HIP PROSTHESIS WITH A MEMBER FOR DAMPING MECHANICAL STRESSES

Abstract: The prosthesis comprises a first femoral metallic or equivalent part (1) engaged with the femoral bone (B) and forming the spherical head (3) of the articulation, and a second acetabular part (6) engaged with the pelvis (A) and forming the seat for said head through an element (9) made of synthetic resin which defines the surface (9A) of said seat; between said element (9) made of synthetic resin and the metallic part (7) which receives it, an elastic thickness or lining (10) is interposed having a damping effect with consequent movability of said seat.

Description: Hip Prosthesis with a member for damping mechanical stresses. In or hopedy, protheses are known for the articu¬ lation of the hip (arthro-prothesis of the hip), which comprises a first rigid and mostly metallic part being brought into engagement-with the femoral bone through a long tapered element (longitudinally received in the upper part of the femur) and through a femoral head, substantially spherical, which is in the position corresponding to the natural one to be replaced; a second part metallic, or equivalent, is engaged with the pelvis and forms a seat or acetabulum for said spherical head, mostly through an element made of sub¬ stantially rigid and self-lubricating synthetic resin. This second part may be cemented and/or screwed to the pelvis in such a position as to keep the position of the .natural seat of the femur articulation. These pro¬ theses are used in case of the degeneration of the natural articulation, with consequent pains and func¬ tional limitations of the hip. These protheses are. subject to a remarkable mechani¬ cal torment both for a static and dynamic load during the deambulation movements or, anyway, the movements made by the subject carrying the prothesis. The mechani¬ cal stresses act directly onto the bony parts in contact with the prothesis and, particularly, onto the bony structure of the pelvis which accomadates said second " part of the prothesis. The consequence of that is a more or less rapid degeneration of the bony tissue which implies the need of another intervention to re¬ place the prothesis with further destruction of the bony tissue of the pelvis and, moreover, with torments and discomforts for the patient. The present invention relates to an improved pro¬ thesis which has been studied with the purpose to avoid the above mentioned drawbacks by reducing the effects of a concentrated torment due to the mechanical stresses on the bony structure of the pelvis and also on the diaphysis of the femur. Substantially, the prothesis according to the in¬ vention has, at least in one of the two parts of the prothesis itself, an elastically yielding lining or thickness, which dampens or cushions the stresses, especially the dynamic ones. An elastically yielding thickness may be disposed in the part of the prothesis applied to the pelvis, in order to obtain a movement of the seat respect to the part whicn is anchored to the pelvis. Advantageously, between the element made of syn¬ thetic resin and the acetabular part which receives it, there is interposed the elastic thickness having a dampening effect. In practice, said dampening elastic seat extension. The dampening thickness may be made of silicone or other elastomeric, elastically yielding material. Said second acetabular part may be supplied with means which realize a perimetrical sealing condition with the element defining the surface of the seat. These sealing means consist of a ring nut engaged with said second part and of a flange of the element, that is tightened between, said ring nut and said second part. To permit the displacements of the element made of synthetic resin, relative to the part applied to the pelvis, said element presents a yielding zone with corrugation or other, between the flange and the por¬ tion forming the seat for the head. According to a further embodiment of the invention, the dampening thickness presents or defines, with the surfaces in contact therewith, some cavities whose volume may vary in relation to the stresses to which said thickness is subjected instantaneously. * Said ca¬ vities may be in communication with the acetabular seat and/or with the spongy structure of the pelvis, by means of holes in either or both parts separated by said thickness. Said cavities may be also directly channels formed in said thickness and/or in the sur¬ faces in contact therewith. The prothesis may include means for the mutual restraint between the components of the acetabular part of the prothesis, like pawl rings, annular chan¬ nels or pads and others. This facilitates the handling during the application of the same prothesis. By the arrangement defined above, it is evident that the stresses are attenuated and distributed and, there¬ fore, the torment on the structure of the body tissue , being in contact with the prothesis parts fitted thereinto, is attenuated up to a such degree as to be bearable even over prolonged periods of time far bejond the ones provided for the present protheses. In parti¬ cular, the possibility is obtained of displacements of the seat for the femoral head relative to the part anchored to the pelvis. The invention will be better understood by following the description and the accompanying drawing which shows a practical non limitative exemplification of the same invention. In the drawing: Pig. 1 shows an ensemble view of an applied prothesis; Pig. 2 shows an enlarged and partially cutaway detail; Pigs. 3 to 7 show the same number of feasible embodi- ents of the invention. According to what is illustrated in the accompanying drawing, by A there is indicated the bony acetabular structure of the pelvis and by B the bony structure of the femur; between these two structures, a prothesis generally indicated by C is disposed (on the right of Pig. 1) , in order to replace the natural articulation CN so as to restore the natural capability of limb movements. On the upper part of the femur B a pertinent prothe¬ sis part is fitted including a body with a spherical head- of articulation 3 and a tapered element 5 which penetrates longitudinally into the femur for a correct positioning of the spherical articulation 3 so as to correspond to that of the natural articulation. In the structure of the pelvis A a seat is formed to receive the second acetabular part 6 of the prothesis, that comprises a body 7 intended to be engaged with said structure as well as an element 9 > made of synthetic resin, forming the surface 9A of the articulation seat for the spherical head 3« A dampening thickness or lining is provided between the components 7 and 9 so that the stresses interacting between the two parts of the prothesis result dampened in contact with the prothesis and, in particular, those of the pelvis. More particularly, a thickness 10 is provided, made of elastomeric material elastically yiel¬ ding with high deformability and resilience, such as the silicone or other; this thiclαiess 10 surrounds the element 9 which is mounted in such a way as to be able to move relative to the body 7 through the elastic yieldings of the. thickness 10. To this aim, between a flange 9B for the anchorage of the element 9 at the body 7 and the portion of said element 9 forming the surface 9A, a zone 9C is provided which is deformable through the reduction of its thickness and/or through shaping with mostly annular corrugations. There is thus obtained the possibility of displacements in all side directions and in depth respect to the axis of the acetabular part of the prothesis. The flange 9B for the anchorage of the element 9 at the metallic or, however, rigid body 7 is shaped so as to also ensure a hermetic sealing against the penetra¬ tion of organic liquid into the virtual cavities between the body 7 and the thickness 10 and between the thickness 10 and the element 9. To this end, according to Fig. 2, a ring nut 12 is provided, engaged, through a screw fit 14, with the body 7, which tightens the flange 9B against the step-shaped edge of body 7 thus ensuring at the same time the engagement of the element 9 and the above mentioned hermetic seal. In the illustrated embodi¬ ment, the body 7 is cup-shaped with a closed bottom unlike the presently used protheses which have an opening on the bottom of said body 7 for the downflow of possible organic liquids. The possibilities of elastic yielding of the thic¬ kness 10 made of elastomeric material with high ela¬ sticity and resilience allow to attenuate the effects of the mechanical stresses due to static and dynamic loads, to which the prothesis is subjected in use, - with the advantages already mentioned and which will be anyway . apparent to those skilled in the art - in the bony structure adjacent to the prothesis and, in particular, to the acetabular structure of the pelvis. According to Pig. 3, between the body 7 and the element 9 a dampening elastic thickness or lining 20 is disposed which is capable of " becoming deformed in order to change the relative position between the body 7 and the ele¬ ment 9 which forms the acetabular seat. Differently from the dampening thickness 10 of the embodiment pre¬ viously described, the dampening thickness 20 surrounds completely the element 9 and reaches the outside by projecting from the body 7. An edge 20A keeps the ele¬ ment 9 inside the dampening thickness. The dampening thickness 20 presents - at the external surface which is in contact with the body 7 - channels 22 which form cavities able to change their onw capacity through the deformation of the dampening thickness 20. These chan¬ nels 22 may also lead outwardly of the prothesis, respec¬ tively may communicate with the acetabular artificial seat 9A, respectively again with the spongy part of the structure A of the pelvis through the same channels 22 which lead outwards respectively into through-holes 24 in the element 9 and through-holes in the thickness 10 and respectively again into through-holes 26 in the body 7. More than one of these dispositions may be pro¬ vided. According to Pig. 4, the dampening thickness 20, in additi to having an annular inner projection 20A for retaining the element 9,- has also an outer bead or pad- 20B which finds its seat elastically in an annular channel formed in the inner surface of the body 7 to achieve a retai¬ ning effect of components 9 and 20 within the body 7. In the modified embodiment of Pig. 5, without preju- dice to the possibilities of communication between the cavities defined by channels 22 and the outside for a possible circulation of organic liquids, and in addition to nrovide an annular pad 20B similarly to what is -nro- vided in the embodiment of Pig. 4, a direct contact of the element 9 with the body 7 in the zone 9X is predi¬ sposed. An elastic, toric, expansion ring or other equivalent, indicated by 28, -is provided in an inner throat formed towards the end part in the body 7 to engage the element 9, 9X and prevent it from coming out spontaneously. In the further modified embodiment of Pig. 6, in place of the elastic ring 28, an elastic annular lamina element 29 is provided having the same function as the elastic toric ring 24. In the embodiment of Pig. 6 there is not an annular pad 20B as in Pig. 5 since all is retained by the lamina ring 29. In the further modified embodiment of Pig. 7, the element 9 forming the artificial acetabular seat 9A has a pair of annular projections 9E between' which an annular channel is defined able to accomodate a toric seal 30 which cooperates with the inner wall of the body 7 which, in that zone, results substan ially cylin¬ drical. An end thread in this cylindrical zone of the wall of body 7 serves to engage a threaded ring 22 able to retain the element 9 ---*■ its seat within the body itself and to prevent it from coming out.. Possible communications of channels 22 with the outside and/or with the spongy part of the -oelvis bony structure, ensure the axial displacement of the element 9 and of the artificial acetabular seat 9A relative to the pelvis through the deformation of the dampening thickness with the effects previously shown. In Pig. 7, a hole 24 through the element 9 and a hole 26 through the element 7 are indicated. One or more of these holes may serve for the passage of orga¬ nic liquid towards and from the channel cavities formed in the thickness 20, like those indicated by 22 or others. The dampening thickness may be also multiple and/or formed with free or bound bodies or granules. Obviously, the dampening elastic thickness is to be made of a biological material, f.es. silicone, compatible with the biological liquids, or covered with such material. The elastic thickness 20 allows, anyway, movements of the seat 9 " respect to the piece 7. Thickness 20 can also be made of compound materials, having the surfaces made of biologically compatible material; The drawing shows one exemplification given only as a practical demonstration of the invention which may vary in the forms and dispositions. The possible pre ¬ sence of reference numbers in the attached claims has the purpose to facilitate the reading of the claims reference being made to the description and drawing, and has not, therefore, the purpose of putting limitations to the ambit of the protection pointed out by the claims.

Claims: CLAIMS 1) A prothesis for the articulation of the hip, characterized in that in at least one of the two parts of the prothesis an elastically yielding thickness or lining is provided. 2) Prothesis according to claim 1, characterized in that an elastically yielding thickness is arranged in the part of the prothesis applied to the pelvis. 3) Prothesis according to claim 2, comprising a first femoral metallic or equivalent part engaged with the femoral bone and forming the spherical head of the articulation, and a second acetabular metallic or equivalent part engaged to the pelvis and forming the seat for said head with an element made of synthetic resin which defines its surface, characterized in that between said element (9) made of synthetic resin and the second part (7) which receives it, the elastic thickness (10) is interposed having a dampening effect in all the reaction directions with corresponding displaceme 4) Prothesis according to claim 3, characterized in that said dampening thickness (10) is developed substantially throught the whole extension of the ace¬ tabular artificial seat (9A). 5) Prothesis according to claims 3 and 4, characte¬ rized in that said dampening thickness (10) is made up of silicone or other elastically yielding ela- stomeric and biologically compatible material. 6) Prothesis according to claims 3 to 5, characte¬ rized in that said second part (6) is provided with means which realize a perimetrical sealing condition with the element (9) which defines the surface (9A) of the seat. 7) Prothesis according to claim 6, characterized in that said sealing means are made up of a ring nut (12) engaged to said second part (6) and of a flange (9B) of the element (9) , which is tightened bewteen said ring nut . (12) and said second part (6). 8) Prothesis according to claims 6 and 7, characte¬ rized in that the element (9) made of synthetic resin has a yieldable zone (90) with corrugation or other, between the flange (9B) and the portion forming the seat (9A) for the head. 9) A prothesis according to claims 1 to 3, characte¬ rized in that the dampening thickness (20) presents or defines, with the surfaces in contact therewith, cavi¬ ties (22) whose volume may change in relation to the stresses to which said thickness is instantaneously subjected. 10) Prothesis according to claim 9 » characterized in that said cavities (22) are in communication with the acetabular seat (9A) and/or with the spongy struc¬ ture (A) of the pelvis, by means of holes (24,26) in either or both of the two parts separated by said thickness. 11) Prothesis according to claims 9 and 10, charac¬ terized in that said cavities are in communication with the outside of the prothesis through channels formed in said thickness and/or in the surfaces in contact therewith. . 12) Prothesis according to claims 1 to 4, characte¬ rized in that it comprises means for the mutual restraint . between the components of the acetabular part of the .prothesis, like pawl rings (28,29,32), annular channels or pads (2δA,2δB) .and other. 13) Prothesis according to claim 12, characterized in • that element (9) forming the acetabular seat is movable at least axially and possibly also sideways respect to element (7) which is fixed to the pelvis. 14) Prothesis for the articulation of the hip, with a member for the dampening of the mechanical stresses; all as above described and represented for exemplification in the accompanying drawing.

Inventors: SOSTEGNI GIULIANO, SOSTEGNI, GIULIANO
Applicants: SOSTEGNI GIULIANO, SOSTEGNI, GIULIANO
Application year: 1985
Main classification: A61F2
IPC codes: A61F2