Adaptable hip prosthesis

Abstract: There is disclosed a hip prosthesis struc­ ture which can be easily fitted to the geometrical characteristics of the patient coxo-femural articu­ lation. This prosthesis essentially comprises a given size stem (1) at the top portion thereto there are provided means (5,20) for firmly coupling one end of a shaped bar or neck (7,23) which bears the spherical head (9) to be coupled to the hip acetabulum. The shaped bar (7,23) having a variable length and a longitudinal axis of any given extension.

Description: BACKGROUND OF THE INVENTION The present invention relates of a hip prosthesis structure,which is adapted to be easily fitted to the specific shape or geometrical characteristics of the patient coxo-femural articulation. As is known in the case of fractures,arthritis and the like of the human hip or its articulated joint with the femur,there are presently used suitable hip prostheses in order to provide the hip joint with renwed mobility. Conventional hip prosthesis structures are usually made as a single piece,consisting of a stem from the top portion of which a neck extends thereon there is applied a spherical head,having any desired diameters. The thus constructed prostheses,however,have the drawback that they can not be used for any patients,unless said prostheses are specifically adapted in size to the geometrical structure of the hip and femur of the patient. In fact these prostheses,though they have been tailored in a satisfactory way for a given patient, can not be adapted to other patients mainly because their neck portions have a greater or smaller length than that suitable for providing a proper coxo-femural articulation. In these cases, as it should be apparent, the prosthesis head can not be properly fitted to the patient acetabulum therewith it should cooperate. Sometimes,moreover, the patient has a so-called "varus" femur, that is having a rather anomalous shape,and for these femurs particular hip prostheses must be adopted in which the neck portion has a specific preset orientation with respect to the stem. In this connection,it should be moreover pointed out that the femur neck is not perpendicular to the patient pelvis thereby a normal neck is reversed at about 10° with respect to the pelvis. Known hip prostheses, on the other hand, are not designed to overcome this drawback and hence they cannot be adapted in a perfect way to the anatomic characteristics of a lot of patients. The EP-A-0257359 reference discloses a hip prosthesis structure which essentially comprises a stem at the top portion of which there are provided means for firmly coupling the end of a shaped small bar or neck, bearing a spherical head adapted for coupling to the acetabulum of the pelvis of a patient, said small bar having a variable length and a longitudinal axis having any desired extensions. SUMMARY OF THE INVENTION Accordingly, the task of the present invention is to overcome the above mentioned drawbacks by providing a hip prosthesis which can be provided with a neck of any desired length,according to requirements. Within the scope of the above mentioned object,a main object of the present invention is to provide such a hip prosthesis in which the axis of the neck is able of forming a different opening angle with respect to the axis of the stem. Yet another object of the present invention is to provide such a hip prosthesis structure in which the axis of the neck has any desired extension, included a broken line extension. According to one aspect of the present invention, the above mentioned task and objects,as well as yet other objects,which will become more apparent hereinafter,are achieved by a hip prosthesis according to the main claim. BRIEF DESCRIPTION OF THE DRAWINGS Further characteristics and advantages of the hip prosthesis structure according to the present invention will become more apparent hereinafter from the following detailed description of a preferred though not exclusive embodiment thereof, which is illustrated, by way of an indicative example, in the figures of the accompanying drawings,in which: figure 1 is a side view of the hip prosthesis structure according to the present invention; figure 2 shows a front view of the prosthesis stem; figure 3 is a cross-sectional view illustrating the coupling between the stem and neck of the prosthesis; figure 4 shows a possible embodiment of the prosthesis neck; figures 5 to 9 show other possible embodiments of necks adapted to be applied on the prosthesis stem and having different extension longitudinal axes; DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the above figures of the accompanying drawings,the hip prosthesis structure according to the present invention essentially comprises a stem 1,consisting of a flat bar,having a given length and a surface provided with a plurality of longitudinal slots 2. The prosthesis stem,in particular,extends according to a suitably curved longitudinal axis and has its bottom end 3 of substantially ogival shape. The stem is moreover provided,at the top thereof,of a portion 4 anlarged at the side of its concave perimetrical line on which there is formed a seat or recess 5 having a suitably slanted axis an oval cross-section and suitably tapered. In this seat there is firmly housed one end 6,also shaped,of a small bar or neck 7 the other end 8 of which is so shaped as to be able of restraining a spherical head 9 adapted in turn for coupling with the acetabulum of the pelvis of the patient. In this connection it should be pointed out that the mentioned small bar may have any desired variable length,depending on the specific use requirements. The mentioned small bar,moreover,may have a differently slanted axis,with respect to its end engaging in the seat 5 of the stem and the axis of which,of course,will coincide with the axis of said seat. This slanting can be essentially obtained according to any of the planes pertaining to the plane assembly passing through the line defining the axis of said seat. More specifically,as is shown in figure 9, an embodiment of the present invention provides for the use of a neck including an insertion end which is offset from its axial extension. Thus,a prosthesis will be formed including a neck which virtually constitutes an extension of the middle curvature,indicated at 10,of the portion of the stem. This configuration,in actual practice,affords the possibility of inserting a neck even in prostheses of minimum thickness,while assuring a perfect and reproducible positioning of the stem-neck assembly,without any risks of a possible disengaging of the two parts. From the above disclosure it should be apparent that the invention fully achieves the intended objects.

Claims: A hip prosthesis comprising a stem (1) at a top portion of which there are provided recess means (5) in which can be fixedly engaged an end portion (6) of a neck member (7, 23) the other end (8, 21) of which is tapering and engageable in a mating tapering bore of a spherical head adapted for coupling to the acetabulum of the pelvis of a patient, said stem (1) including a flat stem bar having an outer surface provided with a plurality of longitudinally extending slots (2), said stem (1) having a substantially ogival bottom end portion (3), said recess means (5) comprising an oval cross-section tapering seat (5) and said end portion (6) of said neck having an oval cross-section for snugly fitting in said oval cross-section tapering seat (5) of said stem, in the fitted condition the axis of said seat (5) substantially coinciding with the axis of said one end portion (6) of said neck. A hip prosthesis according to Claim 1, characterized in that said neck (7) comprises a bar neck body including a central neck portion integral with said one end portion (6) and said other end portion (8) of said neck and arranged therebetween, said central neck portion and said other end portion (8) having, as said one end (6) of said neck (7) is engaged in said seat (5), a common axis which is offset from the axis of said seat (5). A hip prosthesis according to Claims 1 and 2, characterized in that said seat (5) has a flat ellipsoidal cross-section.

Inventors: CREMASCOLI PATRIZIO, CREMASCOLI, PATRIZIO
Applicants: CREMASCOLI SPA G, G. CREMASCOLI S.P.A.
Application year: 1988
Main classification: A61F2
IPC codes: A61F2