DE3426947A1 - Self-adhesive, cementless implantable hip implant - Google Patents

Abstract

An implantable prosthesis rod for the hip is comprised of two prefabricated interconnected parts. The prosthesis rod presents next to the known head (1), a neck (2) and a collar (3), a part (4) comprising on the head side an ondulated surface and supporting an adjustable piece (5) which is partially elastically and/or plastically deformable. Said rod is adjusted in the upper portion of the femur so as to prevent it from rotating and to absorb prejudicial torsion moments.

Description

Self-adhesive, cementless implant

Able hip stem implant For total replacement of diseased hip joints it is known that the implant parts, namely the artificial acetabulum and the femoral shaft implant by means of a hardening polymer, a so-called bone cement, with the bone tied together.

The cementing of the implant comes across in the medical literature and in practice to increasing criticism as it has been shown over time a loosening of the connection between bone cement and bone tends to occur, which leads to loosening of the prosthetic implant. This had in the alloplastic joint surgery means that there is an increasing effort to focus on the Refrain from cementing the implant in the bone.

It is also already known, cementlessly implantable hip stem implants to use that have a surface profile so that the bone on the The implant grows and is anchored in the surface profiling, and / or the sit positively in the medullary cavity of the bone.

The surface profiling, which ensures that the To promote bone to the implant can be designed differently. Either it is a regular honeycomb-like pattern or an irregular one Surface profiling, a so-called madreboric profiling. This surface profiling extends over the entire length of the stem part of the known hip stem implants, but the bone can only grow in the cancellous upper bone bed. The form fit you get with the known implants through an enlarged stem cross-section, which is more or less round inner cross-section of the The shaft jacket of the femur is oriented, which is why the prosthesis stems for positive fit are more or less round, with the round cross-section Extends over the entire length of the stem of the stem prosthesis.

Round prosthesis cross-sections, which are in the round bone cross-section of the Marrow cavity lie, have the disadvantage that they are not rotationally stable, so that after and after a loosening of the stem implant results, in particular by certain Frequent and regularly recurring stressful situations, such as sitting down, getting up from the sitting position or squats while standing. Generated in the upper implant area the form-fitting, mostly round cross-section high hoop stresses, which the Experience has shown that the bone coat has not grown. This often results in admission of the prosthesis during the operation to circumferential stress fractures of the bone. In the end the positive fit of known hip stem implants for cementless Implant on the inner diameter of the bone marrow cavity only in the transverse cross-section and does not take into account that the femur is one in the sagittal direction has front curvature, as a result of which a real form fit cannot be realized is.

The object on which the invention is based was thus to provide a To get a hip stem implant that can be implanted without cement and that Avoids disadvantages of known femoral stem implants of this type, i.e. in particular ensures a firm fit without loosening later.

The hip stem implant according to the invention for cementless implantation, that consists of a head part and a neck part made of steel as well as a shaft part with a profiled Surface consists, the shaft part also at least in the upper area consists of steel, is characterized in that only the one facing the neck part upper area of the shaft part a surface profile and an in Transverse direction has a non-circular elongated cross-section that the one facing away from the neck part The lower area of the shaft part is not surface-profiled, a round cross-section and through longitudinal slots extending from the free end into several of each other spaced ribs is lower part and that between the neck part and the shaft part a collar is formed.

The surface profiling is therefore found in the inventive Hip stem implants only in the area where cancellous bone is present which a growth of the bone and an anchoring in the surface profile enables. In its lower part, however, the shaft part is designed so that there is optimal form fit regardless of the individual bone formation allowed.

The surface profiling in the upper area of the shaft part can be different and have known or new profile shapes. Appropriately chooses a so-called madreboric, i.e. an irregular-grainy surface profile.

To avoid hoop stress fractures of the bone as well as to The upper area of the shaft part does not guarantee torsional stability of a round cross-section, but of a non-circular, elongated cross-section, which extends in the transverse direction. The is useful in this area Cross-section essentially rectangular or elliptical or of a transition shape between these two basic forms.

For additional torsional stability, it is preferred that the shaft part at its upper end a lateral medial, i.e. on the convex side of the Prosthesis arranged projection has that when implanting the hip stem implant in the thigh bone in a recess in the bone jacket made for this purpose beforehand a- and serves as a stop lock. Appropriately extends this lateral protrusion also extends in the transverse direction, i.e. in the direction the longitudinal axis of the elongated cross section of this area of the shaft part.

The collar arranged between the shaft part and the neck part is used as a support on the femur freed from the femoral head and neck, to to avoid sinking of the prosthesis into the medullary canal. For this it is useful to to train the collar as a wide support.

The slotted lower area of the shaft part, the round cross-section possesses, serves to generate the form fit exclusively in the cortical lower shaft area where there is no bone growth. Because the thigh bone has a ventral curvature, it is expedient that the cortical, i.e. lower shaft area has a ventral curvature that extends to the thigh bone adapts.

This lower area of the shaft part can be made of metal, expediently made of steel or a plastic, preferably polyethylene.

Subdivide the longitudinal slots extending from the free end the free end of the shaft part in several, at least two, better four or six Ribs that are spaced apart due to the width of the slot. If the Material in this area has an elastic character with resilience, for example if it is made of steel, the ribs at the free end of the shaft part bend together. As a result of their resilience, however, they are as far as possible again pushed outwards so that they are under pressure on the inner wall of the bone marrow cavity issue. This results in an optimal form fit, combined with force fit, because due to its elasticity, the lower end of the shaft part becomes more individual Circumstances adapts. In the event that the lower area is made of a plastically deformable material, such as polyethylene, there is a plastic form fit.

Depending on body size, gender, etc., the cross-sectional sizes of the Thigh bone and medullary cavity very different. Because of the elasticity of the free end of the shaft part, these individual differences become largely balanced.

For extreme differences in the cross-section of the bone one must of course nevertheless keep differently dimensioned implants available. The inside diameter of the thigh bone can vary between 8 and 18 mm, for example.

In order to now have an overly large inventory of complete hip stem implants and to allow quick selection during surgery the upper region of the shaft part can be produced separately from the lower region. The upper part of the entire prosthesis then only needs to be produced in one unit size and to be held up, while only the lower one to be releasably connected to the upper one Part must be manufactured and stocked in varying sizes.

It is useful, the two individual parts of the shaft part by a To connect screw connection with a unit size. During the Operation in which the need for dimensioning the lower part arises the two parts are then easily screwed together.

Hip shaft implants with the features according to the invention can so are relatively easy to implant, have optimal permanent strength, without loosening up afterwards and allow an immediate full load of the artificial hip joint.

The invention is further illustrated by the drawing.

In this Fig. 1 mean a vertical transverse section through a hip stem implant according to the invention inserted into the femur and FIG. 2 shows a horizontal section along the line II-II in FIG. 1.

That after the removal of the hip joint in the thigh bone inserted hip shaft implant according to the invention, as shown in FIGS. 1 and 2 is shown, consists of a head part 1, a neck part 2, a collar 3, an upper shaft part 4 and a lower shaft part 5. The lower shaft part 5 is connected to the upper shaft part 4 with the aid of a screw connection 8.

The upper shaft part 4 made of steel has a surface profile 13, preferably in the form of an irregular grain, a so-called madreboric Surface profiling. The upper shaft part 4 is not form-fitting and lies in the cancellous bone area 6.

As shown in Fig. 2, the upper shaft part 4 has elongated Cross-section roughly in the shape of a rectangle with rounded corners. At the top At the end below the collar 3, the shaft part 4 has a lateral projection 12, which is in a recess made for this purpose in the upper end 11 of the thigh bone and thus serves as a stop lock to get additional rotational stability.

The form-fitting lower, non-profiled, i.e. smooth shaft part 5 has a round cross-section, which here also consists of steel, for example from its free end extending longitudinal slots 9, the ribs 10 result, which have a distance from each other. As a result of these distances and the resilience of the material of the lower shaft part 5 are the ribs to each other can be pressed, but due to their resilience they are pressed firmly against the inner wall of the cortical shaft area 7 and thus result in good positive and non-positive locking. The implant according to the invention consists of materials known for this purpose, such as Stole.

Claims (9)

Self-adhesive, cementless implantable hip stem implant 1. Hip stem implant for cementless implantation, consisting of a head part and a neck part made of steel and a shaft part with a profiled surface, wherein the shaft part also consists of steel at least in the upper area, d a d u r c h g e k e n n n z e i c h n e t that only the upper part facing the neck Area (4) of the shaft part has a surface profile (13) and one in the transverse direction has a non-circular, elongated cross-section that the one facing away from the neck part lower area (5) of the shaft part is not surface-profiled, a round one Has cross-section and through longitudinal slots (9) extending from the free end in a plurality of spaced apart ribs (10) is divided and that between the Neck part (2) and the shaft part a collar (3) is formed. 2. hip stem implant according to claim 1, characterized in that the longitudinally slotted lower area (5) made of metal or a plastic, preferably Polyethylene. 3. hip stem implant according to claim 1 or 2, characterized in that that the longitudinally slotted lower region (5) is formed by a separate part is releasably connectable to the remaining upper part (4) of the shaft part is. 4. hip stem implant according to one of claims 1 to 3, characterized characterized in that the two separate parts (4, 5) of the shaft part can be releasably connected to one another by a screw connection (8). 5. hip stem implant according to one of claims 1 to 4, characterized characterized in that the longitudinally slotted area (5) of the shaft part has a round cross-section with a smooth surface. 6. hip stem implant according to one of claims 1 to 5, characterized characterized in that the upper area provided with surface profiling (13) (4) the shaft part has a substantially rectangular or elliptical cross-section owns. 7. hip stem implant according to one of claims 1 to 6, characterized characterized in that the surface profile (13) of the upper shaft part (4) madreborisch (irregular-grainy) is. 8. hip stem implant according to one of claims 1 to 7, characterized characterized that at the upper end of the shaft part of a stop lock (12) is arranged in the form of a medial projection. 9. hip stem implant according to one of claims 1 to 8, characterized characterized in that the collar (3) forms a wide bearing surface.