FR2610823A1 - Improved femoral rod for hip prostheses - Google Patents

Abstract

The subject of the invention relates to the technical sector of femoral prostheses in general, more particularly to prostheses intended to replace the head of a femur. According to the invention, the bent part 1d of the femoral rod is provided on at least one of its faces with means allowing it to be engaged in the medullary cavity, and to be centred in the said cavity by clip-fastening contact employing elasticity.

Description

 The object of the invention relates to an improved femoral stem for hip prostheses.

 The object of the invention relates to the technical sector of femoral prostheses in general, # more particularly prostheses intended to replace the head of a femur.

There are known on the market prostheses sold under the name "ISO-ELASTICS" having from the lower end of the spindle or close to the level of the elbow connecting to the plate, at least one slot in the longitudinal axis of the spindle , terminated by an opening of larger dimension, intended to give the spindle a combination with the one or more, a form elasticity ensuring its implantation in the medullary canal by diametrical expansion of the spindle, and without sealant. Such a prosthesis has been illustrated in French Patent No. 2,483,218 in the name of
Applicant of this application.

 We wanted to improve prostheses of this type.

 According to a first characteristic, the improved femoral stem for hip prostheses is of the type comprising a pin having from its lower end up to the proximity of the connection elbow with the plate a longitudinal slot projecting over the faces of the femoral stem, and another slot in a plane perpendicular to said first slot defining strands imparting elasticity in the axial plane of the rod, optional means connecting together the lower end of said strands, said rod being characterized in that the bent part of the femoral stem is arranged on at least one of these faces, with means allowing its engagement in the medullary canal and its centering in said canal by an elastic clipping contact.

 These characteristics and others will become apparent from the following description.

To fix the subject of the invention illustrated in a nonlimiting manner in the figures of the drawings where
Figure 1 is a front view of an improved femoral stem for hip prostheses according to the invention, in a first embodiment allowing an elastic capacity of deformation of the femoral stem in several directions.

 FIG. 2 is a back view of the femoral stem according to FIG. 1.

 FIG. 3 is a partial view on a large scale of the femoral stem according to FIGS. 1 and 2.

 Figure 4 is a cross-sectional view along line A-A of Figure 1.

 FIGS. 5, 6 are alternative views of the production of the femoral stem viewed from the side comprising means made in one piece with the body of the stem allowing elastic deformation in several directions.

 FIG. 7 illustrates another alternative embodiment of the femoral stem seen from the back and comprising means attached to its faces, elastically deformable.

 FIG. 8 illustrates another alternative embodiment in the case where added means are arranged on the front face and the back face between the branches.

 Figure 9 is a partial sectional view illustrating the connection of the ends of the branches of the femoral stem.

 FIG. 10 is a sectional view along line B-B of FIG. 9.

 FIG. 11 is a variant view according to FIG. 7.

 In order to make the object of the invention more concrete, it is now described in a nonlimiting manner illustrated in the figures of the drawings.

 We see in Figure l the longitudinal section of the upper part of a femur (F) whose neck has been surgically cut, in order to implant a femoral stem in the medullary canal (F1).

 The femoral stem comprises in a known manner an implantation pin (ic), a plate (la) bearing on the upper face (F2) of the femur, surmounted by a tette (lb) intended to receive a joint cup in the hip cavity, either directly or through an artificial acetabulum. The pin (lc) of the femoral stem, which is of the "cerebral-cephalic" type, is to say has a pin implanted profundly in the medullary canal present from the lower end to near the elbow <id) of connection with the plate (la) a femoral slot (le) opening on the faces (FA, FB> of the femoral stem. Be made from the end of the rod to its bent part (1d).

 Another slot (lf) perpendicular to the previous one opening on the back of the rod and on the front face of this thus makes it possible to define the strands a, b, c, d giving said rod a certain elasticity while being of continuous shape and regular. An optional connecting means is provided at the end of the rod between the ends of the strands. This means can be a rivet, a hook and all complementary means, a light being made in the thickness of the ionction of the strands Sa-b) and allowing a certain axial movement.

 According to the invention, the improvement provided aims to improve the behavior of the femoral stem in the cavity of the medullary canal. This improvement aims to arrange the bent part (nest) of the femoral stem in particular on at least one of the FA - FE faces with complementary means allowing its engagement in the medullary canal and its retention by an elastic clipping contact distributed over all or part of the periphery of the bent part between the plate and the strands a, bc, d of the femoral stem.

 Thus the femoral stem is centered in the medullary canal according to a better balanced distribution of points or contact areas as appears in Figure 4 given by way of example.

 A first implementation of the invention illustrated in Figures t to 4, consists in giving the bent part an additional reinforcement area of the lateral faces of the femoral stem. Reinforcement is carried out by a dbport (ig) towards the outside of the parts of the strands (a, c) (b, d) lying at the level of the bent part. The femoral stem remains in one piece.

A clipping effect is thus obtained by positioning the femoral stem while playing on both the deformability of the strands and of the filled part defined from the faces of said stem.

 In a variant not illustrated in the figures of the drawings, it could be conceived that a double offset is made for each strand located at the bent part. The double offset is obtained both in the plane of the faces and in the plane of the sides, which places it in external projection of about 459 relative to the intersection of the two base planes, side and face.

According to another variant illustrated in FIGS. 5 and 6, the femoral stem (2) comprises, in its bent part on each face, a tongue (2 made in one piece with the rod capable of elastically deforming. According to FIG. 5, said tongues originate on the strands (2a-2b> from the back of the rod and come substantially opposite the plate (2c) of the rod According to FIG. 6, said tabs (a) arise from the plate (3b) of the femoral rod, and develop on the side of the faces of the rod in the bent part of the latter and opposite the strands (3c-3d). The elasticity of said tongues in the transverse direction of the femoral rod is combined with its elastic deformation capacity in the other plane obtained by the realization of the strands which have been described previously
FIGS. 7-8 aim at another alternative embodiment in which flexible and deformable plates (4) are attached in the transverse direction from at least one face (FA - FB) of the femoral stem. These plates are for example provided with positioning fingers (4-1) capable of adapting and being centered in the openings formed by the slots defined by the different strands constituting the femoral stem. According to FIG. 7, said plates are arranged on at least one transverse face and combine their effects with the elastic capacity of deformation of the femoral stem in the other plane. To ensure a good balance, it is preferable to place a plate from each face of the femoral stem. However, depending on the configuration of the spinal canal, only one plate could be used. The wafer (s) are made of any suitable material. Connection means may be provided between them with elastic capacity for deformation. These means can for example be small springs centered on the fingers (4.1) and are stressed in compression when the femoral stem is positioned in the medullary canal. Illustrated according to FIG. 11. the possibility of producing platelets with a coming profile substantially under the plate to increase the elastic contact surface. Said plates can be flat or curved; deform in their longitudinal and / or transverse plane. They can be arranged with connecting and retaining means between them, removable or not. The fingers can be replaced by an appropriate boss or profile penetrating into said openings established by the slots. said plates can also be retracted inwards against elastic means under the pushing effect during the introduction of the femoral stem into the medullary canal.

 According to FIG. 8, platelets of the same type have also been placed on the back and front sides of the femoral stem and combine their effects with those placed on the faces.

 Given the improvement made to the elasticity of the femoral stem, provision has been made to arrange the end of the strands of the stem, according to FIGS. 9 and 10, by providing an external recess (6) on the periphery of said strands allowing the positioning of a connecting ring (7) absorbing said elastic deformations of the strands relative to each other.

 The advantages emerge clearly from the invention. The better holding of the femoral stem is emphasized by an increase in its bearing zones in the medullary canal and by the retaining effect by clipping obtained by the new arrangement of the bent part under the plate.

Claims (8)

-1- Femoral stem for hip prostheses of the type comprising a pin (Ic) having from its lower end up to the proximity of the elbow (ld) for connection with the plate (la) a longitudinal slot (lc) projecting over the faces of the femoral stem, and another slot (if) in a plane perpendicular to said first slot defining strands a, b, c, d, imparting elasticity in the axial plane of the stem, optional means connecting the lower end of said strands, said rod being characterized in that the bent part (nest) of the femoral rod is arranged on at least one of its faces with means allowing its engagement in the medullary canal and its centering in said canal by a contact elastic clipping. -2- Femoral stem according to claim 1 characterized in that the bent portion (ld) has a one-piece outer bulge area with the body of the stem. -3- Femoral stem according to claim 2, characterized in that said bulge zone is formed on the side of the lateral faces by an external offset (lg) of the strand parts (ase) (b, d). -4- Femoral stem according to claim 2, characterized in that said bulge tgne is produced by a double offset of each strand both in the plane of the faces and in the plane of the sides. -5- Femoral stem according to claim 2, characterized in that said bulge zone is defined by two tabs <2- 1) arranged on the side of each side of the femoral stem. -6- Femoral stem according to claim 5, characterized in that said tongues originate on the strands (2a-2b) of the back of the rod and come substantially opposite the plate (2c). -7- Femoral stem according to claim 5, characterized in that said tongues <3a) originate from the plate (3b) and develop on the side of the faces of the stem to come opposite the strands (3c-3d) . -8- Femoral stem according to claim 1 characterized in that one or more flexible and deformable plates (4) are attached in the transverse direction of the rod on at least one face and are provided with means (4-1) adapting and centering in the openings formed by the slots defined between the strands. - -9- Femoral stem according to claim 8, characterized in that flexible and deformable pads are arranged on the back and front cStés of the femoral stem and combine their effects with the pads arranged on each side of the femoral stem.  -10- Femoral stem according to claim 8 characterized in that the plates by their outer profile come substantially under the plate. -11- Femoral stem according to claim 8 characterized in that the plates (4) are arranged with connecting and retaining means between them removable or not. -12- Femoral stem according to claim 8 characterized in that the plates retract inwardly against elastic means. -13- Femoral stem according to claim 1, characterized in that the end of the strands of the stem is arranged with an external recess (6) allowing the positioning of a connecting ring (7).