FR2538242A1 - New articular prosthesis with cementless anchoring - Google Patents

Abstract

New articular prosthesis with cementless anchoring in particular for femoral prosthesis. The extremity 11 of the tail 3 is without any rough or porous surface, a transition zone being arranged between the smooth end 12 and the external surface 10 of the body 3. In combination the extremity 11 has the general shape of a "bird beak" such that in the final position of the prosthesis the flat surface is placed opposite the internal wall of the medullary canal of the bone.

Description

 The present invention relates to the field of joint prostheses. More particularly, it relates to a new cementless anchoring prosthesis.

 We already know the general technique of planting off composite metal parts, intended to replace or consolidate bones or bone joints alone. The shape of the implant is adapted to the bone part concerned. This is the case, for example, for prostheses intended for hip or knee joints.

 Implants were first used by fixing them in living bone with a cement, in particular with a cement based on acrylic resin. This fixing technique with a cement leads to numerous drawbacks among which one can report a defect in the holding of the prosthesis due to the risks of splitting of the cement. We also note that the recipient's organism and bone tissue can show intolerance towards the foreign body that is cement.

 This is why prostheses have been proposed, the fitting of which does not require the use of cement. To this end, the surface of the implant has been made porous or porous, so as to allow the development of bone tissue. on the surface of the prosthesis itself and thus to anchor it in the bone.

 Patent application FR 82.11.412 filed on June 29, 1982 in the name of the Applicant for new bone prosthesis and its obtaining exposes the state of the art in the field of cementless prostheses. We can therefore refer to this request to better appreciate the prior knowledge in the field of the invention.

 It is always desirable to improve the conditions for fitting prostheses by perfecting their structure in order to better adapt them to practical requirements and thus remedy certain drawbacks which are still observed in a certain number of cases.

Thus, it may happen that the end of the prosthesis which
is deepest in the bone exerts ef
compression forces on the bone surface which may
translate into pain and in some cases even
damage to the bone. You also need to be able to intervene
again to replace the prosthesis because in at least
10% of cases and for a wide variety of reasons, a prosthesis
cementless anchor must be replaced, so a
arrange the prosthesis so as to allow such a replacement
without being forced to practice, as is the case with
the present, a difficult and traumatic intervention
Among the shortcomings of current prostheses, we can
also report certain risks of sinking into the canal
medullary. In addition, when it comes to a metal implant, corrosion and even fracture phenomena can occur in the fatigue areas of the metal.

 The practitioner is well aware of the difficulties enumerated briefly above and seeks to remedy them permanently. The present invention relates to a new joint prosthesis with cementless anchoring which ensures better adaptation to the medullary canal and less rigid anchoring at the lower end. The new prosthesis may also advantageously include other improvements relating to its base and to its general shape, thus making it possible to ensure optimal positioning and as high a resistance as possible.

The invention therefore relates to a new joint prosthesis with cementless anchoring, comprising a neck and a tail, which is intended to be placed inside the bone, characterized in that the end of the tail intended for be pushed deepest into the bone (distal end) present in combination:
a) an external structure in which at least the tip is smooth, a transition zone being formed between the tip and the outer surface of the tail body which may be porous or rough, any surface effect of the tail body being gradually smoothed to the end which is smooth;
b) a non-cylindrical shape according to which the tip has a rounded lateral edge and two curvilinear parts symmetrical with respect to a plane
(axial plane) passing through the axis of the tail and joining on the rounded edge, the distal end thus having a shape in bird's beak, such that in the final position of the prosthesis, the antero-internal flat is placed opposite the anterior wall of the bone marrow canal.

 According to the invention, the area corresponding to the "bird's beak" is smooth and devoid of any anchoring roughness.

In the case of a femoral hip prosthesis, the lower or distal end is anchored less rigidly. A transition is thus made between the upper armed part of the femur and the free, physiologically flexible lower part of the femoral shaft, thanks to the fact that the area corresponding to the smooth bird's beak is # devoid of any roughness. anchor. The upper part, on the proximal side of the prosthesis tail, advantageously has a surface effect, in relief or in hollow. The structure of such a tail, the surface of which is porous or rough, is known to those skilled in the art. According to a preferred embodiment, the external surface of the prosthesis tail, outside the end in bird's beak, is fluted in a direction generally parallel to its mean axis, in accordance with the teaching of the aforementioned patent application 82.11.412. In accordance with this previous application, the profile (cross section) of the flutes is such that it confers a retention capacity of the bone tissue and, in combination, the longitudinal inner surface of the grooves, non-cylindrical, has a shape which tapers from the end of the prosthesis (low or distal end) pressed in deeper into the bone to the other end (upper end than proximal), the prosthesis can thus be extracted from the bone tissue by a pulling movement. The present invention can advantageously use such a teaching while appo the improvement according to which the end says
tale, has a transition zone between the grooved part
rée or fluted and the end in the shape of a bird beak which is
smooth,
Has the mentioned structural characteristic
previously, combines a shape characteristic according to
which the distal end of the prosthesis tail is ar
rounded and- flattened in "bird's beak".
1st that, especially in the case of a joint prosthesis
hip, the placement of the prosthesis should
take into account that the femur tette is facing towards the
front (anatomical situation of anteversion). For reasons
manufacturing practices, all prostheses are recti
lines in an antero # posterior plane, in order to avoid dif-
dentize prostheses for left or right hfflnche.

The fitting of the prosthesis is therefore necessarily done
with a certain angle and straightness of the prosthetic pivot does not respond
not good at anatomical bending of the spinal canal.

It is precisely in the area where the end of the prosthesis
is inserted into the spinal canal that we see
risk of contact or even fracture of the cortex
the bone. According to the invention, the bird beak shape
provides optimal adaptation to the spinal canal. Indeed
fet, during the introduction of the prosthesis, the lateral edge
rounded end of the prosthesis tail ensures
slip effect. In the final position of the prosthesis,
the curved part of the end is opposite
the anterior wall of the spinal canal, thus avoiding
any contact and damage to the bone wall. The concept
tion of the prosthesis according to the invention also allows u
use the same prosthesis for the left side or the side
law. This result is notably achieved thanks to the shape
flattened symmetrical about an axial plane of the tail
prosthesis at its distal end, the body of the tail
also being generally cylindrical, as well as
he is known.

The prosthesis according to the invention can also have the following advantageous characteristics, taken in isolation or in all their technically possible combinations:
- the base of the prosthesis has an enlarged seat, in order to avoid any risk of sinking into the medullary canal,
The prosthesis base has no sharp edges, all of its surfaces being connected by rounded angles, which avoids any risk of corrosion of the metal surfaces and eliminates the possibility of fracture caused by sharp edges (fractures of the greater trochanter in the case of a femoral prosthesis),
The prosthesis base has large grooves or notches, arranged symmetrically with respect to the above-mentioned axial plane and capable of cooperating with an instrument for extracting the prosthesis,
- the tail is in one piece,
- the profile of the tail body is provided to increase the resistance of the load-bearing area (male profile end) and ensure optimal filling of the spinal canal,
- the internal edge of the proximal end of the tail body is thickened to ensure better resistance to compression stresses,
- the prosthesis tail has no fe.

casting net,
- the prosthesis is made of cast or forged metal or a composite material.

 The prosthesis according to the invention can be obtained by any known technique. For example, the general technique of lost wax casting or hot or cold forging can be used. Obtaining a prosthesis whose tail is grooved is described in the aforementioned patent application FR 82.11.412 of June 29, 1982, which describes in particular various means for making the grooves by foundry in lost wax or by forging and / or electro-machining.

The invention will now be illustrated without being limited in any way by the description which follows, which relates to a hip joint prosthesis, with cementless anchoring, with reference to the appended drawings in which:
Fig, 1 shows the prosthesis in elevation.

 Fig. 2 is a section along line II-II of FIG. 1.

 Fig. 3 is a section along line III-III of FIG. 1.

Fig. 4 is a perspective view on an enlarged scale four times showing the distal end of the prosthesis tail
As seen in the drawings, the prosthesis which is designated by the general reference 1 comprises a neck 2 and a tail or pivot 3. The neck 2 has a seat or base 4 enlarged compared to known embodiments, from my pride to avoid any risk of the prosthesis sinking into the medullary canal. For example, the transverse width of a prosthesis for small femurs is approximately 34 mm and the minimum dimension in antero posterior direction is 36 mm. In the case of a prosthesis for large femurs, the transverse width is approximately 38 mm and the minimum anteroposterior dimension is 40 mm.

We also see in Figure 1 that the profile of the neck 2 has rounded angles-such as 5, 6, 7. This eliminates all the sharp angles which are likely to promote the risk of corrosion and even internalize possible bone fractures (greater trochanter) with which QuelleSxse may come into contact. We also see in Figure 1 a groove or notch 8o There is an identical
symmetrically with respect to the plane of the figure. These two lar
ges notches 8 allow the establishment of an extraction instrument.

Reference 9 in Figure 1 shows the thickening
the inner edge of the upper or proximal part of
the prosthesis tail. The curvilinear shape represented in 9
as well as the dimensions chosen for this upper part make it possible to optimally fill the femoral medullary canal while ensuring better resistance to compression stresses.

 As is preferred, the tail 3 has no casting window, Its one-piece design prevents fatigue fractures.

In the example chosen, the #queue 3 has a set of grooves 10 in accordance with the teaching of the aforementioned patent application FR 82.11.412. It is enough to refer to the text and the drawings of this request to know the detailed indications relating to the shape of the grooves as well as their methods of manufacture.
According to the essential characteristic of the invention, the distal end designated by the general reference 11, of the pivot or tail of prosthesis has a rounded shape and flattened in "bird beak #" seen see in the figure 1 and which is shown on a larger scale in Figure 4, Figures 2 and 3 are sections further illustrating the shape and profile of this tee end.

 We see in the drawings that the end 11 has a surface 12 which is smooth, that is to say devoid of grooves. There is a transition zone between the body of the tail 3, which is grooved and the smooth end 12. The grooves 10 gradually disappear in the vicinity of the end 11. At the level of the section Il-Il shown in FIG. 2, we still see on the back of the tail a certain number of residual grooves 10. At a level closer to the extreme edge, as it appears on the coub pe according to the line 111-111 in figure 3, there is only one groove 10. This structure appears clearly on figure 4.We see that the tail of prosthesis steffile and s' flattens in the direction of the end 11. The grooves 10 of the body 3 of the tail or pivot become progressively less, as shown in the drawing. Such an arrangement ensures a less rigid anchoring at the lly end, thus giving a transition elasticity between the proximal part of the femur, which is rigidly anchored due to the presence of the grooves 10, and the lower or distal part 11 which is free and physiologically flexible of the femoral shaft. This characteristic is advantageous, in particular in the case where, as a result of an incident, it is necessary to extract the prosthesis after its installation.

According to another essential characteristic of the invention, the shape of the end 11 is designed to ensure better adaptation to the medullary canal while avoiding the risk of contact or fracture of the anterior cortex. We see in the drawings that the end 11 has a flattened shape and no longer cylindrical. This is particularly highlighted in Figure 2 where we see the circle 1.4 representing a theoretical circular section which includes the end 11. We see two parts
curvilinear flats l2a, 12b which meet on the rounded edge 13. Figure 3 also highlights the tapered shape of the end 11 with its curvilinear parts 12a, 12b and its rounded edge 13.The distal end of the tail prosthesis is thus symmetrical with respect to the plane of the figure, that is to say in relation to a plane passing through the axis of the tail or pivot, The angle of approximately 150 has been represented at r according to which the prosthesis is turned during its installation to take account of
the anteversion to give to the head. In this way, the flat (12a or
12b) antero-internally becomes anterior vis-à-vis the anterior wall of the medullary canal. This arrangement is ensured regardless of the right or left position of the prosthesis.

The rounded shape of the end 11 provides a sliding effect during the introduction of the prosthesis, which is particularly advantageous taking into account the anterior curvature of the femur. Once the prosthesis has been placed in its final position, and has been turned
born according to angle r of 15! the corresponding mSplat 12a or 12b is located opposite the anterior wall of the medullary canal, thereby avoiding excessive contact with the anterior cortex, which eliminates the known drawbacks of such prostheses. #
The prosthesis according to the invention can be made of any suitable material, in particular stainless steel, for example a chrome-cobalt steel, such as that of grade HS 21, as well as in other metallic alloys or also in composite materials.

It goes without saying also that the above description has been given only by way of example. It has been said that the preferred embodiment involves the presence on at least one part of the prosthesis stem or pivot of a fluted polarized surface in accordance with the teachings of the application.
FR 82.11.412. However, other surface effects, in relief or in hollow can be produced, so as to give the surface a porous or rough character. Such achievements are within the reach of the skilled person. The invention essentially provides a prosthesis, the distal end of which has a structure and is shaped like a "bird's beak" as indicated above in detail.

Claims (11)

 1. A cementless anchoring joint prosthesis comprising a neck (2) and a tail (3) which is intended to be placed inside the bone, characterized in that the end (11) of the tail (3), intended  the to be pressed / deeper into ltos (distal end) present in combination  a) an external structure in which at least the tip (12) is smooth, a transition zone being managed between the tip (12) and the external surface of the body (3) of the tail, which can be porous or rough, any surface effect of the body (3) of the tail being progressively attenuated to the end (12) which is smooth;  b) a non-cylindrical shape according to which the tip (12) has a rounded lateral edge (13) and two curvilinear parts (12a, 12b) symmetrical with respect to a plane (axial plane) passing through 1 t axis of the tail (3 ) - and joining on the rounded edge (13), the distal end (11) thus having a bird's beak shape, such that in the final position of the prosthesis (1) the antero-internal flat (l2a or 12b) is placed opposite the anterior wall of the bone marrow canal.  2. Prosthesis according to claim 1, characterized in that the body (3) of the tail or pivot has a surface effect, in relief or in hollow, in particular grooves (10).  3. Prosthesis according to one of claims 1 or 2, characterized in that the base (4) of the neck (2) posb sedes an enlarged seat, in order to avoid any risk of sinking into the medullary canal.  4. Prosthesis according to any one of claims 1 to 3, characterized in that the base (4) has no sharp edge, all its surfaces being connected by rounded angles (5, 6, 7).  5. Prosthesis according to any one of claims 1 to 4, characterized in that the base (4) has large grooves or notches (8) arranged symmetrically with respect to the above-mentioned axial plane and capable of cooperating with an extraction instrument of the prosthesis.  6. Prosthesis according to any one of claims 1 to 5, characterized in that the tail (3) is in one piece.  7. Prosthesis according to any one of claims 1 to 6 characterized in that the profile of the body of the tail (3) is provided to increase the resistance of the load-bearing zone (proximal end) and to ensure optimal filling of the medullary canal.  8. Prosthesis according to any one of claims 1 to 7, characterized in that the internal edge (9) of the proximal end of the body of the tail (3) is thickened to ensure better resistance to compression stresses.  9. Prosthesis according to any one of the resold. cations 1 to 8, characterized in that the tail (3) has no casting window.  10. Prosthesis according to any one of the claims 1 to 9, characterized in that it is made of cast or forged metal or of composite material.  11. Prosthesis according to any one of claims 1 to 10, in the form of a femoral prosthesis.