DE102009011461B4 - bone screw - Google Patents

Abstract

Bone screw comprising a shank (2) provided with a thread (3) and having an outside diameter (D1) in the range of 0.3-1.2 mm, the thread (3) having an outside diameter (D2) of 0, 7-1.6 mm and a thread pitch (S) of 0.2-0.6 mm, and wherein the bone screw (1) is made of a steel containing 20-25% by weight of manganese, 18-25% by weight. -% chromium, at least 0.9 wt .-% nitrogen, at most 0.1 wt .-% nickel and the balance iron.

Description

The present invention relates to a bone screw, in particular for the stabilization of autogenous bone block grafts before implant insertion, z. B. in the field of oral and maxillofacial surgery.

For insertion of z. As intrabony, cylindrical implants, an implant bed must be prepared, which is congruent to the planned implant diameter and length. In the presence of insufficient bone volume in height and width reconstructive, constructive interventions are required.

During the last fifteen years various techniques and materials have been described for the reconstruction of bone defects of the alveolar crest, such as: B. autogenous, allogenic and alloplastic bone grafts. Although the development of allogeneic and alloplastic materials and the technique of guided tissue regeneration (GTR) are promising, there is still a lack of information relative to autogenous bone regarding the associated healing processes and the predictable prognosis.

The superiority of autogenous bone has been demonstrated in comparison to other bone substitute materials on a biological, immunological and even forensic basis. Due to the graft morphology, autogenous bone has additional mechanical (cortical) and osteogenic (cancellous) properties, unsurpassed by allogeneic, xenogeneic or alloplastic materials.

An important criterion for a good healing of the bone graft, z. As in implant bed preparation, is the stabilization of the graft. Usually, osteosynthesis screws and plates are used for this. Most of the screws previously used to stabilize bone block grafts in the mouth are made of titanium and have a diameter of 1.5 to 2 mm. These diameters are too large in many situations to secure small cortical bone parts / blocks (risk of poor fit and fractures). The use of titanium screws with a reduced diameter of 1 to 1.5 mm is problematic due to the material properties, since the screws have to be removed after a period of 4-6 months for implant insertion. This z. B. Difficulties arise when the titanium screws are partially osseointegrated and thus the removal of the screws is considerably more difficult. A wear of the screw head by the screwdriver and a break of the screw (for example, the screw head can break off) can occur and are among the main difficulties.

From the DE 298 09 736 U1 is a medical screw with a shaft diameter in the range between 1 and 5 mm known.

Proceeding from this, it is therefore an object of the invention to provide a bone screw (in particular for the stabilization of autogenous bone block grafts prior to implant insertion) with which the described difficulties can be eliminated as completely as possible.

The object is achieved by a bone screw comprising a threaded shank having an outer diameter in the range of 0.3-1.2 mm, the thread having an outer diameter of 0.7-1.6 mm and a thread pitch of 0.2-0.6 mm, and wherein the bone screw is made of a steel containing 20-25% by weight of manganese, 18-25% by weight of chromium, at least 0.9% by weight of nitrogen, maximum 0.1 wt .-% nickel and the balance iron.

By using the specified steel bone screw according to the invention over conventional titanium screws improved mechanical properties, so that a thread outer diameter in the range of 0.7-1.6 mm even with screw lengths of 4-28 mm is possible and at the same time the risk of Osseointegration of the screw or screw break compared to a titanium screw with the same dimensions is significantly reduced. This can be done with the bone screw z. B. narrow, thin blocks are fixed. The screw length may preferably be in the range of 4-25 mm and in particular in the range of 4-16 mm.

The steel of the bone screw may in particular contain silicon and / or copper and additionally molybdenum, wherein the molybdenum content is 0.5-2% by weight, the silicon content is at most 0.8% by weight and the copper content is at most 0 , 3 wt .-% is.

The ratio of screw length to outer thread diameter may be in the range of 2.5-40, preferably in the range of 2.5-36 and in particular in the range of 2.5-25. Also the range of 4-25 or 5-25 is favorable.

Further, the steel may contain phosphorus, carbon and / or sulfur, the corresponding proportions being at most 0.05% by weight for phosphorus, at most 0.1% by weight for carbon and at most 0.01% by weight for sulfur ,

In particular, the steel may contain 21-24 wt% manganese, 19-23 wt% chromium, at least 0.9 % By weight of nitrogen, maximum 0.05% by weight of nickel, 0.5-1.5% by weight of molybdenum, maximum of 0.75% by weight of silicon, maximum of 0.25% by weight of copper, maximum 0.03 wt .-% phosphorus, a maximum of 0.08 wt .-% carbon, at most 0.01 wt .-% sulfur and the balance iron.

With such a steel excellent mechanical properties can be achieved, which allow very small outer thread diameter and in particular also very small outer shaft diameter without z. B. a substantial risk of breakage exists.

The outer shaft diameter may in particular be in the range of 0.3-1.0 mm or in the range of 0.3-0.9 mm, preferably in the range of 0.3-0.8 mm and particularly preferably in the range of 0.4 to 0.3 mm. 0.8 mm. Furthermore, values are in the range of 0.5-0.8 mm, in the range of 0.6-0.8 mm and in particular in the range of 0.3-0.7 mm or 0.3-0.6 mm advantageous.

Due to the steel used, which may be a stainless steel in particular, screws can be made with these extremely small shank diameters, which still have the strength and stability necessary to break the screw even at screw lengths in the range of 4-28 mm to prevent. Further, a relatively large thread height (difference of thread and shank outer diameter) can be further formed, at the same time extremely small outside diameter thread, so that a very slim bone screw can be provided with a large thread height. The large thread height brings the advantage of a very good anchoring of the screwed bone screw with it.

The outer diameter of the thread of the bone screw according to the invention may be in the range of 0.3-1.3 mm, in particular in the range of 0.3-1 mm and preferably in the range of 0.3-0.5 mm or by a value from the range 0.3-0.4 mm larger than the outer diameter of the shank. This is an excellent fixation of z. B. allows a bone block graft.

The external thread diameter may preferably be in the range of 0.8-1.4 mm and in particular in the range of 1-1.2 mm.

The bone screw may have a cutting edge extending to the tip. The axial length of the cutting edge is preferably at least 1 mm long. It can be up to 2.5 mm in length, whereby it is preferably the longer, the larger the outer thread diameter. Through the cutting edge, the bone screw can be easily screwed into a non-predrilled area.

The thread pitch of the bone screw according to the invention may be in the range of 0.3-0.5 mm or 0.30-0.45 mm and preferably in the range of 0.3-0.4 mm. In particular, a slope in the range of 0.35-0.4 mm, such as. B. 0.38 mm, very beneficial. The smaller the thread pitch, the better the anchoring of the screw in the screwed state. Of course, the bone screw must be rotated more often with decreasing slope in order to achieve the same depth of engagement. With the specified thread pitch a good compromise between the achieved anchoring effect and effort to screw is achieved.

The thread of the bone screw is designed in particular as a self-tapping thread. The thread may have a lower flank angle in the range of 35-50 °, in particular 40-45 °. The upper flank angle of the thread of the bone screw can be in the range of 3-15 °, in particular 5-10 °.

The thread is preferably sharply cut or tapered to have the desired self-tapping effect. The thread crest angle can be in the range of 40-60 °, in particular in the range of 45-55 ° and particularly preferably in the range of 50-53 ° (eg 51 °).

The shaft of the bone screw is designed as a solid material shaft. In particular, the shaft is cylindrical (for example circular-cylindrical). However, it can also be conical and taper towards the screw tip.

In the case of the bone screw according to the invention, the thread preferably extends from the screw tip or slightly spaced from it (in particular to a maximum of 5 mm or preferably smaller than the thread pitch) to the head of the bone screw (here, too, a minimum distance of, for example, less than that Thread pitch possible, if this is necessary, for example, in terms of production technology). The thread pitch is preferably constant over the entire thread length.

The screw head of the screw according to the invention is preferably designed such that it has a recess into which a corresponding tool (eg screwdriver) for rotating the screw can be inserted. Of course, instead of or in addition to the recess, the outer shape of the screw head can be chosen so that with a corresponding tool a screwing in and out of the screw is possible.

With the bone screw according to the invention a bone graft (eg a bone block graft) can be fixed in or on a bone. Of course, several bone screws according to the invention can be used to fix the bone graft. The bone screw (s) can then or after a predetermined period of time, for. B. after four to six months, warm, for example, a good healing has taken place, be removed again. Thus, with these method steps, a healing of the bone graft can be realized. In particular, an implant bed that is congruent with a planned implant or the negative form of the planned implant can be prepared in this way in the bone. After removing the bone screw (s), the implant can be inserted into the implant bed in a further step. Thus, for example, for insertion of an intrabony, cylindrical implant in this way, an implant bed can be prepared, which has the negative mold of the cylindrical implant.

The bone screw according to the invention is preferably used in human medicine, but can also be used in veterinary medicine.

Prior to fixation of the bone graft, the graft retrieval step may be performed. To remove the autogenous bone graft various sites are possible, such. The skull (parietal), the tibia, the rib, the maxillary tuberosity, the palate, the tori (maxillae, mandibulae), the zygomatic arch, the iliac crest, and the lower jaw. For the latter, absorption appears to be lower than at the other sampling sites.

Bone grafts from intraoral donor sites are suitable for the reconstruction of alveolar bone defects. Due to the ease of surgical approach, this technique can be performed as a preparation or in combination with implant placement. In the lower jaw there are in particular the following withdrawal sites: the retromolar region (ramus), the chin region (symphysis), toothless sections and lingual exostoses.

The immediate proximity of the donor site and the bone bed reduce the surgical and anesthetic period; decisive for ideal conditions in outpatient implant surgery. In addition, patients complain of less inconvenience compared to extraoral donor sites.

Mandibles from the lower jaw can be removed with different instruments and in different ways. With Trephan drills and Safe Scrapers it is possible to extract small bone particles to fill cavities (sinus lift) or for augmentation under membranes. Bone blocks are suitable for the reconstruction of extensive bone defects or strongly atrophied alveolar ridges. Bone blocks can also be taken from the lower jaw.

The bone screw according to the invention, which can be designed as a self-tapping and / or self-drilling bone screw, can be used in particular in orthopedics and in oral and maxillofacial surgery. You can z. B. used as an osteosynthesis screw for the treatment of fractures or in the Dysgnathie surgery. Since the bone screw is not integrated into the bone in this case and must be removed after healing of the fractured area, the use of the specified steel is advantageous because it no osseointegration occurs in the bone screw according to the invention and thus the bone screw can be easily removed again ,

It is understood that the features mentioned above and those yet to be explained below can be used not only in the specified combinations but also in other combinations or alone, as far as they are within the scope of the present invention.

The invention will be explained in more detail for example with reference to the accompanying drawings, which also disclose characteristics essential to the invention. Show it:

1 a side view of an embodiment of the bone screw according to the invention;

2 a sectional view AA of the bone screw of 1 , and

3 an enlarged view of detail C of 2 ,

In the in the 1 and 2 illustrated embodiment, the bone screw includes 1 a shaft 2 that with a thread 3 is provided.

The shaft 2 is formed as a solid cylinder with constant outer diameter D1 and has at its one end a tip 4 and at the other end a screw head 5 on.

In the screw head 5 is a recess 6 for example, formed as a hexagon socket, into which a corresponding hex key (not shown) can be inserted to the screw 1 to turn. The recess 6 can z. B. also be designed as square socket, Phillips, etc., in which case a correspondingly adapted screwdriver for screwing in and out of the screw 1 is used.

In the area at the top 4 the screw 1 is a cutting edge 7 formed, whose axial length L1 is in the range of 1-1.5 mm. However, values up to 2.5 mm are possible.

The thread 3 extends over almost the entire shaft 2 and ends here about 0.35 mm from the top 4 (Length L2). The thread pitch S is here 0.38 mm, wherein the outer diameter D1 of the shaft 2 preferably 0.6 or 0.8 mm and the outer diameter D2 of the thread 3 preferably 1 mm (for D1 = 0.6 mm) or 1.2 mm (for D1 = 0.8 mm).

At the specified thread pitch S of 0.38 mm, the length L3 is from the top 4 the screw 1 up to the third complete thread pitch 1.5 mm. Of course, the length L3 depends on the thread pitch S and the length L2. It is quite possible that the thread 3 to the top 4 extends (in this case, the length L2 = 0 mm). Of course, other values are possible for L2, such. B. from the range 0-5 mm, in particular 0-3 mm and preferably 0-1 mm. The shorter the length L2, the faster the screw cuts 1 when used as intended in the bone.

The total length L4 of the screw 1 here is about 6 mm. However, it may be in the range of 4-28 mm or 4-25 mm, and more preferably in the range of 4-16 mm.

As from the enlarged view of detail C in 3 it can be seen, the thread has a lower edge 8th as well as an upper flank 9 on, wherein the flank angle α1 of the lower edge 8th (relative to a perpendicular to the longitudinal axis of the screw 1 ) here about 43 ° and the flank angle α2 of the upper flank 9 here is about 9 °.

The thread 3 runs to a point and is therefore a self-tapping thread 3 , The thread crest angle α3 here is about 52 °.

The bone screw according to the invention is made of a steel which is essentially nickel-free, which is understood here to mean a nickel content of at most 0.1% by weight. Furthermore, the steel contains a high nitrogen content of at least 0.9 wt .-%, a manganese content of 20-25 wt .-%, a chromium content of 18-25 wt .-%, a molybdenum content of 0.5-2 wt. %, a silicon content of less than 0.8% by weight, a copper content of less than 0.3% by weight, a carbon content of less than 0.09% by weight, a maximum phosphorus content of 0.03% by weight and a sulfur content of at most 0.01 wt .-% and the balance iron. In particular, a so-called BioDur 108 alloy marketed by Carpenter Technology Corporation of the USA may be used as the steel.

By using the specified steel, the dimensions given are for the bone screw 1 possible without the risk of breakage of the screw 1 or about twisting off the screw head 5 consists. Due to the small outer diameter of the thread 3 the bone screw 1 It is possible even in narrow areas to securely fix bone material and bone tissue preserving work, as due to the small footprint of the bone screw according to the invention 1 there is more space for bone material at the site to be treated.

Claims (15)

Bone screw, the one with a thread ( 3 ) provided shaft ( 2 ) having an outer diameter (D1) in the range of 0.3-1.2 mm, wherein the thread ( 3 ) has an outer diameter (D2) of 0.7-1.6 mm and a thread pitch (S) of 0.2-0.6 mm and wherein the bone screw ( 1 ) is made of a steel comprising 20-25 wt .-% manganese, 18-25 wt .-% chromium, at least 0.9 wt .-% nitrogen, at most 0.1 wt .-% nickel and the balance iron , Bone screw according to claim 1, wherein the steel additionally contains silicon and / or copper and molybdenum and the silicon content of at most 0.8 wt .-%, the copper content of at most 0.3 wt .-% and the molybdenum content 0 , 5-2 wt .-% is. Bone screw according to claim 1 or 2, wherein the steel additionally contains phosphorus, carbon and / or sulfur, wherein the phosphorus content is not more than 0.05 wt .-%, the carbon content of at most 0.1 wt .-% and the sulfur Content is not more than 0.01% by weight. Bone screw according to one of the preceding claims, wherein the ratio of screw length (L4) to the outer thread diameter (D2) in the range of 2.5-40. Bone screw according to one of the above claims, in which the external diameter (D2) of the thread ( 3 ) is larger by a value in the range of 0.3-0.5 mm than the outer diameter (D1) of the shaft ( 2 ). Bone screw according to one of the above claims, which is one to the tip ( 4 ) running cutting edge ( 7 ), whose axial length (L1) is at least 1 mm. Bone screw according to one of the above claims, wherein the external diameter (D1) of the shaft ( 2 ) is in the range of 0.6-0.8 mm. Bone screw according to one of the above claims, in which the external diameter (D2) of the thread ( 3 ) is in the range of 1.0-1.2 mm. Bone screw according to one of the above claims, wherein the thread pitch (S) is in the range of 0.30-0.45 mm. Bone screw according to one of the above claims, in which the thread ( 3 ) has a lower flank angle (α1) in the range of 40-45 °. Bone screw according to one of the above claims, in which the thread ( 3 ) has an upper flank angle (α2) in the range of 5-10 °. Bone screw according to one of claims 1 to 9, in which the thread ( 3 ) has a crest angle (α3) in the range of 40-60 °. Bone screw according to claim 10 or 11, wherein the thread ( 3 ) has a crest angle (α3) in the range of 45-55 °. Bone screw according to one of the above claims, in which the thread ( 3 ) is designed as a self-tapping thread. Bone screw according to one of the above claims, in which the shaft ( 2 ) is designed as a solid material.

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