System with anterior cervical plate and screw locking element

Abstract

A system is described comprising an anterior cervical plate (10) with receiving openings (12) for bone screws and a locking mechanism for inserted bone screws that are screwed into a vertebral body and press the cervical plate against the vertebral body. The locking mechanism has a plate-like locking element that is movably mounted on the cervical plate. This locking element can be moved from a position that allows as much free access as possible to a locking position in which the screw head located in the receiving opening is covered by the locking element, thus preventing the screw from migrating out of the cervical plate.In order to offer maximum flexibility in the design of the cervical plate while maintaining high security against loosening of the bone screws and ease of use, the locking body is formed by a thin disc (16) rotatably fixed to the anterior cervical plate about an axis of rotation that is essentially perpendicular to the cervical plate (10), which has at least one locking arm (18-1, 18-2) and a support section (20) lying in the plane of the disc distributed angularly around its circumference, which snaps into a detent position by rotating the disc (16) by a predetermined rotation angle (WD), and which can be released by counter-rotation of the disc (16).

Description

Technical FieldThe present disclosure relates to an anterior cervical plate system having at least one locking element for a bone screw inserted therein. Such systems serve for mono- and multisegmental stabilization of the cervical spine.Various cervical plate systems are available on the market, which differ, among other things, with regard to their locking mechanisms for the inserted bone screws. Such plate systems are already marketed by the applicant under the name Quintex and, for example, by the companies Bricon (under the name Shark CP Pro), Zimmmer (Trinica), Medtronic (Zevo), Stryker (0zark), Biomet (Maxan), DePuy Syntheses (Skyline), GlobeMed (Assure), Novasive (C360) and Biomed (Quantum).In the cervical plate system according to U.S. Pat. No. 8 906 077 B2 or EP 2 217 163 B1, a locking element is used in conjunction with a separate fixing element.In the system according to DE 698 35 968 T2, the inserted bone screws are secured by means of a plate-like locking body, which has a locking position that can be produced by locking arms in the form of feather keys projecting axially from the locking body.The locking mechanism of the plate system according to DE 698 35 244 T2 uses plate-like locking bodies which are formed by a screw head which, distributed over the circumference, forms a plurality of locking arms which can be moved by rotating the screw over the respective heads of the bone screws.In the system according to U.S. Pat. No. 7,909,859 B2, the screws are secured by means of clamps before moving out.In the system according to U.S. Pat. No. 8,500,737 B2, either a snap ring that can be moved in a longitudinal guide or a movable plate is used for securing the inserted bone screw.The cervical plate known from the document U.S. Pat. No. 10 492 836 B2 is provided with a locking device in the form of a kind of wing screw which is fixed to the cervical plate by means of a clamping nut inserted from the rear side of the cervical plate. A similar locking element is used in the system according to US8,480,717 B2.A screw securing system according to DE 202 21 560 U1 uses a disk with elongated hole which is displaceable on the underside of the respective screw head.The locking system according to U.S. Pat. No. 8,778,001 B2 provides locking plates which are captured by means of resilient spreading legs in an undercut groove of the cervical plate.The plate system according to US 8 747 441 B2 uses as locking elements resilient C-rings or slotted rings which are accommodated in a corresponding groove of the cervical plate.The lock according to U.S. Pat. No. 8,702,766 B2 uses a rotatable plate body per screw with a radially and circumferentially projecting spring arm, on the distal end of which a claw body is seated. For locking, when the plate body is rotated, the claw body is forced into an undercut guide groove in the plate while the spring arm is elastically deformed, and, when the locking position is reached, it snaps into a recess in the plate. This concept requires a greater plate thickness due to the undercut.The cervical plate system according to U.S. Pat. No. 11 166 755 B2 secures two adjacent bone screws by means of spring rings which can be snapped over the respective screw head and which can be expanded by means of a set screw mounted laterally between adjacent screw holes.In the generic cervical plate system known from the document EP 1 737 365 B1, the locking element for the screws is formed by a resilient plate which is accommodated in longitudinal guidance.The object of the application is to provide a generic system with an anterior cervical plate and locking for inserted bone screws, which is simple to operate and offers flexibility in the design of the cervical plate.This object is achieved with the system according to claim 1.According to the application, the locking body is formed by a thin disc which is fixed on the anterior cervical plate so as to be rotatable about an axis of rotation substantially perpendicular to the cervical plate and which has at least one locking arm distributed angularly over the circumference and a support section lying in the disc plane, which, by rotating the disc by a predetermined angle of rotation, snaps into a latching position which can be canceled again by counter-rotation of the disc. The opening of the locking arms is simple by a rotation opposite to the closing, in order to enable as simple a revision as possible. The special feature of the system according to the application is thus that an anterior cervical plate is equipped with rotatable locking elements with an integrated, optionally elastic, locking mechanism for the bone screws. This makes the arrangement such that the locking or driving of the thin disc does not impair the function of the cervical plate system. The thickness of the plate remains unaffected by this configuration of the locking body.The system is thus equally well suited both for so-called hybrid plates for so-called constrained supplies and for so-called dynamic plates for dynamic supplies. Constrained supplies are referred to as limited stability / rigidity of the connection between cervical plate and screw, and dynamic supplies are referred to as rotational and / or translational mobility between plate and screw. Because of the latching mechanism, the locked state can be easily detected not only visually by the position of the at least one locking arm, but also haptically by the latching effect, which further benefits the operating safety. Because the locking mechanism is deformable, the locking mechanism can be opened and closed not only with a low manual force, but also a multiple opening and closing is possible without the locking moment dropping significantly or perceptibly. In addition, there is a further particular advantage that the thin plate which forms the locking body does not substantially increase the overall thickness of the cervical plate system with the smallest possible weakening of the cervical plate, as a result of which it is possible to better avoid irritation in the region of the cervical spine.The locking can be formed in a particularly space-saving manner if the support section interacts with a latching pin which is attached to the cervical plate and which, when the disk is rotated, deforms the support section before the latching position is reached.In principle, the support section with which the latching pin interacts can be provided at the most varied locations of the pane. It can be formed, for example, by a disk section which is supported on a locking pin which is attached to the cervical plate and lies below the disk section and which, when the disk is rotated, i.e. when the disk section moves over the locking pin, deforms perpendicularly to the disk plane before the disk section snaps into the locking position.The resistance of the latching mechanism can be controlled particularly well if the support section is formed by a disk ring cutout or segment which runs substantially in the shape of a circular arc and which can be deformed in the radial direction by the latching pin when the disk is rotated and forms a latching depression for the latching pin. The deformability can be purely flexurally elastic or elastically-plastic. The deflection or deformation of the latching mechanism thus functions in the radial direction. The resilient component can be formed comparatively long in this way with a small space requirement, which can compensate in particular for tolerances on the plate and on the locking arm without the locking moment thereby being influenced excessively negatively.If the locking body is arranged and / or mounted essentially centrally between at least two receiving apertures for the bone screws, the cervical plate is weakened as little as possible by the mounting of the disk carrying the locking arms, so that the cervical plate can be designed with an even smaller thickness.It has been found that the thin disc forming the locking body, preferably having a thickness in the fraction region of a millimeter, can be equipped with up to four locking arms with a suitable selection of material without mechanically overloading the functional sections of the locking body, i.e. the locking arms and the latching mechanism. For secure locking of the set bone screws, it may be sufficient to cover the bone screw heads only partially. This results in the additional advantage that the drive of the screws can remain accessible even when the locking mechanism is closed, in order to make possible a tightening.Advantageously, the locking pin is spaced radially from the axis of rotation of the disc by only a fraction of the length of the locking arm. In other words, the latching mechanism is thus arranged as close as possible to the axis of rotation of the locking element in order to avoid prying out by the screws. In the case of a radial extension of a locking arm of 3 to 4 mm, the latching pin has, for example, only a radial spacing of between 1.5 and 2 mm.The angle of rotation of the disc from the position leaving a receiving aperture freely accessible into the locking position can be varied within wide limits. Experiments have shown that at rotational angles in the range between 10° and 180°, the locking and latching functions are ensured permanently. At larger angles of rotation, the support section in the form of a substantially circular-arc-shaped disk ring cutout or segment becomes particularly long, as a result of which the flexibility of the latching mechanism can be controlled even better.Experiments have shown that the above-described locking and latching functions can be ensured in a manner which can be repeated a number of times even if the pane is designed with a thickness in the range between 0.25 and 0.75 mm. As a result, the system becomes very flat overall, which additionally contributes to the avoidance of tissue irritations or swallow disorders which may occur.With the above-described construction, it is possible to move the disk into and out of the locking position with manual force, preferably by means of an operating tool, such as a screwdriver, which is advantageous for operating technology, in which screwing tools are used for the actuation of the bone screws anyway. It has been found that even small drive profiles are suitable in the disc in order to transmit the torque required in this case reliably, for example drive profiles with dimensions in the range of less than 2 mm, for example 1.5 mm.Particular advantages in terms of production and operation are obtained if the disk forms a pivot bearing for the disk via a hollow cylindrical bearing journal which is preferably integrally formed and received in a bore of the cervical plate with a clearance fit and the wall thickness of which tapers increasingly towards its end section facing the rear side of the cervical plate and is there caulked to the cervical plate preferably via a chamfer of the bore. The caulking between the cervical plate and the locking body is particularly cost-effective, wherein the deformation or plastic deformation of the locking body during the caulking can be well defined and limited by the chamfer on the underside of the cervical plate. In addition, in this manner, the locking bodies are automatically cannulated to allow a temporary fixation pin to fix the cervical plate to a vertebral body.At the same time, the hollow cylindrical section of the locking body can be equipped with a drive profile, preferably with a polygonal recess for the engagement of an operating tool. This polygonal recess can extend over a length which substantially corresponds to the thickness of the cervical plate, so that its width across the key can be kept very small without having to fear excessive wear.If the polygonal recess has a width which is smaller than the width of a clamping cone on the screwing tool for the bone screw or of a clamping region (internal cone) of the associated bone screws, the particular advantage results that both the bone screws and the locking bodies can be actuated with the same screwdriver. The screwdriver can thus function as a multi-function instrument having a working end with three functions: holding the bone screw via a cone clamp, screwing in the screw via a star profile, and locking the locking mechanism with a smaller drive profile, such as a hexagon.When the disc is received in a shallow depression on the top of the cervical plate, the disc projects a correspondingly lesser amount from the top of the cervical plate, which further benefits the flat construction of the cervical plate system. This protrusion over the plate can be reduced even further if the axis of rotation of the locking body is not arranged perpendicular to the surface of the cervical plate, but is inclined by a few degrees of angle, preferably in the range between 3 and 7° to the surface normal.It is sufficient if the latching pin has only a height in the range between 0.25 and 0.75 mm.The above-described locking allows the anterior cervical plate to be equipped with receiving apertures for the bone screws in the form of bores and elongated holes, whereby the cervical plate system is suitable for all common supply options.A particularly material-saving design of the locking body results if the locking body is produced in the MIM (metal injection molding) method, preferably from a Ti6Al4V or CoCr alloy. With this choice of material, even with a very small thickness of the disc of the locking body, sufficient strength and a suitable latching mechanism can be realized.Several exemplary embodiments of the novel system with an anterior cervical plate and a locking mechanism for inserted bone screws screwed to a vertebral body and pressing the cervical plate against the vertebral body are described in more detail below with reference to schematic drawings. The following are shown:Brief Description of the FiguresFIG. 1 is a bottom view of a first embodiment of an anterior cervical plate with mounted locking bodies for inserted bone screws; FIG. 2 is a side view of the cervical plate shown in FIG. 1; FIG. 3 is a top view of the cervical plate with the locking bodies mounted; FIG. 4 is a sectional view taken along line IV--IV in FIG. 3; FIG. 5 shows the top view of a locking body used in the embodiment according to FIGS. 1, 2, 3 to 4; FIG. 6 is a side view of the locking body according to FIG. 5 ; FIG. 7 shows the view of the locking body according to FIG. 5 from below; FIG. 8 is a sectional view taken along line VIII--VIII in FIG. 5; FIG. 9 is a sectional view taken along line IX--IX in FIG. 7; FIG. 10 is a sectional view along line X--X in FIG. 7; FIG. 11 shows a detail of a schematic plan view of the cervical plate according to FIGS. 1, 2, 3 to 4 with the locking body removed; FIG. 12 is a bottom view; FIG. 13 is an enlarged sectional view XIII-XIII of FIG. 11; FIG. 14 shows a detail of FIG. 13 ; FIG. 15 is a top view of another embodiment of the cervical plate system with modified locking body; FIG. 16 is a side view of the system of FIG. 15 ; FIG. 17 shows the top view of the locking body used in the embodiment according to FIG. 15 to FIG. 23, views and sectional views corresponding to FIGS. 5, 6, 7, 8, 9 to 10, of the locking body used in the system according to FIG. 15 ; FIG. 18 is a side view of the locking body according to FIG. 17 ; FIG. 19 shows the view of the locking body according to FIG. 17 from below; FIG. 20 is a sectional view taken along line XX--XX in FIG. 17 ; FIG. 21 is a sectional view taken along line XXI-XXI in FIG. 19 ; FIG. 22 is a sectional view according to XXII-XXII in FIG. 19 ; FIG. 23 is a sectional view according to XXIII-XXIII in FIG. 19 ; FIGS. 24, 25, 26 to 27 are views corresponding to FIGS. 11, 12, 13 to 14 of a detail of the cervical plate according to FIG. 15 with the locking body removed; FIGS. 28, 29 to 30 are views corresponding to FIGS. 1, 2 to 3 of a further exemplary embodiment of the cervical plate system; FIG. 31 is a perspective view of the cervical plate system according to FIG. 28 in a state in which a bone screw is set by means of a multifunction tool; FIG. 32 shows a sectional view of a bone screw with inserted multifunction tool; FIG. 33 is a view corresponding to FIG. 31 of the cervical plate with the multifunction tool attached for locking the bone screws placed; FIG. 34 is a sectional view of the multifunction tool in use according to FIG. 33 ; FIG. 35 is a top view of another embodiment of the cervical plate system with a modified combination of locking bodies with the bone screws set; FIG. 36 is a side view of the system of FIG. 35 ; FIG. 37 is a plan view of another embodiment of a locking body; FIG. 38 is a side view of the locking body according to FIG. 37 ; FIG. 39 shows the view of the locking body according to FIG. 37 from below; FIG. 40 is a perspective view of another embodiment of the cervical plate system; FIG. 41 is an enlarged detail of the view according to FIG. 40 ; FIG. 42 is a plan view of the cervical plate according to FIG. 40 with the locking bodies removed; FIG. 43 is a sectional view taken along line XLIII-XLIII in FIG. 42 ; FIG. 44 is an enlarged longitudinal section through an end section of a cervical plate with the locking body removed; FIG. 45 is a longitudinal sectional view with the locking body mounted; FIG. 46 is an enlarged side view of a cervical plate; FIG. 47 is an enlarged perspective view of the anterior cervical plate of FIG. 1 with an opposing arrangement of two differently mounted locking bodies; and FIG. 48 is a longitudinal section of the detail according to FIG. 47.DESCRIPTION OF THE EMBODIMENTSHereinafter, embodiments of the present disclosure will be described based on the accompanying drawings.First EmbodimentFIGS. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 to 14 show a first exemplary embodiment of a system with an anterior cervical plate 10 with 6 circular receiving apertures 12 for bone screws not shown in detail and a locking mechanism for inserted bone screws screwed to a vertebral body and pressing the cervical plate against the vertebral body. In addition to the substantially circular receiving apertures 12, the cervical plate 10 also has two windows 14. contact surfaces for the heads of the bone screws are not described in more detail, but they are preferably designed such that-as can be seen from FIG. 3-they consist of a spherical surface in combination with a conical surface, whereby both angularly restricted (constrained) screws and angularly variable screws can be used. The cervical plate 10 shown thus represents a so-called two-segment hybrid plate in which a so-called translatory screw sliding is prevented. Alternatively, the contact surfaces can also consist only of a spherical surface or only a conical surface.In a manner known per se, the cervical plate 10 is prebent in the longitudinal direction and slightly curved in the transverse direction in order to adapt as closely as possible to the shape of the cervical spine.The cervical plate 10 is equipped with a locking mechanism for the set bone screws screwed to the cervical vertebrae, which locking mechanism will be described in more detail below. This locking mechanism prevents the bone screws from migrating out of the plate.The locking mechanism must be designed such that a locking body 16 can be brought from a position that leaves a receiving aperture 12 freely accessible into a locking position in which the screw head located in the receiving aperture 12 is at least partially covered by the locking body 16 and the migration of the screw out of the cervical plate 10 is thus prevented.In the exemplary embodiment shown, three locking bodies 16 are provided, each of which is assigned to two adjacent receiving apertures 12 and is arranged in each case substantially centrally between two adjacent receiving apertures 12. Each locking body 16 is formed by a thin disc 16 which is fixed on the anterior cervical plate 10 so as to be rotatable about an axis of rotation A 16 which is substantially perpendicular to the cervical plate 10 and which has at least one locking arm 18- 1 and 18- 2 distributed angularly over the circumference and a support section 20 which extends about a central angle WZ 20 (see FIG. 7 ) and lies in the disc plane and snaps from the open position shown in FIG. 3 into a locking position locking the bone screws by rotating the disc 16 about a predetermined angle of rotation WD, which is indicated by the two dashed lines in FIG. 3 and substantially corresponds to the central angle WZ 20.The rotation of the disc 16 is provided by a journal 22 best shown in Figs. 6 and 8 to 10, preferably formed integrally with the disc 16, which journal is clearance-fitted in a bore 24 of the cervical plate 10. The bearing journal 22 having a diameter D 22 and a length L 22, which corresponds substantially to the thickness D 10 (see FIG. 4 ) of the cervical plate 10, is formed in the shape of a hollow cylinder in such a way that its wall thickness, as can best be seen from FIGS. 8, 9 to 10, tapers increasingly via an expanding inner cone 26 toward its end section facing the rear side of the cervical plate, i.e. facing away from the disk 16, and is caulked there to the cervical plate 10 via a chamfer 28 of the bore 24 - as best shown in FIGS. 13 and 14. The locking body, in the embodiment as a disk 16 with a hollow bearing pin 22, is cannulated in this way, which can be used to pull the bearing pin 22 as a guide for a temporary fixation pin for fixing the cervical plate 10 to the spinal column.The dimensions of the disc 16 are chosen so as to minimally raise the overall thickness of the cervical plate system. For example, in the case where the thickness D 10 of the cervical plate 10 is between 1.5 and 2.5 mm, the thickness D 16 (see FIG. 6 ) of the disk 16 is in the range between 0.25 and 0.75 mm. The diameter D22 of the bearing journal 22 is in this case in the range between 1.2 and 3.5 mm.The overall thickness of the cervical plate system can be reduced even slightly by the disc 16 being accommodated in a flat depression 44 (see FIGS. 3 and 13 ) on the top side of the cervical plate 10.In order to provide the latching mechanism integrated into the cervical plate system, the support section 20 interacts with a latching pin 30 which is attached to the cervical plate 10 and, when the disc 16 is rotated, deforms the support section 20 before the disc 16 snaps into the latching position.As best shown in FIG. 11, the locking pin 30 has a drop-shaped cross section with a radial extension ER30, which is entered in FIG. 14 and lies in the range between 0.5 and 1.5 mm. In the exemplary embodiment shown, the dimension ER30 is 0.9 mm. The height H 30 (see FIG. 13 ) of the latching pin 30 corresponds substantially to the thickness D 16 of the pane 16.In the exemplary embodiment shown, the support section 20-as best shown in FIGS. 5 and 7-is formed by a disk ring cutout SRA which runs substantially in the shape of a circular arc and which, when the disk 16 is rotated from the position shown in FIG. 3, is deformed in the radial direction by the latching pin 30 and, when the locking position, not shown, is reached, snaps over its surface area onto the latching pin 30 by means of a latching depression 32 (see FIG. 7 ). In other words, the latching pin 30 is captured in an arcuate slotted link 34, in which it can move with play when the disc 16 is rotated before it runs onto a projecting nose 36 before reaching the latching depression 32, as a result of which the disc ring cutout SRA is bent outwards.The disk ring cutout SRA has a small radial extent ERSRA, which is dimensioned in FIG. 7, which is in the range of a fraction of an mm.As soon as the nose 36 is overcome during the further rotation of the disc 16, the disc ring cutout SRA snaps onto the latching pin 30 and fits tightly against the latching depression 32 with it. In this position, the disk 16 has reached the locking position locking the bone screws, in which the locking arms 18- 1 and 18- 2 are pivoted over the receiving apertures 12 and partially conceal them. The latching depression 32 is adapted with regard to its shape and position to the cross section of the latching pin, so that the opening requires a specific torque and can take place by means of manual force.In order that the above-described function of the locking body in the form of the disk 16 with bearing journals 22 can be produced with the least possible production outlay, it is advantageous to produce it in the MIM method (metal injection molding), preferably from a Ti6Al4V or CoCr alloy.Details of the design of the latching pin 30 can be seen from FIGS. 11, 12, 13 to 14. It will be seen that the locking pin 30 has a cross section which assists a sliding within the slotted link 34 and is geometrically adapted to the locking depression 32 in such a way that the disc 16 can be easily brought into and out of the snap-in position, but at the same time care should be taken to ensure that the operator feels the snap-in into the locking position. The locked state can thereby be detected haptically and also visually unambiguously.From the above description, it is clear that the entire central angle WZ 20 can be used to provide the deformation. A spring element is thus provided which has a soft spring characteristic curve, as a result of which tolerances on the cervical plate 10 and on the locking body, that is to say on the disc 16, can be compensated without the torques required for locking and unlocking being adversely influenced.This design of the locking mechanism benefits the ease of use of the locking body. This is because the disk 16 can easily be brought into and out of the locking position with manual force, preferably by means of an operating tool, such as a screwdriver, for example, wherein the drive serving for rotating the disk 16 is dimensioned such that the locking does not lead to any impairment of function, because the deflection or deformation of the latching mechanism functions in the radial direction.In the exemplary embodiment shown, a tool is used for rotating the disk 16, which tool interacts with a polygonal recess in the bearing journal 22. It can be seen from FIGS. 8, 9 to 10 that the polygonal recess 42 only has to be formed with a depth T 42 in the mm range due to the quite small required rotational forces. In addition, the polygonal recess 42 can be formed with a small width W 42 (see FIG. 5 ), which likewise lies in the mm range and is thus smaller than the width of a clamping cone on the screwing tool for the respective bone screws.It has been shown that this central angle WZ 20, which substantially corresponds to the angle of rotation of the disk 16 from the position leaving a receiving aperture 12 freely accessible into the locking position, can vary within wide limits and can be in the range between 10° and 180°.A further feature of the locking mechanism according to the invention is that the latching mechanism requires very little space. This is because, as can be seen best from FIGS. 11, 12, 13 to 14, the latching pin 30 has a radial distance AR 30 from the axis of rotation A 16 of the disc 16, which distance makes up only a fraction of the length L 18 (see FIG. 7 ) of the locking arm 18- 1 or 18- 2. With this arrangement, the receiving apertures 12 and the windows 14 in the cervical plate 10 can be made as large as possible, with the additional advantage being obtained that it prevents prying out by the bone screws.In the above-described embodiment, 2 lock arms 18-1, 18-2 are provided. However, the disk 16 can also form only one locking arm or even up to four locking arms 18.Second EmbodimentIn Figs. 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 to 27 a second embodiment of a cervical plate system is shown. For convenience of description, components corresponding to corresponding components and portions of the first embodiment are denoted by reference numerals preceded by "1".The cervical plate 110 of this exemplary embodiment has only four receiving apertures 112 for the bone screws 50, which, in the locking position shown in FIG. 15, are partially covered by a single locking body in the embodiment as a disk 116 with four locking arms 118- 1 to 118- 4, which are substantially identically designed. This partial covering is sufficient to hold the set bone screws 50 in position and prevent migration out of the cervical plate 110. At the same time, FIG. 15 reveals that the partial covering of the receiving apertures 112 has the result that the drive of the bone screws 50 still remains accessible in the embodiment of a suitable screw entrainment profile, such as a star profile 52, for example, as a result of which a tightening of the screws is also possible in the locking position of the locking arms 118.The disk 116 serving for locking is illustrated in detail in FIGS. 17, 18, 19, 20, 21, 22 to 23 and is comparable with the disk 16 of the first exemplary embodiment as far as its material selection, dimensions with regard to the thickness and length of the locking arms 118 and the configuration of the bearing pin 122 are concerned, so that a new description can be dispensed with.In contrast to the first exemplary embodiment, the cervical plate 110 carries two latching pins 130, as best shown in the plan view according to FIG. 24, which interact with two support sections 120 (see FIGS. 17 and 19 ) positioned point-symmetrically with respect to one another. As in the first exemplary embodiment, the support sections 120 are each formed by a disk ring cutout running essentially in the shape of a circular arc, which is deformed in the radial direction by the associated latching pin 130 when the disk 116 is rotated from a position not shown and, when the locking position shown in FIG. 15 is reached, snaps over its surface onto the latching pin 130 using a latching depression 132 (see FIG. 19 ). The locking pin 130 is thus likewise caught in an arcuate slotted link 134 in the first exemplary embodiment, in which it can move with play when the disc 116 is rotated before it runs onto a projecting nose 136 before it reaches the locking depression 132. In this case, the disk ring cutout SRA is bent outwards before the nose 136 is overcome when the disk 116 is rotated further and it snaps onto the latching pin 130, so that it fits snugly against the latching depression 132. The latching depression 132 is adapted with regard to its shape and position, as in the first exemplary embodiment, to the cross section of the latching pin 130 in such a way that the latching position is held securely and can only be canceled again by overcoming a predetermined holding torque.As shown in FIGS. 24, 25, 26 to 27, the latching pins 130 are also designed substantially identically to the first exemplary embodiment with respect to their position assignment to the axis of rotation A 116, so that a more detailed description can be omitted.Third EmbodimentFIGS. 28, 29, 30, 31, 32, 33 to 34 show a third exemplary embodiment of a cervical plate system according to the invention. Here, too, for convenience of description, components corresponding to corresponding components and portions of the first embodiment are denoted by reference numerals preceded by "2".In contrast to the exemplary embodiments described above, the cervical plate 210 is designed as a so-called dynamic two-segment plate. In addition to two windows 214, it has receiving apertures 212 which are designed as elongated holes and are shaped in such a way that, in addition to so-called constrained screws with a conical screw head, they can also receive so-called variable screws 250 with a spherical screw head.The locking bodies are again configured as a disk 216, but have only one locking arm 218 which is shown in the position in which the receiving apertures 212 are freely accessible, so that the bone screws 250 can be set and can be set by means of a tool 60.The lock mechanism is the same as that of the above-described embodiments, so that the details will be omitted. It can be seen from the illustration according to FIG. 28 that the disk 216 forming the locking body can be rotated by the engagement of a screwdriver in a polygonal recess 242 of the disk 216 into a locking position locking the screws, in which a radially deformable disk ring cutout SRA snaps onto the associated locking pin 230.With reference to FIGS. 32, 33 to 34, it is described how the tool serving for actuating the bone screws 250 is advantageously designed in order to make the handling of the cervical plate system as easy as possible to operate.FIG. 32 shows that the tool 60 is designed as a multifunction tool and has three functional sections offset axially: a polygonal section 62, for example a hexagonal section, at the tip for engagement in the polygonal recess 242 of the locking body. A cone section 64 of larger diameter D 64 for the fitting engagement with an inner cone section 66 of the screw 250 and a subsequent star profile section 68 which protrudes beyond the cone section in its width for the engagement in a screw entrainment profile, preferably in a star profile 252 of the screw 250.FIGS. 31 and 32 show the tool 60 when screwing the cervical plate 210. FIGS. 33 and 34 show the tool 60 when the locking mechanism is operated. Here, only the polygonal section 62 is in use, while the cone section 64 and the star-profile section 68 have no function.Fourth EmbodimentFIGS. 35 and 36 show a fourth exemplary embodiment of a cervical plate system according to the invention. Here, too, for convenience of description, components corresponding to corresponding components and portions of the first embodiment are denoted by reference numerals preceded by a "3".In this embodiment, the cervical plate system employs a cervical plate 310 that substantially corresponds to the cervical plate 210, i.e., a two-segment dynamic plate in which the screws 350 may be received. The screws 350* shown in dot-dash lines indicate the extent to which the screws can be inclined relative to the cervical plate. In contrast to the third exemplary embodiment, the plate 310 is combined with two different locking bodies, which are each designed as a disk 316, but with differently designed locking arms 318, 318- 1 and 318- 2, respectively. The arcuate slotted guides, not designated in any more detail, are designed such that a swivel angle of the locking bodies that is sufficiently large for the release and locking of the screws is provided.Fifth EmbodimentFIGS. 37, 38 to 39 show a modified embodiment of a locking body usable in the cervical plate system according to the invention. Here, too, for convenience of description, components of the locking body corresponding to corresponding components and portions of the first embodiment are denoted by reference numerals preceded by "4".The locking body is again designed as a disk 416 mounted movably in a cervical plate about an axis of rotation A 416 with bearing journals 422 and two locking arms 418- 1 and 418- 2. The support section 420 provided for the functional engagement with a not-shown latching pin, in the embodiment as a disk ring cutout SRA, however, extends over a greater central angle WZ 420 (see FIG. 39 ) of approximately 180° compared to the above-described exemplary embodiments, whereby an even greater length of the deformable support section 420 results. In this case, the not shown latching pin is not caught in a slotted link. Instead, when the disk 416 is pivoted into the locking position, the not-shown latching pin moves, preferably with little play, along the outer side of the deformable support section 420 relative to the disk 416. The deformable support section forms a radially outwardly directed nose 436 which is rounded on both sides (see FIG. 39 ), as a result of which the support section 420 is deformed radially inward before reaching the locking position and, during further rotation, springs back again into the locking position in which the latching pin rests in a latching depression 472.When the disc 416 is rotated to the open position, the tab 436 initially moves under the latch pin with brief deformation of the support portion 420. The disk can then be pivoted without force via the central angle WZ 420 until the latching pin 30 reaches a stop 474 or a stop depression. In this position, the two locking arms 418- 1 and 418- 2 are pivoted so far that they no longer overlap the receiving apertures.Sixth EmbodimentFIGS. 40 and 41 show a further modified exemplary embodiment of a cervical plate system with a varied cervical plate 510 and the locking body described with reference to FIGS. 37, 38 to 39, i.e. a locking body in the embodiment as a disc 516 rotatably mounted on the cervical plate 510. Here, too, for convenience of description, components of the cervical plate and the locking body corresponding to respective components and portions of the above-described embodiments are denoted by reference numerals preceded by a "5".The cervical plate 510 is designed as a 3-segment dynamic plate which is thus equipped with four locking bodies in the embodiment as rotatably mounted disks 516. The shape of the discs 516 corresponds to that of the embodiment according to FIGS. 37, 38 to 39. The support portion 520 is deformed by the latch pin 530 in the manner described with reference to FIGS. 37, 38 to 39.In FIGS. 40 and 41, the washer 516 is shown in the locked position in which the two locking arms 518- 1 and 518- 2 at least partially cover the set screws (not shown). In this locking position, the latch pin 530 rests in the latch trough 572 that is behind the tab 536.From this snap position, the disk 516 can be rotated into the open position by means of a tool engaging into the polygonal recess 542. The latching pin 530 moves away under the nose 536 relative to the support section 520, wherein the support section 520 is radially deformed in this case. Subsequently, i.e. after overcoming the nose 536, the disc 516 can be pivoted further preferably largely free of force, i.e. with slight play between the latching pin 530 and the supporting surface 570, until the stop depression 574 reaches the latching pin 530.When the disk 516 is rotated into the locking position by means of a tool engaging in the polygonal recess 542, the support section 520 is initially deformed radially inward when the nose 536 is reached. When the locking position is reached, the support section 520 snaps onto the locking pin 530 with the locking depression 572, as a result of which the reaching of the locking position is signaled haptically and visually to the operator.This inventive dimensioning of the cervical end section of the cervical plate can be used advantageously for all plate types, as shown in FIG. 46, i.e. also for a single-segment plate 110, as shown in FIGS. 15 and 16.Further AspectsWith reference to Figures 42, 43, 44, 45-46, further specifics of the cervical plate system will be described.A first special feature consists in the fact that the cervical plate 10 has in the central region, i.e. in the region of the central window 14, two keyhole-shaped, i.e. undercut recesses 80 which are open towards the window 14, with which recesses the cervical plate can be coupled to a surgical insertion instrument. This results in the advantage that the insertion instrument no longer protrudes beyond the edge of the cervical plate, whereby collisions of the instrument with bone or with the surgical wound can be avoided. At the same time, these recesses 80 can be used for setting temporary fixation pins, with which a simple and exact alignment of the cervical plate on the cervical spine is supported. The recesses 80 may also be undercut on the underside of the plate to allow insertion of an insertion instrument.The further particular feature lies in a new configuration of the cranial end section of the cervical plate. It can be seen from the representations of FIGS. 42, 43, 44, 45 to 46 that the cervical plate tapers in the longitudinal direction, i.e. in the direction of the X-axis according to FIG. 42, in the region of the cranial end section. In this case, both the width of the plate (ΔY) and the thickness of the plate (ΔZ) decrease in the longitudinal direction. In the transverse direction, i.e. in the direction of the Y axis, a fillet 82 with the radii RA and RZ up to the central plane EM of the plate is provided, which is superimposed along the X axis by a tapering section 84 directed in the Z direction (see FIG. 44 ). The cervical plate, which is designed with a small thickness in the range between 1.5 and 2.5 mm, tapers in the Z direction starting in the region of the cranial receiving aperture 12* initially slightly in an arc shape and starting with a first edge 86 (see FIGS. 42 and 45 ) linearly (see FIGS. 42, 44 and 45 ), which is shown in FIG. 44 by the tangent T, until a rounding section 88 with a thickness D 88 is reached at a second straight edge 87, wherein thickness D 88 still only makes up 60% of the thickness D 10 (see FIG. 44 in which the reference lines shown with dash-dotted lines lie on the lower and upper surface of the plate, respectively) of the cervical plate 10. The thickness D 10 of the plate 10 is thus understood to mean the raw thickness, i.e. the thickness of the plate, before the bearing surfaces for the rotary locks or the disk-shaped locking bodies are milled. In the region of the center of the plate 10, this thickness is, for example, 2 mm. With this design, it is possible to effectively reduce post-surgical swallow disorders.Further Variants:Above, locking bodies are described in the embodiment as discs having an axis of rotation which is perpendicular to the cervical plate. FIGS. 47 and 48 show how a protrusion U of the disk 16 beyond the surface of the cervical plate 10 can be further reduced by pivoting the axis of rotation A 16 only by a few degrees of angle, for example by 5°. With the pivoted position of the axis of rotation A16*, a protrusion U* results which is considerably reduced compared to the dimension U.It is understood that modifications of the described embodiments are possible without departing from the scope of the invention. For example, the support section can also be formed by a disk section which is supported on a latching pin attached to the cervical plate, so that the support section deforms as a rotation of the disk perpendicular to the disk plane.The latching pin of the latching mechanism can also have a symmetrical (e.g. circular) or asymmetrical (composed of circle segments and straight lines, e.g. drop-shaped) cross section.The invention thus provides a system with an anterior cervical plate with receiving apertures for bone screws and a locking mechanism for inserted bone screws screwed to a vertebral body and pressing the cervical plate against the vertebral body. The locking mechanism has a plate-like locking body which is held movably on the cervical plate and can be brought from a position which leaves a receiving aperture as freely accessible as possible into a locking position in which the screw head located in the receiving aperture is covered by the locking body and the migration of the screw out of the cervical plate is thus prevented. In order to offer a maximum degree of flexibility in the design of the cervical plate while maintaining high security against loosening of the bone screws and with simple operation, the locking body is formed by a thin disc which is fixed on the anterior cervical plate rotatably about an axis of rotation substantially perpendicular to the cervical plate and which has at least one locking arm distributed angularly over the circumference and a support section lying in the disc plane and which, by rotating the disc by a predetermined angle of rotation, snaps into a locking position which can be canceled again by counter-rotation of the disc.List of reference characters10 Cervical plate D10 thickness of 10 12, 12* receiving apertures 14 window 16, 16* disk A16 axis of rotation D16 thickness of 16 18, 18-1, 18-2 locking arms L18 length of 18 20 support section WZ20 central angle of 20 22 bearing journals D22 diameter L22 length 24 bore 26 inner cone 28 chamfer 30 locking pin AR30 radial distance of 30 H30 height of 30 32 locking depression 34 link 36 nose 38 chamfer 40 chamfer 42 polygonal recess W42 width of 42 T42 depth of 42 44 depression 50 bone screws 52 star profile 60 tool 62 polygonal section 64 conical section D64 diameter 66 inner cone section 68 star profile section 80 recesses 82 rounded portion 84 tapering section 86 first edge 87 second edge 88 rounded section D88 thickness of the rounded section 470 outer surface 472 locking depression 474 stop depression ES Disk plane EM Center plane WD Angle of rotation SRA Disk ring cutout ERSRA Radial extent of SRA U, U* Projection T Tangent

Claims

System with an anterior cervical plate (10) with receiving apertures (12) for bone screws (50) and a lock for inserted bone screws (50) screwed to a vertebral body and pressing the cervical plate against the vertebral body, wherein the lock has a plate-like locking body held movably on the cervical plate, which locking body can be brought from a position leaving a receiving aperture (12) as freely accessible as possible into a locking position in which the screw head located in the receiving aperture (12) is covered by the locking body and thus the migration of the screw out of the cervical plate is prevented, characterized in that the locking body is formed by a thin disc (16) fixed to the anterior cervical plate rotatably about an axis of rotation (A16) perpendicular to the cervical plate (12), which has at least one locking arm (18) distributed angularly over the circumference and a support section (20) lying in the plane of the disc, which, by rotating the disc (16) through a predetermined angle of rotation, snaps into a latching position which can be canceled again by counter-rotation of the disc (16).System according to claim 1, characterised in that the support section (20) interacts with a latching pin (30) which is mounted on the cervical plate (10) and which, when the disc (16) is rotated, deforms the support section (20) before the latching position is reached.System according to claim 1 or 2, characterised in that the support section is formed by a disc section which is supported on a locking pin mounted on the cervical plate (10) and deforms when the disc is rotated perpendicular to the disc plane (ES).System according to Claim 1 or 2, characterized in that the support section (20) is formed by a disc ring cutout (SRA) which runs substantially in the shape of a circular arc and which, when the disc (16) is rotated by the latching pin (30), is deformable in the radial direction and forms a latching depression (32) for the latching pin (30).System according to one of Claims 1 to 4, characterized in that the locking body is arranged substantially centrally between at least two receiving apertures (12) for the bone screws (50).The system according to any one of claims 1 to 5, characterized in that the disk (16) has up to four locking arms (18), with which heads of the set bone screws (50) can be partially covered.System according to claim 6, characterised in that the locking arms (18) are chamfered at the ends in the radial and / or circumferential direction.System according to any one of claims 1 to 7, characterised in that the locking pin (30) is spaced radially from the axis of rotation (A16) of the disc (16) by a distance (AR30) which is only a fraction of the length (L18) of the locking arm (18).System according to one of Claims 1 to 8, characterized in that the angle of rotation of the disc (16) from the position which leaves a receiving aperture (12) as freely accessible as possible into the locking position is in the range between 10° and 180°.System according to any one of claims 1 to 9, characterised in that the disc (16) has a thickness (D16) comprised between 0.25 and 0.75 mm.System according to one of Claims 1 to 10, characterized in that the disc (16) can be brought into and out of the locking position with manual force, preferably by means of an operating tool (60), such as a screwdriver.System according to one of Claims 1 to 11, characterized in that the disc (16) forms a pivot bearing for the disc (16) via a hollow-cylindrical bearing journal (22) which is received in a bore (24) of the cervical plate (10) with clearance fit and the wall thickness of which tapers increasingly towards its end section facing the rear side of the cervical plate (10) and is caulked there to the cervical plate (10) preferably via a chamfer (28) of the bore (24).System according to claim 12, characterised in that a section of the bearing pin (22) facing the disc (16) has a polygonal recess (42) for the engagement of an operating tool (60).The system according to claim 13, characterized in that the polygonal recess (42) has a width (W42) which is smaller than the width (diameter D64) of a clamping cone section (64) on a screwing tool (60) for the bone screw (50).The system according to any one of claims 1 to 14, characterized in that the disc (16) is at least partially accommodated in a shallow depression (44) on the top side of the cervical plate (10).The system according to any one of claims 1 to 15, characterized in that the locking pin (30) has a height in the range between 0.25 and 0.75 mm.System according to one of Claims 1 to 16, characterized in that the anterior cervical plate (10) has bores and / or slots as receiving apertures (12) for the bone screws (50).System according to one of Claims 1 to 17, characterized in that the locking body is produced by the MIM (metal injection moulding) method, preferably from a Ti6Al4V or CoCr alloy

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