FR2661328A1 - Femoral shaft for hip prosthesis - Google Patents

Abstract

Published without abstract.

Description

 "Femoral stem for hip prosthesis".

 The invention relates to hip prosthesis.

 The duration of a hip orthoplasty depends on the subject's anatomy, the materials used, the operating technique, the age and activity of the subject, and the size of the implant.

 The study of the evolution of femoral implants during these last twenty years, shows a general tendency to the use of more massive prostheses, limiting or eliminating the use of cement, while seeking to fill as well as possible the medullary cavity and especially metaphyseal of the femur. This development is intended to best compensate for the considerable changes in the biomechanics of the end of the femur, changes brought about by the installation of a femoral prosthesis. In fact, the stresses transmitted to the femoral cortices are communicated to the femur via the femoral prosthesis. As a result, the primary stability of a prosthesis, whether placed with or without cement, seems essential for the duration of this prosthesis.

 One of the objects of the present invention is precisely to obtain excellent primary stability from a prosthesis of the type whose diaphyseal part is rectilinear and is extended by a proximal part inclined with respect to the sagittal plane and with respect to the plane vertical front to provide the anteversion angle to the tenon for receiving a spherical head.

 Another object of the invention is to increase stability over time by improving bone rehabitation.

 According to the present invention, the proximal part of the prosthesis is in the shape of an anatomical tulip and has, on the one hand, at least on its faces, respectively anterior and posterior, generatrices connecting to the generatrices of its diaphyseal part and having, each and successively, a concave profile, of constant radius, then a convex profile of constant radius, going towards the top of the rod where these generatrices are connected by a rounding of small radius with the surface of which the stud protrudes and, d 'on the other hand, an elliptical cross section with progressive decrease between the aforementioned face and an area joining the bases of the small and large trochantera.

 Thanks to the anteversion of the proximal part and its anatomical shape, this prosthesis ensures good metaphyseal filling ensuring a uniform distribution of pressures and eliminating as much as possible the areas of hyper and hypopressure. Its anatomical and freestanding shape allows it to be placed with or without cement.

 In one embodiment, the proximal part of this prosthesis comprises, over its entire periphery, spaced grooves and of substantially vertical direction, for stabilization and rehabitation, while the periphery of this proximal part is covered by an undercoat. made of porous titanium forming a bond for a thin layer of sprayed ceramic.

 Thanks to this arrangement, bone rehabitation, which is easily carried out on the ceramic layer, is improved by the porous titanium under layer and by the grooves. In this way, at the end of re-habitation, the proximal part of the rod is really one with the femur and is perfectly wedged in it, both vertically and transversely.

 Other characteristics and advantages will emerge from the description which follows with reference to the appended schematic drawing showing by way of nonlimiting examples an embodiment of this femoral stem.

FIG. 1 is a partial view in elevation in the sagittal plane of the prosthesis,
Figures 2 and 3 are partial views, in partial section, and respectively in the frontal plane and in the sagittal plane of the femur, showing another embodiment of this prosthesis.

 In known manner, this prosthesis rod is composed of a diaphyseal part indicated by A in FIG. 2 and a proximal or metaphyseal part indicated by B.

 In its diaphyseal part A, the rod 2 has a cross section going from an elliptical shape to a circular shape in the direction of its distal and external part.

 Its proximal part is integral with a post 3 with frustoconical head 4, capable of receiving a femoral head, not shown. This post is inclined at an angle (a) relative to the sagittal median plane P1 containing the axis x'x of the diaphyseal part A of the rod and is inclined at an angle (b) relative to the frontal median plane P2 containing the aforementioned x'x axis. Thanks to this double inclination, the neck of the prosthesis, formed by the tenon 3 and the frustoconical part 4, is, with respect to the lower part of its stem, in the same anteversion position as the head of a femur.

 The proximal part B of the rod 2 is in the shape of an anatomical tulip. More precisely, and as shown in FIG. 1, at least the faces, respectively, anterior 5 and posterior 6, of the proximal part B comprise generatrices which, connecting to the straight generatrices of the lower part, present, successively and going towards the top of the rod, respectively, a concave profile 5a-6a, of constant radius R1-R2, and a convex profile, respectively 5b-6b, of constant radius R3-R4. These generatrices are connected to the face 7, from which the stud 3 protrudes, by a rounded radius, designated by 8. It is obvious that the anteroposterior faces 5 and 6 are connected by transition zones to the faces d 'support 9 and 10 with a straight tendency.

 Furthermore, the proximal part B has an elliptical cross section, extending between the face 7 and a zone C defined by a plane which, substantially parallel to this face 7, passes approximately beneath the large trochanterus 11 and the small trochanterus 12 as shown in figure 2. This section goes up to face 7.

 Thanks to this tulip shape conforming to the shape of the end of the medullary canal 14, the proximal part of the prosthesis provides very good metaphyseal filling and completes, in the trochanteric massif, the self-locking already ensured by the bearing faces. 9 and 10, by increasing, by the anteroposterior faces, the contact zones between the rod and the bone. This arrangement improves the distribution of pressures between the prosthesis and the bone and removes all areas of hyper and hypopressure which are detrimental to the longevity of the orthoplasty.

 Such a prosthesis can be placed with or without cement.

 It is obvious that to facilitate its perfect filling of the medullary cavity, such a rod is produced with a right or left orientation and in several sizes, and for example seven sizes, having dimensions going from the smallest rod to the most large stem.

 It should also be noted that this growth also applies to the length of the post 3, which makes it possible, by using femoral heads having different cone diameters, to obtain an adjustment of the position of the distance from the head relative to on face 7 in relation to the patient's morphology.

 In a preferred embodiment, and as shown in Figures 2 and 3, the proximal part of the prosthesis comprises over its entire periphery spaced grooves 16 and of substantially vertical direction, that is to say parallel to the axis x 'x. These grooves ensure the stabilization of the prosthesis and promote bone rehabitation.

 Advantageously, this rehabitation is also favored by covering the proximal part of the prosthesis, on the one hand, by an under layer of porous titanium and, on the other hand, by a thin layer of ceramic 17. The titanium layer and the layer ceramic are, in known manner, placed on the peripheral face of the prosthesis, including in the grooves 16, by projection with a plasma torch.

 The combination of a ceramic layer, known for its ability to promote bone rehabitation, with a porous titanium under layer, providing cavities improving the bonding, considerably accelerates the rehabitation time and greatly promotes rehabitation in the grooves. 16.

 As shown in Figure 2, the grooves 16 are associated with at least one rib 18, arranged in the interval between two grooves, and projecting outside the proximal part, parallel to the axis x'x. This rib, which is arranged on at least one of the faces 5 and 6, strengthens the stability of the implant and opposes any rotation on itself of the prosthesis, that is to say any movement tending to implicate bone rehabitation, but also the orthoplesty itself.

Claims (4)

 1. Femoral stem for hip prosthesis of the type whose diaphyseal part A is rectilinear and is extended by a proximal or metaphyseal part B, inclined relative to the sagittal median plane P1 and relative to the frontal median plane P2 to provide an angle of anteversion to the post 3 for receiving a femoral head, characterized in that its proximal part B is in the shape of an anatomical tulip and has, on the one hand, at least on its faces, respectively, anterior 5 and posterior 6, generatrices connecting to the generatrices of its diaphyseal part and each having a successively concave profile 5a-6a, at constant radius, and convex 5b-6b, at constant radius, going towards the top of the rod where it is connected by a rounded 8 of small radius with the face 7 from which the stud 3 protrudes, and, on the other hand, an elliptical cross section with progressive decrease between the aforementioned face 7 and an area C arranged below the small and large trochanter substantially parallel to face 13.  2. Rod according to claim 1, characterized in that its proximal part B comprises, over its entire periphery, grooves 16, spaced apart and of substantially vertical direction, for bone stabilization and rehabitation.  3. Rod according to all of claims 1 and 2, characterized in that the proximal part B is provided with at least one rib 18 which, projecting from its periphery in the interval between two grooves 16, is parallel to these grooves.  4. Rod according to any one of claims 1 to 3, characterized in that the periphery of its proximal part B is covered by an under layer of porous titanium and by a thin layer of ceramic 17.