SLEEVE AUGMENT DEVICE FOR AN ARTICULATED JOINT

Abstract

An augment device for a joint endoprosthesis, the device including a sleeve surrounding a channel extending through the sleeve. The sleeve is formed of porous material for ingrowth of bony material, the sleeve comprising an inner face and an outer face. The sleeve further comprises a wall surrounding the channel, the wall being made of solid material and forming a sandwich structure with the porous material, wherein the wall forms a bulkhead between the inner face and the outer face. Thereby, the bulkhead wall will stop inflow of any cement across the sleeve from its inner to its outer face. The porous material on the outer face will be kept free from cement and its capability to promote bone ingrowth is reliably preserved. The augment devices are preferably provided as a set having different sizes and straight or stepped bottoms for improved versatility and maximum preservation of natural bone matter.

Claims

1. An augment device for a joint endoprosthesis, the device comprising: a sleeve having a top and a bottom, a distance between said top and said bottom defining an entire height of said sleeve, wherein the sleeve surrounds a channel extending through the sleeve from the top to the bottom of the sleeve wherein the channel is configured to receive a stem of the joint endoprosthesis, the sleeve comprising an inner face and an outer face, the inner face defining the channel, and a distance between the inner face and the outer face defining a thickness, the sleeve further comprising a porous material configured for ingrowth of bony material, the sleeve further comprising a wall that surrounds the channel and extends along the entire height of the sleeve, the wall being made of solid material and forming a layered structure with the porous material, wherein the sleeve comprises a compensator element configured for adjusting a circumference of the sleeve, wherein the compensator element comprises a gap, wherein the gap is dimensioned to block cement flow between the inner face and the outer face.

2. The augment device of claim 1, wherein the sleeve is compressible in at least one of a media-lateral direction and an anterior/posterior direction.

3. The augment device of claim 1, wherein the wall forms a complete bulkhead reaching over the entire device between the inner face and the outer face, the bulkhead being configured for blocking cement flow between the inner face and the outer face.

4. The augment device of claim 1, wherein the wall serves as a reinforcing element.

5. The augment device of claim 1, wherein the wall is located at an intermediate position along a direction of the thickness such that the porous material is formed on an inward facing side and an outward facing side of the wall.

6. The augment device of claim 1, wherein the sleeve is of a generally conical shape.

7. The augment device of claim 6, wherein the sleeve is wider at its top and has a cone angle between 10 and 45.

8. The augment device of claim 1, wherein the augment device is a tibial augment for a knee joint endoprosthesis.

9. The augment device of claim 1, wherein the porous material comprises interconnected pores.

10. The augment device of claim 1, further comprising a top cover made of solid material, wherein the top cover completely covers a top surface of the sleeve and leaves the channel open.

11. The augment device of claim 10, wherein the sleeve comprises at least one recess and the top cover further comprises at least one extension cover which is configured to cover side faces or a bottom face of the recess.

12. The augment device of claim 11, wherein the top cover and the extension cover are connected such as to provide a continuous top bulkhead.

13. The augment device of claim 1, wherein edges of the sleeve are at least partly rounded, at least partly beveled, or at least partly rounded and beveled.

14. The augment device of claim 1, wherein a raised structure having embossments is formed on the inner face.

15. The augment device of claim 1, wherein a passageway extends through the entire sleeve, said passageway oriented to run across the channel.

16. The augment device of claim 1, further comprising at least one bending joint, said at least one bending joint having a lower bending stiffness in a lower portion than in an upper portion and extending for the entire height.

17. The augment device of claim 16, wherein the at least one bending joint comprises a void in the sleeve and a metal strip, wherein the metal strip spans the void.

18. The augment device of claim 17, wherein the metal strip is oriented oblique with respect to the wall such that a lower end of the metal strip is positioned closer toward the outer face and the upper end of the metal strip is closer to the inner face.

19. The augment device of claim 17, wherein the metal strip is oriented substantially parallel to a center axis of the channel.

20. The augment device of claim 1, wherein the compensator element is configured as two overlapping tongues arranged in a sliding relationship.

Description

[0026] FIG. 1 a, b is a perspective view of a first exemplary embodiment;

[0027] FIG. 2 is a schematic view showing an augment device according to the invention in situ;

[0028] FIG. 3 is a cross section of the embodiment depicted in FIG. 1;

[0029] FIG. 4 is a detailed view of a wall of the augment device;

[0030] FIG. 5 a, b are perspective views of a second and third embodiment having windows and a passageway, respectively;

[0031] FIG. 6 a-c are detail views showing a raised structure on an inner face;

[0032] FIG. 7 is a top view of a fourth embodiment having bending joints;

[0033] FIG. 8 is a detailed cross section trough one of the bending joints; and

[0034] FIG. 9 shows a set of augment devices of different types.

[0035] A first embodiment of an augment device 1 according to the present invention is shown referring to FIGS. 1-4. The augment device 1 of this embodiment is preferably a tibial augment which is made of a biocompatible metallic material. It is preferably selected from a group comprising titanium alloys, pure titanium, cobalt chromium, stainless steel, tantalum and zirconium. Further preferably, the material is pure titanium (for example Ti Grade 2). This combines excellent biocompatibility with good strength and stiffness characteristics. Another preferred material is a titanium alloy (for example Ti6Al4V). This material is more regularly available, also it has a higher stiffness.

[0036] The tibial augment has a generally conic form of a sleeve 10. The sleeve 10 surrounds a channel 11 which runs entirely through the augment device 1 from its top 12 to its bottom 13. The channel 11 is configured for receiving a stem of an endoprosthesis, in particular the stem 94 of a tibial part 92 of a knee prosthesis 9.

[0037] The sleeve 10 is made in a sandwich configuration having a wall 3 combined with two layers of porous metal material 2. It is to be noted that the porous portion at the inner face is optional; alternative configurations are shown in FIG. 6a, b, c. The wall 3 runs from the bottom 13 to the top 12 of the sleeve 10 surrounding completely the channel 11. On the top 12 the wall 3 meets a top cover 4 which covers a complete top side 12 of the sleeve 10. The top cover 4 and the wall 3 form a unitary piece. Thereby, the wall 3 in conjunction with the top cover 4 act as a bulkhead blocking any passage of cement from the channel 11 to an external side of the sleeve 10.

[0038] The tibial augment 1 is configured such as to be anatomically sized and shaped to fill a cavity in an upper part of a distal bone 99, namely the tibia. The augment device 1 is formed generally conically for better fitment. Its bottom side 13 is generally planar as well as its top 12.

[0039] As it can be appreciated in FIG. 2, the augment 1 is placed in the cavity of an upper portion of the bone 99, thereby forming a base on which a tibial plate 93 of the tibial component 92 of the knee prosthesis 9 is to be positioned. The knee prosthesis 9 further comprises a femur component 91 configured for rotatable interaction with the tibial portion 92. The tibial component 92 further comprises a stem 94 configured to be anchored in a medullary channel of the tibia 99. The stem 94 is routed through the channel 11 of the tibial augment 1. In order to provide sufficient room for any ribs 94, or other projections on the stem 94 or the tibial part 92 generally, the tibial augment 1 is further provided with recesses 16 in order to provide additional room for the stem 94 and its projections 94. The recesses 16 may be configured like depressions as depicted in FIG. 3, having a bottom face 16 and side face 16. In order to provide a continuous top bulkhead, the bottom face 16 and the side face 16 is closed by an extension cover 45 which functions as an extension of the top cover 4. Thereby, a continuous bulkhead on the top side is achieved, thereby avoiding any unwanted leakage of cement trough the recesses 16.

[0040] A porous material 2 placed on the outer face of the wall 3 is preferably a highly porous material having a degree porosity of at least 60-90%. Further, the pores are interconnected and elementary cells defining the pores are arranged in a regular order. The interconnected pores provide for a much improved ingrowth of bony material, and thereby ensure a good stabilization of the tibial augment 1 in the tibial bone 99.

[0041] Examples for alternative embodiments of the inner face are shown in FIG. 6a-c. FIGS. 6a and 6b show the inner face without and FIG. 6c with a porous portion on the inner face, however it is to be noted that the porous portion is entirely optional and either embodiment may be provided with or without it. In these embodiments the inner face is provided with a raised structure 61 having embossments 62 there between. In a first variant shown in FIG. 6a, the embossments 62 are configured to have a diamond shape and to be arranged in a matrix like fashion. This provides for additional fixation in both, horizontal as well as vertical direction. In FIG. 6b a variant is shown having the embossments configured as groovings 62, the groovings 62 being oriented to run in a direction form the bottom to the top of the sleeve 10. This provides for an improved fixation effect in respect to a horizontal direction, but allows for a facilitated removal of the augment device in a vertical direction. In FIG. 6c a variant is shown having a lattice structure 6 provided on the inner face. The lattice 6 comprises laths as raised structure 61 and interspaces 62 as embossments. The laths 61 define a grid, with the interspaces 62 being arranged there between. The interspaces 62 are configured to be optionally filled by the porous material 2, preferably such that it will be flush with the surface of the laths 61 in a filled state. The lattice structure 6 enhances fixation and has a considerable reinforcing effect on the sleeve 10, thereby providing addition mechanical strength. For implantation cement may be applied for fixation of the stem 94. For this reason, the cement will be applied within the channel 11 around the stem 94. The cement may flow into the porous material 2 placed on an inner face of the wall 3, thereby providing a strong, interlocked bonding. However, in order to preserve the positive bone ingrowth effect of the porous material 2, the cement shall not reach the outer face.

[0042] For this purpose the wall 3 is provided acting as a bulkhead confining the cement to an inner portion, thereby keeping the outer face essentially cement-free. The top cover 4 ensures that no cement could spill over towards the top. A bottom cover is not necessary. However, it may be provided at the section of the bottom outward of and including the wall, thereby blocking any unwanted influx of cement in the porous material 2 on the outer face.

[0043] In order to allow a smooth influx of the cement into porous material 2 on the inner face it is necessary to remove air displaced by the cement from the inner portion. In order to facilitate removal of air in order to avoid the air being trapped, a plurality of small holes 32 are provided in a regularly arranged manner at the wall 3, preferably at the entire wall 3. This is depicted in FIG. 4. The size of the holes 32 is dimensioned such as to allow passage of gases like air, but has to block any passage of a cement. A preferred size is between 0.3 to 0.5 mm.

[0044] Now referring to FIG. 5, second and third embodiments are shown being provided with additional means for fixation. To this end, windows 34 are provided in a row close to a top end of the sleeve 10. The windows 34 configured such as to penetrate the wall 3 and preferably the porous material 2 on either side. Upon implantation and application of cement, the cement flows freely through the windows 34 from the channel 11 outwards to the exterior. Since that flow of cement is confined to the vicinity of the windows 34 no adverse effect are encountered with respect to promoting bone ingrowth capability of the porous material 2 on the outer face. Yet, the cement flowing through the windows 34 acts like additional fixation pins securing the tibial implant 1 into its place. This allows for a better and considerable faster fixation of the augmentation device 1. A further advantage of this configuration is, that in a case of a required removal of the augment device 1 the cement pins reaching through the windows 34 could be easily cut from the outside owing to the proximity of the windows 34 to the top 12 of the sleeve 10. Thereby any removal will be facilitated by maintaining the high degree of stabilization during implantation.

[0045] Additionally or alternatively, as depicted in figure in 5b a rather large passageway 36 can be formed in a more central area of the sleeve 10. The passageway 36 runs through the wall 3 and the porous material 2. The passageway 36 is oriented essentially perpendicular to a center axis of the channel 11.

[0046] The dimension of the passageway 36 through the wall 2a is selected such that it has more than three times the area of any of the windows 34. Thereby, by flowing of cements trough the passageway 36 a rather massive trunnion for additional fixation strengths will be formed. Similarly as explained above in respect to the windows 34, this additional fixation could be rather easily removed in case of a removal by cutting of the cement trunnion. In the depicted exemplary embodiment the passageway is dimensioned to be 108 mm.

[0047] A further embodiment is shown in FIGS. 7 and 8. This embodiment features two sets of bending joints 7, 7. The bending joints allow a bending of the sleeve 10 such that it will be compressed as a whole, thereby reducing the size of the channel 11 and the outer dimension of the sleeve 10. The bending joints 7, 7 is formed by a void 17 in the sleeve 10 combined with a metal strip 71 which spans the void 17. As best appreciated in FIG. 8, the metal strip 71 is of solid material and runs from a top 12 to a bottom 13 of the sleeve 10. The strip 71 is oriented oblique with respect to the wall 3 such that a lower end 73 of the strip 71 is positioned closer toward the outer face of the wall 3 and the upper end 72 of the strip 71 is placed closer to the inner face of the wall 3. By virtue of this arrangement, the strip 71 is oriented essentially parallel to a center axis of the channel 11. Thickness of the strip 71 at a lower portion 74 is reduced. To this end, the strip 71 is configured such as to have a tapering width towards its lower end 73. By virtue of this tapering, the most bending force will be created by the upper part of the strip 71, whereas the lower portion 74 will only contribute to the bending force to a much lesser degree. The bending force and movement effected thereby is depicted with respect to FIG. 7. Two pairs of bending joint 7, 7 are provided in a mirror symmetric configuration. A first set of bending joints 7 is placed at a rear wall of the sleeve 10. By exerting a bending force, the bending joints 7 allow for a movement in a rotational direction as indicated by the single arrow. Thereby an axis of bending defined by the bending joints 7 provides for an elasticity in a medio-lateral (ML) direction.

[0048] A second set 7 is provided which is arranged in a mirror symmetric configuration at the side portion of the sleeve 10. The bending joints 7 provide a range of motion as depicted by the double arrow. This provides for an axis of bending which gives anterior/posterior (AP) elasticity. As a result, by providing both pairs of bending joints 7, 7 compressibility in two dimensions is achieved, namely one in ML direction and another in AP direction.

[0049] By exerting bending force the width of the inner channel will be reduced. Thereby, its circumference will be reduced. In order to enable the sleeve 10 for such a reduction, a compensator element 8 is provided. In the depicted embodiment (see FIG. 7) it is arranged at an opposite, front side of the sleeve 10 to the bending joints 7. The compensator element is comprised of two tongues 81, 82 arranged at a left and a right portion of the sleeve 10. The tongues 81, 82 are arranged in an overlapping configuration, leaving just a tiny gap 83 there between. The tongues 81, 82 slide along each other under the effect of a bending motion with the bending joints 7, 7. The gap 83 is dimensioned such as to small enough to block leakage of cement.

[0050] The bottom 13 of the augment device 1 may be flat or stepped (see FIG. 9). In the stepped variant, a portion 13 with a reduced height is present on either the left or the right side. A transition surface 19 connects the portion with full height with the portion 13 having a reduced height.

[0051] Further, additional types are provided that have a reduced height over the entire area. This type is depicted as type 1 in FIG. 9. The type having the stepped bottom is depicted as type 1 whereas the original type as depicted in FIG. 1-8 is shown as type 1 in FIG. 9.

[0052] Preferably, a full set of augment devices is provided. The set comprising the types as mentioned above. Additionally, the types are provided in different sizes I, II, III and IV, with I being extra small, IT being small, III being medium; and IV being large. This allows the surgeon a rather broad range of options in order to select an appropriate augment device 1 depending on the actual conditions of the implant site.