WO2008046734A1

WO2008046734A1 - Endoprosthesis for a hip joint

Info

Publication number: WO2008046734A1
Application number: PCT/EP2007/060440
Authority: WO
Inventors: Jacques Valloton
Original assignee: Jacques Valloton
Priority date: 2006-10-19
Filing date: 2007-10-02
Publication date: 2008-04-24
Also published as: EP2091470A1

Abstract

An endoprosthesis for a hip joint has at least an adapter area (3) or adapter neck provided for the arrangement of a joint head, and a shaft (5) for fixing the prosthesis in the femur. The surface of the shaft (5) has at least one groove or notch (7, 9) extending in the shaft direction.

Description

Endoprosthesis for a hip joint

The present invention relates to an endoprosthesis for a hip joint and to a method for implanting an endoprosthesis.

While the use of conventional arthroplasty in the elderly patient shows good results, the care of young patients remains problematic because of the significantly worse prognosis. In particular, the bone loss at the time of revision justifies the search for implants with better bone preservation over the implantation period of the primary prosthesis. The analysis of the aseptic loosening shows that the physiological adaptation reaction of the bone to a non-physiological load introduction usually represents the primary cause for rearrangement of the bone structure and possibly for bone loss. Since 1991, femoral prostheses have been used to avoid stress shielding due to meta- or epiphyseal load introduction. The replacement of the hip joint with an endoprosthesis has become an extremely successful procedure in orthopedics. Current techniques and implants allow the most elderly patients a sufficient life span for the remaining life span, so that can be considered as a rule that in over 65 -year only about 5% still need revision. The subjective success of the joint replacement is also usually good, if not always sufficient. The result evaluation using points systems shows occasionally incomplete rehabilitation, for example in the form of early fatigue when walking, from onset or stress pain or a not fully normalized gait. The residual complaints are usually however low and the profit over the previous condition is convincing. With the operation, the condition is substantially improved, but the patient is not cured. By alleviating previous ailments, the patient remains patient for the rest of his life, as statistics show that the rate of loosening increases with increasing time, slower in older patients but dramatically faster in younger patients. In the much cited "Sweden Study", revision rates up to 30% within the first 10 years are reported for patients younger than 55 years old at the time of surgery. Cementless implants did not significantly improve the prognosis. Therefore, the previous concepts do not seem sufficient for the young patients. In addition, we experience an increase in life expectancy and an increase in the proportion of older people in the population (demographic shift of the age pyramid). Mobility and self-employment in old age are becoming increasingly important. The search for new concepts, especially for people under the age of 65, but also for older patients with even longer life expectancy, seems to be sufficiently justified. The analysis of the causes of the failure trap in the so-called "Sweden Study" gives aseptic loosening a top priority of over 75%, with polyethylene wear only appearing in eighth place on the list. Even if at the time of the revision often multiple Changes in the implants and bony structures of the implant site are found, but it is worth the question why it may come to aseptic loosening despite the sophisticated surgical techniques, the optimized implant sizes and the quality of the materials used and which primary cause for the failure of the permanent Integration is responsible. Since cementless stem prostheses do not significantly improve the prognosis, the so-called particle disease due to abrasion products is not likely to be the primary or sole cause of the loosening. If one has regular X-ray checks of the joint (as prescribed in the so-called prosthesis passes), characteristic changes are recognizable before the clinically apparent relaxation. Of great importance are the natural reactions of the bone to the changed mechanical conditions. In the development of endoprosthetics on the proximal femur, the development from cartilage replacement ("resurfacing") to proximal femoral replacement with anchoring of a prosthetic stem in the femoral diaphysis was due to technical and biological reasons. If it is quite feasible to replace the joints of supporting structures with "connectors" in the field of mechanics, this can lead to problems in the area of the bony structures. Bone reacts as living tissue to increased pressure load with hypertrophy, to relief with atrophy. For example, following the onset of a hip prosthesis, the altered loading patterns very often follow a structural adaptation with unfavorable consequences for the prosthetics: in the pressure-relieved area In sections, the bone will atrophy according to Wolff's law; in the zones of load transfer from the prosthesis to the bone, hypertrophy of adaptation can be observed. It has been shown that femoral stem prostheses have a nonphysiological force introduction. This can lead to bone remodeling and disassembly, which eventually ends in the prosthetic loosening described above, necessarily associated with a revision surgery. In addition, all the systems known from the prior art have a relatively far laterally located resection plane and sacrifice a large part of the femoral neck.

Systems which attempt to sacrifice as few femoral neck bones as possible usually use so-called lag screws for fixation, which transmit the tensile forces via a pressure disc to the lateral side of the femoral cortex. This too does not correspond to a physiological introduction of force.

Systems that effectively preserve the femoral neck and are not simply shortened standard prostheses are extremely rare. For this purpose, for example, DE 10 2004 038 281 proposes to use a shaft which has the shape of a polygon in cross-section in the proximal region, and wherein the dorsal surface and the medial surface form a wedge shape as clamping surfaces. Although this proposal largely preserves the femoral neck, this prosthesis offers little resistance to rotational forces or the primary stability is insufficient. To the applied rotational forces To counteract, large-scale, often provided with ribs shafts are often proposed, such as in DE 25 17 702. Although the ribbed shanks preserve the outer cortical bone of the femoral neck, but still sacrifice a large part of the force-transmitting trabecular structure.

It is therefore an object of the present invention to achieve a physiological introduction of force in the proximal femur. This is to be achieved by a design of an implant, which allows implanting the implant in the area of the force-transmitting trabecular structure. As little bone as possible should be sacrificed on the proximal femoral neck. In addition, in order to achieve maximum stability against the rotational forces occurring, a design is to be found, which offers maximum strength and rotational stability with minimal space requirements, the loads are transmitted physiologically correct cranial and caudal.

Finally, the design should maintain blood flow in the femoral neck so that the bone remains vital and counteracts bone loss.

According to the invention, an endoprosthesis for a hip joint according to the wording, in particular according to claim 1, is accordingly proposed. It is proposed that the endoprosthesis has a shaft for fixing the prosthesis in the thigh neck, which has on its surface at least one extending in the longitudinal direction of the groove or notch. According to a variant embodiment, it is proposed to provide at least two grooves or indentations, these extending at least in the proximal region, which is intended to be arranged in the femoral neck region or proximal femur.

One embodiment variant is a modular femoral neck implant, which is cementlessly implanted in the proximal femur, more precisely in the femoral neck. Due to the special design of the cross section, which is designed according to a variant I- or double-T- similar, optimum strength combined with a high rotational stability and a maximum of bone care is achieved. By way of example, each laterally in the direction of the shaft extending grooves or indentations remain sufficient clearance around the implant obtained to ensure the trabecular structure sufficient blood supply.

The femur implant proposed according to the invention allows a maximum due to its special shape and modern implantation technique

Bone preservation while maintaining the vascularization of the femoral neck combined with an optimized force transmission and a sufficient strength and rotational stability. In order to increase bone integration, it is further proposed according to the invention to provide the shaft with a plasma titanium layer or a calcium phosphate layer in the proximal region. This allows bony integration. The proximal portion of the entire shaft length amounts to at least 30%, preferably at least 1/3, at most 2/3.

In the distal region, for example, 1/10 to 1/3 of the shaft length, the shaft is polished, anodized or dot-coated, for example, to prevent bony growth in the femur, which additionally ensures better implantability during implantation. Furthermore, a load transfer distal is preferably avoided.

According to a further embodiment variant, the groove or indentation depth is designed to decrease in the distal direction towards the shaft end, or the distal tip of the shaft is thinned out. The I-like or double-T-like cross-section extends distally in a round, oval or rectangular or in the form of an "8" shaped cross section.

The implant proposed according to the invention can also have a collar in the transition from the neck to the shaft of the implant. This collar, which is placed on a corresponding adapter portion of the endoprosthesis, can either serve to take over a part of the force transmission to the cortical bone or merely as a shield against any possible abrasion particles from the sliding pair.

The collar is preferably formed tilted laterally relative to the longitudinal axis of the femoral neck, in particular if the collar is formed lying on the resection plane. The material used for the implant may be titanium (possibly coated), titanium alloys (possibly coated), cobalt chrome alloys (possibly coated), stainless steels (possibly coated), polymers such as in particular PEEK (possibly coated) CF / PEEK (possibly coated).

The coating consists of either titanium or combined titanium-hydroxyapatite layers or other calcium phosphate compounds which are plasma, vacuum plasma, or chemical or electrochemical

Deposition method or sol-gel coatings are applied.

The implantation of the implant or the endoprosthesis proposed according to the invention can be minimally invasive both by navigation or without navigation, and aims to optimally restore the center of rotation. Furthermore, the natural antetorsion of the femur is taken over.

The implantation takes place after resection of the femoral head, whereby it is to be ensured that as much as possible can be spared from the intact femoral neck bone, but at least half the length of the femoral neck (to and with isthmus).

The invention will now be further explained by way of example and with reference to the accompanying drawings.

Showing: 1 in perspective an inventive implant,

2 shows a cross section through the implant along the line I-I,

3 shows a cross section through the implant along the line H-II,

4 shows a further cross section through the implant along the line III-III,

5 in Frontdrauf looks in accordance with arrow direction A of Figure 1 shows a further embodiment variant of an inventive implant,

6 shows a front view again a further embodiment variant of an implant,

7 again shows a further embodiment variant in front view, and FIG. 8 shows again a further embodiment variant in front view of an implant according to the invention.

FIG. 1 shows in perspective an endoprosthesis 1 according to the invention for a hip joint. The endoprosthesis or the implant 1 consists primarily of a neck or adapter region 3, provided for the placement of a condyle and a shaft 5, provided to be arranged in the femur or femur. The curvature of the shaft is adapted to the anatomy of the femur or the approach of the

Thigh neck to the bone. The shaft 5 basically comprises two parts 15 and 17, like the proximal region 15, provided around the femoral neck or femoral neck to be arranged, as well as the distal portion 17, provided to be inserted in the actual thigh bone.

According to the invention, the shank 5 has a lateral notch or groove 7 formed in the longitudinal direction of the shank and correspondingly curved, as well as a groove or notch 9 correspondingly visible on the back and in FIG.

In particular, in Figure 2, showing a cross-section along the line I-I of Figure 1, the quasi-I-shaped cross-section is clearly visible, comprising the two lateral notches or grooves 7 and 9 and the central projection 3, provided for the arrangement of the condyle. In the lateral direction of the shank, this has a convex surface 6 which is rounded towards the outside, while the surface 8, directed inwards, is designed to be largely flat in area or, for example, concave / convex. Of course, this is only one possible embodiment variant, and both shaft surfaces may also be formed in a more straight-lined or rather rounded manner, as explained in more detail below with reference to FIGS. 5 to 8.

As can now be seen from the further FIGS. 3 and 4, which represent further cross sections along the lines II-II and III-III, the I-like cross section extends distally into a round, oval or rectangular cross-section. In particular in Figure 4, a largely round cross-section of the shaft 5 is shown. Of course, these two cross-sections are also a possible embodiment, and the groove or notch can also be made more or less deep as far as the end of the shaft. Can be seen that the shaft 5 in the proximal region 15 with a corresponding layer, such as a plasma-titanium layer or a calcium phosphate layer, such as hydroxyapatite is provided to allow bony integration or this in Optimize the area of the femoral neck. In contrast, the shaft is largely polished in the distal region 17, in order to prevent as much as possible bone contact. As a result, a bony growth is prevented, thus ensuring that the power overflow is achieved primarily in the region of the femoral neck and not in the region of the femur.

As already mentioned above, further possible embodiments of an implant according to the invention are shown in FIGS. 5 to 8, in particular having different cross-sections, especially in the region of the projection of the adapter region 3, as shown for example in FIG. The further embodiment variants are shown in a Frontdraufsieht corresponding arrow direction A as indicated in Figure 1. Figure 5 shows a largely I-shaped cross-section having both an outwardly directed, rectilinear surface 6, as well as corresponding downwardly directed rectilinear surface. The two lateral notches or grooves 7 or 9 are formed in the form of rechteckformigen channels.

The embodiment variant according to FIG. 6 is similar to that in FIG. 5, with the difference that the two lateral indentations or grooves 7 or 9 have a rounded portion 12 towards the I-leg.

FIG. 7, in turn, clearly differs from the two variants shown in FIGS. 5 and 6 in that the flat closure against the adapter 3 has a rearwardly or rearwardly directed bend 10, which is quasi collar-shaped.

Finally, the embodiment according to FIG. 8 has a considerably larger cross-section of the adapter region 3, compared with the implant shown in FIG. 7. In addition, the shaft 5 extends much more strongly against the shaft end 19 than the two preceding implants.

The design of the implant depends on the requirement on the implant, which are dependent on the design of the femur, the damage to the hip joint, the aging of the bone or the person, gender of the person, etc., etc.

Of course, the implants or shaft geometries illustrated with reference to FIGS. 1 to 8 are only possible examples of implants according to the invention and other dimensions and designs are possible. It is essential that the shaft has at least one groove or notch extending in the longitudinal direction of the shaft.

Claims

claims

1. endoprosthesis for a hip joint, comprising at least one adapter portion (3) or adapter neck, provided for the placement of a condyle, and a shaft (5) for fixing the prosthesis in the femur, characterized in that the shaft (5) on its surface Has at least one extending in the direction of the shank groove or notch (7, 9).

2. endoprosthesis according to claim 1, characterized in that at least two grooves or notches in

Are provided extending longitudinally.

3. Endoprosthesis according to one of claims 1 or 2, characterized in that the grooves or indentations (7, 9) are arranged at least in the proximal region of the shaft, provided to be arranged in the femoral neck or proximal femur.

4. Endoprosthesis according to one of claims 1 to 3, characterized in that the grooves or indentations (7, 9) are each designed to extend laterally in the direction of the shaft.

5. Endoprosthesis according to one of claims 1 to 4, characterized in that the shank is left / right-symmetrical or asymmetrical.

6. endoprosthesis according to one of claims 1 to 5, characterized in that the groove or notch depth is formed in the distal direction against the shaft end (19) hm decreasing.

7. Endoprosthesis according to one of claims 1 to 6, characterized in that the shaft (5) at least in proximal region is formed quasi I-shaped or I-like or double-T-shaped.

8. Endoprosthesis according to one of claims 1 to 7, characterized in that the proximal region (7) is coated with a plasma titanium layer or a combined titanium calcium phosphate layer, such as hydroxyapatite, Bonit, the proximal region being at least 30%, preferably between 35 to 70% of the shaft or the shaft length.

9. Endoprosthesis according to one of claims 1 to 8, characterized in that the distal region (17) is polished, anodized or dot-coated, wherein the distal region at least 10%, preferably between 10 to 35% of the shaft or the shaft length is.

10. endoprosthesis according to one of claims 1 to 9, characterized in that as the material titanium (possibly coated), a titanium alloy (possibly coated), cobalt chrome alloys (possibly coated), stainless steels (possibly coated), polymers, in particular PEEK (possibly coated) and / or CF / PEEK (possibly coated) is used.

11. A method for implanting an endoprosthesis according to one of claims 1 to 10, characterized in that the shaft is preferably fixed cementless in the femoral neck, wherein the implantation by means of navigation or without navigation, for example, minimally invasive.

12. The method according to claim 11, characterized in that the implantation or anchoring takes place via an initially given Pressfitverbindung.