Femoral prosthesis device

Abstract: The present invention provides a femoral prosthesis to be utilized as an implant into a human femur to connect the coxa. The femoral prosthesis comprises a stem body (2) to be inserted into a femur bone, a neck portion (3) fixed integrally at the proximal portion of the stem body, a spherical head member having an opening to receive the neck portion (3), and a cross pin (6) for fixing the stem body (2) to the femur bone, wherein the stem body (2) is formed with a pinning hole (5) through a proximal portion thereof corresponding to a greater trochanter of the femur bone, and the cross pin (6) is in a unthreaded cylindrical shape and inserted into the pinning hole (5), both ends of the cross pin (6) being projected out of the stem body (2) to be engaged with the bone wall of the femur bone.

Description: BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a femoral prosthesis for applying to a human body. Prior art Conventionally, artificial coxae have been composed of a socket inserted into an innominate bone and a femoral prosthesis which has a stem and a spherical head at the end capable of rotatably engaging the socket. Generally, the stem, made of a metal such as stainless steel or cobalt-chromium alloy, is inserted into a femoral canal and fixed by using cementing compound between the stem and the canal wall. On the acetabular side, the socket is cemented to a pelvic bone, which receive the spherical head of the stem. Particularly, the stem is inserted deeply within the elongated canal of the femur, and when the artificial coxa is loaded, some difference in Young's modulus between the metal stem and the born tissue causes the different amounts of their deformation, then leading to a sinking of the stem to the bone due to relaxation between the cement compound and the bone or between the metal stem and the bone. This resulting in losing join function of the coxa through looseness between the members or, in the extreme case, separation of the stem out of the femoral cavity. Attempts have been made to prevent the looseness between the cement and bone or the metal stem. For example, the stem material has been replaced to titanium or its alloy from prior stainless steel or Co-Cr alloy, to approach the Young's modulus of the stem to that of the bone tissue, then bending readily the stem subject to the deflection of the bone. This attempt failed to completely resolve the looseness problem. Another improvement has been attempted, in which the stem is formed such that the outside of the stem approaches to inner dimensions of the cosmetic portion in the born, to reduce the gap between the stem surface and the bone canal as narrow as possible, then attaching the stem into the bone without use of any cementing compound. It was, however, difficult to configure the stem in a duplicate shape so accurately to the inner canal profile. Practically, sufficiently available coxal products, except in the case of custom-ordered products, have not been obtained because of patients having great difference in inner femoral profiles. Recently, in another attempt, USP No. 4,895,572 describes a interlocking femoral prosthesis utilizing surgical screws which pass through the openings formed through the stem, then fixing the stem directly to the femoral cavity without use of the cement material. The screw comprises a straight portion and a wider threaded portion by screw thread within the screw length than the straight portion, and, on the other hand, the opening formed within the prosthesis stem is set to have a inner diameter wide enough to pass the threaded portion of the screw therethrough, resulting in loose gaps between the screw and the inner wall of the opening. This method can cause severe mechanical instability problems of relative movement, such as micro-movement, of the stem with regard to the bone. SUMMARY OF THE INVENTION Considering the above problems inherent in prior art, an object of the invention is to provide a femoral prosthesis having a stem body for a long lifetime to be implanted within a femur bone, wherein the stem body is capable of fixing within the femur bone by using a system for relaxing the stress loaded to the femur bone to make the bone and the stem body bend easily when the outer force is applied to the femoral prosthesis and the femur bone. In the present invention, the femoral prosthesis having a stem body comprises a pinning hole perpendicular to the axis of the stem body, at a portion of a greater trochanter which is formed through the stem body, and a cylindrical cross pin having an unthreaded cylindrical shape passing through the pinning hole with both ends of the pin projected to both sides out of the stem body. Particularly, the stem body is implanted into the femoral so as to the pinning hole of the stem body is inserted within the femoral canal and a cross pin is inserted into the pinning hole through openings formed through the bone wall so that the cross pin can fix the stem body to the bone preventing even slight movement between the femoral bone and the stem body. The femoral prosthesis according to the present invention includes a stem body having a specific configuration at its distal potion in order to ascertain attachment of said stem body portion to bone tissue which will have grown inside the femoral canal. particularly, the distal portion of the stem body may be corrugated with a plurality of edges and as many grooves alternatively and longitudinally aligned outside. This configure of the stem body can promote the anchoring effect of the stem body due to the bone tissue growth and extension. The femoral prosthesis in accordance with the present invention can be advantageously utilized not only for a replacement of a upper part of a femur bone, for example for healing a failure of the head of femur, but also for a total hip replacement in conjunction to a hip prosthesis. BRIEF DESCRIPTION OF THE DRAWINGS The present invention is described in further detail below, referring to the accompanying drawings, in which: Fig. 1 shows a side view of a femoral prosthesis according to a embodiment of the present invention; Fig. 2 shows a front view of the a femoral prosthesis shown in Fig. 1; Fig. 3 shows a elongated sectional view of the femoral prosthesis, which is seen along the arrows A-A shown in Fig. 1; Fig. 4 shows a elongated sectional view of the femoral prosthesis, which is seen along the arrows B-B shown in Fig. 1; Fig. 5 shows a side view of a bolt to be inserted into the femoral prosthesis for fixing the cross pin, according to an embodiment of the invention; and, Fig. 6 shows a cross sectional view of a distal portion of a stem body of the femoral prosthesis according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The femoral prosthesis comprise: a stem member having stem body to be implanted into the femoral bone, which is provided with a neck portion in a taper shape on a shoulder portion of the stem member; a spherical head member having an opening capable of receiving the neck portion; and, a cross pin being capable of fixing the stem body to the femoral bone. The stem member 1 has a stem body 2 which is totally slight tapered toward its distal portion in a shaft like shape to be capable of being inserted into a femoral bone (not shown), The stem member 1 may be formed of metal material harmless to the human body, such as pure titanium, a titanium alloy or a cobalt-chromium alloy. In the invention, there is formed a pinning hole 5, i.e. a through hole formed through the stem body 2, which is located at the trochanter portion 4 of the stem body 2, i.e., an upper portion corresponding to a greater trochanter of the femur bone. The pinning hole may be substantially perpendicular to the longitudinal axis of the stem body 2. A cross pin 6 is designed to be a unthreaded cylinder capable of inserting into the pinning hole 5 of the stem body 2 with both ends projected from the both outsides of the stem body by the depth of the femur bone. In the invention the femoral prosthesis is implanted within the femur such that the stem body 2 is inserted into the femoral canal, the cross pin being inserted into the pinning hole 5 formed through the stem body 2 via openings (not shown) in the bone wall of the femur, then the projected end portions of the cross pin 6 being engaged in the bone wall, to secure the femoral prosthesis to the femur bone. Furthermore, in the implantation process of utilizing the cross pin 6 for fixation between the prosthesis and a femur bone, firstly, the femoral prosthesis is positioned to a bone by driving the stem body 2 into the femoral canal of the femur bone. The stem body 2 have in advance been provided with the pinning hole which is positioned with some predetermined length from the reference point such as a shoulder portion of the stem body or a specific point on the neck portion 3. Second, after insertion of the stem member into the femur bone, there is formed openings in the wall of the femur bone by drilling such that the openings of the bone wall is capable of connecting through the pinning hole 5 of the stem body 2. In this step, a specified drill guide may preferably be utilized, having a guide hole for guiding a drill shaft, the drill guide being attached to the neck portion or shoulder portion exposed out of the top end of the bone, then, positioning a drill to aim along the center line of the pinning hole. A drill is advanced from one point outside the femur bone toward the center of the pinning hole 5 of the stem body 2, first boring its wall to form an opening, and next, passing through the pinning hole 5, and lastly boring another diametrically opposed point of the wall of the femur bone to form another opening through the femur bone. This procedures can result in one perfect pinning hole which passes through both the wall openings of the femur bone and the pinning hole 5 of the stem body 2 inserted within said bone. Third, the cross pin 6 is inserted from one of the openings of the bone to the other by way of the pinning hole of the stem body 2. Thus, this pinning system body 2 can connect stiffly the femoral prosthesis to the femur. Thereafter, a spherical head member is connected to the top of the neck portion 3 of the stem member 1 during a common surgical practice. The above embodiment has been shown the spherical head member as a separate type, which is departed from the stem member. This type of spherical head member is advantageous in that spherical head members are possible to prepare their dimensions and profiles independently from the stem members. In the present a spherical head member may be previously affixed integrally to the stem member the neck portion to composing a femoral prosthesis. In the present invention, the femoral prosthesis may utilize a means for preventing the cross pin 6 from removing and otherwise displacing inside the pinning hole 5 of the stem body 2 which is connected to the femur bone during the medical healing and also during practical using of the prosthesis after the healing. Said means for preventing the pin movement may comprise a bolt hole 8 which is formed into the stem body 2 below from a shoulder point 7 of the stem body 2 as shown in Fig. 3, so that the bolt hole 8 can reach or cross the pinning hole 5 in the stem body, and a bolt 9 to be inserted through the bolt hole 8, an end portion of the bolt 9 being capable of engaging the cross pin 6 inserted in the pinning hole 5. Particularly, the axis of the bolt hole 8 may be deviated from the axis of the pinning hole 5 such that the bolt in the bolt hole 8 can cut in part cross the pinning hole 5. In this case, as shown in Fig. 4, the cross pin 6, in a unthreaded, cylindrical shape, may preferably be formed with a notch 6a or a groove in a part of the round surface at the midst point of its length. The notch 6a is formed capable of in part receiving a part of the surface of the bolt when inserted in the pinning hole 5. When screwed into the bolt hole 8, the bolt 9 is engaged to the notch 6a on the cross pin 6 which have been inserted within the pinning hole 5, then preventing movement of the cross pin 6 inside the pinning hole 5. Thus, the positioning of the cross pin 6 is completed at a fixed location, enabling the femoral prosthesis to be secured to the femur bone. Additionally, as shown in Fig. 5, the bolt is cylindrically tapered at the middle portion 9a and threaded at the further end portion 9c, wherein when the bolt 9 is screwed down into the bolt hole 8, the tapered periphery 9b of the middle portion 9a can generate great force to enforce the cross pin 6 toward a opposite hole wall 5a in the pinning hole 5 of the stem body 2, resulting in fixation of the cross pin 6 with respect to the pinning hole 5 without any cross pin 6 movement. For a stem body 2 to be introduced in the femoral canal, the stem body 2 may be formed in a slightly tapered cylindrical shape at its distal portion 12 corresponding to the inner profile of the femoral canal. In another aspect of the present invention, the distal portion 12 of the stem body 2 may be selected to be made polygonal in cross section with a plurality of edges 10 and as many grooves 11 alternatively and longitudinally aligned outside, as shown in Fig. 6. This configuration of the corrugated distal portion 12 of the stem member 2 can exhibit a great fixing force to connect the stem body 2 to the femur body for the earlier period of implanting. Thereafter, during the healing process, this corrugation can effectively promote the anchoring effect of the distal portion of the stem member due to the bone tissue growth and extension between the distal portion and the femur bone. Thus, the present invention can adopt a combination of the above pinning mechanism to the corrugation profile of the stem member. The basic idea of the present invention for constituting a femoral prosthesis is to ensure the fixation at the proximally portion of the stem body due to the pinning mechanism and at the distal portion due to the specified profile. Generally, distal portions of the femoral canals have high profile compliance to inserted prosthesis while the proximal portions of the femoral canals are poor in profile compliance because of different dimensions and profiles of the proximal femoral canal for each patient. Accordingly, it have been conventionally difficult to comply the stem body profile with the proximal inside of the femoral canal, even after having adjusted the outer shape of the stem body, resulting in the uncertain fixing of the prosthesis. In the present invention, by utilizing the cross pin 6 through the bone and through the stem body 2 to connect them, the cross pin 6 serves as a support point to greatly support both the stem body and the bone, independently of patient difference. The cross pin 6 stated above, also, has a feature of having an high resistance to pulling of the stem body 2 out of the femoral canal since the cross pin 6 remains inserted into the opening which is formed in the bone wall, effectively to prevent the stem body from moving in the longitudinal direction of the bone. Furthermore, it is advantageous that the pinning mechanism in the present invention can district relative micro-movement between the stem body 2 and the femur bone, since the cross pin 6 is possible to be accurately made with a very narrow gap between the cross pin 6 and the pinning hole 5, and easy to fit with the openings formed through the femur bone. Also, both the end portions of the cross pin 6 are supported under almost the same conditions by both sides of the femoral walls, so that fixing force to act between the femur bone and the stem body is balanced about the axis of the stem body 2, reducing deviation of the loads therebetween. The present invention have been described according to the embodiments and accompanying drawings, but is not limited to the above embodiments. It will be apparent to those skilled in the art that modification may be made without departing from the scope of the invention as set out in the following claims.

Claims: A femoral prosthesis, which comprises a stem body (2) to be inserted into a femur bone, a neck portion (3) fixed integrally at the proximal portion of the stem body (2); a spherical head member having an opening to receive the neck portion (3) and a cross pin (6) for fixing the stem body (2) to the femur bone, wherein the stem body is formed with a pinning hole (5) through a proximal portion thereof corresponding to a greater trochanter of the femur bone, and the cross pin (6) is inserted into the pinning hole (5), both ends of the cross pin being projected out of the stem body (2) to be engaged with the bone wall of the femur bone, characterised in that the cross pin is in an unthreaded cylindrical shape. A femoral prosthesis according to claim 1, wherein the stem body (2) is formed with a bolt hole (8) into the stem body (2) below from a shoulder point (7) of the stem body so as to reach the pinning hole (5) and a bolt (9) is inserted in the bolt hole (8) to engage the cross pin (6) which is held through the pinning hole (5). A femoral prosthesis according to claim 2, wherein the cross pin (6) is provided with a notch (6a) in a part of the surface of the cross pin at the midst point of its length, the notch (6a) being capable of receiving the bolt (9). A femoral prosthesis according to claim 3, wherein the bolt (9) has a cylindrically tapered periphery at its middle portion (9a) which engages to the notch (6a) so as to enforce the cross pin (6) toward an inner wall of the pinning hole (5), then fixing the cross pin (6) and the pinning hole (5). A femoral prosthesis according to claim 1, wherein the stem body (2) has a distal portion (12) which is polygonal in cross section with a plurality of edges (10) and as many grooves (11) alternatively and longitudinally aligned outside the distal portion (12).

Inventors: ISHIDA NORIYUKI, ITOMAN MORITOSHI, MABUCHI KIYOSHI, TAMABUCHI SHINGO, UENO MASARU, ISHIDA, NORIYUKI, ITOMAN, MORITOSHI, MABUCHI, KIYOSHI, TAMABUCHI, SHINGO, UENO, MASARU, Ishida, Noriyuki, c/o Kyocera Corporation, Tamabuchi, Shingo, c/o Kyocera Corporation, Ueno, Masaru, c/o Kyocera Corporation
Applicants: KYOCERA CORP, KYOCERA CORPORATION
Application year: 1999
Main classification: A61F2
IPC codes: A61F2, A61B17