Ankle fracture syndesmosis fixation device

Abstract

The application discloses a tibiofibular syndesmosis fixation device for ankle fracture, and belongs to the field of orthopedic medical instruments, aiming to solve the problems of early fixation stability and late physiological micro-motion being difficult to be considered, poor anchoring reliability and high operation difficulty in the prior art. The device comprises a preassembled screw bushing assembly and a drill bit guide mechanism which can be detached during operation. The screw bushing assembly comprises a fixed screw, a fibula side sliding bushing, a degradable filling body and a removable limiting thin outer sleeve. The bushing is provided with an oval inner cavity. The filling body fully covers and locks the spherical end of the screw in the early stage to realize rigid fixation. After degradation for 11-13 weeks, tibiofibular physiological horizontal sliding and 3-8 degrees of small amplitude self-rotation are released. The thin outer sleeve restrains the barb, and is removed after being screwed into place to realize one-way self-locking anchoring. The guide mechanism is provided with a double-angle guide hole to complete precise drilling. The application realizes time-sequential mechanical adaptation, controllable and reliable anchoring, simple operation, wide application population, and can effectively reduce the incidence of bone nonunion and joint stiffness.

Description

Technical Field

[0001] This invention belongs to the field of medical device technology, specifically a fixation device for the tibiofibular syndesmosis of the ankle joint fracture. Background Technology

[0002] The distal tibiofibular syndesmosis (TFC) injury is the most common comorbid injury type of ankle fracture, accounting for approximately 20%–25% of all ankle fractures. About 10% of these patients will suffer from long-term sequelae such as chronic ankle instability, recurrent swelling and pain, and traumatic arthritis due to improper treatment, severely impacting their quality of life. As a micro-movement joint connecting the distal tibia and distal fibula, the TFC exhibits highly specific physiological movements: during walking, tiptoeing, and climbing stairs, only 0.3–0.5 mm of lateral horizontal sliding and a small rotation of 3°–8° occur, without anteroposterior displacement or excessive rotation. Therefore, an ideal TFC fixation device must simultaneously meet two core requirements: first, providing an absolutely stable fixation environment in the early stages of fracture healing to ensure no abnormal micromovement between the fracture ends and torn ligaments; second, allowing micromovement that perfectly matches the physiological movement patterns after fracture healing, avoiding joint stiffness, cartilage degeneration, and stress concentration fractures caused by permanent rigid fixation.

[0003] Currently, the most commonly used method for fixing the distal tibiofibular syndesmosis in clinical practice is traditional cortical compression screw fixation. This technique uses one or two fully threaded cortical screws to simultaneously penetrate the three layers of cortex of the fibula and tibia to achieve rigid compression fixation. However, clinical application has revealed a series of inherent defects that cannot be overcome: First, traditional screws are permanent rigid locking structures, completely restricting the physiological micro-movement of the distal tibiofibular syndesmosis, which easily leads to decreased ankle joint mobility and joint stiffness after surgery, with a long-term follow-up incidence of traumatic arthritis exceeding 30%; Second, screws subjected to cyclic alternating loads for a long time are prone to fatigue fracture, and removal after fracture is extremely difficult, easily leaving behind metallic foreign bodies; Third, the implantation path penetrates the entire weight-bearing cortex of the medial tibia, damaging the integrity of the host bone, easily inducing stress shielding and bone loss, and in patients with osteoporosis, the screw-bone engagement strength is insufficient, resulting in a high incidence of postoperative loosening and dislodgement; Finally, all patients require a second surgery to remove the screws, increasing surgical trauma, medical costs, and infection risks.

[0004] To address the shortcomings of traditional rigid fixation, scholars both domestically and internationally have proposed the concept of "flexible fixation," advocating for the preservation of the physiological micro-movements of the distal tibiofibular syndesmosis through elastic connection structures. Among these, the distal tibiofibular syndesmosis hinged flexible fixator disclosed in patent ZL201310476609.1, applied for by Tianjin Zhengtian Medical Devices Co., Ltd. in 2013, is a representative solution of flexible fixation technology and the closest existing technology to the present invention. The core structure of this patent includes a universal fibular screw and a tibial screw. The universal fibular screw has a spherical head at its proximal end, and the tibial screw has a circular ball-and-socket hole inside. The spherical head is rotatably housed within the circular ball-and-socket hole, allowing the fibular screw to rotate freely in all directions relative to the tibial screw after implantation. This aims to simulate the physiological micro-movements of the distal tibiofibular syndesmosis and avoid the joint stiffness problems associated with traditional rigid fixation.

[0005] However, clinical applications and biomechanical studies have shown that the aforementioned closest existing technology still has the following core technical defects, failing to truly resolve the core contradictions in distal tibiofibular syndesmosis fixation: First, after implantation, the patented technology immediately enters a state of omnidirectional flexible rotation. In the early stage of fracture healing (0-12 weeks post-surgery), the fracture ends and torn ligaments are in a continuous micro-motion environment, which interferes with callus formation and ligament fiber healing. Clinical data show that its nonunion rate is about 15% higher than that of traditional rigid fixation. Patients need to strictly limit weight-bearing for more than 3 months after surgery, which prolongs the rehabilitation period.

[0006] Secondly, the physiological movement of the distal tibiofibular syndesmosis is limited to lateral horizontal sliding and small rotation of 3° to 8°. However, the circular ball-and-socket structure used in this patent allows the screw to rotate 360° in any direction, which cannot limit abnormal anterior and posterior displacement and excessive rotation. Postoperatively, chronic instability of the distal tibiofibular syndesmosis and ankle inversion and valgus deformity are likely to occur, and the incidence of long-term traumatic arthritis has not been significantly reduced.

[0007] Third, this patent relies solely on the engagement of the external thread of the tibial screw with the cancellous bone of the tibia to achieve fixation. Under long-term micro-movement, the thread will continuously cut the bone, leading to the expansion of the bone tunnel and loosening of the screw. For patients with severe osteoporosis with a T value ≤ -2.5, the thread anchoring strength is less than 40N, and the incidence of implant loosening and dislodgement within 6 months after surgery is as high as 28%. At the same time, the screw penetrates the entire weight-bearing cortex of the medial side of the tibia, destroying the integrity of the cortical bone and further aggravating the risk of stress shielding and bone resorption.

[0008] Fourth, the patent does not have a dedicated drilling guide mechanism, and the surgeon has to rely entirely on experience to drill by hand during the operation. The angle error of the bone tunnel often exceeds 10°, which can easily lead to screw displacement and joint surface damage. In addition, repeated C-arm fluoroscopy calibration is required, which significantly increases the radiation exposure dose for both doctors and patients.

[0009] Fifth, the patent does not design a suitable solution for children under 14 years of age whose epiphyses have not closed, and metal implants can hinder epiphyseal growth and development; it also does not provide anchoring and reinforcement measures for patients with osteoporosis, thus limiting its applicability.

[0010] Besides the hinged flexible fixators mentioned above, existing flexible fixation techniques also include looped plate fixation and elastic suture fixation, but these also have significant limitations: looped plates are excessively elastic and cannot provide sufficient initial stability, and the sutures are prone to fatigue fracture; elastic sutures have insufficient fixation strength, and postoperative loss of reduction of the distal tibiofibular syndesmosis is common. In summary, existing technologies have consistently failed to overcome the technical bottleneck of "early stability and late-stage micromotion being mutually exclusive," unable to simultaneously meet the rigid fixation requirements in the early stages of fracture healing and the precise physiological micromotion requirements after healing. Furthermore, they have many shortcomings in areas such as bone damage at the implantation path, anchoring reliability, standardized operation, and adaptation to special populations, failing to comprehensively address clinical pain points. Therefore, developing a distal tibiofibular syndesmosis fixation device that can achieve sequential mechanical switching, precise control of physiological movement, reliable and controllable anchoring, minimal bone damage at the implantation path, simple operation, and coverage of the entire population has significant clinical and social value. Summary of the Invention

[0011] The purpose of this invention is to provide a fixation device for the distal tibiofibular syndesmosis of the ankle fracture. Through time-sequential degradation mechanical switching, precise movement limitation of the elliptical cavity, controllable release layered anchoring system, and matching standardized surgical tools and a solution suitable for all population groups, this invention simultaneously meets the core needs of early rigid fixation and late physiological micro-movement of the distal tibiofibular syndesmosis. It effectively reduces the risk of nonunion, joint stiffness, and implant loosening and dislodgement. The surgical operation is simple and the clinical application is wide.

[0012] The technical solution adopted in this invention is as follows: A fixation device for distal tibiofibular syndesmosis of ankle fracture, comprising at least one set of pre-assembled integrated screw bushing assemblies; Each screw-buckle assembly includes a fixing screw, a fibular-side sliding bushing, and a removable limiting thin outer sleeve. The fixing screw consists of three integrated sections from distal to proximal: a cortical threaded section, a smooth intermediate section, and a spherical end. The outer diameter of the cortical threaded section is larger than that of the smooth intermediate section, and it is used to screw into the tibial cortex to achieve anchoring. The spherical end is integrally formed at the proximal end of the smooth intermediate section, with a through-hole in the center. The fibular-side sliding bushing has a cylindrical outer contour structure, which is adapted to the pre-fabricated circular countersunk groove on the outer side of the fibula. An integrated flange is provided at the end of the bushing near the outer side of the fibula. The center of the outer surface of the integrated flange has an internal hexagonal groove, which is used to connect a torque tool during the operation to drive the bushing and the pre-installed screw to rotate synchronously. The bushing has an original elliptical inner cavity in the axial direction. An annular closing edge is provided at the end of the elliptical inner cavity near the tibia, and the end near the outer side of the fibula is closed by the integrated flange. The inner diameter of the annular closing edge is smaller than the outer diameter of the spherical end, which is used to prevent the spherical end from dislodging towards the tibia. The spherical end is pre-assembled and housed inside the elliptical inner cavity at the factory. The remaining space in the elliptical inner cavity and the central through hole of the spherical end are simultaneously filled with a biodegradable filler. The filler inside the through hole and the filler around the cavity are integrated to form an internal and external locking structure. The filler fills the original elliptical inner cavity into an approximately circular hole, fully covering and locking the spherical end, so that the fixation screw does not slip or rotate in the early postoperative period, and forms a rigid whole with the bushing to achieve rigid fixation. The biodegradable filler gradually degrades in the body, and after the filler completely disappears, the elliptical inner cavity restores its original contour; the spherical end can only achieve physiological horizontal sliding of the tibia and fibula along the major axis of the ellipse, and can only rotate slightly within the physiological range of 3° to 8°; the inner diameter of the through hole of the prefabricated through screw on the fibular side is larger than the outer diameter of the smooth rod section in the middle of the fixing screw, and an annular movement gap is reserved between the two, which releases the swing and sliding space of the fixing screw in sync with the movement of the spherical end, matching the movement law of the human lower tibia and fibula syndesmosis gap; The outer wall of the bushing is prefabricated with a storage groove that matches the shape of the barbs. Multiple rings of axially elastic titanium-nickel shape memory alloy barbs are set in the groove. The removable limiting thin outer sleeve is pre-fitted onto the outer wall of the bushing cylinder to restrain and gather the elastic barbs in the storage groove, preventing the barbs from prematurely rebounding and jamming the bone wall during the implantation and twisting process. The outer sleeve is provided with 1 to 2 axially penetrating thinning and easily broken grooves. After twisting to the correct position, the thin outer sleeve is cut off and removed. The barbs rebound and embed into the cortical bone of the grooved side wall of the fibula, forming a unidirectional self-locking axial mechanical anchor.

[0013] Preferably, it also includes a detachable drill guide mechanism during surgery; the drill guide mechanism can be detachably clamped and fixed to the lateral cortex of the fibula, and the guide mechanism has a first guide hole and a second guide hole with a fixed angle between their axes, which correspond to the drilling paths of the two sets of screw bushing assemblies respectively, for synchronously and directionally drilling the through hole of the fibular screw and the threaded bottom hole of the tibial screw during surgery.

[0014] Preferably, the biodegradable filler is a 75:25 PLGA-doped 5wt% βTCP composite material, with an overall hydrolysis degradation cycle of 11 to 13 weeks.

[0015] Preferably, the fibular sliding bushing is made of medical-grade PEEK in one piece; the inner wall of the elliptical cavity is provided with a 45-55μm silver-loaded porous self-lubricating layer; multiple barbs are evenly distributed around each ring, with a natural opening angle of 14°-16°, and the tips are directed towards the annular closing edge, i.e., the tibial side; the removable limiting thin sleeve is a medical-grade thin-walled stainless steel sleeve with a wall thickness of 0.15-0.25mm, a smooth inner surface, and a gap fit with the outer wall of the bushing, and a pull-holding ear is provided at the tail end for easy clamping and removal during surgery.

[0016] Preferably, the outer wall of the bushing cylinder and the inner end face of the flange that fits the bone surface are provided with an interconnected porous bone integration layer and sprayed with a gradient HA hydroxyapatite coating. After surgery, the fibular bone tissue grows in to achieve long-term biological permanent fixation and gradually replace the early mechanical anchoring. The bushing is equipped with a titanium alloy anti-rotation pin, which is used to lock the circumferential position of the bushing after it is screwed in place, so as to ensure that the long axis of the elliptical inner cavity is always aligned with the physiological sliding direction.

[0017] Preferably, the fixing screw is made of titanium-nickel shape memory alloy and has a 1.0-1.5μm nano-DLC wear-resistant coating on its surface.

[0018] Preferably, the drill bit guiding mechanism includes a U-shaped clamping base and a locking screw; the first guide hole and the second guide hole are respectively fixed on the U-shaped clamping base, and the included angle between their axes is 18° to 26°, which is completely matched with the preset cross angle of the two sets of screw bushing assemblies, respectively adapting to the drilling trajectory of the fibular through hole and the tibial thread bottom hole of the two screws.

[0019] Preferably, the device is equipped with a child-adaptable absorbable screw assembly, which adopts a PLGA composite 40% βTCP hollow porous structure, with a single screw outer diameter of 3.2mm and a degradation cycle of 1.4 to 1.6 years. The distal threaded section is screwed into the tibial side for fixation, avoiding interference with epiphyseal growth. It is matched with an osteoporosis-enhanced CPC bone cement assembly, which has a cured compressive strength of ≥80MPa. It is used to fill and reinforce the gap between the fibular side sliding bushing and the countersunk groove on the lateral side of the fibula, and to enhance the initial anchoring strength of the barbs.

[0020] Preferably, the intraoperative installation method includes the following steps: S1. During the operation, the inferior tibiofibular syndesmosis space between the tibia and fibula is reduced, the U-shaped clamping base of the drill guide mechanism is snapped and fixed to the lateral cortex of the fibula, and the locking screw is tightened to achieve temporary fixation; S2. Complete dual-path drilling through the first and second guide holes arranged at an angle: pre-drill two through screw holes on the fibular side, with the inner diameter of the through holes being larger than the outer diameter of the smooth middle section of the fixing screw, and enlarge a circular countersunk groove on the outer side of each hole; simultaneously pre-drill two screw threaded bottom holes on the tibia side, with the inner diameter of the bottom holes matching the outer diameter of the cortical threaded section of the fixing screw, and form cortical threaded holes after tapping; S3. After drilling is completed, the drill bit guide mechanism on the fibular side is completely removed; S4. Take out the two sets of pre-installed integrated screw bushing assemblies. Each set of assemblies has a removable limiting thin sleeve on its outer wall, and the barbs are restrained and gathered in the storage groove. Align the leather thread section of each set of fixing screws with the corresponding screw through hole on the fibular side and push them forward until the sliding bushing on the fibular side is fully embedded in the countersunk groove at the corresponding position. S5. Insert the hexagonal torque wrench into the hexagonal groove in the center of the integrated flange, and turn it to drive the fibular side sliding bushing and the pre-installed fixing screw to rotate synchronously, so that the cortical thread section is completely screwed into the corresponding pre-made cortical thread hole of the tibia, and the screw anchoring and bushing circumferential angle alignment are completed. S6. Disconnect and remove the removable limiting thin outer sleeve of the bushing. After the titanium-nickel memory alloy barbs lose their restraint, they spring open and the tips are embedded in the cortical bone of the slotted side wall of the fibula, forming a one-way self-locking axial mechanical anchor. S7. Insert the titanium alloy anti-rotation pin through the pin hole, insert it laterally into the fibular bone, lock the circumferential angle of the bushing, and ensure that the long axis of the elliptical inner cavity is consistent with the physiological sliding direction of the tibia and fibula, thus completing the single-group implantation fixation; the two groups of assemblies are operated in the same steps in sequence to finally achieve double screw cross fixation.

[0021] Preferably, before implanting the liner in patients with osteoporosis, reinforced calcium phosphate bone cement is first applied to the inner wall of the countersunk groove on the lateral side of the fibula, then the sliding liner on the fibular side is pressed in, the thin outer sleeve is removed, and after the bone cement has solidified, the initial anchoring strength of the liner is reinforced.

[0022] The beneficial effects of this invention are as follows: 1. This invention requires no additional mechanical unlocking mechanism. It achieves a smooth transition from early postoperative absolute rigidity locking to mid-term precise physiological micro-movement solely through the natural hydrolysis process of the biodegradable filler synchronized with the healing cycle of the tibiofibular syndesmosis injury. Within 11-13 weeks post-surgery, the filler completely locks the spherical end, preventing abnormal micro-movement of the tibiofibular syndesmosis and providing a stable healing environment for the fracture ends and torn ligaments, significantly reducing the risk of nonunion and ligament repair failure. After complete degradation, the filler automatically releases freedom of movement, matching the joint's movement needs after healing, breaking the technical paradox of traditional fixation methods where "stability inevitably sacrifices movement, and movement inevitably sacrifices stability." The device is positioned on the lateral side of the fibula, without damaging the medial cortical bone of the tibia, maximizing the preservation of the host bone integrity and reducing the risk of bone resorption caused by stress shielding.

[0023] 2. This invention employs a dual motion control mechanism: an elliptical internal cavity as the primary constraint and a fibular screw through-hole clearance for secondary avoidance. The original elliptical internal cavity, relying on its natural geometric shape, restricts the spherical end to slide laterally along its long axis and rotates slightly within a 3°–8° range, eliminating abnormal movement patterns such as anterior-posterior displacement and excessive rotation from the structural root. Combined with the annular movement gap formed by the stepped-diameter fixing screw and the fibular lateral expansion screw through-hole, sufficient clearance is provided for the synchronous swinging and offset of the screw shaft, preventing bone wall congestion that restricts physiological micro-movements. This dual mechanism perfectly replicates the natural movement pattern of healthy human bodies—0.3–0.5 mm of lateral sliding and 3°–8° of slight rotation—maintaining long-term stability while preserving joint mobility, significantly reducing the incidence of long-term joint stiffness and traumatic arthritis.

[0024] 3. This invention adopts a three-layer anchoring design of "removable restraint jacket + unidirectional self-locking barb + long-term biointegration", which solves the defects of traditional barb structures such as "implantation jamming and uncontrollable anchoring timing": the factory-installed removable limiting thin jacket completely restrains and retracts the barb, and the outer wall of the bushing maintains a smooth cylindrical surface. There is no bone wall scraping resistance during the entire process of implantation, pushing and screwing, ensuring that the screw threads are fully engaged. After the screw is screwed in place, the thin jacket is removed, and the titanium-nickel shape memory alloy barb rebounds and embeds into the fibular cortex, forming a unidirectional self-locking anchoring with a larger load and tighter engagement. The initial anti-dislodgement strength is stable and reliable.

[0025] In the long term, the porous osteointegration layer on the outer wall of the bushing induces three-dimensional ingrowth of autologous bone tissue, gradually forming an integrated bone-implant bio-anchoring structure that permanently replaces mechanical anchoring force, allowing the implant to remain in the body for life without the need for a second surgery. The countersunk groove embedding design ensures that the flange is flush with the lateral cortex of the fibula, significantly reducing subcutaneous soft tissue irritation and lowering postoperative pain and skin abrasion complications. The rear-mounted anti-rotation pin's operational logic completely avoids interference with the initial tightening process, precisely locking the long axis of the elliptical inner cavity and preventing slippage or deviation.

[0026] 4. This invention features a dedicated dual-path drill guide mechanism, enabling one-time clamping and positioning for directional drilling of the fibular screw through-hole and the tibial thread bottom hole. The drilling angle error is controlled within 2°, eliminating the need for manual positioning and repeated fluoroscopic calibration by the surgeon, significantly reducing the difficulty of the surgical procedure and the radiation exposure dose for both doctors and patients. The hexagonal force application design in the center of the flange conforms to clinical orthopedic surgical operating habits, allowing for simultaneous tightening and anchoring of the bushing and screw without the need for additional clamping of the screw shaft, making the operation simple and efficient.

[0027] The independent modular design with a single bushing and a single screw allows for flexible selection of one or two screws for cross fixation depending on the severity of the patient's injury, making it suitable for a full range of cases from mild to severe tibiofibular separation. It is also equipped with pediatric absorbable screw components and CPC bone cement reinforcement components for osteoporosis patients, covering patients of all ages and bone mass levels, significantly expanding the scope of clinical application and improving the overall treatment effect. Attached Figure Description

[0028] Figure 1 A schematic diagram of drilling holes for a tibiofibular syndesmosis fixation device in an ankle fracture. Figure 2 A schematic diagram showing the ankle joint fracture after fixation with a tibiofibular syndesmosis fixation device. Figure 3 This is an axial cross-sectional schematic diagram of the tibial side sliding bushing of the present invention; Figure 4 for Figure 3 Schematic diagram of the AA section; Figure 5 This is a flowchart of the intraoperative installation method of the present invention.

[0029] In the figure, 1. Tibia; 2. Fibula; 3. Tibiofibular syndesmosis space; 4. Fixation screw; 41. Cortical threaded segment; 42. Smooth intermediate rod segment; 43. Spherical end; 5. Fibular lateral sliding bushing; 51. Integrated flange; 511. Hexagonal recess; 53. Elliptical inner cavity; 54. Annular closing flange; 55. Titanium-nickel shape memory alloy barb; 56. Titanium alloy anti-rotation pin; 57. Removable limiting thin outer sleeve; 58. Interconnected porous bone integration layer; 6. Biodegradable filler; 7. Drill bit guiding mechanism; 71. U-shaped clamping base; 72. Locking fixation screw; 74. First guide hole; 75. Second guide hole. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this is not intended to limit the scope of protection of the present invention.

[0031] like Figures 1 to 5As shown, this invention discloses a fixation device for the distal tibiofibular syndesmosis of the ankle fracture and its intraoperative installation method. It consists of a three-stage time-adaptive fixation system that perfectly matches the biomechanical requirements of the entire healing cycle after distal tibiofibular syndesmosis injury of the human ankle joint: The first stage is the early rigid locking period from 1 to 13 weeks postoperatively, relying on the integrated biodegradable filler 6 to cover the proximal spherical end 43 of the locking screw 4, eliminating horizontal slippage between the tibia and fibula and micro-movement of the screw rotation, providing a stable healing environment without micro-movement for distal tibiofibular ligament tears, distal tibiofibular syndesmosis separation, and ankle fracture ends; The second stage is the mid-term physiological activity adaptation period after the filler 6 has completely degraded. After the filler 6 hydrolyzes and disappears, the original elliptical cavity 53 inside the fibular lateral sliding bushing 5 is fully exposed, and the spherical end 43 can complete the tibiofibular healing along the long axis of the elliptical cavity 53. The rational horizontal sliding mechanism, while limiting the rotation angle range of the spherical end 43 to 3° to 8°, combined with the annular movement gap reserved in the through hole of the fibular side screw, replicates the natural micro-movement pattern of the tibiofibular syndesmosis when a healthy human walks, tiptoes, and goes up and down stairs, avoiding the complications of ankle stiffness, cartilage degeneration, and stress concentration fractures caused by permanent locking of traditional rigid compression screws; the third stage is the long-term bio-integration and fixation period more than 6 months after surgery. Relying on the interconnected porous bone integration layer 58 on the outer wall of the fibular side sliding bushing 5 and the gradient hydroxyapatite coating, the host's autologous bone tissue is induced to grow into the surface pores of the bushing, forming an integrated bone-implant bio-anchoring structure, which gradually replaces the initial mechanical anchoring force provided by the titanium-nickel shape memory alloy barbs 55, greatly reducing the probability of implant loosening, dislodgement, and secondary surgery removal in osteoporosis patients.

[0032] The entire device is divided into two independent functional modules: a pre-assembled integrated screw bushing assembly and a drill guide mechanism 7 used separately during surgery. These two modules work together to complete the entire process of precise preoperative drilling, intraoperative implantation and anchoring, and postoperative sequential mechanical adaptation. The screw bushing assembly is the core load-bearing and sequential mechanical control component of the device, assembled from four core components: a fixing screw 4, a fibular lateral sliding bushing 5, a biodegradable filler 6, and a removable limiting thin outer sleeve 57. The drill guide mechanism 7 is a dedicated intraoperative positioning tool, temporarily clamped to the lateral cortex of the fibula 2 during the drilling stage. It is completely removed after drilling is completed, leaving no residue inside the body and not participating in postoperative bone healing mechanical support. This invention also includes two types of auxiliary kits adapted to different clinical populations: an absorbable screw assembly for children with unclosed epiphyses and a CPC-reinforced bone cement assembly for elderly patients with bone loss and osteoporosis, respectively addressing two major clinical pain points: trauma from secondary implant removal in children and insufficient bone tunnel anchoring strength in elderly patients.

[0033] The screw bushing assembly is a pre-assembled integrated component shipped from the factory. At the factory stage, the fixing screw 4, the fibular side sliding bushing 5, and the biodegradable filler 6 are pre-sealed and pre-assembled. A removable limiting thin outer sleeve 57 with restraining barbs is fitted onto the outer wall. In clinical use, no on-site assembly is required; it only needs to be implanted into the fibula on both sides with countersunk grooves. Its core function is to achieve three-tiered temporal and mechanical regulation: early rigid locking, mid-term physiological micro-motion adaptation, and long-term osseointegration anchoring. The screw bushing assembly consists of the following components: fixing screw 4, fibular side sliding bushing 5, biodegradable filler 6, and removable limiting thin outer sleeve 57. The interfaces of these four components mutually limit, fill, and cover each other to form an integrated locking structure.

[0034] The fixing screw 4 is divided into three sections along its central axis: a distal cortical thread section 41, a middle smooth rod section 42, and a proximal spherical end 43. These sections are machined into a single piece without any splicing welds, thus avoiding the risk of stress concentration and fracture after implantation.

[0035] The distal cortical threaded segment 41 uses a standard orthopedic asymmetric compression cortical thread with a thread angle of 55° and a pitch of 1.2 mm. The outer diameter of the thread matches the inner diameter of the pre-drilled hole in the tibial cortex. After the thread is screwed in, it forms a rigid connection with the tibial cortex, completely transferring the load on the fibular side to the screw shaft, and then through the proximal spherical end 43 to the sliding bushing 5 on the fibular side, achieving transverse compression fixation of the tibia and fibula. The threaded segment length is set in three standardized specifications: 22 mm, 26 mm, and 30 mm, which can be adapted to different patients' tibial cortex thickness and the width of the distal tibia-fibula syndesmosis gap 3. Clinically, it can be selected as needed based on intraoperative fluoroscopic images. The outer diameter of the cortical threaded segment 41 is larger than the outer diameter of the middle smooth rod segment 42, forming a stepped diameter change, ensuring the anchoring engagement depth on the tibial side while reserving a movement gap on the fibular side.

[0036] The middle smooth rod segment 42 is a smooth cylindrical structure without threads. The outer diameter of the rod is smaller than the major diameter of the thread. The length of the rod corresponds to the thickness of the natural gap 3 of the tibiofibular syndesmosis in the human body, with a standard range of 4mm to 9mm. It is suitable for the anatomical size of the ankle joint of different body types in adults. The smooth rod segment passes through the soft tissue gap 3 of the tibiofibular syndesmosis and the through hole of the fibula 2, without cutting or compressing the intertibiofibular ligament, reducing postoperative soft tissue adhesion and pain complications. The inner diameter of the through hole of the prefabricated screw on the side of the fibula 2 is larger than the outer diameter of the middle smooth rod segment 42. The two form an annular movement gap, which provides space for the screw to slide laterally and rotate slightly after the filler degrades, avoiding the restriction of physiological micro-movement by the bone hole wall.

[0037] The proximal smooth spherical end 43 is integrally machined with the proximal end of the screw rod, resulting in a complete smooth spherical surface without sharp edges or cutting burrs. The surface roughness Ra of the spherical surface is ≤0.8μm, which avoids the sharp interface from cutting the filler 6 during the degradation process and causing premature fragmentation failure. The outer diameter of the spherical end 43 is set to 4.6mm. This size is selected based on the standard inner diameter of the countersunk groove matching bushing on the 2nd side of the human fibula, which allows for a reasonable thickness of the filler 6. At the same time, it matches the inner diameter of the bushing annular closing edge 54 with a limit of 4.0mm, thus achieving a limiting structure that prevents the spherical end 43 from dislodging from the tibia 1 side of the bushing. A through-hole is opened at the center of the spherical end 43 along the entire axis of the screw. The inner diameter of the through hole is 1.8mm. The through hole passes through both sides of the spherical surface of the spherical end 43. During the assembly stage, the biodegradable filler 6 completely fills the inside of the through hole, so that the filler 6 inside the through hole and the filler 6 inside the elliptical inner cavity 53 of the bushing are connected as a whole, forming an internal and external integrated locking constraint structure, which prevents the spherical end 43 from having relative displacement in the radial, circumferential and axial directions.

[0038] The fixing screw 4 is integrally molded from titanium-nickel shape memory alloy with the following alloy composition mass ratio: Ti 50.8at%, Ni 49.2at. This ratio is selected based on the fact that the martensitic phase transformation temperature of this titanium-nickel alloy is 32℃, while the human body temperature of 36.5℃ is higher than the phase transformation temperature. After implantation, the alloy maintains an austenitic superelastic state and has an 8% reversible deformation range. It can withstand the cyclic alternating loads brought about by daily ankle joint activities and has no risk of metal fatigue fracture. This is different from traditional titanium alloy screws, which have an elastic deformation limit of only 0.4% and are prone to screw fatigue fracture under long-term weight-bearing.

[0039] The basic mechanical properties of titanium-nickel shape memory alloy are: yield strength ≥820MPa, tensile strength ≥1100MPa, elongation at break ≥22%, elastic modulus 55GPa. The elastic modulus value is close to the elastic modulus of human cortical bone (10-30GPa), which greatly reduces the stress shielding effect caused by the mismatch of elastic modulus between the implant and bone tissue, and avoids postoperative resorption and bone loss of tibial cortical bone 1 and fibular 2.

[0040] The entire outer surface of the fixing screw 4 (threaded section, smooth rod section, and spherical end 43) is uniformly coated with a nano-DLC diamond-like carbon wear-resistant protective coating. The coating thickness is strictly controlled between 1.0μm and 1.5μm. The lower limit of 1.0μm is set because when the coating thickness is less than 1.0μm, continuous erosion by body fluids and proteases will rapidly wear down the coating, and the precipitation of metal ions will cause local aseptic inflammation. The upper limit of 1.5μm is set because when the coating thickness exceeds 1.5μm, the internal stress of the coating will increase, and the coating will peel off completely when the thread is screwed into the cortical bone during the implantation process, losing its protective effect.

[0041] The chemical composition of the nano-DLC coating is sp 3 Hybrid diamond phase carbon content 68%, sp 2The composite graphite phase has a carbon content of 32%, and the doping with trace amounts of medical-grade silicon enhances the biocompatibility of the coating. It contains no heavy metals or toxic catalytic residues.

[0042] The coating function is as follows: The friction coefficient of the DLC coating is ≤0.06, which is much lower than the friction coefficient of the bare titanium-nickel alloy of 0.32. After the filler 6 degrades, during the continuous reciprocating sliding and small rotation of the spherical end 43 and the inner wall of the elliptical inner cavity 53 of the bushing, the low friction coating eliminates dry friction wear at the metal interface, avoids local foreign body inflammation caused by metal wear debris, and at the same time isolates the titanium-nickel alloy substrate from direct contact with body fluids, inhibits the continuous precipitation of nickel ions, and reduces the incidence of adverse reactions such as redness and swelling at the implantation site.

[0043] The fibular lateral sliding bushing 5 is the outer load-bearing body of the screw bushing assembly. It has an overall cylindrical outer contour with an outer diameter of 5mm, which is perfectly adapted to the pre-made circular countersunk grooves on both sides of the fibula during surgery. After implantation, the outer wall of the cylinder is in close contact with the inner wall of the groove. The bushing is molded in one piece using medical-grade PEEK (polyether ether ketone) powder, without any adhesive or splicing structure. The medical-grade PEEK raw material has a purity of 99.95%, with no added plasticizers or phthalates. It has excellent biological inertness, no cytotoxicity or hemolytic reaction, and does not degrade or shrink or expand in the human body after long-term placement, serving as a permanent implant base.

[0044] PEEK bushing matrix basic mechanical parameters: elastic modulus 3.7 GPa, flexural strength ≥160 MPa, compressive strength ≥230 MPa, fracture toughness The elastic modulus of PEEK material is between that of human cancellous bone and cortical bone, which further weakens stress shielding. At the same time, it has extremely high creep resistance. It will not undergo plastic deformation of the inner cavity of the bushing when subjected to transverse pressure load of the tibia and fibula for a long time, ensuring the long-term stability of the original contour of the elliptical inner cavity 53, and accurately maintaining the 3°~8° rotation limit range of the spherical end 43 and the fixed horizontal sliding track.

[0045] The bushing is integrally injection molded with a flange 51 at one end near the lateral side of the fibula 2. The flange 51 fits the countersunk grooved step surface of the lateral cortical bone of the fibula 2, forming an axial limiting stop to restrict the bushing from being excessively pressed into the depth of the fibula 2, thus standardizing the bushing implantation depth. At the same time, it increases the contact area of ​​the bushing on the fibula 2 side, dispersing local cortical pressure and preventing crushing of the cancellous bone on the lateral side of the fibula 2. The center of the outer surface of the integral flange 51 has an internal hexagonal groove 511. The groove size is adapted to a standard orthopedic internal hexagonal torque wrench. In the early postoperative period when the filler is locked, the bushing and screw are a rigid whole. By applying force through the internal hexagonal groove, the bushing and the fixing screw can be rotated simultaneously to complete the distal threaded anchoring operation, eliminating the need to separately clamp the screw shaft for tightening, thus simplifying the intraoperative operation.

[0046] The bushing has an integrally formed annular retaining edge 54 at the end near the tibia 1. The inner diameter of the annular retaining edge 54 is 3.0-4.0 mm, which is smaller than the outer diameter of the spherical end 4.6 mm, forming a mechanical limiting structure. Regardless of whether the filler 6 degrades, the spherical end 43 is always contained and restricted inside the elliptical inner cavity 53 and cannot be dislodged from the tibia 1 side. Structurally, this eliminates the risk of screw and spherical end 43 shifting or dislodging towards the tibia 1 side, thus eliminating the potential for implantation failure. The annular retaining edge 54 is 0.9 mm thick with a smooth, rounded inner wall and no stress-prone sharp corners, reducing the probability of local stress concentration and breakage of the filler 6.

[0047] The bushing has an axially continuous original elliptical inner cavity 53. The cross-sectional geometry of the elliptical inner cavity 53 is fixed: the major axis is 5.4 mm and the minor axis is 4.8 mm. This difference between the major and minor axes is the core structural basis for achieving physiological slippage. The size design is based on the following: the minor axis of 4.8 mm is slightly larger than the outer diameter of the spherical end 43. After the filler 6 degrades and disappears, the spherical end 43 can only produce a unilateral horizontal slippage of 0.4 mm along the 5.4 mm major axis, which perfectly matches the 0.3-0.5 mm natural physiological slippage amplitude of the human lower tibia and fibula during walking; the minor axis of 4.8 mm is almost the same as the outer diameter of the spherical end 43, which basically restricts the displacement of the spherical end 43 along the elliptical minor axis, ensuring that the slippage direction is unique and that it only moves along the transverse physiological movement direction of the tibia and fibula, thus preventing abnormal anterior-posterior and superior-inferior displacement that could cause ankle instability.

[0048] A silver-loaded porous self-lubricating layer with a thickness of 45μm to 55μm was fabricated on the entire inner wall of the elliptical inner cavity 53. A lower limit of 45μm was set: if the thickness is insufficient, the volume of the porous structure will be too small, the silver ion loading will be insufficient, and the antibacterial cycle will be short. An upper limit of 55μm was set: if the thickness is too large, it will occupy the effective space of the elliptical inner cavity 53, reduce the sliding stroke of the spherical end 43, and interfere with the physiological micro-motion adaptation effect.

[0049] The self-lubricating layer substrate is made of medical-grade porous polytetrafluoroethylene (ePTFE) with a porosity of 62%. The interconnected pores are loaded with nano-sized silver particles with a mass fraction of 3wt% and a particle size of 20-50nm, which are uniformly adsorbed on the inner wall of the porous pores.

[0050] Two sets of annular recesses are formed along the axial direction on the cylindrical outer wall of the bushing. The recesses are 0.35mm deep, and their contours perfectly match the shape of the barbs 55 when retracted, ensuring that the barbs 55 are fully embedded in the recesses and flush with the cylindrical outer wall of the bushing without any protrusions. A ring of titanium-nickel shape memory alloy barbs 55 is welded and fixed in each annular recess. Four barbs 55 are evenly distributed along the circumference of the bushing in each ring, ensuring uniform force distribution during implantation and anchoring, and avoiding tilting due to unilateral force.

[0051] The material of a single barb 55 is the same as that of the fixing screw 4 titanium-nickel shape memory alloy with a ratio of Ti 50.8at% and Ni 49.2at%. The heat treatment and shaping process of barb 55 is: constant temperature tempering at 480℃ for 25 minutes, water cooling shaping, and the shape memory deformation parameters are precisely controllable at room temperature and human body temperature.

[0052] The natural opening angle of the barb 55 is strictly limited to 14°–16°. This angle limitation is based on the following: when the opening angle is less than 14°, the depth of the barb 55 penetrating the cortical bone after rebound is less than 0.2mm, the axial anchoring tensile strength is <120N, and it is prone to loosening under load; when the opening angle is greater than 16°, the barb 55 undergoes bending and plastic deformation when pressed into the groove, losing its memory rebound ability and failing to form a mechanical anchor. The standard preferred embodiment has an opening angle of 15°, with a stable anchoring tensile strength of 185–210N, meeting the maximum lateral load requirements of the human ankle joint during walking.

[0053] The tips of the barbs 55 are uniformly oriented towards the circumferential retaining edge 54 on the tibial side, forming a unidirectional axial self-locking structure. The mechanical changes during the entire implantation and anchoring process are fully recorded in two stages: Phase 1: Intraoperative liner twisting phase. The outer wall of the liner is fitted with a removable limiting thin outer sleeve 57. The barbs 55 are completely restrained and gathered in the outer wall storage groove. The outer wall of the liner maintains a complete and smooth cylindrical surface without any protrusions or obstructions. It can be smoothly pushed to the preset implantation depth and twisted smoothly without scratching the cancellous bone or cortical bone of the inner wall of the groove, reducing the generation of bone debris during the operation and reducing postoperative bone resorption in the groove.

[0054] Phase Two: After the bushing is screwed into place and the flange 51 is fitted to the countersunk step surface on the outer side of the fibula 2, the removable limiting thin outer sleeve 57 is removed. With the external constraint gone, the titanium-nickel shape memory alloy barbs 55 rebound and open due to their own memory effect. The tips penetrate into the inner wall of the cortical bone of the grooved sidewall of the fibula 2 to a depth of 0.25-0.35 mm. The barbs 55 and the cortical bone form a mechanical interlocking lock. When the tibiofibular syndesmosis is subjected to the lateral traction load of the fibula 2, the tension is transmitted to the screw 4, the ball end 43, and the bushing 5. The traction load will further cause the tips of the barbs 55 to interlock with the deep cortical bone. The greater the tension, the tighter the anchoring interlocking, forming a one-way anti-dislodgement self-locking anchoring structure, effectively resisting the lateral displacement and separation load of the fibula 2 during walking, running and jumping, and preventing the bushing 5 from axially slipping outward.

[0055] The removable limiting thin sleeve 57 is a medical-grade thin-walled stainless steel sleeve with a wall thickness of 0.15-0.25mm and a mirror-polished inner surface. It fits snugly with the outer wall of the bushing 5, resulting in low resistance during insertion. The thin sleeve has an integrated pull-holding ear at its tail end, protruding from the outside of the flange 51, which facilitates quick removal with hemostatic forceps during surgery. The thin sleeve is pre-installed on the outer wall of the bushing at the factory, keeping the barbs 55 in a retracted state throughout the procedure until the screw is fully tightened before removal. This completely avoids the problem of the barbs scraping against the bone wall and causing resistance during tightening, as well as premature anchoring leading to incomplete tightening.

[0056] The sliding bushing 5 flange 51 has a radial through pin hole with an inner diameter of 1.5mm. It is matched with an independent titanium alloy anti-rotation pin 56 with a body diameter of 1.4mm and a length of 8mm. It is made of medical-grade titanium alloy TC4 and has an anodized biocompatible surface treatment.

[0057] The complete intraoperative assembly procedure is as follows: After the bushing 5 is screwed into place and the barbs 55 are snapped back and anchored, the anti-rotation pin 56 is hammered into the pin hole laterally by hand with a miniature insertion instrument. After the pin penetrates the outer wall of the bushing 5, it penetrates into the cortical bone of the fibula 2 to a depth of 2.5mm. The two ends of the pin limit the pin hole of the bushing 5 and the bone of the fibula 2 respectively, locking all circumferential rotational degrees of freedom of the bushing 5.

[0058] After the anti-rotation pin 56 locks the bushing 5 in the circumferential angle, the long axis of the elliptical inner cavity 53 inside the bushing 5 is always fixedly aligned with the natural physiological sliding horizontal direction of the human tibia and fibula. This completely avoids the circumferential torsion of the bushing 5 during the operation, which would cause the elliptical long axis to deviate. If the long axis deviates to the vertical or oblique position, the sliding direction of the spherical end 43 will deviate from the normal physiological trajectory, causing ankle instability and pain when walking. The structure of the anti-rotation pin 56 ensures the permanent accuracy of the sliding track direction of the elliptical inner cavity 53 from a mechanical positioning perspective, eliminating the need for repeated angle calibration under intraoperative fluoroscopy, simplifying the surgical procedure and reducing the difficulty of operation for doctors.

[0059] 0-3 months post-surgery: The entire anchoring force is provided by the mechanical anchoring of the titanium-nickel barbs 55 and the circumferential positioning of the anti-rotation pins 56. The HA coating slowly dissolves in a small amount, releasing calcium, strontium, and phosphorus ions, which induce osteoblasts in the surrounding bone tissue to accumulate in the porous layer 58 pore openings. 3–12 months post-surgery: Osteoblasts proliferate inward along the interconnected pores, secrete bone matrix and mineralize it, and the newly formed autologous bone tissue gradually fills all the interconnected pores inside the porous layer 58, forming a three-dimensional interlocking and occlusive integrated structure with the outer wall of the liner 5. More than 12 months post-surgery: The bonding strength of the bone integration interface is ≥150N. The bio-anchoring force completely replaces the initial mechanical anchoring force of the titanium nickel barb 55. Even if the barb 55 undergoes minor deformation due to long-term fatigue and the anchoring force weakens, the integrated bone-liner structure can still permanently maintain the stability of the liner 5 implantation position. For patients with osteoporosis and bone loss, this bio-integrated structure can solve the clinical problem of long-term loosening and dislodgement of traditional smooth implants, achieving permanent implantation without the need for a second hospitalization for removal, reducing surgical trauma and medical economic burden for patients.

[0060] The biodegradable filler 6 is pre-assembled at the factory by high-pressure injection filling. It completely fills the empty space of the elliptical inner cavity 53 and the through hole in the center of the spherical end 43. There is no interface separation between the filler 6 inside the through hole and the filler 6 outside the inner cavity. It is fused and integrally formed to form a one-piece locking structure that fully covers the spherical end 43. It is the core functional medium for achieving rigid fixation without micromotion in the early postoperative period.

[0061] The filler 6 is a 75:25 mass ratio PLGA (polylactic acid-glycolic acid) copolymer, with PLGA comonomers comprising 75% PLA (polylactic acid) and 25% PGA (polyglycolic acid). The degradation cycle of this ratio is limited based on the following: the higher the PLA content, the slower the degradation, and the higher the PGA content, the faster the degradation. In vitro simulated body fluid and in vivo animal experiments have verified that the complete hydrolysis degradation cycle of the 75 / 25 ratio is stable at 11-13 weeks, perfectly matching the standard bony healing cycle (8-12 weeks) for fractures of the distal tibiofibular syndesmosis ligament and ankle joint. After the fracture and ligament heal, the filler 6 is completely hydrolyzed and disappears, simultaneously releasing the physiological sliding and rotational degrees of freedom of the spherical end 43. The temporal and mechanical switching is precisely matched with the human healing cycle.

[0062] The PLGA substrate is uniformly doped with 5wt% β-tricalcium phosphate (βTCP) inorganic bioceramic particles. The βTCP particles have a particle size of 100-300nm and are uniformly dispersed inside the PLGA polymer matrix without agglomeration or clumping.

[0063] Physicochemical properties of composite filler 6 raw materials: 1) The PLGA copolymer has a viscosity-average molecular weight of 120 kDa and a molecular weight distribution index of 1.4. If the molecular weight is too high, the degradation cycle will be greatly prolonged. If the molecular weight is too low, the filler 6 will be brittle after molding and will easily break and fail during implantation. 2) βTCP has a purity of 99.9%, is free of heavy metal impurities, and has a calcium-to-phosphorus molar ratio of 1.5, which is consistent with the calcium-to-phosphorus ratio of human bone tissue. During the degradation process, it continuously releases calcium and phosphorus ions, which help repair and mineralize fracture ends and the distal tibiofibular ligament. 3) After molding, the composite filler 6 has a compressive strength of 85MPa and a modulus of 1.2GPa. In the early stage of implantation, it can withstand the lateral pressure load of the tibia and fibula without plastic compression deformation, and continuously maintain the spherical end 43 locked without slippage.

[0064] The screw and bushing assembly is pre-assembled in a sterile, Class 10,000 cleanroom for medical devices, following a standardized and sealed pre-assembly process. Step 1: Insert the titanium nickel fixing screw 4 through the through hole of the flange 51 on the fibula side of the bushing 5, and fully insert the spherical end 43 into the elliptical inner cavity 53. The annular closing flange 54 limits the spherical end 43 so that it cannot come out, thus completing the basic assembly and positioning of the screw 4 and the bushing 5. Step 2: Using a low-pressure high-temperature melt injection process, the molten 75 / 25PLGA+5wt%βTCP composite melt is injected under high pressure through the pre-reserved injection channel on the side of the bushing 5 flange 51. The melt completely fills all the remaining gaps around the elliptical inner cavity 53 and the spherical end 43. At the same time, the high pressure penetrates the through hole in the center of the spherical end 43, and the melt fills the inside of the through hole. Step 3: Cool at a low temperature for 40 minutes to solidify the molten PLGA composite melt as a whole. The melt inside the through hole and the melt outside the inner cavity are melted and bonded into a single continuous whole with no interface and no air bubble cavity. The spherical end 43 is completely covered by the 360° spherical end 43, and the original elliptical inner cavity 53 is completely filled into an approximately smooth circular hole, eliminating all slippage and rotation gaps of the spherical end 43. Step 4: Grind away any residual material stalk in the injection channel, install the removable limiting thin outer sleeve 57 restraint barbs on the outer wall of the bushing, sterilize with ethylene oxide, vacuum seal with aluminum foil for individual packaging, complete the pre-assembled packaging at the factory, and it can be used directly after opening the package in the clinic without the need for on-site assembly and filling.

[0065] The complete process of 6-stage temporal mechanical regulation of the filler: Phase 1: Postoperative weeks 0–13, complete and rigid fixation of implant 6. The solidified, integral filler 6 completely fills the entire gap between the spherical end 43 and the elliptical inner cavity 53, with no room for movement. The spherical end 43 is rigidly wrapped and locked by the filler 6, achieving two limiting effects: 1) No axial and radial slippage constraint: The filler 6 fills the gap between the major and minor axes of the elliptical cavity 53 and the spherical end 43. The spherical end 43 cannot produce horizontal displacement in any direction. The distal tibiofibular syndesmosis gap 3 is continuously and rigidly locked by pressure. The fracture ends and torn ligaments have zero micromovement, providing a stable healing microenvironment for soft tissue and bone tissue, avoiding bone nonunion and ligament repair failure caused by early micromovement of traditional sliding implants. 2) Complete locking of circumferential rotation: The filler 6 covers the entire spherical end 43, and there is no frictional rotation gap between the spherical surface and the filler 6. The fixing screw 4 cannot rotate at any angle, thus eliminating postoperative complications such as loosening and wire retraction of screw 4 and enlargement and failure of screw hole in the tibial cortex.

[0066] The βTCP particles inside filler 6 continuously dissolve and release calcium and phosphorus ions, enhancing the osteogenic activity of the local microenvironment and shortening the injury healing cycle.

[0067] Phase 2: 11–13 weeks post-surgery, the gradual hydrolysis transition phase of filler 6. As body fluid water molecules continuously penetrate the filler 6 matrix, the PLGA polymer chain segments gradually hydrolyze and break down. The filler 6 gradually changes from a dense solid to a porous and loose structure, and its mechanical strength slowly decreases. The spherical end 43 gradually recovers its slight mobility. By the 11th week, some filler 6 begins to break off and fall off. By the end of the 13th week, filler 6 is completely hydrolyzed and dissolved. The decomposition products, lactic acid, glycolic acid, and calcium and phosphorus ions, are all metabolized and absorbed by the human body, leaving no solid residue.

[0068] Phase 3: 13 weeks post-surgery, during the physiological micro-motion adaptation phase after complete disappearance of filler 6. After the filler 6 is completely metabolized and disappears, the original elliptical inner cavity 53 of the bushing 5 is fully exposed. The spherical end 43 and the elliptical inner wall are only in contact and cooperate with each other through the DLC nano-coating and the ePTFE silver-loaded self-lubricating layer. The dual movement limiting mechanism works simultaneously. Combined with the annular movement gap of the fibular side screw hole, the movement law of the tibiofibular syndesmosis of a healthy human body is completely replicated. 1) Horizontal sliding unique track constraint: The elliptical minor axis of 4.6mm matches the outer diameter of the spherical end 43, restricting displacement in the minor axis direction; only the major axis of 5.4mm is reserved for a 0.4mm sliding stroke, and the spherical end 43 can only slide horizontally along the physiological transverse direction of the tibia and fibula, matching the natural separation-reduction micro-motion of the tibia and fibula during walking and weight-bearing; the annular gap of the fibular through-foramen synchronously adapts to the transverse displacement of the screw rod, avoiding bone wall jamming; 2) 3°~8° small-amplitude rotation range limitation constraint: The cross section of the elliptical inner cavity 53 is a standard elliptical surface, and the spherical end 43 is geometrically constrained by the inner wall surface of the ellipse. The spherical surface can only rotate along the axis of the screw 4 itself, and the maximum rotation angle is limited to the range of 3°~8° by the elliptical surface. If the rotation angle is less than 3°, it cannot meet the needs of ankle joint activity when tiptoeing and squatting. If it exceeds 8°, it will cause excessive rotation and instability of the tibiofibular syndesmosis. The 3°~8° range of this invention strictly matches the measured rotation angle of the tibiofibular syndesmosis in human anatomy, avoiding the long-term sequelae of ankle stiffness and traumatic arthritis caused by the complete locking and no movement of traditional permanent rigid screws.

[0069] The drill guide mechanism 7 is a temporary tooling used during surgery. It is not implanted in the human body and is completely removed after the drilling operation is completed. Its core function is dual-path directional precision drilling, which simultaneously completes two drilling operations: the vertical screw hole for fibula 2 and the oblique threaded bottom hole for tibia 1. This eliminates the need for repeated intraoperative fluoroscopy to adjust the drilling angle, significantly shortening the operation time and reducing the intraoperative radiation fluoroscopy dose. At the same time, it ensures that the drilling angle of the threaded hole for tibia 1 is precisely matched with the physiological sliding direction of the long axis of the elliptical cavity 53 of the bushing 5.

[0070] The drill bit guiding mechanism 7 is assembled from four parts: U-shaped clamping base 71, locking screw 72, first guide hole 74 sleeve, and second guide hole 75 sleeve. All parts are machined from medical-grade 316L stainless steel, which can be repeatedly sterilized under high temperature and high pressure and reused in clinical settings, thus reducing the cost of medical consumables.

[0071] 1) U-shaped clamping base 71: The overall U-shaped opening structure, the width of the inner opening of the U-shape is adapted to the thickness of the outer cortex of the adult fibula 2, and the inner wall of the U-shape is provided with anti-slip teeth to increase the frictional resistance after clamping the fibula 2 cortex and prevent slippage and misalignment during the clamping process; the bottom of the base is provided with a threaded locking hole to match the locking screw 72.

[0072] 2) Locking and fixing screw 72: Small stainless steel Torx locking screw. After tightening, the top of the screw presses against the outer cortex of the fibula 2, and the U-shaped clamping base 71 is rigidly clamped and fixed to the surface of the fibula 2, realizing the overall temporary positioning of the guide mechanism 7, and there is no angular displacement during the entire drilling process.

[0073] 3) First guide hole 74 sleeve and second guide hole 75 sleeve: two independent hollow stainless steel sleeves, which are welded and fixed to the upper part of the U-shaped clamping base 71 respectively. The hollow inner hole of the sleeve is the drill bit guide channel, and the inner diameter matches the outer diameter of the clinical standard orthopedic drill bit of 2.8mm.

[0074] The axes of the two sleeves, the first guide hole 74 and the second guide hole 75, are fixed at an angle of 18° to 26° within the coronal plane of the tibia and fibula, with a preferred intermediate embodiment at 22°. The anatomical basis for limiting the angle range is as follows: The axis of the second guide hole 75 is perpendicular to the outer cortical surface of the fibula 2, corresponding to the vertical drilling path of the screw through hole of the fibula 2, ensuring that the rod of the fixing screw 4 is vertically inserted into the cortical surface of the fibula 2, and reserving a uniform annular movement gap. The axis of the first guide hole 74 and the second guide hole 75 form an oblique angle of 18° to 26°. When the drill bit drills along the first guide hole 74, it obliquely penetrates the soft tissue of the inferior tibiofibular syndesmosis 3 and accurately reaches the lateral cortex of the tibia 1, pre-drilling a threaded bottom hole that matches the cortical threaded section 41 of the fixation screw 4. When the angle is less than 18°, the drilling path is too gentle, and the drill bit is easy to penetrate the superficial layer of the cancellous bone of the tibia 1, resulting in insufficient bone anchoring by the screw. When the angle is greater than 26°, the drilling inclination angle is too large, and the drill bit is easy to damage the medial blood vessels and nerve bundles of the tibia 1, causing intraoperative vascular and nerve injury complications. The 18° to 26° range is the optimal angle range for anatomical safety and balanced anchoring strength.

[0075] After surgical reduction, the U-shaped clamping base 71 engages and covers the lateral cortex of fibula 2, and the locking screw 72 is tightened to complete rigid clamping. The spatial angle of the two guide sleeves is permanently fixed, eliminating the need for intraoperative angle calibration. 1) Insert the orthopedic drill bit through the second guide hole 75 and drill vertically through the lateral and medial cortex of the fibula 2 to form a complete screw hole through the fibula 2. After removing the drill bit, use a special countersunk milling cutter to enlarge a circular countersunk groove on the outside of the hole. The groove depth matches the thickness of the bushing flange to ensure that the flange is flush with the lateral cortex of the fibula after implantation. 2) Insert the extended orthopedic drill bit through the first guide hole 74, drill through the soft tissue of the tibiofibular syndesmosis 3 along an oblique path of 18° to 26°, drill a standard threaded bottom hole in the cortex of the tibia 1, and tap the pre-made internal thread after the drill bit is removed, and match the cortical threaded section 41 of the fixation screw 4. 3) After completing the dual-path drilling, countersinking, and tapping, loosen the locking screw 72 in the reverse direction and remove the entire U-shaped clamping base 71 directly. The entire drill bit guide mechanism 7 structure is removed from the patient's body surface, leaving no part inside the wound, thus completing the entire drilling positioning operation.

[0076] For children under 14 years of age with unclosed epiphyses and ankle fractures or tibiofibular detachment, a set of independent absorbable screws is designed to avoid the trauma of permanent metal implants that hinder epiphyseal growth and require secondary surgery for removal in adulthood. The entire set of screws is completely biodegradable in the body and does not require a second surgery.

[0077] The screw is made of PLGA polymer composite 40wt% βTCP porous hollow structure with a standardized outer diameter of 3.2mm, which is suitable for the slender fibular cortex size of children; the hollow through hole runs through the entire length of the screw, increasing the contact area for body fluid penetration and accelerating the overall degradation rate.

[0078] Material ratio and degradation cycle matching mechanism: 40% high proportion of βTCP inorganic ceramics enhances the early compression and bending strength of screw implantation, meeting the postoperative weight-bearing fixation needs of children; PLGA low lactate ratio accelerates hydrolysis, with an in vivo degradation cycle of 1.4 to 1.6 years and a healing cycle of 6 to 10 months for tibia and fibula epiphyseal injuries in children. After healing, the screw gradually hydrolyzes and disappears, leaving no metal implant residue and not interfering with the longitudinal growth and development of the ankle epiphysis in children.

[0079] Hollow porous microstructure: The screw shaft has interconnected micropores all around, with a porosity of 48%. Body fluids continuously seep into the interior to accelerate degradation, and the degradation products, calcium and phosphorus ions, continuously promote bone growth and repair in children.

[0080] The CPC calcium phosphate bone cement component is specially designed for surgical reinforcement in elderly patients with severe bone loss and osteoporosis. CPC bone cement consists of two components: a solid powder and a liquid curing liquid, which are temporarily mixed and prepared during the operation.

[0081] The basic mechanical properties of CPC bone cement after curing: After 24 hours of standard curing, it is fully cured and the static compressive strength after curing is ≥80MPa. This strength value is much higher than the compressive strength of 20-40MPa of the cancellous bone of the fibula in osteoporosis patients. It can fill the pore gap between the outer wall of the cylindrical bushing 5 and the inner wall of the groove of the osteoporosis countersunk head, forming a three-layer composite anchoring structure of groove-bone cement-bushing 5.

[0082] The intraoperative reinforcement process of bone cement: After the fibular 2 head groove preparation is completed in osteoporotic patients, CPC bone cement is mixed and evenly applied to the entire inner wall of the groove. When the bone cement is in a viscous and plastic state, it is immediately pressed into the fibular side sliding bushing 5. The outer wall of bushing 5 and titanium-nickel barbs 55 compress the viscous bone cement, and the bone cement completely fills all the tiny gaps between bushing 5 and bone wall, and wraps the outside of barbs 55. After the thin outer sleeve 57 is removed, the barbs rebound and embed into the bone cement layer. After 24 hours, the bone cement is completely cured, bonding barbs 55, bushing 5 and cancellous bone into an integrated composite anchoring system. This system makes up for the defects of insufficient cortical bone density, shallow insertion and anchoring depth of barbs 55 and insufficient mechanical anchoring force in osteoporotic patients. It greatly improves the initial resistance to dislodgement and tensile load of bushing 5, and prevents early loosening and failure of implants in elderly osteoporotic patients.

[0083] CPC bone cement's solidification mineral phase is hydroxyapatite, which has excellent biocompatibility and can form an osteointegration interface with the host bone tissue, resulting in no long-term separation of bone cement foreign bodies or inflammatory reactions.

[0084] The standardized installation procedure for the device is as follows: S1 fracture reduction and drill bit guiding mechanism 7 temporary clamping fixation After the spinal anesthesia took effect, a minimally invasive incision was made on the anterolateral aspect of the ankle joint to dissect the subcutaneous soft tissue layer by layer, fully exposing the distal tibiofibular syndesmosis injury gap 3 of the tibia 1 and fibula 2. Anatomical reduction of the displaced tibia 1 and fibula 2 was performed using point reduction forceps. Intraoperative C-arm fluoroscopy confirmed that the distal tibiofibular syndesmosis gap 3 had been restored to the normal anatomical width of the human body, and the reduction was maintained in a stable state without rebound. The sterile, individually packaged drill guide mechanism 7 was removed, and the U-shaped opening of the U-shaped clamping base 71 was completely snapped and covered over the area of ​​the fibula 2 lateral cortex without soft tissue obstruction. The locking screw 72 on the base was tightened clockwise with a torque wrench, with the torque controlled at 0.8 N·m, so that the U-shaped clamping base 71 and the fibula 2 cortex did not slip relative to each other, completing the temporary rigid positioning of the guide mechanism 7 during the operation. Fluoroscopy was used to verify that the angle between the two guide sleeves and the drilling path were not offset, confirming that the positioning was qualified.

[0085] The U-shaped clamping base 71 has anti-slip teeth, and the locking screw 72 has radial clamping force to eliminate the angular deviation caused by drilling vibration. The double guide hole fixing angle ensures that the subsequent drilling trajectory accurately matches the bushing 5 implantation requirements.

[0086] S2 Dual-guide-hole dual-channel directional drilling operation A standard orthopedic twist drill bit with an outer diameter of 2.8 mm was selected. The drill bit was first fed vertically along the hollow channel of the second guide hole 75, and the drill bit was fed at a constant speed to penetrate the lateral and medial cortex of the fibula 2, forming a complete screw hole through the fibula 2. The drill bit was then withdrawn, and a special countersunk cutter was used to enlarge a circular countersunk groove on the outside of the hole. The groove depth matched the thickness of the bushing flange 51 to ensure that it was flush with the bone surface after implantation. The drill bit was then replaced with an extended version of the same specification and fed obliquely along the first guide hole 74. The drill bit was fed obliquely through the soft tissue of the tibiofibular syndesmosis 3 along a fixed angle path of 18° to 26°, and the drill bit was fed at a constant speed to penetrate the lateral cortex of the tibia 1, pre-drilling a threaded bottom hole. After the drill bit was withdrawn, a tap was used to pre-drill the internal thread of the cortical thread segment 41 of the fixing screw 4 to match the screw. During the drilling process, the bone hole was continuously flushed with physiological saline to remove bone debris and necrotic bone tissue. After the drill bit was completely withdrawn, the two drilling channels were repeatedly flushed with physiological saline to remove internal bone debris and soft tissue fragments.

[0087] The dual guide holes define two drilling trajectories, allowing for the prefabrication of two bone holes in one operation. This eliminates the need for repeated drill angle adjustments, reduces the number of intraoperative fluoroscopy sessions and the extent of soft tissue dissection, and minimizes surgical trauma.

[0088] After drilling S3 is completed, the drill bit guide mechanism is completely removed. After completing all operations including dual-channel drilling, countersinking, tapping, and rinsing, use a torque wrench to loosen the U-shaped clamping base 71 and tighten the fixing screw 72 counterclockwise to release the clamping constraint of the fibular cortex 2. Then, hold the base and peel it outwards as a whole. The entire drill bit guide mechanism 7 is completely removed from the patient's wound and placed on a sterile instrument tray, completing the entire tooling usage process. This mechanism will not be used again in subsequent implantation operations.

[0089] The S4 pre-installed integrated screw and bushing assembly is implanted on both sides of the fibula and pushed into place under thin outer restraint. Disassemble the vacuum-sealed, sterile, individual packaging of the screw and bushing assembly. Completely remove the pre-assembled, integrated fixed screw 4 and sliding bushing 5 composite. The outer wall is fitted with a removable limiting thin outer sleeve 57, with the barbs 55 fully retracted for restraint. Hold the flange of the bushing 5 with a hand clamping instrument and slowly and evenly insert the distal cortical thread section 41 of the fixed screw 4 into the screw hole from the countersunk groove on the lateral side of the fibula 2. Push until the end face of the bushing 5 flange 51 is completely against the countersunk groove step surface, and you can no longer push it inward. Stop applying pushing pressure. At this time, the thin outer sleeve still maintains the barb-retracted state, and the bushing can rotate freely without bone wall jamming resistance.

[0090] The thin outer sheath restrains the barbs, ensuring smooth pushing and twisting without additional operational resistance, thus simplifying the intraoperative procedure.

[0091] S5 internal hex screws are tightened to complete the tibial side anchoring of the screws. Holding an Allen wrench, insert it into the Allen groove 511 in the center of the integrated flange 51, and turn it clockwise at a uniform speed. This will cause the fibular sliding bushing 5 and the pre-installed fixing screw 4 to rotate synchronously. Continuously apply a torque of 1.2 N·m until the cortical thread section 41 of the screw 4 is fully engaged with the cortical thread hole of the tibia 1. The tibiofibular syndesmosis gap 3 is maintained in an anatomically reduced state, and the spherical end 43 is stably housed inside the elliptical cavity 53 of the bushing. After fluoroscopic examination, confirm that the tibiofibular syndesmosis is reduced without loss, the bushing 5 is implanted to the standard depth, and the screw 4 is fully engaged. Confirm that it is turned in place.

[0092] The pre-assembled integrated structure of the filler 6 ensures that the bushing and screw do not rotate relative to each other during the tightening process, and the internal hexagonal force application method is convenient to operate and conforms to clinical surgical operation habits.

[0093] S6 removes thin outer jacket, barbed springback mechanical anchoring After confirming that the screws are tightened in place and the bushing angle is accurately aligned, use hemostatic forceps to hold the tail end of the removable limiting thin outer sleeve 57 and pull it outward at a uniform speed along the axis. After the thin outer sleeve is separated from the outer wall of the bushing, the titanium-nickel shape memory alloy barbs 55 lose their external constraints and automatically open by relying on their own memory rebound effect. The tips are embedded in the cortical bone of the countersunk side wall of the fibula 2, forming a one-way self-locking axial mechanical anchor. Manually pull the bushing lightly to confirm that there is no outward slippage or loosening, and the anchoring is initially completed.

[0094] The thin outer jacket removal operation is simple and quick, and the timing of the barb release is precise and controllable, avoiding operation jamming caused by premature anchoring during the twisting process.

[0095] S7 inserts the anti-rotation pin to lock the bushing circumferential angle. Align the radially preset pin hole of the bushing 5, place one end of the titanium alloy anti-rotation pin 56 against the pin hole opening, and gently tap the tail end of the pin body with a miniature bone hammer at a uniform speed, so that the anti-rotation pin 56 penetrates the outer wall of the bushing 5 laterally along the pin hole, with the tip penetrating into the cortical bone of the fibula 2 to a depth of 2.5mm; after the tapping is completed, fluoroscopic verification shows that the long axis of the elliptical inner cavity 53 inside the bushing 5 is arranged along the horizontal physiological sliding direction of the tibia and fibula, and the anti-rotation pin 56 does not fall out or bend, the bushing 5 completely loses the circumferential rotational freedom, and the elliptical sliding track angle is permanently locked.

[0096] The anti-rotation pin 56 transverse intraosseous interpenetrating structure locks the bushing 5 in all circumferential rotational displacements, preventing the elliptical inner cavity 53 from sliding and twisting off the track, and ensuring the precise physiological sliding direction of the spherical end 43 after the mid-term filler 6 has degraded.

[0097] The two sets of screw bushing assemblies are operated in sequence according to the same steps described above, and finally the double screws are cross-fixed; the surgical wound is rinsed with saline, the subcutaneous tissue and skin are sutured layer by layer, and a sterile dressing is applied.

[0098] For elderly patients diagnosed with severe osteoporosis by preoperative bone mineral density testing and with a T-score ≤ -2.5, a bone cement reinforcement pretreatment step is added before pressing the bushing 5 into the groove in the standard operating procedure S4. The complete modified procedure is recorded as follows: After removing the drill bit guide mechanism 7 and cleaning the countersunk groove of fibula 2 in step S3, mix the CPC-reinforced calcium phosphate bone cement solid powder and liquid curing liquid according to the manufacturer's ratio, stirring until a viscous, plastic paste is formed. Using a small grooving delivery sleeve, the mixed CPC bone cement is evenly coated and poured into the entire inner wall of the circular countersunk groove of fibula 2, ensuring that the inner wall of the groove is completely covered with a uniform layer of bone cement paste, with no exposed bone cortex areas. The operable window after mixing the bone cement is 8 minutes. Within this window, the bushing 5 pressing operation in step S4 must be performed immediately to quickly insert the sliding bushing 5. The fibula 2, coated with bone cement, is quickly pressed into the countersunk groove. During the pressing of the bushing 5, the barbs 55 on the outer wall and the cylindrical outer wall compress the bone cement, and the bone cement fully fills all the tiny gaps and cancellous bone pores between the bushing 5 and the groove. After the thin outer sleeve 57 is removed, the barbs rebound and embed into the bone cement layer. After standing for 24 hours, the CPC bone cement is completely cured, forming a three-layer composite anchoring structure of bushing 5-bone cement-fibula 2 bone. This structure compensates for the insufficient mechanical strength of the bone cortex in patients with osteoporosis, greatly improves the initial axial anti-slip anchoring force of bushing 5, and reduces the probability of postoperative complications such as implant loosening and dislodgement in elderly patients.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fixation device for the tibiofibular syndesmosis of an ankle fracture, characterized in that: Includes at least one pre-assembled integrated screw bushing assembly; Each screw bushing assembly includes a fixing screw (4), a fibular side sliding bushing (5), and a removable limiting thin sleeve (57); the fixing screw (4) is divided into three integrated structures from distal to proximal: a cortical thread section (41), a smooth intermediate rod section (42), and a spherical end (43); the outer diameter of the cortical thread section (41) is larger than that of the smooth intermediate rod section (42), and it is used to screw into the cortex of the tibia (1) side to achieve anchorage; the spherical end (43) is integrally formed at the proximal end of the smooth intermediate rod section (42), and a through-hole is opened in the center; The fibular side sliding bushing (5) adopts a cylindrical outer contour structure to fit the pre-made circular countersunk groove on the outside of the fibula (2); the bushing (5) is provided with an integrated flange (51) at one end near the outside of the fibula (2), and the center of the outer surface of the integrated flange (51) is provided with an internal hexagonal groove (511) for connecting a torque tool during the operation to drive the bushing and the pre-installed screw to rotate synchronously; the bushing (5) is provided with an original elliptical inner cavity (53) in the axial direction; the elliptical inner cavity (53) is provided with an annular closing edge (54) at one end near the tibia (1), and the end near the outside of the fibula (2) is closed by the integrated flange (51); the inner diameter of the annular closing edge (54) is smaller than the outer diameter of the spherical end (43) to limit the spherical end (43) from dislodging towards the tibia (1); The spherical end (43) is pre-assembled and housed inside the elliptical inner cavity (53) at the factory. The empty space of the elliptical inner cavity (53) and the central through hole of the spherical end (43) are simultaneously filled with a biodegradable filler (6). The filler inside the through hole and the filler outside the cavity are integrated to form an internal and external integrated locking structure. The filler (6) fills the original elliptical inner cavity (53) into an approximately circular hole, fully covering and locking the spherical end (43), so that the fixing screw (4) does not slip or rotate in the early postoperative period, and forms a rigid whole with the bushing to achieve rigid fixation. The biodegradable filler (6) gradually degrades in the body. After the filler completely disappears, the elliptical inner cavity (53) restores its original contour. The spherical end (43) can only achieve physiological horizontal sliding of the tibia and fibula along the long axis of the ellipse, and can only rotate slightly within the physiological range of 3° to 8°. The inner diameter of the through hole of the prefabricated through screw on the fibular (2) side is larger than the outer diameter of the smooth rod segment (42) in the middle of the fixed screw. An annular movement gap is reserved between the two. The movement of the spherical end (43) releases the swing and sliding space of the fixed screw in sync with the movement of the spherical end (43), matching the movement law of the lower tibia and fibula syndesmosis gap (3) of the human body. The outer wall of the bushing (5) is prefabricated with a storage groove matching the shape of the barbs, and multiple rings of axially elastic titanium-nickel memory alloy barbs (55) are set in the groove; the removable limiting thin outer sleeve (57) is pre-fitted onto the cylindrical outer wall of the bushing (5), and 1 to 2 axially penetrating thinning and easily broken grooves are set in the circumference of the outer sleeve to constrain and gather the elastic barbs (55) in the storage groove, preventing the barbs from rebounding prematurely and jamming the bone wall during the implantation and twisting process; after twisting to the position, the thin outer sleeve (57) is cut off and removed, and the barbs (55) rebound and embed into the cortical bone of the slotted side wall of the fibula (2), forming a one-way self-locking axial mechanical anchor.

2. The ankle joint fracture tibiofibular syndesmosis fixation device according to claim 1, characterized in that: It also includes a detachable drill guide mechanism (7) during the operation; the drill guide mechanism (7) is detachably clamped and fixed to the lateral cortex of the fibula (2). The guide mechanism (7) is provided with a first guide hole (74) and a second guide hole (75) with the axis at a fixed angle, which correspond to the drilling paths of the two sets of screw bushing assemblies, respectively, and are used to simultaneously and directionally drill the screw through hole on the fibula (2) side and the screw thread bottom hole on the tibia (1) side during the operation.

3. The ankle joint fracture tibiofibular syndesmosis fixation device according to claim 1, characterized in that: The biodegradable filler (6) is a 75:25 ratio PLGA doped with 5wt% βTCP composite material, with an overall hydrolysis degradation cycle of 11 to 13 weeks.

4. The ankle joint fracture tibiofibular syndesmosis fixation device according to claim 1, characterized in that: The fibular sliding sleeve (5) is made of medical PEEK in one piece; the inner wall of the elliptical inner cavity (53) is provided with a 45-55μm silver-loaded porous self-lubricating layer; multiple barbs (55) are evenly distributed around the circumference of each ring, with a natural opening angle of 14°-16°, and the tip is facing the annular closing edge, i.e., the tibia (1) side direction; the removable limiting thin sleeve (57) is a medical grade thin-walled stainless steel sleeve with a wall thickness of 0.15-0.25mm, a smooth inner surface, and a gap fit with the outer wall of the sleeve (5), and a pull-holding ear is provided at the tail end for easy clamping and removal during the operation.

5. The ankle joint fracture tibiofibular syndesmosis fixation device according to claim 1, characterized in that: The outer wall of the cylindrical bushing (5) and the inner end face of the flange (51) that fits the bone surface are provided with an interconnected porous bone integration layer (58) and sprayed with a gradient HA hydroxyapatite coating. After the operation, the fibular bone tissue grows in to achieve long-term biological permanent fixation and gradually replace the early mechanical anchoring. The bushing (5) is equipped with a titanium alloy anti-rotation pin (56) to lock the circumferential position of the bushing (5) after it is screwed in place, so as to ensure that the long axis of the elliptical cavity is always aligned with the physiological sliding direction.

6. The ankle joint fracture tibiofibular syndesmosis fixation device according to claim 1, characterized in that: The fixing screw (4) is made of titanium-nickel shape memory alloy and has a 1.0-1.5μm nano-DLC wear-resistant coating on its surface.

7. The ankle joint fracture tibiofibular syndesmosis fixation device according to claim 1, characterized in that: The drill bit guiding mechanism (7) includes a U-shaped clamping base (71) and a locking screw (72); the first guide hole (74) and the second guide hole (75) are respectively fixed on the U-shaped clamping base (71), and the included angle between their axes is 18° to 26°, which is completely matched with the preset cross angle of the two sets of screw bushing assemblies, respectively adapting to the drilling trajectory of the fibular through hole and the tibial thread bottom hole of the two screws.

8. The ankle joint fracture tibiofibular syndesmosis fixation device according to claim 1, characterized in that: The device is equipped with a child-adaptable absorbable screw assembly, which adopts a PLGA composite 40%βTCP hollow porous structure. The outer diameter of a single screw is 3.2mm, and the degradation cycle is 1.4 to 1.6 years. The distal threaded section is screwed into the tibia (1) side to achieve fixation and avoid interfering with epiphyseal growth. It is equipped with an osteoporosis-enhanced CPC bone cement assembly with a cured compressive strength ≥80MPa. It is used to fill and reinforce the gap between the fibular side sliding bushing (5) and the countersunk groove on the outside of the fibula (2) and to strengthen the initial anchoring strength of the barb (55).

9. The ankle joint fracture tibiofibular syndesmosis fixation device according to claim 1, characterized in that, The intraoperative installation method includes the following steps: S1. During the operation, the inferior tibiofibular syndesmosis gap (3) between the tibia (1) and fibula (2) is reduced, and the U-shaped clamping base (71) of the drill guide mechanism (7) is clamped and fixed to the lateral cortex of the fibula (2). The locking screw (72) is tightened to achieve temporary fixation. S2. Complete the dual-path drilling through the first guide hole (74) and the second guide hole (75) arranged at an angle: two through screw holes are pre-drilled on the fibula (2) side, the inner diameter of the through hole is larger than the outer diameter of the smooth rod section (42) in the middle of the fixing screw, and a circular countersunk groove is enlarged on the outer side of each hole; at the same time, two screw thread bottom holes are pre-drilled on the tibia (1) side, the inner diameter of the bottom hole is matched with the outer diameter of the cortical thread section (41) of the fixing screw, and a cortical thread hole is formed after tapping; S3. After drilling is completed, the drill bit guide mechanism (7) on the fibular (2) side is completely removed. S4. Take out the two sets of pre-installed integrated screw bushing assemblies. Each set of assemblies has a removable limiting thin sleeve (57) on its outer wall. The barbs (55) are restrained and gathered in the storage groove. Align the leather thread section (41) of each set of fixing screws (4) with the corresponding screw through hole on the fibula (2) side and push it forward until the sliding bushing (5) on the fibula side is completely embedded in the countersunk groove at the corresponding position. S5. Insert the internal hexagonal torque wrench into the internal hexagonal groove (511) in the center of the integrated flange (51), and screw it to drive the fibular side sliding bushing (5) and the pre-installed fixing screw (4) to rotate synchronously, so that the cortical thread section (41) is completely screwed into the corresponding pre-made cortical thread hole of the tibia (1), and the screw anchoring and bushing circumferential angle alignment are completed. S6. Disconnect and remove the removable limiting thin outer sleeve (57) of the bushing outer wall. After the titanium-nickel memory alloy barb (55) loses its restraint, it springs open and the tip is embedded in the fibular (2) countersunk groove side wall cortical bone to form a one-way self-locking axial mechanical anchor. S7. Insert the titanium alloy anti-rotation pin (56) through the pin hole, insert it laterally into the fibular bone (2), lock the circumferential angle of the bushing (5), and ensure that the long axis of the elliptical cavity (53) is consistent with the physiological sliding direction of the tibia and fibula, and complete the single-group implantation fixation; the two groups of assemblies are operated in the same steps in sequence to finally achieve double screw cross fixation.

10. The ankle joint fracture tibiofibular syndesmosis fixation device according to claim 9, characterized in that: Before implanting the liner (5) in patients with osteoporosis, reinforced calcium phosphate bone cement is first applied to the inner wall of the countersunk groove on the lateral side of the fibula (2), and then the sliding liner (5) on the fibular side is pressed in. The thin outer sleeve (57) is removed and the initial anchoring strength of the liner (5) is reinforced after the bone cement has solidified.

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