FR2728160A1 - Hip prosthesis shank and medullary cavity file - Google Patents

Abstract

The hip prosthesis shank, designed to be fitted with or without cement, is inserted into the medullary cavity of the femur after shaping with a file which has a body (10) of an appropriate cross-section and abrasive teeth (11). The shank fitted without cement has a cross-section (20) more or less identical to that of the file, while the cemented shank has a smaller cross-section (30), reduced along at least one lateral surface (33,34). The cement-less shank has lengthwise ribs (21) for anchoring and for bone re-growth, while the cemented one has lengthwise rounded projections (31,32) on its sides to wedge it in place. The projections fit basically within the outer section of the file, or exceed it slightly to provide a compression fit.

Description

HIP PROSTHESIS SYSTEM
WITH CEMENTED RODS AND WITHOUT CEMENT USING
A UNIVERSAL RAPE
The present invention relates to a hip prosthesis system.

 The invention finds a particularly advantageous application in the field of internal prostheses of the hip joint.

 Two main categories of femoral rods are known in the state of the art of hip prostheses intended to be implanted in a cavity produced inside the intramedullary canal of the femur of a patient, using in particular a rasp forming a reamer.

 There are, on the one hand, so-called cemented femoral stems because immobilized in the intramedullary cavity by means of an acrylic cement.

 On the other hand, there are also cementless rods which must have excellent contact with the wall of the cavity, at least in part proximal, in order to obtain a fixation of the bone by bone regrowth, which is favored by a adapted surface condition and / or the use of an osteoinductive material, of hydroxyapatite for example.

 As the conditions for implanting these two types of rods are not identical, it is common for a practitioner to choose between two different ranges of femoral rods, one cemented and the other without cement.

 However, there are known rods for total hip prosthesis that can be placed cemented or not with the same instrumentation.

 This possibility of interchangeability must be considered as a progress because the operating technique is then the same whatever the type of rod chosen and especially the ancillary device, in particular the rasp used to make the femoral cavity, which has become unique, acquires a universal character.

In this case, the general shape of the body of the rasp and of the rods is identical for the two fixing methods, with or without cement, only the surface coating of said rods changes.

 However, this known hip prosthesis system with interchangeable rods has the disadvantage of favoring the cementless fixing method since the rods of each type are most often given a volume filling the femoral cavity with micux. Consequently, when the so-called cemented rod is put in place, the cement is found in the form of a thin layer which can in the long term be fragmented, thus harming the longevity of the implant.

 Also the technical problem to be solved by the object of the present invention is to propose a hip prosthesis system, comprising a rasp intended to produce a femoral cavity, a so-called cementless femoral stem and a so-called cemented femoral stem, intended to be indifferently implanted in said cavity, said rasp comprising a body of determined section on which abrasive teeth are formed, a system which would make it possible to obtain optimal conditions of fixation in the same cavity produced by the single rasp, both for femoral stems without cement than cemented.

 The solution to the technical problem posed consists, according to the present invention, in that, on the one hand, said cementless femoral stem comprises a body of section substantially identical to the section of said rasp body, and, on the other hand, that said cemented femoral stem has a body of section smaller than the section of said rasp body on at least one lateral surface.

 Thus, due to the virtual identity of its section with that of the femoral cavity, the cementless rod of the system of the invention is perfectly immobilized inside the femoral cavity. In addition, with regard to the cemented rod, it should be observed that the narrowed section at the level of the lateral surface, relative to the section of the cavity, allows the formation of a regular thickness of cement.

 This regular thickness of cement, also called the cement mantle, ensures the fixation of the rod in the bone. The durability of the implant is guaranteed because, as many clinical publications demonstrate, when the cement thickness is regular, it tends to age less and, in the long term, loosening is avoided.

 The hip prosthesis system according to the invention is also advantageous in that it allows the practitioner to modify his choice, until the last moment, between one or the other type of rod, depending on the bone condition, which is particularly interesting in the case of the elderly.

 According to a particular embodiment of the invention, the body of the cementless femoral stem carries longitudinal ribs for anchoring and bone regrowth, making it possible to perfect the immobilization of said cementless stem in the femoral cavity.

 Similarly, the invention provides that the body of the cemented femoral stem carries on said lateral surface a longitudinal wedging boss substantially inscribing in the section of the rasp body.

 The description which follows with reference to the appended drawing, given by way of nonlimiting example, will make it clear what the invention consists of and how it can be implemented.

 Figure 1 is a top view of the sections of a rasp, a cementless femoral stem and a cemented femoral stem of a hip prosthesis system according to the invention.

 The hip prosthesis system, object of the invention, comprises a rasp intended to produce a cavity inside the femoral barrel of a patient.

This rasp comprises a body 10, an example of section of which is given in FIG. 1, and on which abrasive teeth 11 are formed.

 Two femoral stems, one without cement and the other cemented, are designed to be indifferently implanted in the cavity formed by the rasp body 10.

 For this purpose, the cementless femoral stem comprises a body 20 which, as shown in FIG. 1, has a section identical to that of the rasp body 10, which ensures good positioning of said cementless stem in the femoral cavity. as well as the contact necessary to induce bone regrowth.

 In order to increase the anchoring of the cementless rod inside the femoral cavity and to stimulate the osteoinductive effect, sharp longitudinal ribs 21 are formed on the body 20 of the rod in order to penetrate into the wall of said rod. cavity.

 As can be seen in FIG. 1, the cemented femoral stem has a body 30 having a smaller section than that of the rasp body 10 on two lateral surfaces 33,34, this in order to spare, between the stem body 30 and the cavity, compartments 35, 36 of sufficient width to constitute a coat of cement of thickness compatible with a fixing which is both of good mechanical quality and durable over time.

 FIG. 1 also shows the presence on the lateral faces 33, 34 of the body 30 of the cemented rod, of two longitudinal bosses 31, 32 of wedging intended to ensure a perfectly centered positioning of said rod in the femoral cavity so as to obtain a cement coat as uniform as possible.

 These bosses 31, 32 are inscribed substantially inside the common section of the body 10 of the grater and of the body 20 of the rod without cement. More specifically, in the example of FIG. 1, said bosses 31, 32 of the free cemented rod protrude slightly from the section of the rasp body 10, which makes it possible to obtain, at implantation, an immobilizing effect by compression. against the wall of the femoral cavity.

 Finally, it will be observed in FIG. 1 that the section of the body 30 of the cemented rod is also slightly projecting from the section of the rasp body 10, at the end of the lateral surfaces 33, 34, always to allow an effect of placement by compression of said cemented rod against the wall of the femoral barrel, thus guaranteeing an ideal centering of the rod in the cavity.

Claims (4)

1. Hip prosthesis system, comprising a rasp intended to produce a femoral cavity, a so-called cementless femoral stem and a so-called cemented femoral stem, intended to be indifferently implanted in said cavity, said rasp comprising a section body (10) determined on which abrasive teeth (11) are formed, characterized in that, on the one hand, said cementless femoral stem comprises a body (20) of section substantially identical to the section of said rasp body (10), and, on the other hand, in that said cemented femoral stem comprises a body (30) of section smaller than the section of said body (10) of rasp on at least one lateral surface (33,34). 2. Hip prosthesis system according to claim 1, characterized in that the body (20) of the cementless femoral stem carries longitudinal ribs (21) for anchoring and bone regrowth. 3. hip prosthesis system according to one of claims 1 or 2, characterized in that the body (30) of the cemented femoral stem carries on said lateral surface (33,34) a longitudinal boss (31,32) of wedging registering substantially in the section of the rasp body (10). 4. hip prosthesis system according to any one of claims 1 to 3, characterized in that the section of the body (30) of the cemented femoral stem projects beyond the section of the body (10) of rasp, at the end of said lateral surface (33,34).