parts.

  This type of assembly has the disadvantage of having an uncertain hold over time. Indeed, the torsional stresses undergone by a femoral stem can be very important, particularly during

  patient lifting motion, and are repeated frequently.

  A play may arise between the parts, producing not only wear of the cone and of the walls delimiting said conical cavity but

  also a harmful diffusion of metallic particles in the organism.

  In addition, the titanium or titanium alloy frequently used to produce a femoral stem has the particularity of being extremely "seizing", so that the release of the cone from the cavity is

  difficult for the case where a slight tightening would have been achieved.

  In addition, the more or less pronounced degradation of the patient's bone induces a risk of progressive sinking of the rod into the femur, and performing a trochanterotomy can be tricky with existing implants i 5 recovery or reconstruction , the part of femur cut on this occasion (called "WAGNER flap") being made unstable by the

conformation of these implants.

  The present invention aims to remedy all of these drawbacks. The set of parts which it relates to comprises, in a manner known per se, at least one tapered diaphyseal part and at least one metaphyseal part having a neck intended to receive a spherical articulation head, one of these two parts having a conical portion with a slight slope while the other part has a complementary conical cavity, suitable for receiving said conical portion with wedging to allow the assembly of the two parts in an angular position

  determined in order to orient the cervix adequately in relation to the femur.

  According to the invention, - said conical portion and said cavity have diameters

  such that the cavity can be arranged on the external side of the rod, that is to say

  say on the side opposite to that on which the neck protrudes, so that the cavity is delimited on at least a large part of its circumference by a relatively thin wall, of the order of 1 to 2 millimeters, capable of slight elastic deformation by stretching; - Said conical portion is extended, on the side of its free end, by a toothed circular portion having a diameter less than that of said free end, this toothed portion being arranged coaxially with this free end and being connected thereto by a flared zone which operates a gradual transition between the diameter of the toothed portion and the diameter of said free end; and - a recess is arranged coaxially with said cavity and opens into the bottom thereof, this recess defining a toothed portion whose teeth are suitable for engaging with the teeth of the toothed portion connected to the conical portion, said portion conical, cavity, toothed portion and recess being shaped so that the teeth delimited by said toothed portions mutually engage before the conical portion and the cavity

  are in the jamming position.

  The teeth of the toothed portions reciprocally engage to allow precise determination of the angular position of the metaphyseal part with respect to the diaphyseal part. The practitioner can thus easily search for the angular orientation of the cervix most suited to the

patient specific morphology.

  After implantation, these teeth ensure perfect resistance of the assembly to the significant and repeated torsional stresses that the femoral stem undergoes; the torsional forces undergone by the toothed portion connected to the conical portion are distributed over the whole of this conical portion, and this under favorable conditions, thanks to said flared zone by which this toothed portion is connected to this conical portion, notwithstanding the relatively small diameter of these conical portions and

toothed.

  The conical portion and the cavity have large contact surfaces, not limited by the presence of toothed portions, the latter being arranged respectively in the extension of the end of the conical portion and beyond the bottom of the cavity, in the room wall. The jamming that they allow is therefore quite resistant, although their diameters are reduced, and makes it possible to eliminate

  the residual play between the pieces perfectly.

  This reduced diameter of the conical portion also allows a reduced diameter of the cavity, and therefore to arrange this cavity on the external side of the femoral stem, in particular on the external side of the metaphyseal piece. This cavity can thus be delimited over a large part of its circumference by a relatively thin wall, capable of being slightly elastically deformed around the conical portion. This deformation ensures perfect wedging of the conical portion in the cavity, notwithstanding the relatively small diameter of the conical portion and the cavity. Preferably, the conical portion is arranged in the end

proximal of the diaphyseal part.

  After implantation of this part, the conical portion projects from the bone and can serve as a mounting point and angular orientation for ancillary sighting material, with a view to the possible placement of distal screws through the bones and holes provided for this purpose in the part

distal of the diaphyseal part.

  Said cavity is then arranged in the metaphyseal part, on the external side of the latter. The metaphyseal part therefore protrudes very little on the external side with respect to the diaphyseal part. The replacement of the "WAGNER flap" in case of trochanterotomy is found

significantly facilitated.

  Advantageously, each metaphyseal part is shaped so as to have an internal edge projecting on the internal side with respect to the diaphyseal part, so that the distal end face of each metaphyseal part defines a surface perpendicular to the axis.

longitudinal of the rod.

  The metaphyseal part can come to bear, by this surface, on a rim of the femur arranged by an appropriate resection. This support makes it possible to perfectly effectively prevent any sinking of

  the stem in the femur, even in the case of very degraded bone.

  The abovementioned wedging may be sufficient to carry out the assembly of the two parts, but, for safety, each diaphyseal part comprises a tapped hole while each metaphyseal part comprises a hole which passes through it, these holes being intended for the installation of a screw ensuring the

  maintaining these two parts in the assembled state.

  Preferably, the set of elements according to the invention comprises different types of diaphyseal and metaphyseal parts of different lengths, conformations and dimensions, adapted to the

  different morphs of femur.

  For its proper understanding, the invention is again described below with reference to the appended schematic drawing representing, by way of nonlimiting example, a preferred embodiment of two parts

  that comprises the set of parts according to this invention.

  Figure 1 is a perspective view of these two parts before their assembly, and a screw for this assembly; Figure 2 is a perspective view from another angle of these parts after assembly; Figure 3 is a longitudinal sectional view of these parts before assembly; Figure 4 is a longitudinal sectional view of these parts after assembly and implantation on a femur, and Figure 5 is a view of these parts in section along the line

V-V of figure 4.

  The figures represent, from different angles, a metaphyseal part 2 and a diaphyseal part 3 which can be assembled together to form a femoral stem 1 of hip prosthesis, called "recovery" or "reconstruction". such rod 1 is intended to be implanted in replacement of a rod previously put in place and

more or less degraded bone.

  The metaphyseal piece 2 is made of titanium or a titanium alloy commonly used to produce such a femoral stem 1. It comprises: - a neck 5, having a conical profile with a slight slope at its free end 5a; this neck 5 is intended to receive a spherical head 6 comprising a suitable conical cavity, this head 6 itself being intended to be received in the corresponding cavity of an acetabular implant (not shown); - A conical cavity 7 opening into the distal face of the part 2, which has a maximum diameter of around 15 mm and a slope of around 3; this cavity 7 is arranged on the external side of

  the rod 1, that is to say on the side opposite to that on which the neck 5 projects.

  It is thus delimited, over a large part of its circumference, by a wall 2a of relatively small thickness, of the order of 2 mm, capable of slight elastic deformation by stretching; - A recess 8 arranged coaxially with the cavity 7, on the proximal side, opening into the bottom thereof; this recess defines twenty-four teeth 9 projecting inwards - a counterbore 10 coaxial with the recess 8, to receive the head of a screw 1 1 making it possible to assemble the metaphyseal part 2 and the diaphyseal piece 3; - An internal edge 2b projecting from the internal side of the rod 1 relative to the diaphyseal part 3, so that the distal face 2c of the metaphyseal part 2 defines a surface perpendicular to the longitudinal axis of the rod 1; - A transverse hole 12, suitable for receiving a rod for holding the part 2 in rotation when the screw 1 1 is tightened, in order to prevent any rotation of this part 2 during this tightening, and suitable for then receiving one or more strapping son for replacing and maintaining the portion of bone 25c cut in the case of a trochanterotomy; - At least one facet 13, and in particular three in the example shown, arranged in said wall 2a of relatively small thickness, on the side opposite to that on which said neck 5 projects; these facets 13 delimit with the wall of the part 2 and, where appropriate, between them edges 14 suitable for ensuring stabilization in rotation of the trochanteric "flap" 25c (or "WAGNER flap>) in the case of trochanterotomy; these facets each preferably has a slightly concave shape The diaphyseal part 3 comprises - a tapered medullary tail 15, which is cannulated in the example shown to secure the stem 1 in rotation; - a conical proximal portion 16, complementary to the cavity 7, that is to say which can be engaged in this cavity 7 to produce an assembly of the metaphyseal 2 and diaphyseal 3 parts, by wedging; a circular toothed portion 17, extending the conical portion 16 on the side of the free end of the latter and delimiting teeth 18 complementary to those delimited by the recess 8, that is to say adapted to come into engagement with these teeth 9; this toothed portion 17 has a diameter be less than that of said free end, and is arranged coaxially with the latter; the toothed portion 17 is further connected to said free end by a flared area 19, which operates a gradual transition between the diameter of this toothed portion 17 and the diameter of said free end; - a threaded bore 20 opening into the proximal face

  end of the conical portion 16, to receive the screw 1 1.

  It appears in the figures that the engagement of the respective teeth 9 and 18 is possible before the wedging of the portion 16 in

cavity 7.

  In practice, the femur 25 is resected in a manner adapted to the reception of the rod 1, that is to say with a bore of the medullary canal 25a and an arrangement of an internal rim 25b suitable for receiving the face 2c when the part 2 is assembled with part 3. A trochanterotomy is optionally performed for the removal of the previously implanted femoral stem. The diaphyseal part 3 is then inserted into the housing as well

  fitted out and fixed to the bone with synthetic cement.

  The metaphyseal piece 2 can be engaged on the portion 16 without jamming, so that the teeth 9 and 18 mutually engage. These teeth make it possible to precisely determine the angular position of the part 2 relative to the part 3 to allow the practitioner to easily find the angular orientation of the neck 5 most

  adapted to the specific morphology of the patient.

  Once this orientation has been determined, the screw 11 is put in place and is tightened to carry out the final assembly of the parts 2 and 3 in this determined relative position. The conical adjustment thus ensures the holding and the final maintenance in position of parts 2 and 3, following the simple tightening of the screw 11. It is therefore not necessary to carry out this assembly by impaction, which could damage a degraded bone , become fragile. Parts 2 and 3 are part of a set of metaphyseal and diaphyseal parts of different lengths, conformations and

  dimensions, adapted to the different femur morphologies.

  The invention thus provides a set of parts for constituting a femoral stem for hip prosthesis, in particular a so-called "recovery" or <reconstruction "stem, making it possible to remedy the drawbacks of the homologous stems of the prior art. Indeed, the slight elastic deformation of the wall 2a ensures perfect 8 wedging of the portion 16 in the cavity 7, by clamping, and the teeth 9 and 18, in engagement, allow the rod 1 to perfectly resist the significant stresses and repeated, exerted in torsion, which it undergoes; as shown in FIG. 4, the part 2 comes to bear against the rim 25b, which makes it possible to prevent any sinking of the rod 1 in the femur 25; in addition, thanks to the reduced diameter of the portion 16 and cavity 7, the part 2 does not

  that very little protrusion on the outside of the bone, which allows easy replacement of the portion of bone 25c cut in case of trochanterotomy.

Claims (5)

  1 - Set of parts for constituting a femoral hip prosthesis rod, comprising at least one tapered diaphyseal part (3) and at least one metaphyseal part (2) having a neck (5) intended to receive a spherical head d articulation (6), one of these two parts (3) having a conical portion (16) with a slight slope while the other part (2) has a complementary conical cavity (7), suitable for receiving said conical portion (16) with wedging to allow the assembly of the two parts (2, 3) according to a determined angular position in order to orient the neck (5) adequately with respect to the femur; assembly characterized in that - said conical portion (16) and said cavity (7) have diameters such that the cavity (7) can be arranged on the external side of the rod (1), that is to say on the side opposite to that on which the neck (5) projects, so that the cavity (7) is delimited over at least a large part of its circumference by a wall (2a) of relatively small thickness, of the order of 1 at 2 millimeters, susceptible to slight elastic deformation by stretching; said conical portion (16) is extended, on the side of its free end, by a circular toothed portion (17) having a diameter less than that of said free end, this toothed portion (17) being arranged coaxially with this free end and being connected thereto by a flared area (19) which operates a gradual transition between the diameter of the toothed portion (17) and the diameter of said free end; and - a recess (8) is arranged coaxially with said cavity (7) and opens into the bottom thereof, this recess (8) delimiting a toothed portion whose teeth (9) are adapted to engage with the teeth of the toothed portion (17) connected to the conical portion (16), said conical portion (16), cavity (7), toothed portion (17) and recess (8) being shaped so that the teeth (9, 18) delimited by said toothed portions reciprocally engage before the portion   conical (16) and the cavity (7) are in the jamming position.   2 - assembly according to claim 1, characterized in that the conical portion (16) is arranged in the proximal end of the part diaphyseal (3).   3 - assembly according to claim 1 or claim 2, characterized in that each metaphyseal part (2) is shaped so as to have an internal edge (2b) projecting on the internal side with respect to the diaphyseal part (3), such that the distal end face (2c) of each metaphyseal piece (2) defines a surface   perpendicular to the longitudinal axis of the rod (1).   4- assembly according to one of claims 1 to 3, characterized   in that each diaphyseal part (3) comprises a tapped hole (20) while each metaphyseal part (2) comprises a hole (10, 8) which passes through it, these holes being intended for the installation of a screw ( 11) ensuring   maintaining these two parts (2, 3) in the assembled state.   - Assembly according to one of claims 1 to 4, characterized   in that the metaphyseal part (2) comprises at least one facet (13), and in particular three, arranged in said wall (2a) of relatively small thickness, on the side opposite to that on which said neck (5) projects, these facets (13) delimiting with the wall (2a) of the part (2) and, if necessary, between them edges (14) suitable for ensuring the stabilization in rotation of the   Trochanteric "flap" (25c) in case of trochanterotomy.   6- assembly according to claim 5, characterized in that   each facet (13) has a slightly concave shape.