DE20007908U1 - Contoured bone plate - Google Patents

Description

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Contoured bone plate Field of application of the invention

The present invention relates to a bone plate that can be attached using bone screws and is used in particular as a reconstruction system for the maxillofacial area of the human skull, e.g. for the lower jaw. In a special embodiment, the bone plate and screws can be interlocked. Until further notice, the terms "plate", "screw" and "plate-screw connection" will be used for short. Such plates are used, for example, to reinforce weakened, atrophied bone structures. In the case of large continuity defects, the plates must provide stability over longer periods of time and absorb the loads that the missing bone would have to bear. In their simplest form, plates of this type consist of a straight, elongated branch with a large number of plate members, each of which has a screw hole to accommodate a screw. Bridging plates have an angled side branch on the left or right. In the case of total bridging plates, angled side branches extend from the elongated branch on both sides. The plates can be cut to the required length by removing excess plate segments and bent to adapt to the patient's anatomy.

The following requirements are placed on such bone plates and the plate-screw connections constructed with them:

- high strength and stability of the bone plate;

- high rigidity of the plate-screw connection;

- Flexibility of the plate in all planes with little loss of strength both in and around the plane of the plate, including torsion;

- Possibility of attaching different types of biological tissue to the plate;

- lowest possible surface pressure of the plate on the periosteum;

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- often additional securing (so-called locking) of the screws penetrating the plate in order to more reliably prevent the screws from loosening themselves; and

- advantageous applicability by the surgeon.

State of the art

Plates of the relevant type as straight, elongated branches, as bridging plates with side branches angled to the right or left of the main branch or as total bridging plates with side branches angled to both sides of the main branch (double angled) have been described in the literature for some time, by many suppliers on the market and in widespread clinical use. Examples of this are contained in the company documents.

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by LEIBINGER , Freiburg / Germany, entitled "Titanium Locking Screw Mandibular Reconstruction Plating System", 90-01680,10/95; ®
and "MARX - titanium mandibular bridging plate system", 90-01637, 05/94. Some products have a reinforced angle segment at the transition between the main branch and the angled side branches, see.

the SYNTHES company publications "The Locking Reconstruction Plate, Technique Guide, Maxillofacial"; and "COMPACT 2,4 Recon", 3/96.

When applied, these plates must be bent to a relatively high degree to fit the patient's anatomy. In the patient, the plates are basically exposed to constantly changing bending stresses due to his activities, e.g. through swallowing and chewing. Depending on the intensity of the bending processes, the surgical bending during insertion reduces the long-term fatigue strength of the plates, which are usually made of titanium, and thus reduces their resistance to fracture and service life in the patient. This is a key aspect of the imperfection of the bone plates of this type known to date.

Another problem is the locking between the inserted plate and the fixing screws. In order to keep the surface pressure of the plate on the periosteum low, US 5,810,823 suggests

Insertable or fixed spacers with an internal thread are placed on the underside of the plate. These spacers rest on the bone and are penetrated by the threaded shafts of the screws. Variable positionable spacers also allow the screws to be aligned in a way that deviates from the vertical. Although this design prevents the plate from being pressed onto the periosteum over a large area, increased pressure is created at the points where the spacers are placed. The relatively small insertable spacers complicate the surgical procedure. Regardless of whether the spacers are fixed or insertable, they do not provide any improved protection against accidental loosening of the screws.

WO 96/39975 describes a blocked plate-screw connection where countersunk locking elements are provided on the underside of the plate in the area of the screw holes. The threadless neck section of the screw shaft, which has a smaller diameter than the threaded part, protrudes through the individual locking element. First, the threaded part can be pushed through the locking element and screwed into the bone, with the screw head coming to rest in a countersink on the top of the plate. After heat treatment, the locking element shrinks so that the plate is kept at a distance from the periosteum and the screw is secured against unscrewing. This system requires special locking elements and equipment and is therefore complex to handle and manufacture.

In the company brochure "SYNTHES® - THORP reconstruction set" from STRATEC Medical, Waidenburg / Switzerland, a plate system is disclosed in which anchoring screws are first screwed into the bone through the screw holes in the plate. An expansion screw is screwed into the slotted head of the anchoring screw, which sits in the screw hole. This presses the head of the anchoring screw against the wall of the screw hole in the plate. This secures the anchoring screw against unscrewing and the plate is kept at a distance from the periosteum. Bending inserts are provided as insertable cores so that the screw holes in the plate do not narrow when bent. The higher number of parts

len requires more time and instrumentation during the operation and is overall more difficult.

A further development of a blockable plate-screw connection is known from US 5,709,686. The bone plate has several holes in the direction of the longitudinal axis of the plate for the passage of screws. The screw hole is oval, with its main axis lying in the longitudinal axis of the plate. On the top of the plate, the screw hole is surrounded by a spherical countersink. A partial internal thread is present over the shorter secondary axis of the screw hole, the threads of which run out towards the main axis of the oval screw hole. The internal thread is used to accommodate a threaded section on the screw under its head, which is wider in diameter than the threaded shaft of the screw. The screw hole opens towards the bottom of the plate in the area of the two ends of the main axis, i.e. outside the internal thread on the longitudinal axis of the plate.

When the plate is applied clinically, the threaded shaft of the screw extends into the bone, while the threaded part engages with the internal thread in the screw hole. The plate is thus supported and is not pressed against the periosteum by the tensile force of the screw. The screw is secured against accidental unscrewing by the threaded connection between the internal thread in the screw hole and the threaded part of the screw. The plate and screw are blocked. The countersink around the screw hole allows compression to be created between bone compartments when a screw without a threaded part is inserted eccentrically. Screws without a threaded part for blocking can also be screwed in deviating from the vertical. There is greater freedom for this in the direction of the plate's long axis due to the oval hole shape and the only partial internal thread in the screw hole.

With the plate-screw connection according to US 5,709,686, a perfect blocking and additional securing of the screws is possible, but there remain significant disadvantages, such as:

- To prevent deformation of the internal thread in the screw holes when bending the plate, bending inserts must still be used.

- Even with low torques when screwing in the screw, the internal thread in the screw hole can be overtightened. Such critical torques can easily be applied using standard screwdrivers. A damaged plate is unusable; a new plate and possibly a new screw must be used.

- In a blocked plate-screw connection, the screwed-in screws can only be positioned vertically, which requires the use of drill guides that are positioned exactly vertically.

- Due to the overall geometry of the plate holes, machining must be done from two directions, which makes plate production more complex.

Object of the invention

In view of the imperfections of the previously known bone plates, the invention is based on the object of proposing a bone plate of the relevant type, where the number and intensity of the bends required are significantly reduced during surgical adaptation to the patient's anatomy. This is primarily to increase the long-term bending fatigue strength of the plates and, as a synergistic effect, to reduce the surgical effort for the surgeon.

In addition, the invention has the task of proposing an improved blockable plate-screw connection for the plates that need to be improved in terms of adaptation. In this case, it is particularly important to do without third parts, such as inserts or expansion screws for blocking and bending inserts. The connections should be less sensitive to overtightening and angular misalignment of the screws in relation to the vertical and the plate's longitudinal axis. It is desirable to achieve a high unscrewing torque for the screws within the plate-screw connection in order to more strictly prevent the screws from loosening themselves. The clinical application should be as simple as possible for the surgeon. The options for osteosynthetic

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to induce bone compression and to use the connection with conventional screws without blocking. Finally, the parts of the connection must be able to be mass-produced efficiently.

Overview of the invention

To solve the problem, a contoured bone plate is proposed for the osteosynthesis of fractures in curved or arched bones, e.g. a lower jaw, which extends in a plate plane and whose plate longitudinal axis is at least essentially circular. The circular longitudinal axis of the plate between the central axes of the webs and the central axis of the adjacent screw hole results in an offset of e.g. 1° to 10°, preferably 2.5°. The plate has several plate elements which are connected to one another by webs. At least some plate elements, preferably each plate element, have a screw hole.

The bone plate consists of at least one circular arc-shaped main segment. For special tasks, the main segment is provided with a lateral segment attached to it on one or both sides, which lies in the plane of the plate and extends straight or curved. Some screw holes on the bone plate may not be designed for blocking, but as cylindrical standard screw holes or as direction-oriented compression holes. Preferably, the circular arc-shaped bone plate is given its shape without deformation, i.e. the plate is worked out of the material during production, so that the plates manufactured in this way reach the surgeon without an initial weakening due to bending stresses.

The inventive further development of the locking is based on a bone plate and screws with a locking thread according to the type from US 5,709,686. The screw holes in the plate elements are surrounded by a spherical countersink on the top of the plate. Internally, there is an engagement contour in the screw hole, which consists of contour valleys that partially run horizontally and radially around the wall of the screw hole and adjacent remaining contour peaks. The diameter

the countersink for receiving the screw head is larger than the clear width of the engagement contour. This tapers off towards the edges of the engagement contour, so that smooth, uncontoured wall areas remain in the screw hole. In relation to the threaded shaft of the screw, the screw hole is an elongated hole. The engagement contour is preferably produced by milling and has, for example, a pointed, round, trapezoidal or sawtooth shape.

The screw suitable for locking has a locking thread below the screw head which has a diameter that is the same or larger than the thread on the threaded shaft intended for engagement with the bone. When the plate is fixed to the bone, the screw's threaded shaft projects through the screw hole and the thread of the threaded shaft turns into the bone. In the final phase of screwing in the screw, the locking thread below the screw head reaches the engagement contour in the screw hole. Since the locking thread, with its helical course and its pitch, is not complementary in shape to the engagement contour, both are deformed and the connection is therefore more resistant to loosening. A locking of reduced strength can still be achieved if the screw has a continuous thread whose uppermost threads clamp under the engagement contour.

The bone plate according to the invention with a circular-arc-shaped longitudinal axis - at least in the main segment, if the bone plate is provided with a lateral segment attached to it on one or both sides - offers the following advantages:

- After bending the bars, from the plane of the plate, almost across the surface, you often achieve a basically perfect fit between the bone plate and the bone. This results in an ideal adaptation of the bone plate in its length and inclination across the width of the plate.

- There is no need for additional bending in the plane of the panel, i.e. twisting or bending over the edge.

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- Due to the circular arc-shaped initial geometry, the bone plate takes on the inclination of a circular section of the lateral surface of a cone.

- This reduces the surgical effort required to adjust the plate and its loss of strength due to less deformation.

The improved blocking also provides the following advantages:

- In clinical use, the plate-screw connection is efficient because no third parts are needed for locking. Even when the plate is bent, no bending inserts are needed. Even if there is a deformation within the screw hole, the functionality of the locking is not impaired.

- When locking, no forces are exerted on the periosteum, so it is protected. The plate can be positioned at a distance from the bone, similar to a fixator.

- The internal engagement contour in the screw hole also allows a slight angular offset of the screwed-in screw in relation to the vertical and the longitudinal axis of the plate. This is without any loss of function of the locking mechanism.

- When compression is generated, the screws are not subjected to tensile stress because the locking of the screw in the plate does not allow any axial movement between the plate and the bone.

- The screwed-in screws are better protected against accidental loosening because a high unscrewing torque must be applied. This is due to the deformations during locking on the internal engagement contour at the screw hole and on the screw thread involved.

- The risk of overtightening and thus damaging the plate is reduced. With conventional plates, the screws overtighten even at lower screwing torques, which can be easily applied with standard screwdrivers.

- The engagement contour arranged internally in the screw holes causes a significantly lower notch effect than conventional internal threads, which reduces the risk of the plate breaking.

- The plate can be fitted with different screws, namely those that create a locking mechanism and those without locking mechanisms. In the latter case, the screw holes function as neutral

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Compression holes to accommodate the screw head. This is used, for example, when applying small screws to fix a bone compartment. The screw can also be placed at an angle.
- Since the complete geometry of the screw holes in the plate can be machined from one side, there is no need for reclamping during machining, resulting in a cost-effective production process that can also be carried out precisely with reasonable effort.

Brief description of the attached drawings
Show it:

Figure 1A - a bone plate with a circular longitudinal axis Z and 16 screw holes;

Figure 1B - an enlarged view of three plate members according to Figure

1A;

Figure 1C - a schematic representation of a human lower jaw with the adapting circular-arc-shaped bone plate according to Figure 1A and a straight bone plate drifting away from the lower jaw according to Figure 5A;

Figure 2 - a bone plate with a circular plate longitudinal axis Z and 8 screw holes of different types;

Figure 3A - a bone plate for the left jaw branch with a circular arc-shaped main segment according to Figure 1A, a straight, ascending lateral segment and reinforced angle area with

an additional screw hole;

Figure 3B - the bone plate according to Figure 3A with curved lateral segment and reinforced angle area without additional screw hole;

Figure 3C - the bone plate according to Figure 3B with additional screw hole in the reinforced angle area;

Figure 3D - the bone plate according to Figure 3A without additional screw hole in the reinforced angle area;

Figure 3E - the bone plate according to Figure 3A with reduced distance between the screw holes in the lateral segment;

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Figure 4A - a bone plate screwed onto a fractured mandible;

Figure 4B - a bone plate screwed onto the lower jaw to bridge a continuity defect;

Figure 5A - a straight bone plate with uniformly aligned screw holes in top view;

Figure 5B - the representation according to Figure 5A with differently aligned

screw holes;

Figure 5C - the bone plate according to Figure 5A in section on the line AA with the engagement contour of the first embodiment, principle sketch;

Figure 5D - the representation according to Figure 5C with the engagement contour, real contour;

Figure 5E - the bone plate according to Figure 5A in section on the line B-B;

Figure 6A - a two-start bone screw with locking thread in the

neck area;

Figure 6B - the double-start bone screw according to Figure 6A with locking thread in the neck area and thicker screw shaft;
Figure 6C - a bone screw with locking thread in the neck area

and self-drilling and self-tapping thread on the

screw shaft;
Figure 6D - the bone screw according to Figure 6C with locking thread in the neck area and self-drilling and self-tapping thread on the screw shaft and additional cutting groove;

Figure 6E - a single-start self-tapping bone screw with pointed

thread flanks;
Figure 6F - a two-start self-tapping bone screw with pointed thread flanks and thicker screw shaft;
Figure 6G - the double-start self-tapping bone screw according to

Figure 6F with round thread in the neck area;
Figure 6H - the single-start self-tapping bone screw according to Figure

6E with pointed thread flanks, larger pitch and larger

Outside diameter of the screw shaft;

the bone screw is screwed vertically into a screw hole in Figure 5E as shown in Figure 6A;

the view according to Figure 7A with the bone screw screwed in at an angle;

Bone screws according to Figure 6A are screwed into screw holes with engagement contours of the first embodiment according to Figure 5E of a curved bone plate;
Bone screws are screwed into a curved and twisted bone plate as shown in Figure 5A;

the bone screw according to Figure 6A with locking thread, deformed after locking;

a screw hole with an engagement contour of the first embodiment from Figure 5E, deformed after blocking;

a screw hole with an engagement contour of a second embodiment in plan view;

the representation according to Figure 9A as a section on the line CC;
the representation according to Figure 9A as a section on the line DD;
the bone screw is screwed into the screw hole in Figure 9B in accordance with Figure 6E;

Figure 10A - a screw hole with an engagement contour of a third embodiment in plan view;
Figure 10B - the representation according to Figure 10A as a section on the line EE;

Figure 10C - Insert the bone screw into the screw hole according to Figure 6F

Figure 10B screwed in blocked;

Figure 11A - a screw hole with an engagement contour of a fourth embodiment in plan view;

Figure 11B - the representation according to Figure 11A as a section on the line FF;
Figure 11C - the bone screw according to Figure 6G is screwed into the screw hole in Figure 11B;

Figure 12A - a screw hole with an engagement contour of a fifth embodiment in plan view;

figure 7A figure 7B 5 figure 7C figure 7D 10 figure 8A figure 8B 15 figure 9A figure 9B figure 9C 20 figure 9D

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Figure 12β - the representation according to Figure 12A as a section on the line GG;
Figure 12C - the bone screw according to Figure 6H is screwed into the screw hole in Figure 12B;

Figure 13A-the situation before closing a fracture using compression

sion osteosynthesis;

Figure 13B- the situation during closure of the fracture;
Figure 13C - the situation after closure of the fracture;

Figure 14A- a bone screw without locking thread;

Figure 14B - the bone screw without locking thread according to Figure

14A with thicker screw shaft;
Figure 14C- Insert the bone screw according to Figure 14A into a screw hole in

Figure 5E unblocked and screwed vertically;

Figure 14D - the representation according to Figure 14C with unblocked and obliquely screwed bone screw;

Figure 14E - the situation in a lag screw osteosynthesis with a bone screw without locking thread according to Figure 14A screwed unblocked into a screw hole with engagement contours of the first embodiment according to Figure 5E;

Figure 15A- the bone screw according to Figure 6E into a screw hole in

Figure 5C unblocked and screwed vertically; and

Figure 15B - the representation according to Figure 15A with unblocked and obliquely screwed bone screw.

Examples of implementation

With reference to the accompanying drawings, the following is a detailed description of embodiments of the osteosynthetic bone plate according to the invention. A special variant of the bone plate with lockable bone screws can be found in the second part of the description, starting with Figure 4A.

The following definition applies to the entire further description. If reference numbers are included in a figure for the purpose of graphic clarity, but in the

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If a component is not explained in the directly associated description text, reference is made to its mention in the preceding or following figure descriptions. In the interests of clarity, repeated designations of components in other figures are generally omitted, provided that it is clearly evident from the drawing that these are "recurring" components.

Figures 1A , 1B and 2

The bone plate Y has a circular-arc-shaped longitudinal plate axis Z with a large number of plate members 2 that are connected to one another by webs 3. In the unbent initial state, the plate 1' extends in the plate plane Y. A screw hole 4 is provided in each of the plate members 2. Depending on requirements, all or individual screw holes 4 can be designed as cylindrical standard screw holes 40 or as known direction-oriented compression holes 41. Alternatively, all or individual screw holes 4 can be provided with a special engagement contour 8 for blocking, which will be described later.

The combination pattern of screw holes 4 shown in Figure 2 is merely intended to illustrate the design variety, without being relevant in practice. The outer screw holes 4 have the shape of cylindrical standard screw holes 40, while the three screw holes 4 in front are compression holes 41 acting in different directions or have the engagement contour 8 intended for blocking. Depending on the intended use, the plate 1 ¹ is manufactured in the required length or brought to the desired length by cutting off plate members 2 and webs 3. The number, positioning, spacing and type of screw holes 4 can also be selected depending on the intended use. The circular longitudinal axis Z of the plate results in an offset β between the central axes Zi of the webs 3 and the central axis Z ₂ of the adjacent screw hole 4 with, for example, 1° < β > 10° and preferably β = 2.5°. Between two adjacent screw holes 4 there is a displacement of 2ß with e.g. 2° < β > 20° and preferably β = 5°. Preferably

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The circular plate 1' takes its shape without deformation, but is worked out of the material during production.

Figure 1C

This figure illustrates, as a principle representation, the direction of extension and the geometric adaptation of a plate 1 ¹ contoured according to the invention with a circular-arc-shaped plate longitudinal axis Z or a plate 1 with a conventionally straight plate longitudinal axis Z, wherein both plates 1', 1 are attached to a human lower jaw and, in the fully bent state, extend between the ascending jaw branches, enclosing the lower jaw.

The straight plate 1 attached to the left jaw branch drifts away from the lower jaw after bending in the bars 3 out of the plate plane Y - almost over the surface. In order for this plate 1 to encompass the lower jaw, additional bending must be carried out in the plate plane Y in each bar 3 - almost over the edge. Only then does the plate 1 follow the course of the lower jaw. Since the lower jaw does not have any vertical surfaces in principle, but rather extends apically, subsequent bending or twisting of the plate elements 2 is necessary in order to ensure that the plate 1 fits properly against the jawbone. The greater bending of the plate 1 required to adapt to the patient's anatomy reduces the fatigue strength and thus the service life of the plate 1 inserted into the patient, which is subjected to constantly changing bending with the patient's movements.

The inventively contoured plate Y fits much more easily against the jawbone when the plate's longitudinal axis Z is in a circular arc. The plate 1' only needs to be bent in the webs 3 out of the plate plane Y, almost across the surface, in order to bring the plate into the U-shape that encompasses the lower jaw. The bending usually takes place essentially in the area of the webs 3. The additional bending in the plate plane Y, almost across the edge, as well as the bending or twisting

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are omitted here. This means that this plate 1' is subjected to considerably less strain as a result of the adjustment, i.e. it is significantly less weakened due to the significantly reduced pre-load.

Due to the circular arc starting geometry, the plate 1', after bending out of the plate plane Y, takes on the inclination of a circular section of the surface of a cone. This means that both the essentially horizontal, U-shaped encirclement of the lower jaw in the longitudinal direction of the plate 1' and the close nestling of the plate 1' across its width to the apically protruding bone are realized. The circular arc starting geometry significantly reduces the surgical effort for the surgeon when adjusting the plate 1', the plate 1' nestles perfectly against the lower jaw and the loss of strength is reduced as a result of less deformation - only out of the plate plane Y. The positive effects occur essentially when the circular arc plate 1' is manufactured without forming, so that the plates 1' reach the surgeon in the arc-shaped geometry but without prior bending.

Figures 3A to 3E

In this series of figures, various modified plates 1' with a circular-arc-shaped longitudinal plate axis Z are shown. All plates 1' have a circular-arc-shaped main segment 10', to which a lateral segment 11' is attached on the right or left or on both sides. The main segment 10' is here, for example, uniformly provided with 16 screw holes 4 suitable for blocking. In the transition between the main segment 10' and the lateral segment 11' there is an angle segment 12', which is preferably reinforced in width in relation to the webs 3. The angle segment 12' can be hole-free (see Figures 3B and 3D) or have at least one screw hole 4 (see Figures 3A, 3C and 3E). The lateral segment 11" can extend in the plate plane Y straight (see Figures 3A, 13D and 3E) or curved (see Figures 3B and 3C). The modification according to Figure 3E shows a plate 1' with a circular arc-shaped main segment 10' and a straight lateral segment 11' with a reduced distance between the 5 screw holes 4 shown, whereby the

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the angle segment 12' lying therebetween has a screw hole 4. If a curved lateral segment 11' is provided on one or both sides of the circular arc-shaped main segment 10', the latter can have a different bending radius than the main segment 10'.

The further sequence of figures 4A to 15B primarily serves to explain the special, inventive engagement contour 8 for blocking, which is optionally present in the screw holes 4.

Figures 4A and 4B

The pair of figures shows two typical applications of the bone plate 1 that can be locked in place according to the invention, which together with bone screws 9 creates a plate-screw connection. The plate 1 is particularly suitable for the osteosynthesis of a mandible that has fractured into bone compartments (see Figure 4A). Another main application is bridging a continuity defect, i.e. if a piece of bone is missing, the plate 1 must permanently absorb the load and create stability in the mandible (see Figure 4B). Both the pressing of the plate 1 onto the periosteum and the accidental loosening of the screwed-in screws must be avoided, so a solid locking is particularly important here.

Figures 5A to 5E

To explain the function of the interlocking, the simplest form of the plate 1 is initially assumed as an elongated, unbranched branch through which the longitudinal axis Z of the plate extends in a straight line. The plate 1 is made up of a large number of plate elements 2, each of which is connected to one another by webs 3. The webs 3 form tapered transitions between adjacent plate elements. At least in some plate elements 2, but preferably in every plate element, there is a screw hole 4. On the upper side 5 of the plate, the screw holes 4 emerging on the lower side 6 of the plate are surrounded by a spherical countersink 7. Inside the screw hole 4 is the

-17-Intervention contour
8th.

The engagement contour 8 only resembles a partial thread at first glance; in fact, the engagement contour 8 consists of contour valleys 80 extending along the wall of the screw hole 4 parallel to the plate plane Y and alternating adjacent contour peaks 81. The contour valleys 80 and peaks 81 run partially around the screw hole 4, i.e. to the edges of the engagement contour 8, so that uncontoured wall areas 82 remain in the screw hole 4. The countersink 7 has a depth to accommodate the screw heads in a countersunk manner. The diameter of the countersink 7 is larger than the clear width of the engagement contour 8. The distance between opposite contour valleys 80 and contour peaks 81 is smaller than the distance between the opposite uncontoured wall areas 82, so that the exit 83 of the screw hole 4 on the underside 6 of the plate is in the shape of an elongated hole. The contour valleys 80 and contour peaks 81 forming an engagement contour 8 can be arranged essentially parallel to the longitudinal axis Z of the plate or at an angle to it, so that the longitudinal extension of the outlet 83 lies on the longitudinal axis Z of the plate (see Figure 5A) or assumes different angles to the longitudinal axis Z of the plate (see Figure 5B). The uncontoured wall areas 82 are distributed accordingly along the longitudinal axis Z of the plate or offset from it. In the first embodiment of the engagement contour 8 here, the contour valleys 80 and contour peaks 81 form trapezoidal passages.

Figure 6A

The bone screw 9 has the screw head 90 at the top, which is dome-shaped at the bottom, complementary to the countersink 7 in the plate 1. The screw head 90 has a recess 91, e.g. a Phillips, which can be accessed from above with a screwing tool. Below the screw head 90 there is a locking thread 92, here designed as a trapezoidal thread - corresponding to the engagement contour 8. The two-start bone thread 94 is arranged along the screw shaft 93. The bone thread 94 has an outer diameter of 2.5 mm, for example, while the outer diameter of the locking thread 92 is significantly larger and is 3.2 mm, for example.

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Figure6B

If the diameter of e.g. 2.5 mm on the bone thread 94 is too small according to the previous screw 9 because the screw hole in the bone was drilled too large or the strength is insufficient, a modified screw 9 with a larger diameter can be used on the bone thread 94, which is e.g. 3.2 mm. Even with this diameter, the bone thread 94 can be moved effortlessly through the engagement contour 8 in the plate 1. The wide trapezoidal flanks of the locking thread 92, on the other hand, lead to a locking with the engagement contour 8.

Figures 6C and 6D

For a blockable plate-screw connection, the self-drilling screw 9 shown can alternatively be used, which also has a trapezoidal locking thread 92 below the screw head 90, from which the bone thread 94 extends. For example, the bone thread 94 has a maximum external diameter of 2.5 mm and the locking thread 92 has an external diameter of 3.2 mm. The screw 9 according to Figure 6D is additionally provided with a cutting groove 96 on the shaft tip 95.

Figures 6E, 6F and 6H

These screws 9 have a uniform thread with pointed thread flanks that runs throughout the screw shaft 93 and is used with the appropriately contoured engagement contours 8 in the plates 1 in the upper part as a locking thread 92 and in the lower part as a bone thread 94. The screws 9 according to Figures 6E and 6H are single-threaded, the screw 9 in Figure 6F is double-threaded.

Figure 6G

Shown here is a two-start screw 9 with round thread flanks on the locking thread 92 and pointed thread flanks on the bone thread 94.

Figures 7A to 7D

The engagement contour 8 in the plate 1 allows the screw 9 with the locking thread 92 to be screwed into the screw hole 4 both vertically (see Figure 7A) and with an angular offset α in relation to the longitudinal axis Z of the plate (see Figure 7B). Even if the screw 9 is positioned at an angle, a fully effective locking is achieved; the locking thread 92 also moves into the engagement contour 8. The uncontoured wall areas 82 at the ends of the engagement contour 8 with the longitudinal extension of the outlet 83 offer free space for the inclined locking thread 92 to approach. Due to the inclined position of the screw 9, the screw head 90 comes to lie at an angle in the countersink 7. The practically full and seamless support of the screw head 90 in the countersink 7 results from the complementary spherical surfaces lying on top of one another.

Bending the plate 1 out of the plate plane Y - i.e. over the surface (see Figure 7C) - or in the plate plane Y - i.e. over the edge - or twisting the plate 1 (see Figure 7D) does not affect the functionality of the blocking. On the one hand, the essential change in shape of the plate 1 occurs in the area of the webs 3 and on the other hand, the engagement contour 8 does not lose its effectiveness due to a limited deformation.

Figures 8A and 8B

This shows the deformation caused by the locking between the engagement contour 8 and the locking thread 92 entering the latter, which very effectively secures the screw 9 against unwanted loosening. The engagement contour 8 and the locking thread 92 are not complementary to each other. The locking thread 92 has a thread tooth that continues in a spiral shape; with a two-start thread, this has two teeth. The engagement contour 8, on the other hand, consists of the contour valleys 80 and contour peaks 81, which do not run at a pitch angle, as with a thread as a spiral. When the locking thread 92 enters between the contour peaks 81, an intentional collision occurs and

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mutual deformation. The locking thread 92 requires helical internal threads as a supplement and the horizontally running contour peaks 81 brace themselves against the incoming locking thread 92. This opposition causes the locking thread 92 and the engagement contour 8 to deform, i.e. opposing bending edges 920,810 are created on both, which collide with one another when the screw 9 is unscrewed and thus form a considerable resistance to accidental loosening. When the screw 9 is unscrewed, a strong torque must be applied in order to achieve a partial re-deformation of the bending edges 920,810 and to overcome the increased frictional resistance. For the engagement contour 8, the preferred range of the vertical distance between repeating structures - the contour valleys 80 or the contour peaks 81 - is between 0.5 mm and 1.0 mm. The contour valleys 80 can be conveniently produced by milling so that the contour peaks 81 remain between the milled contour valleys 80.

Figures 9A to 9D

The second embodiment of the engagement contour 8 is also formed from contour valleys 80 and contour peaks 81, which are incorporated into the wall of the screw hole 4 parallel to the longitudinal axis Z of the plate and end in uncontoured wall areas 82 at their ends. The special feature here is that contour valleys 80 and contour peaks 81 are offset from one another on both sides of the longitudinal axis Z of the plate. In this way, the thread on the screw shaft 93, which is uniform in itself, acts in the upper part as a locking thread 92, the thread teeth of which engage behind the contour peaks 81, while the lower part serves as a bone thread 94 for screwing into the bone. The dome-shaped screw head 90 at the bottom sits in the spherical countersink 7.

Figures 10A to 10C

The third embodiment of the engagement contour 8 is composed of contour valleys 80 and contour peaks 81, which extend within the screw hole 4 parallel to the plate longitudinal axis Z and are saw-shaped.

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the contour valleys 80 and contour peaks 81 on both sides of the plate's longitudinal axis Z are at the same height and run out at the ends of the engagement contour 8 in uncontoured wall areas 82. The two-start screw 9 used in the plate-screw connection here also has a uniform thread on its screw shaft 93, the upper part of which engages under the contour peaks 81 as a locking thread 92 and the lower part of which is intended as a bone thread 94 for screwing into the bone. The screw head 90 is in turn embedded in the spherical countersink 7.

Figures 11A to 11C

In this fourth embodiment of the engagement contour 8, the contour valleys 80 and the contour peaks 81 have a round shape. Complementary to the round shape of the engagement contour 8, a screw 9 with a two-start locking thread 92, which is designed as a round thread, is used. The pointed, two-start bone thread 94 extends below the locking thread 92. The rounded contour valleys 80 and contour peaks 81 are located on both sides of the plate's longitudinal axis Z at the same height with uncontoured wall areas 82 at the ends of the engagement contour 8. The locking thread 92 comes into locked engagement with the contour valleys 80 and peaks 80,81. The screw head 90 finds space in the countersink 7.

Figures 12A to 12C

The special feature of the fifth embodiment of the engagement contour 8 is that the contour peaks 81 in the screw hole 4 are offset from each other in the plate plane Y by 120° and are arranged in a step-like manner in height - in relation to the plate plane Y. Contour valleys and peaks 80, 81 have a square shape. Corresponding to the engagement contour 8, the screw 9 used has a uniform thread running along its screw shaft 93, the upper part of which engages under the contour peaks 81 as a locking thread 92 and the lower part of which represents the bone thread 94. The spherical countersink 7 provides space for the screw head 90.

Fiquren 13Abis 13C

The clinical application of the plate-screw connection is shown using the example of compression osteosynthesis. In the initial situation (see Figure 13A), i.e. before the fracture is closed, eccentric holes 100 are made in the two bone compartments K1.K2 to be connected - in relation to the screw holes 4 in the plate 1. The distance between the holes 100 is greater than the distance between the screw holes 4 in the plate 1, which is positioned above the fracture site with the bone gap X. The screw holes 4 have the engagement contours 8 and the countersinks 7.

To close the fracture (see Figure 13B), screws 9 are inserted through the screw holes 4 of the plate 1 into the bores 100. Initially, with the screw heads 90 still protruding, the screws 9 are positioned eccentrically in the screw holes 4. As the screws 9 are screwed in deeper, the bone thread 94 penetrates deeper into the bores 100 and the spherical surfaces at the bottom of the screw head 90, in conjunction with the dome-shaped countersinks 7 in the screw holes 4, cause the screws 9 to be gradually centered. At the same time, the locking thread 92 of the screws 9 begins to move into the engagement contour 8. When the screws 9 are centered, they are moved towards one another, taking the bone compartments K1, K2 with them; the bone gap X begins to close.

In the final position (see Figure 13C), the screw heads 90 are maximally embedded in the countersinks 7 and the screws 9 are centered to such an extent that the bone gap X is completely closed. The bone compartments K1, K2 are now pressed against one another. The locking is established between the locking thread 92 of the screws 9 and the engagement contours 8; the screws 9 are thus secured against loosening on their own.

Figures 14A to 14D

The two screws 19 shown (see Figures 14A and 14B) have no

blocking thread 92. The screw 19 from Figure 14A, e.g. with an external thread diameter of 2.5 mm, is too weak to lock with the engagement contour 8. The screw 19 from Figure 14B, with a stronger external thread diameter of e.g. 3.0 mm, has a recess 97 below the screw head 90, so that there is no blocking thread 92 here either. These screws 19 without a blocking thread 92, i.e. only with the bone thread 94, can also be used together with the plate 1, which has engagement contours 8 in its screw holes. A blocking does not occur here, as may be desired in the specific application (see Figure 14C). The screw 19 can also be applied without any problems at an angle, together with the plate 1, without the locking thread 92 (see Figure 14D).

Figure 14E

This illustration shows a lag screw osteosynthesis with the plate 1 that can be locked according to the invention and a conventional screw 19 without locking thread 92. The screw head 90 rests at an angle in the screw hole 4 and the screw shaft 93 extends through the two bone compartments K1, K2, which are to be pressed together. In the upper bone compartment K1 there is a through hole 101 of a width that the bone thread 94 cannot engage. In the lower bone compartment K2 there is a hole 100 with a reduced diameter where the bone thread 94 engages. When the screw 19 is screwed in, the lower bone compartment K2 is pulled towards the upper bone compartment K1. The engagement contour 8 is not used here; the thin screw shaft 93 extends through the engagement contour 8 without locking.

Figures 15A and 15B

For the sake of completeness, the two figures are intended to illustrate that small fragment screws 29, e.g. with an external thread diameter of 2.0 mm, can also be inserted vertically or obliquely into the plate 1. The small screw head 90 rests deep in the screw hole 4 and the engagement contour 8 remains without function. Such small fragment screws 29 with

a screw shaft 93 protruding from the exit 83 and the bone thread 94 serve to attach smaller bone fragments.

Claims (17)

1. Contoured bone plate ( 1 ') with: a) a plurality of plate members ( 2 ) which are connected to one another by waist-shaped webs ( 3 ) and lie on a plate plane (Y) in the unbent state; b) at least in some plate members ( 2 ) one screw hole ( 4 ); and c) bone screws ( 9 ) which can be inserted through the screw holes ( 4 ) for fixing the bone plate ( 1 '), characterized in that d) the plate longitudinal axis (Z) of the bone plate ( 1 ') extending in the plate plane (Y) is at least substantially circular in shape. 2. Contoured bone plate ( 1 ') according to claim 1, characterized in that the circular-arc-shaped longitudinal plate axis (Z) between the center axes ( _Z1 ) of the webs ( 3 ) and the center axis ( _Z2 ) of the respective adjacent screw hole ( 4 ) results in an offset (β) with, for example, 1° ≤ β ≥ 10° and preferably β = 2.5°. 3. Contoured bone plate ( 1 ') according to claim 1 or 2, characterized in that a) all or individual screw holes ( 4 ) are designed as cylindrical standard screw holes ( 40 ) or as direction-oriented compression holes ( 41 ); b) alternatively, all or some of the remaining screw holes ( 4 ) have an engagement contour ( 8 ) for blocking the bone plate ( 1 ') by means of a blocking thread ( 92 ) present on the bone screw ( 9 ); and c) the individual bone screw ( 9 ) has a screw head ( 90 ) with a thicker diameter, the locking thread ( 92 ) located underneath and a bone thread ( 94 ) which extends at least partially over the screw shaft ( 93 ), which has a smaller cross-sectional diameter than the screw head ( 90 ). 4. Contoured bone plate ( 1 ') according to one of claims 1 to 3, characterized in that the bone plate ( 1 ') a) consists of a main segment ( 10 ') with a circular plate longitudinal axis (Z); and b) on one or both sides of the main segment ( 10 ') a lateral segment ( 11 ') is attached, which also extends in the plate plane (Y) and is straight or curved; c) the transition between the main segment ( 10 ') and the lateral segment ( 11 ') is formed by an angle segment ( 12 ') extending in the plate plane (Y). 5. Contoured bone plate ( 1 ') according to claim 4, characterized in that a) the angle segment ( 12 ') a) is free of holes; or b) has at least one screw hole ( 4 ) which is a cylindrical standard screw hole ( 40 ) or a direction-oriented compression hole ( 41 ) or has the engagement contour ( 8 ) for blocking; and c) is preferably reinforced with respect to the webs ( 3 ) connecting the plate members ( 2 ); and b) the lateral segment ( 11 ') is provided with screw holes ( 4 ), where alternatively: a) all or some of the remaining screw holes ( 4 ) are designed as cylindrical standard screw holes ( 40 ); or b) all or some of the remaining screw holes ( 4 ) are designed as direction-oriented compression holes ( 41 ); or c) all or some of the remaining screw holes ( 4 ) have the engagement contour ( 8 ) for blocking. 6. Contoured bone plate ( 1 ') according to one of claims 1 to 5, characterized in that the circular arc shape of the bone plate ( 1 ') is produced without deformation. 7. Contoured bone plate ( 1 ') according to one of claims 1 to 6, characterized in that a) the bone plate ( 1 ') is configured to enclose the human jawbone, in particular the lower jaw, in a substantially horizontal, U-shaped manner; b) the ends of the bone plate ( 1 '), which consists of only one main segment ( 10 ') or of one or two additional lateral segments ( 11 '), are dimensioned to overlap at least one ascending jaw branch. 8. Contoured bone plate ( 1 ', 1 ) according to claim 3 or 5, characterized in that a) the engagement contour ( 8 ) consists of contour valleys ( 80 ) and contour peaks ( 81 ) adjacent thereto, which are arranged at least substantially horizontally and partially run around the wall of the screw hole ( 4 ); b) with respect to the height relative to the plate plane (Y), there is no alignment in the sense of a thread between one contour valley ( 80 ) and the next contour valley ( 80 ) and between one contour peak ( 81 ) and the next contour peak ( 81 ). 9. Contoured bone plate ( 1 ', 1 ) according to claim 3, 5 or 8, characterized in that the screw hole ( 4 ) a) has a dome-shaped countersink ( 7 ) on the upper side of the plate ( 5 ) for partially receiving the lower part of the screw head ( 90 ) and for centering the bone screw ( 9 ); and b) on the underside of the plate ( 6 ) at its outlet ( 83 ) is shaped like an elongated hole. 10. Contoured bone plate ( 1 ', 1 ) according to claim 3, characterized in that the locking thread ( 92 ) of the bone screw ( 9 ) a) single or multiple threads; and b) is of different or the same geometry as the bone thread ( 94 ); c) the bone thread ( 94 ) can be self-drilling and/or self-tapping. 11. Contoured bone plate ( 1 ', 1 ) according to claim 8, characterized in that the contour valleys ( 80 ) and the contour peaks ( 81 ) are in the direction of the plate longitudinal axis (Z) or at an angle to it. 12. Contoured bone plate ( 1 ', 1 ) according to one of claims 3, 5 or 8, characterized in that the engagement contour ( 8 ) (a) is similar to a pointed, round, trapezoidal or saw thread; and b) is preferably produced by milling. 13. Contoured bone plate ( 1 ', 1 ) according to one of claims 3, 5, 8 or 12, characterized in that the engagement contour ( 8 ) a) runs out at the horizontal ends, whereby uncontoured wall areas ( 82 ) remain in the screw hole ( 4 ); and b) the uncontoured wall regions ( 82 ) preferably lie on the theoretical main axis of the elongated screw hole ( 4 ) in the region of the engagement contour ( 8 ). 14. Contoured bone plate ( 1 ', 1 ) according to one of claims 1, 3 or 9, characterized in that the bone screws ( 9 ) can be inserted into the screw holes ( 4 ) vertically or with an angular offset (α) in relation to the plate longitudinal axis (Z) and plate plane (Y). 15. Contoured bone plate ( 1 ', 1 ) according to claim 3, characterized in that during the blocking at the blocking thread ( 92 ) and at the engagement contour ( 8 ) bending edges ( 920 , 810 ) are formed by deformation, which bring about increased security against spontaneous loosening of the bone screw ( 9 ). 16. Contoured bone plate ( 1 ', 1 ) according to claim 8 or 11, characterized in that the vertical distance between adjacent contour valleys ( 80 ) and contour peaks ( 81 ) is preferably in the range between 0.5 mm and 1.0 mm. 17. Contoured bone plate ( 1 ', 1 ) according to one of claims 3, 5, 8, 9, 11, 12 or 13, characterized in that bone screws ( 19 , 29 ) without a locking thread ( 92 ) can also be inserted vertically or obliquely into the screw holes ( 4 ) with the engagement contour ( 8 ) for blocking.