Medical implant with implant screw

Abstract

The present invention relates to a medical implant 2 equipped with an implant screw 4, particularly a pedicle screw. The implant screw 4 comprises a screw head 41 and a threaded rod 43, and is manufactured from a plastic material. The implant 2 is equipped with radiopaque markers 44, 45, 53 to enable the spatial position of the implant screw 4 within the scope of imaging diagnostic methods. In this case, a ring in which the ring center M is positioned within the screw head 41 is formed together by one or more markers 53, and further markers 44, 45 are positioned on or within the threaded rod 43. The present invention also relates to a method for irradiation planning in medical radiotherapy. In this method, one or more radiopaque markers 44, 45 positioned on or within the threaded rod 43 of an implant screw 4 fixed in the body are used for therapeutic irradiation planning.

Description

Technical Field

[0001] The present invention relates to a medical implant provided with implant screws, preferably pedicle screws, and also relates to a method for irradiation planning in medical radiotherapy.

Background Art

[0002] Medical implants, especially spinal implants, often connect the implant to one or more of the patient's bones by implant screws (bone screws), for example, by screwing the implant screws into the bone through an opening in another part of the implant. Among these, the implant screws can be connected to each other by other implant components, such as in the case of a spinal implant system comprising pedicle screws and connecting rods.

[0003] Implants, especially implant screws and bone screws, are usually made of metal, such as titanium and / or titanium alloys. Such implants are radiopaque and enable the exact position of the implant (e.g., pedicle screw) to be identified during examination of the patient using imaging diagnostic techniques such as computed tomography (CT). Despite these advantages, such metal implants are radiopaque, which hinders the visibility of the bone and surrounding tissue connected to the implant during the radiographic process and also causes artifacts in the region of the implant due to the scattering effect during the radiographic process. Metal implants cause scattering phenomena by relatively large metal masses due to their radiopacity, reducing the effectiveness of the radiation, so more radiation dose is required, which may result in side effects on the surrounding tissue and thus also interfere with radiotherapy for cancer patients.

[0004] To overcome the aforementioned disadvantages of metal bone implants, bone implants or bone implant systems have been developed that are generally radiolucent and do not exhibit the aforementioned disadvantages, and are made from non-metallic composite materials. Implants or implant systems made from carbon fiber-reinforced polyetheretherketone (PEEK)-based non-metallic composite materials are preferred in the market. Such implants may be, for example, cages, bone plates, pedicle rods, tulips, or pedicle screws.

[0005] Due to their radiolucency, these non-metallic implants require markings (markers) for detection in imaging diagnostic procedures such as X-ray, CT, and magnetic resonance imaging (MRI). These markers are typically made from a metal base, particularly tantalum or titanium and their alloys, and are inserted into or attached to the implant, respectively. Known designs of such markers include spherical, wire-shaped, or coated forms.

[0006] Patent Document 1 describes various embodiments of bone screws made of composite materials. In particular, this may be a pedicle screw partially covered with a metal outer layer.

[0007] Patent Document 2, like Patent Document 1, describes various embodiments of bone screws made of composite materials. Embodiments are disclosed in which the screw tip or the end of the threads is covered with a radiopaque material in the direction of the longitudinal axis.

[0008] Patent Document 3 discloses a pedicle screw made from a composite material, in which the threads and screw tip are covered with a titanium layer.

[0009] The current state of implant technology described above has two drawbacks: on the one hand, the radiopaque coating is used, which severely limits the radiopaqueness of the components; and on the other hand, it makes it difficult to accurately determine the spatial position and orientation of the implant. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent No. 10,154,867 [Patent Document 2] U.S. Patent No. 10,617,458 [Patent Document 3] U.S. Patent Application Publication No. 2015 / 0297267 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] The object of the present invention is to provide a medical implant that is as radiotransparent as possible and that allows for particularly accurate determination of the spatial position and orientation of the implant in imaging diagnostic procedures. [Means for solving the problem]

[0012] To solve this problem, a medical implant described in claim 1 is proposed. Claim 16 describes a method for irradiation planning in medical radiotherapy, preferably based on such a medical implant. Advantageous embodiments of the present invention are described in the dependent claims.

[0013] Accordingly, the present invention provides a medical implant comprising an implant screw, particularly a pedicle screw, wherein the implant screw comprises a screw head and a threaded rod, is made of a plastic material, and the implant comprises radiopaque markers to enable the spatial position and preferably orientation of the implant screw in imaging diagnostic procedures. Here, one or more of the markers together form a ring with the ring center located within the screw head. Another of the markers is located on or within the threaded rod.

[0014] By placing one of the markers on or within the threaded rod of an implant screw, and forming a ring with one or more markers centered within the screw head, it is possible to determine not only the position of the implant but also its orientation with great accuracy, particularly in imaging diagnostic processes such as computed tomography (CT). For this purpose, the position of the screw head can be determined by one or more markers forming the ring, and the direction in which the threaded rod extends from the screw head can be determined by additional markers. Since the geometry of the implant screw, particularly the length of the threaded rod, is usually known, the position and orientation of the implant screw can be determined with great accuracy. Although the one or more markers forming the ring are not part of the implant screw, if, preferably (but not required), another part of the implant has these one or more markers forming the ring, the orientation of the implant screw, i.e., the inclination of the implant in particular relative to the other part of the implant, can also be determined. In imaging diagnostic methods, a marker ring is displayed in the screw head region, for example, instead of a single marker point. This allows for particularly accurate identification of not only the position of the screw head, but also its orientation, or the orientation of another part of the implant relative to the screw (due to the arrangement where the ring center is located within the screw head). The combination of a visible ring and, for example, a point in the imaging diagnostic process not only allows for immediate identification of the screw by the observer, but also enables intuitive recognition of the orientation of the screw within the body in images that are typically presented in two dimensions. Therefore, positioning the ring center within the screw head has proven to be particularly advantageous.

[0015] Markers can be designed to be relatively clearly visible, particularly in imaging procedures; that is, they provide strong contrast, especially through high radiopaqueness, thereby allowing for particularly accurate identification of the spatial position and orientation of the implant. Radiopaqueness affects only geometrically limited markers, and therefore is concentrated in a few locations on the implant; otherwise, the implant can be designed to be generally radiolucent.

[0016] By using imaging diagnostic methods, i.e., non-contact, the spatial position and orientation of implants, particularly implant screws, can be determined with high precision, making it possible to check or even monitor implants after they have been implanted in the body of a human or animal. In a pedicle system, for example, the inclination / angle of the pedicle screw relative to the fastening member (often called a tulip in technical terms) that connects the pedicle screw to the connecting rod can be determined. By using time-delayed CT images, the stability of vertebral fixation using implants can be verified, or it can be detected whether the fixation of the tulip to the connecting rod has loosened.

[0017] Medical imaging techniques, particularly in the medical field, are procedures that enable non-contact visualization of implants and / or surrounding tissues within the body of a human or animal patient. Specifically, medical imaging techniques refer to various device-based examination methods that provide two-dimensional, three-dimensional, or higher-dimensional image data of a patient's organs and structures and / or implants therein, often primarily used to diagnose disease-related changes. Examples of medical imaging techniques include X-ray, computed tomography (CT), ultrasound, and magnetic resonance imaging (MRI).

[0018] A medical implant is an artificial device that is implanted or can be implanted in the body of a human or animal, and is usually intended to remain in the body permanently or at least for a long period of time, i.e., for at least several hours or several days. For this purpose, implants are usually fixed to a part of the body, usually bone or cartilage, using implant screws. Implant screws usually have a male thread that allows them to be screwed into the corresponding part of the body.

[0019] The threaded rod of an implant screw typically extends from the screw head to the free end of the rod, i.e., the screw tip. The male thread is not mandatory, but preferably extends continuously along the entire length of the rod. In certain embodiments, the rod may have one or more unthreaded sections, i.e., the male thread may be interrupted once or more times longitudinally. These unthreaded sections may be located particularly in areas adjacent to the screw head. However, it is preferable that the male thread extends to the screw tip.

[0020] A threaded rod, especially a male thread, defines the main longitudinal central axis of the implant screw, which extends through the center of the threaded rod in the longitudinal direction.

[0021] The screw head of the implant screw is preferably rounded, and more preferably essentially spherical. “Essentially spherical” means that it is preferably spherical overall, but may include flat sections, particularly due to the engagement structure. The screw head is suitable for mounting to another component, such that the implant screw is multiaxially rotatable relative to this component. The engagement structure is advantageous for screwing in the implant screw using a suitable tool. The aforementioned other component may be further parts of the implant. Depending on the case, the implant screw may be provided with rotatability before it is finally fastened to the other component, for example, by tightening a clamp component, or it may be provided with rotatability after it has been fastened. Multiaxial rotatability can be provided, in particular, by a certain type of ball joint.

[0022] The implant screw may be a pedicle screw, specifically a screw designed to be screwed into the vertebral body of a human or animal spine. In this case, the screw head is preferably designed to be connected to a connecting rod using, for example, a tulip-shaped fastening member. The implant screw and connecting rod also form a component of the pedicle system. However, the implant screw may also serve to attach the implant plate to the bone, for example. Therefore, the implant may have multiple implant screws, in which case some or all of the implant screws may be equipped with the radiopaque markers described above.

[0023] The identification of the spatial position of the implant screw described above means that the location of the implant screw in the patient's body can be identified using an imaging diagnostic technique. It is advantageous for this location to be specified with respect to a reference point that can be located inside or outside the body. However, when specifying the spatial position, it is generally not necessarily the case that the spatial orientation of the implant screw is specified. This means that, for example, it is only possible to specify the location where the screw is located as a whole, for example in relation to the center of mass of the screw, and it is not possible to specify, for example, where the screw is located and in which direction the threaded rod extends. On the other hand, the spatial orientation of the implant screw in the implant described in this specification can be specified by a combination of one or more markers forming a ring and another marker arranged on or within the threaded rod.

[0024] Radiopacity, also known as X-ray opacity, is referred to in terms of the property of a material or component to allow X-rays to pass through. A radiopaque material or component is less permeable to X-rays than other surrounding materials or components, and thus, when X-rays pass through them, the X-rays are attenuated. Thus, in this example, the markers described above relate 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. Thus, in an imaging diagnostic procedure, the markers appear brighter or darker than the surrounding area, depending on the type of imaging.

[0025] The radiopacity of the markers is preferably different from the radiopacity of the plastic material of the pedicle screw by at least an integer multiple, preferably at least 2 times, more preferably at least 5 times, and most preferably at least 10 times.

[0026] A ring is generally considered a geometric structure that rotates around a central point and can extend both radially and axially. By extending radially, a ring may be formed, for example, by a plane extending between two concentric circles. By extending axially, a ring may also be formed, for example, by a hollow cylindrical structure. Typically, a ring formed by markers (there may be more than one) has both certain radial dimensions and certain axial dimensions. This means that a ring can be formed, for example, by a hollow cylindrical structure which may have certain wall thicknesses (due to its radial dimensions). Therefore, in the context of this specification, an entire hollow cylindrical structure is also considered a ring, in which case the center of the ring is located at the axial center of the hollow cylindrical structure. A ring is preferably, though not required, a perfect circle.

[0027] In particular, when a ring is formed by multiple markers together, the ring can be formed by the common outline of the corresponding single or multiple markers. Each marker can be, for example, point-shaped or spherical and can form the vertices of any regular polygon. The number of vertices of the polygon can be three, four, five, or six or more.

[0028] However, it is preferable that the ring be formed by a single marker that is continuous in the circumferential direction. Such a ring marker not only particularly facilitates the manufacture of the implant, but also allows the position and orientation of the implant screw to be easily recognized in imaging diagnostic procedures.

[0029] A ring formed by one or more markers, with the ring centered within the screw head and additional markers positioned on or within the threaded rod, allows for clear and highly accurate measurement of the implant screw's position and orientation during the imaging process. This enables non-contact monitoring of the implant screw, particularly after implantation. In pedicle systems, for example, a change in the screw's angle relative to the connecting rod, detected during monitoring using time-delayed CT images, may indicate loosening of the tulip's fixation to the rod. Conversely, monitoring can also be used to verify the stability of the fixation.

[0030] In a particularly preferred embodiment, the center of the ring is precisely located at the center of the screw head. This allows the position of the screw head to be particularly intuitively recognized in imaging procedures. When one or more markers forming the ring are preferably located on another part of the implant rather than inside or on the implant screw itself, the arrangement in which the ring center is at the center of the screw head also has the advantage that the position of the screw head is always accurately indicated, regardless of whether the screw is rotating relative to this other part. It is particularly preferred when the ring center is also located at the center of rotation, point of rotation, or axis of rotation of the implant screw. When the implant has a fastening member for attaching, particularly for fixing, the implant screw, preferably to a connecting rod, it is preferable that the ring center is located at the center of rotation, point of rotation, or axis of rotation of the implant screw once the fastening member is fixed to the implant screw. It is also preferable that the ring formed by one or more markers has an inner diameter larger than the outer diameter of the screw head.

[0031] The markers placed on or within the threaded rod are preferably positioned one-third of the way from the end of the threaded rod, along the longitudinal direction extending from the screw head to the free end of the threaded rod. This makes it easier to determine the orientation of the screw compared to when the markers are placed near the screw head. Furthermore, it is particularly preferable that the markers placed on or within the threaded rod be located at the free end of the threaded rod, i.e., at the tip of the screw. This not only makes it particularly easy to determine the orientation of the screw, but also allows the observer to instantly and intuitively recognize the length of the implant screw in the imaging diagnostic process.

[0032] In particular, to enable simple manufacturing and to make the implant screw especially stable and highly efficient, it is preferable that the implant screw be designed as a completely one-piece component.

[0033] In a particularly preferred embodiment, the implant has a fastening member for attaching, in particular, an implant screw, and for fixing it. It is preferable to fasten the implant screw to a connecting rod using a fastening member that may be particularly tulip-shaped. Furthermore, the implant screw is preferably a pedicle screw. In such a design, the fastening member is preferably provided with one or more markers that form a ring. By placing markers (which may be more) on the fastening member, it becomes possible to specify not only the position and orientation of the implant screw but also its inclination relative to the fastening member. In other embodiments, of course, the screw head may also have one or more markers that form a ring.

[0034] The one or more markers forming the ring are preferably formed by threaded members that can be screwed into the fastening member. The fastening member and / or threaded members are preferably formed as a completely integral part. The threaded members that can be screwed onto or into the fastening member are preferably made of a radiopaque material as a whole. Alternatively, the threaded members may have a radiopaque coating.

[0035] In a particularly preferred embodiment, the screw member serves to hold the implant screw in place of the fastening member.

[0036] It is advantageous that the implant screw attached to the fastening member, along with the threaded rod, is rotatable in multiple axes around the ring center relative to the fastening member. The marking provided by the ring allows for the identification of the inclination of the implant screw relative to the fastening member during the imaging diagnostic process.

[0037] One or more markers can be placed on or inside the threaded rod. The one or more markers placed on or inside the threaded rod can be of any shape. However, according to a preferred embodiment, at least one of the markers placed on or inside the threaded rod has a spherical shape. This makes the marker particularly easy and clear to recognize during the imaging process. Also, for manufacturing reasons, it is easier to place just one marker on the threaded rod.

[0038] In another equally preferred embodiment, the marker positioned on or within the threaded rod is ring-shaped, particularly sleeve-shaped. Such shapes of markers are particularly suitable for cannula-shaped implant screws. Channels extending longitudinally through the threaded rod further extend through the ring-shaped or sleeve-shaped marker, thereby allowing, for example, medication or bone cement to be delivered to the patient through the marker along the main longitudinal central axis of the implanted screw.

[0039] The ring center of a ring formed by one or more markers is preferably located on the main longitudinal axis of the implant screw. Markers located on or within the threaded rod also preferably form center points located on the main longitudinal axis of the implant screw. In this way, the position of the implant screw can be directly identified based on the position of markers visible in imaging.

[0040] It is advantageous for the markers to be made from metals, particularly tantalum or titanium. Metals are generally particularly suitable as radiopaque materials. Tantalum and titanium are especially biocompatible and suitable for manufacturing applications.

[0041] The plastic material for implant screws is preferably a thermoplastic material. Particularly preferred are so-called high-temperature thermoplastics belonging to polyaryletherketones, polyimides, and polysulfones. Polyetheretherketone (PEEK) has been found to be a particularly suitable plastic material. PEEK, as a plastic material, is particularly suitable for pedicle screws in spinal implants, but it has also been found to be particularly suitable for other implants due to its hardness and durability, as well as its excellent processability and biocompatibility.

[0042] The plastic material of the implant screw is fiber-reinforced, and preferably carbon fiber-reinforced. In this way, particularly high strength can be achieved for the implant screw. Therefore, the plastic material of the implant screw can be a composite material, preferably carbon fiber-reinforced PEEK.

[0043] The fiber length is preferably at least 1 mm. To achieve particularly excellent strength of the implant screw, it is advantageous for the fiber to have a length at least corresponding to the total length along the main extension direction of the implant screw. The fiber volume content is preferably in the range of 20% to 80%, more preferably in the range of 35% to 70%, and particularly preferably in the range of 45% to 60%.

[0044] Implant screws can, in principle, be manufactured using methods generally known in the field of composite materials. These methods include, in particular, press forming, wrap forming, tape lamination, and pultrusion methods. The press forming method described in German Patent No. 4445305 is preferred for the manufacture of implant screws and, if present, fastening members in the form of, for example, a tulip head. Implants can also be manufactured using so-called additive manufacturing methods such as 3D printing, or a combination of the above methods. Preferred starting materials for these methods are so-called unidirectional prepregs and woven prepregs. Both are geometrically flat or rounded starting materials. In the above methods, the prepreg is usually preformed into a preform, which is then pressed and heated and welded, for example, in a press tool, and then cooled.

[0045] Markers can be mechanically inserted or positioned. This can be done, for example, by pressing or screwing the marker onto the tip of an implant screw, or by inserting the marker into a mold using, for example, the press forming method described in German Patent No. 4445305, so that the marker is formed in the mold during the manufacture of the implant component and thus integrated with the implant component. In the case of fastening members, this can be done, for example, by inserting a ring-shaped marker into a mold. Alternatively, a ring-shaped marker can be attached and positioned on a fastening member so that the marker is screwed into, locked, or hooked into place on the main component of the fastening member. One or more markers can be attached to or integrated on the outside or inside of a fastening member.

[0046] Furthermore, the marker(s) may be applied to other implant components, such as implant screws or fasteners, in particular, using known coating methods. Such coating methods include, for example, electroplating, plasma coating, laser cladding, flame spraying, and 3D printing.

[0047] The above-described method for manufacturing medical implants with integrated markers is preferably a near-net-shape manufacturing method, which means that implants manufactured by this method typically require only minor post-processing in terms of shape and dimensions, and the positioning of the markers is maintained during post-processing.

[0048] The present invention also relates to a method for planning irradiation in medical radiotherapy. In this method, one or more radiopaque markers are used as spatial references for planning the irradiation of a human or animal patient in an imaging diagnostic method, and one or more markers are attached to the surface or inside the patient's body. One or more markers are each placed on or inside the threaded rod of an implant screw, preferably a pedicle screw, the implant screw being made of a plastic material and fixed inside the patient's body, preferably in bone. The screw on which one or more markers are placed is preferably, in particular, an implant screw of a medical implant as described above.

[0049] Therefore, the procedure for irradiation planning in medical radiotherapy includes the step of using one or more radiopaque markers in imaging diagnostic procedures as spatial references for therapeutic irradiation planning. Radiopaque markers placed on implant screws and used for irradiation planning may also be called registration markers or reference markers, or in English, they may be called so-called fiducial markers.

[0050] One or more radiopaque markers placed on a threaded rod can be used in the method described above, in particular, to pinpoint the spatial location of one or more irradiation target areas of the body. Since one or more screws made of plastic material are usually firmly fixed in the body in any case, one or more radiopaque markers placed on the screws can be used very readily, especially for highly accurate and reliable therapeutic irradiation planning. For patients who require therapeutic irradiation and have at least one such screw already implanted in their body, this means that further medical procedures for positioning reference markers can be partially or even completely eliminated. Thus, using the method described, it is possible to omit the implantation of markers that specifically function as irradiation references, since markers on implant screws already fixed in the patient can be used for the same purpose.

[0051] It is particularly advantageous when multiple such radiopaque markers, each fixed within the patient's body by screws, are used for therapeutic irradiation planning. In this case, the radiopaque markers can be used to identify a spatial reference system for irradiation planning.

[0052] Therefore, this method is particularly useful for spatially positioning a patient during medical radiotherapy, in which case three or more radiopaque markers are typically used in the imaging procedure to provide a spatial reference point for a human or animal patient. For this purpose, preferably at least three markers are attached to the patient's body surface or inside the body to ensure accurate positioning. Positioning usually refers to the patient's actual state relative to the target state that can be seen from the irradiation plan. It is advantageous when the three markers can be clearly distinguished from each other in imaging during irradiation. For irradiation planning, it is preferable that the markers be positioned near, i.e., in the immediate vicinity of, the volume to be irradiated, for example, formed by a tumor. When the volume to be irradiated is located in the immediate vicinity of the spine, or, for example, within the abdominal cavity, and the spine is the nearest bone structure, implant screws to which the markers are fixed are particularly suitable for irradiation planning. Depending on the situation, the irradiation plan may also be based on a combination of markers (sometimes multiple) on implant screws and additional markers implanted in the patient's body, specifically for this purpose. The markers used for irradiation planning typically have a defined geometric shape (e.g., cylindrical, spherical, or ring-shaped) and are therefore preferably automatically recognizable by positioning imaging and planning software. The described method is preferably automated. The implant screws are preferably pedicle screws and are advantageously made from fiber-reinforced plastic material.

[0053] Preferred embodiments of the present invention are described below with reference to the drawings. The drawings are for illustrative purposes only and should not be construed as limiting. [Brief explanation of the drawing]

[0054] [Figure 1] Figure 1 is a schematic diagram of a medical implant according to the present invention, showing the configuration of a pedicle system equipped with multiple pedicle screws, where each pedicle screw is embedded in the vertebral body and connected to one another using a connecting rod. [Figure 2]Figure 2 is an exploded perspective view of the pedicle screw of the implant shown in Figure 1, the tulip head attached to the connecting rod, and the washer. [Figure 3] Figure 3 is a plan view of the screw head of the pedicle screw of the implant shown in Figure 1, held within the tulip head. [Figure 4] Figure 4 is a side view of a possible first modification of the pedicle screw of the implant shown in Figure 1, held within a tulip head, with the screw tip region shown as a central cross-sectional view. [Figure 5] Figure 5 is a side view of a possible second modification of the pedicle screw of the implant shown in Figure 1, held within a tulip head, with the screw tip region shown as a central cross-sectional view. [Figure 6a] Figure 6a is a side view of the pedicle screw held within the tulip head, with the threaded rod in the first rotational position. [Figure 6b] Figure 6b is a side view of the pedicle screw held within the tulip head, with the threaded rod in the second rotational position. [Figure 7] Figure 7 is a central cross-sectional view of the tulip head of the implant according to the present invention, in which a ring marker according to the first embodiment is screwed in. [Figure 8] Figure 8 is a central cross-sectional view of the tulip head of the implant according to the present invention, in which a ring marker according to the second embodiment is screwed in. [Figure 9a] Figure 9a is a schematic diagram of the conical space extending from the ring marker on the tulip head to an additional marker at the screw tip of the pedicle screw in one of the implants shown in Figures 1-8. [Figure 9b] Figure 9b is the same schematic diagram as Figure 9a, but it is viewed from a different viewing angle. [Figure 10a] Figure 10a is a schematic diagram showing the dimensions of the tulip head of the pedicle screw in Figure 9a in the direction of the central axis (xy plane). [Figure 10b]Figure 10b is a schematic diagram showing the dimensions of the pedicle screw in Figure 9a in the direction perpendicular to the central axis of the tulip head (yz plane). [Figure 11] Figure 11 is a schematic diagram showing the dimensions of the pedicle screw in Figure 9a in any direction relative to the central axis of the tulip head. [Figure 12] Figure 12 is a schematic diagram of a medical implant equipped with multiple pedicle screws, each of which is implanted in the vertebral body and has a radiopaque marker used as a spatial reference for therapeutic irradiation planning in the medical radiotherapy method according to the present invention. [Modes for carrying out the invention]

[0055] Figures 1 to 8 show various embodiments of the medical implant and its components according to the present invention. Figures 9a to 11 show the geometric representations and dimensions obtained from imaging of the markers of these implants. The same reference numerals are used for elements that are identical or have similar functions in different embodiments.

[0056] Figure 1 shows a preferred embodiment of the medical implant according to the present invention, in the form of a pedicle system 1. The pedicle system comprises a plurality of implant screws 4, sometimes also called pedicle screws, each of which is screwed into a vertebral body W of the patient's spine. Each of the implant screws 4 is attached to a connecting rod 3 by a tulip head 5. Thus, the connecting rod 3 connects the implant screws 4 to each other, thereby restricting the movement of the vertebral body W. The pedicle system 1 can, for example, serve to decompress an intervertebral disc B located between the vertebral bodies W.

[0057] In principle, the entire pedicle system 1 forms a medical implant 2. However, each individual implant screw 4, as well as each typical pair of implant screws 4 and tulip heads 5, also forms a medical implant 2.

[0058] Figure 2 shows a medical implant 2 according to the present invention, comprising an implant screw 4, a tulip head 5, and a washer 6. The implant screw 4 of this implant 1 has a spherical screw head 41, and a threaded rod 43 extends from the screw head 41 to the screw tip S. The threaded rod 43 is provided with a male thread, which allows the implant screw 4 to be screwed into and fixed to the patient's bone, particularly the vertebral body. The screw head 41 has an engagement structure 42, which in this example has a Torx® shape (Figure 3) and is used to screw in the implant screw using a suitable tool.

[0059] The tulip head 5 serves to attach and secure the implant screw 4 shown in Figure 2 to the connecting rod 3, thus forming a fastening member. The tulip head 5 is equipped with a rod receiving opening 51, which opens longitudinally on the side opposite to the implant screw 4, so that the connecting rod 3 can be inserted from this side.

[0060] The tulip head 5 is secured to the connecting rod 3 using a clamp component (not shown). This clamp component has a male thread that can be screwed into a female thread 52 located inside the tulip head 5. Thus, the connecting rod 3, inserted into the rod receiving opening 51, can be clamped between the clamp component and the tulip head 5. In this way, the implant screw 4 can be attached and secured to the connecting rod 3 using the tulip head 5 and the clamp component. As is known from the prior art, the screw head 41 of the implant screw 4 is located inside the tulip head 5.

[0061] In the embodiment shown in Figure 2, the tulip head 5 is a two-part design comprising a main component 54 that forms a rod receiving opening 51 and a ring marker 53 that can be screwed onto the main component 54. When fully assembled, the screw head 41 of the implant screw 4 is located within the area of ​​the tulip head 5 defined by the main component 54 and the ring marker 53. Thus, the ring marker 53 also serves to fix and lock the implant screw 4 to the tulip head 5. For this reason, the ring marker 53 can also be referred to as a locking ring. A cross-sectional view of the tulip head 5 with the ring marker 53 screwed outwards is shown in Figure 7. As can be clearly seen there, both the main component 54 and the ring marker 53 of the tulip head 5 form an internal space with a rounded interface for receiving the screw head 41. Before the connecting rod 3 is inserted, the engagement structure 42 is accessible through the tulip head 5 (Figure 3).

[0062] The screw head 41 and the threaded rod 43 are integrally formed and made from the same material. This material is a radiopaque plastic material. Preferably, the plastic material used is a fiber-reinforced composite material such as carbon fiber reinforced PEEK. The fibers preferably extend along the longitudinal direction of the threaded rod 42 and have a length greater than the longitudinal dimension of the implant screw 4.

[0063] A marker is inserted into the threaded rod 43 at the tip S of the screw. The marker here has a sleeve-shaped design and is therefore referred to as a sleeve marker 45.

[0064] The ring marker 53 and sleeve marker 45 are made from a material that is significantly more radiopaque than the plastic material of the implant screw 4. Therefore, in imaging procedures, particularly in X-ray images and computed tomography (CT) scans, the ring marker 53 and sleeve marker 45 provide clear contrast to other parts of the implant 2, especially the screw head 41 and threaded rod 43, as well as the surrounding tissue, and the ring marker 53 and sleeve marker 45 are well recognizable in the images. In particular, the clear visibility of the markers 53 and 45 in the provided images makes it possible to accurately determine the position and orientation of the implant screw 4 within the patient's body. Since the tulip head 5 is equipped with the ring marker 53, and the ring marker 53 is firmly fixed to the main component 54, the position of the tulip head 5 and the inclination of the implant screw 4 relative to the tulip head 5 (and thus the connecting rod 3) can also be determined based on the illustrated markers 53 and 45. As can be seen from the comparison between Figure 2 and Figure 7, when fully assembled, the ring marker 53 is positioned so that its ring center precisely corresponds to the center of the spherical screw head 41.

[0065] Once implant 2 is fully assembled, washer 6 is positioned between the screw head 41 and the connecting rod 3. The ring-shaped washer 6 can transmit the clamping force applied by the clamping component to the screw head 41. The connecting rod 3 is then pressed against the washer 6 by the clamping component, and further, the screw head 41 is pressed against the ring marker 53, which is designed as a locking ring. Alternatively, washer 6 can also be used to separate the clamping force applied by the clamping component on the one hand and the clamping force applied by the ring marker 53, which is designed as a locking ring on the other hand, so that the tulip head 5 can be fastened to the connecting rod 3 and the implant screw 4 with independently different clamping forces.

[0066] Depending on the embodiment, the clamp component and / or washer 6 may be made from a radiolucent plastic material or a radiopaque material, for example, preferably a metal such as tantalum or titanium. When the clamp component and / or washer 6 are made from a radiopaque material, they can be useful in locating the implant screw 4 in imaging diagnostic procedures. The main component 54 of the tulip head 5 is preferably made as a single piece from a radiolucent plastic material such as carbon fiber reinforced PEEK.

[0067] Figure 4 shows one embodiment of an implant screw 4 designed as a pedicle screw, with a marker inserted into the screw tip S. The marker is referred to as a ball marker 44 because of its spherical design. Due to its spherical design, the image of the marker becomes a point shape with high contrast in the image diagnostic process.

[0068] Figure 5 shows a further embodiment, which differs from the embodiment in Figure 4 in that the implant screw 4 is cannular, i.e., has a longitudinally extending through channel for supplying, for example, medication or bone cement. To enable continuous longitudinal delivery through the screw tip S, a sleeve marker 45 is inserted at the screw tip S instead of the ball marker 44 in the embodiment of Figure 4.

[0069] As can be clearly seen in Figures 4 and 5, the markers 44 and 45 positioned on the threaded rod 43 are directly located on the main longitudinal axis H of the implant screw 4, respectively. Similarly, the ring center formed by the ring marker 53 is directly located on the main longitudinal axis H.

[0070] Figures 6a and 6b show that the implant screw 4 is rotatable in multiple axes relative to the tulip head 5. This rotatability is achieved by the ball-and-socket connection between the tulip head 5 and the screw head 41. During the first step of implanting the implant 2, by only slightly or not tightening the clamp component, the tulip head 5 with the connecting rod 3 inserted can still be moved, i.e., rotated in multiple axes relative to the implant screw 4, even if the implant screw 4 is already firmly fixed. Only after the clamp component is tightened in the second step is the connecting rod 3 firmly, i.e., immovably fixed to the implant screw 4 via the tulip head 5. After tightening the locking ring formed by the ring marker 53, the ring center of the ring marker 53 is located within the screw head 41, and further corresponds to the center of the screw head 41, and thus to the rotation point of the implant screw 4. This allows the position of the implant screw 4 relative to the tulip head 5, and thus to the connecting rod 3, to be intuitively recognized and identified with high accuracy using imaging techniques.

[0071] As already mentioned, Figure 7 shows a modified tulip head 5 with the ring marker 53 screwed on the outside. Figure 8 shows another modified version in which the ring marker 53 is screwed inside the main component 54 of the tulip head 5. Naturally, other modifications are also conceivable. For example, the ring marker 53 can also be applied in the form of a coating on a tulip head manufactured as a single piece.

[0072] Figure 9a schematically shows a cone K extending from a ring marker 53 positioned on the tulip head 5 to a ball marker 44 or sleeve marker 45 positioned on the screw tip S of the implant screw 4. Figure 9b shows the same cone K, but from a different angle than in Figure 9a. This viewing angle reveals that the cone K in three-dimensional space is actually an oblique cone. This indicates that the implant screw 4 is inclined relative to the tulip head 5 (as shown, for example, in Figure 6b). Based on the spatial position information of the ring center M formed by the screw tip S and the ring marker 53, the connecting line drawn as a dashed line in Figures 9a and 9b can be derived, which corresponds to the main longitudinal axis H of the implant screw 4 and thus indicates the spatial position of the implant screw. The main longitudinal axis H always extends from the screw tip S through the center of the screw head 41 and through the ring center point M of the ring marker 53. Therefore, the orientation of the implant screw 4 can be clearly identified using the markers.

[0073] Figure 10a schematically shows the dimensions of the tulip head 5 in the direction of its longitudinal central axis (xy plane), which may be presented, for example, in a two-dimensional CT image. The image diagnostic technique shows a ring marker 53 with a ring center M and radius r, and a point-shaped ball marker at the screw tip S. Figure 10b schematically shows the same configuration as Figure 10a, but from a different field of view or recording angle, here from a direction perpendicular to the longitudinal central axis of the tulip head 5 (yz plane). Dimensions a and b are perpendicular to each other, and similarly, dimensions c and d are perpendicular to each other. Of these, dimensions b and c have the same value. By using two images taken using the image diagnostic method described 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 can be easily calculated and accurately determined, for example, using trigonometric calculations based on measured distances a, b, c, d, and m. The two images can be taken from any direction, but it is preferable that they be taken from directions 90° apart.

[0074] Due to the known arrangement where the ring center M is at the rotation point or axis of rotation of the implant screw 4, the position of the implant screw 4 relative to the tulip head 5 and, consequently, the connecting rod 3, can be intuitively recognized and identified with high accuracy during the diagnostic imaging process.

[0075] Figure 11 is similar to Figure 10b, but shows a change in the inclination of the implant screw 4 relative to the tulip head 5, resulting in the screw tip S being positioned here as the screw tip S' in a new position. The angle of the main longitudinal central axis H of the implant screw 4 relative to the tulip head 5 can also be calculated using the two images here and can be used to verify the stability of the mutual locking between the tulip head 5 and the implant screw 4.

[0076] Figure 12 illustrates a method of irradiation planning in medical radiotherapy according to the present invention, based on radiopaque ball markers 44. Each of the ball markers 44 is attached to the tip of the threaded rod 43 of an implant screw 4. Here, the volume to be treated is formed by a tumor T located directly on the spine. Instead of the ball markers 44, sleeve-shaped or other markers of any shape may be used.

[0077] Since the implant screws 4 are preferably made from fiber-reinforced plastic material and fixed to each vertebral body W, the radiopaque ball markers 44 can be used in imaging diagnostic procedures as particularly accurate and reliable spatial references for therapeutic irradiation planning. Therefore, patients who already have implant screws 4 do not need to undergo further medical procedures to insert position markers for radiotherapy.

[0078] By using imaging techniques, the ball marker 44 can be used to establish a spatial three-dimensional reference system x, y, z for identifying the area of ​​the body to be treated with irradiation using the irradiation device 7, particularly the location of the tumor T. Therefore, the ball marker 44 at the tip of the implant screw 4 serves as a reference point for patient positioning during irradiation and "image-guided" radiotherapy. This is made possible, in particular, by the defined and consistently geometric shape of the marker. [Explanation of Symbols]

[0079] 1. Pedicle System 2. Implants 3 connecting rods 4. Implant screws 41 Screwhead 42 Latch structure 43 threaded rod 44 Spherical Markers 45 Sleeve Markers 5 Tulip Head 51 Rod receiving opening 52 Female thread 53 Ring Markers 54 Main parts 6 washers 7 Irradiation device W vertebral body B Intervertebral disc T tumor H Main longitudinal central axis S,S' Screw tip Center point of the M ring r radius K cone

Claims

1. An implant screw (4), particularly a medical implant (2) equipped with a pedicle screw, wherein the implant screw (4) comprises a screw head (41) and a threaded rod (43), and is made of a plastic material. The implant (2) is equipped with radiopaque markers (44; 45, 53) to enable the spatial position of the implant screw (4) to be identified in imaging diagnostic procedures. The implant is characterized in that one or more of the markers (53) together form a ring, the center (M) of the ring is located within the screw head (41), and further markers (44; 45) are located on or within the threaded rod (43).

2. The implant according to claim 1, wherein the markers (44; 45) positioned on or within the threaded rod (43) are positioned one-third of the way from the end of the threaded rod (43) along the longitudinal direction extending from the screw head (41) to the free end (S) of the threaded rod (43).

3. The implant according to claim 2, wherein the markers (44; 45) positioned on or within the threaded rod (43) are positioned at the free end (S) of the threaded rod (43).

4. The implant according to any one of claims 1 to 3, wherein the implant (2) comprises a fastening member (5) for attaching the implant screw (4) to a connecting rod (3), and the fastening member (5) comprises one or more markers (53) that form a ring.

5. The implant according to claim 4, wherein one or more of the markers (53) forming the ring are formed by screw members that can be screwed onto the fastening member (5).

6. The implant according to claim 5, wherein the screw member serves to hold the implant screw (4) to the fastening member (5).

7. The implant according to any one of claims 4 to 6, wherein the implant screw (4) attached to the fastening member (5) can be rotated in multiple axial directions about the ring center point (M) relative to the fastening member (5) together with the threaded rod (43).

8. The implant according to any one of claims 1 to 7, wherein the marker (44) disposed on or within the threaded rod (43) is spherical in shape.

9. The implant according to any one of claims 1 to 7, wherein the marker (45) disposed on or inside the threaded rod (43) is ring-shaped, and the implant screw (4) is preferably cannula-shaped.

10. The implant according to any one of claims 1 to 9, wherein the ring formed by one or more markers (53) has an inner diameter larger than the outer diameter of the screw head (41).

11. The implant according to any one of claims 1 to 10, wherein the ring center point (M) is located on the main longitudinal central axis (H) of the implant screw (4).

12. The implant according to any one of claims 1 to 11, wherein the marker (45) positioned on or within the threaded rod (43) forms a center point located on the main longitudinal central axis (H) of the implant screw (4).

13. The implant according to any one of claims 1 to 12, wherein the markers (44; 45, 53) are each made from a metal, particularly tantalum or titanium.

14. The implant according to any one of claims 1 to 13, wherein the plastic material of the implant screw (4) is a thermoplastic material, preferably polyetheretherketone, and more preferably polyetheretherketone (PEEK).

15. The implant according to any one of claims 1 to 14, wherein the plastic material of the implant screw (4) is fiber-reinforced, and in particular carbon fiber-reinforced.

16. A method for planning irradiation in medical radiotherapy, wherein one or more radiopaque markers (44; 45) are used as spatial references for planning therapeutic irradiation for a human or animal patient in an imaging diagnostic procedure, and the one or more markers are attached to or inside the patient's body. The method, wherein the one or more markers (44; 45) are respectively positioned on or within the threaded rod (43) of an implant screw (4), preferably a pedicle screw, and more preferably an implant screw (4) of a medical implant according to any one of claims 1 to 15, the implant screw (4) being made of a plastic material and fixed in the patient's body, preferably in bone.

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