WO2003043545A1

WO2003043545A1 - Femoral implant for hip prosthesis

Info

Publication number: WO2003043545A1
Application number: PCT/FR2002/003997
Authority: WO
Inventors: Patrick Surer
Original assignee: Newdeal Technologies; Surer, Charles; Gouray, Jacqueline; Surer, Philippe; Surer, Guillaume; Surer, Anne; ANDRIEUX, Béatrice; Surer, Isabelle
Priority date: 2001-11-21
Filing date: 2002-11-21
Publication date: 2003-05-30
Also published as: FR2832310A1; FR2832310B1; AU2002365960A1

Abstract

The invention concerns a femoral implant (1) comprising: a femoral stem (2) including a diaphyseal portion (4) designed to extend into the diaphysis of a human femur, and a metaphyseal portion (6) designed to extend into the femur metaphysis; a neck (8) including a base (10) linked to the metaphyseal portion (6) of the stem; and a lug (20) integral with the neck base (16), arranged transversely to the longitudinal direction of the metaphyseal portion (6) of the stem (2), extending at least on two among the inner, posterior and outer sides of the neck (8) and wherein are provided holes (24) adapted to receive each a removable assembly (25) securing the lug to the femur, the lug (20) -securing assembly (25) unit fixing the implant (1) on the femur.

Description

"Femoral implant for hip prosthesis"

The present invention relates to a femoral implant for hip prosthesis, of the type comprising a femoral stem which comprises a diaphyseal part intended to extend in the diaphysis of a human femur, and a metaphyseal part intended to extend in the metaphysis of the femur ; a neck for receiving a femoral head which comprises a base connecting to the metaphyseal part of the femoral stem; and means for fixing the implant to the femur.

In the following, the terms "anterior", "posterior", "internal" and "external" are understood in their anatomical sense, that is to say in relation to a femur of the human skeleton.

A hip prosthesis has two essential sets: a femoral implant fixed on the femur bone and a cotyloid implant fixed on the iliac bone. The cooperation of these two implants is intended to restore to a patient fitted with the hip prosthesis, the same capacities of movement and displacement as those allowed by a natural hip. The femoral part of the hip prosthesis undergoes both rotational stresses, especially when the patient sits down, and compression stresses which tend to push the femoral implant into the femur. Due to the cantilevered positioning of the neck of the implant relative to its femoral stem, these constraints cause the implant to tilt. Also, the stability of the implant relative to the bone must firstly be

"primary", that is to say that the implant must be positioned adequately with respect to the femur when the implant is placed. The shape and technique of implant placement contribute to primary stability.

The stability of the implant must on the other hand be "secondary", that is to say that the implant must remain in place after implantation, in particular for prostheses without cement by bone rehabitation from the bone structure of the femur. To improve the secondary stability of cementless prostheses, it is known for example to treat the surface of the prosthesis.

In order to ensure cementless attachment of the implant to the femur, various means have been or are currently used. To ensure a blockage, in particular in rotation, of the femoral stem relative to the femur, several possible arrangements have been considered:

- The diaphyseal part of the stem of the implant can be of substantially rectangular section, ensuring a diaphyseal blocking of the implant by wedge effect; - the diaphyseal anchoring can possibly be improved by locking by means of keys extending transversely to the rod and passing right through the diaphysis of the femur and the rod of the implant;

- The metaphyseal part of the rod can be of enlarged dimension, so as to increase the contact surface between the rod and the internal surface of the metaphysis bore; and or

- a bonding effect between the bone and the implant can be ensured by placing a cement between the stem and the femur.

All of these blocking means prove to be insufficient in terms of resistance to compression and especially rotation forces. Diaphyseal blockage generally induces an excess of stresses detrimental over time to the femur and leads to difficulties in extracting the implant. A large contact surface between the rod and the metaphysis involves a great deal of bone destruction for the implantation of the implant and puts the patient at risk from a fracture of the femur in the presence of an irregularity between the rod and the cavity metaphyseal of the femur.

Furthermore, to improve the resistance, especially primary, to compressive forces, some implants have been provided with a support flange on the internal edge of the end of the femur, at the level of the Merckel spur.

The presence of this flange is very often annoying since either it rests on the Merckel spur before the insertion of the femoral stem is completed, preventing its good fixation in the metaphysis, or the insertion is carried out without the collar coming to bear on the Merckel spur, making the collar unnecessary.

The object of the invention is to propose a femoral implant of the aforementioned type, which does not have the drawbacks mentioned above, which does not prevent good metaphyseal congruence of the prosthesis, and which ensures very good retention, both in compression in rotation of the implant relative to the femur.

To this end, the subject of the invention is a femoral implant of the type defined above, and in which the fixing means comprise a tab integral with the base of the neck, arranged transversely to the longitudinal direction of the metaphyseal part of the femoral stem. , extending at least on two of the internal, posterior and external sides of the neck and in which are provided holes adapted to each receive a removable assembly for securing the tab to the femur.

According to other characteristics of this implant, taken in isolation or in all technically possible combinations: - the femoral stem, the neck and the leg of the femoral implant are made in one piece;

- At least one receiving hole for a securing assembly is formed in each of the internal, posterior and external parts of the tab; - The base of the neck is connected substantially continuously to the metaphyseal part of the femoral stem at least on the anterior side of the neck;

- The holes are oriented in oblique directions relative to each other;

- The respective directions of at least some of the receiving holes of a securing assembly are substantially perpendicular to the face facing the free end of the neck of the tab;

- the thickness of the tab is substantially constant;

- the side facing the femoral stem of the lug is substantially flat;

- The surface facing the free end of the neck of the outer part of the leg is inclined relative to the face facing the femoral stem of the leg so that the direction of the or each hole formed in said outer part is substantially perpendicular to said inclined surface;

each fastening assembly comprises an anchoring rod for the implant in the bone material of the femur, and means for blocking the anchoring rod relative to the tab;

- the fastening assemblies allow a "pilotis" structure;

- The anchor rod is a screw comprising a threaded body intended to be anchored in the femur; and

- The locking means comprise a threaded counter-screw adapted to cooperate with an associated thread formed in the part facing the free end of the neck of the corresponding hole.

The invention will be better understood on reading the description which follows, given solely by way of example, and made with reference to the drawings in which:

- Figure 1 is a perspective and exploded view of a femoral implant according to the invention;

- Figure 2 is a front view along arrow 2 indicated in Figure 1;

- Figure 3 is a front view along arrow 3 indicated in Figure 1, of the implant of Figure 1 put in place and fixed on a human femur seen in internal-external section; and - Figure 4 is a sectional view along the plane IV-IV shown in Figure 3, of a portion of the implant fixed on the femur with a removable assembly of possible attachment.

The implant 1 shown in FIGS. 1 and 2 comprises a femoral stem 2 constituted by a diaphyseal part 4 adapted to extend inside the diaphyseal medullary canal of a human femur and by a metaphyseal part 6 adapted for s extend inside the metaphyseal segment of the femur. As is known in the art, the diaphyseal and metaphyseal parts of the stem extend in different respective directions in order to respect the anatomy of the femur. The implant 1 comprises a neck 8 for fixing a not shown femoral head, such as a spherical articular head intended to cooperate with a recess of shape substantially complementary to a cotiloid implant also not shown.

More specifically, the neck 8 comprises, from the rod 2, a base 10 of frustoconical shape, a cylinder 12 and a Morse cone 14 for receiving the aforementioned femoral head. The base of the neck 10 is connected substantially continuously to the metaphyseal part of the rod 6 along the anterior face of the neck, as is more visible in FIG. 2.

The neck 8 comprises a tab 20 extending substantially perpendicular to the longitudinal direction of the metaphyseal part of the rod 6. The tab 20 extends circumferentially around the base 10 along its internal, posterior and external sides, forming parts of tab referenced respectively 20A, 20B and 20C.

This tab is preferably made in one piece with the rest of the femoral implant 1, which is made of any suitable material, for example stainless steel or titanium, made if necessary rehabitable and coated or not with ceramic.

The tab 20 thus cleans a face 21 facing the Morse taper 14 and a face 22 facing the femoral stem 2. It is important to note, as will be explained in more detail during the description of the installation of the implant 1 on the femur, that this face 22 is intended to remain at a distance from the bone during placement and use of the implant.

The entire face 22 is substantially planar, while the face 21 is substantially parallel to the face 22 for the internal 20A and rear 20B parts of the tab, and is inclined relative to the face 22 for the external part 20C. The parts 20A and 20B of the tab are thus of a substantially constant thickness and the part 20C is reinforced by a greater thickness. Through holes 24 are formed in the tab 20, in oblique directions therebetween. These holes are adapted to each receive a removable assembly 25 for securing the femoral implant 1 to the femur, as best represented in FIG. 3. The radial extent, relative to the axis of the neck, of the tab 20 is dimensioned to allow the production of the holes 24 for receiving the assemblies 25. The example of an implant shown comprises three removable assemblies whose corresponding holes 24 are formed respectively in the internal parts 20A, posterior 20B and external 20C, so as to secure the implant relative to the femur on its internal, posterior and external sides.

In the embodiment shown in Figure 4, the part facing the free end of the neck 8 of each hole 24 forms a threaded housing 26, and the part intended to be turned towards the femur of each hole forms a passage 28 opening onto the face 22 of the tab 20. The cross section of this passage 28 is smaller than that of the housing 26 so that an inclined shoulder 30 is formed in the bottom of the housing.

In addition, each securing assembly 25 comprises a rod, threaded or not, which is intended to be anchored in the femur and which is adapted to be locked in the lug 20. In the embodiment shown, this rod anchoring is in the form of a screw 32 comprising a threaded body 33 adapted to be introduced into the corresponding hole 24 and intended to be anchored in the femur, in the direction imposed by the corresponding hole, and a head 34 of cross section larger than that of the body 33 and adapted to bear against the shoulder 30 of the hole 24. In addition, each securing assembly 25 comprises a part 36 for blocking the anchor rod, bearing against the shoulder 30 This blocking part 36 is, in the embodiment shown, a threaded counter-screw cooperating with the thread of the corresponding housing 26. The locking piece 36 secures each screw 32 to the lug 20 and requires the transmission of forces between the femur and the implant 1 via the lug assembly 20-screw 32. Advantageously, for at least some of the fastening assemblies 25, the face 22 of the tab 20 comprises, around the corresponding hole 24, a zone whose inclination is substantially perpendicular to the direction of anchoring of the screw 32 of the fastening assembly, that is ie the direction of the hole 24. This is the case for the connection assembly anchored in the rear part of the metaphysis, as well as for the connection assembly anchored in the exterior part of the metaphysis by the appropriate choice of the orientation of the face area 22 corresponding to the outer part 20C of the tab as a function of the direction of the corresponding securing assembly. The transmission of forces between the screws and the tab 20 is thereby improved. The use of the femoral implant according to the invention is as follows:

The upper end of the femur is prepared so as to receive the femoral stem of the implant 1, for example by means of metaphyso-diaphyseal rasps. The neck of the femur is cut so that the tab 20 remains at a distance from the neck and does not prevent the implantation of the implant. Once the preparation is complete, the femoral stem 2 is introduced into the medular canal of the femur until it takes an anatomically correct position relative to the femur, with good metaphyseal congruence. The tab 20, formed on the base of the neck 10 of the implant, remains at a distance from the upper end of the femur by forming a clearance j_ (Figures 3 and 4) of for example a few millimeters relative to the femur once the implant stabilized in a primary way in the metaphysis.

Then the screws 32 are introduced into the holes 24 and are anchored in the bone material on the internal, posterior and external sides of the femur. Once the bone has been penetrated by the screws 32, the latter are made integral with the tab 20 (by screwing locking pieces 36 in the example shown in FIG. 4)

The implant according to the invention is thus secured to the bone by metaphyseal anchors distributed on the internal, posterior and external sides of the femur, ensuring the compression and rotation retention of the implant relative to the femur, while ensuring the congruence of the prosthesis to the metaphysis. The compressive strength is distributed over the entire length of the screw bodies 33, advantageously oriented along the lines of force established between the femur and the hip during their respective movements. The resistance to rotary forces is obtained by the plurality of integral screws 32 positioned circumferentially at the neck 8 of the implant 1, in particular on its internal and external sides. The implant according to the invention requires only slight metaphyseal bone damage, thus limiting the risk of fracture, and can be easily removed, if necessary, by unscrewing and removing the removable fastening assemblies 25.

In variants not shown, other assemblies 25 for securing the implant to the femur are conceivable insofar as they allow the screws 20 to be secured to the lug 20 according to a "pilotis" structure, that is to say with the face 22 of the lug 20 which may be distant from the bone, or possibly by providing contact without pressure with this bone. Thus, fastening assemblies with a lock nut, with an expanding ring during the progression of the screw head, with cylindrical or frustoconical housing threaded or not and cooperating with a threaded or not threaded screw head, with locking of the screw head by keying or by a plate screwed on the lug 20, etc. are possible without departing from the scope of the invention.

By way of variants, the shape of the tab is not limited to that described and shown in the example developed above. Thus, its thickness can be constant, its profile can be, at least in part, curved, its peripheral periphery can be more rounded, etc.

Claims

1. Femoral implant for hip prosthesis, of the type comprising a femoral stem (2) which comprises a diaphyseal part (4) intended to extend in the diaphysis of a human femur, and a metaphyseal part (6) intended for s 'extend into the metaphysis of the femur; a neck (8) for receiving a femoral head which comprises a base (10) connecting to the metaphyseal part (6) of the femoral stem (2); and means for fixing the implant to the femur, characterized in that said fixing means comprise a tab (20) integral with the base of the neck (10), arranged transversely to the longitudinal direction of the metaphyseal part (6) of the femoral stem (2), extending at least on two of the internal, posterior and external sides of the neck (8) and in which are provided holes (24) adapted to each receive a removable assembly (25) for securing the leg to the femur.

2. Implant according to claim 1, characterized in that the femoral stem (2), the neck (8) and the tab (20) of the femoral implant (1) are made in one piece.

3. Implant according to one of claims 1 or 2, characterized in that at least one hole (24) for receiving a securing assembly (25) is formed in each of the internal (20A), posterior (20B) parts. ) and external (20C) of the tab (20).

4. Implant according to any one of the preceding claims, characterized in that the base (10) of the neck is connected substantially continuously to the metaphyseal part (6) of the femoral stem (2) at least on the anterior side of the neck ( 8).

5. Implant according to any one of the preceding claims, characterized in that the holes (24) are oriented in oblique directions relative to each other.

6. Implant according to any one of the preceding claims, characterized in that the respective directions of at least some of the holes (24) for receiving a securing assembly (25) are substantially perpendicular to the face (21) turned towards the free end of the neck (8) of the tab (20).

7. Implant according to any one of the preceding claims, characterized in that the thickness of the tab (20) is substantially constant.

8. Implant according to any one of the preceding claims, characterized in that the face (22) facing the femoral stem (2) of the tab (20) is substantially planar.

9. Implant according to claim 8, characterized in that the surface facing the free end of the neck (8) of the external part (20C) of the tab (20) is inclined relative to the face (22) facing the femoral stem (2) of the leg (20) so that the direction of the or each hole (24) formed in said outer part (20C) is substantially perpendicular to said inclined surface.

10. Implant according to any one of the preceding claims, characterized in that each connection assembly (25) comprises a rod (32) for anchoring the implant (1) in the bone material of the femur, and means ( 36) for locking the anchor rod (32) relative to the lug (20).

11. Implant according to claim 10, characterized in that the securing assemblies (25) allow a "pilotis" structure.

12. Implant according to claim 10 or 1 1, characterized in that the anchor rod is a screw (32) having a threaded body (33) intended to be anchored in the femur.

13. Implant according to any one of claims 10 to 12, characterized in that the locking means (36) comprise a threaded counter-screw (36) adapted to cooperate with an associated thread formed in the part (26) facing the free end of the neck (8) of the corresponding hole (24).