Anchoring system for attaching a prosthesis to a human body

Abstract

The present invention relates to an anchoring system for attaching a prosthesis to a human body, comprising: an anchoring element, an abutment, an abutment screw for attaching the abutment to the anchoring element, the anchoring element comprises a connection area for the abutment, the connection area comprising a press-fit portion such that the abutment is attached to the anchoring element in the connection area by a press-fit connection, wherein the connection area comprises an anti-rotation geometry and the abutment comprising a corresponding mating anti-rotation geometry proximal to the press-fit portion, and where in the connection area comprises a conical portion proximal to the anti-rotational geometry forming a mating geometry for a corresponding conical portion in the through-hole of the abutment.

Claims

1. A anchoring system for attaching a prosthesis to a human body, said anchoring system comprising: an anchoring element comprising an outer threaded profile for anchoring to bone tissue of the human body, an abutment comprising a distal portion for linking the anchoring system to an external prosthetic component, an abutment screw for attaching the abutment to the anchoring element for providing a mechanical connection between the anchoring element and the abutment, wherein, said anchoring element comprises a through-hole having an opening with an inner profile for providing a connection area for the abutment, said connection area comprising a press-fit portion in a distal portion of said connection area, said press-fit portion having an opening dimension smaller than a dimension of a press-fit portion of said abutment such that said abutment is attached to said anchoring element in the connection area by a press-fit connection, wherein said connection area comprises an anti-rotation geometry proximal to the press-fit portion, said abutment comprising a corresponding mating anti-rotation geometry proximal to said press-fit portion of said abutment configured to engage with the anti-rotation geometry of said anchoring element, and wherein said connection area comprises a conical portion proximal to the anti-rotational geometry forming a mating geometry for a corresponding conical portion of the abutment.

2. The anchoring system according to claim 1, wherein the outer threaded profile of the anchoring element comprises: a first thread portion with a first thread depth (h.sub.d), and a second thread portion with a second thread depth (h.sub.s), wherein the first thread depth is larger than the second thread depth, and wherein the first thread portion is arranged in a proximal portion of the anchoring element and the second thread portion is arranged in a distal portion of the anchoring element.

3. The anchoring system according to claim 2, wherein the first thread portion and the second thread portion extend over an entire total length from a proximal-most end to a distal-most end of the anchoring element.

4. The anchoring system according to claim 2, wherein the second thread portion extends over a length (Ls) from the distal portion to beyond the connection area.

5. The anchoring system according to claim 1, wherein the press-fit portion of the connection area extends from a distal-most end of the distal portion of the anchoring element and in a proximal direction.

6. The anchoring system according to claim 1, wherein the press-fit portion of the connection area is cylindrical.

7. The anchoring system according to claim 6, wherein a length of the press-fit portion is in the range of 2 to 15 mm.

8. The anchoring system according to claim 1, wherein the press-fit portion of the connection area is conical.

9. The anchoring system according to claim 8, wherein a cone angle of the conical press-fit portion is in the range between 0.2° to 30°.

10. The anchoring system according to claim 8, wherein the connection area comprises a straight portion arranged on a distal-most part of the connection area adjacent to the conical press-fit portion.

11. The anchoring system according to claim 10, wherein a length of the straight portion is less than a length of the conical portion.

12. The anchoring system according to claim 1, wherein the anti-rotation geometry has a polygon cross-section.

13. The anchoring system according to claim 1, wherein mating surfaces between the anchoring element and the abutment have been surface treated for providing wear and fretting resistance properties for the anchoring element and the abutment.

14. The anchoring system according to claim 1, wherein a cone angle of the conical portion of the abutment is in the range of 25° to 65°.

15. The anchoring system according to claim 1, wherein a cone angle of the conical portion of the abutment is about 45°.

16. The anchoring system according to claim 1, wherein the abutment comprises a through-hole in a proximal-distal direction, wherein for retaining the abutment to the anchoring element the abutment screw is arranged through the through-hole and fastened to inner threads in the anchoring element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

(2) FIG. 1 is a schematic illustration of the fixation and abutment parts of a prior art anchoring system placed in the femur bone of an amputation stump,

(3) FIG. 2 is a schematic view illustrating an embodiment of the invention having a cylindrical press-fit,

(4) FIG. 3 is a schematic view illustrating more in detail the connection between an anchoring element and an abutment with a cylindrical press-fit,

(5) FIG. 4 illustrates the outer profile of an anchoring element according to an exemplary embodiment of the invention,

(6) FIG. 5 illustrates in more detail the inner profile of a first embodiment of the anchoring element according to FIG. 2 having a cylindrical press-fit,

(7) FIG. 6 is an enlarged view of the thread profiles illustrating the difference in thread depth between the deeper threads and the shallow threads,

(8) FIG. 7 illustrates an alternative to the embodiment illustrated in FIG. 5 in which the diameter of the distal inner hole of the fixture has a step where the wall thickness has been increased,

(9) FIG. 8 is a schematic view illustrating an embodiment of the invention having a conical press-fit,

(10) FIG. 9 illustrates two views of an exemplary abutment for the anchoring system,

(11) FIG. 10 is an example of an abutment screw for the anchoring system, and

(12) FIG. 11 is a table with parameters intervals for embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(13) The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Like reference characters refer to like elements throughout.

(14) FIG. 1 is a schematic illustration of an anchoring system 1 placed in the femur bone 4 of an amputation stump for attaching a prosthesis. The anchoring system has a proximal end 2 and a distal end 3. The proximal end 2 of the anchoring system is anchored to the bone tissue 4 and the distal end 3 links the system to an external prosthetic component (not shown here), such as a limb prosthesis or prosthetic knee. The anchoring system 1 comprises an anchoring element 5 generally in the form of a screw (a so-called fixture) 5, an abutment 6 and an abutment screw 7 for attaching the abutment 6 to the fixture 5 thus providing the mechanical coupling between the anchoring element 5 and the abutment 6. The abutment screw 7 may be arranged through a proximal-distal through-hole of the abutment 6. However, other means of attaching the abutment to the anchoring element are possible. Further, the anchoring element 5 may have a pathway (percutaneous gateway, not shown) for communication of physical and biological signals between inside and outside of the human body. The through pathway is not shown in this figure, it is referred to for instance the U.S. Pat. No. 9,067,057 or EP 0 595 782, both which are incorporated by reference.

(15) The external prosthetic component (not shown) is anchored to the bone by means of the anchoring element 5 that is surgically inserted into the bone 4. The anchoring element 5 is preferably completely implanted inside the bone and osseointegrated and serves as a fixture for the skin penetrating connection provided by the abutment 6. The abutment 6 is attached to the anchoring element 5 and is partly protruding out from the bone 4 and skin 8. The external prosthetic component, such as an artificial limb, is then attached at the protruding abutment part.

(16) Bone anchored prostheses which are based on osseointegration allow a direct connection of an artificial limb prosthesis to the patients skeleton, thus avoiding the use of a socket. Osseointegrated prostheses for rehabilitation of amputees (OPRA system) have been developed and commercialized by Integrum AB, Molndal, Sweden, and will not be described in any further detail here. See also Integrum U.S. Pat. No. 9,067,057 incorporated by reference.

(17) A typical length of a fixture 5 used in this type of prostheses is 10 mm-120 mm, partly depending on the size of the bone and partly related to the anatomy of the remaining skeleton. All parts of the system are made out of titanium or other tissue friendly/biocompatible material. As to the proximal portion of the fixture it could for instance be designed with slits, spirals and holes like illustrated in the EP 0 595 782 and U.S. Pat. No. 9,067,057 and such design will not either be described in any detail here.

(18) FIG. 2 and FIG. 3 are schematic cross-sectional views of a preferred embodiment of the invention. FIG. 2 and FIG. 3 show the anchoring element, also known as a fixture 5, comprising an outer threaded profile 9 for anchoring to bone tissue of a human body. There is further shown in an abutment 6 comprising a distal portion 3 for linking the anchoring system to an external prosthetic component. A connection area 10 of the fixture 5 comprises a press-fit 11(11′) (shown in FIG. 3), an anti-rotational geometry 12 (e.g. hexagon or other geometrical shape such as triangle, rectangle, square etc) shown in FIG. 3, and a conical portion 13 at the bottom of the anti-rotational geometry forming an additional mating surface for the abutment 6, best seen in FIG. 3. With further reference to FIG. 3, the conical portion 13′ of the abutment and the corresponding conical portion 13 on the fixture 5 provide a secure and stable contact interface of the proximal end of the abutment 6 to the anchoring element 5. In other words, the conical portion 13 of the fixture 5 and the corresponding mating conical portion 13′ of the abutment 6 provide a stable contact point at the most proximal end of the connection area 10 for the abutment 6. The press-fit 11 is located in the most distal part of the through hole 16, at the opening 14 of the fixture 5.

(19) In addition, as shown in FIG. 3, the connection area 10 in the through-hole 16 comprises fastening means in the form of inner threads 15 for the abutment screw 7. There is further an inner portion 40 of the through hole 16 used as a pathway for communication or transmission of biological and physical parameters. The inner portion 40 in the through hole 16 is located on the proximal side of the inner threads 15 and is schematically indicated by dotted lines. The optional inner portion 40 may be sealed by a central screw (not shown). The abutment screw 7 is arranged through the axial through-hole 35 ranging through the abutment 6 in the proximal-distal direction and is fastened at the inner threads 15 for fastening the abutment 6 to the fixture 5.

(20) As illustrated more in detail in FIG. 4 the anchoring element 5 (i.e. the fixture) has a threaded outer profile of two different thread profiles in this exemplary embodiment. Specifically, the total length L of the fixture is divided into a first portion 17 with a deeper thread depth in the proximal portion 18 of the fixture 5 to improve the bone anchoring surface area. The distal, second portion 19 has a shallower thread depth to increase the wall thickness (t.sub.w) of that portion of the fixture 5 thus increasing the mechanical strength in the second portion 19 substantially. In this exemplary embodiment, the length of the portion 19 with the shallower thread L.sub.s is defined by the inner geometry of the fixture.

(21) As illustrated in FIG. 5 the length L.sub.s of the second portion 19 covers more than the total length L.sub.c of the mating geometry (comprising the press-fit portion 11, the anti-rotation geometry 12 and the conical portion 13) to improve the wall thickness and thus increasing the strength of the distal portion of the fixture 5. FIG. 5 illustrates a schematic partial cross-section of an anchoring element 5 comprising a conical portion 13, an anti-rotation geometry 12, a connection area 10 having length L.sub.c, a (cylindrical) press-fit portion 11, inner threads 15 adapted to receive and engage with an abutment screw 7 (see FIG. 10).

(22) FIG. 6 is an enlarged view of the thread profiles. The difference in thread depth Δh between the deeper thread h.sub.d and the shallow thread h.sub.s is in this example set between an interval as indicated in Table 1 in FIG. 11.

(23) The distal part of the inner profile of the fixture 5 is the female portion of the connection between the fixture 5 and the abutment 6, where the abutment 6 is the male part of the connection. The fixture 5 and the abutment 6 are retained by an abutment screw 7 shown in FIG. 10, which goes through the through-hole 35 (see e.g. FIG. 2 or 3) of the abutment 6 and is fastened in the fixture by fastening means in the form of the inner threads 15 or the like.

(24) With further reference FIG. 3 and FIG. 5 in conjunction with FIG. 9, where FIG. 9 shows two views of an abutment 6 according to an embodiment of the invention, the anti-rotational geometry 12′ of the abutment is used for installation in surgery but also acts as an anti-rotational safety function as the fixture 5 (FIG. 3 or 5) has geometrically mating part. In addition, and also with reference to FIG. 3 or 5, the connection area 10 comprises a conical surface 13 forming an additional mating surface for the abutment 6, for improving load distribution (due to an increased distance between contact points) and stability of the abutment. The connection area further comprises a cylindrical press-fit 11 (11′) at the most distal part of the connection area, illustrated in e.g. FIG. 3. The length of the press-fit L.sub.pf has been increased compared to previous connection geometries. As indicated in the table in FIG. 11 L.sub.pf could be 2-15 mm for a typical fixture length of 60-100 mm.

(25) Referring now to FIG. 7, as an alternative to the embodiment illustrated in FIG. 5 the diameter of the distal portion of the through-hole 16 of a fixture 55 may have a step 20 with a larger wall thickness t.sub.w has been compared to the adjacent portion. The increased wall thickness t.sub.s due to the step 20 will help to gradually increase the strength of the fixture. As illustrated in the table in FIG. 9 the increased wall thickness t.sub.s might be in the interval of 1 t.sub.w−2 t.sub.w. Due to the described outer and inner profile it has been possible to increase the diameter of the inner through hole in the fixture to allow for a larger diameter abutment.

(26) FIG. 8 discloses another embodiment of the invention. In FIG. 8 there is shown, as an alternative to the design with the cylindrical press-fit, a conical press-fit 21 having a the cone angle θ.sub.cone and a cone length L.sub.cone, see example parameters in the table in FIG. 9. The straight portion 22 at the distal most end of the fixture 85 acts as a stress relief to avoid high stress singularities and has a length L.sub.st where L.sub.st is less than the length of the cone L.sub.cone. The abutment 86 comprises a corresponding conical press-fit portion 21′.

(27) The inner surface of the connection area 10 in the fixture 5, either with a cylindrical or a conical press-fit 11, 21 could be treated with surface treatments known in the art, such as burnishing, Diamond-like-Carbon (DLC) coating, nitriding, etc, in order to enhance wear resistance.

(28) As already mentioned the abutment 6 (86) is the link between the anchoring system and the prosthesis and it is the male part of the connection described above. FIG. 9 illustrates an example of an abutment for the anchoring system, having a proximal portion 23, a distal portion 24 and an intermediate longitudinal stem 25. The distal portion 24 has a geometrical form, such as square, hex, sphere, cylinder, etc, and acts as a connection to a safety device which is connected to the actual prosthesis. The geometry of the conical surface 26 is to accommodate to a press-fit with a cylindrical as well as a conical design. A conical portion 13′ at the most proximal end of the abutment provides for stability and load distribution when mated with a corresponding conical portion 13 of an anchoring element 5. The conical portion 13′ of the abutment and the corresponding mating conical portion 13 of the anchoring element 5 provides a stable contact point at the most proximal end of the connection area 10 (see above description of connection area), compared to for example flat to flat surface connections. The interface 28 between the cylindrical stem 25 and the geometrical distal portion 24 has radiuses of different sizes to act as stress relief for stress concentrations in that area. The surface of the abutment could be treated with special surface treatments known in the art, such as Nitride diffusion, Diamond-like-Carbon (DLC) coating, Physical Vapor Deposition (PVD) coating, etc, to reduce wear and increase fretting resistance properties in the connection area.

(29) FIG. 10 is an example of an abutment screw for the anchoring system. The screw is used as a retention mechanism between the fixture and the abutment. The screw has rolled formed threads 29 at the proximal end accommodated to the inner threads 15 in the fixture. The screw has a slight conical portion 30 next to the threads 29 and an increased diameter portion 31 is provided under the screw head 32 that strengthens the design in that region for avoiding fractures. At least the threads 29 and the increased diameter portion 31 are preferably surface treated (e.g. DLC coating) after machining to provide a lower friction coefficient. In some implementations the entire abutment screw is surface treated.

(30) The table in FIG. 11 indicates preferred design parameters intervals for the invention.

(31) In addition, variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. For example, it should be understood that the invention is not limited to femur bone and limb prostheses but could be used for other types of long bones in the human body. Furthermore, in the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.