FR2870717A1 - Hip prosthesis for restoring articulation of femur and acetabular bone, has prosthesis rod with retaining bracket having portions with trapezoidal and circular sections tapering off between respective bracket ends and intermediate section - Google Patents

Abstract

The prosthesis has a prosthesis rod (2) with a retaining bracket (3) and a collar whose axis makes an angle beta with the bracket axis. A spherical head is integrated to the collar`s end (13). The bracket has portions (21, 22) having transversal trapezoidal and circular sections tapering off in a continuous manner between a bracket end (5) and an intermediate section (23), and between the section (23) and a bracket end (6), respectively.

Description

2870717 1

HIP PROSTHESIS

  The present invention relates to hip prostheses, that is to say the prostheses able to restore the joint between the femur and the acetabulum of the pelvis of a person.

  Many hip prosthesis structures are already known. In a general schematic manner, a hip prosthesis comprises an acetabular cup capable of being implanted in the acetabulum of the pelvis and a prosthesis stem adapted to cooperate by rotulian rotation with the acetabulum, the prosthesis stem comprising a suitable fixation lug. to be implanted in the medullary canal of the femur so that its axis is substantially merged with the axis of this medullary canal, this tab thus having a proximal end and a distal end, a collar having a first end integral with the proximal end of the fixing rod, the axis of the flange making with the axis of the fixing lug an angle f3 of a given value, and a spherical head integral with the second end of the collar and able to cooperate rotulienne rotation with a hemispherical cavity made in the acetabulum.

  In order to properly seat the bracket in the medullary canal of the femur, its cross section is generally substantially trapezoidal shape, it being understood that, in some cases, the small base and the large base may have very similar dimensions.

  In addition, to absorb the torsional forces exerted on the prosthesis stem when it is implanted in a femur, the face of the fastening tab corresponding to the large base of the trapezoidal cross section is generally substantially flat and parallel. to the axis of the bracket. As a result, the face of the fixing lug corresponding to the small base of the trapezoidal cross-section joins the face of the fixing lug corresponding to the large base by an oblique pan with respect to the axis of the fixing lug.

  The implantation of such a prosthesis rod is done by placing a layer of cement or the like between the bracket and the wall of the medullary canal of the femur. But it happens, for various reasons, including the replacement of the prosthesis, that it is necessary to unseal the initial fixing lug to implant a new one.

  2870717 2 Before proceeding with the implantation of the bracket of a new prosthesis, which is generally longer than the initial leg, it is necessary to eliminate the initial layer of cement. The removal of the initial cement layer is generally carried out using drill bits mounted in rotation on the mandrel of a hand drill. The elimination of the portion of cement layer on the wall of the medullary canal is generally not difficult, because the wick is naturally guided on the longitudinal axis of the medullary canal of the femur.

  On the other hand, when the end of the wick abuts against the oblique end of the cement plug lying below the distal end of the first fastening lug, it is deflected and can pierce the cortex of the femur.

  The present invention therefore aims to provide a hip prosthesis that overcomes the disadvantages of hip prostheses known in the prior art and which favors the work of practitioners when they must proceed to replace a bracket by another .

  More specifically, the subject of the present invention is a hip prosthesis comprising an acetabular cup capable of being implanted in the acetabulum of a person's pelvis, said acetabulum comprising a hemispherical cavity, and a prosthesis stem comprising a suitable fixing lug. to be implanted in the medullary canal of the femur so that its axis is substantially merged with the axis of the medullary canal, said fixing lug thus comprising a proximal end and a distal end, a collar whose first end is integral with the proximal end of the fixing lug, the axis of the flange forming with the axis of the fixing lug an angle R of a given value, a spherical head secured to the second end of the flange, said spherical head being able to cooperate in rotational rotation with said hemispherical cavity, characterized in that the fixing lug presents a first a portion defined between its proximal end and an intermediate section defined at a non-zero distance from the distal end, said first portion having cross-sections of substantially trapezoidal shape continuously decreasing between the proximal end and the intermediate section to substantially conform to the shape of the medullary canal, and a second portion defined between said intermediate section and the distal end, said second portion having cross sections of substantially circular shape centered on the axis of the bracket and decreasing continuously between the section intermediate and the distal end.

  According to another characteristic of the invention, the angle f3 between the axis of the flange and the axis of the fixing lug has a value substantially between two values (31 and 132 predetermined, with (32 <(31, advantageously respectively substantially equal to 130 degrees and 120 degrees.

  According to another characteristic of the invention, for a second prosthesis stem adapted to be implanted on a person in replacement of a first prosthesis stem previously implanted on the same person, the distance separating the center of the spherical head and the point d intersection of the axis of the flange with the axis of the fixing lug is substantially equal to L sin R, sin R2, in which L is the distance separating the center of the spherical head and the point of intersection of the the axis of the flange with the axis of the fastening tab for the first prosthesis stem, and f31 and (32 are the values of the angle between the axis of the flange and the axis of the fastening rod in respectively the first and second prosthesis stems.

  Other features and advantages of the invention will become apparent from the following description given with reference to the accompanying drawings for illustrative but not limiting purposes, in which: FIG. 1 represents the block diagram of an embodiment of a hip prosthesis according to the invention, wherein certain dimensions have been expanded relative to those on a given scale for an industrial embodiment, in order to better highlight the characteristics of the invention, and Figures 2 and 3 show two transverse sections of a structural element of the hip prosthesis according to the invention as illustrated in FIG. 1, respectively referenced II-II and III-III in this FIG.

  It is clearly stated that, in the figures, the same references designate the same elements, whatever the figure on which they appear and whatever the form of representation of these elements.

  Similarly, if elements are not specifically referenced in one of the figures, their references can be easily found by referring to another figure.

  It is also stated that the figures represent a single embodiment of the object according to the invention, but that there may be other embodiments that meet the definition of this invention.

  It is furthermore specified that, when, according to the definition of the invention, the object of the invention comprises "at least one" element having a given function, the described embodiment may comprise several of these elements, and whereas, if the embodiments of the object according to the invention as illustrated comprise several elements of identical function and if, in the description, it is not specified that the object according to this invention must obligatorily comprise a particular number of these elements, the object of the invention may be defined as comprising "at least one" of these elements.

  Lastly, it is specified that when, in the present description, an expression alone defines, without any specific specific reference to it, a set of structural characteristics, [for example E = 1 (a, t, y, ...)] , these characteristics can be taken, for the definition of the object of the protection requested, when technically possible, either separately, [for example a, and / or T, and / or y,

  .], whether in full and / or partial combination, [eg E (a, T, y), and / or E (a, t), and / or E (T, y), and / or E (a , y)] ... DTD: The three figures represent, in schematic form, an embodiment of a hip prosthesis according to the invention, being underlined that the diagram according to this representation does not respect the proportions of a prosthesis as it is or can be actually realized. Indeed, in these schematic representations, some of the dimensions of the prosthesis have been deliberately dilated compared to those on a given scale for an industrial realization, only to better illustrate and highlight the structural features of the prosthesis according to the invention.

  The prosthesis comprises an acetabular cup 1 capable of being implanted, in a manner known to those skilled in the art, in the cotyloidal bone of a patient's pelvis, this acetabulum comprising a hemispherical cavity 12, and a prosthesis stem 2.

  The prosthesis stem 2 comprises a fixing lug 3 adapted to be implanted in the medullary canal of the femur so that its axis 4 is substantially merged with that of the medullary canal, the fixing lug 3 thus having a proximal end 5 and a distal end 6.

  The prosthesis stem 2 further comprises a flange 7 which may have different shapes, the one illustrated being only one possible form among many others. A first end 8 of the collar 7 is secured to the proximal end 5 of the bracket, the axis 10 of the flange making with the axis 4 of the bracket an angle of a given value.

  The prosthesis stem also comprises a spherical head 11 secured to the second end 13 of the collar 7, this spherical head 11 being able to cooperate, in a manner known per se, in rotulian rotation with the hemispherical cavity 12.

  According to a characteristic of the invention, the fixing lug 3 has a first part 21 defined between its proximal end 5 and an intermediate section 23 defined at a non-zero distance from its distal end 6, this first part 21 having transverse sections 24 of substantially trapezoidal shape, or close to this shape as specified in the preamble of the present description, decreasing continuously between the proximal end 5 and the intermediate section 23 to substantially match the shape of the medullary canal, and a second part 22 defined between the intermediate section 23 and the distal end 6, this second portion 22 having cross sections 25 of substantially circular shape centered on the axis 4 of the fixing lug 3 and decreasing continuously between the intermediate section 23 and the end distal.

  Advantageously, this second portion 22 is defined in an envelope 25 of substantially conical shape of revolution whose angle at the top is preferably equal to at most one hundred twenty degrees.

  The structure of the hip prosthesis described above is particularly advantageous, especially when it is necessary to proceed, for various reasons, to replace such a first prosthesis with a second.

  Indeed, to secure the fastening lug 3 with the bony part of the femur, is used in a known manner a cement or the like which completely encapsulates the leg portion which is in the medullary canal of the femur, by linking it with the bone part of the femur.

  However, for various reasons, a few years after a hip prosthesis has been implanted, for example generally about fifteen years except accident or the like, it sometimes happens that it is necessary to replace this first prosthesis by a so-called second "recovery" ", of course taking into account the morphological changes of the person that occurred after the first prosthesis was placed.

  To do this, it is necessary to separate the fixing lug 3 of the first prosthesis rod 2 and the femur, which is done in a relatively conventional manner without much difficulty.

  On the other hand, to implant the fixing lug 3 of the second prosthesis, it is first necessary to clean the medullary canal of all the cement which encapsulated the fixing lug of the first prosthesis and which is glued to the bony part of the femur. As explained in the preamble, use is essentially strawberries or wicks of a diameter substantially equal to the cross section of the medullary canal, immersed in it while being driven by a rotational movement. These wicks are used to remove the cement stuck on the wall of the medullary canal, but also the cement plug located below the distal end of the first bracket, without risking damage to the cortex of the femur. Indeed, they are guided by the conical portion corresponding to the indentation of the second portion 22 of the bracket 3 of the first prosthesis, which plays the role of a perfectly centered pilot hole.

  Moreover, as mentioned above, the replacement of a first prosthesis with a second is generally carried out after a relatively large number of years and on persons who are of certain age and who have undeniably undergone morphological changes. , for example a settlement of their bone structure.

  This poses a problem, for example, when the person wears a hip prosthesis only on one side. Indeed, it is obvious that, since the prostheses are made of solid materials such as a titanium alloy or the like, there is no sagging of this material. A collapse occurs on the other hand on the hip which does not have a prosthesis and, to restore a morphological balance and symmetry and to avoid problems in particular spinal, it is necessary to replace the first prosthesis with a second prosthesis which must take into account the modifications. morphological changes in the hip without prosthesis.

  Also, the prosthesis according to the invention further comprises the following structural features.

  Firstly, the value of the angle R between the axis 10 of the flange 7 and the axis 4 of the fixing lug 3 is substantially between two predetermined values R1 and J32, with 132 <J31, the difference between these two values being illustrated in Figure 1 by the angle a.

  The experiment has demonstrated to the applicants that the two predetermined values 131 and 32 are respectively substantially equal to 130 degrees and 120 degrees, and that the value of the angle a is most often of the order of eight degrees.

  According to the invention also, the second prosthesis stem adapted to be implanted on a person, replacing a first prosthesis stem previously implanted on the same person, is defined so that the distance separating the center of the spherical head 11 and the point of intersection 26 of the axis 10 of the flange 7 with the axis 4 of the fixing lug 3 is substantially equal to L S'nPI, in which L is the distance separating the center of the spherical head 11 sin132 and the point of intersection 26 of the axis 10 of the flange 7 with the axis 4 of the fixing lug 3 for the first prosthesis stem, and R1 and (32 are the values of the angle between the axis 10 of the collar 7 and the axis 4 of the fixation rod 3 in the first and second prosthesis rods respectively.

  In addition, to enable the practitioner to better respect the morphology of the patient, the spherical head 11 of the second prosthesis stem is chosen from a set of spherical heads having radii of values progressing arithmetically between two predetermined limits, for example 2 mm in 2 mm, and / or the second prosthesis stem 2 is chosen from a set of prosthesis rods having distance values I progressing arithmetically between two predetermined limits, for example 10 mm in diameter. 10 mm.

Claims (8)

  Hip prosthesis comprising an acetabulum (1) adapted to be implanted in the acetabulum of the hip of a person, said acetabulum having a hemispherical cavity (12), and a prosthesis stem (2) comprising a fixation (3) adapted to be implanted in the medullary canal of the femur so that its axis (4) is substantially merged with the axis of the medullary canal, said fixing lug (3) thus having a proximal end (5) and a distal end (6), a collar (7) whose first end (8) is integral with the proximal end (5) of the fixing lug, the axis (10) of the collar forming with the axis (4) of the fixing lug an angle (3 of a given value, a spherical head (11) integral with the second end (13) of the flange (7), said spherical head (11) being able to cooperate in rotulienne rotation with said hemispherical cavity (12), characterized in that the fixing lug (3) has a first portion (21) defined between its proximal end (5) and an intermediate section (23) defined at a non-zero distance from the distal end (6), said first portion (21) having cross-sections (24) of substantially trapezoidal shape decreasing continuously between the proximal end (5) and the intermediate section (23) to substantially conform to the shape of the medullary canal, and a second portion (22) defined between said intermediate section (23) and the distal end (6), said second portion (22) having cross sections (25) of substantially circular shape centered on the axis (4) of the fixing lug (3) and decreasing continuously between the intermediate section (23) and the distal end (6).   2. Prosthesis according to claim 1, characterized in that said second portion (22) is defined in an envelope of substantially conical shape of revolution.   3. Prosthesis according to claim 2, characterized in that the apex angle of the substantially conical envelope of revolution is equal to at most one hundred twenty degrees.   4. Prosthesis according to one of claims 1 to 3, characterized in that said angle f3 has a value substantially between two values [31 and (32 predetermined, with [32 <(31.   5. Prosthesis according to claim 4, characterized in that the two values (31 and [32 predetermined are respectively substantially equal to 130 degrees and 120 degrees.   6. Prosthesis according to one of claims 4 and 5, characterized in that for a second prosthesis rod adapted to be implanted on a person to replace a first prosthesis stem previously implanted on the same person, the distance I separating the center of the spherical head (11) and the point of intersection (26) of the axis (10) of the flange (7) with the axis (4) of the fixing lug (3) is substantially equal at L sinR ', where L is the sin R2 distance between the center of the spherical head (11) and the point of intersection (26) of the axis (10) of the flange (7) with the axis ( 4) of the fixing lug (3) for the first prosthesis stem, and 131 and 02 are the values of the angle between the axis (10) of the collar (7) and the axis (4) of the fixation rod (3) in the first and second prosthesis stems, respectively.   7. Prosthesis according to claim 6, characterized in that the spherical head (11) of the second prosthesis stem is selected from a set of spherical heads having rays of values progressing arithmetically between two predetermined limits.   8. Prosthesis according to one of claims 6 and 7, characterized in that the second prosthesis rod (2) is selected from a set of prosthesis rods having distance values I progressing arithmetically between two predetermined limits.