Surgical instrument

1. Surgical instrument, comprising:

a handling part, and

a tool part, the tool part comprising at least one movably mounted tool, which is actuable by means of a force-transmitting and/or actuating mechanism that is operable from the handling part, and

the force-transmitting and/or actuating mechanism comprising a fluid-operable drive unit, the drive unit comprising two double-acting fluid cylinders;

wherein:

with the drive unit in a first driving position the movably mounted tool is subjected to a first actuating force in an actuating direction and in at least a second driving position is subjected to at least a second actuating force in the actuating direction; and

in an inoperative position of the instrument, in which no actuating force is exerted by the force-transmitting and/or actuating mechanism in the actuating direction on the tool, a retaining force is exerted on the tool by at least one of the two double-acting fluid cylinders in a retaining direction opposite to the actuating direction.

2. Instrument according to claim 1 , wherein with the drive unit in a third driving position the movably mounted tool can be subjected to a third actuating force in the actuating direction.

3. Instrument according to claim 2 , wherein the third actuating force corresponds to the sum of the first and second actuating forces.

4. Instrument according to claim 1 , wherein a ratio of the first and second actuating force lies in a range of 4:1 to 9:1.

5. Instrument according to claim 1 , wherein the drive unit comprises a linear drive.

6. Instrument according to claim 5 , wherein the two double-acting fluid cylinders comprise two coupled, separately controllable double-acting fluid cylinders.

7. Instrument according to claim 6 , wherein the two double-acting fluid cylinders have different effective cross sections.

8. Instrument according to claim 7 , wherein a ratio of the effective cross sections lies in a range of 4:1 to 9:1.

9. Instrument according to claim 1 , wherein the at least one two double-acting fluid cylinders are pneumatic and/or hydraulic cylinders.

10. Instrument according to claim 1 , wherein the instrument is designed for the removal of bone, cartilage or similar tissue, and the instrument further comprises a shank, which extends in a longitudinal direction and carries on its distal end a cutting plate, which is disposed transversely of the longitudinal direction or inclined relative to the longitudinal direction,

wherein the movably mounted tool is a cutting element mounted displaceably on the shank and carrying on its distal end a cutting edge, which is directed towards the cutting plate and is movable towards the cutting plate for the cutting of tissue.

11. Instrument according to claim 10 , wherein:

there is disposed on a proximal end of the shank a first coupling element for detachable, positive connection to the force-transmitting and/or actuating mechanism,

the force-transmitting and/or actuating mechanism has a second coupling element corresponding to the first coupling element, and

the first coupling element is a polygon, outer faces of which are directed radially outwards from a longitudinal axis of the shank.

12. Instrument according to claim 10 , wherein the polygon is a quadrilateral, a hexagon or an octagon.

13. Instrument according to claim 10 , wherein the shank at a proximal end is shaped like a sleeve and the cutting element penetrates the sleeve-like end of the shank.

14. Instrument according to claim 10 , wherein the cutting element at a proximal end carries a third coupling element, which is detachably connectable to a drive element of the force-transmitting and/or actuating mechanism, and the third coupling element is adjoined by stops acting in the longitudinal direction of the shank.

15. Instrument according to claim 1 , wherein the force-transmitting and/or actuating mechanism comprises an actuating member for actuating the drive unit, the actuating member is movable from a non-actuated basic position, in which the instrument occupies the inoperative position, into a first activation position, in which the drive unit occupies the first driving position, and into at least a second activation position, in which the drive unit occupies the second driving position.

16. Instrument according to claim 15 , wherein the actuating member is held under spring bias in the basic position.

17. Instrument according to claim 15 , wherein the actuating member is mounted pivotably.

18. Instrument according to claim 15 , wherein:

in the first activation position a first resetting force acts upon the actuating member, in the second activation position a second resetting force acts upon the actuating member, and

the second resetting force is greater than the first resetting force.

19. Instrument according to claim 18 , wherein the second resetting force is at least twice as great as the first resetting force.

20. Instrument according to claim 18 , wherein for generating the first and second resetting force there is provided a resetting unit comprising a first elastic resetting member and a second elastic resetting member.

21. Instrument according to claim 20 , wherein at least one of the first resetting member and the second resetting member is a spring element.

22. Instrument according to claim 20 , wherein the resetting unit is configured to act directly or indirectly upon a control member for controlling the drive unit or upon the actuating member.