Porous spinal pedicle screw based on bone density distribution and method of designing the same

Abstract

This application relates to the field of spinal pedicle screw technology, and particularly to porous spinal pedicle screws based on bone density distribution and their design methods. The proposed technical solution includes the following steps: S1, data processing and porosity gradient construction; S11, three-dimensional reconstruction and path planning; S12, bone density sampling; S13, target porosity mapping; S14, construction of gradient porosity porous structures; S2, construction of porous pedicle screws. The gradient porosity design of this application enhances fixation by increasing the porosity of the screw in the pedicle region; it makes the porous structure in the dense bone pedicle region more porous, facilitating bone ingrowth and interlocking; while in the osteoporotic vertebral body region, the porosity is relatively low, ensuring the overall mechanical strength of the screw. The inner solid titanium alloy core ensures the screw's overall fatigue resistance, fracture resistance, and other core mechanical strengths, meeting load-bearing requirements; enhanced initial and long-term fixation holding force, and immediate stability are provided by the double-pitch thread and tapered design.

Description

Technical Field

[0001] This application relates to the field of spinal pedicle screw technology, and more particularly to porous spinal pedicle screws based on bone density distribution and their design methods. Background Technology

[0002] Pedicle screws are important implants used in spinal surgery. In the field of spinal surgery, these screws are frequently used when procedures such as spinal correction, fixation, or fusion are required. By being accurately inserted into the pedicles of the spine, pedicle screws provide stability and support to the spine, helping patients restore the spine's normal physiological curvature and promoting bone healing.

[0003] Traditional pedicle screws are typically made of medical-grade metals such as titanium alloys. They are solid cylindrical in shape and rely primarily on the mechanical friction between the screw's threads and the pedicle and vertebral body bone to achieve immediate fixation and long-term retention. However, existing pedicle screws have the following drawbacks: Traditional screws rely solely on mechanical friction for fixation. In patients with osteoporosis, due to sparse trabeculae and decreased bone strength, the holding force between the screw and bone is significantly insufficient, making screw loosening and pull-out highly likely, leading to internal fixation failure and surgical failure. Solid titanium alloy screws have an elastic modulus (approximately 110 GPa) far exceeding that of human cancellous bone (approximately 0.1-2 GPa) and cortical bone (approximately 12-18 GPa). This significant modulus mismatch causes stress to be primarily borne by the screw, while the surrounding bone lacks stress stimulation, resulting in disuse bone resorption (i.e., stress shielding effect), further exacerbating the risk of long-term loosening.

[0004] Strengthening methods carry risks: In clinical practice, injected bone cement (PMMA) is often used to enhance screw fixation in patients with osteoporosis. However, bone cement reinforcement carries serious risks of complications such as bone cement leakage, pulmonary embolism, allergic reactions, and difficulty in revision surgery.

[0005] Insufficient bone ingrowth: Traditional solid screws with smooth or sandblasted surfaces lack space for bone ingrowth, making it difficult to achieve true osseointegration and interlocking fixation.

[0006] In view of this, this application proposes a porous spinal pedicle screw based on bone density distribution and its design method. Summary of the Invention

[0007] The purpose of this application is to address the technical problems pointed out in the background art by proposing a porous spinal pedicle screw based on bone density distribution and its design method.

[0008] The technical solution of this application: On the one hand, this application proposes a design method for porous spinal pedicle screws based on bone density distribution, including the following steps: S1. Data processing and porosity gradient construction; S11, 3D reconstruction and path planning; S12, Bone density sampling; S13, Target porosity mapping; S14. Construction of gradient porosity porous structures; S2, construction of porous pedicle screws.

[0009] Preferably, step S11 includes: S111. Using the patient's spinal CT scan data, the target vertebral body is reconstructed in three dimensions, and the trajectory of the pedicle screw is planned. S112. Determine the entry point on the vertebral surface as... The internal endpoint of the vertebral body is Set the maximum diameter of the screw to be The minimum diameter is , construct With axis Frustum of a circle with a base diameter As a simulation of screw trajectory.

[0010] Preferably, step S12 includes: S121, on the truncated cone axis Take a little upon taking office , and The distance is Create a circular cross-section perpendicular to the axis in the 3D CT reconstruction data. ; S122. Extract cross sections from CT metadata. CT values ​​for all pixels, and calculate the cross section. Average CT value of all pixels .

[0011] Preferably, step S13 includes: S131. According to the mapping formula between porosity P and CT value K, P = m × K 0.5 +n(-4 < m < -2, 60 < n < 140), average CT value Converted into the corresponding target porosity ; S132. Establish the porosity distribution function P along the length of the screw trajectory. .

[0012] Preferably, step S14 includes: S141. The pores are formed by the periodic arrangement of helical units on three-period surfaces. The structure of the helical units can be derived from implicit functions. The structure is constructed, where c is a controllable parameter that can adjust the overall element density, and the X, Y, and Z spatial coordinates of the element structure surface are calculated accordingly. S142. For each helical unit on the outer layer of the screw, assume that the unit is perpendicular to the screw axis. The foot of the perpendicular is , and The distance is ; S143. Calculate the gradient porosity P from step S13. ; S144, Order The unit structure is calculated to generate a micropore structure that varies continuously along the screw axis; S145, at screw distance A pore-free area of ​​0-3mm is established to reduce the cutting of the pedicle cortex.

[0013] On the other hand, this application proposes a porous spinal pedicle screw based on bone density distribution, including a screw head, a screw rod, a threaded portion, a pore, and a tip; The nail head is fixedly connected to the outer end of the screw, the tip is fixedly connected to the insertion end of the screw, the threaded part is provided on the outer wall of the screw, and the hole is opened on the side wall of the screw.

[0014] Preferably, the screw head has a U-shaped cylindrical structure, the inner wall of the screw head is provided with an internal thread and a connecting rod groove, the side wall of the screw head is provided with a circular groove for the connecting rod to pass through; the top center of the screw head is provided with an internal hexagonal groove or a quincunx groove for screwdriver torque transmission.

[0015] Preferably, the diameter of the screw gradually decreases from the head towards the tip.

[0016] Preferably, the screw includes an inner layer and an outer layer; The pores are formed in the outer layer of the screw, and the inner layer is a solid titanium alloy.

[0017] Preferably, the threaded portion includes thread a and thread b; The thread a is set to a fine pitch to increase the contact area with the cortical bone; The thread b is set to a wide pitch to increase the holding volume of cancellous bone.

[0018] Compared with the prior art, this application has the following beneficial technical effects: This application employs a gradient porosity design, which enhances fixation by increasing the porosity of the screw in the pedicle region. Instead of a uniform porosity design, it precisely maps the bone density distribution of the patient's preoperative CT data to the gradient porosity of the outer layer of the screw. This results in porous pedicle regions with dense bone, which facilitates bone ingrowth and interlocking. In osteoporotic vertebral regions, the porosity is relatively low, ensuring the overall mechanical strength of the screw.

[0019] This application features a composite screw design with an inner solid titanium alloy core, ensuring the screw's overall mechanical strength, including fatigue and fracture resistance, to meet load-bearing requirements. The outer, approximately 1mm thick, gradient porous structure reduces the elastic modulus and provides space for bone ingrowth. This design achieves a perfect balance between biological fixation and mechanical properties while ensuring implant safety.

[0020] Enhanced initial and long-term holding force, with immediate stability provided by a dual-pitch thread and tapered design for mechanical holding. Long-term stability relies on the outer porous structure that allows newly formed bone trabeculae to grow into the pores, creating a microscopic interlock between bone and implant, extending the interfacial friction intensity from the surface friction of the thread to an interlocking effect between the trabeculae and the bone.

[0021] Interactive design process: The design process integrates medical imaging and advanced manufacturing, allows users to select target screw trajectories, and uses algorithms to transform macroscopic imaging data into controllable microstructural gradient parameters. Finally, the screw is printed using titanium alloy additive manufacturing technology, realizing personalized design from patient anatomical information to implant performance. Attached Figure Description

[0022] Figure 1 This is a flowchart of a design method for porous spinal pedicle screws based on bone density distribution; Figure 2 This is a schematic diagram of the porosity structure in this application; Figure 3 This is a three-dimensional diagram of a porous pedicle screw for the spine based on bone density distribution.

[0023] Reference numerals: 1. Nail head; 2. Screw; 3. Threaded part; 31. Thread a; 32. Thread b; 4. Hole; 5. Tip. Detailed Implementation

[0024] The technical solution of this application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] The components of the embodiments of this application described and shown in the accompanying drawings can be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of this application provided in the drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application.

[0026] Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] In the description of this application, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," and "the other end," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0028] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0029] Example 1, as Figures 1-2 As shown, the design method for porous spinal pedicle screws based on bone density distribution proposed in this application includes the following steps: S1. Data processing and porosity gradient construction: The screw trajectory is planned using preoperative CT data to obtain the bone density (CT value) distribution along the trajectory. Based on the characteristics of spinal anatomy, a micro-porosity gradient is constructed by combining manual positioning and mapping algorithms. This makes the porosity of the porous structure of the outer layer of the screw change in a gradient along the long axis, enhancing the ability of bone in the pedicle region with high bone density and high bone growth rate to grow into the screw pores, thereby enhancing the long-term screw holding force.

[0030] S11, 3D reconstruction and path planning; S111. Using the patient's spinal CT scan data, the target vertebral body is reconstructed in three dimensions, and the trajectory planning of the pedicle screw is performed manually. S112. Determine the entry point on the vertebral surface as... The internal endpoint of the vertebral body is Set the maximum diameter of the screw to be The minimum diameter is , construct With axis Frustum of a circle with a base diameter As a simulation of screw trajectory.

[0031] S12, Bone density sampling; S121, on the truncated cone axis Take a little upon taking office , and The distance is Create a circular cross-section perpendicular to the axis in the 3D CT reconstruction data. ; S122. Extract cross sections from CT metadata. CT values ​​for all pixels, and calculate the cross section. Average CT value of all pixels And record the average value. .

[0032] S13. Target porosity mapping (the mapping of pore structure can be based on CT values, or on bone mineral density data obtained from quantitative CT or MRI scans); S131. According to the mapping formula between porosity P and CT value K, P = m × K 0.5 +n(-4 < m < -2, 60 < n < 140), average CT value Converted into the corresponding target porosity ; S132, Based on the above target porosity Establish the porosity distribution function P along the length of the screw trajectory. This results in higher porosity in areas with higher CT values, providing more space for bone ingrowth and thus improving screw stability.

[0033] S14. Construction of gradient porosity porous structures; S141. The pores are formed by the periodic arrangement of helical units on three-period surfaces. The structure of the helical units can be derived from implicit functions. The structure is constructed, where c is a controllable parameter that can adjust the overall element density, and the X, Y, and Z spatial coordinates of the element structure surface are calculated accordingly. S142. For each helical unit on the outer layer of the screw, assume that the unit is perpendicular to the screw axis. The foot of the perpendicular is , and The distance is ; S143. Calculate the gradient porosity P from step S13. ; S144, Order The unit structure is calculated to generate a microporous structure that continuously varies along the screw axis; this makes the porosity in the dense pedicle region conducive to bone ingrowth and interlocking, improving the stability of the contact; while the porosity in the osteoporotic vertebral body region is relatively low, ensuring the overall mechanical strength of the screw, and thus ensuring the overall stability of the screw.

[0034] S145, at screw distance A 0-3mm non-porous area is established to reduce cutting of the pedicle cortex and decrease discomfort.

[0035] S2, a porous pedicle screw construction method, ensures the screw meets the patient's physical needs, inducing bone tissue ingrowth into the screw pores to form a microscopic bio-locking, improving long-term stability; it conforms to the characteristics of vertebral bone density distribution, increasing the porosity of the pedicle area to enhance screw holding force; it is a high-holding force solution that does not rely on bone cement reinforcement and conforms to traditional surgical procedures, making it safe and reliable. The design concept of this application is also applicable to hollow screws, pelvic screws, or long bone screws in vertebroplasty.

[0036] The working principle of this embodiment is as follows: First, using the patient's preoperative CT data, the bone density (CT value) distribution along the screw implantation trajectory is extracted, and the macroscopic bone density distribution is accurately mapped to a microscopic porosity gradient. The screw shaft adopts a composite design, with a solid titanium alloy core (tantalum metal, polyetheretherketone composite material, or biodegradable magnesium alloy, etc., suitable for 3D printing, can also be used) to ensure overall fatigue resistance and load-bearing capacity. The outer layer (approximately 1 mm thick) is a gradient porous structure based on helical units, with its porosity varying along the long axis of the screw. This reduces stress shielding and provides space for bone ingrowth, enhancing biological fixation. In addition, the screw adopts a tapered screw design to enhance the compaction effect, and a dual-pitch composite thread is added to address the different gripping properties of the pedicle cortex and vertebral cancellous bone, with a cancellous bone thread in the front section and a cortical bone thread in the rear section, taking into account the immediate mechanical holding force during implantation. The spiral unit in this application can also be body-centered cubic, face-centered cubic, diamond structure, truncated octahedron, or other lattice or other minimal surface structures.

[0037] Example 2, based on Example 1, combined with... Figure 3This application proposes a porous spinal pedicle screw based on bone density distribution, comprising a screw head 1, a screw rod 2, a threaded portion 3, a hole 4, and a tip 5. The screw head 1 is fixedly connected to the outer end of the screw rod 2, and the tip 5 is fixedly connected to the insertion end of the screw rod 2, making it easier to insert into the bone area during operation, facilitating chip removal and self-tapping, and reducing implantation torque. The threaded portion 3 is located on the outer wall of the screw rod 2, and the hole 4 is opened on the side wall of the screw rod 2. The screw head 1 has a U-shaped cylindrical structure, with an internal thread and a connecting rod groove on its inner wall, and a circular groove on its side wall for the insertion of the connecting rod, facilitating operation. The top center of the screw head 1 has an internal hexagonal groove or a quincunx groove for screwdriver torque transmission, resulting in more stable force distribution during operation.

[0038] Specifically, the diameter of the screw 2 gradually decreases from the head 1 towards the tip 5, increasing the pull-out force generated by bone compression. The screw 2 comprises an inner layer and an outer layer. The pores 4 are formed in the outer layer of the screw 2. The inner layer is a solid titanium alloy, ensuring the screw's resistance to bending and fracture. The outer layer is a porous layer with a thickness of 1 mm, exhibiting the gradient spiral void structure described in Example 1, where the porosity increases along the long axis with increasing P. The layer directly contacts the bone, providing low-modulus matching and a scaffold for bone ingrowth. The threaded portion 3 includes thread a31 and thread b32. Thread a31 is configured with a fine pitch, designed for cortical bone, to increase the contact area with the cortical bone; thread b32 is configured with a wide pitch, designed for cancellous bone, to increase the holding volume of cancellous bone, and improve stability.

[0039] The above specific embodiments are merely preferred embodiments of this application. Based on the technical solutions of this application and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments. The above specific embodiments are merely explanations of this application and are not limitations on this application.

Claims

1. A method for designing a porous pedicle screw for a spine based on a bone density distribution, characterized by, Includes the following steps: S1. Data processing and porosity gradient construction; S11, 3D Reconstruction and Path Planning; S12, Bone density sampling; S13, Target porosity mapping; S14. Construction of gradient porosity porous structures; S2, construction of porous pedicle screws.

2. The method of designing a porous pedicle screw based on bone density distribution of a spine according to claim 1, wherein, Step S11 includes: S111. Using the patient's spinal CT scan data, the target vertebral body is reconstructed in three dimensions, and the trajectory of the pedicle screw is planned. S112. Determine the entry point on the vertebral surface as... The internal endpoint of the vertebral body is Set the maximum diameter of the screw to be The minimum diameter is , construct With axis Frustum of a circle with a base diameter As a simulation of screw trajectory.

3. The design method for porous spinal pedicle screws based on bone density distribution according to claim 2, characterized in that, Step S12 includes: S121, on the truncated cone axis Take a little upon taking office , and The distance is Create a circular cross-section perpendicular to the axis in the 3D CT reconstruction data. ; S122. Extract cross sections from CT metadata. CT values ​​for all pixels, and calculate the cross section. Average CT value of all pixels .

4. The design method for porous spinal pedicle screws based on bone density distribution according to claim 3, characterized in that, Step S13 includes: S131. According to the mapping formula between porosity P and CT value K, P = m × K 0.5 +n(-4 < m < -2, 60 < n < 140), average CT value Converted into the corresponding target porosity ; S132. Establish the porosity distribution function P along the length of the screw trajectory. .

5. The design method for porous spinal pedicle screws based on bone density distribution according to claim 4, characterized in that, Step S14 includes: S141. The pores are formed by the periodic arrangement of helical units on three-period surfaces. The structure of the helical units can be derived from implicit functions. The structure is constructed, where c is a controllable parameter that can adjust the overall unit density, and the X, Y, and Z spatial coordinates of the unit structure surface are calculated accordingly. S142. For each helical unit on the outer layer of the screw, assume that the unit is perpendicular to the screw axis. The foot of the perpendicular is , and The distance is ; S143. Calculate the gradient porosity P from step S13. ; S144, Order The unit structure is calculated to generate a micropore structure that varies continuously along the screw axis; S145, at screw distance A pore-free area of ​​0-3mm is established to reduce the cutting of the pedicle cortex.

6. The porous spinal pedicle screw based on bone density distribution according to any one of claims 1-5, characterized in that, Includes a nail head (1), a screw (2), a threaded part (3), a hole (4), and a tip (5); The nail head (1) is fixedly connected to the outer end of the screw (2), the tip (5) is fixedly connected to the insertion end of the screw (2), the threaded part (3) is provided on the outer wall of the screw (2), and the hole (4) is opened on the side wall of the screw (2).

7. The porous spinal pedicle screw based on bone density distribution according to claim 6, characterized in that, The nail head (1) has a U-shaped cylindrical structure. The inner wall of the nail head (1) is provided with an internal thread and a connecting rod groove. The side wall of the nail head (1) is provided with a circular groove for the connecting rod to pass through. The top center of the nail head (1) is provided with an internal hexagonal groove or a plum blossom-shaped groove for the transmission of screwdriver torque.

8. The porous spinal pedicle screw based on bone density distribution according to claim 6, characterized in that, The diameter of the screw (2) gradually decreases from the head (1) towards the tip (5).

9. The porous spinal pedicle screw based on bone density distribution according to claim 6, characterized in that, The screw (2) includes an inner layer and an outer layer; The pores (4) are formed on the outer layer of the screw (2), and the inner layer is a solid titanium alloy.

10. The porous spinal pedicle screw based on bone density distribution according to claim 6, characterized in that, The threaded portion (3) includes thread a (31) and thread b (32); The thread a (31) is set to a fine pitch to increase the contact area with the cortical bone; The thread b (32) is set to a wide pitch to increase the holding volume of cancellous bone.

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