Intervertebral dissection tool

Description

[0001] The invention relates to an intervertebral preparation tool, i.e. a removal tool for intervertebral preparation, a so-called paddle shaver.

[0002] For intervertebral disc preparation, i.e., for removing the intervertebral disc material between the vertebrae before inserting an implant, special ablation tools, so-called paddle shavers, are known. For example, WO 2008 / 035849 A1 discloses such an instrument, which has a cutting head with two blades at its distal end. The blades are oriented diametrically opposite to the longitudinal axis of the cutting head and are movable via an actuating rod. For this purpose, the blades are each pivotally connected via two levers and are pushed outwards by a spring element. The two levers allow the blades to tilt relative to the longitudinal axis of the instrument. Such tilting is undesirable in certain cases.

[0003] US 6,224,604 B1 discloses an expandable orthopedic drill that can be used in spinal fusion surgery. The drill has external cutting elements that can be expanded via a lever mechanism. This lever mechanism has two pairs of levers, each pivotally attached to a common pivot point on the cutting element. Of the first pair of levers, one lever is fixed to an outer sleeve of the drill, and a second lever, together with the first lever of the second pair, is fixed to a movable sleeve. The movable sleeve slides on a central shaft. At the distal end of the central shaft, the second lever of the second pair of levers is pivotally attached. In this way, by moving the shaft within the sleeve, the cutting element can be moved radially outward while remaining aligned parallel to the longitudinal axis of the shaft.This arrangement requires a relatively large amount of space for the two pairs of levers and the movable sleeve, so the minimum diameter of the instrument is quite large.

[0004] The object of the invention is to provide an improved removal tool for intervertebral preparation, i.e. a paddle shaver, which ensures defined guidance of the removal blades with a small minimum diameter.

[0005] This problem is solved by an inter-vortex preparation tool, i.e., a material removal tool for inter-vortex preparation with the features specified in claim 1. Preferred embodiments are described in the dependent claims, the following description, and the accompanying figures.

[0006] The intervertebral preparation tool according to the invention is designed for use as a removal tool for intervertebral preparation, i.e., a so-called paddle shaver, and has a cutting head with at least one movable blade. The blade is movable, in particular, so that after insertion into the intervertebral space, i.e., between two vertebrae, it can be moved to a position radially spaced with respect to the longitudinal axis in order to remove intervertebral disc material throughout the entire intervertebral area. The at least one movable blade is held by at least three pivotable levers. That is, the pivotable levers connect the blade to the cutting head or the supporting structure of the cutting head and provide the desired mobility of the blade. The levers themselves are rigidly designed. A first and a second lever are each attached at a first pivot point on the blade and at a spaced-apart second pivot point on a supporting element or structure.A cutting head is pivotally connected to a support structure. The first and second pivot points are preferably located at opposite ends of the levers. A third lever is pivotally connected at a first pivot point on the blade and at a spaced-apart second pivot point on an actuating rod. This actuating rod is displaceable relative to the support structure. The first and second pivot points on the third lever are also preferably located at opposite ends of this lever. By displacing the actuating rod, the third lever can thus be moved relative to the support structure, thereby enabling movement of the blade or spreading of the instrument in the area of ​​the cutting head to increase the diameter. The pivot points are designed as pivot joints whose pivot axes extend parallel to each other.In particular, the levers can be pivoted, causing the cutting blade to move radially around the longitudinal axis of the instrument or cutting head to increase its diameter. The arrangement of three levers supporting the blade on the cutting head has the advantage of preventing the blade from tilting in such a way as to alter its angle relative to the longitudinal axis of the cutting head, which runs from the proximal to the distal end. This ensures the blade is held at a defined angle. The angle relative to the longitudinal axis can remain constant or change in a defined manner with the movement of the third lever. However, the use of three levers prevents undefined tilting of the blade.

[0007] Preferably, the cutting tool has a second blade. This blade can be rigid. Preferably, however, the cutting head has two movable blades, each of which is held by three pivotable levers as described above. That is, each of the two blades is held on the cutting head by three rigidly designed levers, with a first and a second lever each being pivoted at a pivot point on the corresponding blade and at a spaced-apart second pivot point on the support element. The first and second levers of the two blades can be pivoted at separate second pivot points on the support element. However, it would also be conceivable that the two first levers are pivotally pivoted at a common second pivot point and / or the two second levers are pivotally pivoted at a common second pivot point on the support element.Furthermore, each blade has a third lever, which is articulated at a first pivot point on the corresponding blade and at a spaced-apart second pivot point on the actuating rod, which is displaceable relative to the support element. The pivot points are designed as pivot joints with parallel pivot axes, whereby, in particular, the pivot axes of the pivot points of both blades also run parallel to each other. A common second pivot point on the actuating rod could also be provided for both third levers. Furthermore, the third levers on each blade could each be articulated to a second lever at a common first pivot point.

[0008] The at least one blade or blades are advantageously designed such that their longitudinal edges, i.e., their long edges which preferably extend substantially in the longitudinal direction of the instrument, are designed to cut or act as cutting edges. The blades thus cut or remove material in the circumferential direction with respect to the longitudinal axis of the instrument or tool. In this way, the tool can be used in such a manner that cutting or material removal can be effected by a movement transverse to the longitudinal axis of the instrument and / or rotation about the longitudinal axis of the instrument.

[0009] The two third levers preferably form a toggle-lever mechanism which, by moving the actuating rod, pushes the two blades apart or, conversely, pulls them together, so that the instrument can be widened or narrowed in the diameter direction in the area of ​​the cutting head, the diameter being defined by the radial distance between the blades. The arrangement of the three levers on each blade precisely defines the angular position of the two blades relative to each other; that is, the two blades cannot pivot unpredictably or change their angular position relative to each other.

[0010] Preferably, the two blades are arranged on opposite sides of a longitudinal axis of the cutting head. The longitudinal axis of the cutting head is the axis extending from the proximal to the distal end. The blades are further preferably arranged on diametrically opposite sides with respect to the longitudinal axis, such that the blades, or rather the distance between their outer surfaces, define the diameter of the cutting head. By moving one or both blades in a direction transverse to the longitudinal axis, particularly in a radial direction, the diameter or the distance between the blades can be changed. More preferably, the two blades are arranged symmetrically to each other, i.e., in particular as mirror images with respect to the longitudinal axis or a plane in which the longitudinal axis lies.In particular, if both blades are movable, the blades are preferably moved symmetrically to each other away from or towards the longitudinal axis, which is achieved as described above via the third levers, which then form a kind of toggle joint.

[0011] The second pivot points of the three levers for holding a blade, i.e., a single blade, are preferably spaced apart in a direction transverse to the pivot axes. If two blades are provided, the second pivot points of the three levers of both blades are further preferably spaced apart in a direction transverse to the pivot axes. The direction transverse to the pivot axes is preferably a direction parallel to the longitudinal axis of the cutting head. The pivot axes preferably extend transversely, and in particular perpendicularly, to the longitudinal axis of the cutting head. The spaced arrangement of the pivot points achieves high stability. For example, the first and second levers, together with the blade and the support element, could form a parallelogram structure.A third lever preferably extends not parallel to, but at an angle to, the other two levers, thus preventing tilting and enabling force transmission in all directions. Preferably, at least two levers do not extend parallel to each other when the blade is radially extended. The radially extended state is a state in which the blade is further away from the support element or the longitudinal axis of the cutting head in the radial direction than in its rest position. In the rest position, the blade is in the position where it has the smallest distance to the longitudinal axis of the cutting head and preferably rests directly against the support element. In this rest state, all three levers supporting a blade can extend substantially parallel to each other or along an axis, so that the overall diameter of the instrument is minimized in this state.

[0012] Preferably, on the cutting head, the first lever forms a distal lever and the third lever forms a proximal lever, with the second lever being arranged between the first and third levers. The distal lever is the one located furthest towards the distal end of the cutting head, while the proximal lever is the one located furthest towards the proximal end. Thus, the three levers for each blade, which is articulated via three levers, are arranged offset from one another along the longitudinal axis of the cutting head. The levers are preferably offset to such an extent that, in the folded state, with the cutting blade in its rest position and radially innermost position, they lie completely one behind the other in the longitudinal direction. This allows for the smallest possible instrument diameter in the folded or retracted state.In this state, the second pivot point of the first lever is preferably located furthest distally, and the first pivot point of the first lever is located further distally than the second pivot point of the second lever. The first pivot point of the second lever is again located further distally than the third lever, particularly than the first pivot point of the third lever. Most preferably, the second pivot point of the third lever is located furthest proximally on the actuating rod.

[0013] According to a further preferred embodiment, the first pivot points of the first and second levers, and preferably the first pivot points of the first, second, and third levers, are spaced apart from one another in a direction transverse to the pivot axes, i.e., preferably parallel to the longitudinal direction of the cutting head. This enables, firstly, a parallelogram structure as described above. Secondly, and independently of this, a uniform force transmission between the blade and the support element can be achieved, which in particular prevents the blade from tilting. Furthermore, this arrangement, together with the spacing of the second pivot points and corresponding lever lengths, allows for a rest position in which the levers lie one behind the other in the axial direction as described above.If two blades are each movably arranged on the support element via three levers, the pivot points are preferably arranged on both blades in a corresponding manner, preferably symmetrically to the longitudinal axis or a plane extending along the longitudinal axis in the manner described above.

[0014] The levers and their pivot points are preferably positioned and dimensioned such that by pivoting the levers about their second pivot points, the associated blade can be moved from a first position close to the support element to at least a second position further away from the support element. The position close to the support element is the aforementioned rest position. During pivoting, the levers rotate about their second pivot points on the support element, so that the distance of the first pivot points on the blade increases radially to the longitudinal axis of the support element, and the blades are extended radially or moved away from the support element and the longitudinal axis.

[0015] Preferably, the first and second levers are articulated such that they pivot in the same direction of rotation to move the connected blade. Preferably, the levers pivot such that the first pivot points, along with the blade, move radially and simultaneously distally in the longitudinal direction. This can be achieved, for example, by means of a parallelogram linkage. If the levers are of different lengths, a defined inclined position of the blade can be achieved, which may deviate from a true parallelogram linkage.

[0016] The third lever is preferably articulated such that, to move the connected blade, it pivots in a direction of rotation opposite to the direction of rotation of the first and / or second levers when they pivot simultaneously. That is, the third lever can, for example, move such that, relative to the second pivot point, the first pivot point of the third lever on the blade pivots in a proximal direction. However, the movement of the actuating rod preferably causes the second pivot point to move simultaneously in a distal direction, so that overall the entire third lever either maintains its position relative to the support element or is moved in a distal direction.By pivoting in the opposite direction, the third lever extends at an angle to the second lever and preferably to the first and second levers, so that all three levers together do not form a parallelogram arrangement, thus preventing the blade from tilting. That is, the second and third levers preferably extend at angles opposite to the radius with respect to the longitudinal axis. If two blades are provided, their third levers are moved, as described above, via the actuating rod, preferably in the manner of a toggle joint, so that the axial displacement of the actuating rod pushes the first pivot points of the third levers radially outwards, thus moving the two blades apart. In the opposite direction, the blades can be moved back together, i.e., back to a rest position against the support element.

[0017] The first and second levers, which are hinged to a blade, i.e., the same blade, can have the same length between their first and second pivot points. If, at the same time, the distance between the first pivot points and the distance between the second pivot points are equal, then essentially a parallelogram shape or parallelogram arrangement is created, as described above.

[0018] Furthermore, it is possible for the second and third levers, which are articulated to a blade, to have the same length between their first and second pivot points. This causes the second and third levers to form a triangular or trapezoidal shape relative to each other when pivoting, which, in particular, enables force transmission in both distal and proximal directions between the blade and the support element or the actuating rod. This design prevents the blade from tilting, thus preventing the blade's angular position relative to the longitudinal axis of the cutting head from changing unpredictably.

[0019] In a specific embodiment, the first and second levers, which are articulated to the same blade, can have different lengths between their first and second pivot points. For example, the first lever, which forms a distal lever on the cutting head, can be longer than the second lever. Alternatively, the first lever could be shorter than the second. This allows the blade's angle relative to the longitudinal axis of the cutting head to change simultaneously when the blade is moved radially outward by pivoting the third lever. That is, the blade does not move parallel in the radial direction, but pivots by a certain amount during the radial movement. This creates a lordotic angle, which may be desirable for certain applications.

[0020] The second and third levers, which are articulated to the same blade, can have different lengths between their first and second pivot points, with, for example, the second lever being longer than the third. A different length for the third lever can be advantageous with regard to its function in the blade's extension or radial movement. Furthermore, it can be advantageous to make the third lever shorter if the first lever is longer, in order to achieve a desired lordosis angle, i.e., a conical shape of the cutting head. Conversely, the third lever could be longer if, for example, the first lever is shorter.

[0021] Preferably, the cutting head is located at the distal end of an instrument shaft, and the actuating rod is guided longitudinally along or within the instrument shaft so as to be slidable. This creates a relative movement at the distal end between the actuating rod and the instrument shaft or a support element rigidly connected to the instrument shaft. This relative movement displaces the second pivot point of the third lever, so that this lever, in conjunction with the first and second levers, causes the associated cutting blade to be displaced radially outward with respect to the longitudinal axis, thus widening the cutting head. Preferably, the widening is achieved by advancing the actuating rod distally, and the retraction of the cutting head is accomplished by moving the actuating rod in the opposite direction, proximally.

[0022] The cutting head is preferably designed such that, when the blade(s) are in their resting position, it has a blunt tip at its distal end, which is preferably attached directly to the support element or formed by the support element itself. The blunt tip absorbs the forces occurring when the instrument is driven into the intervertebral space. In this state, the blade(s), or the blade in the longitudinal direction, is preferably located behind the blunt tip, so that the lever mechanism of the blades is not subjected to the forces of impact. When the blades expand, they can shift distally in addition to their radial movement, so that they protrude distally beyond the blunt tip or end. This allows for ablation even in the region of the distal end of the cutting head.

[0023] The second pivot points of the three levers, which are articulated to a blade, i.e., to the same blade, are preferably located on a straight line that extends further preferably parallel to the direction of movement of the actuating rod, i.e., preferably parallel to the longitudinal axis of the instrument shaft or the cutting head. This arrangement facilitates the simultaneous pivoting of the three levers in such a way that the cutting blade is moved radially outwards. In particular, a parallelogram-like structure, as described above, can thus be created.

[0024] According to a further preferred embodiment, the first pivot points of the three levers, which are articulated to a blade, i.e., the same blade, lie on a straight line extending parallel or at an angle to the direction of movement of the actuating rod. It is also possible for the angle between this straight line and the direction of movement or longitudinal axis to change during pivoting or widening in order to create a lordotic angle as described above. In the folded rest state, i.e., in the state where the blade rests against the support element, the straight line on which the first pivot points lie preferably extends parallel to the direction of movement or longitudinal axis.

[0025] For example, to provide a desired lordosis angle, at least one outer surface of the blade can extend at an angle to a longitudinal axis of the cutting head or instrument in at least one position. In this way, a constant lordosis angle can be created that is independent of the lever deflection. The levers can then be designed such that the cutting blade is displaced radially in a parallel direction to the longitudinal axis, and the lordosis angle, determined by the angle of the blade's outer surface, remains constant.

[0026] The cutting head is preferably arranged at the distal end of an instrument shaft, with a handle at the proximal end of the instrument shaft. This handle has an actuating device that is coupled to the actuating rod for its movement. Thus, by actuating the actuating device, the actuating rod can be moved linearly as desired. The actuating device can, for example, be a spindle drive with a rotary wheel rotating on a threaded spindle. The rotary wheel is axially fixed in the handle, so that by rotating the actuating wheel, the spindle can be moved forwards and backwards in the longitudinal direction. This linear movement can be transmitted to the actuating rod. For this purpose, the actuating rod can be rigidly connected to an actuating device such as the threaded spindle. Preferably, a detachable coupling is provided.For example, the instrument shaft and the operating rod can be designed to be detachable from the handle, allowing the instrument shaft with the cutting head to be designed as a single-use item, while the handle can be reused. Furthermore, the handle can be equipped with a fixing device for the instrument shaft to be releasably secured to the handle. This could, for example, be a clamping screw.

[0027] According to a further preferred embodiment, the actuating device has a scale that indicates the degree of expansion of the cutting head, i.e., the extent of the radial movement of the blade(s). Since the radial displacement of the blade(s) is achieved by deflecting the levers, there may not be a linear relationship between the distance the actuating device is moved and the deflection of the blade. This can be taken into account in the design of a scale on the handle; for example, the scale can be non-linear and indicate the distance the blades are deflected at the respective position of the actuating device, such as the linear feed position of the actuating rod.

[0028] The invention is described below by way of example with reference to the accompanying figures. These show: Fig. 1 shows an overall view of the removal tool for intervertebral preparation according to the invention, Fig. 2 shows a detailed view of the cutting head of the removal tool according to the invention. Figure 1 in the expanded state, Fig. 3 a top view of the cutting head according to Figure 2 , Fig. 4 a partially cutaway view of the cutting head according to Figure 2 , Fig. 5 a view of the cutting head according to Figure 4 in the resting state, Fig. 6 an alternative embodiment of a cutting head according to the invention in the expanded state, Fig. 7 a detail view of the handle and Fig. 8 enlarges the section VIII in Figure 7 .

[0029] Figure 1 Figure 1 shows a side view of the removal tool as a complete instrument. The complete instrument essentially consists of three parts: a cutting head 2 at the distal end, a handle 4 at the proximal end, and an instrument shaft 6, which extends distally from the handle 4 to the cutting head 2.

[0030] In this embodiment, the cutting head 2 is fixedly arranged at the distal end of the instrument shaft. As will be described below, the instrument shaft is detachably connected to the handle 4. Thus, for example, the instrument shaft and cutting head 2 can be designed as a single-use instrument, while the handle can be reused multiple times, or the handle 4 and instrument shaft 6 can be separated, for example, for cleaning.

[0031] The cutting head 2 has two blades 8 which are articulated to a support element 10 via levers. The support element 10 is attached to the distal end of the instrument shaft 6 or can also be formed wholly or partially integrally with it. The distal end of the support element 10 is designed as a blunt tip 12 which absorbs the forces occurring when the instrument is inserted or driven in.

[0032] Each of the blades 8 is connected to the support element 10 via three levers: a first lever 14, a second lever 16, and a third lever 18. The first lever is located distally, the third lever proximally, and the second lever 16 in between. The arrangement of the two blades 8 with their levers 14, 16, and 18 is symmetrical about the longitudinal axis X of the instrument or cutting head 2, which extends from the proximal to the distal end.

[0033] The levers 14, 16, and 18 are pivotally connected to the blades 8 via first pivot points 20, which form pivot axes or are designed as pivot axes. The levers 14, 16, and 18 can pivot about the pivot points 20 relative to the blades 8. At their opposite longitudinal ends, the first lever 14 and second lever 16 are each pivotally attached to the support element 10 via a second pivot point 22. The third levers 18 are each pivotally connected at their ends opposite the first pivot points 20 to an actuating rod 26 via a second pivot point 24. The actuating rod extends in the direction of the longitudinal axis X inside the instrument shaft 6 and is displaceable forwards and backwards in the longitudinal direction X relative to the instrument shaft and relative to the support element 10.The pivot axes defined by the pivot points 20, 22 and 24 extend normal to the longitudinal direction X and thus to the direction of movement of the actuating rod 26.

[0034] In the Figures 4 and 5 In the example shown, the first levers 14 and the second lever 16 are of the same length, and their first pivot points 20 are spaced equidistant in the direction of the longitudinal axis X as the second pivot points 22. Thus, the first and second levers 14, 16, together with their respective blades 8, form a parallelogram arrangement. Figure 4 Figure 8 shows the blades 8 in their extended state, in which they are maximally spaced from the longitudinal axis X in the radial direction, i.e., in this state the cutting head has its largest diameter. Figure 5Figure 1 shows the resting state in which the cutting blades 8 are essentially in contact with the support element 10. In this state, the blades 8 are positioned proximally behind the tip 12, so that the blunt tip 12 protects the blades 8 when they are inserted or driven in. In the extended state, which is shown in Figure 4 As shown, the blades 8 are not only moved radially, but also distally by the parallel pivoting with the levers, so that the distal ends of the blades 8 protrude beyond the tip 12. This allows the cutting head to act as a cutting tool right up to its distal end.

[0035] To remove the blades 8 from the in Figure 5To move the blades 8 from their resting position radially outwards, the first and second levers 14 and 16 pivot in the same direction about their second pivot points 22 and second pivot axes 22, respectively, such that the first pivot points 20 of the first levers 14 and second levers 16 move distally in an arc towards the tip 12, thus moving the blades 8 radially outwards and simultaneously distally, with the blades 8 remaining constantly parallel to the longitudinal axis X. This movement is initiated by pushing the actuating rod 26 distally. This movement shifts the second pivot points 24 of the third levers 18 distally, causing the third levers 18 to pivot about their second pivot points 24 and thus pushing the first pivot points 20, by which they are attached to the blades 8, radially outwards.The third levers 18 of the two blades 8 form a kind of toggle lever with the actuating rod 26, in which the actuating rod 26 acts centrally at the "knee". In this way, a large force in the radial direction transverse to the longitudinal axis X can be achieved with a comparatively small force in the longitudinal direction X.

[0036] The third levers 18 pivot in the opposite direction to the second levers 16 on the respective blade 8 as they move. This causes the third levers 18 to not extend parallel to the second levers 16, but to always be angled relative to them, so that the second lever 16 and the third lever 18 on each of the blades 8 are oriented in a V-shape or trapezoidal shape relative to each other, with their first pivot points 20 being closer together parallel to the longitudinal axis X than the second pivot points 22 and 24. This design prevents the angular positions of the blades 8 relative to the longitudinal axis X from changing unintentionally.While the first and second levers 16 and 18 extend obliquely in a proximal direction from the support element 10 to their first pivot points 20, the third levers 18 extend obliquely in a distal direction from the actuating rod 26 to their first pivot points 20. Depending on how far the actuating rod 26 is advanced distally, the blades 8 move radially outwards to varying degrees from the longitudinal axis X. Thus, the diameter or spacing of the blades 8 perpendicular to the longitudinal axis X can be varied and adjusted.

[0037] In the Figure 5In the rest position shown, the levers 14, 16, and 18 of each of the two blades 8 extend essentially in a straight line, with only very small angles to the longitudinal axis X. To ensure that the levers pivot from this rest position when the actuating rod 26 is advanced, it is important that the force applied to the levers 18 via the actuating rod 26 does not extend exactly in a straight line through the first pivot point 20 and the second pivot point 24 of the third lever 18. That is, the line connecting the centers of the first pivot point 20 and the pivot point 24 extends in the rest position shown in Figure 5The first levers 14 and second levers 16, which extend through the centers of the first pivot points 20 and associated pivot points 22, are angled to the longitudinal axis X. The correspondingly defined longitudinal axes of the first levers 14 and second levers 16, which extend through the centers of the first pivot points 20 and associated pivot points 22, extend at an acute angle to the longitudinal axis X. In the example shown here, all first pivot points 20 on a blade 8 lie on a straight line parallel to the longitudinal axis X. Similarly, the associated second pivot points 22 and 24 of each blade 8 also lie essentially on a straight line parallel to the longitudinal axis X. To enable the pivoting movement of the third levers 18 opposite to the pivoting movement of the first levers 14 and second levers 16, the third levers 18 on the associated blade 8 are each arranged such that the first pivot point 20 is located further distally than the associated second pivot point 24.For the first lever 14 and the second lever 16, this is reversed. In each case, the second pivot point 22 is located further distally than the first pivot point 20.

[0038] In the Figures 2 to 5 In the examples shown, the outer surfaces of the blades 8 extend essentially parallel to the longitudinal axis X, i.e., there is essentially no lordotic angle between the blades 8. One possibility for forming a lordotic angle would be to shape the outer surfaces of the blades 8 obliquely to the line passing through the first pivot points 20. A second alternative is shown in Figure 6 shown. In the embodiment shown according to Figure 6A lordotic angle is achieved by the fact that the levers 14', 16', and 18', which pivot the blades 8 to the support element 10, are not of the same length. In the example shown here, the first levers 14' are longer between their first pivot points 20 and pivot points 22 than the second levers 16'. The third levers 18' are, in turn, shorter than the second levers 16'. This means that the first levers 14' and 16' on each of the blades 8 are no longer arranged exactly parallel and do not form a perfect parallelogram structure. This results in a corresponding change in the lordotic angle when the blades 8 are extended or pivoted from a rest position. Figure 5The blades 8 are increasingly angled to the longitudinal axis X as they expand. This means that a constant lordosis angle is not created; rather, the lordosis angle increases significantly with the expansion or extension of the blades 8 in the radial direction, in the example shown from approximately 0 degrees to 9 degrees.

[0039] The Figures 7 and 8Figure 1 shows a detailed view of the handle 4. The instrument shaft 6, or rather its outer shaft, is clamped to the handle 4 by a retaining arm 28. For clamping, the retaining arm 28 can be adjusted relative to a grip base 32 via a knurled screw 30, so that the instrument shaft 6 can be clamped between the retaining arm 28 and the grip base 32. The actuating rod 26 is connected at its proximal end by a positive fit to a slide 36, which slides along the grip base 32 in the direction of the longitudinal axis X. A threaded rod 38 is attached to the slide 36, extending in the direction of the longitudinal axis X and engaging with an actuating device in the form of an adjusting wheel 40. The adjusting wheel 40 is secured in the axial direction in the handle base 32, so that when the adjusting wheel 40 is turned, the threaded rod 38 is moved in the longitudinal direction X inside it via a threaded engagement.The coupled actuating rod 26 is also moved in the axial direction or longitudinal direction X via the threaded rod 38 in order to be able to move the blades 8 apart or towards each other in the manner described.

[0040] To enable the position of the blades 8 to be determined at the handle 4, a scale 42 is provided on the handle base 32. This scale, in conjunction with the slider 36, indicates the degree of radial deflection or expansion of the blades 8. Because the lever mechanism means that the displacement of the actuating rod 26 is not translated linearly into a radial movement of the blades 8, the scale 42 is not linear. As the slider 36 is moved distally, the intervals between the scale markings increase. The degree of radial expansion, i.e., the diameter of the cutting head between the blades 8, can be read at the handle 4 from the relative position of the slider 36 to the scale 42. Reference symbol list

[0041] 2 Cutting head 4 Handle 6 Instrument shaft 8 Blades 10 Support element 12 Tip 14, 14' first lever 16, 16' second lever 18, 18' third lever 20 first pivot point 22, 24 second pivot point 26 Actuating rod 28 Holding arm 30 Knurled screw 32 Handle base 34 Handle piece 36 Slider 38 Threaded rod 40 Adjustment wheel 42 Scale X Longitudinal axis

Claims

1. An intervertebral preparation tool comprising a cutting head (2), which has at least one movable blade (8) which is held by at least three pivotable levers, wherein the levers (14, 16, 18) are each rigid, a first (14) and a second (16) lever are each articulated at a first articulation point (20) on the blade (8) and at a distanced second articulation point (22) on a carrier element (10) of the cutting head (2), a third lever (18) is articulated at a first articulation point (20) on the blade (8) and at a distanced second articulation point (24) on an actuation rod (26) which is displaceable relative to the carrier element (10), and wherein the articulation points (20, 22, 24) are configured as pivot joints with pivot axes which are parallel to one another.

2. The intervertebral preparation tool according to claim 1, in which the cutting head (2) has two movable blades (8) which are each held by three pivotable levers (14, 16, 18), wherein the levers (14, 16, 18) are each rigid, a first (14) and a second (16) lever are each articulated at a first articulation point (20) on the associated blade (8) and at a distanced second articulation point (22) on the carrier element (10), a third lever (18) is articulated at a first articulation point (20) on the associated blade (8) and at a distanced second articulation point (24) on the actuation rod (26) which is displaceable relative to the carrier element (10), and wherein the articulation points (20, 22, 24) are configured as pivot joints with pivot axes which are parallel to one another.

3. The intervertebral preparation tool according to claim 2, in which the two blades (8) are arranged at opposite sides of a longitudinal axis (X) of the cutting head (2), preferably symmetrically to one another.

4. The intervertebral preparation tool according to any one of claims 1 to 3, in which the second articulation points (22, 24) of the three levers (14, 16, 18) for holding a blade (8) are distanced from one another in a direction transverse to the pivot axes.

5. The intervertebral preparation tool according to any one of the preceding claims, in which on the cutting head (2) the first lever (14) forms a distal-side lever and the third lever (18) forms a proximal-side lever and the second lever (16) is arranged between the first (14) and the third (18) lever.

6. The intervertebral preparation tool according to any one of the preceding claims, in which on a blade (8) the first articulation points (20) of the first (14) and the second (16) lever and preferably the first articulation points (20) of the first (14), the second (16) and the third (18) lever are distanced from one another in a direction transverse to the pivot axes.

7. The intervertebral preparation tool according to any one of the preceding claims, in which the levers (14, 16, 18) and their articulation points (20, 22, 24) are situated and dimensioned such that by way of pivoting the levers (14, 16, 18) about their second articulation points (22, 24) the associated blade (8) is movable from a first position which is close to the carrier element (10) into at least one second position which is distanced further from the carrier element (10).

8. The intervertebral preparation tool according to any one of the preceding claims, in which the first (14) and the second (16) levers are articulated such that for moving the connected blade (8) the first and the second levers pivot in the same rotation direction.

9. The intervertebral preparation tool according to any one of the preceding claims, in which the third lever (18) is articulated such that for moving the connected blade (8) the third lever pivots in a rotation direction which is opposite to the rotation direction of the first (14) and / or second (16) lever in their simultaneous pivoting.

10. The intervertebral preparation tool according to any one of the preceding claims, in which the first (14) and the second (16) lever which are articulated on a blade (8) have the same length between their first (20) and second (22) articulation points.

11. The intervertebral preparation tool according to any one of the preceding claims, in which the second (16) and the third (18) lever which are articulated on a blade (8) have the same length between their first (20) and second (22, 24) articulation points.

12. An intervertebral preparation tool according to any one of the preceding claims, in which the first lever (14') and the second lever (16') which are articulated on a blade (8) have different lengths between their first (20) and second (22) articulation points, wherein the first lever (14'), which forms a distal-side lever on the cutting head (2), is longer than the second lever (16').

13. The intervertebral preparation tool according to any one of the preceding claims, in which the second lever (16') and the third lever (18') which are articulated on a blade (8) have different lengths between their first (20) and second (22, 24) articulation points, wherein the second lever (16') is preferably longer than the third lever (18').

14. The intervertebral preparation tool according to any one of the preceding claims, in which the cutting head (2) is situated at a distal end of an instrument shank (6) and the actuation rod (26) is displaceably guided in the longitudinal direction (X) of the instrument shank (6) on or in the instrument shank (6).

15. The intervertebral preparation tool according to any one of the preceding claims, in which the second articulation points (22, 24) of the three levers (14, 16, 18) which are articulated on a blade (8) lie on a straight line which preferably extends parallel to a displacement direction (X) of the actuation rod (26).

16. The intervertebral preparation tool according to any one of the preceding claims, in which the first articulation points (20) of the three levers (14, 16, 18) which are articulated on a blade (8) lie on a straight line which extends parallel or at an angle to the displacement direction (X) of the actuation rod (26).

17. The intervertebral preparation tool according to any one of the preceding claims, in which at least one outer side of the blade (8) in at least one position extends at an angle to a longitudinal axis (X) of the cutting head (2).

18. The intervertebral preparation tool according to any one of the preceding claims, in which the cutting head (2) is arranged at the distal end of an instrument shank (6) and a handle (4) is arranged at the proximal end of the instrument shank (6), which handle has an actuation device (40) which is coupled to the actuation rod (26) for displacement thereof.