EP1239782A1

EP1239782A1 - Assembly for positioning a femoral stem of a hip prosthesis on a femur

Info

Publication number: EP1239782A1
Application number: EP00993376A
Authority: EP
Inventors: Jacques Afriat; Frédéric LARROUY
Original assignee: Dedienne Sante SAS
Current assignee: Dedienne Sante SAS
Priority date: 1999-12-13
Filing date: 2000-12-12
Publication date: 2002-09-18
Also published as: AU2855401A; WO2001043650A1; FR2802080B1; FR2802080A1

Abstract

The inventive assembly comprises the femoral stem (2) and two instruments for positioning said stem (2). One of these instruments is used for processing the metaphysiary cortical bone in the area of the inner wall of the femur (1), according to a curve shape. The other instrument is used for processing the metaphysiary cortical bone in the areas of the front, rear and outer walls of the femur, according to two non-parallel directions which are offset in the inner-outer plane. This allows two bores to be made in the cortical bone with non-parallel axes, one of these being situated on the outer side of the femur. The femoral stem (2) has (i) an inner edge (46) whose curve corresponds exactly to the curve of the inner wall of the bone as processed with the first instrument (3) and (ii) two bulges (47) whose shape corresponds to that of the bores made in the bone using the second instrument (4), in the area of the metaphysiary part of said femur.

Description

ASSEMBLY FOR THE PLACEMENT OF A FEMALE HIP PROSTHESIS ROD ON A FEMUR

The present invention relates to an assembly for the establishment of a femoral stem for hip prosthesis on a femur, this assembly comprising this femoral stem on the one hand and the instruments for setting up this stem on the other hand.

A femoral hip prosthesis stem undergoes significant and repeated stresses transmitted by the patient's weight. Therefore, it must be perfectly stabilized with respect to the bone, both in rotation and in the direction of its insertion relative to this bone and in tilting.

The lack of stability of the rod causes, in addition to pain, a progressive weakening of the bone or even the appearance of secondary fractures in the latter. A delicate intervention must then be made to implant a "recovery" prosthesis. Fixing a femoral stem using a polymerizable cement is a classic technique, but it is not without drawbacks such as the uncertainty of the long-term hold of the cement and the bone necrosis that polymerization causes. of this cement.

The fixation of a femoral stem by growth of bone cells through a porous coating makes it possible to obtain good stability of the stem but on condition that the latter is perfectly stabilized with respect to bone while this growth s 'operates.

On existing femoral stems, this stability is sought by a close form complementarity between the metaphyseal part of the stem and the cavity arranged in the metaphyseal region of the bone.

The arrangement of this cavity is however carried out by means of rasps which compact or smooth the cancellous bone. The shape obtained remains relatively imprecise and such rasps present the risk, when impacted with a hammer in the medullary canal of the bone, of jamming in the cavity, or even of causing a fracture of the bone in the event of weakened bone.

The imprecision of shape of the cavity leads to a poor complementarity of shape between the metaphyseal part of the stem and the cavity. This results in micro-movements of the rod which compromise the growth of bone cells through the porous coating and leads to the risk of greater clearance between this rod and the bone. Other "tailor-made" rod fitting techniques or three-dimensional mechanized machining have been proposed. However, these techniques have the drawback of being expensive and of being relatively difficult to implement. The present invention aims to remedy all of the drawbacks set out above, by providing a solution to the problem of the stability of a femoral stem while bone growth takes place, which ensures the definitive anchoring of this stem to bone, on the basis of a relatively inexpensive and easy to implement technique. To this end, the set of instruments according to the invention comprises:

- a first machining instrument making it possible to machine the metaphyseal cortical bone at the level of the internal wall of the femur, in a curved shape; this instrument comprises (i) a base forming a diaphyseal rod shaped to be engaged and blocked in the medullary canal of the bone, (ii) a cutter adapted to machine said metaphyseal cortical bone according to said curved shape, and (iii) means guiding this cutter for carrying out said machining;

- a second machining instrument for machining the cortical metaphyseal bone at the level of the anterior, posterior and external walls of the metaphysis of the femur; this instrument comprises (i) a base forming a diaphyseal rod shaped to be engaged and blocked in the medullary canal of the bone, this base being closely supported on the internal wall of the bone as machined by said first instrument, (ii) a cutter with a diameter suitable for simultaneously machining the anterior and posterior walls of the bone, as well as the external wall of the latter when it is placed in an external position, and (iii) means for guiding the milling cutter, allowing it to be placed in at least two bore directions offset in the internal-external plane, including said external position, so that this milling cutter makes it possible to arrange in said cortical bone a cavity defined by the shape of this cutter and by these positions; and the femoral stem has, at its metaphyseal part, (i) an internal edge whose curvature precisely corresponds to the curvature of the internal wall of the bone as machined by said first instrument, and (ii) at minus a correspondingly shaped bulge to that of the cavity formed in the bone by means of said second instrument.

The assembly according to the invention thus allows machining not only of the cancellous bone but also of the cortical bone. The support of the rod on the cortical bone ensures a perfect seat of this rod against the bone.

The machining is carried out according to forms which correspond precisely to that of the metaphyseal part of the femoral stem, and which are precisely positioned with respect to each other thanks to the support taken by the diaphyseal rod of said second instrument on the curved inner wall machined by said first instrument. This not only results in perfect shape complementarity between said metaphyseal part of the rod and the metaphyseal cortical bone, but also a homogeneous distribution of the stresses exerted by the weight of the patient, over a large contact surface.

The shape of the metaphyseal part of the rod, thanks to its internal curvature and its bulge, ensures perfect maintenance of this rod not only in rotation but also in the direction of insertion and tilting of this rod relative to the 'bone. Preferably, said second instrument as well as the cutter that this instrument comprises are shaped so that the bore arranged by the cutter when the latter is in said external position delimits, after machining, an external wall inclined relative to the longitudinal axis of the femur, this inclination being such that this external wall approaches the axis of the femur in the distal direction; the rod has, at its metaphyseal part, an external wall of corresponding shape.

This inclined wall makes it possible, together with said internal support zone, to further strengthen the seat of the rod on the bone by cone effect, preventing any risk of it sinking.

Preferably, the cutter of said second instrument has at least one portion of frustoconical shape, the section of which is reduced in the distal direction; the rod has, at its metaphyseal part, walls of corresponding shape. This cutter thus arranges at least one bearing of corresponding frustoconical shape, which further increases the seat of the stem in the bone. Advantageously, in this case, said cutter has two frustoconical portions, one of which located at the distal level has a steeper slope than that located at the proximal level; the rod then has, at its metaphyseal part, walls of corresponding shape, including those located at the distal level constitute frustoconical shoulders.

This distal frustoconical portion arranges, at the distal end of each bore that this cutter makes it possible to arrange, a frustoconical shoulder at the base of the metaphyseal part of the bone, against which bears a wall of complementary shape which the rod comprises . This support further increases the longitudinal seat of the rod relative to the bone.

The assembly according to the invention can include at least one instrument for boring the femoral shaft, making it possible to calibrate the shaft. It may be at least one boring instrument with a rigid and rectilinear structure, suitable for fitting a rod with a straight diaphyseal part, and / or at least one boring instrument with a flexible structure , guided or not by a central rod, suitable for the installation of a rod with curved diaphyseal part.

Advantageously, the rod has a distal end part which is split so that this distal end part can adapt to the anatomical curvature of the femur and can have sufficient elasticity to adapt to the deformations of the resulting femur. movements of the joint.

This slot preferably makes an angle of 45 ° with the internal-external plane.

For a good understanding, the invention is again described below with reference to the appended diagrammatic drawing representing, by way of nonlimiting example, a preferred embodiment of the assembly which it relates to. Figure 1 is a side view of a first instrument it comprises, placed on the resected upper end of a femur; Figure 2 is a side view of a second instrument it comprises, placed on the same end of the femur; Figure 3 is a view, in the anteroposterior plane, of a hip prosthesis femoral stem which it comprises; Figure 4 is a view of this rod in the internal-external plane; Figures 5 and 6 are views of this rod in section respectively along the lines VV and VI-VI of Figure 4, and Figure 7 is a view of another embodiment of said first instrument.

The figures represent an assembly for the placement of a femoral stem 2 of hip prosthesis on a femur 1.

This assembly comprises said first and second instruments 3, 4 on the one hand and this femoral stem 2 on the other hand.

The instrument 3 comprises a base 5 and a cutter 6. The base 5 has a diaphyseal rod 1 0 similar in shape to that of the diaphyseal part 2b of the rod 2, a proximal rod 1 1 fixed to the rod 10, a distal slide 1 2 and a proximal slide 1 3. The rods 10 and 1 1 are adapted to be engaged closely in the medullary canal of bone 1 and to bear against the cancellous bone so as to be immobilized with respect to this bone. In this immobilized position, shown in Figure 1, the rod 1 1 protrudes beyond the proximal end of the bone. The slides 1 2 and 1 3 are slidably mounted along the rod 1 1 and are guided on the latter without lateral play or tilting play.

The distal slide 1 2 has an oblique blind bore 1 5 whose axis forms an angle of the order of 20 ° with the axis of the rod 1 1. This bore constitutes the bearing of a distal journal which comprises the cutter 6. The proximal slide 1 3 comprises, on the internal side of the bone, an oblique bore whose axis makes the same angle with the axis of the rod 1 1 than that formed by the axis of the bore 1 5 with this same rod 1 1.

The cutter 6 has a conical shape which widens from its distal end towards its proximal end, the generatrix of this cutter 6 corresponding to a curved shape which it is desired to give to the internal cortex of the bone. At its proximal end, this cutter 6 is integral with a shaft 1 6 which is engaged and can rotate in the oblique bore of the slide 1 3. This shaft 1 6 is connected to a means of known type (not shown) for its rotational drive. The instrument 4 also includes a base 20 and a cutter 21. The base 20 forms a diaphyseal rod 22 identical to the rod 10 and a proximal frame 23.

It appears in FIG. 2 that the rod 22, like the rod 10, has a slot 25 in its distal part, which allows these rods 10, 22 to adapt to the anatomical curvature of the femur to be treated or to be able to s '' erase in case of any bone growth inside the spinal canal. This slot 25 also allows jamming of the rods 10, 22 by elastic deformation of this distal part. This slot 25 is arranged in a direction such that it forms an angle of 45 ° with the internal-external plane of the bone.

The chassis 23 has a distal end 30 connected to the proximal end of the rod 22. This distal end 30 has a bore of an anteroposterior axis in which is engaged and can pivot a cylinder 31 which is pierced with a radial hole , and a lumen is arranged in the proximal face of this distal end 30 to reveal this radial hole. The latter receives the distal end of a guide rod 32, on which the cutter 21 is mounted axially sliding and around which it can rotate.

From this distal end, the frame 23 curves on the internal side of the bone, according to a curvature which precisely corresponds to that of the generator of the cutter 6, then takes a rectilinear shape at the level of its proximal part which protrudes of the bone when the base 20 is in its position shown, immobilization with respect to the bone.

This proximal part of the chassis 23 comprises a plate 35 on which two curved rods 36 are fixed, the curvature of which is centered on the axis of the cylinder 31. At their free end, these rods 36 have end caps 37 forming stops, and a slide 38 is engaged and can slide on these rods 36. This slide is pierced with a bore which forms a bearing for the proximal shaft 39 to which the strawberry 21 is connected. This milling cutter 21 and its shaft 39 are pierced with an axial bore which allows their engagement on said guide rod 32. The sliding of this milling cutter 21 on this guide rod 32 takes place between a retracted non-machining position and a advanced position in which this bur 21 can machine the bone. The bur 21 has a diameter such that, in its advanced position, it can simultaneously machine the cortical bone of the anterior and posterior walls of the bone.

It has two frustoconical bearing surfaces 21 a, 21 b, the section of which is reduced in the distal direction. The scope 21 b located at the distal level has a steeper slope than the scope 21 a located at the proximal level.

The shaft 39 is connected to a means of known type (not shown) for its rotational drive. It appears in FIG. 2 that the stop positions of the slide

38 against the end pieces 37 on the one hand and against the plate 35 on the other hand define two machining positions by means of the cutter 21, which are offset in the internal-external plane, namely an internal position, shown in lines interrupted in this figure, in which the milling cutter 21 machines the anterior and posterior cortical walls of the bone, and an external position, shown in solid lines by this figure, in which the milling cutter 21 not only mills the anterior and posterior walls of the bone 'bone but also the outer wall of it. In this external position, the axis of the bur 21 is inclined relative to the longitudinal axis of the femur, this inclination being such that this axis approaches the axis of the femur in the distal direction.

Referring to Figures 3 to 6, it appears that the diaphyseal part 2b of the femoral stem 2 has a shape identical to that of the stems 10 and 22, and that it also has a slot 45 identical to the slot 25 of these same stems 10, 22.

The metaphyseal part 2a of this rod 2 has, on its internal side, an edge 46 of curved shape in the internal-external plane, which precisely corresponds to the shape of the generator of the cutter 6. This same edge 46 also has a shape rounded which, in the anteroposterior plane (see Figure 3), widens in the proximal direction, this flare also corresponding to the flared conical shape of the cutter 6.

The metaphyseal part 2a also has two rounded bulges 47, each of which has a shape corresponding to that of the cutter 21, that is to say has a frustoconical proximal part 47a and a frustoconical distal part 47b having a steeper slope than part 47a. The parts 47b thus form shoulders 48 of frustoconical shape at the base of the metaphyseal part 2a.

The arrangement of these bulges 47 relative to each other corresponds to the two machining positions of the cutter 21 shown in Figure 2, and the positioning of these bulges 47 relative to the edge

46 corresponds precisely to the arrangement of said two machining positions relative to the concave face of the curved part of the chassis 23.

The metaphyseal part 2a thus has an inclined outer edge 49, which approaches the axis of the rod 2 in the distal direction. In addition, the rod 2 comprises a neck 50 whose end is shaped as a Morse taper, this neck 50 being intended to receive a spherical articulation head 51.

In practice, the neck of the femur is resected at its base so as to open the bone marrow canal 1. The base 5 is engaged in the bone until it is immobilized, then the sliders 1 2, 13 and the cutter 6 driven in rotation are advanced, so that this cutter 6 machines the internal cortex of the bone according to the shape which corresponds to its generator.

Once this machining has been carried out, that is to say when the slider 12 has come into abutment against the rod 10, the instrument 3 is withdrawn.

The instrument 4 is then put in place until its base 20 is immobilized in the medullary canal and comes from the distal concave wall of the chassis 23 bearing against the internal wall of the bone 1.

The slider 38 is then placed in one of its two abovementioned abutment positions, and the cutter 21 is advanced to carry out one of the two abovementioned machining operations. The cutter 21 is then moved back, then the slide 38 is moved to its other stop position, and the cutter 21 is then again advanced to carry out the second machining.

This instrument 4 is then removed and the femoral stem 2 is put in place. The perfect shape correspondence of the metaphyseal part 2a with the bone cavity as machined ensures perfect seating of this rod 2, both in rotation relative to the bone 1 and in the direction of its insertion into this bone and in tilting .

FIG. 7 shows an alternative embodiment of the instrument 3, in which the cutter 6 is in the form of a ball. This cutter 6 is driven by a motor 60 and a transmission rod 61; she is guided according to a curved movement by sliding of cylindrical pins 62 in two curved grooves 63, the curvature of which corresponds to that desired for the internal wall of the bone. In the case of this instrument 3, the internal edge 46 of the rod 2 does not flare, although it is possible to also provide lateral guidance of the cutter 6 to perform machining flaring in the proximal direction, at like that allowed by the cutter of the instrument shown in Figure 1.

The invention thus provides an assembly for the placement of a femoral stem of a hip prosthesis on a femur which makes it possible to remedy many drawbacks of the homologous assemblies of the prior art. Indeed, this set provides a solution to the problem of the stability of a femoral stem while bone growth takes place which ensures the final anchoring of this stem to the bone, on the basis of a relatively little technique. expensive and easy to implement.

It goes without saying that the invention is not limited to the embodiment described above by way of example but that it embraces, on the contrary, all the variant embodiments. Thus, the cutter 21 can be moved, while it is rotated, between the internal and external positions shown in Figure 2, thus forming a cavity defined by the shape of this cutter 21 and by the movement of this cutter between these positions; the rod 2 then has a single bulge 47, the shape of which corresponds to this cavity.

Claims

1 - Assembly for the installation of a femoral stem (2) of hip prosthesis on a femur (1), comprising this femoral stem (2) on the one hand and the instruments (3, 4) for positioning this rod (2) on the other hand; assembly characterized in that it comprises: - a first machining instrument (3) making it possible to machine the metaphyseal cortical bone at the level of the internal wall of the femur (1), in a curved shape; this instrument (3) comprises (i) a base (5) forming a diaphyseal rod (10) shaped to be engaged and blocked in the medullary canal of the bone, (ii) a cutter (6) adapted to machine said cortical bone metaphyseal according to said curved shape, and (iii) guide means (1 1 to 1 6; 61 to 63) of this cutter (6) for carrying out said machining; - a second machining instrument (4) making it possible to machine the metaphyseal cortical bone at the level of the anterior, posterior and external walls of the metaphysis of the femur (1); this instrument (4) comprises (i) a base (20) forming a diaphyseal rod (22) shaped to be engaged and locked in the medullary canal of the bone, this base (20) being closely supported on the internal wall of the bone as machined by means of said first instrument (3), (ii) a cutter (21) of diameter suitable for simultaneously machining the anterior and posterior walls of the bone, as well as the external wall of the latter when it is placed in an external position, and (iii) means (22 to 39) for guiding the cutter (21), making it possible to place the latter in at least two bore directions offset in the internal-external plane, including said external position, so that this cutter (21) makes it possible to arrange in said cortical bone a cavity defined by the shape of this cutter and by these positions; and in that the femoral stem (2) has, at its metaphyseal part (2a), (i) an internal edge (46) whose curvature precisely corresponds to the curvature of the internal wall of the bone such that machined by means of said first instrument (3), and (ii) at least one bulge (47) of shape corresponding to that of the cavity formed in the bone by means of said second instrument (4). 2 - assembly according to claim 1, characterized in that said second instrument (4) and the cutter (21) that includes this instrument are shaped so that said bore arranged when the latter is in said external position defines, after machining, an external wall inclined relative to the longitudinal axis of the femur (1), this inclination being such that this external wall is approximates the axis of the femur (1) in the distal direction; the rod (2) has, at its metaphyseal part (2a), an external wall (49) of corresponding shape.

3 - assembly according to claim 1 or claim 2, characterized in that the cutter (21) of said second instrument (4) has at least one portion (21a, 21b) of frustoconical shape, the section of which is reduced in the distal direction; the rod (2) has, at its metaphyseal part (2a), walls (47a, 47b) of corresponding shape.

4 - assembly according to claim 3, characterized in that said cutter (21) has two frustoconical portions (21 a, 21 b), of which that located at the distal level has a steeper slope than that located at the proximal level; the rod (2) has, at its metaphyseal part (2a), walls (47a, 47b) of corresponding shape, of which those located at the distal level constitute shoulders (48) of frustoconical shape.

5 - Assembly according to one of claims 1 to 4, characterized in that it includes at least one instrument for boring the femoral diaphysis, making it possible to calibrate the diaphyseal canal.

6 - assembly according to one of claims 1 to 5, characterized in that the rod (2) has a distal end portion which is slotted so that this distal end portion can adapt to the anatomical curvature of the femur (1) and can have sufficient elasticity to adapt to deformations of the femur resulting from movements of the joint.

7 - An assembly according to claim 6, characterized in that the slot (45) makes an angle of 45 ° with the internal-external plane.