FR2678162A1 - Femoral component of a hip prosthesis, which is to be cemented - Google Patents

Abstract

The femoral component of a hip prosthesis is intended to be embedded with the aid of a cement in a cavity formed in the epiphysis of the femur, following resection of the natural neck. It comprises a neck (5) projecting from a shaft (1) which will be inserted in the cavity. The shaft (1) comprises, at its lower part, a diaphyseal blade (2), and, at its upper part, an epiphyseal section (3) which is connected to the neck (5) via a base (4). The shaft (1) is limited by a plane rear wall (25) and a front wall (24) which, symmetrical with the rear wall (25) over the extent of the diaphyseal blade, curves inwards and forwards to connect with the base (4) of the neck (5). The neck (5) has an axis (11) which coincides at (12) with the axis (10) of the epiphyseal blade, and these two axes (10, 11) define a plane which forms, with the frontal plane passing through the axis (10), a dihedron of approximately 10@ towards the front. This position, which leads to distinct right-hand and left-hand components, is better adapted to the anatomy than are the usual components.

Description

Femoral component of hip prosthesis, to be cemented "
The invention relates to a femoral hip component, comprising a neck terminated in a truncated cone for the fitting of a spherical prosthetic head, and projecting from a barrel capable of being sealed with a polymer cement in a cavity practiced. in the upper epiphysis of the femur from a resection plane of the natural neck to the medullary canal, this bole comprising, between the neck and a diaphyseal blade with a rectilinear axis which tapers towards a lower terminal point, a section epiphyseal which widens from the blade to a neck base around a median fiber forming an arc whose amplitude corresponds to the natural cervico-diaphyseal angle, to connect the axis of the diaphyseal blade to that of the neck.

 In the present text, the terminology applied to the components of the prosthesis component will be modeled on the terminology relating to the anatomy of the femur and the coxo-femoral joint, and the adjectives used to define the relative position of the elements, referring, in the usual way, at this position relative to the human body. Thus, the diaphyseal blade will be placed in the upper part of the diaphysis of the femur, consisting of a tubular cortical wall surrounding the medullary canal, and the epiphyseal section will be inserted in the upper epiphysis of this femur. cortical wall enveloping a mass of cancellous bone, the sealing cavity being formed in this mass.

The cervico-diaphyseal angle is the angle formed by the respective axes of the neck and the diaphysis in its upper part.

 Joint prostheses, and in particular hip prostheses, are intended to be substituted for natural elements of the joint, damaged to restore the freedom of movement of the healthy joint.

 Now, the restitution of the freedom of movement of the joint has two aspects: a first aspect relates to the shape of the elements which are substituted for the deleted natural elements, and to their relative position with respect to the preserved natural elements. This essential aspect is that which is often limited to the state of the art.

 The other aspect, which aims to perfect the restitution of freedom of movement, relates to the connection of the prosthesis components to the bones which they complete, in order to obtain a transmission of the forces as close as possible to the natural transmission to which the bone structure is adapted, or at least, to which the organism is accustomed.

 Originally, the femoral components of hip prosthesis were sealed in a cavity dug in the upper epiphysis, using a biologically compatible crosslinking polymer; then appeared cementless implantable components: a first type sought the rigid connection of the barrel to the femur by wedging the barrel against the cortex; a second sought the rigid connection, at least in the long term, by a surface treatment of the barrel to provide the latter with a porous layer in which the spongy bone, growing, penetrates to form anchoring (this phenomenon is commonly called rehabitation ).

 However, the components to be cemented retain their interest in a certain number of indications, for example when the cortex cannot withstand without risk of bursting the jamming of the barrel, or when the growth of the cancellous bone surrounding the barrel risks be insufficient to rehabilitate the porous coating of the barrel.

 The component of the invention is intended to be cemented.

 Frequently, in the state of the art, it has been admitted that it was sufficient for the prosthesis component to correctly reproduce the cervico-diaphyseal angle for it to fulfill its function, adjusting the orientation of the axis of the neck projected onto a plane perpendicular to the axis of the diaphysis can be adjusted at the time of implantation by appropriately fitting the sealing cavity in the epiphysis. As a corollary, these prostheses can be used indifferently for coxo-femoral joints.

 The Applicants have found that, in particular for the femoral components to be cemented, the correct transmission of the forces from the hip joint to the leg bones requires an adaptation of the component to the structure of the upper epiphysis and the top of the diaphysis interested in the diaphyseal blade.

 For this adaptation, the invention provides a femoral component of a hip prosthesis, comprising a neck finished in a truncated cone for the fitting of a spherical prosthetic head and projecting from a barrel capable of being sealed by a polymer cement in a cavity made in the upper epiphysis of the femur from a plane of resection of the natural neck to the medullary canal, this bole comprising, between the neck and a diaphyseal blade with a rectilinear axis which tapers towards a lower terminal point , an epiphyseal section which widens from the diaphyseal blade to a neck base, around a median fiber forming an arc whose amplitude corresponds to the natural cervico-diaphyseal angle, to connect the axis of the blade diaphyseal to that of the neck, characterized in that, the component being structurally defined in relation to its implanted position, either right or left, the barrel has a flat posterior face and an anterior face which, being flat and symmetrical from the posterior face with respect to a frontal plane passing through the axis of the diaphyseal blade over the extent thereof, curves outward along the epiphyseal section to the base neck, while the axes of the neck and the diaphyseal blade are concurrent and jointly define a cervico-diaphyseal plane which forms with the median plane of the diaphyseal blade, and in front of this plane, a dihedral angle between 80 and 120 .

 By this arrangement, the barrel, and in particular the diaphyseal blade are suitably oriented relative to the femur around the axis of the blade, this axis coinciding with the axis of the diaphysis; this results from the fact that the diaphyseal cortex has a triangle-shaped section, with an anterior base and two external and internal sides forming a posterior angle, so that the diaphyseal blade can bear on the cortex with its median frontal plane parallel to the anterior base, against sides also inclined, near the angles with the base which are strongly rounded.Moreover, the tip of the diaphyseal blade is almost centered in the cortex, and does not bear on the cortical wall; this support of the tip of the diaphyseal blade on the cortical wall, which include many prostheses of the state of the art, is a source of pain for the implanted subject, and can cause loosening of the barrel.

 The defined orientation of the diaphyseal blade ensures the proper orientation of the axis of the neck of the femur, this neck being placed, on the upper epiphysis of the femur, in its natural position.

 In addition, the posterior flat face of the barrel constitutes a reference surface for the insertion of this barrel into the prepared cavity, while the front face curved outwards forms a cap to close the sealing cavity at the end of insertion, when the base of the neck base coincides with the resection plane of the natural neck, in order to prevent the cement being set backing up outside the epiphysis.

 In preferred arrangement, the barrel has rounded edges connecting its posterior and anterior faces, an internal edge which, rectilinear at the bottom of the diaphyseal blade, curves in a regular concave curve away from the axis of the blade. diaphyseal to join the neck base substantially parallel to the axis thereof, while the outer edge is formed of two straight concurrent segments, one extending along the diaphyseal blade approaching the axis of this towards the point, and the other over the extent of the epiphyseal section approaching the axis of the diaphyseal blade away from the point.

 Such a shape facilitates the insertion of the barrel into the cavity, insertion carried out by gradually raising the neck to fold down the diaphyseal blade until its axis coincides with that of the diaphysis in the area concerned; indeed, the convergence of the barrel edges along the diaphyseal blade ensures precise positioning of the axis of the blade in a frontal plane, while the shape of the outer edge along the epiphyseal section makes it possible to save the greater trochanter and the ligament insertions located there.

 Preferably, the terminal tip of the diaphyseal blade is in the form of a spherical cap. This means that the thicknesses of the diaphyseal blade at its tip in the frontal plane and perpendicular to this plane are equal, which allows the tip to be located away from the cortical wall, with security.

 Preferably also, the epiphyseal section has, on the external side of the base of the neck, a substantially planar upper facet and perpendicular to the axis of the diaphyseal blade. This facet will be struck to perfect the positioning of the component by "impaction", the shocks thus acting in the axis of the diaphyseal blade.

The characteristics and advantages of the invention will appear more clearly from the description which follows by way of example, with reference to the appended drawings in which:
- Figure 1 is an elevation, seen from the front side, of a femoral component according to the invention;
- Figure 2 is an elevation, seen from the external side, of the component of Figure 1;
- Figure 3 is a plan view, from above, of the component of Figures 1 and 2;
- Figures 4 and 5 are views, corresponding to Figures 1 and 2, of a femoral component, equipped with a spherical head, this component being of the minimum size of a family with increasing sizes.

 Depending on the embodiment chosen and shown in Figures 1 to 3, the prosthesis component comprises a barrel 1, which will be engaged in the femur properly prepared by a subject, and a neck 5 which projects from the barrel 1 to which it connected by a base 4, and ends with a truncated cone 6 (Morse cone) on which a spherical head will be fitted which will be engaged in a cup, natural or prosthetic, to establish the natural joint, the neck 5 and the head of the femoral component replacing, in location and function, the natural elements of the same name.

 The barrel 1 is intended to be engaged over its entire length, and sealed using a polymer cement, often of the acrylic type, in a cavity of shape formed in the upper epiphysis of the femur of the subject, the cavity s' extending from a plane of resection of the natural cervix to the medullary cavity of the diaphysis.

 The barrel 1 comprises a diaphyseal blade 2 with a rectilinear axis 10 which tapers towards a lower end point 7, and an epiphyseal section 3 which widens from the diaphyseal blade 2 to the base 4 of neck 5, and which s' extends around a median fiber 13 in an arc which connects the axis 10 of the diaphyseal blade to the axis 11 of the neck 5. The amplitude of the arc of the median fiber 13 corresponds to the natural cervico-diaphyseal angle from subject. The average cervico-diaphyseal angle being 1350, the arc of the median fiber 13 subtends an angle of 450, supplementing the cervico-diaphyseal angle. The axes 10 of the diaphyseal blade 2 and 11 of the neck 5 are concurrent in point 12, and the cervico-diaphyseal angle comprises three components in three orthogonal planes: a frontal component 15 in a frontal plane (by anatomical reference) which is the plane of FIG. 1, a horizontal component 16 in a horizontal plane (plane of FIG. 3), and a sagittal component 17 in a plane passing through the axis 10 of the diaphyseal blade 2 and perpendicular to the frontal plane, ie the plane of FIG. 2.

 The horizontal component 16 corresponds to a dihedral angle made by a cervico-diaphyseal plane which contains the two axes 10 of the diaphyseal blade 2, and 11 of the neck 5 with the frontal plane which passes through this axis 10 of the diaphyseal blade 2.

 The femoral component shown in Figures 1-3 is intended for a straight femur. The axis 11 of the neck 5 is directed forward, from the dihedral angle 16, of the frontal plane passing through the axis 10 of the diaphyseal blade 2, to reproduce the arrangement of the human pelvis, in which, in upright standing, the general axes of the femoral diaphyses are parallel to a frontal plane passing through the center of the acetabulum and a little behind. The dihedral angle 16 reproduces the natural angle of the neck of the femur in projection on a horizontal plane with the frontal plane, which is approximately 100, and this angle 16 will be between 80 and 120.

 The representations of the corresponding left femoral component will be the specular image of the representations of the right component.

 The barrel 1 has a flat rear face 25, and a front face 24 which is flat and symmetrical with the rear face 25 over the extent of the diaphyseal blade 2 relative to the frontal plane passing through the axis 10 of the diaphyseal blade; the two faces 24 and 25 converge towards the terminal tip 7, making a dihedral angle of the order of 10 each with the frontal plane, as can be seen in FIG. 2 where the faces and the frontal plane are seen at the end.

 The anterior face 24 curves outwards over the extent of the epiphyseal section 3 from the diaphyseal blade 2 to its connection 24a to the base 4 of the neck 5.

 The rear 25 and front 24 faces are joined by rounded edges, an internal edge 20, 22 and an external edge 21, 23.

Over the extent of the diaphyseal blade 2, the internal edge 20 and external edge 21 parts are straight, symmetrical with respect to the axis 10 of the diaphyseal blade, and converging towards the terminal tip 7, the half-angle of convergence being about 30
The terminal point 7 has the shape of a cap, approaching an ellipsoid, and is connected without breaking to the faces 24 and 25 and to the edges 20 and 21.

 The internal edge, over the extent of the epiphyseal section 3 curves in a regular concave curve 22 away from the axis 10 of the diaphyseal blade 2 to join the base 4 of the neck 5 substantially parallel to the axis 11 of the last.

 Furthermore, the outer edge is composed of two concurrent straight segments 21 and 23. The first segment 21 extends from the point 7 beyond the diaphyseal blade 2, where it formed the symmetrical part of the internal edge part 20 relative to the axis 10. The second segment 23 approaches the axis 10 from the segment 21 to a facet 8 which crowns the epiphyseal section 3, is flat and perpendicular to the axis 10 of the diaphyseal blade 2, and merges into the base 4 of neck 5.

 It will be understood that the succession of the axis 11 of the neck, of the arcuate middle fiber 13, and of the axis 10 of the epiphyseal blade 2 constitutes substantially the neutral fiber of the beam formed by the femoral component, in order to be placed in approximate coincidence at best with the neutral fiber of the healthy natural femur while the inner edge 20, 22, and the segment 21 of the outer edge are in contact distributed over the majority of their length on the cortex, to ensure precise centering of the axis of the barrel, and a non-localized transmission of forces. This not only restores a joint which has the same freedom of movement as the healthy natural joint, but also makes the pelvic bones and the leg adjacent to work the joint under the same conditions of application of forces as the healthy joint, the lines of force to which the organism is adapted or accustomed being respected.

 The component is made of TA6V titanium alloy, and the faces 24, 25 and edges 20, 22; 21, 23 are treated by microbeading to promote the adhesion of the cement.

 For the establishment, after resection of the natural cervix by a plane substantially perpendicular to the axis which spares the trochanters as well as possible, a cavity is practiced in the epiphysis starting from the resection plane to open into the medullary canal, the cavity having a shape corresponding to that of the barrel 1. This will be introduced into the cavity previously filled with cement with its frontal plane in coincidence with the frontal plane of the femur, the posterior face 25, flat, resting on a surface, cut in the upper epiphysis, also flat. On the other hand, the cavity being arched in the frontal plane to connect the axis of the neck to the axis of the diaphysis, the barrel 1 will be introduced along the frontal plane by gradually tilting to straighten the axis 10 of the diaphyseal blade. shape in two rectilinear segments 21 and 23 of the outer edge of the barrel 1 is suitable for insertion in a curve, and makes it possible to reduce the grip of the cavity in the greater trochanter.

 The stripped shape of the barrel 1 provided by the convergence towards the point 7 of the faces 24 and 25 and of the edges 20 and 21 ensures that the cement is distributed in a thin layer of almost uniform thickness, guaranteeing good resistance to service trips.

 Furthermore, due to the slight curvature of the diaphysis of the femur in a sagittal plane, with concavity towards the front, the anterior face 24 will bear, at the origin of the medullary canal, on the anterior face of the cortex, while the posterior face 25 of the barrel 1 door, a little above the terminal tip 7, in the angle of the internal and external faces of the cortex, this double support ensuring good coincidence of the frontal planes of the diaphysis of the femur and of the diaphyseal blade 2.

 This arrangement allows the terminal tip 7, in a cap, to be substantially centered in the medullary canal.

 It will also be noted that the increase in thickness of the barrel 1 towards the base of the neck 5, resulting from the outward curving of the front face 24 has the effect that the connection 245a of this face to the base 4 of the neck closes, in the last phase of implantation of the femoral component, the cavity where the barrel 1 is housed, so that the sealing cement cannot be extruded outside.

 In addition, this arrangement prohibits rotation of the barrel around the diaphyseal axis during implantation, rotation which would distort the desired orientation of the neck relative to the femur.

 The component represented corresponds in structure to that which has been described with reference to FIGS. 1 to 3: however, it is shown provided with a spherical head 9 except the frustoconical recess for the engagement of the truncated cone of the neck 5, and the frustoconical peripheral zone which surrounds the recess. This head is in itself classic, and made of alumina ceramic.

 As it is necessary to adapt the dimensions of the femoral component to the dimensions of the femur, a family of components has been provided which all have the same basic structure, but have suitable sizes. These variations will be of two kinds, bearing on the one hand the length of the neck 5, on the other hand the size of the barrel.

 The neck length must be provided independent of the size of the barrel; three lengths are adapted, namely counted from the point 12 of coincidence of the axes 10 of the diaphyseal blade and 11 of the neck, to the center 9a of the head, substantially 60.4, 56 and 51.5 mm.

 For the size of the barrel, we adopted 8 sizes, which are distinguished by three parameters which vary jointly: the length of the barrel between the facet 8 and the terminal tip 7, the thickness of the barrel between faces 24 and 25, and the width between edges 20, 22 and 21, 23, while are kept: the development of the internal edge 20, 22, the angles at the top between edges 20 and 21 and between faces 24 and 25; however, the axis 10 of the reference diaphyseal blade 2 for the point of competition 12 of this axis with the axis of the neck 11 will be that of the component of the minimum size, that is to say always in the same position relative to the internal edge 20, 22.

 Thus for example, the length of the barrel will range between 141 and 162 mm, the width (at the height of the transition between diaphyseal blade and epiphyseal section) will range between 11.5 and 18.5 mm, and the thickness ( at the same height) between 7.8 and 12.2 mm.

 These size normalizations are intended to establish a compromise between the anatomical requirements of the subjects, and the industrial constraints of rational execution of prosthesis components.

Claims (4)

 1- Femoral component of hip prosthesis, comprising a neck (5) terminated in a truncated cone (6) for the fitting of a spherical prosthetic head (9) and projecting from a barrel (1) capable of being sealed by a polymer cement in a cavity made in the upper epiphysis of the femur from a resection plane of the natural neck to the medullary canal, this barrel (1) comprising, between the neck (5) and a diaphyseal blade ( 2) with a rectilinear axis (10) which tapers towards a lower terminal point (7), an epiphyseal section (3) which widens from the diaphyseal blade (2) to a base (4) of neck (5) ), around a median fiber (13) forming an arc whose amplitude corresponds to the natural cervico-diaphyseal angle, to connect the axis (10) of the diaphyseal blade (2) to that (11) of the neck (5), characterized in that, the component being structurally defined in relation to its implanted position, either right or left, the barrel (1) has a post face flat (25) and an anterior face (24) which, being plane and symmetrical with the posterior face (25) with respect to a frontal plane passing through the axis (10) of the diaphyseal blade (2) over the extent of the latter, curves outwards along the epiphyseal section (3) to the base (4) of the neck (5), while the axes (11, 10) of the neck (5) and of the diaphyseal blade (2) are concurrent and jointly define a cervico-diaphyseal plane which forms with the median plane of the diaphyseal blade (2), and in front of this plane, a dihedral angle (16) between 80 and 120.  2- Component according to claim 1, characterized in that the barrel (1) has rounded edges (20, 22; 21, 23) connecting its front (24) and rear (25) faces, an internal edge (20, 22 ) which, rectilinear (20) to the lower part of the diaphyseal blade (2), curves in a regular concave curve (22) away from the axis (10) of the diaphyseal blade (2) to join the base (4) of the neck (5), substantially parallel to the axis (11) of the latter, while the outer edge (21, 23) is formed of two concurrent straight segments, one (21) s 'extending along the diaphyseal blade (2) approaching the axis (10) thereof towards the tip (7), and the other (23) extending along the epiphyseal section (3) by approaching the axis (10) of the diaphyseal blade (2) away from the tip (7).  3- Component according to one of claims 1 and 2, characterized in that the terminal tip (7) of the diaphyseal blade is in the form of a cap connecting without break to the faces (24, 25) and edges (20, 21) blade (2)  4- Component according to any one of claims 1 to 3, characterized in that the epiphyseal section (3) has, on the external side of the base (4) of the neck (5), a facet (8) substantially planar and perpendicular to the axis (10) of the diaphyseal blade (2).