FR2802080A1 - ASSEMBLY FOR PLACING A HIP PROTHESIS FEMALE ROD ON A FEMUR - Google Patents

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

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

A femoral stem of hip prosthesis undergoes important and repeated constraints transmitted by the weight of the patient. Therefore it must be perfectly stabilized relative to the bone, both in rotation and in the direction of its depression relative to the bone and tilting.

lack of stability of the stem causes, in addition to pain, a gradual weakening of the bone or even the appearance of secondary fractures in the latter. A delicate intervention must then be made to implant a prosthesis "recovery".

fixation of a femoral stem by means of a polymerizable cement is a conventional technique, but which is not without drawbacks such as the uncertainty of the long-term behavior of the cement and the bone necrosis caused by the polymerization of this cement.

fixation of a femoral stem by growth of the bone cells through a porous coating makes it possible to obtain good stability of the stem but provided that the latter is perfectly stabilized relative to the bone as long as this growth operates.

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

The arrangement of this cavity is however performed by means of rasps compacting or lining the cancellous bone. The shape obtained remains relatively imprecise and such rasps present the risk, when they are impacted by the hammer in the medullary canal of the bone, to lock in the cavity, or even to cause a fracture of the bone in case of bone weakened.

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 stem which compromise the growth of bone cells through the porous coating and leads to the risk of greater play between this rod and the bone.

Other "custom-made" rods or three-dimensional mechanized machining techniques have been proposed. These techniques, however, have the disadvantage of being expensive and relatively difficult to implement.

The present invention aims to remedy all of the disadvantages set out above, by providing a solution to the problem of the stability of a femoral stem the time that occurs bone growth ensures the final anchoring of the stem to the on the basis of a relatively inexpensive and easy to implement technique.

this effect, the set of instruments according to the invention comprises - a first machining instrument for machining the metaphyseal cortical bone at the inner wall of the femur, in a curved shape; this instrument comprises (i) a base forming a diaphyseal stem shaped to be engaged and locked 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 performing said machining; a second machining instrument for machining metaphyseal cortical at 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 locked in the medullary canal of the bone, this base taking a close bearing on the inner wall of the bone as machined by means of said first instrument, (ii) a milling cutter of suitable diameter for simultaneously machining the anterior and posterior walls of the bone, as well as the outer wall of that when placed in an external position, and (iii) means for guiding the milling cutter, allowing placing it in at least two boring directions offset in the inner-outer plane, including said external position, so that the cutter allows to develop in said cortical bone a cavity defined by the shape of the cutter and by these positions; and the femoral stem has, at its metaphyseal portion, (i) an inner edge whose curvature corresponds precisely to the curvature of the inner wall of the bone as machined by means of said first instrument, and (ii) to less a corresponding bulge corresponding to that of the cavity formed in the bone by means of said second instrument. The assembly according to the invention thus makes it possible to perform machining not only of the cancellous bone but also of the cortical bone. The support rod on the cortical bone ensures perfect seating of this rod against the bone.

machining is carried out according to shapes that correspond precisely to that of the metaphyseal part of the femoral stem, and which are precisely positioned relative to each other by 'taking support of the diaphyseal stem of said second instrument on the inner wall machined curve by means of said first instrument. It results only a perfect complementarity of form between said metaphyseal part of the stem and the metaphyseal cortical bone, but also homogeneous distribution of stresses exerted by the weight of the patient, a large contact surface.

shape of the metaphyseal part of the stem, thanks to internal curvature and its bulge, ensures a perfect maintenance of this rod not only in rotation but also in the direction of the depression and tilting of this rod relative to the bone .

Preferably, said second instrument as well as the cutter that comprises this instrument are shaped so that the bore formed by the cutter when it is in said external position delimits, after machining, an outer wall inclined with respect to the axis. longitudinal of the femur, this inclination being such that this outer wall is close to the axis of the femur in the distal direction; the stem has, at its metaphyseal portion, an outer wall of corresponding shape.

This inclined wall allows, together with said inner bearing area, further strengthen the seat of the rod on the bone by cone effect, preventing any risk of depression thereof.

Preferably, the cutter of said second instrument has at least one portion of frustoconical shape, whose section is reduced in the distal direction; the stem has, at its metaphyseal part, walls of corresponding shape.

This cutter thus arranges at least one scope of corresponding frustoconical shape, which further increases the seat of the rod in the bone. Advantageously, in this case, said cutter has two frustoconical portions, of which that located at the distal level has a steeper slope than that located at the proximal level; the stem then has, at its metaphyseal portion, walls of corresponding shape, those located at the distal level form shoulders of frustoconical shape.

This distal frustoconical portion arranges, at the distal end of each bore that this cutter allows to develop, a frustoconical shoulder based on the metaphyseal part of the bone, against which rests a wall of complementary shape that includes the stem. This support further increases the longitudinal base of the rod relative to the assembly according to the invention may include at least one instrument for boring the femoral shaft, to calibrate the diaphyseal canal. It may be at least one rectilinear rigid structure boring instrument, suitable for the implementation of a rod with a right diaphyseal portion, and / or at least one flexible structure boring instrument. , guided not by a central rod, adapted to the establishment of a stem with diaphyseal curve.

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

This slot preferably has an angle of 45 with the inner-outer plane.

For a good understanding, the invention is again described below with reference to the attached schematic drawing showing, by way of non-limiting example, a preferred embodiment of the assembly it relates.

Figure 1 is a side view of a first instrument that includes, placed on the resected upper end of a femur; Figure 2 is a side view of a second instrument that includes, placed on the same end of the femur; FIG. 3 is an anteroposterior view of a femoral stem of a hip prosthesis that it comprises; Figure 4 is a view of this rod in the inner-outer plane; Figures 5 and 6 are views of this rod sectioned along the lines V-V and VI-VI of Figure 4, and Figure 7 is a view of another embodiment of said first instrument.

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

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

The instrument 3 comprises a base 5 and a cutter The base 5 has a diaphyseal rod 10 of similar shape to that of the diaphyseal portion 2b of the rod 2, a proximal rod 1 fixed to the rod 10, a distal slide 12 and a proximal slide 13.

rods 10 and 11 are adapted to be engaged tightly in the medullary canal of the bone 1 and to bear against the cancellous bone so as to be immobilized relative to this bone. In this immobilization position, shown in Figure 1, the rod 11 protrudes beyond the proximal end of the bone.

slides 12 and 13 are slidably mounted along the rod 1 1 and are guided thereon without lateral play or play tilting. distal slide 12 has an oblique blind bore 15 whose axis forms an angle of the order of 20 with the axis of the rod 11. This bore constitutes the bearing of a distal trunnion included in the cutter 6.

The proximal slide 13 comprises, on the inner side of the bone, an oblique bore whose axis is at the same angle with the axis of the rod 11 as that formed by the axis of the bore 15 with this same rod <B > 11. </ B>

The cutter 6 has a conical shape that flares from its distal end towards its proximal end, the generator of this cutter 6 corresponding to a curved shape that is desired to give to the internal cortex of the bone. At its proximal end, this cutter 6 is integral shaft 16 which is engaged and can rotate in the oblique bore of the slider 13. This shaft 16 is connected to a known type of means (not shown) for its rotational drive.

The instrument 4 also comprises a base 20 and a bur 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 portion, which allows these rods 22 to adapt to the anatomical curvature of the femur to be treated or to be able to fade cases of possible bone outgrowth within the medullary canal. This slot 25 also allows jamming of the rods 10, 22 by elastic deformation of this distal portion. This slot is arranged in a direction such that it forms an angle of 45 with the inner outer plane of the bone.

frame 23 has a distal end connected to the proximal end of the shaft 22. This distal end 30 has an antero-posterior axis bore in which is engaged and can pivot a cylinder which is pierced with a radial hole, and a lumen is provided in the proximal face of this distal end 30 to reveal this radial hole. last receives the distal end of a guide rod 32, on which the cutter is mounted axially sliding and around which it can rotate.

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

This proximal portion of the frame 23 comprises a plate 35 on which are fixed two curved rods 36 whose curvature is centered on the cylinder axis 31. At their free end, these rods 36 comprise end-pieces 37 forming stops, and a slide 38 is engaged and can slide on these rods 36. This slider is pierced with a bore which forms a bearing for the proximal shaft 39 to which the cutter 21 is connected.

This 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 cutter 21 on this guide rod 32 is between a retracted position of non-machining and a advanced position in which the cutter 21 can machine The cutter 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 21a, 21b, whose section is reduced in the distal direction. The range 21b located distally has a steeper slope than the reach 21a located at the proximal level.

The shaft 39 is connected to a known type of means (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 plane internal-external, namely an internal position, represented in dashed lines in this figure, in which the cutter mills the anterior and posterior cortical walls of the bone, and an external position, shown in solid lines by this figure, in which the Strawberry mills not only the anterior and posterior walls of the bone but also the outer wall of it. In this external position, the axis of the cutter 21 is inclined relative to the longitudinal axis of the femur, this inclination being such that this axis is close to the axis of the femur in distal direction.

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

The metaphyseal portion 2a of this rod 2 has, on its inner side, an edge 46 of curved shape in the inner-outer plane, which corresponds precisely 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), flares in the proximal direction, this flare also corresponding to the flared conical shape of the strawberry 6.

The metaphyseal portion 2a furthermore has two rounded bulges 47, each of which has a shape corresponding to that of the bur, that is to say has a frustoconical proximal portion 47a and a frustoconical distal portion 47b having a steeper slope than the portion 47a. . parts 47b thus form shoulders 48 of frustoconical shape based on 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 FIG. 2, and positioning of these bulges 47 with respect to edge 46 corresponds precisely to the arrangement of said two positions. machining ratio to the concave face of the curved portion of the frame 23.

The metaphyseal portion 2a thus has an inclined outer edge 49, which is close to the axis of the rod 2 in the distal direction.

In addition, the rod 2 comprises a neck 50 whose end is shaped Morse taper, the neck 50 being intended to receive articular spherical head 51.

In practice, the femoral neck is resected at the basal level to open the medullary canal of bone 1.

The base 5 is engaged in the bone until immobilization, then the slides 12, 13 and the milling cutter 6 driven in rotation are advanced, so that the milling cutter 6 mills the internal cortex of the bone according to the shape that corresponds to its generator.

once this machining performed, that is to say when the slider 12 has come into abutment against the rod 10, the instrument 3 is removed. The instrument 4 is then put in place until immobilization of its base 20 in the medullary canal and coming from the distal concave wall of the frame 23 bearing against the inner wall of the bone 1.

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

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

Figure 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; it is guided in a curved movement by sliding cylindrical pins 62 in two curved grooves 63, whose curvature corresponds to that sought for the inner wall of the bone. In the case of this instrument 3, the inner edge 46 of the rod 2 does not flare, although it is possible to also provide a lateral guide of the cutter 6 to perform a machining flaring in the proximal direction, to similar to that allowed by the cutter of the instrument shown in Figure 1.

The invention thus provides together for the establishment of a hip prosthesis femoral stem on a femur which overcomes many of the disadvantages of prior art counterparts. Indeed, together provides a solution to the problem of the stability of a femoral stem the time that occurs the bone growth that ensures the final anchoring of the stem to the bone, based on a relatively expensive technique and easy to implement.

It goes without saying that the invention is not limited to the embodiment described above by way of example but embraces, on the contrary, all the variants. Thus, the cutter 21 can be moved, while it is rotated, between the internal and external positions shown in FIG. 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, whose shape corresponds to this cavity.

Claims (1)

<B> CLAIMS </ B> 1 - Set for the establishment 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) of placing this rod (2) on the other hand; characterized in that it comprises - a first machining instrument (3) for machining the metaphyseal cortical bone at the inner wall of the femur (1) in a curved shape; this instrument (3) comprises (i) a base (5) forming a diaphyseal shaft (10) shaped to be engaged and locked in the medullary canal of the bone, (ii) a milling cutter (6) adapted to machine said cortical bone metaphyseal according to said curved shape, and (iii) guiding means (11 to 16; 61 to 63) of this cutter (6) for performing said machining; a second machining instrument for machining the metaphyseal cortical bone at 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 bone, this base (20) being closely supported on the inner wall of the bone as machined by means of said first instrument (3), (ii) a milling cutter (21) of diameter adapted to simultaneously machine the posterior anterior walls of the bone, as well as the external wall thereof when it is placed in an external position, and (iii) means (22 to 39) for guiding the cutter (21), making it possible to place it in at least two bore directions offset in the inner-outer plane, of which said external position, so that the cutter (21) allows to develop in said cortical bone a cavity defined by the shape of this mill and positions; and in that the femoral stem (2) has, at its metaphyseal portion (2a), (i) an inner edge (46) whose curvature corresponds precisely to the curvature of the inner wall the bone as 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, characterized in that said second instrument (4) and the cutter (21) that comprises the instrument are shaped such that said bore arranged when it is in said outer position defines after machining an outer wall inclined with respect to the longitudinal axis of the femur (1), this inclination being such that this outer wall is close to the axis of the femur (1) in the distal direction; the rod (2) has, at its metaphyseal portion (2a), an outer 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, whose section is reduced in the distal direction ; the rod (2) has, at its metaphyseal portion (2a), walls (47a, 47b) of corresponding shape .. 4 - Assembly according to claim 3, characterized in that said cutter (21) has two frustoconical portions ( 21a, 21b), 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 portion (2a), walls (47a, 47b) of corresponding shape, those located at the distal level form shoulders (48) of frustoconical shape. 5 - assembly according to one of claims 1 to 4, characterized in that it includes at least one boring instrument of the femoral shaft, for calibrating 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 the distal end portion can adapt to anatomical curvature of the femur (1) and may have sufficient elasticity to adapt to the deformations of the femur resulting from movements the joint. 7 - assembly according to claim 6, characterized in that slot (45) is an angle of 450 with the inner-outer plane.