Extension device for a bone anchor, in particular for a pedicle screw

1. An extension device ( 2 ) for a bone anchor ( 4 ), having an axial longitudinal direction ( 16 ), a circumferential direction ( 18 ) concentric thereto and a radial direction ( 20 ), wherein the extension device ( 2 ) is extended in the axial longitudinal direction ( 16 ) and, via a radial projection ( 38 ), engages behind an engageable area ( 14 ) on a head ( 8 ) of the bone anchor ( 4 ) in the longitudinal direction ( 16 ) and also in the radial direction ( 20 ) and is detachably but nevertheless rigidly and also torque proof fixable in the longitudinal direction ( 16 ), on the head ( 8 ) of the bone anchor,

wherein the extension device ( 2 ) comprises two shell parts ( 22 ) that are separated from each other and extended in the longitudinal direction ( 16 ), each of which comprises a radial projection ( 38 ) for engaging behind the engageable area ( 14 ) on the head ( 8 ) of the bone anchor ( 4 ),

wherein the respective shell part ( 22 ) is designed to be predominately dimensionally stable, and wherein

the extension device further comprises a sleeve-like housing part ( 60 ) that can be slid in the axial longitudinal direction ( 16 ) onto the two shell parts ( 22 ) which are separated from each other and detachably fixed to the head of the bone anchor, and wherein the sleeve-like housing part ( 60 ) has a radially inwardly configured run-in bevel ( 66 ) against which the shell parts ( 22 ) run up if the sleeve-like housing part ( 60 ) is slid in the axial longitudinal direction ( 16 ) onto the shell parts ( 22 ) and, wherein the sleeve-like housing part ( 60 ), in the applied state, limits and defines a tunnel-like access ( 106 ) to the bone anchor ( 4 ) that extends in the axial direction ( 16 ).

2. The extension device of claim 1 , wherein the sleeve-like housing part ( 60 ) in the slid-on state surrounds at least 70%, of the longitudinal extent of the two shell parts ( 22 ) in the axial longitudinal direction.

3. The extension device of claim 1 , wherein the sleeve-like housing part ( 60 ) has one projection ( 64 ) protruding radially inward that serves as a spacer between the two shell parts ( 22 ) that are separated from each other and spaced apart transverse to the axial longitudinal direction ( 16 ).

4. The extension device of claim 1 , wherein the sleeve-like housing part ( 60 ) is designed so that the two shell parts ( 22 ) are bent towards each other when the sleeve-like housing part ( 60 ) is slid on transverse to the axial longitudinal direction ( 16 ).

5. The extension device of claim 1 , wherein the two shell parts ( 22 ) are first bent towards each other in the area proximal to the two projections ( 64 ) protruding radially inward when the sleeve-like housing part ( 60 ) is slid on.

6. The extension device of claim 1 , wherein at least one shell part ( 22 ) is detachably connected to the sleeve-like housing part ( 60 ) in such a manner that the sleeve-like housing part ( 60 ) cannot be pulled off of the shell part ( 22 ) in the proximal direction.

7. The extension device according to claim 6 , characterized in that the at least one shell part ( 22 ) can be connected to the sleeve-like housing part ( 60 ) in such a manner that the shell part ( 22 ) is first bent radially inward in the area proximal to its free end ( 68 ) and then goes radially outward into a locked position with the sleeve-like housing part ( 60 ) when sleeve-like housing part ( 60 ) is slid on.

8. The extension device of claim 1 , wherein the run-in bevel ( 66 ) designed radially inward is formed from a projection or extension ( 72 ) extending from one wall of the sleeve-like housing part ( 60 ) and that this projection or extension ( 72 ) can be locked to a recess ( 70 ) of the shell part ( 22 ).

9. The extension device of claim 1 , wherein the sleeve-like housing part ( 60 ) has an axial abutment area ( 78 ) with which it runs against an axial stop on at least one of the shell parts ( 22 ) when sleeve-like housing part ( 60 ) is slid onto the shell parts ( 22 ), whereby a distal end position of the sleeve-like housing part ( 60 ) is defined.

10. The extension device of claim 1 , wherein the sleeve-like housing part ( 60 ) has a slit ( 84 ) extending in the axial longitudinal direction in its wall that extends from a distal end ( 82 ).

11. The extension device of claim 1 , wherein the sleeve-like housing part ( 60 ) has a thread ( 88 ), in the area of its proximal end ( 86 ), by which a sleeve-like closure element ( 62 ) is screwable.

12. The extension device of claim 11 , wherein the thread ( 88 ) is an internal thread and the internal thread in the circumferential direction ( 18 ) is provided only in an area between the two shell parts ( 22 ) that are separated from each other and is omitted in the area of the shell parts ( 22 ).

13. The extension device of claim 1 , wherein the sleeve-like housing part ( 60 ) is dimensioned in the axial direction ( 16 ) in such a way that the shell parts ( 22 ) in the axial direction project over distal ends ( 82 ) and/or over proximal ends ( 86 ) of the sleeve-like housing part ( 60 ) when the sleeve-like housing part ( 60 ) is slid until it is in its final end position on the shell housing part ( 22 ).

14. The extension device of claim 11 , wherein the closure element ( 62 ) in its state of being screwed to the sleeve-like housing part ( 60 ) braces the sleeve-like housing part ( 60 ) and the two shell parts ( 22 ) in the axial longitudinal direction ( 16 ) against each other.

15. The extension device of claim 11 , wherein the closure element ( 62 ) in its state of being screwed to the sleeve-like housing part ( 60 ) axially runs against proximal free ends ( 68 ) of the two shell parts ( 22 ).

16. The extension device of claim 11 , wherein the closure element ( 62 ) has a flange area ( 98 ) that is extended continuously or interruptedly in the circumferential direction ( 18 ) and in that the closure element ( 62 ) can rest axially against proximal free end ( 68 ) of at least one of the shell parts ( 22 ) with this flange area ( 98 ).

17. The extension device according to claim 11 , wherein the closure element ( 62 ) has or limits a cylindrical annular space ( 102 ) into which proximal free ends ( 68 ) of the two shell parts ( 22 ) engage when the closure element ( 62 ) is screwed to the housing part ( 60 ).

18. The extension device of claim 1 , wherein one of the respective shell parts ( 22 ) has a spring element ( 28 ) extended in the axial longitudinal direction ( 16 ), which is deflectable transverse thereto, wherein the spring element has a support area ( 36 ) projecting radially inward by means of which the shell part ( 22 ) can be supported at least in the axial longitudinal direction ( 16 ) against the head ( 8 ) of the bone anchor ( 4 ) so that, by this, the shell portion ( 22 ) is detachably fixable to the head ( 8 ) of the bone anchor ( 4 ) when the projection ( 38 ) engages behind the engageable area ( 14 ) on the head ( 8 ) of the bone anchor ( 4 ), and that the spring element ( 28 ) is capable of being deflected radially outward in order to release the extension device ( 2 ) so that its support area ( 36 ) comes free from the head ( 8 ) of the bone anchor ( 4 ), and the shell part ( 22 ) with respect to the head ( 8 ) of the bone anchor ( 4 ) is capable of being moved out of the engageable area ( 14 ) on the head ( 8 ) of the bone anchor ( 4 ).

19. A set of items comprising the extension device ( 2 ) of claim 1 , and an adapter sleeve ( 114 ) for forming a tunnel-like access ( 24 ) to the bone anchor ( 4 ) that can be affixed directly to the head ( 8 ) of the bone anchor ( 4 ).

20. The set of items of claim 19 , wherein the sleeve-like housing part ( 60 ) and the adapter sleeve ( 114 ) have the same outer diameter.