A percutaneous minimally invasive multi-hole pedicle screw

Abstract

The application discloses a percutaneous minimally invasive porous pedicle screw, which comprises a screw tip, a screw body and a screw seat; the screw is integrally formed by using an additive manufacturing technology; the screw body comprises a threaded segment, the thread teeth of the threaded segment are formed by a dense solid metal, and the screw groove bottoms and the screw rod main body region between the thread teeth are formed by a three-dimensionally communicated porous structure; the screw is provided with a through minimally invasive hole along an axis; a bone cement hole which is in communication with the outside is arranged on the side wall of the minimally invasive hole; the edge of the bone cement hole is provided with a solid wall with a thickness of 0.2-0.4 mm; the minimally invasive hole is arranged on the screw axis, and the bone cement hole which is in communication with the outside is arranged on the side wall of the minimally invasive hole, so that the problems, such as jamming, deviation from the track and generation of metal debris due to the rough edges of the porous structure, and outflow and solidification of bone cement at the specified position, can be effectively avoided; and the design that the thread teeth are in a solid structure and the screw rod main body between the thread teeth is a three-dimensionally communicated porous structure guarantees the mechanical strength and instant holding force of the screw.

Description

Technical Field

[0001] This invention relates to the field of medical device technology, specifically to a percutaneous minimally invasive perforated pedicle screw. Background Technology

[0002] Pedicle screw fixation systems are core instruments in spinal surgery. With the development of minimally invasive surgery, percutaneous pedicle screw placement has been widely adopted due to its advantages such as less trauma, less bleeding, and faster postoperative recovery.

[0003] Referring to the existing Chinese patent with publication number CN115068091A, a 3D-printed lateral hole pedicle screw with a porous support core is disclosed, which includes a screw body. The screw body has a hollow structure and a porous support core. The screw body has a screw head at the upper end, a screw body in the middle, and a screw tip at the lower end. The screw body has external threads around its periphery and a side hole communicating with the porous support core. The screw head has a cross groove.

[0004] The aforementioned 3D-printed lateral-hole pedicle screw with a porous scaffold core enhances screw anchorage strength and reduces postoperative loosening after implantation in the vertebral body, making it particularly suitable for osteoporosis patients and thus beneficial for their rehabilitation. However, this type of 3D-printed lateral-hole pedicle screw with a porous scaffold core still has some drawbacks, such as: the edge of the lateral hole is directly connected to the porous structure, resulting in a rough surface. When the minimally invasive guide needle passes through the lateral hole, it is prone to jamming, deviating from the intended path, and even generating metal fragments, affecting the precision and safety of the surgery.

[0005] Referring to the existing Chinese patent with publication number CN223614912U, a 3D printed porous pedicle screw is disclosed, which includes a screw body and a screw head. The screw body includes a cortical bone thread area near the screw head and a cancellous bone thread area away from the screw head. A porous structure area is provided at the end of the screw body that is not connected to the screw head. The porous structure area includes an inner core column, a reinforcing beam, and a porous structure extending along the axial direction of the screw body. At least one reinforcing beam is provided and the reinforcing beam extends outward from the periphery of the inner core column. The porous structure is arranged around the outer periphery of the inner core column.

[0006] The aforementioned 3D-printed porous pedicle screw, through its porous structure, efficiently induces bone ingrowth, connecting the screw to the vertebral body as a whole. This effectively disperses stress and increases screw stability. The porous structure, located at the screw's anterior vertebral portion, prevents screw breakage due to stress concentration in the pedicle region. Furthermore, the reinforcing beam further enhances screw stability and reduces the likelihood of breakage in the porous area, making it more widely applicable and improving the user experience. However, this 3D-printed porous pedicle screw still has some drawbacks. For example, while it promotes bone ingrowth, it doesn't consider the need for guide pins in minimally invasive surgery and lacks corresponding channel design. Some traditional hollow screws, although equipped with side holes, are solid structures with high elastic modulus, exhibiting stress shielding effects and insufficient long-term pull-out resistance. Summary of the Invention

[0007] The purpose of this invention is to provide a percutaneous minimally invasive porous pedicle screw to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A percutaneous minimally invasive porous pedicle screw includes a screw tip, a screw body, and a screw seat: The screw is integrally formed using additive manufacturing technology; The nail body includes a threaded section, the thread teeth of which are made of dense solid metal, while the bottom of the thread grooves between the thread teeth and the main body area of ​​the screw are formed by a three-dimensional interconnected porous structure. The screw has a through-hole along its axis; The sidewall of the minimally invasive orifice is provided with a bone cement hole that communicates with the outside. The edge of the bone cement hole is provided with a solid wall with a thickness of 0.2-0.4 mm.

[0009] Preferably, the porosity of the porous structure is 60%-85%, and the pore size of the porous structure is 300μm-800μm.

[0010] This porosity and pore size range can provide sufficient three-dimensional space for bone tissue ingrowth and ensure nutrient exchange, while maintaining sufficient mechanical strength in the porous region to prevent fatigue fracture of the screw under long-term load.

[0011] Preferably, the bone cement hole is located in the first 1 / 3 of the nail body, and the solid wall is a smooth curved surface at the bone cement hole outlet.

[0012] The first 1 / 3 section corresponds to the part where the screw enters the vertebral body, which facilitates the accurate entry of the guide pin into the cancellous bone of the vertebral body after it exits through the bone cement hole; the smooth curved surface can further reduce the frictional resistance at the exit of the guide pin and prevent the guide pin from bending or deviating.

[0013] Preferably, the surface roughness of the solid wall is less than that of the porous structure, forming a smooth guiding surface and serving as a flow-limiting barrier for bone cement outflow.

[0014] The smooth guide surface can guide the minimally invasive guide needle to pass smoothly through the bone cement pores, preventing jamming or metal debris caused by rough edges; the solid wall can also restrict the bone cement to flow out only from the bone cement pores, preventing excessive bone cement penetration into the porous structure and affecting bone ingrowth.

[0015] Preferably, the number of bone cement holes is 1-3, and the bone cement holes are distributed along the axial direction or circumferential direction of the nail body.

[0016] Multiple bone cement measurement holes allow for different bone cement injection directions or guide needle exit positions to be selected according to intraoperative needs. Axial distribution facilitates multi-point fixation along the screw length, while circumferential distribution helps to form uniform bone cement diffusion within the vertebral body.

[0017] Preferably, the stiffness of the porous structure decreases gradually from near the thread teeth toward the screw axis, forming a smooth stiffness gradient, which is achieved through lattice density gradient or topology optimization structure.

[0018] The high stiffness near the thread teeth effectively transmits the shear force between the thread and the core interface; the stiffness gradually decreases towards the axis, which avoids local stress concentration and allows the load to be evenly transferred to the porous core area, reducing the risk of screw breakage.

[0019] Preferably, the stiffness gradient is achieved through a porosity gradient, wherein the porosity increases from a lower value near the thread teeth toward the screw axis.

[0020] The low-porosity (high-stiffness) outer layer supports the thread engagement force, while the high-porosity (low-stiffness) inner layer is closer to the elastic modulus of cancellous bone, thereby reducing the stress shielding effect and promoting uniform bone tissue ingrowth.

[0021] Preferably, the cross-sectional diameter of the micro-invasive hole has a smooth and continuous non-uniform change along the axial direction, gradually decreasing and then gradually increasing from the nail seat to the nail tip in a smooth curve, forming the minimum cross-sectional diameter at the location of the bone cement hole. The inner diameter of the micro-invasive hole is 1.2-1.8mm, which is compatible with the size of commonly used clinical micro-invasive guide needles, ensuring smooth passage of the guide needle without obvious gaps.

[0022] The non-uniform diameter design allows the guide needle to be slightly clamped by the "narrowed" channel wall near the bone cement hole, thereby accurately guiding the guide needle through the bone cement hole and preventing the guide needle from wobbling significantly within the channel; the larger diameter at both ends facilitates guide needle insertion and bone cement injection.

[0023] Preferably, the lattice form of the porous structure is selected from one or more of rhombic dodecahedrons, tetrahedrons, Thiessen polygons, or Gyroid lattices.

[0024] Rhombic dodecahedrons and Gyroid lattices have high permeability and isotropy, which is conducive to the uniform ingrowth of bone tissue; tetrahedral structures have high strength and are suitable for load-bearing areas; Thiessen polygons can simulate the morphology of natural bone trabeculae, and different lattices can be matched and selected according to the mechanical and biological requirements of different parts of the screw.

[0025] A method for preparing percutaneous minimally invasive porous pedicle screws involves selective laser melting or electron beam melting technology, adjusting laser / electron beam scanning parameters, and densifying and sintering the area around the bone cement hole to form a solid wall integrally connected with the porous area.

[0026] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention provides a through-hole on the screw axis and a bone cement hole communicating with the outside on the side wall of the through-hole. A solid wall with a thickness of 0.2-0.4 mm is formed at the edge of the bone cement hole. This solid wall has a smooth surface and a roughness less than that of a porous structure, forming a reliable guiding surface. When the minimally invasive guide needle passes through the bone cement hole, it effectively avoids problems such as jamming, deviation from the track, and metal debris caused by the rough edges of the porous structure, ensuring smooth needle passage and significantly improving the accuracy and safety of percutaneous minimally invasive surgery.

[0027] 2. This invention employs a design where the thread profile is a solid structure and the screw body between the threads is a three-dimensional interconnected porous structure. The solid thread ensures the screw's mechanical strength and immediate holding force, while the porous structure significantly reduces the overall elastic modulus of the screw, mitigating stress shielding effects and facilitating the reconstruction of the normal mechanical environment of the vertebral body. Furthermore, the three-dimensional interconnected porous structure efficiently induces bone tissue ingrowth, achieving bio-integration between the screw and the vertebral body, significantly enhancing the screw's long-term pull-out resistance and stability. Simultaneously, this screw is integrally formed through additive manufacturing, and its structural design considers both the guide pin guidance requirements of minimally invasive surgery and the biological requirements of bone integration, overcoming the shortcomings of existing technologies that either lack guide pin channels or suffer from severe stress shielding due to solid structures. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the main structure of the present invention; Figure 2 This is a schematic diagram of the structure of the present invention; Figure 3 for Figure 2 Enlarged view of point A in the middle.

[0029] In the diagram: 1. Screw tip; 2. Screw body; 3. Screw seat; 4. Threaded section; 5. Porous structure; 6. Bone cement hole; 7. Minimally invasive hole. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0031] Please see Figures 1-3 The present invention provides a technical solution: A percutaneous minimally invasive porous pedicle screw includes a screw tip 1, a screw body 2, and a screw seat 3. The screw is integrally formed using additive manufacturing technology, specifically selective laser melting (SLM) or electron beam melting (EBM) technology.

[0032] The staple seat 3 is a clinically applicable percutaneous minimally invasive low-profile U-shaped tailstock structure. The staple seat 3 has an axial through hole in the center, which is coaxially connected with the micro-invasive hole 7 through which the screw axis passes. The staple seat 3 is sized to fit the percutaneous minimally invasive working sleeve and the micro-invasive hollow screw wrench. During the operation, it can be screwed into the vertebral body through a small percutaneous channel under the protection of the micro-invasive sleeve without the need for open dissection of soft tissue. The U-shaped groove structure at the tail end of the staple seat 3 can be matched with the micro-invasive connecting rod and the micro-invasive locking screw plug to complete the posterior minimally invasive fixation of the spine. The micro-invasive guide needle can be inserted into the micro-invasive hole 7 through the central through hole of the staple seat 3 and travel along the entire length of the screw axis to achieve percutaneous micro-invasive placement under the guidance of the guide needle. It is fully compatible with the operation of instruments in the entire percutaneous minimally invasive surgical procedure.

[0033] The screw body 2 includes a threaded section 4, where the thread profile is made of dense solid metal to ensure the screw's mechanical strength and immediate holding force; while the main body of the screw between the threaded teeth is a three-dimensionally interconnected porous structure 5. The porosity of the porous structure 5 is 60%-85%, and the pore size is 300μm-800μm. This parameter range can accommodate both bone tissue ingrowth requirements and screw mechanical strength. To optimize mechanical properties, the stiffness of the porous structure 5 decreases gradually from near the threaded teeth towards the screw axis, forming a smooth stiffness gradient. This stiffness gradient is achieved through a porosity gradient, specifically, the porosity increases from a lower value near the threaded teeth towards the screw axis, making the screw stiffness compatible with the bone stiffness of the human vertebral body and pedicle, reducing stress shielding effects. Alternatively, it can be achieved through lattice density gradients or topology optimization structures. The lattice form of the porous structure 5 is selected from one or more of rhombic dodecahedrons, tetrahedrons, Thiessen polygons or Gyroid lattices, which can be flexibly selected according to clinical needs to ensure that bone tissue can grow in smoothly and form a strong bone-screw complex.

[0034] The screw has a through-hole 7 along its axis. The cross-sectional diameter of this through-hole 7 varies smoothly and continuously along the axial direction, exhibiting a non-uniform variation: it gradually decreases and then gradually increases along a smooth curve from the screw base 3 towards the screw tip, forming the minimum cross-sectional diameter at the location of the bone cement hole 6. This design can position and guide the guide needle, preventing guide needle deviation. The inner diameter of the through-hole 7 is 1.2-1.8 mm, suitable for commonly used clinical minimally invasive guide needle sizes, which range from 1.0-2.0 mm. The 1.2-1.8 mm inner diameter ensures smooth guide needle passage without significant gaps.

[0035] A bone cement hole 6 communicating with the outside is provided on the side wall of the minimally invasive hole 7. The bone cement hole 6 is located in the anterior 1 / 3 of the screw body 2, adapting to the needs of guide pin guidance and bone cement injection in percutaneous minimally invasive surgery. The number of bone cement holes 6 is 1-3, which can be distributed along the axial or circumferential direction of the screw body, and can be flexibly set according to the patient's bone condition and surgical needs. A solid wall with a thickness of 0.2-0.4mm is provided at the edge of the bone cement hole 6. This solid wall is a smooth curved surface at the exit of the bone cement hole 6, based on the following considerations: Clinical studies have shown that pedicle screws mainly bear axial pull-out force and cyclic bending load in the body, and the root of the thread is the area of ​​maximum stress. The bone cement hole 6 is located in the anterior 1 / 3 of the screw body, which refers to the area about 1 / 3 of the screw tip length. This area is mainly subjected to compressive stress after screw implantation, and the peak load is about 30%-50% of the normal physiological load. When using titanium alloys (such as Ti-6Al-4V, tensile strength ≥900MPa, yield strength ≥800MPa) for additive manufacturing, the theoretical stress value of a 0.2mm thick solid wall under a 100N cyclic load is far below the material's fatigue limit. Finite element simulation verification (simulation conditions: axial load 200N, 5 million cycles) shows that the maximum equivalent stress in the solid wall region is 78.5MPa, the safety factor is ≥10, and the stress concentration factor is controlled within 1.5, indicating that the design has sufficient fatigue life reserve and can meet the requirements for long-term in-vivo service. The surface roughness of the solid wall is less than that of the porous structure 5, forming a smooth guiding surface and simultaneously acting as a flow-limiting barrier for bone cement outflow.

[0036] The surgical procedure for using the screw in this embodiment is as follows: (1) Guide needle placement: Under fluoroscopic guidance, a clinically commonly used minimally invasive guide needle is placed into the predetermined position of the pedicle to ensure accurate positioning of the guide needle; The tail end of the nail seat 3 is coaxially connected with the minimally invasive hollow nail placement wrench. The nail placement wrench clamps the nail seat 3 and drives the screw to rotate and be screwed in. The outer diameter of the nail seat 3 is smaller than the inner diameter of the minimally invasive sleeve, which can pass smoothly through the minimally invasive soft tissue channel and meet the requirements of percutaneous minimally invasive low-trauma placement. (2) Screw insertion: The percutaneous multi-hole pedicle screw of this embodiment is slowly introduced along the guide needle. The guide needle passes through the micro-hole 7 of the screw. Since the inner diameter of the micro-hole 7 is adapted to the size of the guide needle, and the solid wall of the bone cement hole 6 is smooth, the guide needle passes through without jamming or deviation. (3) Guide pin adjustment and penetration: When it is necessary to adjust the direction of the guide pin, retract the guide pin to the position of bone cement hole 6, gently push it in, and after the tip of the guide pin contacts the smooth curved surface of the solid wall, slide smoothly into bone cement hole 6 along the smooth surface and accurately penetrate to the predetermined bone area. No metal debris is generated throughout the process. The micro-hole 7 of this screw features a smooth diameter change design, supporting two guide pin operation modes: Mode 1 (guide needle through bone cement hole 6): When the guide needle needs to pass through the side hole into the vertebral cancellous bone, the surgeon advances the guide needle to the area with the smallest diameter of the channel. Since the inner wall of the channel forms a smooth guide slope here, the tip of the guide needle naturally deviates towards the direction of bone cement hole 6. It can be easily pushed out without additional adjustment.

[0037] Mode 2 (Guide Needle Directly Reaching the Screw Tip): When the guide needle only needs to serve a positioning and guiding function and does not need to exit through the side hole, the surgeon can choose a guide needle with a diameter slightly smaller than the minimum channel diameter (e.g., a 1.0mm guide needle is suitable for a 1.2mm minimum diameter), or directly choose a guide needle with a blunt, rounded head. The guide needle will smoothly pass through the diameter-changing area directly to the screw tip, without any jamming or scratch risk. Experiments show that under the processing conditions of a channel inner wall surface roughness Ra≤0.8μm, no obvious scratches or metal debris were observed after the guide needle reciprocated through 500 times.

[0038] (4) Complete implantation: After the screw is fully inserted, the solid thread provides sufficient immediate holding force to ensure the initial fixation stability of the screw; 3-6 months after the operation, bone tissue gradually grows into the porous structure 5, forming a strong bone-screw complex, realizing long-term bone integration and significantly improving the screw's pull-out resistance.

[0039] When used for osteoporosis patients, a bone cement reinforcement step can be added: After the screw is inserted, the guide needle is withdrawn, and the bone cement injection device is connected to the end of the micro-invasive hole 7. Under fluoroscopic monitoring, the bone cement is slowly injected. The bone cement flows along the micro-invasive hole 7 to the bone cement hole 6. Under the flow restriction effect of the solid wall, it flows precisely out from the bone cement hole 6 to the predetermined bone area, avoiding backflow or disordered leakage of bone cement. After the bone cement solidifies, it achieves immediate reinforcement of the screw. At the same time, the porous structure 5 retains space for bone ingrowth, achieving the dual effect of "immediate reinforcement of bone cement + long-term bone integration". Example

[0040] The difference between Example 2 and Example 1 is that: A method for preparing a percutaneous minimally invasive porous pedicle screw: The preparation method employs selective laser melting (SLM) or electron beam melting (EBM) technology. The specific steps are as follows: (1) Based on the three-dimensional model of the screw (including the solid structure of the thread profile, the porous structure 5, the micro-invasive hole 7 and the solid wall of the bone cement hole 6), slice and layer and plan the path; (2) Spread metal powder (such as titanium alloy, cobalt-chromium alloy or stainless steel) evenly on the forming platform; (3) Under the protection of inert gas, the powder is selectively melted using a laser beam or an electron beam according to a preset scanning strategy; (4) During the molding process, by adjusting the laser / electron beam scanning parameters, the thread profile, micro-hole 7 and solid wall area are densified by high laser power and low scanning speed to form a dense solid structure; the porous structure 5 area is formed by using a lower laser energy density and a specific scanning interval. (5) Specifically, in the area surrounding the bone cement hole 6, densification sintering is performed by further increasing the laser power or reducing the scanning speed to form a solid wall integrally connected with the porous area. The thickness of the solid wall is 0.2-0.4 mm, the surface is smooth and it transitions smoothly with the sidewall of the micro-invasive hole 7. (6) After molding, remove the unmelted powder and perform post-treatment such as heat treatment and sandblasting to obtain the final percutaneous micro-invasive porous pedicle screw.

[0041] The screw prepared by the above method has a solid wall at the edge of the bone cement hole 6 that is seamlessly connected to the porous structure 5, without the need for subsequent machining, thus ensuring the smoothness of the guide surface and the overall mechanical properties.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A percutaneous minimally invasive porous pedicle screw, comprising a screw tip (1), a screw body (2), and a screw seat (3), characterized in that: The screw is integrally formed using additive manufacturing technology; The nail body (2) includes a threaded section (4), the threaded portion of which is a dense solid metal, while the bottom of the threaded groove between the threaded teeth and the main body area of ​​the screw are formed by a three-dimensional interconnected porous structure (5). The screw has a through-hole (7) along its axis; The sidewall of the minimally invasive hole (7) is provided with a bone cement hole (6) that communicates with the outside; The edge of the bone cement hole (6) is provided with a solid wall with a thickness of 0.2-0.4 mm.

2. The percutaneous minimally invasive multi-porous pedicle screw according to claim 1, characterized in that: The porosity of the porous structure (5) is 60%-85%, and the pore size of the porous structure (5) is 300μm-800μm.

3. The percutaneous minimally invasive multi-porous pedicle screw according to claim 1, characterized in that: The bone cement hole (6) is located in the first 1 / 3 of the nail body (2), and the solid wall is a smooth curved surface at the outlet of the bone cement hole (6).

4. The percutaneous minimally invasive multi-porous pedicle screw according to claim 1, characterized in that: The surface roughness of the solid wall is less than that of the porous structure (5), forming a smooth guiding surface and serving as a flow-limiting barrier for the outflow of bone cement.

5. The percutaneous minimally invasive multi-porous pedicle screw according to claim 1, characterized in that: The number of bone cement holes (6) is 1-3, and the bone cement holes (6) are distributed along the axial direction or circumferential direction of the nail body.

6. The percutaneous minimally invasive porous pedicle screw according to claim 1, characterized in that: The stiffness of the porous structure (5) decreases gradually from near the thread teeth toward the screw axis, forming a smooth stiffness gradient, which is achieved through lattice density gradient or topology optimization structure.

7. The percutaneous minimally invasive porous pedicle screw according to claim 6, characterized in that: The stiffness gradient is achieved through a porosity gradient, where the porosity increases from a lower value near the thread teeth toward the screw axis.

8. The percutaneous minimally invasive multi-porous pedicle screw according to claim 1, characterized in that: The cross-sectional diameter of the micro-invasive hole (7) changes smoothly and continuously along the axial direction, gradually decreasing and then gradually increasing from the nail seat (3) towards the nail tip in a smooth curve, forming the minimum cross-sectional diameter at the location of the bone cement hole (6). The inner diameter of the micro-invasive hole (7) is 1.2-1.8mm, which is compatible with the size of commonly used clinical micro-invasive guide needles, ensuring smooth passage of the guide needle without obvious gaps.

9. The percutaneous minimally invasive multi-porous pedicle screw according to claim 1, characterized in that: The lattice form of the porous structure (5) is selected from one or more of rhombic dodecahedron, tetrahedron, Thiessen polygon or Gyroid lattice.

10. A method for preparing a percutaneous minimally invasive porous pedicle screw as described in any one of claims 1-9, characterized in that: By using selective laser melting or electron beam melting technology, and adjusting the laser / electron beam scanning parameters, densification sintering is carried out in the area surrounding the bone cement pores (6) to form a solid wall integrally connected with the porous area.

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