Bone anchoring element

p0001The invention relates to a bone anchoring element.

p0002For fixation of bone fractures or for stabilizing the spine fixation and stabilization devices are known which consist of at least two anchored in the bone or vertebrae and connected by a plate or rod bone screws. Such rigid systems do not allow movement of the relatively fixed bone parts or vertebrae.

p0003However, a dynamic stabilization is desirable for certain indications, in which to be stabilized bone parts or vertebrae to perform a controlled limited movement therebetween. One possibility for realizing a dynamic stabilization device is the use of a movable member in place of connecting the bone anchoring elements rigid rod, as for example in the<patcit id="pcit0001" dnum="EP0669109B1"><text>EP 669 109 B1 0</text></patcit> or in the <patcit id="pcit0002" dnum="US20030109880A1"><text>US 2003/0109880 A1</text></patcit> is described.

p0004From the <patcit id="pcit0003" dnum="US5474555A"><text>US 5,474,555</text></patcit> is a bone anchoring element in the form of a polyaxial bone screw is known with a screw element and a receiving part for connection to a rod, wherein said connected in bone anchoring screw member with the receiving member such that pivotal movements between the screw member and the receiving part are also possible. However, the solution described does not allow stabilization of the bone parts to one another with a controlled partial movement.

p0005From the <patcit id="pcit0004" dnum="EP1273269A"><text>EP 1273269</text></patcit> discloses a bone screw with a flexible shaft. The screw is inserted so as to connect two bone parts or two bones together and serves as a tension element. Thanks to the flexible shaft, a relative movement is hindered in the pulling direction, movements of smaller scope in other directions are allowed against it. If two or more screws are used, they are not interconnected. A similar screw each of the<patcit id="pcit0005" dnum="DE29915204U1"><text>DE 299 15 204 U1</text></patcit> and from <patcit id="pcit0006" dnum="US4959064A"><text>US 4,959,064</text></patcit> known. <patcit id="pcit0007" dnum="JP2002172119A"><text>JP-A-2002172119</text></patcit> discloses a screw having a threaded portion frein elastic headless. The preamble of claim 1 is based on this prior art.

p0006The object of the invention to provide a bone anchoring element that allows or stabilization of bones or vertebrae with a controlled partial motion to be stabilized bone parts or vertebrae.

p0007The problem is solved by a bone anchoring element according to claim. 1

p0008Further developments of the invention are specified in the subclaims.

p0009The invention has the advantage that the bone anchoring element takes up axial forces in the direction of its shaft axis, bending forces and torsional forces due to an elastic segment. This is a limited by the restoring force movement of the bone part or vortex, in which it is anchored, allowed. The elastic properties of the bone anchoring element can be realized in the production in a simple way by changing the dimensions of the elastic portion. The bone anchoring element is connected to the known connecting elements such as plates and rods. Thus, a dynamic stabilization device with a desired movement limitation by selection of bone anchoring elements are provided with suitable elastic properties using conventional plates or rods.

p0010Further features and advantages of the invention will be apparent from the description of exemplary embodiments with reference to FIGS. Only exemplary embodiments in which the bone anchoring element is a Schanz screw, are according to the invention.

p0011Of the figures:<dl id="dl0001"><dt>Fig. 1</dt><dd>a sectional view of a first embodiment of the bone anchoring element;</dd><dt>FIG. 2</dt><dd>a schematic representation of a stabilization device according to a first embodiment, the bone anchoring element according to the <figref idrefs="f0001">Fig. 1</figref> comprising;</dd><dt>Fig. 3a</dt><dd>a side view of the bone anchoring element according to a second embodiment with an inserted rod; </dd><dt>FIG. 3b</dt><dd>a partial sectional view of the bone anchoring element according to the line II of <figref idrefs="f0002">Fig. 3a</figref>;</dd><dt>FIG. 3c</dt><dd>a perspective view of the bone anchoring element of <figref idrefs="f0002">Fig. 3a</figref> without inserted rod;</dd><dt>Figure 4</dt><dd>a partial sectional view of a third embodiment of the bone anchoring element;</dd><dt>Fig. 5</dt><dd>a schematic view of a stabilization device according to a second embodiment that uses the bone anchoring element according to the third embodiment;</dd><dt>Fig. 6a</dt><dd>an exploded view of a fourth embodiment of the bone anchoring element;</dd><dt>Fig. 6b</dt><dd>a sectional view of part of the embodiment of <figref idrefs="f0004">Fig. 6a</figref> with a refinement;</dd><dt>Fig. 6c</dt><dd>a sectional view of the portion of <figref idrefs="f0004">Fig. 6b</figref> taken along the line AA;</dd><dt>Fig. 7a</dt><dd>a side view of the bone anchoring element according to a fifth embodiment; </dd><dt>Fig. 7B</dt><dd>a sectional view of the bone anchoring element according to <figref idrefs="f0005">Fig. 7a</figref>; and</dd><dt>Fig. 8</dt><dd>a schematic representation of a third embodiment of the stabilization device.</dd></dl>

p0012As seen from <figref idrefs="f0001">Figures 1 and 2</figref> be seen, the bone anchoring element 1 is formed in a first embodiment as an integral bone screw having a shank 2 with a first in the bone to be anchored portion 3 with a bone thread and an adjoining to the first portion 3 second bone thread-free section 4, and a second to the having adjacent section head. 5 Starting from the free end of the head 5 extends coaxially with the screw axis A, a blind hole 6 having a predetermined diameter by the head 5 and the second section 4 therethrough. In the area of ​​the second portion 4, the shaft 2 in a direction of the screw axis spirally with a predetermined pitch and a predetermined length extending, opening out in the radial direction into the bore 6 recess 7 on. Characterized the second portion 4 is formed as an elastically in the form of a coil spring. The length L of the elastic portion in the direction of the screw axis, the height H of the recess 7 in the direction of the screw axis, the pitch of the spiral and the diameter of the coaxial bore 6 are chosen so that a desired stiffness of the coil spring against axial forces, bending forces and torsional forces that act on the bone screw, is provided.

p0013The head 5 is formed like a lens in the illustrated embodiment and has a hexagonal recess 8 for an Allen key to its free end. However, it is also a different head shape and / or other recess, such as a Phillips head, for engagement with a screwing-in possible.

p0014A stabilization device according to a first embodiment includes, as shown in <figref idrefs="f0001">FIG. 2</figref> As shown, a first bone anchoring element 1 in the form of the bone screw of <figref idrefs="f0001">Fig. 1</figref> and a second bone anchoring element 11 which can be formed as a conventional bone screw without elastic portion, and a plate 12 with recesses 12, 13 for passing the shank of the bone screws.

p0015In which, in <figref idrefs="f0001">FIG. 2</figref> Example shown is the stabilizing device for stabilizing two vertebrae 15, 16, after removal of the disc or after removal of an intervening vertebra via a fusion element 17, for example a titanium cylinder, to be rigidly connected with one another provided.

p0016In operation, first, the shafts of the bone screws 1, 11 passed through the recesses 12, 13 of the plate, and then screwed into the respective vertebrae 15, 16 until the plate 12 abuts the vertebrae. The elastic portion 4 of the bone screw 1 is submerged in the fluid. In this case, a limited movement of the vertebra is enabled only in the direction of the screw axis. If the ingrowth of the fusion element sinking of the same takes place in the bone, the bone screw is due to the elastic portion for something. This prevents unfavorable stresses.

p0017In the stabilization device described, two or more bone screws may be used with an elastic portion 4th When more than two screws, the plate has a corresponding number of recesses. The stabilizing means is not only suitable for use in the spine, but also in other cases where a plate fixation is made applicable.

p0018A bone anchoring element 21 after the <figref idrefs="f0002">FIGS. 3a to 3c</figref> second embodiment shown is designed as a monoaxial bone screw for connection to a rod 100th The monoaxial bone screw includes a shaft 22 having a first, bone-anchoring portion 23 with a bone thread and an adjoining the first portion 23 of bone thread-free portion 24 and an integrally connected to the shank 21 receiving part 25 for receiving the rod 100th The receiving part 25 is substantially cylindrical and has, starting from its free end a recess 26 having a U-shaped cross-section, which is just sized so large that the rod 100 is inserted and fitted in the bottom of the recess 26th The U-shaped recess 26 two free legs 27, 28 are formed, the adjacent exhibit at its free end an internal thread 29, which cooperates with a corresponding external thread 30 a to be screwed between the legs of the female screw 31 for fixing the rod 100th

p0019In particular from <figref idrefs="f0002">FIG. 3b</figref> It can be seen, a coaxial bore 24. As extends from the bottom of the U-shaped recess 26 in the direction of the bone screw portion 23 32 of a predetermined depth by means of the bone thread-free section and in the first embodiment, the shank in the region of the second section 24 is a helically in the direction of the screw axis extending to recess 33 which opens radially into the bore 32nd Thereby, the second portion 24 is elastic and acts as a coil spring.

p0020A stabilization device according to a second embodiment includes at least one bone anchoring element which is designed as a monoaxial screw with the elastic portion 24, a second bone anchoring element, which is designed as a conventional monoaxial or polyaxial bone screw without a resilient portion as well as a rod. Instead of a conventional Monoaxial- or a polyaxial bone screw as the second anchoring element, the stabilizing means also two monoaxial bone screws according<figref idrefs="f0002">Fig. 3 a - 3 c</figref> exhibit.

p0021In operation, the bone anchoring elements are screwed into the respective bone or for application to the spine into the respective vertebrae, then the rod 100 is inserted into the receiving parts and then fixed via the inner screw. The monoaxial bone screw 21 is thereby screwed in that the elastic portion 24 protrudes above the surface of the bone or vertebra at least partially. With a movement of the bone or vertebra from being stabilized rest position a restoring force to the bone or vertebra is exerted on the elastic part 24, which brings him back to the rest position and thus limits the movement.

p0022Alternatively, the bone screw can be screwed so far, that the resilient portion 24 is not, or only slightly protruding over the surface of the bone. In this case, can take place due to the spring effect of the elastic portion yielding after adjustment.

p0023In a fourth to <figref idrefs="f0003">Fig. 4</figref> Illustrated embodiment, the bone anchoring element 41 formed as a polyaxial bone screw. This has an integrally formed screw element with a shank 42 having a first section to be anchored in the bone 43 and adjacent thereto a second bone thread-free portion 44, and a region adjacent to the second portion 44 spherical segment-shaped head 45. The head 45 is held in a receiving part 46th The second section 44 is formed as in the preceding embodiments as a helical spring and comprises a coaxial bore 47 which extends from the free end of the head by the second portion therethrough and a spirally extending recess in the wall 48.

p0024The receiving part 46 is substantially cylindrical and has at one end an axially symmetric aligned first bore 49, whose diameter is larger than that of the shaft 42 and smaller than the head of the 45th Further, the receiving portion 46 has a coaxial second bore 50 which is open on the side opposite to the first 49 end of hole and the diameter of which is so great that the screw element can be passed through the open end of the shaft through the first bore 45 until the head 45 stops at the edge of the first hole 49th The receiving part 46 has, like the receiving part 25 of the preceding embodiment, to 49 extending U-shaped recess, formed by the two free legs 52, 53 from the free end toward the first hole. In a region adjacent to its free end, the legs 52, 53 has an internal thread which cooperates with a corresponding external thread of a female screw 54 for fixing the rod 100th

p0025There is a pressure element is also 55 provided for fixing the head in the receiving part, which is designed so that it on its head 45 side facing spherical recess 56, whose radius is substantially equal to the radius of the spherical segment-shaped section of the head 45th The outer diameter of the pressure element 55 is chosen so that the pressure element in the receiving part 46 to the head 45 is movable towards. The pressure element further comprises a coaxial bore 57 for the access to a not shown recess in the screw head 45 for engagement with a screwing-in tool.

p0026A stabilization device according to a third embodiment includes at least two bone anchoring elements and a rod, wherein at least one of the bone anchoring elements is formed as a polyaxial bone screw having a shaft with an elastic portion 44th The second bone anchoring element may be formed as conventional monoaxial or polyaxial bone screw without the elastic part or it can be used as a monoaxial bone screw or a polyaxial bone screw with an elastic section, as described be formed.

p0027In operation the screw element is first inserted in the receiving part until the head 45 rests against the edge of the first bore 49th Then, the screw member is screwed into the bone or vertebra, wherein the resilient portion 44 at least partially protrudes above the bone surface. Then the rod is inserted, adjusting the angular position of the receiving part relative to the screw member and then fixed by tightening the inner screw. The elastic portion moves to the rest position in a limited way be allowed as in the previous embodiment.

p0028Alternatively, the shank as far screwed into the bone, that the elastic portion is not or protrudes only slightly above the bone surface.

p0029<figref idrefs="f0003">Fig. 5</figref> is an example of application of the stabilization device according to the third embodiment for stabilizing two vertebrae 58, 59 which are connected to each other via a fusion element 60, to replace a removed disc. The operation takes place as previously described. The limited movement ability of the vertebrae 58, 59 to one another leads to increased cyclic part load, whereby the bone growth is stimulated and progresses faster ossification.

p0030In the <figref idrefs="f0004">Fig. 6a</figref> fourth embodiment shown the bone anchoring element 61 differs from that in <figref idrefs="f0003">Fig. 4</figref> third embodiment shown by the formation of the screw member. All other components are identical to the third embodiment.

p0031When the screw member according to the fourth embodiment of the bone screw portion 63, the elastic portion 64 and the head 65 are formed as separate parts. The elastic portion 64 consists of a cylindrical tube having a coaxial through bore 66 and a spiral extending in the direction of the cylinder axis recess 67 in the wall which opens out in radial direction into the bore 66th Characterized a coil spring as in the previous embodiments is formed. Adjacent to its respective free end, the elastic portion 64 a over a predetermined length extending internal thread 68 at both ends. The bone screw portion 63 has on its side opposite to the end to be screwed tip on a cylindrical extension 69 with an external thread which cooperates with the internal thread 68 of the elastic portion 64th

p0032The head 65 has on its side opposite to the flattened end side of a cylindrical projection 70 with an external thread which cooperates with the internal thread 68 of the elastic portion, on.

p0033In operation the screw element is assembled by screwing together of the bone screw portion 63, the elastic portion 64 and the head 65 and then introduced into the receiving part in contrast to the previous embodiment first. The further operation is carried out as in the previous embodiment.

p0034The bone anchoring element according to this embodiment has the advantage that its production is simplified. Furthermore, it has the advantage that elastic portions 64 of different length and different stiffness can be kept and be selected depending on the application prior to use and predetermined with heads of a size and threaded shanks length can be assembled to form a screw member.

p0035<figref idrefs="f0004">Fig. 6b</figref> shows a development of the flexible section 64 of <figref idrefs="f0004">Fig. 6a</figref>, The elastic portion 640 in accordance with<figref idrefs="f0004">Fig. 6b</figref> includes a core 641 in its interior. The core 641 is at its ends 642 cylindrically formed with a diameter which is so dimensioned that the core is insertable into the hollow space of the elastic portion 640th The cylindrical portions 642 and the elastic portion 640 have transverse bores, are pushed into the pins 643 for fixing the core. Between the ends of the cylindrical core has a portion 644 having a substantially rectangular cross-section, in particular from<figref idrefs="f0004">Fig. 6c</figref> is visible. In a modification, the core has a different cross section, such as oval or asymmetric. The core permits the Einstelluhg the flexural rigidity and / or torsional rigidity of the elastic portion. The rigidity of the elastic portion to bending in a particular direction depends on the orientation of the core within the elastic portion. Preferably, the core is formed of a material having a lower stiffness compared with the material of the elastic portion. The mounting shown of the core is shown only by way of example.

p0036In a further, in the <figref idrefs="f0005">Fig. 7a and 7b</figref> illustrated embodiment, the bone anchoring element is designed as Schanz screw 81st The Schanz screw 81 has a first threaded section 82 and an adjoining cylindrical threadless shank portion 83 without head, extending from the free end to the threaded portion coaxial blind bore 84 through which extends. In a predetermined area 85 of the cylindrical portion 83 is a spiral in the direction of the coil axis over a predetermined length extending recess 86 is provided in the wall, an elastic portion is formed in the form of a helical spring through as in the previously described embodiments. Further, the cylindrical shaft portion 83 has circumferentially spaced at a predetermined distance circular notches 87th Adjacent to its free end, the cylindrical shaft portion on a hexagon-shaped recess 88 or any other recess for engagement with a screwing-in tool.

p0037In operation, the Schanz screw 81 is used in particular with external fixator with conventional Schanz screws and conventional fasteners and fixation rods. The Schanz screw 81 is screwed into the bone fragment to be fixed, so that the elastic portion 85 optionally protrude above the bone surface through the skin surface. Depending on the rigidity of the elastic portion is limited movement allows at a predetermined location.

p0038<figref idrefs="f0006">Fig. 8</figref> shows a development of Schanz screw after <figref idrefs="f0005">Fig. 7a and 7b</figref> in the application in an external fixator for stabilizing bones parts 90, 91 of a fractured long bone. The Schanz screw 92 has for this purpose as the polyaxial screw 41 of a third embodiment (not shown) spherical segment-shaped head, which is held in a receiving part 93rd The bone portions 90, 91 are on the Schanz screw 92 and conventional polyaxial bone screws 94, which are connected via a connecting element 95 with rods 100, 101, stabilized.

p0039Modifications of the embodiments described above are possible. In particular, elements of one embodiment may be combined with the elements of another embodiment. The multi-part design of the screw member in the embodiment of<figref idrefs="f0004">Fig. 6a</figref> is also in the monoaxial bone screw according to the <figref idrefs="f0002">FIGS. 3a to 3c</figref> possible, in which case the receiving part in the elastic section can be screwed. Further, the Schanz screw according to<figref idrefs="f0005">Fig. 7a and 7b</figref> be a multipart design. In a further modification of the bone thread portion and the elastic portion are integrally connected, and only the head or the receiving part screwed.

p0040In another embodiment, a separate cylindrical core is provided, which is inserted into the bore which passes through the elastic portion. Thus, the rigidity of the elastic portion can be also set. In a further embodiment, the elastic section has a different diameter than the bone thread section. With a larger diameter increased rigidity can thus be achieved. The core may also have other than a cylindrical shape, for example it may have a portion of rectangular cross-section as shown in<figref idrefs="f0004">Fig. 6b and 6c</figref> is shown having.

p0041The invention is not limited to the specifically described embodiments of the monoaxial and polyaxial bone screw. It may be possible, other configurations thereof, in particular the receiving parts and the fixing. It is crucial that the shaft has an elastic portion. An embodiment not according to the invention is applicable to hooks.

p0042In a further embodiment the elastic portion is provided with a hose-like coating, which prevents tissue ingrowth material or vessels.

p0043In all the aforementioned embodiments, there is the advantage that the limited possibility of movement of the bone parts or vertebrae resulting in increased cyclic part load, which stimulates bone growth.

p0044An embodiment of a stabilization device comprising at least two bone anchoring elements which are each connected with an external device such as a plate or rod. The connection between the bone anchoring elements and the plate or rod is preferably solid. The event of a movement of the bones or bone parts on the external device acting on the head of the bone anchoring element forces are decoupled by the elastic shank of the anchor, so that the risk of becoming loose of the anchoring in the bone is reduced. The stabilization device is particularly applicable to the stabilization of the spine.

p0045As materials for the bone anchoring element or its components body-friendly materials can be used. For example, body-friendly metals such as titanium, or a patient-friendly thermoplastic used. The use of a shape memory alloy with known super-elastic properties, such as Nitinol, is possible. Here, the bone anchoring element may be formed as a whole from such an alloy, including a core in the elastic portion, or only the core or the elastic portion can be formed therefrom. The use of different materials for different components of the anchoring element is also conceivable.