Medical implant with an implant screw

Abstract

The invention relates to a medical implant (2) with an implant screw (4), in particular a pedicle screw, which comprises a screw head (41) and a threaded shaft (43) and which is produced from a plastics material. The implant (2) comprises radiopaque markers (44, 45, 53) in order to allow a determination of the spatial position of the implant screw (4) within the scope of an imaging method. In this case, a ring with a ring center (M) arranged within the screw head (41) is formed by one of the markers (53) or by a plurality of the markers together, and a further marker (44, 45) is arranged on or in the threaded shaft (43). The invention also relates to a method for irradiation planning in medical radiotherapy, in which one or more radiopaque markers (44, 45) arranged on or in the threaded shaft (43) of an implant screw (4) anchored in the body are used for planning the therapeutic irradiation.

Description

[0001] TITLE

[0002] MEDICAL IMPLANT WITH AN IMPLANT SCREW

[0003] TECHNICAL FIELD

[0004] The present invention relates to a medical implant with an implant screw, in particular a pedicle screw, and a method for planning irradiation in medical radiotherapy.

[0005] STATE OF THE ART

[0006] Medical implants, and especially spinal implants, often feature implant screws (bone screws) to connect the implant to one or more bones of a patient, for example, by screwing the implant screws into the bone through an opening in another part of the implant. The implant screws may be connected to each other by other implant components, as is the case, for example, with spinal implant systems using pedicle screws and connecting rods.

[0007] Implants, and especially the implant and bone screws, are typically made of metal, for example, titanium and / or a titanium alloy. Such implants are radiopaque and allow the precise position of the implant (e.g., the pedicle screw) to be determined during a patient imaging examination, such as computed tomography (CT). Despite this advantage, such metal implants obstruct the view of the bone connected to the implant and the surrounding tissue during fluoroscopy because they are radiopaque. Furthermore, scattering effects occur during fluoroscopy, which in turn create artifacts in the area of ​​the implant when visualized.Due to their radiopacity, metallic implants also impair the radiotherapy of cancer patients, as the relatively large metallic mass causes scattering phenomena that reduce the effectiveness of the radiation and thus require a higher radiation dose, which in turn can cause side effects in the surrounding tissue.

[0008] To overcome these aforementioned disadvantages of metallic bone implants, bone implants or bone implant systems made of non-metallic composite materials have been developed. These are generally radiotransparent and do not exhibit these disadvantages. Implants or implant systems made of non-metallic composite materials based on carbon fiber-reinforced polyetheretherketone (PEEK) are preferred on the market. These implants can include cages, bone plates, pedicle rods, tulips, or pedicle screws.

[0009] Due to their radiotransparency, these non-metallic implants require markers for detection during imaging procedures such as X-rays, CT scans, and magnetic resonance imaging (MRI). These markers are typically made of metals, particularly tantalum or titanium, or their alloys, and are inserted into or applied to the implant. Common designs of such markers are spherical, wire-shaped, or in the form of a coating.

[0010] Document US 10,154,867 B2 describes various embodiments of a bone screw made of composite material. This can, in particular, be a pedicle screw partially coated with a metallic outer layer.

[0011] Document US 10,617,458 B2, like US 10,154,867 B2, describes various embodiments of a bone screw made of composite material. Embodiments are disclosed in which the screw tip or the end of the screw thread in the direction of the longitudinal axis is coated with a radiopaque material.

[0012] Document US 2015 / 0297267 A1 discloses a pedicle screw made of a composite material, the thread and screw tip of which are coated with a titanium layer. The aforementioned prior art implants have the disadvantage that, due to the radiopaque coatings used, the radiotransparency of the components is severely limited, and, secondly, the determination of the spatial position and orientation of the implants is inaccurate.

[0013] PRESENTATION OF THE INVENTION

[0014] It is an object of the present invention to provide a medical implant that is as radiotransparent as possible and which enables a particularly precise determination of the spatial position and orientation of the implant in an imaging method.

[0015] To achieve this object, a medical implant is proposed as defined in claim 1. Claim 16 specifies a method for planning radiation in medical radiotherapy, which is preferably based on such a medical implant. Advantageous embodiments of the invention are defined in the dependent claims.

[0016] The present invention therefore provides a medical implant with an implant screw, in particular a pedicle screw, which has a screw head and a threaded shaft and is made of a plastic material, wherein the implant has radiopaque markers to allow a determination of the spatial position and preferably the orientation of the implant screw in an imaging method.

[0017] One or more of the markers together form a ring with a center point located within the screw head. Another marker is located on or within the threaded shaft.

[0018] By arranging one of the markers on or in the threaded shaft of the implant screw and one or more of the markers forming a ring whose center is located within the screw head, it is possible to use an imaging technique, such as computer tomography (CT), to very precisely determine not only the position of the implant but also its orientation. To do this, the position of the screw head can be determined using the marker(s) forming a ring, and the direction in which the threaded shaft extends from the screw head can be determined using the additional marker. Since the geometry of the implant screw, and in particular the length of the threaded shaft, is usually known, the position and orientation of the implant screw can be very precisely determined from this.If the marker(s) forming a ring are not part of the implant screw, but rather, which is preferred (but not mandatory), another part of the implant has this or these markers forming a ring, the orientation, i.e. in particular the inclination, of the implant screw relative to this other part of the implant can also be determined. Since a marker ring can be seen in the imaging procedure in the area of ​​the screw head instead of, for example, just a marker point, not only the position of the screw head can be determined particularly precisely (due to the arrangement of the ring center within the screw head), but also its orientation or the orientation of another part of the implant relative to the screw. The combination of ring and, for example,Furthermore, this point is not only immediately identifiable as a screw for the observer, but also allows them to intuitively recognize the screw's orientation within the body in the typically two-dimensional images. The arrangement of the ring center within the screw head has therefore proven particularly advantageous.

[0019] In particular, the markers can be designed in such a way that they are relatively clearly visible in imaging procedures, i.e., they create a strong contrast by being particularly radiopaque, which allows for particularly precise determination of the spatial position and orientation of the implant. Since the radiopacity only affects the geometrically limited markers and thus occurs in a concentrated form at a few locations on the implant, the implant can otherwise still be largely radiotransparent.

[0020] The precise determination of the spatial position and orientation of the implant, and in particular of the implant screw, using a non-contact imaging technique enables, for example, the inspection or even monitoring of the implant after its implantation in a human or animal body. For example, in a pedicle system, the tilt / inclination of the pedicle screw relative to a fastening element, often referred to in technical jargon as a tulip, which serves to connect the pedicle screw to a connecting rod, can be determined. Delayed CT images can be used to verify the stability of the vertebral interlocking using the implant or to detect any loosening of the interlocking of the tulip to the connecting rod.

[0021] Imaging procedures are considered to be procedures, particularly those known in medicine, that advantageously enable non-contact visualization of the implant implanted in the body of a human or animal patient and / or the surrounding body tissue. In particular, imaging procedures are understood to include various instrumental examination methods that provide two-, three-, or higher-dimensional image data of the patient's organs and structures and / or the implant implanted in them and are often used primarily, for example, to diagnose disease-related changes. Examples of imaging procedures include X-rays, computed tomography (CT), ultrasound, and magnetic resonance imaging (MRI).

[0022] A medical implant is an artificial device implanted or implantable in the human or animal body, usually intended to remain there permanently or at least for an extended period of time, i.e., at least several hours or days. For this purpose, the implant is typically anchored in a body part, usually a bone or cartilage, using an implant screw. The implant screw generally has an external thread, allowing it to be screwed into the corresponding body part.

[0023] The threaded shaft of the implant screw typically extends from the screw head to a free end of the threaded shaft, i.e., the screw tip. The external thread preferably, but not necessarily, extends continuously along the entire length of the threaded shaft. In certain embodiments, the threaded shaft can also have one or more threadless sections, meaning the external thread can be interrupted one or more times in the longitudinal direction. A threadless section can be present, in particular, in the area adjacent to the screw head. However, the external thread preferably extends to the screw tip.

[0024] The threaded shaft and in particular the external thread define a main longitudinal central axis of the implant screw, which extends centrally and longitudinally through the threaded shaft.

[0025] The screw head of the implant screw is preferably round, more preferably substantially spherical. "Substantially spherical" means that it may have flattened portions, particularly due to an engagement structure, but preferably has a spherical overall envelope. The screw head is thus suitable for being attached to another component such that the implant screw can pivot polyaxially relative to it. The engagement structure advantageously serves to screw in the implant screw using a suitable tool. The aforementioned other component can, in particular, be another part of the implant. Depending on the situation, the pivotability can be provided before a definitive attachment of the implant screw to the other part, for example, by tightening a clamping part, or also afterwards. The polyaxial pivotability can, in particular, be provided by a type of ball joint.

[0026] The implant screw can, in particular, be a pedicle screw, i.e., a screw designed to be screwed into a vertebral body of a human or animal spine. The screw head is then preferably designed to be connected to a connecting rod using, for example, a tulip-shaped fastening element. The implant screw and the connecting rod then form components of a pedicle system. However, it is also possible for the implant screw to be used, for example, to attach an implant plate to a bone. The implant can therefore also comprise multiple implant screws, in which case some or all of the implant screws can have the aforementioned radiopaque markers.

[0027] The aforementioned determination of the spatial position of the implant screw means that the location where the implant screw is arranged in the patient's body can be determined using an imaging procedure. The location is advantageously determined in relation to a reference point, which can be located inside or outside the body. When determining the spatial position, however, the spatial orientation of the implant screw does not generally have to be determined. This means that, for example, it is possible to only determine where the screw is arranged as a whole, for example in relation to its center of mass, but not, for example, in which position the screw is arranged and in which direction the threaded shaft extends.However, a determination of the spatial orientation of the implant screw is possible with the implant specified here due to the combination that one or more of the markers together form a ring and that another of the markers is arranged on or in the threaded shaft.

[0028] Radiopacity, also called x-ray opacity, refers to the property of the radiolucency of materials or components for X-rays. A radiopaque material or component is less permeable to X-rays than other surrounding materials or components and therefore attenuates the X-rays when penetrated by them. In this case, the markers mentioned therefore refer to a material or component (or part of a component) that is less permeable to X-rays than other parts of the implant. In particular, the markers are less permeable than the plastic material of the pedicle screw. In imaging procedures, the markers therefore appear lighter or darker compared to the surrounding areas, depending on the type of display.

[0029] The radiopacity of the markers preferably differs by at least an integer multiple, more preferably by at least twice, even more preferably by at least five times, most preferably by at least ten times, from that of the plastic material of the pedicle screw.

[0030] A ring is generally considered to be a geometric structure encircling a center point, which can have a certain extension in both the radial and axial directions. Due to its radial extension, the ring can, for example, be formed by a surface extending between two concentric circles. Due to its axial extension, the ring can also be formed, for example, by a hollow cylindrical structure. Typically, the ring formed by the marker(s) has both a certain radial and a certain axial extension. This means that the ring can, for example, be formed by a hollow cylindrical structure, which (due to the radial extension) can have a certain wall thickness. Thus, in the context of the present document, a hollow cylindrical structure as a whole is also considered to be a ring, with the ring center then being located in the axial center of the hollow cylindrical structure.The ring is preferably, but not necessarily, exactly circular.

[0031] In particular, if the ring is formed by several markers together, it can be formed by a common envelope of the corresponding marker(s). The markers can, for example, each be point-shaped or spherical and form the vertices of any regular polygon. The number of vertices of the polygon can be three, four, five, or more than five.

[0032] Preferably, however, the ring is formed by a single, continuous marker in the circumferential direction. Such a ring marker not only enables particularly simple implant production but also allows for particularly clear visualization of the position and orientation of the implant screw in imaging procedures.

[0033] With the help of the ring formed by the marker(s), with the ring center within the screw head, and the additional markers arranged on or in the threaded shaft, the position and orientation of the implant screw can not only be identified using imaging, but also clearly and precisely measured. This enables, in particular, non-contact monitoring of the implant screw after implantation. In a pedicle system, for example, a change in the inclination of the screw relative to a connecting rod detected during monitoring via time-delayed CT images can indicate a possible loosening of the locking of the tulip to the rod. Conversely, the stability of the locking can be verified using monitoring.

[0034] In a particularly preferred embodiment, the ring center is located precisely at the center of the screw head. The position of the screw head can therefore be identified particularly intuitively in the imaging process. If the marker(s) forming the ring are not located in or on the implant screw itself, but rather, as is preferred, on another part of the implant, the arrangement of the ring center at the center of the screw head also has the advantage that the position of the screw head is always displayed correctly, regardless of the pivoting of the screw relative to this other part. It is particularly preferred if the ring center is also located at a center of rotation, pivot point, or pivot axis of the implant screw.If the implant has a fastening element for attaching, in particular fixing, the implant screw, preferably to a connecting rod, the ring center is preferably arranged in a center of rotation, pivot point or in a pivot axis of the implant screw when the fastening element is firmly fixed to the implant screw. It is also preferred if the ring formed by the one or more markers has an inner diameter that is larger than an outer diameter of the screw head. The marker arranged on or in the threaded shaft is preferably arranged in the last third of the threaded shaft along a longitudinal direction that extends from the screw head to a free end of the threaded shaft. Compared to an arrangement of the marker close to the screw head, the orientation of the screw can thus be determined more easily.Particularly preferably, the marker located on or in the threaded shaft is positioned at the free end of the threaded shaft, i.e., at the screw tip. This not only allows the orientation of the screw to be determined particularly well, but also allows the viewer to directly and intuitively identify the length of the implant screw in the imaging procedure.

[0035] In order to enable particularly simple production and to make the implant screw particularly stable and well-dissipating in force, it is preferably designed as a single piece.

[0036] According to a particularly preferred embodiment, the implant has a fastening element for attaching, in particular fixing, the implant screw. The fastening element, which can in particular be tulip-shaped, is preferably used to fasten the implant screw to a connecting rod. The implant screw is then preferably a pedicle screw. In such an embodiment, the fastening element preferably has one or more markers forming a ring. By arranging the marker(s) on the fastening element, not only the position and orientation of the implant screw can be determined, but also its inclination relative to the fastening element. In other embodiments, it is of course also possible for the screw head to have the marker(s) forming a ring.

[0037] Preferably, the marker(s) forming a ring are formed by a screw element that can be screwed tightly onto the fastening element. The fastening element and / or the screw element are preferably each formed as a single piece. The screw element, which can be screwed onto or into the fastening element, is preferably made entirely of a radiopaque material. Alternatively, the screw element can also have a radiopaque coating.

[0038] In a particularly preferred embodiment, the screw element serves to hold the implant screw to the fastening element. The implant screw attached to the fastening element can advantageously be pivoted polyaxially around the ring center with its threaded shaft relative to the fastening element. Based on the ring marking, the inclination of the implant screw relative to the fastening element can be determined using imaging techniques.

[0039] One or more markers can be arranged on or in the threaded shaft. The marker(s) arranged on or in the threaded shaft can, in principle, have any shape. However, according to a preferred embodiment, at least one of the markers arranged on or in the threaded shaft is spherical. This makes the marker particularly easy and clearly recognizable in imaging. Furthermore, it is easier to manufacture if exactly one marker is arranged on the threaded shaft.

[0040] In another, likewise preferred embodiment, the marker arranged on or in the threaded shaft is ring-shaped, particularly sleeve-shaped. This marker shape is particularly suitable for a cannulated implant screw. A channel running longitudinally through the threaded shaft then preferably extends through the ring- or sleeve-shaped marker, so that, for example, medication or bone cement can be delivered to the patient through the marker along the main longitudinal central axis of the implanted screw.

[0041] The center point of the ring formed by the marker(s) is preferably located on the main longitudinal center axis of the implant screw. Preferably, the marker arranged on or in the threaded shaft also forms a center point that is located on the main longitudinal center axis of the implant screw. In this way, the position of the markers visible in the imaging can be used to directly determine the position of the implant screw.

[0042] The markers are preferably made of a metal, particularly tantalum or titanium. Metals are generally well-suited as radiopaque materials. Tantalum and titanium are particularly biocompatible and suitable for manufacturing.

[0043] The plastic material for the implant screw is preferably a thermoplastic. High-temperature thermoplastics from the polyaryletherketone, polyimide, and polysulfone families are particularly preferred. Polyetheretherketone (PEEK) has emerged as a particularly suitable plastic material. PEEK has proven particularly suitable for pedicle screws in spinal implants, but also for other implants, particularly due to its hardness and durability, as well as its good processability and biocompatibility.

[0044] The plastic material of the implant screw is preferably fiber-reinforced, especially carbon fiber-reinforced. This allows for a particularly high level of implant screw strength. The plastic material of the implant screw can therefore be a composite material, preferably in the form of carbon fiber-reinforced PEEK.

[0045] The fiber length is preferably at least 1 mm. To achieve particularly good strength of the implant screw, the fibers advantageously have a length that corresponds at least to the entire length of the implant screw along its main extension direction. The fiber volume content is preferably in a range of 20 to 80%, more preferably in a range of 35 to 70%, particularly preferably in a range of 45 to 60%.

[0046] The basic manufacturing process for the implant screw can be carried out using a process conventionally known in the composites sector. These include pressing processes, winding processes, tape-laying processes, and pultrusion processes. For the production of the implant screw and, if present, the fastening element, for example, in the shape of a tulip head, the pressing process described in document DE 44 45 305 C1 is preferred. The implant can also be manufactured using so-called additive manufacturing processes, such as 3D printing, or a combination of the aforementioned processes. Unidirectional prepregs and fabric prepregs are preferred as starting materials for these processes. Both are geometrically flat or round-shaped starting materials.As a rule, in the above-mentioned processes, the prepregs are preformed into preforms and welded under pressure and temperature, for example in a press tool, and then cooled.

[0047] The insertion or positioning of the markers can, for example, be done mechanically, e.g. by pressing or screwing a marker into the tip of the implant screw or by inserting the marker into a tool mold in which this marker is deformed during manufacture of the implant part, e.g. using the pressing process described in document DE 44 45 305 C1, and thus integrated into the implant part. In the case of the fastening element, this can be done, for example, by inserting a ring-shaped marker into a tool mold. Alternatively, the attachment and positioning of a ring-shaped marker on the fastening element can be done in such a way that the marker is screwed, snapped into place, or locked onto a main part of the fastening element. The marker(s) can be attached or integrated on the outside or inside of the fastening element.

[0048] Furthermore, the marker(s) can be applied to the implant screw or another implant component, such as the fixation element, using known coating methods. Such coating methods include, for example, electroplating, plasma coating, laser cladding, flame spraying, and 3D printing.

[0049] The above-mentioned processes for manufacturing a medical implant with integrated markers are preferably near-net-shape manufacturing processes, which means that such manufactured implants generally require only minor post-processing in terms of shape and dimensions, during which the positioning of the markers is maintained.

[0050] The invention also relates to a method for planning irradiation in medical radiotherapy, in which one or more radiopaque markers are used in an imaging method as a spatial reference for planning the therapeutic irradiation of a human or animal patient, wherein the one or more markers are attached to or in the body of the patient.

[0051] The marker(s) are each arranged on or in the threaded shaft of an implant screw, preferably a pedicle screw, which is made of a plastic material and anchored in the patient's body, preferably in a bone. The aforementioned screw, on or in whose threaded shaft the marker(s) are arranged, is particularly preferably an implant screw of a medical implant according to the above explanations.

[0052] The procedure for planning radiation therapy in medical radiotherapy therefore includes the step of using one or more radiopaque markers in the imaging procedure as a spatial reference for planning therapeutic radiation. The radiopaque markers arranged on the implant screws and used for radiation planning can also be referred to as fiducial markers.

[0053] The one or more radiopaque markers arranged on the threaded shaft can be used in the aforementioned method, in particular, to determine the spatial position of the body region(s) to be irradiated. Since the one or more screws made of a plastic material are usually firmly anchored in the body anyway, the radiopaque marker(s) arranged on them can be very easily used for particularly precise and reliable planning of therapeutic radiation. For patients who require therapeutic radiation and who already have at least one such screw implanted in their body, a further medical procedure for positioning reference markers can thus be partially or even completely eliminated.With the specified procedure, it is therefore possible to dispense with the implantation of markers specifically used as a reference for the irradiation, since the markers of the implant screws already anchored in the patient can be used for the same purpose.

[0054] It is particularly advantageous to use several such radiopaque markers for planning therapeutic radiation, each anchored in the patient's body via a screw. The radiopaque markers can then be used, in particular, to determine a spatial reference system for radiation planning.

[0055] The method is therefore used in particular for the spatial positioning of patients during medical radiotherapy, whereby three or more radiopaque markers are generally used in an imaging procedure for the spatial referencing of a human or animal patient. Preferably, at least three markers attached to or in the patient's body are used for this purpose so that clear positioning can be achieved. Positioning generally means the patient's actual situation vs. the desired situation, which is evident from the radiation planning. Advantageously, the three markers are clearly distinguishable from one another in the imaging during radiation therapy. For radiation planning, markers are preferably used that are positioned close to, i.e. in the immediate vicinity of, the volume to be irradiated, which is formed by a tumor, for example.Implant screws containing markers that are anchored in the spine are particularly suitable for radiation planning in cases where the volume to be irradiated is in the immediate vicinity of the spine or, for example, in the abdominal cavity and the spine forms the closest bony structure. Depending on the situation, radiation planning can be based on the marker(s) of the implant screw(s) in combination with other markers that have been implanted in the patient's body specifically for this purpose. The markers used for radiation planning usually have a defined geometry (e.g. cylindrical, spherical or ring-shaped) and are therefore preferably automatically detectable by the positioning imaging and the planning software. The specified procedure is preferably automated.The implant screws are preferably pedicle screws, which are advantageously made of a particularly fiber-reinforced plastic material.

[0056] BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Preferred embodiments of the invention are described below with reference to the drawings, which are for illustrative purposes only and are not to be construed as limiting. In the drawings:

[0058] Fig. 1 is a schematic view of a medical implant according to the invention in the form of a pedicle system with a plurality of pedicle screws, each implanted in a vertebral body and connected to one another by means of a connecting rod;

[0059] Fig. 2 is an exploded perspective view of a pedicle screw and a tulip head used for attachment to a connecting rod and a washer of the implant of Fig. 1;

[0060] Fig. 3 is a plan view of the screw head of a pedicle screw of the implant of Fig. 1 held in the tulip head;

[0061] Fig. 4 is a side view of a possible first variant of a pedicle screw held in a tulip head of the implant of Fig. 1, wherein the area of ​​the screw tip is shown as a central cross-sectional view;

[0062] Fig. 5 is a side view of a possible second variant of a pedicle screw held in a tulip head of the implant of Fig. 1, wherein the area of ​​the screw tip is shown as a central cross-sectional view;

[0063] Fig. 6a shows a side view of a pedicle screw held in a tulip head with the threaded shaft in a first pivoting state; Fig. 6b shows a side view of a pedicle screw held in a tulip head with the threaded shaft in a second pivoting state;

[0064] Fig. 7 is a central cross-sectional view of a tulip head of an implant according to the invention with a screwed-on ring marker according to a first embodiment;

[0065] Fig. 8 is a central cross-sectional view of a tulip head of an implant according to the invention with a screwed-on ring marker according to a second embodiment;

[0066] Fig. 9a is a schematic representation of a conical space defined by the ring marker on the tulip head and another marker on the screw tip of a pedicle screw of one of the implants of Figures 1 to 8;

[0067] Fig. 9b the same schematic representation as in Fig. 9a, but from a different viewing direction;

[0068] Fig. 10a is a schematic representation of the dimensions in the direction of the central axis of the tulip head of the pedicle screw of Fig. 9a (xy plane);

[0069] Fig. 10b is a schematic representation of the dimensions in the direction perpendicular to the central axis of the tulip head of the pedicle screw of Fig. 9a (yz plane);

[0070] Fig. 11 is a schematic representation of the dimensions in any direction to the central axis of the tulip head of the pedicle screw of Fig. 9a; and

[0071] Fig. 12 is a schematic view of a medical implant with a plurality of pedicle screws, each implanted in a vertebral body and having a radiopaque marker, which are used in a method of medical radiotherapy according to the invention as a spatial reference for planning the therapeutic irradiation.

[0072] DESCRIPTION OF PREFERRED EMBODIMENTS

[0073] Figures 1 to 8 show various embodiments of medical implants according to the invention and parts thereof. Figures 9a to 11 show geometric representations of the markers of these implants and the dimensions resulting from imaging. Elements of different embodiments that have the same or similar effects are each provided with the same reference numerals. Figure 1 shows a preferred embodiment of a medical implant according to the invention in the form of a pedicle system 1. The pedicle system has a plurality of implant screws 4, which can also be referred to as pedicle screws and are each screwed into a vertebral body W of a patient's spine. By means of a tulip head 5, each of the implant screws 4 is fastened to a connecting rod 3. The connecting rod 3 thus connects the implant screws 4 to one another and thereby locks the vertebral bodies W.The pedicle system 1 can, for example, serve to relieve the intervertebral discs B arranged between the vertebral bodies W.

[0074] In principle, the pedicle system 1 as a whole forms a medical implant 2. However, a medical implant 2 is also formed by each of the implant screws 4 itself as well as by each common pair of an implant screw 4 and a tulip head 5.

[0075] A medical implant 2 according to the invention, which comprises an implant screw 4, a tulip head 5, and a washer 6, is shown in Figure 2. The implant screw 4 of this implant 1 has a spherical screw head 41, from which a threaded shaft 43 extends to a screw tip S. The threaded shaft 43 is provided with an external thread, which allows the implant screw 4 to be screwed in and anchored in a bone, in particular in a vertebral body, of the patient. The screw head 41 has an engagement structure 42, which here has a Torx shape (Figure 3) and serves to screw in the implant screw using a suitable tool.

[0076] A tulip head 5 serves to attach and fix the implant screw 4 shown in Figure 2 to a connecting rod 3, thus forming a fastening element. The tulip head 5 has a rod receiving opening 51, which is open in the longitudinal direction on the side opposite the implant screw 4, thus allowing the insertion of the connecting rod 3 from this side.

[0077] To secure the tulip head 5 to the connecting rod 3, a clamping part (not shown in the figures) is used. This clamping part has an external thread and can be screwed into an internal thread 52 of the tulip head 5. The connecting rod 3, inserted into the rod receiving opening 51, can thus be clamped between the clamping part and the tulip head 5. The implant screw 4 can thus be attached and fixed to the connecting rod 3 by means of the tulip head 5 and the clamping part. The screw head 41 of the implant screw 4 is arranged within the tulip head 5, as is well known in the art.

[0078] In the present embodiment shown in Figure 2, the tulip head 5 is formed in two parts, with a main part 54, which forms the rod receiving opening 51, and a ring marker 53, which can be screwed onto the main part 54. In the fully assembled state, the screw head 41 of the implant screw 4 is arranged in an area of ​​the tulip head 5 that is delimited by the main part 54 and the ring marker 53. The ring marker 53 thus serves in particular to fasten and secure the implant screw 4 to the tulip head 5. The ring marker 53 can therefore also be referred to as a locking ring. A cross-sectional view of the tulip head 5 with the screw-on ring marker 53 is shown in Figure 7. As can be clearly seen there, the main part 54 of the tulip head 5 and the ring marker 53 together form an interior space provided with rounded boundary surfaces for receiving the screw head 41.Before inserting the connecting rod 3, the engagement structure 42 is accessible through the tulip head 5 (Figure 3).

[0079] The screw head 41 and the threaded shaft 43 are formed in one piece and made of the same material, which is a radio-transparent plastic. A fiber-reinforced composite material, such as carbon fiber-reinforced PEEK, is preferably used as the plastic material. The fibers preferably run along the longitudinal direction of the threaded shaft 42 and advantageously have a length that is greater than the longitudinal extent of the implant screw 4.

[0080] At the screw tip S, a marker is inserted into the threaded shaft 43, which here has a sleeve-like shape and is therefore referred to as sleeve marker 45.

[0081] The ring marker 53 and the sleeve marker 45 are made of a material that is significantly more radiopaque than the plastic material of the implant screw 4. In imaging procedures, i.e., in particular in X-ray images and computed tomography (CT), the ring marker 53 and the sleeve marker 45 therefore exhibit a clear contrast with other parts of the implant 2, in particular the screw head 41 and the threaded shaft 43, as well as the surrounding tissue, whereby the ring marker 53 and the sleeve marker 45 are clearly visible in the imaging. In particular, the markers 53 and 45, which are clearly visible in the images provided, enable a precise determination of the position and orientation of the implant screw 4 in the patient's body.Since the tulip head 5 has the ring marker 53, which is firmly fixed to the main part 54, the position of the tulip head 5 and the inclination of the implant screw 4 relative to it (and thus to the connecting rod 3) can also be determined using the illustrated markers 53 and 45. As can be seen from a comparison of Figures 2 and 7, the ring marker 53 is arranged in the fully assembled state such that its ring center precisely corresponds to the center of the spherical screw head 41.

[0082] In the fully assembled state of the implant 2, the washer 6 is arranged between the screw head 41 and the connecting rod 3. The ring-shaped washer 6 can serve to transmit the clamping force emanating from the clamping part to the screw head 41. The connecting rod 3 is then pressed by the clamping part onto the washer 6, which in turn presses the screw head 41 against the ring marker 53 designed as a locking ring. Alternatively, the washer 6 can also be used to decouple the clamping forces exerted by the clamping part on the one hand and the ring marker 53 designed as a locking ring on the other, so that the tulip head 5 can be fastened to the connecting rod 3 and the implant screw 4 independently and with different clamping forces.

[0083] Depending on the embodiment, the clamping part and / or the washer 6 can be made of a radio-transparent plastic material or of a radiopaque material, for example, a metal such as tantalum or titanium. If the clamping part and / or the washer 6 are made of a radio-opaque material, they can contribute to determining the position and orientation of the implant screw 4 in the imaging process. The main part 54 of the tulip head 5 is preferably made in one piece and made of a radio-transparent plastic material, such as carbon fiber-reinforced PEEK.

[0084] Figure 4 shows an embodiment of an implant screw 4 designed as a pedicle screw with a marker inserted into the screw tip S, which is referred to as a spherical marker 44 due to its spherical design. The spherical design results in a point-like image of the marker with high contrast in the imaging process. Figure 5 shows a further embodiment, which differs from that of Figure 4 in that the implant screw 4 is cannulated, i.e., has a longitudinally continuous channel for supplying medication or bone cement, for example. To continue to enable supply along the longitudinal direction through the screw tip S, a sleeve marker 45 is inserted at the screw tip S, instead of a spherical marker 44 as in the embodiment of Figure 4.

[0085] As can be clearly seen in Figures 4 and 5, the markers 44 and 45 arranged on the threaded shaft 43 are each arranged directly on the main longitudinal central axis H of the implant screw 4. Likewise, the ring center formed by the ring marker 53 is located directly on the main longitudinal central axis H.

[0086] Figures 6a and 6b show the polyaxial pivotability of the implant screw 4 relative to the tulip head 5. This pivotability is achieved by connecting the tulip head 5 and the screw head 41 to one another in a ball-and-socket manner. By tightening the clamping part only slightly or hardly at all in a first step during implantation of the implant 2, the tulip head 5 with the connecting rod 3 inserted therein can still be moved, i.e. pivoted polyaxially relative to the implant screw 4, while the implant screw 4 is already firmly anchored. Only after the clamping part is tightened in a second step is the connecting rod 3 firmly, i.e. immovably, fixed to the implant screw 4 via the tulip head 5.Since, after tightening the locking ring formed by the ring marker 53, the ring center point of the ring marker 53 is arranged inside the screw head 41 and here even corresponds to its center point and thus to the pivot point of the implant screw 4, the position of the implant screw 4 relative to the tulip head 5 and thus to the connecting rod 3 can be intuitively recognized and precisely determined in the imaging process.

[0087] As already mentioned, Figure 7 shows a variant of the tulip head 5 with a screw-on ring marker 53. Figure 8 shows another variant in which the ring marker 53 is screwed into the main part 54 of the tulip head 5. Of course, further variants are conceivable. For example, the ring marker 53 could also be applied in the form of a coating to a one-piece tulip head.

[0088] Figure 9a schematically shows a circular cone K, spanned by the ring marker 53 arranged on the tulip head 5 and the ball or sleeve marker 44 or 45 arranged on the screw tip S of the implant screw 4. Figure 9b shows the same circular cone K, but from a different angle than in Figure 9a. Due to the viewing direction, it can be seen here that the circular cone K is actually an oblique cone in three-dimensional space, which indicates an inclination of the implant screw 4 relative to the tulip head 5 (e.g. as in Figure 6b). Based on the knowledge of the spatial positions of the screw tip S and the ring center M formed by the ring marker 53, the connecting line shown in dashed lines in Figures 9a and 9b can be derived. This line corresponds to the main longitudinal center axis H of the implant screw 4 and thus indicates the spatial position of the implant screw.The main longitudinal central axis H, starting from the screw tip S, always runs centrally through the screw head 41 and through the ring center point M of the ring marker 53. The orientation of the implant screw 4 can thus be clearly determined using the markers.

[0089] Figure 10a schematically illustrates the dimensions in the direction of the longitudinal center axis of the tulip head 5 (xy plane), as they can be presented, for example, in a two-dimensional CT image. The imaging process images the ring marker 53 with the ring center M and the radius r, as well as the point-like spherical marker at the screw tip S. Figure 10b schematically shows the same arrangement as in Figure 10a, but from a different viewing or recording direction, here perpendicular to the longitudinal center axis of the tulip head 5 (yz plane). The dimensions a and b, as well as the dimensions c and d, are each perpendicular to one another. The dimensions b and c have the same values.Using two images acquired using the imaging technique shown in Figures 10a and 10b, the angle of the main longitudinal central axis H of the implant screw 4 relative to the tulip head 5, for example, can be easily calculated and precisely determined using trigonometric calculations based on the measured distances a, b, c, d, and m. The two images can, in principle, be acquired from any direction, but preferably from directions 90° apart.

[0090] Due to the known arrangement of the ring center M in the pivot point or in the pivot axis of the implant screw 4, the position of the implant screw 4 relative to the tulip head 5 and thus to the connecting rod 3 can be intuitively recognized and precisely determined in the imaging procedure.

[0091] Figure 11 shows the same image as in Figure 10b, but with the implant screw 4 having changed its inclination relative to the tulip head 5, so that the screw tip S is now positioned at a new position of the screw tip S'. The angle of the main longitudinal central axis H of the implant screw 4 relative to the tulip head 5 can be calculated again using two images and used to verify the stability of the interlocking between the tulip head 5 and the implant screw 4.

[0092] Figure 12 illustrates a method according to the invention for planning irradiation in medical radiotherapy based on radiopaque spherical markers 44, each attached to the tip of the threaded shaft 43 of an implant screw 4. The volume to be irradiated is formed here by a tumor T located directly on the spine. Instead of spherical markers 44, these could equally well be sleeve-shaped or any other shaped markers.

[0093] Due to the anchoring of the implant screws 4, which are preferably made of a fiber-reinforced plastic material, in each vertebral body W, the radiopaque spherical markers 44 can be used in an imaging procedure as a particularly precise and reliable spatial reference for planning therapeutic radiation therapy. The patient, who already has the implant screws 4, does not need to undergo another medical procedure to insert position markers for radiation therapy.

[0094] Using an imaging method, the spherical markers 44 can thus be used to establish a spatial, three-dimensional reference system x, y, z, with which the position of the area of ​​the body, and in particular of the tumor T, is determined, which is being therapeutically irradiated using an irradiation device 7. The spherical markers 44 at the tip of the implant screws 4 thus serve as a reference point for positioning the patient for irradiation and during image-guided radiotherapy. This is made possible in particular by the defined and consistently consistent geometric shape of the markers. List of Reference Symbols

[0095] Pedicle system 53 Ring marker 54 Main part

[0096] Implant

[0097] 6 washers

[0098] connecting rod

[0099] 7 Irradiation device

[0100] Implant screw Screw head W Vertebral body Intervention structure B Intervertebral disc Threaded shaft T Tumor Ball marker Sleeve marker H Main longitudinal axis

[0101] S, S' screw tip

[0102] Tulip head M ring center

[0103] Rod receiving opening r radius

[0104] Internal thread K circular cone

Claims

PATENT CLAIMS 1. Medical implant (2) with an implant screw (4), in particular a pedicle screw, which has a screw head (41) and a threaded shaft (43) and is made of a plastic material, wherein the implant (2) has radiopaque markers (44; 45, 53) in order to allow a determination of the spatial position of the implant screw (4) in an imaging method, characterized in that one of the markers (53) or several of the markers together form a ring with a ring center point (M) arranged within the screw head (41), and in that another of the markers (44; 45) is arranged on or in the threaded shaft (43).

2. Implant according to claim 1, wherein the marker (44; 45) arranged on or in the threaded shaft (43) is arranged in the last third of the threaded shaft (43) along a longitudinal direction extending from the screw head (41) to a free end (S) of the threaded shaft (43).

3. Implant according to claim 2, wherein the marker (44; 45) arranged on or in the threaded shaft (43) is arranged at the free end (S) of the threaded shaft (43) 4. Implant according to one of the preceding claims, wherein the implant (2) has a fastening element (5) for attaching, in particular fixing, the implant screw (4), preferably to a connecting rod (3), and wherein the fastening element (5) has the marker(s) (53) forming a ring.

5. Implant according to claim 4, wherein the marker(s) (53) forming a ring are formed by a screw element that can be screwed tightly onto the fastening element (5).

6. Implant according to claim 5, wherein the screw element for holding the Implant screw (4) on the fastening element (5).

7. Implant according to one of claims 4 to 6, wherein the implant screw (4) attached to the fastening element (5) with the threaded shaft (43) can be pivoted polyaxially about the ring center point (M) relative to the fastening element (5).

8. Implant according to one of the preceding claims, wherein the marker (44) arranged on or in the threaded shaft (43) is spherical.

9. Implant according to one of claims 1 to 7, wherein the marker (45) arranged on or in the threaded shaft (43) is ring-shaped and the implant screw (4) is preferably cannulated.

10. Implant according to one of the preceding claims, wherein the ring formed by the one or more markers (53) has an inner diameter which is larger than an outer diameter of the screw head (41).

11. Implant according to one of the preceding claims, wherein the ring center (M) is arranged on the main longitudinal center axis (H) of the implant screw (4).

12. Implant according to one of the preceding claims, wherein the marker (45) arranged on or in the threaded shaft (43) forms a center point which is arranged on the main longitudinal center axis (H) of the implant screw (4).

13. Implant according to one of the preceding claims, wherein the markers (44; 45, 53) are each made of a metal, in particular tantalum or titanium.

14. Implant according to one of the preceding claims, wherein the plastic material of the implant screw (4) is a thermoplastic plastic material, in particular polyetheretherketone (PEEK).

15. Implant according to one of the preceding claims, wherein the The plastic material of the implant screw (4) is fiber-reinforced, in particular carbon fiber-reinforced.

16. A method for planning irradiation in medical radiotherapy, in which one or more radio-opaque markers (44; 45) are used in an imaging method as a spatial reference for planning the therapeutic irradiation of a human or animal patient, wherein the one or more markers are attached to or in the body of the patient, characterized in that the one or more markers (44; 45) are each arranged on or in the threaded shaft (43) of an implant screw (4), preferably a pedicle screw and particularly preferably an implant screw (4) of a medical implant according to one of the preceding claims, which is made of a plastic material and anchored in the body, preferably in a bone, of the patient.

Images