SHELL TO BE DRIVEN INTO A BONE SUBSTANCE FOR A PROSTHETIC JOINT

Abstract

A shell (1) for a prosthetic joint to be driven into a bone substance. The shell having an outer lateral surface (4) which is convexly curved in cross section and on which a plurality of ribs (5) is arranged. All ribs extend in the same direction at a preferably increasing gradient angle of 45° to 85° at the equatorial end (6) to a pole-side end (7). The cumulative flank projection area of all ribs (5) corresponds to at least a fifth of the entire outer lateral surface. As a result of this measure, a very high primary stability is achieved once the shell has been driven in, the shell being screwed into the bone substance very precisely and without bone material being sheared off. This arrangement can also be applied, similarly, to a concavely curved inner lateral surface.

Claims

1-20. (canceled)

21. A shell to be driven into a bone substance for a prosthetic joint, having an outer lateral surface which is convexly curved, in cross-section, or having an inner lateral surface which is convexly curved, on which outer or inner lateral surface there is arranged a plurality of ribs, wherein all ribs extend in the same direction under a pitch angle from 45° to 85° at the equatorial end toward a pole-sided end on the outer lateral surface or on the inner lateral surface, and each rib has a flank projection area based on a plane running through a longitudinal extent of the rib and perpendicularly to the outer lateral surface or to the inner lateral surface, and a sum of the flank projection area of all ribs corresponds to at least one fifth of the entire outer lateral surface or the entire inner lateral surface.

22. The shell as claimed in claim 21, wherein said outer lateral surface or said inner lateral surface is spherical.

23. The shell as claimed in claim 21, wherein said pitch angle increases from the equatorial end toward the pole-sided end.

24. The shell as claimed in claim 21, wherein the ratio between the sum of the flank projection area of all ribs and the outer lateral surface or the inner lateral surface is in the range from 0.2:1 to 1:1.

25. The shell as claimed in claim 21, wherein at least 20 ribs are arranged on the outer lateral surface or on the inner lateral surface.

26. The shell as claimed in claim 21, wherein between 30 and 80 ribs are arranged on the outer lateral surface or on the inner lateral surface.

27. The shell as claimed in claim 21, wherein an interval between adjacent ribs, at the equatorial end from rib center to rib center on the outer lateral surface or on the inner lateral surface, is in the range from 0.2 mm to 4 mm.

28. The shell as claimed in claim 21, wherein at least 30% of the ribs extend over more than half a height of the shell, based on the longitudinal central axis thereof.

29. The shell as claimed in claim 21, wherein at least 50% of the ribs extend over more than half a height of the shell, based on the longitudinal central axis thereof.

30. The shell as claimed in claim 21, wherein ribs of differing length are arranged on the outer lateral surface or on the inner lateral surface.

31. The shell as claimed in claim 30, wherein the ribs of differing length are arranged in a regular sequence.

32. The shell as claimed in claim 21, wherein a rib height from a rib foundation to a rib vertex is in the range from 0.1 mm to 4 mm.

33. The shell as claimed in 21, wherein ribs of differing rib height are arranged on the outer lateral surface or on the inner lateral surface.

34. The shell as claimed in 33, wherein the ribs of differing rib height are arranged in a regular sequence.

35. The shell as claimed in claim 21, wherein ribs of differing rib height are arranged on a certain latitude based on a circumference of the outer lateral surface or the inner lateral surface.

36. The shell as claimed in claim 21, wherein the ribs have a cross-section which tapers from a rib foundation toward a rib vertex, based on a plane running perpendicularly to a longitudinal extent of the rib and perpendicularly to the outer lateral surface or to the inner lateral surface.

37. The shell as claimed in claim 36, wherein the ribs have a wedge-shaped cross-section.

38. The shell as claimed in claim 21, wherein opposing flank surfaces of the individual ribs have different roughness values such that the flanks subjected to a greater load during drive-in have a lower roughness value than the flanks subjected to a greater load during pull-out.

39. The shell as claimed in claim 21, wherein at least some of the ribs are interrupted to form individual rib teeth.

40. The shell as claimed in claim 39, wherein the rib teeth of a rib have a differing configuration between an equatorial end and a pole-sided end.

41. The shell as claimed in claim 39, wherein the rib teeth form irregular, multisurface bodies having a quadrangular footprint, two flank sides inclined against one another, a pole side facing the pole, and an equator side facing the equator.

42. The shell as claimed in claim 40, wherein the successive rib teeth of a rib are configured such that displacement of bone material takes place in a drive-in direction and an anchoring in the bone material takes place in a screw-out direction.

43. The shell as claimed in claim 39, wherein the gaps between the rib teeth do not extend as far as the outer lateral surface or the inner lateral surface.

44. The shell as claimed in claim 21, wherein at least one of said outer lateral surface or said inner lateral surface and the ribs is fully or partially provided with an osteoinductive coating.

45. The shell as claimed in claim 21, wherein the shell is a joint shell for a prosthetic hip joint to be driven into an acetabulum, and a ratio between the sum of the flank projection area of all ribs and the outer lateral surface is in the range from 0.2:1 to 0.8:1.

46. The shell as claimed in claim 21, wherein the shell is a humeral anchor to be driven into a humerus, and a ratio between the sum of the flank projection area of all ribs and the outer lateral surface is in the range from 0.3:1 to 1:1.

47. The shell as claimed in claim 21, wherein a course of the ribs is chosen such that each rotation by a predetermined angular value brings about a constant advance of the shell.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Further individual features and advantages of the invention are revealed by the exemplary embodiments described below and by the drawings, where:

[0030] FIG. 1: shows the side view of a greatly enlarged representation of a joint socket,

[0031] FIG. 2: shows one half of a top view of the joint socket as per FIG. 1,

[0032] FIG. 3: shows a perspective view of the joint socket as per FIG. 1,

[0033] FIG. 4: shows one half of a schematically represented side view containing different rib teeth,

[0034] FIGS. 5 to 10: show greatly enlarged and schematic representations of various rib profiles,

[0035] FIG. 11: shows a top view of rib teeth offset against one another,

[0036] FIG. 12: shows a perspective view of an individual tooth,

[0037] FIG. 13: shows a cross-section through the rib tooth as per FIG. 12,

[0038] FIG. 14: shows the schematic representation of a prosthetic hip joint in the acetabulum,

[0039] FIG. 15: shows the schematic representation of a prosthetic shoulder joint with humeral anchor,

[0040] FIG. 16: shows a side view of the broad side of a humeral anchor with ellipsoidal cross-section,

[0041] FIG. 17: shows a side view of the narrow side of the humeral anchor as per FIG. 16,

[0042] FIG. 18: shows a top view of the humeral anchor as per FIG. 16,

[0043] FIG. 19: shows a cross-section through the plane I-I of the humeral anchor as per FIG. 18,

[0044] FIG. 20: shows a schematic and greatly enlarged perspective view of a rib with drawn-in flank projection area, and

[0045] FIG. 21: shows the schematic representation of a prosthetic shoulder joint as surface replacement comprising an anchor-free joint shell.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] As depicted in FIGS. 1 to 3, a joint socket 1 consists of a shell-shaped body having an outer lateral surface 4 on which a plurality of ribs 5 are arranged distributed over the entire circumference. They extend from an equatorial end 6 up to a pole-sided end 7. The joint socket is flatted in the pole region and a pole opening 18 is arranged on the longitudinal central axis 8. Each individual rib consists of a plurality of rib teeth 12 arranged one after another. In addition, not all ribs run as far as into the proximity of the pole. Every second rib 5′ only extends up to a latitude B, which is somewhat further from the pole. At the equator, the hemispherical shell has a shell diameter DM which is somewhat larger than the diameter of the cutter with which the bone substance is milled out.

[0047] The distance a between two ribs, based in each case on the center of an individual rib at the rib foundation, is greatest at the equatorial end and decreases toward the pole-sided end. As mentioned in the introduction, said distance is between 0.2 mm to 4 mm. The pitch angle α is in the range from 45° to 85° at the equator and increases toward the pole.

[0048] The length b of a rib is based in each case on the spatial course thereof or on the development thereof, as depicted in FIG. 3. The cumulative length of all ribs is therefore yielded by the addition of the length of all ribs, irrespective of whether a mixture of longer and shorter ribs is concerned.

[0049] Each rib has rib flanks 11 and 11′ on two sides. The flank projection area P of a rib is yielded by the rib length b multiplied by the rib height d or by the averaged rib height, if said rib height varies over the length of the rib, minus the gaps between the teeth. Using this type of calculation, what is evidently ascertained is the net projection area of a rib flank without taking the inclination and curvature thereof into account. The projection area is, however, that area which plays the greatest role with regard to primary stability. Altogether, the cumulative flank projection area of a socket is thus calculated from the number of ribs multiplied by the flank projection area of an individual rib.

[0050] Details of a rib profile are depicted in FIG. 4. Here, the ribs are divided into individual rib teeth 12, with rib teeth 12′ which are trapezoidal in cross-section being arranged in the near-equatorial region about as far as half of the joint socket height c. In the near-pole region, the rib teeth 12″ have a triangular cross-section. The cross-section is, then, based on the longitudinal extent of a rib from the near-equatorial end 6 up to the pole-sided end 7. The trapezoidal rib teeth 12′ have a clearance angle γ on their vertex line in relation to the radius of curvature of the rib, this improving the displacement of bone material in the critical range of larger diameters.

[0051] FIG. 5 shows schematically two ribs 5 of identical cross-section with the rib foundation 9 and the rib vertex 10. The rib flanks 11, 11′ meet in the rib vertex, therefore yielding a triangular shape in the cross-section transverse to the longitudinal extent of a rib. The rib height d is measured from the rib foundation 9 up to the rib vertex 10. In the exemplary embodiment depicted here, the rib flanks 11′ inclined in the same direction are provided with an osteoinductive coating 14. It extends as far as into the region of the outer lateral surface 4 between two ribs. The interval a between two ribs, i.e., the interval from center to center rib foundation, is depicted again here for better understanding. Depicted here as representative of all exemplary embodiments is the flank projection area P of a rib, which is yielded by the rib height d and the rib length b, provided that the rib height stays constant and the rib has no interruptions.

[0052] As per FIG. 6, the ribs 5 have a similar cross-sectional shape as in the case of the exemplary embodiment as per FIG. 5. In all exemplary embodiments, the flank angle β can be in the range from 10° to 90°.

[0053] The flank angle can either run in a constant manner or vary between the equator region and the near-pole region.

[0054] Instead of an osteoinductive coating, the rib flanks 11′ inclined in the same direction are, as per FIG. 6, provided with a higher surface roughness in comparison with the opposite flanks 11, this being indicated by the faceted surface. The roughness value Ra can be, for example, less than 3 μm to 5 μm in the drive-in direction and greater than 30 μm in the pull-out direction. It is evidently possible to achieve the differing surface roughness with different processing methods, such as, for example, by one-sided machining, irradiation or coating of the respective rib flanks.

[0055] FIG. 7 shows one exemplary embodiment in which only the outer lateral surface 4 between two adjacent ribs 5 is provided with an osteoinductive coating 14.

[0056] FIGS. 8a and 8b show exemplary embodiments in which the rib vertex does not run as a line, but in a flat manner or with slight curvature. As per FIG. 8a, the rib flanks 11, 11′ run exactly or approximately in parallel, therefore forming ribs 5 which are lamellar or rectangular in cross-section. In contrast, the ribs 5 as per FIG. 8b have a configuration which is trapezoidal in cross-section and has a flat rib vertex 10.

[0057] In the exemplary embodiment as per FIG. 9, the ribs 5 have a pagoda-shaped cross-section with a rather broad rib foundation 9 and an acute rib vertex 10. The rib flanks 11 and 11′ run in a curved manner.

[0058] FIG. 10 shows schematically one exemplary embodiment having alternately arranged ribs 5 and 5′ of differing height d1 and d2. The rib intervals a1 and a2 can also be correspondingly different.

[0059] FIG. 11 shows a top view of individual rib teeth 12 which each represent irregular multisurface bodies, as additionally depicted in FIGS. 12 and 13. The rib teeth of the left row run in a regular manner and those of the right row run such that they are offset in relation to one another. Each rib tooth 12 has a quadrangular, especially trapezoidal, footprint, two teeth flanks 15, 15′ inclined against one another, a pole side 16 and an equator side 17. The drive-in direction is depicted with the arrow e and the screw-out direction is depicted with the arrow f. The gaps 13 between the individual teeth are relatively small. The successive teeth 12′ and 12″ of the right row are offset against one another such that, based on the drive-in direction e, the footprint respectively projects to the right or to the left. As a result, sometimes the tooth flank 15 and sometimes the tooth flank 15′ is somewhat further over the axis of symmetry of the total groove. The offset angle can be between 2° and 15°. This results in alternately protruding flanks 19, 19′ which hamper the detachment of the joint socket in the screw-out direction f, since said flanks assume the function of barbs. By contrast, drive-in in the drive-in direction e is not hampered by this configuration. Additionally contributing to this is the fact that the pole side 16 encloses an acute angle with the base, whereas the equator side 17 is approximately perpendicular to the base.

[0060] The table below shows, by way of example, the relationship between rib interval, rib height and number of ribs and the resultant cumulative flank projection area on three hip-joint shell sizes, 48 mm, 52 mm and 64 mm. A rib interval of 3 mm is regarded as ideal, this allowing a rib height of 1.1 mm. To this end, the cumulative flank projection areas achievable here are each specified in mm2. The remaining values are specified in mm. In addition, the number of ribs is also additionally specified, and also the ratios between the cumulative flank projection areas and the outer lateral surface.

TABLE-US-00001 Min. Ideal Max. Rip interval a 0.2 3 4 Rib height d 0.1 1.1 4 Parameters calculated on size 52 shell Outer lateral surface: 4412 mm2 Cum. flank 1416 1085 3270 projection area Number of 834 56 42 ribs Ratio 0.32 0.25 0.74 Parameters calculated on size 64 shell Outer lateral surface: 6637 mm2 Cum. flank 2127 1651 4846 projection area Number of 1022 70 52 ribs Ratio 0.32 0.25 0.73 Parameters calculated on size 48 shell Outer lateral surface: 3771 mm2 Cum. flank 1209 935 2909 projection area Number of 770 52 40 ribs Ratio 0.32 0.25 0.77

[0061] FIG. 14 shows a symbolic depiction of a prosthetic hip joint 2, of which the shaft with the joint ball is depicted in outline only. The hip-joint socket 1 with its ribs 5 has been driven into the acetabulum 3 in arrow direction e, said hip-joint socket carrying out a slight rotation in arrow direction g.

[0062] In contrast, FIG. 15 shows a symbolic depiction of a shaft-free prosthetic shoulder joint 22 in which the shell according to the invention is not a joint socket, but assumes the function of a humeral anchor 21 which has been driven into the humerus 23. In this case, the humeral head 24 connected to the humeral anchor assumes the function of the joint ball.

[0063] FIGS. 16 to 19 depict further details of a humeral anchor 21. What is striking in this case is the different shape of the cross-section and footprint in comparison with the hip-joint socket. As is evident especially from FIG. 19, the outer lateral surface 26 has a configuration which is ellipsoidal in cross-section and which has a rib-free, but closed, pole face 27. The individual ribs 25, 25′ alternately extend up to the pole face or as far as a slight distance therefrom. Despite the ellipsoidal cross-section based on the longitudinal central axis, the shell has a circular shell shape at the equator. However, owing to the shell cross-section and the differing rib height at the equator of the individual ribs 25, 25′, there is also an ellipsoidal outer footprint having a broad side BS and having a narrow side SS. As depicted, the individual ribs in the case of the humeral anchor preferably run in an uninterrupted manner, but with varying rib height and differing rib length in some cases. However, an interruption of individual ribs or all ribs to form individual teeth would be conceivable, too. Provided on the interior of the humeral anchor 21 are suitable fasteners 30 (FIG. 19) for fastening the humeral head following drive-in.

[0064] By analogy with the above-described hip-joint shell, what is depicted below, likewise by way of example, is a table with the relationships between rib interval, rib height and especially with the ratio between the cumulative flank projection area and the outer lateral surface. In this case, the shell sizes are, for a humeral anchor, naturally smaller than in the case of a hip-joint shell.

TABLE-US-00002 Min. Ideal Max. Rip interval 0.2 3 4 a Rib height d 0.1 1.1 4 Parameters calculated on size 28 shell Outer lateral surface: 1321 mm2 Cum. flank 517 426 1379 projection area Number of 456 32 24 ribs Ratio 0.391 0.32 1.04 Parameters calculated on size 38 shell Outer lateral surface: 2389 mm2 Cum. flank 935 739 2337 projection area Number of 614 42 32 ribs Ratio 0.391 0.31 0.98 Parameters calculated on size 47 shell Outer lateral surface: 3619 mm2 Cum. flank 1411 1115 3304 projection area Number of 754 52 38 ribs Ratio 0.390 0.31 0.91

[0065] FIG. 20 shows again schematically and at great enlargement the flank projection area P using the example of a rib 5 having an interruption 31 in the rib vertex 10. However, said interruption does not reach as far as the rib foundation 9, there evidently being no interruption arising as a result, but merely a cutout in the flank projection area P. Here too, the rib length b corresponds to the longitudinal extent of the rib 5 from the equatorial end 6 up to the pole-sided end, which is not depicted here. The flank projection area P runs perpendicularly to the outer lateral surface 4, as indicated by the arrow x. Here, the rib flanks 11 and 11′ form a wedge-shaped cross-section, specifically one based on a plane running perpendicularly to the longitudinal extent of the ribs and perpendicularly to the outer lateral surface, as indicated by the arrows y and z. This yields here the flank angle β. Here too, what is again depicted is the rib height d and the rib interval a as radian measure between the centers of adjacent ribs on the equator-sided rib foundation.

[0066] FIG. 21 shows the example of a shell according to the invention, in which the ribs are not arranged on the outer lateral surface, but on an inner lateral surface. The example relates to a shaft-free prosthetic shoulder joint 22, wherein a hemispherical anchor shell 32 directly forms the surface replacement on the humerus 23. In contrast to the prosthetic shoulder joint as per FIG. 15, a humeral anchor is not required because the anchor shell 32 is directly driven onto the humerus by means of the inner ribs 33 and anchored thereon in this way. In this connection, the inner ribs 33 run on the inner lateral surface 34 toward the pole in the same manner as if the ribs were arranged on an outer lateral surface. In the present exemplary embodiment, the outer lateral surface 35 of the anchor shell 32 directly forms the joint surface, analogous to humeral head 24 in the case of the exemplary embodiment as per FIG. 15. When driving the anchor shell 32 onto the humerus 23, there is evidently likewise a rotation by a few angular degrees until the end position is reached.

[0067] Self-evidently, it would also additionally be possible to use a shell according to the invention for alternative joint constructions, for example for an inverse prosthetic shoulder in which the joint socket on the shoulder blade is replaced by an artificial joint ball and the joint ball on the upper arm is replaced by an artificial joint socket. In such a case too, it would be possible to anchor the joint socket in the humerus without a shaft.