Bone reconstruction screw and system for modifying a human or animal bone

Description

[0001] The invention relates to a screw intended for use as a bone grafting screw for the modification of a human or animal bone, in particular for therapeutic use in the field of plastic or dental surgery. It further relates to a threaded nut adapted to this screw and to a system for modifying a human or animal bone.

[0002] Known screws for use in bone modification are disclosed from DE69533129 T2, US2005 / 059864 A1, US2005 / 192578 A1, US2004 / 073218 A1 and DE9017101 U1.

[0003] Particularly in the fields of plastic or dental surgery, there may be a need for targeted modification of existing bone. Additive modifications, in which additional bone mass is added to the existing bone mass, can be especially desirable.

[0004] Such additive modifications, in the form of bone augmentation, can be necessary or desirable, particularly in the fields of traumatology, plastic surgery, or implantology, such as dental implantology, to provide sufficient bone volume and primary stability for secure implant placement. Bone augmentation is generally required when the amount of existing bone is insufficient for implantation or when the jawbone structure is inadequate to firmly anchor the dental implant. This can be caused, for example, by bone loss or resorption resulting from infections, tooth loss, or dental diseases, which will progress without appropriate treatment. In such cases, the remaining teeth are also at risk of serious consequences for dental health and further tooth loss.Generally, surgery involves building up missing bone or removing excess bone, if necessary or desired. Bone augmentation may be required, for example, after an accident, tumor removal, tooth loss, or in cosmetic or plastic surgery.

[0005] If bone augmentation becomes necessary, bone volume can be increased using an autologous bone graft, by harvesting bone from another area and implanting it at the recipient site. A disadvantage of this method is that it requires two surgeries, thus increasing the risk of complications. Alternatively, bone volume can be increased by introducing so-called bone substitute material. This typically involves creating implants from bone substitute materials (human or animal donor bone or synthetic materials, particularly alloplastic materials) and inserting them into the area requiring augmentation. However, allogeneic donor bone carries an immunological and / or infection risk. Furthermore, the available quantity of donor material is limited for ethical and legal reasons.The alternative interspecies transfer of biomaterials (materials of animal origin, xenogeneic bone substitute material) can present immunological problems and limitations arising from structural or anatomical differences. Typically, implanted xenogeneic bone substitute material is encased in bone regeneration or even just connective tissue for extended periods. The biological potential of such materials for bone regeneration is limited.

[0006] In comparison to autogenous bone grafts, the implantation of synthetic bone substitute materials results in replacements that, without exception, and especially in the case of ceramic implants, must be considered incomplete restorations. An ideal bone substitute does not currently exist.

[0007] In any case, and regardless of which specific bone substitute material is chosen, it is desirable to protect the particulate bone substitute or particulate bone from pressure by the surrounding tissue, such as the tongue, cheek, mucous membrane, etc. For optimal bone regeneration, space, stability, and a scaffold are necessary. Bone blocks (i.e., solid pieces) can be harvested from the angle of the jaw, the iliac crest, or from another person (allogeneic bone). These provide the necessary space and stability themselves when screwed into place. Particulate material, on the other hand, is not volume-stable but is significantly easier to integrate and is absorbed more quickly.

[0008] In addition, particularly in cases of significant bone or substance loss in the area of ​​the alveolar ridge, the further problem can arise that one has to work with comparatively thin-walled remaining structures of intact bone material, which have only comparatively low mechanical stability and load-bearing capacity and thus offer only limited mechanical support when carrying out augmentation measures.

[0009] The invention therefore aims to provide a screw particularly suitable for bone augmentation procedures, even in challenging environments, for use in modifying human or animal bone, especially for therapeutic applications in plastic or dental surgery. This screw enables reliable bone augmentation, particularly when using particulate material, in a particularly simple and biocompatible manner. Furthermore, the invention aims to provide a threaded nut particularly suitable for use in combination with the bone augmentation screw, as well as a system particularly suitable for the intended bone augmentation procedures.With regard to the screw, this problem is solved according to the invention with a screw shaft provided with a thread in a threaded area, at the first end of the shaft a substantially convex screw head is arranged, and the threaded area comprises at least two threaded segments, wherein in a first, distal threaded segment, positioned in the area of ​​the end of the screw shaft opposite the screw head, the thread is a metric ISO threaded screw with an outer diameter of less than the outer diameter, preferably less than the core diameter, of the thread in a second threaded segment, arranged on the screw shaft between the screw head and the first threaded segment. , is designed as a self-tapping thread thread segment.

[0010] The invention is based on the premise that, for a particularly well-tolerated and reliable modification of bone volume, the natural mechanisms of bone formation and growth should be utilized. The natural formation of bone, or the remodeling or healing of a bone injury, is carried out by osteoblasts. These bone-forming cells and their precursors are found in the periosteum, around the blood vessels (pericytes), in the inner periosteum (endosteum), and in the bone itself. In expanded bone tissue, for example, in the case of cleft formation resulting from bone fractures, pericytes migrate from the vessel walls of the expanded tissue, developing into osteoprogenitor cells and later into osteoblasts. Vascular anastomoses from the bone (Volkmann vessels) are connected to vessels in the stratum fibrosum of the periosteum.Osteoprogenitor cells, or osteoblasts, in the cambium of the periosteum are also involved in the synthesis of new bone. Therefore, deformations of the periosteum, especially gradual distraction from the bone surface, lead to new bone formation (bone deposition) on an existing bone surface.

[0011] By specifically utilizing these findings, the plan is now to create a space above the bone and below the periosteum (the membrane covering the bone) for bone regeneration. This space allows percytes to migrate into the bone and subsequently initiate bone formation. In the past, metal plates or meshes were used to create this space. The soft tissue was mechanically separated from the bone by the metal components, which perforated the tissue. This procedure carries a risk of infection due to the perforation, and the desired bone shape is only partially achieved.In contrast, to create the aforementioned space, the invention, in a configuration considered to be independently inventive, provides a screw with a screw head specifically designed for this purpose and with a comparatively flat shape. This screw head is inserted between the bone and periosteum and anchored in the bone to facilitate bone formation. The screw head lifts the periosteum relative to the bone and supports it against the bone. If, however, no periosteum is present, a space is similarly maintained above the bone, filled with particles (autologous, allogeneic, xenogeneic, synthetic, or a mixture thereof), covered with or without a membrane, and the tissue is sutured over it. In both cases, the aforementioned space is specifically created, and bone formation can then take place.

[0012] In an embodiment considered to be independently inventive, the screw head is suitably shaped for this application. Particular attention is preferably paid to the criteria that, when the screw is mounted or inserted into the bone, it should form a comparatively large bearing surface for the periosteum, so that excessive point loads on the periosteum and the associated cracks, perforations, or injuries to the periosteum are avoided or at least minimized. In the other case, where no periosteum is present in the area in question, the screw head, through its shape and dimensions, should maintain a particularly suitable space in which bone formation can occur.For this purpose, the screw head, with regard to the preferred thickness or diameter of the screw shank of, for example, 1.2 mm, has a correspondingly enlarged surface, preferably with an outer diameter of 3 to 7 mm, particularly preferably of about 5 mm. In this particularly preferred embodiment, which is considered to be independently inventive, the screw head thus has a bearing surface facing the periosteum that is 20 to 25 times the cross-sectional area of ​​the screw shank.

[0013] Furthermore, the contour of the screw head is advantageously chosen such that, due to its shape, the possibility or probability of injury or perforation of the periosteum or the overlying skin flap is largely minimized. For this purpose, the screw head is preferably relatively flat and without sharp edges in the bearing surface, and in a particularly preferred embodiment, substantially convex. The aim of the design is, in particular, that the screw head supports the periosteum in a tent-like manner, whereby the applied forces are harmoniously distributed over a comparatively large area.

[0014] In addition, the screw shaft should also be designed appropriately with regard to the aforementioned design objectives. On the one hand, this takes into account the fact that the screw shaft allows for stable and load-bearing anchorage of the screw in the bone material, so that the screw head can be supported by the shaft like a cup and thus serve as a bearing surface for the periosteum. To enable this, the screw shaft should be provided with a suitably selected external thread in at least one shaft segment, ensuring secure anchorage in the bone.

[0015] To further improve usability in dental therapy with this design, an additional component is provided: the screw shaft can also be equipped with a bearing surface on its otherwise free end, opposite the screw head, which can be used as a support surface, e.g., for periosteum. This design could be particularly useful when the remaining bone is relatively thin, so that penetration of the screw shaft into the bone is to be expected. To make the screw usable even in such a situation, a threaded nut should be screwable onto its free end, providing the additional bearing surface if needed.The screw described here comprises two segments on its shank, each equipped with differently designed threads. One segment serves for anchoring in the bone, while the other is threaded as a screw thread onto which a precisely matching internal thread of the nut can be screwed. To ensure precise positioning of the nut, the thread parameters, particularly the respective diameters, should be appropriately selected so that the transition from the segment intended for anchoring to the segment intended for fastening the nut provides a suitable stop surface for the nut.

[0016] Advantageous embodiments of the invention are the subject of the dependent claims.

[0017] This thread is designed as a self-tapping thread, similar to those widely used in dental implants. A bone augmentation screw designed in this manner, comprising a screw shaft with a self-tapping external thread in at least one shaft segment and a screw head designed according to the above specifications, is considered to be independently inventive.

[0018] Regarding the definition of the respective thread types, the widely accepted convention is used that a self-tapping screw cuts its own internal thread when inserted into a softer material, while a threaded screw is inserted into a pre-drilled hole and then tightened with a nut whose internal thread fits exactly onto the external thread of the screw.

[0019] The bone augmentation screw is designed in a particularly advantageous manner to facilitate its removal from the bone following successful bone formation. For this purpose, the screw is preferably made of a suitable non-osseointegrable material such as medical-grade steel. In an alternative or additional advantageous embodiment, the screw shaft, in addition to the threaded section, has a threadless shaft section, preferably located adjacent to the screw head, with a shaft diameter of at least 0.8 mm and at most 1.5 mm, preferably approximately 1.2 mm. This shaft section, designed in the manner of a "free neck," reduces the potential adhesion of the formed bone to the screw segment and thus particularly facilitates subsequent removal.

[0020] In a further advantageous embodiment, the screw thread in the second thread segment has a core diameter of at least 0.8 mm and at most 1.5 mm, preferably approximately 1.2 mm. Such a parameter selection, particularly in combination with the aforementioned parameter range for the threadless shaft section, provides a comparatively thin screw shaft overall. This allows for relatively ample space for the desired bone formation, thus promoting it, and also enables relatively easy removal of the screw from the bone after bone formation has occurred.

[0021] This choice of parameters is particularly advantageous and preferred in combination with the aforementioned choice of parameters, especially a diameter of about 5mm for the screw head, because in such a combination a comparatively thin shaft is combined with a shield-like, comparatively far-projecting screw head that offers a support surface for the periosteum 20 to 25 times the cross-sectional area of ​​the shaft.

[0022] In the first thread segment, the thread is a metric ISO thread, preferably an M-thread with an outer diameter of at least 0.8 mm and at most 1.3 mm, preferably approximately 1 mm. With regard to the threaded nut, intended in particular for use with a screw of the aforementioned type, the problem is solved by a substantially disc-shaped base body which has a central area with an internal thread bore whose parameters are adapted to the screw thread. Such a threaded nut could, if required, provide an additional support surface for the periosteum or, if necessary, for support at other suitable locations in the area to be treated.

[0023] When inserting the bone graft screw, very limited spatial flexibility and extremely confined spaces must generally be expected. This can make it difficult to mount the threaded nut, i.e., to screw its internal thread onto the first threaded segment of the screw shaft. To address this, in a particularly preferred embodiment, the threaded nut is provided with an assembly aid that facilitates screwing it onto the first threaded segment. For this purpose, an assembly aid could be molded onto the base of the threaded body via a predetermined breaking point. After screwing, this aid can be easily removed, for example, by breaking it off at the predetermined breaking point.

[0024] Alternatively or additionally, the base body of the threaded nut, with respect to its longitudinal axis, is advantageously designed with a non-circular outer contour, preferably as a polygon, and particularly preferably as a square or hexagon. This allows the use of a conventional tool, such as an open-end wrench or the like, to facilitate installation.

[0025] Regarding the system for modifying a human or animal bone, the aforementioned task is solved with a screw of the aforementioned type, and with a threaded nut of the described type adapted to the thread of the first thread segment of the screw with respect to its internal thread.

[0026] The advantages achieved with the invention lie particularly in the fact that the design of the bone augmentation screw, especially the shape of its screw head, enables the creation and artificial formation of a cavity between the periosteum and bone in a comparatively gentle manner, avoiding injuries or perforations of the periosteum, which promotes bone growth. Furthermore, due to its design with two threaded segments, the screw is suitable for various applications, namely, on the one hand, in which anchorage in the bone is achieved solely via the self-tapping thread, or on the other hand, in combination with the threaded nut, in which, in appropriate treatment situations, an additional support surface for the periosteum can be provided via the threaded nut in addition to the screw head.

[0027] An embodiment of the invention is explained in more detail with reference to a drawing. The drawing shows: FIG. 1 a bone graft screw, FIG. 2 one for use with the screw according to FIG. 1 provided threaded nut, FIG. 3 a number of each from a combination of a screw acc. FIG. 1 and a threaded nut FIG. 2 formed systems for bone regeneration in the inserted state, and FIG. 4 the threaded nut according to FIG. 2 with assembly aid.

[0028] Identical parts are marked with the same reference symbols in all figures.

[0029] The screw 1 according to FIG. 1 This device is designed for use in modifying human or animal bones, particularly for therapeutic applications in plastic or dental surgery, in a particularly gentle and patient-friendly manner. It comprises a screw shaft 2, at the first shaft end 4 of which a screw head 6 is arranged. The screw shaft 2 is provided with a thread 10 in a threaded section 8. The threaded section 8 is segmented and, in the exemplary embodiment, comprises two threaded segments 12, 14, which differ from each other in the type of their respective threads 16, 18.In the first, distal thread segment 12, positioned in the area of ​​the end 20 of the screw shaft 2 opposite the screw head 6, the thread 10 is designed as a threaded screw 16, whereas in the second thread segment 14, arranged on the screw shaft 2 between the screw head 6 and the first thread segment 12, it is designed as a self-tapping thread 18.

[0030] The screw head 6 is suitably designed and contoured for the use described below, in particular to form a comparatively large, flat, and edge- or corner-free bearing surface 22. For this purpose, the screw head 6 has a correspondingly increased outer diameter of approximately 5 mm, relative to the preferred thickness or intended diameter of the screw shank 2, which in the exemplary embodiment is 1.2 mm. Furthermore, the screw head 6 is comparatively flat and essentially convex. The bearing surface 22 it forms is thus approximately 20 to 25 times the cross-sectional area of ​​the screw shank 2.

[0031] In the exemplary embodiment, screw 1 is made of a non-osseointegrable material suitable for medical use, namely medical-grade steel. In addition to the threaded section 8, the screw shank 2 has a threadless shank section 24 located adjacent to the screw head 6, with a shank diameter of approximately 1.2 mm.

[0032] In the first thread segment 12, the thread 16 in the exemplary embodiment is designed as a metric ISO thread, in particular as an M thread, with an outside diameter of approximately 1 mm. In the second thread segment 14, i.e., the thread segment 14 between the first thread segment 12 and the screw head 6, the thread 18 is designed as a self-tapping thread 18, and it has a core diameter of approximately 1.2 mm.

[0033] In the exemplary embodiment, the screw has a total length of 11 mm; however, other total lengths such as 8 or 13 mm are also possible.

[0034] In FIG. 2 A top view shows a threaded nut 26, designed for use with the screw 1. The threaded nut 26 comprises a substantially disc-shaped base body 28, which has a threaded bore 32 in a central area. The bore 32 has an internal thread 30 whose parameters are adapted to the thread 16 of the screw 1. The threaded nut 26 can thus be easily screwed onto the first threaded segment 12. The threaded nut 26 has an outer diameter adapted to the outer diameter of the screw head 6, which in this embodiment is also 5 mm.

[0035] The combination of a screw 1 with a threaded nut 26 screwed onto it forms a system 40 for modifying a human or animal bone. Two of these systems 40 are in FIG. 3 shown in the inserted, i.e., bone-anchored, state.

[0036] The systems 40, each consisting of a screw 1 and an associated threaded nut 26, are designed for an operating principle considered to be in accordance with the invention for achieving a desired bone augmentation or bone formation. The extensive, essentially convex bearing surface 22 of the respective screw head 6 is positioned between the bone 42 and the periosteum or the periosteum 44. This is achieved by screwing the respective screw shaft 2, with its second threaded section 14 in which the thread 10 is designed as a self-tapping thread 18, into the bone 42, thus anchoring the respective screw 1 there. The screw 1 is screwed in such a way that a certain, predetermined residual distance remains between the screw head 6 and the interface of the bone 42. This ensures that the periosteum or the periosteum 44 is not damaged.A respective skin flap, supported by the respective bearing surface 22, is lifted from the actual bone 42, so that a space 46 is created between the bone 42 and the periosteum 44. Percytes can migrate into this space 46 from the vessel walls of the expanded tissue, subsequently causing new bone formation in the created space 46, or bone can grow into this space 46 from the surrounding bone.

[0037] Due to the design and shape of the respective screw head 6, namely, in particular, its relatively flat shape without sharp edges in the bearing surface 22 and its essentially convex form, the possibility or probability of injury or perforation of the periosteum or the periosteum 44 is largely minimized. The screw head 6 supports the periosteum in a tent-like manner, with the applied forces being harmoniously distributed over the comparatively large bearing surface 22.

[0038] Due to the aforementioned design of screw 1, in particular with the at least two threaded segments 12, 14, it can also be used in therapeutic situations where the available bone 42 has a comparatively small amount of substance and thickness. This aspect is in FIG. 3 also shown. The threaded nut 26 used in combination with the respective screw 1 also creates a bearing surface 48 for the periosteum or the periosteum 44 located there on the shaft end 20 opposite the screw head 6, so that the space 46 desired for bone formation can also be created on this side of the bone 42.

[0039] When inserting the respective system 40 into the bone 42, the screw 1 is first screwed into the bone 42 in the area of ​​its self-tapping thread 18, and only then is the associated threaded nut 26 screwed onto the first threaded segment 12. To accommodate this, the threaded nut 26 can be provided with an assembly aid that facilitates positioning, adjustment, and / or final assembly (i.e., screwing on) for the operator or surgeon during insertion. FIG. 4 Two embodiments of a threaded nut 26, 26' prepared in this manner are shown; of course, any number of further analogous embodiments are also conceivable.

[0040] In FIG. 4a The top view shows an embodiment of a threaded nut 26 with a base body 28 that is essentially plate-shaped or has a circular base. A mounting aid 52, in the form of a handle, lever, or actuating nipple, is integrally formed onto the base body via a predetermined breaking point 50. This mounting aid can be easily removed after the threaded nut 26 has been screwed onto the first threaded segment 12, for example, by breaking it off at the predetermined breaking point 50.

[0041] Alternatively, this shows FIG. 4b In plan view a threaded nut 26', the base body 28 of which, with respect to its longitudinal axis, is designed with a non-round outer contour, namely as a square. InIn this case, the threaded nut 26' could be provided with an associated holding or assembly tool 54, for example, one supplied with the product, to which an actuating handle or lever 56 is also integrally formed, and which can be pulled off or otherwise removed after the threaded nut 26 has been inserted. The assembly tool 54 can thus be designed as a disposable, single-use product, or alternatively as a sterilizable, reusable tool. Reference symbol list

[0042] 1 Screw 2 Screw shank 4 First shank end 6 Screw head 8 Thread area 10 Thread 12, 14 Thread segment 16, 18 Thread 20 Shank end 22 Bearing surface 24 Shank area 26, 26' Threaded nut 28 Base body 30 Internal thread 32 Threaded bore 40 System 42 Bone 44 Periosteum 46 Clearance 48 Bearing surface 50 Breakaway point 52 Mounting aid 54 Mounting tool 56 Operating handle

Claims

1. A screw (1) for use in the modification of a human or animal bone (42), in particular for therapeutic use in the field of plastic or dental surgery, with a screw shaft (2) which is provided with a thread (10) in a threaded region (8) and which has a substantially convexly-shaped screw head (6) disposed at the first shaft end (4) thereof, and the threaded region (8) thereof comprises at least two threaded segments (12, 14), characterized in that in a first, distal threaded segment (12) which is positioned in the region of the end (20) of the screw shaft (2) opposite the screw head (6), the thread (16) is constructed as an ISO metric screw thread with an outer diameter of less than the outer diameter, preferably less than the core diameter, of the thread (18) in a second threaded segment (14) disposed on the screw shaft (2) between the screw head (6) and the first threaded segment (12) and formed as a self-tapping thread (18).

2. The screw (1) as claimed in claim 1, the screw shaft (2) of which, in addition to the threaded region (8), having a thread-free shaft region (24) which is preferably disposed adjacent to the screw head (6), with a shaft diameter of at least 0.8 mm and at most 1.5 mm, preferably of approximately 1.2 mm.

3. The screw (1) as claimed in claim 1 or claim 2, the thread (18) in the second thread segment (14) of which having a core diameter of at least 0.8 mm and at most 1.5 mm, preferably of approximately 1.2 mm.

4. The screw (1) as claimed in one of claims 1 to 3, the thread (16) in the first thread segment (12) of which being constructed as an M thread (16) with an outer diameter of at least 0.8 mm and at most 1.5 mm, preferably of approximately 1 mm.

5. A system (40) for the modification of a human or animal bone (2), with a screw (1) as claimed in one of claims 1 to 4, and with a threaded nut (26, 26') which has a substantially plate-like main body (28) which is provided in a central area with a threaded hole (32) carrying an internal thread (30) which is adapted to the thread (16) of the first threaded segment (12) of the screw (1) by selection of its parameters.

6. The system (40) as claimed in claim 5, in which an installation assistance member (52) is integrally formed on the main body (28) of the threaded nut (26, 26') via a predetermined breaking point (50).

7. The system (40) as claimed in claim 5 or claim 6 in which, with respect to its longitudinal axis, the main body (28) of the threaded nut (26, 26') is formed with a non-circular outer contour, preferably constructed as a polygon, particularly preferably as a square or hexagon.