FR2651118A1 - Cementless hip prosthesis - Google Patents

Abstract

The prosthesis comprises a number of modular elements (1), (2) and (3) which are designed in combination in order to ensure a support and fixation in the metaphysis without contact at the level of the diaphysis. This prosthesis comprises in particular a metaphyseal support element (1) which is intended to receive a femoral head. The said element (1), which is designed to be fixed in the corresponding part of the medullary cavity, is equipped at the end with a diaphyseal shaft (2) which is engaged freely in the said cavity and whose free end receives a centring element (3) which is able to be positioned bearing in the foot of the medullary cavity.

Description

 Cementless hip prosthesis.

 The invention relates more particularly to total hip prostheses placed without cement.

 In the case of an unsealed prosthesis, to obtain a secure, effective and durable fixation, the prosthesis must transmit the body weight in an optimal way, especially when walking, on the supporting bone, i.e. - say, the femur.

The fixation must be essentially metaphyseal so that the pressure forces are transmitted to the level of the internal cortex of the femur and to the level of the MER spur
CKEL.

 This fixation must allow traction forces to exert on the external cortex of the metaphysis.

 In a particularly important way, the fixation must not create a spongialization of the cortical bone at any point, which is antiphysiological. This results in risks of mobility of the implant under the effect of the reaction of the bone with respect to the forces exerted.

 Femoral implants for total hip prosthesis as known, are not suitable, given their design, to solve, in a satisfactory manner, this fixation problem having regard to the constraints to be observed and the different sizes of femur in particular, that exist.

 Generally, most hip prostheses are monobloc at the level in particular of the metaphyseal and diaphyseal parts, with pre-established shapes. Such prostheses are performed in different sizes to best suit the different sizes of femur. However, it appears that during an increase, all parts of the prosthesis are increased in the same proportions, which does not correspond to reality.

 Non-monobloc prostheses have also been proposed, comprising in particular a metaphyseal part and a diaphyseal part made of two independent elements coupled to one another. Such a state of the art can be illustrated without limitation by the teaching of the European patent N.

0257359.

 However, such a type of prosthesis does not solve the problem posed in particular with regard to the condition to be met at the level of the diaphyseal fixation.

 The object of the invention is to remedy the drawbacks mentioned in a simple, efficient and rational manner.

 To solve the problem posed of an effective and durable secure fixation in the case of a cementless prosthesis, a prosthesis composed of several modular elements shaped in combination has been designed and developed to provide metaphyseal support and fixation without contact at the level of the diaphysis.

Advantageously, the problem posed is solved in that the prosthesis comprises a metaphyseal support element arranged to receive a femoral head, said element which is shaped to be fixed in the corresponding part of the medullary canal, is equipped, at the end, with a diaphyseal rod freely engaged in said canal and the free end of which receives a centering element capable of being positioned in abutment in the bottom of the medullary canal
The problem posed of the diaphyseal fixation is solved in that the centering element is in the form of a cylindrical body of variable length and diameter whose ends are tapered and rounded. The ends of the diaphyseal rod are arranged to receive in a reported manner the centering element and the metaphyseal support element
Another problem which the invention makes it possible to solve, taking into account the modular nature of the prosthesis, is to avoid removing the cancellous bone. For this purpose, the metaphyseal support element has a determined shape and profile, so as to be applied without a guide, pushing and crushing the cancellous bone against the cortex.

According to another characteristic, the components of the diaphyseal part, namely the rod and the centering element, are determined in shapes and dimensions so as not to transmit stresses to the diaphysis
To solve the problem of taking into account the dimensional differences between several femurs, the different modular elements, in particular the metaphyseal support element, the coupling rod and the diaphyseal centering element are determined independently in terms of shapes and dimensions, depending of each type of femur in particular.

Still aiming to make the entire prosthesis modular to solve the problem of good cementless fixation, whatever the size of the femur, the metaphyseal support element is arranged to receive in a way reported, the femoral head. The metaphyseal support element has directly, or in a reported manner, a lateralized neck capable of receiving the body of the femoral head
The invention is set out below in more detail with the aid of the accompanying drawings, in which
Figure 1 shows the different components of the modular prosthesis according to the invention, before assembly.

 Figure 2 is a longitudinal sectional view of the prosthesis, after implantation in the medullary canal of the femur.

 Figure 3 is a cross-sectional view taken along line 3-3 of Figure 2.

 As shown in Figure 1, the femoral implant for hip prosthesis is performed from a set of modular elements essentially comprising a metaphyseal support element (1), a coupling rod (2) and an element diaphyseal centering (3).

The metaphyseal support element (1) is arranged to receive directly or in a reported manner, a femoral head (4). Advantageously, the metaphyseal support element (1) has in particular in a reported manner, a lateralized neck (5) suitably inclined to correspond, in a known manner, to the cervico diaphyseal and anteversion angle. This neck receives the body of the femoral head. In addition, the upper end of the metaphyseal element (1) has a support flange (la) to ensure a better distribution of forces
The metaphyseal support element has, in a known manner, any type of arrangement such as grooves, surface treatment or the like capable of ensuring very good adhesion in the cancellous tissue and in the cortex while having the objective of facilitating bone rehabilitation.

 The end of the metaphyseal element (1) opposite to the part receiving the femoral head is arranged to receive, in a removable manner, the coupling rod (2) This rod of length, radius of curvature and diameter variables is intended to be freely engaged in the medullary canal of the bone, at the level of the diaphysis. At the end of this rod, can be fixed, in a demountable manner, the physical centering element (3) able to be positioned in abutment in the bottom of the medullary canal. In the example illustrated, each of the free ends (2a) and (2b) of the rod (2) have a conical surface cooperating with a complementary imprint formed respectively in the metaphyseal (1) and diaphyseal (3) elements.

 As shown in particular in Figure 1, the diaphyseal centering element (3) is in the form of a cylindrical body of variable length and diameter and the ends of which are tapered and rounded. Advantageously, this element (3) can be executed in a slowly absorbable material.

 Given the modular design of the hip prosthesis according to the invention, it is possible to change the size of each of the constituent elements, independently, to obtain a metaphyseal fixation best suited to the bone. In addition, in a particularly important way, the diaphyseal centering element (3), in combination with the coupling rod (2) makes it possible to obtain primary stability, without creating poor transmission of the forces of support. The entire prosthesis is fixed essentially at the level of the metaphysis, taking into account the shape and the particular arrangements of the support element (1). We therefore eliminate any risk of spongialization of the cortical bone at one point or another, since there is no diaphyseal fixation as such, the rod (2) not participating in this fixation.

 The diaphyseal part is thus adapted so that only a sliding of the centering element is possible, without at any time transmitting the stresses to the diaphysis.

 Advantageously, the metaphyseal support element (1) has a shape and a profile determined so that it can be applied, without a guide, by pushing and crushing the cancellous bone against the cortex.

 The various modular elements, in particular the metaphyseal support element (1), the coupling rod (2) and the diaphyseal centering element (3) are determined independently in shapes and dimensions according to each type of femur. Advantageously, the shapes, profiles and anatomical dimensions of each of the constituent elements can be calculated by computer, to take account of the dimensional differences of the femurs whose coordinates may have been digitized beforehand, for example.

 The implantation of the prosthesis is carried out using an ancillary fitting adapted to the design, as defined, of said prosthesis. One can use, for example, a member receiving, at the end an interchangeable tool capable of making the medullary canal of the femur circular over a determined length greater than the length of the diaphyseal centering element (3), since said channel is generally conical in shape. The diameter of the recess thus produced is very slightly greater than the diameter of the selected metaphyseal centering element (3). Then just take a set of spindles on which we adapt a test guide receiving the diaphyseal centering element at the end. We penetrate the spindle starting from the smallest size, until we arrive to the desired size, which makes it possible, under these conditions, to determine the dimensions of the coupling rod (2). Note that a test neck is adapted on the spindle, the different criteria of which are chosen, taking into account the femoral head to be implanted.

 The advantages emerge clearly from the description, in particular it underlines and recalls the possibility of changing the size of each of the constituent elements of the prosthesis, independently, so as to obtain a metaphyseal fixation of the implant best suited to the bone, while obtaining primary stability, by the two diaphyseal elements (rod and centering element), and by eliminating any risk of spongialization of the bone. We therefore obtain a fixation, without cement of the implant, particularly safe and effective, respecting the anatomy.

Claims (10)

-1- Cementless hip prosthesis, composed of several modular elements (1) (2) and (3) shaped in combination to provide support and non-contact metaphyseal fixation, at the level of the diaphysis. -2- Prosthesis according to claim 1, characterized in that it comprises a metaphyseal support element (1) arranged to receive a femoral head, said element (1) which is shaped to be fixed in the corresponding part of the medullary canal , is equipped at the end with a diaphyseal rod (2) freely engaged in said canal and the free end of which receives a centering element (3) capable of being positioned in abutment in the bottom of the medullary canal. -3- Prosthesis according to claim 2, characterized in that the centering element (3) is in the form of a cylindrical body of variable length and diameter whose ends are tapered and rounded. -4- Prosthesis according to claim 2, characterized in that the ends of the diaphyseal rod (2) are arranged to receive in a reported manner the centering element (3) and the metaphyseal support element (I) . -5- Prosthesis according to any one of claims 1 and 2, characterized in that the metaphyseal support element (1) to determined shapes and profiles, so as to be applied without guide, pushing and crushing the cancellous against the cortex. -6- Prosthesis according to any one of claims 1 and 2, characterized in that the components of the diaphyseal part, namely the rod (2) and the centering element (3), are determined in shapes and dimensions so as not to transmit constraints to the diaphysis. -7- Prosthesis according to any one of claims 1 to 6, characterized in that the various modular elements, in particular the metaphyseal support element (1), the coupling rod (2) and the centering element diaphyseal (3) are determined independently in shape and size, depending on each type of femur in particular.  -8- Prosthesis according to claim 1, characterized in that the metaphyseal support element (1) is arranged to receive in a reported manner, the femoral head (4). -9- Prosthesis according to claim 8, characterized in that the metaphyseal support element has directly, or in a reported manner, a lateralized neck (5) adapted to receive the body of the femoral head (4). -10- Prosthesis according to claim 9, characterized in that the upper end of the metaphyseal element (1) has a support flange (la) to ensure a better distribution of forces.