FR2868689A1 - Femoral rod for hip prosthesis, has reliefs each of which is constituted by winglet, where each relief has apex forming acute and sharp angle for permitting winglets to penetrate in cortical bone during implantation - Google Patents

Abstract

The rod (1) has reliefs, each of which is constituted by a winglet (12), where the reliefs are provided on sides (7A, 7B), and each relief is provided in longitudinal axes for introduction in a femoral cavity. Each relief in pyramidal shape has an apex (12A) that is sharp. The apex forms an acute and sharp angle for permitting the winglets to penetrate in a cortical bone during the implantation.

Description

FEMALE ROD FOR HIP PROSTHESIS

  The present invention relates to a femoral stem for hip prosthesis of the type comprising an anti-rotation relief, so as to allow its implantation into the medullary cavity of the cementless femur.

  In this type of prosthesis, it is imperative and usual to anchor the stem by fitting into the femoral shaft previously prepared using rasps.

  It is essential in this type of prosthesis to ensure the blocking of the rod, because any twisting movement induces pain for the patient and eventually causes the desoldering of the prosthesis.

  In order to ensure the immobilization of the stem, it is known to give a square section to it, but this requires the use of a rasp of corresponding shape and moreover it induces a weakening of the femur by effect corner, which can lead to its break.

  To avoid this, we then tend to undersize the stem, which may cause, moreover, the depression of it in the femoral shaft.

  It has already been proposed to give a particular relief to the faces of the rod such as for example by practicing on it flutes.

  Nevertheless, these have proved insufficiently effective because their cooperation with the bone is limited to its cortico-spongy part which is not sufficiently resistant to obtain an anti-rotatory effect of the stem, due to the lack of resistance of this part of the bone.

  The object of the present invention is therefore to provide a prosthetic femoral stem of traditional ovoid section which, moreover, has a non-invasive face facing the greater trochanter.

  For this and according to a first phase of the inventive step, it was sought a specific anti-rotatory relief to attack the cortical bone rather than the cortico-cancellous bone.

  For this purpose, the invention relates to a femoral stem for a hip prosthesis comprising an antirotational relief, so as to allow its implantation in the medullary cavity of the femur, without cement, characterized in that it comprises on each of its faces, at the less a relief constituted by a straight wing, made prominently, along a longitudinal axis of introduction into the medullary cavity, or one or more axes parallel thereto.

  When the stem is placed in the femoral shaft, the fins penetrate the cortical bone, providing mechanical stabilization while promoting early osteogenesis, the first stage of anchoring.

  2868689 3 To this primary anchorage, purely mechanical, will be added a secondary anchorage, made by bone regrowth on the metal surface of the stem.

  Bone regrowth may be promoted by osteogenic stimulating agents, such as surface sandblasting or hydroxyapatite coating.

  The present invention also relates to the features which will emerge during the following description, which should be considered in isolation or in all their possible technical combinations.

  This description given by way of non-limiting example, will better understand how the invention can be made with reference to the accompanying drawings in which: Figure 1 is a front view of a femoral stem according to the invention.

  FIG. 2 is a sectional view, on an enlarged scale, along the line II, II of FIG. 1.

  FIG. 3 shows a partial sectional view of the rod and a fin along the line III, III of FIG.

  The femoral stem 1, generally designated in the figures, is intended for a hip prosthesis and has a conventional and known shape, tapered in its distal portion which is intended to be engaged in the femoral shaft and surmounted by a platinum 2 with a neck 3 ending in a truncated cone 4 for cooperating with a prosthetic femoral head.

  The stem 1 comprises a diaphyseal blade 5 which tapers towards an end point 6 and an epiphyseal section 7 which widens from the diaphyseal plate 5 to the plate 2.

  The general direction of the neck 3 forms an angle with the axis 9 corresponding to the cervicodiaphyseal angle of the patient.

  The epiphyseal section 7 has a section of ovoid shape with two faces 7A, 7B, generally joined together by rounded edges 10, 11.

  According to the purpose of the present invention, the femoral stem 1 comprises an anti-rotatory relief, so as to allow its implantation in the medullary cavity of the femur, without cement.

  For this purpose, the rod 1 comprises on each of its faces 7A, 7B at least one relief consisting of a straight fin 12 made prominently along a longitudinal axis X, X 'for introduction into the femoral cavity, or one or more parallel to this one.

  According to the embodiment shown in the figures, each of the fins 12 is of pyramidal shape, the top 12A is sharp.

  The angle formed by the apex 12a is sufficiently acute and sharpened to allow the vanes 12 to penetrate the cortical bone during implantation.

  Of course, the fins 12 could be of any other shape, such as, for example, constituted by an in-line succession of a plurality of conical pins.

  In fact, the height h of the fins 12 is such as to allow these to register in a volume V1 greater than that V2 of the medullary cavity resulting from its penetration, so as to generate a clearance j between the faces 7A, 7B of the stem 1 and the cortical bone V2, less than the height h of the fins, so that they can be anchored in the latter.

  In fact, the number of fins 12 is determined as a function of the surface of the faces 7A, 7B of the rod 1.

  According to the present embodiment, not limiting, for a rod 1 of ovoid shape whose largest dimension L is 2.5 mm, the fins 12 are five in number, parallel and spaced apart according to a space e of 4mm .

  Still according to the present embodiment, the height h of the pyramidal fins 12 is between 1 and 3mm, the clearance j between the faces 7A or 7B of the rod 1 and the cortical bone, being less than said height h.

  The game j is according to this example of 0.5mm.

  As clearly shown in Figure 1, the fins 12 are arranged in a sagittal plane, mainly in the proximal portion.

  Preferably, the fins 12 are arranged, as shown in Figure 1, in the upper third of the rod.

  According to another characteristic of the invention, the height h of the fins 12 is decreasing in a direction from the proximal portion to the distal portion.

  One could also consider making fins 12 of height h different from one side of the rod to the other.

  This would allow, when the practitioner impacts the prosthesis, to give him the opportunity to adjust the anteversion of the stem in the first centimeters of depression thereof.

  Advantageously, the fins have at their upper ends a first chamfer 13 at the femoral section and at their lower end, a second chamfer 14 for facilitating the introduction of the rod 1 into the medullary cavity.

Claims (2)

7 CLAIMS   1. femoral stem (1) for hip prosthesis comprising a rotational relief, so as to allow its implantation in the medullary cavity of the femur, without cement, characterized in that it comprises on each of its faces (7A, 7B), at least one relief consisting of a straight fin (12), made prominently, along a longitudinal axis (X, X ') for introduction into the medullary cavity, or one or more axes parallel thereto.   2. Rod according to claim 1, characterized in that each of the fins (12) is of pyramidal shape, the top (12a) is sharp.   3. Rod according to claim 2, characterized in that the height h fins (12) is such that it allows them to register in a volume (V1) greater than that (V2) of the medullary cavity resulting from its penetration, so as to cause a clearance j between the faces (7A, 7B) of the rod (1) and the cortical bone (V2), less than the height h fins, so that they can be anchored in the latter.   Rod according to one of claims 2 or   3, characterized in that the number of fins (12) 30 is determined as a function of the surface area of the faces (7A, 7B) of the rod (1).   5. Rod according to claim 4, characterized in that, for a rod (1) of ovoid shape whose largest dimension (L) is 2.5 mm, the fins (12) are five in number, parallel and spaced apart according to a space e of 4mm.   6. Rod according to one of claims 3 to 5, characterized in that the height h of the pyramidal fins (12) is between 1 and 3mm, the clearance j between the faces (7a or 7b) of the rod (1). and the cortical bone, being less than said height h.   7. Rod according to one of claims 2 to 6, characterized in that the fins (12) are arranged in a sagittal plane, mainly in the proximal portion.   8. Rod according to one of claims 2 to 7, characterized in that the height h fins (12) is decreasing in a direction from the proximal portion to the distal portion.   9. Rod according to one of claims 2 to 8, characterized in that the fins have at their upper ends a first chamfer (13) at the femoral section. and at their lower end, a second chamfer (14) for facilitating the introduction of the stem (1) into the medullary cavity.