CEMENT RETAINING IMPLANT STEM FOR PERMANENT FIXATION

Abstract

The present invention relates to a stem for or of an implant having a longitudinal axis and at least one recess adapted for cemented implantation into the medullary cavity and/or a cavity created by surgery of a long bone, characterized in that the recess is interrupted by a barrier. Further the present invention relates to a method for preparing a stem of an implant according to any one of the preceding claims for implantation, comprising the step of placing cement into the recess (12) on both sides of the barrier.

Claims

1. A stem for or of an implant, the stem being adapted for implantation into a cavity of a long bone, wherein the stem has a longitudinal axis and at least one recess, wherein said at least one recess is interrupted by at least one barrier.

2. The system or implant of claim 1, wherein the recess is formed as a groove, preferably a longitudinal groove.

3. The system or implant of claim 1, wherein the barrier is solidly integrated into the shape and material of the stem.

4. The system or implant of claim 1, wherein the recess has a minimum width of 1 to 5 mm and a maximum width of 6 to 10 mm.

5. The system or implant of claim 1, wherein the recess has a depth of 0.5 mm to 4 mm.

6. The system or implant of claim 1, wherein the outer contour of the stem at the barrier is continuous.

7. The system or implant of claim 1, wherein the outer contour of the stem at the barrier is circular.

8. The system or implant of claim 1, wherein the outer surface of the barrier is cylindrical.

9. The system or implant of claim 1, wherein at least a segment of the outer surface of the barrier forms a continuous part of an outer surface of the stem outside the recess.

10. The system or implant of claim 7, wherein at least one segment of the outer surface of the barrier and the outer surface of the stem outside the recess are cylindrical.

11. The system or implant of claim 1, wherein the geometry of the stem is adapted to be at least partly implanted into the medullary cavity of a humerus.

12. The system according to claim 1, wherein the system has different elements adapted to be mounted together in a variety of combinations to form respective different implants.

13. An implant comprising a stem according to claim 1.

14. A method for preparing a stem of an implant of claim 1 for implantation, comprising the step of filling the at least one recess on both sides of the barrier with bone cement and placing bone cement on the outer surface of the stem adjacent to the recess.

Description

SHORT DESCRIPTION OF THE FIGURES

[0021] The following figures illustrate preferred embodiments of the present invention. These embodiments are not to be construed as limiting but merely to enhance the understanding of the invention together with the following description. In these figures, same reference signs refer to features throughout the drawings that have the same or an equivalent function and/or structure. In summary, the figures illustrate the following:

[0022] FIG. 1 shows a side view of an implant comprising two stems according to the disclosure;

[0023] FIG. 2 shows a perspective view of the implant of FIG. 1 implanted into a human humerus;

[0024] FIG. 3 shows an exploded perspective view of the implant of FIG. 1;

[0025] FIG. 4 shows a perspective view of an alternative implant assembled using one of the stems of the implant of FIG. 1; and

[0026] FIG. 5 shows a perspective view of another alternative implant assembled using one of the stems of the implant of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0027] FIGS. 1 to 3 show an implant 2 (namely a diaphyseal segment prosthesis 2) comprising two stems 4 being adapted for cemented implantation into the medullary cavity 6 (after preparing the cavity 6 by surgery) of a long bone and in particular a human humerus 8. The implant 2 has a longitudinal axis 10.

[0028] Each of the stems 4 in this exemplary embodiment comprises two recesses 12 in a circumferential direction of the stems 4. Nonetheless any number of recesses 12 in the circumferential direction of above may be formed. The same applies to above-noted dimensions and shap for the recesses 12.

[0029] In this exemplary embodiment, the recesses are formed as grooves, i. e. elongated recesses. As illustrated, they may be located parallel to each other, be on opposite sides of the stem and/or extend in the direction of or along the longitudinal axis 10.

[0030] Each recess 12 is interrupted by a barrier 14 in the longitudinal direction of the stem 4, which is preferably solidly integrated into the shape and material of the respective stem 4 and in particular about half way along the length of the respective stem. It is also possible to provide more than one barrier along a recess 12, such as two, three, four, or five barriers. Nonetheless, only one or two barriers is preferred.

[0031] The at least one barrier allows advantageously that cement 16 on both sides of the barrier 14 supports fixation in both longitudinal directions (against pulling and pushing forces in the humerus 8) by establishing a form fit. This also applies to bone tissue growing into the recesses 12 in case of cementless fixation using a stem 4 that has an outer surface adapted for bone ingrowth.

[0032] In case of fixation by bone cement, the form fit is established between the barrier 14 and the cement 16 in the recesses 12 on both sides of the barrier 14 as well as between bone tissue surrounding the implantation site of the stems 4, preferably cancellous bone tissue 18, and the respective stem. In case of cancellous bone tissue, the form fit may be enhanced by causing bone cement to enter into the cancellous bone's surface 18 resulting in a better interlock between the stem and the bone tissue. In case of fixation by bone ingrowth, a form fit is achieved directly between the bone tissue and the stem 4.

[0033] In particular for anchoring of a diaphyseal segment prosthesis 2 (e. g. after a resection in cancer treatment), permanent fixation, in particular using bone cement, is advantageous since a replacement of the prosthesis is unlikely compared to artificial joints. In comparison to a diaphyseal segment prosthesis, artificial joints are exposed to friction and wear during everyday use and may thus need replacement during the lifetime of the patient.

[0034] If being adapted for cemented implantation into the medullary cavity of a long bone, the outer contour of the cross section of the stem 4 at the barrier 14 is preferably continuous. It preferably has a smooth and even more preferably a polished surface. Further, the outer contour of the stem in cross-section along and except for the recesses 12 and barrier 14 is in particular round or circular (preferably forming a full circle). Likewise, the outer surface 20 of the barrier 14 is in particular round or circular (preferably forming a full circle). As described above, the outer contour of the stem 4 and/or barrier 14 may be cylindrical or tapered.

[0035] The outer surface 20 of the barriers 14 preferably forms a continuous part of the outer surface 22 of the stem 4 outside its recesses 12. The outer surface 22 may be, as shown in the exemplary embodiment of the figures, circular cylindrical. In other words, the entire outer surface 22 of each stem 4 outside the recesses 12 and along the recesses is preferably circular cylindrical forming one continuous outer surface with an integrally formed and circular cylindrical outer surface 20 of the barriers 14. Compared to a tapered shape, the cylindrical shape has no influence on the depth of the recesses 12.

[0036] As discussed above, a circular cylindrical surface of the stem 14 is particularly preferred since it provides on the one hand a strong anchoring within the bone tissue (by cemented implantation or bone ingrowth) and on the other hand allows for a revision of the stem while preserving bone tissue, in particular using a core drill. Such a core drill may be guided by the circumferential surface of the stem 14 while removing material (bone tissue and/or cement) surrounding and being in contact with the stem. As a result, the material anchoring the stem 14 within the bone cavity is interrupted and the stem 14 may easily be pulled out of the cavity. As described above, these advantages are provided by the shape of the stem 14 being generally cylindrical instead of being tapered.

[0037] Consequently, the basic shape of the stem 14 is preferably cylindrical and even more preferably circular cylindrical. The basic shape is defined by the shape of the outer surface of the stem except for the at least one recess 12, the distal end 28, and the connective end 24.

[0038] Each stem 4 comprises one connective end 24 adapted to be mounted to a diaphyseal segment body 26 and one continuously integrated preferably rounded and in particular semi-spherical distal end 28. The latter prevents damage to bone tissue during insertion.

[0039] As shown in the exemplary illustrative embodiments of the figures, the stems 4 are members of a system of different elements like the diaphyseal segment body 26, the adapter 30, or the connective screw 32 (cf. FIG. 3). These elements are adapted for being mounted to each other in a variety of combinations to respectively form different implants 2, 2′, 2″.

[0040] For example, FIGS. 4 and 5 show implants 2′ and 2″, respectively, wherein the stem 4 is mounted to provide anchorage for an artificial elbow joint. The implants 2′ and 2″ are mounted as a combination of a variety of elements like the stem 4, adapter 30, and connective screw 32 also shown in FIG. 3, and additionally an elbow joint replacement 34 and a segment 36 for replacing a section of a long bone.

REFERENCE SIGNS

[0041] 2, 2′, 2″ implant [0042] 4 stem [0043] 6 medullary cavity [0044] 8 human humerus [0045] 10 longitudinal axis [0046] 12 recess [0047] 14 barrier [0048] 16 cement [0049] 18 cancellous bone [0050] 20 outer surface of barrier 14 [0051] 22 outer surface of stem 4 outside the recess 12 [0052] 24 connective end [0053] 26 diaphyseal segment body [0054] 28 distal end [0055] 30 adapter [0056] 32 connective screw [0057] 34 shoulder joint group [0058] 36 joint adjacent segment