FR2578738A1 - Self-stable femoral rod with maximum support for hip prosthesis - Google Patents

Abstract

The anterior and posterior edges of this rod are capable of coming into contact over their whole length with the internal and external corticals of the medullary canal and are each formed by a flange 7-8 with decreasing cross section extending over the whole length of the rod, these flanges, connected together at the top by a transverse flange 9, connected to the receiving tenon 3 of the femoral head, delimiting together, with the transverse flange 9, and on either side of the rod, a concave housing 10 extending over almost the whole height of the rod, emerging at its bottom part and constituting a lateral receptacle for the connecting cement.

Description

 "Freestanding femoral stem with maximum support for hip prosthesis".

 The hip prostheses are composed of a femoral stem able to penetrate the femur and of a femoral head of general hemispherical shape which, able to pivot in the acetabular cavity of the hip, is fixed by axial interlocking on a protruding post of the femoral stem.

 This femoral stem is placed in a housing produced in the medullary canal by means of a shaped rape. Cement is interposed between the rod and its housing to ensure its connection with the femur, but especially to ensure its blocking in rotation and the distribution of forces between the rod and the femur.

 In practice, under the effects of the load supported by the femoral stem and under the oscillating transverse movements urging this stem, it happens that the cement loses its power of connection and authorizes a loosening of the stem. Although infrequent, this loosening requires a new operation, that is to say an expensive and painful intervention for the patient.

 To remedy this, it is already known to ensure the connection of the lower part of the rod, without recourse to cement and by its only mechanical wedge directly between the cortices, respectively internal and external. However, if this assembly improves the reliability of the connection of the lower end of the rod, it retains in upper part the disadvantages inherent in the presence of cement between the anterior and posterior edges of the prosthetic rod and respectively the internal cortices and external.

 One of the objects of the present invention is to remedy these drawbacks by providing a prosthetic stem not requiring cement between its anterior and posterior edges and the corresponding faces of the medullary canal.

 In addition, most of the femoral stems are provided with an upper flange, the bearing face of which rests, at the end of introduction into the medullary canal, on the cortical bone (MERCKEL SPUR).

 This flange therefore limits the engagement of the rod in the channel.

If this limitation is not annoying for prostheses fixed to cement, case in which the cement fills the intervals between medullary canal and prosthetic stem, in the case of prostheses at least partially freestanding, it disturbs direct contact with the walls of the canal and fixing by wedging.

 Another object of the invention is to provide a prosthetic stem, the insertion of which into the medullary canal is not limited by a collar.

 To this end, according to the invention the anterior and posterior edges of the femoral stem are capable of coming into contact over their entire length with the cortices, internal and external, of the medullary canal and are each formed by a bead of decreasing section and s extending over the entire length of the rod, these beads, connected to each other in the upper part by a transverse bead connected to the tenon for receiving the femoral head, delimiting between them, with the transverse bead, and on each side of the rod, a concave housing extending over almost the entire height of the rod, opening from its lower part and constituting a lateral receptacle for the bonding cement.

 When this prosthesis is engaged in a medullary canal produced by a rape having the same external profile as it, the anterior and posterior edges of its beads come into contact directly against the internal and external cortices and therefore provide maximum support insensitive to transverse stresses . The cement introduced into the canal, intended to ensure the connection of the prosthesis with the femur, is distributed in the lateral concave housings of the stem and thus opposes the transmission of oscillatory stresses. Due to the replacement of the traditional collar with an upper transverse bead, the femoral stem is introduced into the medullary canal until the maximum support, thus compensating for the dimensional defects of the medullary canal produced by the rape.

 In one embodiment of the invention, the rod comprises, on the one hand, a blind housing of polygonal section which, formed in the transverse upper bead and emerging from the upper face of this bead, is capable of receiving the end, of complementary section, of an impact and orientation tool of this rod, and, on the other hand, at least one lateral notch, opening laterally and downwards, and able to cooperate with the end d a tool for disimpaction.

 Thanks to the polygonal section of the blind housing, the surgeon can orient the rod precisely with respect to the medullary canal by transmitting to this rod a force of rotation by means of a simple tool.

 Advantageously, the protruding tenon of the rod has a conical shape and constant dimensions whatever the various dimensions of the rod, and is associated with several series of femoral heads, spherical differentiated by variations in external diameter, each of the heads of each series differing in several dimensions from the exit diameter of the internal cone to modify the value of the distance between the base, the base of the post and the top of the femoral head.

 Thus, the vertical position of the femoral head relative to the femur can be adjusted according to the applications, or to compensate for the more or less significant penetration of the rod into the medullary canal.

 This possibility of adjustment makes it possible to adapt various elements, such as a cephalic piece in the case of a cephalic prosthesis, a femoral head with an acetabulum to be sealed or screwed in the case of a total prosthesis, and a femoral head with cup in the case of an intermediate prosthesis, and in case of reoperation, to interchange the upper elements of the prosthesis, for example to switch from a cephalic prosthesis to a total prosthesis, or from an intermediate prosthesis to a total prosthesis . It should be noted that this interchangeability takes place without the need to unseal the femoral stem.

 This prosthesis also covers all clinical cases by using far fewer elements than current specialized prostheses.

 Other characteristics and advantages will emerge from the description which follows with reference to the appended diagrammatic drawing representing, by way of nonlimiting example, an embodiment of this femoral stem.

Figures 1 and 2 are elevational views respectively from the front and from the side
Figures 3, 4 and 5 are sectional views along respectively 3-3, 4-4 and 5-5 of Figure l #;
Figure 6 is a cross-sectional view showing the prosthesis produced with the femoral stem implanted in a medullary canal;
Figure 7 is a side view in section along substantially 7-7 of Figure 6 showing on an enlarged scale the distribution of cement around the femoral stem.

Figure 8 is a partial perspective view showing an embodiment of the upper end of the rod with blind impaction housing and deimpaction notch
Figures 9, 10 and 11 are partial views of the upper end of the rod illustrating the adjustment provided by the inner cones of the femoral heads.

Figures 12 and 13 are partial side views in elevation of the upper end of the rod showing other femoral heads,
Figures 14 to 17 are views similar to Figures 1 to 4 showing an alternative embodiment of the rod,
FIG. 18 is a view similar to FIG. 7 showing in cross section and on an enlarged scale the rod of FIGS. 14 to 17 placed in the medullary canal,
FIG. 19 is a perspective view of an embodiment of a corner associable with the prosthesis,
Figure 20 is a sectional view along 20-20 of Figure 6 showing the corners in place.

 As shown in Figure 6, this prosthesis consists, in known manner, of a femoral stem (2) carrying a stud (3) on which is fitted a hemispherical femoral head (4) pivoting in a cup (5) fixed in the acetabular cavity (6).

 According to the invention, the anterior and posterior edges of the femoral stem (2) are formed by beads (7-8) of decreasing section from top to bottom and extending over its entire length. These beads are connected, to each other and to their upper part, by a transverse bead (9) with which they delimit, on each side of the - rod, a concave lateral housing (10). This housing extends over the entire height of the rod and opens at the lower end thereof. As shown in more detail in FIGS. 4 and 5, the front bulges (7-8) have a generally cylindrical cross-section in connection with the concave bottom of the housing (10). In addition, the rear bulge (8) has, in each of the cross sections of the rod, of transverse dimensions and in particular a radius greater than the radius of the bead (7) in the same cross section.

 As shown in FIG. 3, the upper transverse bead (9), also of generally cylindrical shape, is connected to the bottoms of the housings (10) by flat faces (12) forming a "V" of angle (a) and it giving a wedge shape.

 The beads (7-8) are connected near a shoulder (13) from which protrudes the stud (3) capable of receiving the femoral head (4).

 Before placing this rod in a femur (15), the medullary canal (16) is enlarged by means of a rape having, in front view, a profile identical to that of the rod (2) seen from the front. Thus, when the prosthesis is introduced into this canal, its edges and in particular its anterior (7) and posterior (8) beads come, over almost the entire height, in contact with the internal and external faces of the femoral cortex. As shown in Figure 6, contact is maximum on all areas capable of supporting the prosthesis, namely, on the cortices of the metaphysis and on the spur of Merckel; only the lower end of the rod is not in contact with the cortex, but this is not a problem, given the area where this lower end is placed and the intimate contact between the rest of the prosthesis and the medullary canal.

 It should be noted that the insertion of the rod into the channel is not limited as is the case with the rods comprising a flange and that it can therefore be carried out up to maximum contact. Under these conditions, the upper transverse bead (9) acts in the form of a wedge and engages without difficulty in the diaphysis.

 During this insertion, the cement, previously placed in the medullary canal (16), is naturally distributed in the lateral housings (10) of the rod, as shown in (17) in FIG. 7. As a result, the cement does not is not placed in the force transmission zones between the rod and the femur and is therefore not likely to cause loosening by loss of connection between the rod and the femoral. By its arrangement, the cement fulfills a unique function of locking the rod in the medullary canal.

 It emerges from the above that this rod, thanks to its structure, its shape and its thickness, makes it possible to obtain the maximum support sought, support leading to very great stability of the prosthesis in the femur.

In addition, the stresses exerted on the bone are distributed in an extremely diffuse manner, which prevents any localized wear. Furthermore, if under the effect of the prosthesis the prosthesis is subjected to a migration, this does not take place at the expense of localized wear of the neck, but like a nail which penetrates deeply into its housing. In other words, this migration has little effect on the overall stability of the prosthesis.

 In the embodiment shown in FIG. 8, the rod comprises an impaction housing (20) and at least one lateral disimpaction notch (22). The housing (20) which is blind, has a polygonal section and is formed in the upper bead (9). It emerges from the upper face of this bead. This housing is able to cooperate with the end (23a) of the same cross section of an impact tool (23). In the embodiment shown, the housing (20) and the end (23a) of the tool have a hexagonal section but they can have any other polygonal section. When the rod is placed in the medullary canal, the introduction of the end (23a) into the housing (20) makes it possible to use the impaction tool as a means of orienting the rod and its tenon (3).

 The notch (22) opens laterally downwards and is able to cooperate with a deimpaction tool (24) of the type shown in FIG. 8.

The housing (20) and the notch (22) do not affect the physical characteristics of the femoral stem but on the other hand facilitate its installation, its orientation and possibly its extraction if necessary.

 Advantageously, the post (3) of the femoral stem always has the same dimensions, that is to say the same base diameter, the same conicity and the same height whatever the dimensions of the stem which vary according to the dimensions of the femurs. meeting normally. This post is able to cooperate with several series of femoral heads differentiated by their diameters, as shown for the heads (4a-4b-4c) of Figures 10, 12 and 13, but also by the size of their inner cone. For this purpose, as shown in Figures 9 to 11, the cones (25) of the femoral heads (4al-4a2) have the same conicity but differ in their depth and in their diameter of exit from the head. More specifically, the diameters outlet go from the head (4al) to the head (4a) and to the head (4a2) so that, once placed on a tenon (3), the distance (1) between the base of the flat ( 13) and the top of the corresponding head decreases. In practice, the outlet diameters of the heads (4al-4a2) are determined so that once placed on the post, the head (4al) is higher than that (4a) and that (4a2) is lower than the latter. This arrangement, used for each series of heads (4a-4b-4c) allows by selecting the most suitable head in each series, to adjust the height of the head according to the insertion of the rod into the medullary canal or depending on the upper element of the prosthesis to be fitted. Furthermore, this possibility of adaptation makes it possible, from the same rod, to install either a cup to be sealed or a cup to be screwed in the case of a total prosthesis, an intermediate cup in the case of a intermediate prosthesis, and a cephalic part in the case of a cephalic prosthesis.

 Thanks to this interchangeability of the upper elements of the prosthesis, it covers practically all clinical needs and thus considerably reduces the stocks that every surgeon must have.

 This interchangeability is also advantageous in the case of a new intervention because it makes it possible to replace the top element of the prosthesis without having to unseal the stem, which, on the one hand, simplifies the operation, and on the other hand, reduces post-operative trauma.

 Figures 14 to 17 show an alternative embodiment in which the rod (2a) has in each of its beads (7-8) a groove respectively (30-31). Each of these grooves has a rectangular cross section with a rounded bottom and is connected to the corresponding bead by rounded sections (32). It extends from the collar (33) of the rod to the lower part of the latter.

 As shown in Figure 18, this rod (2a) is intended to be placed in the channel (16a) delimited by the broken lines. Under these conditions, the grooves (30-31) coming in the immediate vicinity of the femoral cortex form rehabilitation housing for the coming bone. The connection is ensured with or without cement.

 To improve the wedging of the rod (2 or 2a) in the cancellous body (34) of the bone, the rod is associated with corners (35) of the type represented in FIG. 19. Each corner, comprising two sloping side faces (36a) and at least one sloping longitudinal face (36b) has at least one convex longitudinal face giving it in cross section the shape of a segment of a circle. In Figures 19 and 20, the two convex faces give it the shape of a meniscus. Each corner is provided with a groove (37) allowing its possible withdrawal. As shown in Figure 20, each corner (33) is pressed into the upper part of the medullary canal on either side of the rod (2 or 2a) by forcing in the spongy body (34). Although more particularly interesting for laying without cement, these corners can also be used for fixing with cement, in which case they reduce the volume of the cement used and the risk of loosening.

 These corners are part of a series of corners differentiated by their thickness so as to be able to be adapted to the needs, and to the interval between the rod (2 or 2a) and the internal wall of the medullary canal (16). When they have only one convex face, this one leans against the spongy body (34).

Claims (8)

 1. Self-supporting femoral stem with maximum support for hip prosthesis of the type provided with a tenon (3) capable of receiving a hemispherical femoral head (4) characterized in that its anterior and posterior edges are capable of coming into contact on any their length with the internal and external cortices of the medullary canal and are each formed by a bead (7-8) of decreasing section and extending over the entire length of the rod, these beads, connected together and in the upper part by a transverse bead (9), connected to the receiving post (3) of the femoral head, delimiting between them, with the transverse bead (9) and on each side of the rod, a concave housing (10), extending over the almost the entire height of the rod, emerging from its lower part and constituting a lateral receptacle for the bonding cement.  2. Femoral stem according to claim 1 characterized in that the posterior bead (8) has, at least for its part corresponding to the femoral neck and for each of its cross sections, larger transverse dimensions than those of the anterior bead (7) .  3. Femoral stem according to any one of claims 1 and 2 characterized in that the transverse bead (9) is connected to the faces of the lateral housings (10) by planar "V" faces giving it a wedge shape.  4. Femoral stem according to any one of claims 1 to 3 characterized in that the anterior (7) and posterior (8) beads, of generally cylindrical section, are connected directly to the concave faces of the lateral housings (10).  5. Femoral stem according to claim 1 and any one of claims 2 to 4 characterized in that the stem comprises, on the one hand, a blind housing (20) of polygonal section which, formed in the upper transverse bead (9 ) and emerging from the upper face of this bead (9) is capable of receiving the end of complementary section of a tool (23) for impaction and orientation of this rod and on the other hand, at least one lateral notch (22) opening laterally downwards and able to cooperate with the end of a disimpaction tool (24).  6. Femoral stem according to claim 1 and any one of claims 2 to 5 characterized in that the stud (3) projecting from the stem, has a conical shape and constant dimensions, whatever the various dimensions of the stem, and is associated with several series of spherical femoral heads (4a-4b-4c) differentiating by variations in external diameter, each head of each series (4al-4a4a2) differentiating by several dimensions from the exit diameter of the internal cone to modify the value of the distance (I) between the base, the base of the post and the top of the femoral head.  7. femoral stem according to claim 1 and any one of claims 2 to 6 characterized in that a groove (30-31) with rounded bottom and rounded edges is formed in each of the anterior (7) and posterior (8) ).  8. Femoral stem according to claim 1 and any one of claims 2 to 7 characterized in that it is associated with at least one lateral corner (35) comprising lateral (36a) and longitudinal (36b) sloping faces and at minus a convex longitudinal face for backing onto the spongy body.