CENTROMEDULLARY FIXATION STEM FOR JOINT PROSTHESIS

Abstract

An anchoring stem for a joint prosthesis with a centromedullary fixation includes a metaphyseal-diaphyseal (M-D) portion intended to be inserted into the medullary canal of the long bone of the joint to be prosthesized. It receives an epiphyseal-diaphyseal (E-D) portion, having its upper portion protruding from the considered bone and intended to receive in turn an articular element. The M-D portion and the E-D portion are independent from each other but may be fastened to each other. The E-D portion is received within the M-D portion along a direction parallel or substantially parallel to the main dimension of the M-D portion, along a length of cooperation of the portions with each other such that the ratio of the length of reception of the E-D portion within the M-D portion to the total length of the M-D portion is in the range from 0.5 to 0.85. The M-D portion is provided with means capable of forbidding any rotation or angular displacement of the E-D portion once the latter has been received within the M-D portion.

Claims

1. An anchoring stem for a joint prosthesis with a centromedullary fixation, comprising a metaphyseal-diaphyseal portion configured for insertion into a medullary canal of a long bone of a joint to be prosthesized, and receiving an epiphyseal-diaphyseal portion, the epiphyseal-diaphyseal portion having an upper portion protruding from the long bone, and configured to receive in turn an articular element, and wherein the metaphyseal-diaphyseal portion and the epiphyseal-diaphyseal portion are independent from each other but fastenable to each other: wherein the epiphyseal-diaphyseal portion is received into the metaphyseal-diaphyseal portion along a direction parallel to a main dimension of said metaphyseal-diaphyseal portion, along a length of cooperation of the epipheseal-diaphyseal and metaphyseal-diaphyseal portions with each other such that a ratio of a length of reception of the epiphyseal-diaphyseal portion within the metaphyseal-diaphyseal portion to a total length of the metaphyseal-diaphyseal portion is in the range from 0.5 to 0.85; and wherein the metaphyseal-diaphyseal portion is provided with (i) wings or fins extending from a surface in an upper area of the metaphyseal-diaphyseal portion or (ii) substantially planar surfaces cooperating with an inner surface of an upper portion of the metaphyseal-diaphyseal portion, once the epiphyseal-diaphyseal portion has been received within the metaphyseal-diaphyseal portion.

2. The anchoring stem for a joint prosthesis with a centromedullary fixation of claim 1, wherein the epiphyseal-diaphyseal portion is fastenable to the metaphyseal-diaphyseal portion by mechanical wedging or by cold welding.

3. The anchoring stem for a joint prosthesis with a centromedullary fixation of claim 1, wherein the means capable of forbidding any rotation or angular displacement of the epiphyseal-diaphyseal portion once the latter has been received within the metaphyseal-diaphyseal portion are formed of wings or fins extending from a surface in an upper area of the metaphyseal-diaphyseal portion.

4. The anchoring stem for a joint prosthesis with a centromedullary fixation of claim 1, wherein the means capable of forbidding any rotation or angular displacement of the epiphyseal-diaphyseal portion once the latter has been received within the metaphyseal-diaphyseal portion are formed of substantially planar surfaces cooperating with an inner surface of an upper portion of the metaphyseal-diaphyseal portion.

5. The anchoring stem for a joint prosthesis with a centromedullary fixation of claim 1, wherein the cooperation between the epiphyseal-diaphyseal portion and the metaphyseal-diaphyseal portion is achieved by a dovetail-type assembly, one of said portions being provided with a protrusion capable of cooperating with a recess of complementary shape formed within the other portion.

6. The anchoring stem for a joint prosthesis with a centromedullary fixation of claim 5, wherein a cross-section of the protrusion is circular, trapezoidal, or has any other shape enabling to fasten the two epiphyseal-diaphyseal and metaphyseal-diaphyseal portions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The way in which the embodiments may be implemented and the resulting advantages will better appear from the following non-limiting embodiments, in relation with the accompanying drawings, and in relation with a femoral stem for a hip prosthesis.

[0023] FIG. 1 is a simplified perspective representation of a first embodiment.

[0024] FIG. 2 is a simplified representation in lateral view and in disassembled mode of the femoral stem of FIG. 1.

[0025] FIG. 3 is a simplified three-quarters front perspective representation of the metaphyseal-diaphyseal portion of the femoral stem of FIG. 1.

[0026] FIG. 4 is a lateral view of a second embodiment of the femoral stem.

[0027] FIG. 5 is a simplified representation in lateral view and in disassembled mode of the femoral stem of FIG. 4.

[0028] FIG. 6 is a simplified three-quarters front perspective representation of the metaphyseal-diaphyseal portion of the femoral stem of FIG. 4.

[0029] FIG. 7 schematically illustrates another fastening mode for the femoral stem in assembled mode.

[0030] FIG. 8 is a view of the femoral prosthesis of FIG. 7 in exploded view.

[0031] FIG. 9 schematically illustrates different variations of the metaphyseal-diaphyseal portion for a same epiphyseal-diaphyseal portion of the femoral stem.

[0032] FIG. 10 schematically illustrates different variations of the epiphyseal-diaphyseal portion for a same metaphyseal-diaphyseal portion of the femoral stem.

DETAILED DESCRIPTION

[0033] Although the following description is more particularly directed towards a stem for a femoral hip prosthesis, it should be understood that the disclosed embodiments aim at applying to any type of joint prosthesis inducing a centromedullary fixation of a stem, and particularly a shoulder prosthesis, a knee prosthesis, etc.

[0034] A first embodiment of a stem for a femoral hip prosthesis has thus been shown in relation with FIGS. 1 to 3.

[0035] The stem is basically formed of two different portions intended to be fastened to each other, respectively a metaphyseal-diaphyseal portion (1) and an epiphyseal-diaphyseal portion (2) which can be better observed in FIG. 2, outside of the wound. The assembly, previously fastened, preferably, on a sterile table and outside of the patient, is intended to be introduced according to conventional techniques into the medullary canal of the femur, after a bone preparation by the surgeon, particularly by means of scrapers. Said epiphyseal-diaphyseal portion (2) has by construction a prosthetic neck (3) provided at its free end with a Morse taper (4) having a head or ball (11), itself intended to be received into the acetabular cavity of the considered joint or into an acetabulum or a cup, previously affixed in said acetabular cavity, fitting thereon by wedging. However, said head may also be machined in one piece on the epiphyseal-diaphyseal portion (see FIG. 10), and this, in known fashion.

[0036] According to an essential feature of the invention, the cooperation of the epiphyseal-diaphyseal portion (2) with the metaphyseal-diaphyseal portion (1) to form the actual stem, is achieved along the diaphyseal axis of the femur and along a cooperation length such that the ratio of insertion length B of the epiphyseal-diaphyseal portion (2) within the metaphyseal-diaphyseal portion to the total length A of the metaphyseal-diaphyseal portion is close to 0.6. This length ratio has been illustrated in FIG. 6.

[0037] By adopting such a cooperation mode, and in the case of the described example of a hip prosthesis, said portions (1, 2) forming the stem cooperate together along the medial-lateral plane of the considered joint, schematized by reference frame (X, Y) in FIG. 2.

[0038] According to an essential feature of the invention, once the epiphyseal-diaphyseal portion has been introduced within the metaphyseal-diaphyseal portion, it is rotationally locked with respect to the diaphyseal axis of the metaphyseal-diaphyseal portion. Such a locking results from the presence of lateral wings (8, 9) extending from one of the surfaces of said metaphyseal-diaphyseal portion, and in the case in point, extrados. Thereby, once the stem thus formed is in place within the medullary canal of the femur, it remains properly oriented given the desired angular displacement in the medial-lateral plane.

[0039] The cooperation between the epiphyseal-diaphyseal portion (2) and the metaphyseal-diaphyseal portion (1) is advantageously performed by mechanical wedging and/or by cold welding, after the introduction of a protrusion (5) extending substantially all along a lateral surface (10) of the epiphyseal-diaphyseal portion within a recess (6, 7) of complementary shape formed inside of the metaphyseal-diaphyseal portion (1). A dovetail-type assembly is typically used. For this purpose, and advantageously, the cross-section of the protruding portion (5) of the epiphyseal-diaphyseal portion is typically circular, as can for example be observed in FIG. 3.

[0040] Thereby, due on the one hand to the length of the area of cooperation between the epiphyseal-diaphyseal portion and the metaphyseal-diaphyseal portion (1) and, in the case in point, along substantially the entire height of the epiphyseal-diaphyseal portion (2), and on the other hand, to the reception and to the lateral hold of the epiphyseal-diaphyseal portion (2) between the upper lateral wings (8, 9) of the metaphyseal-diaphyseal portion, the stress distribution area is significantly increased with respect to modular femoral stems of the prior state of the art.

[0041] The epiphyseal-diaphyseal portion being monoblock, risks of breaking the prosthetic necks, as can be observed in said prior art devices, are thus drastically reduced.

[0042] A second embodiment has been shown in relation with FIGS. 4 to 6. The principle underlying the second mode is strictly identical to that described in relation with FIGS. 1 to 3, except however for upper lateral wings which are smaller at the level of the diaphyseal portion. This embodiment is simpler to form, but does not modify the general principle underlying the general embodiments. FIG. 6 also shows the ratio of the respective lengths of the epiphyseal-diaphyseal and metaphyseal-diaphyseal portion, especially by showing the lower reception area of said epiphyseal-diaphyseal portion. Length B actually corresponds to the total height of the epiphyseal-diaphyseal portion.

[0043] Another embodiment has been shown in relation with FIGS. 7 and 8. This mode is for the most part equivalent to the previous embodiment, with the difference that, however, the recess (11) is formed within the epiphyseal-diaphyseal portion (2), which is thus introduced on a protrusion (10) of complementary shape extending within the metaphyseal-diaphyseal portion (1). In this embodiment, the means capable of locking any rotation of the epiphyseal-diaphyseal portion once it has been fastened to the metaphyseal-diaphyseal portion (1) are formed of substantially planar surfaces (12, 13) extending parallel or substantially parallel to the recess (11), said surfaces cooperating with the inner surface (14) of the upper area of the metaphyseal-diaphyseal portion.

[0044] Due to the general principle underlying the present embodiments, it becomes possible for the practitioner to compose and to calibrate the femoral stem according to the patient's specific anatomy and pathology. He/she may in particular at leisure select the metaphyseal-diaphyseal portion of the stem, typically with a variable extrados according to the size to be implemented, and assemble thereto an epiphyseal-diaphyseal portion independent, particularly in terms of neck length, from the neck angle.

[0045] Such a modularity has in particular been illustrated at the level of FIGS. 9 and 10.

[0046] In other words, whatever the size of the extrados used (metaphyseal-diaphyseal portion), a plurality of neck lengths may be provided for the epiphyseal-diaphyseal portion, thereby eliminating the need for a wide range of femoral heads. Thereby, the practitioner can select the best adapted epiphyseal-diaphyseal portion so that the Morse taper, receiving the femoral ball, is entirely covered and non-overlapping, which, as above-targeted, then enables to do away with risks of wearing of the polyethylene insert, particularly in the context of dual-mobility hip prostheses.

[0047] The advantage of the stem, which provides at the same time an adaptability, an adjustment, a composition, a calibration, and a dimension depending on the pathology and on the anatomy encountered by the practitioner, including intraoperatively, and not, as in the prior state of the art, only based on the X-rays previously obtained, thus appears.

[0048] In addition to such an optimized modularity, the described embodiments further enable to significantly decrease the necessary stock in the range of prostheses to be used.