Degradable magnesium metal skull fixation system

Abstract

The application provides a degradable magnesium metal skull fixation system, which comprises a skull screw and a connecting sheet, the connecting sheet comprises a connecting bridge and fixing holes arranged at two ends of the connecting bridge, the width of the connecting bridge is not greater than the width of the fixing holes; the skull screw is arranged in each fixing hole of the connecting sheet in correspondence, and the number of the skull screws is not more than the number of the fixing holes, and the skull screw and the connecting sheet are made of pure magnesium or magnesium alloy of the same brand. In the application, the skull screw and the connecting sheet are prepared by using magnesium materials with the same composition, so that the early fracture caused by galvanic corrosion due to different electrode potentials is avoided, and meanwhile, based on the different emphasis of the skull screw and the connecting sheet on strength and shaping, different processing processes are used to meet the performance requirements of the two.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical devices, in particular, to a degradable magnesium metal skull fixation system. BACKGROUND

[0002] In recent years, with the progress of science and technology and the continuous improvement of people's living standards, the incidence of intracranial injury accidents and cerebrovascular diseases is increasing, and the number of craniotomy surgeries is increasing year by year. The skull fixation system currently applied in the clinical field of neurosurgery is mainly made of non-degradable titanium alloy, polyether ether ketone, etc., and is mainly used for re-fixing free skull flaps during craniotomy surgery. Although the above materials used for skull fixation systems have their unique advantages, many problems have also appeared in the process of clinical application. Although titanium alloy has excellent biocompatibility, its long-term retention in the body will cause long-term immune rejection, and the patient himself will also have a foreign body reaction, which is not conducive to the recovery of his physical and mental health. In addition, the use of non-degradable materials for skull fixation will affect the normal development of the skeleton, especially for children with unclosed skull.

[0003] Based on the above reasons, degradable and absorbable materials have begun to be applied in the field of skull fixation, among which magnesium metal has developed most rapidly. Magnesium is one of the essential trace elements for the human body, can catalyze and activate more than 300 known enzyme systems, participate in the storage and transportation of intracellular energy, and assist in completing complex physiological activities such as muscle contraction. Magnesium has good biocompatibility, and magnesium ions can promote bone and accelerate fracture healing. At the same time, magnesium also has good biodegradability and can self-degrade and disappear in the body within a certain period of time after achieving the healing effect.

[0004] There are precedents for using absorbable degradable magnesium metal to make nail plate systems for fixing the human skeleton. Patent CN200710012805.8 discloses a biodegradable skull repair body, which is an early attempt in this field. The patent applies magnesium metal to the field of skull fixation and proposes that the repair body (a thin plate of 0.03mm-1mm with screw holes) and the bone screw inserted into the screw hole are used to fix the skull defect or free bone flap, and the surface has surface modification or is coated with a degradable bioactive coating. In the following period, researchers in this field have made continuous research and improvement. Patent CN201711003495.3 discloses a magnesium-based metal and polymer high molecular material combined craniofacial bone biodegradable material, which further subdivides the design of the magnesium-based skull fixation system with a polymer coating. Patent CN201810275833.7 discloses a low-alloyed degradable micro internal fixation assembly, a magnesium alloy preparation method and a magnesium alloy material, which is a typical representative although it is aimed at the field of maxillofacial surgery. The basic structure has been determined, and the main idea is to convert the non-degradable titanium alloy maxillofacial fixation system into a degradable magnesium metal maxillofacial fixation system by changing the material and imitating the structure.

[0005] According to the above idea, a degradable magnesium metal skull fixation system is made by imitating the design of the titanium alloy skull fixation system (connecting piece plus skull screw). The skull screw is designed according to YY 0018-2016 "Metal bone screw for bone joint implant". It is found during the research that the degradable magnesium metal skull fixation system with the same design as the titanium alloy skull fixation system will be twisted off when implanted. After implantation, the skull screw is prone to break off, and the connecting piece is prone to loosen prematurely.

[0006] After failure analysis, it is found that the magnesium metal skull screw imitating the size and structure of the titanium alloy skull screw is easy to be twisted off when used with an electric drill due to the mechanical properties of the titanium alloy skull screw material being much higher than that of the magnesium alloy. The titanium alloy material used to prepare the skull screw on the market mainly conforms to GB / T 13810-2017 "Titanium and titanium alloy processing materials for surgical implants". According to the requirements of Table 7 in item 3.3.2.3 of the above standard, the tensile strength of TC4 metal bar with a diameter of 7.0mm-50mm is not less than 930MPa. According to the requirements of Table 4 in item 4.4.1 of T / CSBM 0005-2021 "Degradable magnesium alloy hot extruded metal bar", the tensile strength of the degradable magnesium alloy hot extruded metal bar with a diameter of 4.0mm-30mm is at least 225MPa. Therefore, under the condition that the structure and size are basically the same, the decrease in the tensile strength of the material leads to the decrease in the fracture torque when implanted.

[0007] After failure analysis, it was found that the fracture and dislodgement of skull screws after implantation was related to the rapid degradation of the screw shaft. When an electric drill is used with the implant, the excessive torque of the drill causes the screw to undergo a certain amount of plastic deformation (but not breakage). A certain amount of internal stress accumulates in the screw shaft, which accelerates corrosion after implantation, leading to severe localized corrosion and fracture. Increasing the screw's base diameter d1 can alleviate the plastic deformation during implantation and use with an electric drill, reducing accumulated internal stress. However, the screw base diameter d1 cannot be increased indefinitely. In the initial stage of implantation, the fixation of the skull fixation system relies primarily on the threaded portion between the screw base diameter d1 and the screw top diameter d2. Therefore, the matching range of the ratio of the screw base diameter d1 to the screw top diameter d2 needs to be properly explored.

[0008] After failure analysis, it was found that the premature loosening of the connecting piece after implantation was related to the rapid degradation of the supporting part of the fixing hole of the connecting piece. During implantation, the supporting part of the fixing hole fits tightly with the lower surface of the skull screw head, bearing the pressure of the skull screw. This is the weak link in the corrosion process of the connecting piece after implantation.

[0009] Furthermore, based on the principles of crystallography, studies have shown that the corrosion rate of most hot-extruded magnesium alloys in the cross-section (the direction parallel to the extrusion nozzle plane during extrusion is the cross-section direction) is significantly greater than the corrosion rate in the longitudinal section (the direction perpendicular to the extrusion nozzle plane during extrusion is the longitudinal section direction). The main reason for this is that magnesium metal has an HCP structure (hexagonal close-packed structure), and the matrix structure of most magnesium alloys is also a hexagonal close-packed structure. The XRD analysis results of the cross-section and vertical sections after extrusion will be significantly different. After normalization of the XRD data, the diffraction peak intensity of the (0 0 0 2) crystal plane representing the basal plane will vary in the cross-section and vertical sections, and the uniform manifestation is that the diffraction peak intensity of the (0 0 0 2) crystal plane in the longitudinal section is significantly greater than the diffraction peak intensity of the (0 0 0 2) crystal plane in the cross-section. Studies have shown that the corrosion rate of the basal (0 0 0 2) crystal plane of magnesium alloys with a hexagonal close-packed structure should be significantly lower than that of the (1 0 -1 1) crystal plane and the (1 0 -1 0) crystal plane.

[0010] Figure 12 This is the XRD spectrum of the cross section of EK30 magnesium alloy hot extruded metal bar. Figure 13 This is the XRD spectrum of the longitudinal section of the EK30 magnesium alloy hot-extruded metal bar. It can be seen from the figure that after normalization, the diffraction peak intensity of the (0 0 0 2) crystal plane representing the basal plane will be different in the horizontal and vertical sections, and the diffraction peak intensity of the (0 0 0 2) crystal plane in the longitudinal section is significantly greater than that of the (0 0 0 2) crystal plane in the cross section. Figure 14The hydrogen evolution curves of the in vitro degradation test of the cross-section and longitudinal sections of the EK30 magnesium alloy hot-extruded metal bar are shown in FIG. 1 . As can be seen from the figure, when other conditions are the same, the cross-sectional corrosion rate of the EK30 magnesium alloy hot-extruded metal bar is greater than the longitudinal corrosion rate.

[0011] Studies have shown that magnesium alloys of different compositions have different electrode potentials. When used together, galvanic corrosion will occur due to the difference in electrode potential. The corrosion will be concentrated at the contact points, forming local corrosion pits, which will seriously endanger the performance of magnesium metal implants and shorten their effective support time in the body. Summary of the Invention

[0012] In view of the defects in the prior art, the purpose of the present invention is to provide a degradable magnesium metal skull fixation system.

[0013] The degradable magnesium metal skull fixation system provided by the present invention comprises a skull screw and a connecting piece, wherein the connecting piece comprises a connecting bridge and fixing holes provided at both ends of the connecting bridge, and the width of the connecting bridge is no greater than the width of the fixing hole;

[0014] The skull screws are correspondingly inserted into the fixing holes of the connecting piece, and the number of the skull screws does not exceed the number of the fixing holes. The skull screws and the connecting piece are made of pure magnesium or magnesium alloy of the same grade.

[0015] Preferably, the bottom diameter of the skull screw is d1, the top diameter of the skull screw is d2, and the ratio of d1 to d2 is in the range of 70% to 85%.

[0016] Preferably, the thickness H of the connecting piece is 0.6 mm to 2 mm;

[0017] The fixing hole includes an outer fixing hole and an inner fixing hole, the outer fixing hole and the inner fixing hole are sequentially connected and coaxially arranged, the diameter of the outer fixing hole is larger than the diameter of the inner fixing hole, and a fixing hole supporting portion is arranged between the outer fixing hole and the inner fixing hole;

[0018] The fixing hole supporting portion includes an inclined section and a vertical section connected in sequence, one end of the inclined section starting from the upper surface of the connecting piece, the other end of the inclined section extending toward one end of the vertical section until it is connected to the one end of the vertical section, and the other end of the vertical section extending in a direction parallel to the central axis of the fixing hole until it is connected to the lower surface of the connecting piece, and the through hole surrounded by the vertical sections is the inner hole of the fixing hole;

[0019] The thickness h of the vertical section is 0.12 mm to 0.4 mm. When the skull screw is inserted into the fixing hole, the lower surface of the screw head at the front end of the skull screw fits into the inclined section.

[0020] Preferably, when the skull screw is inserted into the fixing hole, the clearance between the skull screw and the inner hole of the fixing hole in the radial direction does not exceed 0.5 mm.

[0021] Preferably, the skull screw and the connecting piece are both made of one of pure magnesium, magnesium-calcium alloy, magnesium-manganese alloy, magnesium-zinc alloy, magnesium-zirconium alloy, magnesium-yttrium alloy, magnesium-rare earth alloy and magnesium-lithium alloy.

[0022] Preferably, the top diameter d2 of the skull screw is 1.0 mm to 3.0 mm, and the bottom diameter d1 of the skull screw is 0.7 mm to 2.6 mm;

[0023] The lower surface of the screw head at the front end of the skull screw is spherical, and the upper surface of the screw head is provided with a slot, a cross slot or a hexagonal slot.

[0024] Preferably, the diameter D of the screw head is 1.5 mm to 4.5 mm, the length L3 of the skull screw is 3 mm to 12 mm, and the screw tail of the skull screw is provided with 2 to 4 chip removal grooves.

[0025] Preferably, both ends of the connecting bridge are provided with a pair of fixing holes, and the number of the fixing holes does not exceed 6;

[0026] The width L2 of the fixing hole is 3.0 mm to 6.0 mm, and the length L1 of the connecting piece is 8 mm to 40 mm.

[0027] Preferably, the outer surfaces of the connecting piece and the skull screw are both provided with one or more layers of gain coating;

[0028] The gain coating comprises one or more of magnesium fluoride, hydroxyapatite, tricalcium phosphate, magnesium-containing apatite, dibasic calcium phosphate dihydrate, monobasic calcium phosphate, dibasic calcium phosphate, poly(lactic-co-glycolic acid) (PLGA), racemic poly(lactic acid) (PDLLA), poly(L-lactic acid) (PLLA), and polycaprolactone (PCL);

[0029] The thickness of the gain coating is 0.5 to 50 microns, and the preparation methods of the gain coating include chemical conversion method, thermal spraying method, plasma spraying method and solvent spraying method.

[0030] Preferably, the skull screw is formed by extrusion of a metal rod, and the cross-sectional direction of the metal rod is parallel to the cross-sectional direction of the screw shank of the skull screw;

[0031] The connecting piece is formed by extrusion of a metal plate, and the cross-sectional direction of the metal plate is parallel to the length / width direction of the connecting piece.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention adopts the technical means of using the same magnesium material for the skull screw and the connecting piece to avoid premature fracture caused by galvanic corrosion due to different electrode potentials. At the same time, based on the different emphasis on strength and shaping of the skull screw and the connecting piece, different processing techniques are used to meet the performance requirements of both.

[0034] 2. The present invention is based on the corrosion characteristics of magnesium alloy, combined with the corrosion characteristics of skull screws after implantation, that is, the longitudinal section direction of the skull screw rod is the weakest direction for corrosion, and combined with the corrosion characteristics of the connecting piece after implantation, that is, the thickness direction of the connecting piece is the weakest direction for corrosion. The present invention adopts technical means to ensure that the cross-sectional direction of the metal rod is parallel to the cross-sectional direction of the skull screw rod, and that the cross-sectional direction of the metal plate is parallel to the length / width direction of the connecting piece during the extrusion process, which is conducive to extending its effective fixation time after implantation.

[0035] 3. Based on the design of the titanium alloy skull fixation system, the present invention adopts the technical means of increasing the thickness H of the connecting plate, increasing the thickness h of the vertical section of the fixing hole support part, and at the same time limiting the diameter of the inner hole of the fixing hole, thereby reducing the gap between the inner hole of the connecting plate fixing hole and the skull screw after implantation, and avoiding premature failure of the key parts of the connecting plate during corrosion degradation.

[0036] 4. Based on the design of the titanium alloy skull fixation system, the present invention adopts the technical means of increasing the screw bottom diameter d1 and increasing the ratio of the screw bottom diameter d1 to the screw top diameter d2 to avoid the phenomenon of twisting during implantation and premature failure during corrosion degradation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0038] Figure 1 It is a structural schematic diagram of the present invention;

[0039] Figure 2 Schematic diagram of the structure of the skull screw in the present invention;

[0040] Figure 3 This is a schematic diagram of the dimensions of the skull screws in the present invention;

[0041] Figure 4 Schematic diagram of the connecting piece structure in the present invention;

[0042] Figure 5 This is a schematic diagram of the dimensions of the connecting piece in the present invention;

[0043] Figure 6 is a schematic diagram of the upper surface of the connecting piece in the present invention;

[0044] Figure 7 Schematic diagram of the lower surface of the connecting piece in the present invention;

[0045] Figure 8 is a cross-sectional schematic diagram of the fixing hole in the present invention;

[0046] Figure 9 is a cross-sectional schematic diagram of the skull screw of the present invention when assembled in the fixing hole;

[0047] Figure 10 This is a schematic structural diagram of the present invention in which the connecting piece has two pairs of fixing holes;

[0048] Figure 11 This is a schematic structural diagram of the present invention when the connecting piece has three pairs of fixing holes;

[0049] Figure 12 This is the XRD spectrum of the cross section of EK30 magnesium alloy hot extruded metal bar;

[0050] Figure 13 This is the XRD spectrum of the longitudinal section of EK30 magnesium alloy hot extruded metal bar;

[0051] Figure 14 These are the hydrogen evolution curves of the in vitro degradation test on the transverse and longitudinal sections of EK30 magnesium alloy hot-extruded metal bars.

[0052] The figure shows:

[0053] Skull screw 1 Fixation hole 22

[0054] Screw head 11 fixing hole outer hole 221

[0055] Nail head lower surface 111 fixing hole inner hole 222

[0056] Screw rod 12 fixing hole supporting portion 223

[0057] Screw tail 13 fixing hole center axis 224

[0058] Chip removal groove 131 connecting piece upper surface 23

[0059] Connecting piece 2 Connecting piece lower surface 24

[0060] Connecting Bridge 21 DETAILED DESCRIPTION

[0061] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0062] The present invention discloses a degradable magnesium metal skull fixation system. Compared with the traditional skull fixation system designed based on titanium alloy, the system can prevent the premature failure of key parts of screws and connecting plates during corrosion degradation, and avoid the phenomenon of skull screws breaking and falling out, and premature loosening of connecting plates.

[0063] According to the degradable magnesium metal skull fixation system provided by the present invention, Figure 1-8 As shown, it includes a skull screw 1 and a connecting piece 2, the connecting piece 2 includes a connecting bridge 21 and fixing holes 22 provided at both ends of the connecting bridge 21, and the width of the connecting bridge 21 is smaller than the width of the fixing holes 22; the skull screws 1 are correspondingly inserted into each fixing hole 22 of the connecting piece 2, and the number of skull screws 1 does not exceed the number of fixing holes 22. The skull screw 1 and the connecting piece 2 are made of the same brand of pure magnesium or magnesium alloy.

[0064] like Figure 4-5 As shown, the base diameter of the skull screw 1 is d1, the top diameter of the skull screw 1 is d2, and the ratio of d1 to d2 ranges from 70% to 85%. Properly increasing the base diameter d1 of the skull screw 1 can increase the maximum torque of the skull screw 1. Studies have found that for the same model of skull screw 1, appropriately increasing the ratio of the base diameter d1 to the top diameter d2 can significantly increase the maximum torque value of the skull screw 1.

[0065] The thickness H of the connecting piece 2 is 0.6mm to 2mm; the fixing hole 22 includes an outer fixing hole 221 and an inner fixing hole 222, the outer fixing hole 221 and the inner fixing hole 222 are connected in sequence and are coaxially arranged, the diameter d4 of the outer fixing hole 221 is larger than the diameter d3 of the inner fixing hole 222, and a fixing hole supporting portion 223 is provided between the outer fixing hole 221 and the inner fixing hole 222; the fixing hole supporting portion 223 includes an inclined section and a vertical section connected in sequence, one end of the inclined section Starting from the upper surface 23 of the connecting piece, the other end of the inclined segment extends toward one end of the vertical segment until it is connected to one end of the vertical segment. The other end of the vertical segment extends in a direction parallel to the central axis 224 of the fixing hole until it is connected to the lower surface 24 of the connecting piece. The through hole surrounded by the vertical segment is the inner hole 222 of the fixing hole; the thickness h of the vertical segment is 0.12mm~0.4mm. When the skull screw 1 is inserted into the fixing hole 22, the lower surface 111 of the screw head 11 at the front end of the skull screw 1 is in contact with the inclined segment.

[0066] like Figure 6As shown, when the skull screw 1 is inserted into the fixing hole 22, the gap between the skull screw 1 and the inner hole 222 of the fixing hole in the radial direction does not exceed 0.5 mm, wherein the gap between the inner hole 222 of the fixing hole and the skull screw 1 is L4, the gap between the inner hole 222 of the fixing hole and the skull screw 1 on the left side is L41, and the gap between the inner hole 222 of the fixing hole and the skull screw 1 on the right side is L42.

[0067] The skull screw 1 and connecting plate 2 are both made of one of pure magnesium, magnesium-calcium alloys, magnesium-manganese alloys, magnesium-zinc alloys, magnesium-zirconium alloys, magnesium-yttrium alloys, magnesium-rare-earth alloys, and magnesium-lithium alloys. The top diameter d2 of the skull screw 1 ranges from 1.0 mm to 3.0 mm, and the bottom diameter d1 ranges from 0.7 mm to 2.6 mm. The lower surface 111 of the screw head 11 at the front end of the skull screw 1 is spherical, and the upper surface of the screw head 11 is provided with a slot, a cross slot, or a hexagonal socket. The diameter D of the screw head 11 ranges from 1.5 mm to 4.5 mm, and the length L3 of the skull screw 1 ranges from 3 mm to 12 mm. The screw tail 13 of the skull screw 1 is provided with two to four chip removal grooves 131. Pairs of fixing holes 22 are respectively provided at both ends of the connecting bridge 21 , and the number of the fixing holes 22 does not exceed 6; the width L2 of the fixing holes 22 is 3.0 mm to 6.0 mm, and the length L1 of the connecting piece 2 is 8 mm to 40 mm.

[0068] The outer surfaces of the connecting piece 2 and the skull screw 1 are both provided with one or more layers of gain coating; the gain coating comprises one or more of magnesium fluoride, hydroxyapatite, tricalcium phosphate, magnesium-containing apatite, dibasic calcium phosphate dihydrate, monocalcium phosphate, dibasic calcium phosphate, polylactic acid-co-glycolic acid (PLGA), racemic polylactic acid (PDLLA), levorotatory polylactic acid (PLLA), and polycaprolactone (PCL); the thickness of the gain coating is 0.5 to 50 microns, and the preparation method of the gain coating comprises chemical conversion, thermal spraying, plasma spraying, and solvent spraying. The skull screw 1 is formed by extrusion of a metal rod, such as Figure 9-11 As shown, the corrosion characteristics of the skull screw 1 after implantation are that the longitudinal section direction of the skull screw 1 rod is the weak direction of corrosion, and the corrosion characteristics of the connecting piece 2 after implantation are that the thickness direction of the connecting piece 2 is the weak direction of corrosion. The cross-sectional direction of the metal rod is parallel to the cross-sectional direction of the screw rod 12 of the skull screw 1; the connecting piece 2 is extruded by a metal sheet, and the cross-sectional direction of the metal sheet is parallel to the length / width direction of the connecting piece, which is conducive to prolonging its effective fixation time after implantation.

[0069] The present invention adopts the following experiments to detect each performance:

[0070] Strength and flexibility: refer to the standard GB / T 228.1-2021 metal material tensile test part 1: room temperature test method, when the tensile test is carried out, the metal bar adopts 5d0 circular cross section proportional sample, numbered R7, and the metal plate adopts rectangular cross section proportional sample, numbered P7;

[0071] In vitro degradation test (hydrogen evolution method), refer to the standard YY / T 0695-2008 standard test method for cyclic potentiodynamic polarization of corrosion sensitivity of small implant devices; ASTM G1-03 Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens; ASTM G31-12a Standard Practice for Laboratory Immersion Corrosion Testing of Metals; ASTM F3268 Standard Guide for in vitro Degradation Testing of Absorbable Metals. The other outer surface of the sample is closed by cold inlay method, only the cross section to be tested is leaked, and the amount of hydrogen evolution is recorded regularly.

[0072] Torsion test: refer to the standard YY / T 0662-2008 mechanical property requirements and test methods for metal bone screws with asymmetric threads and spherical lower surfaces of surgical implants; YY 0018-2016 bone joint implant metal bone screw.

[0073] Example 1:

[0074] The embodiment provides a degradable EK30 magnesium alloy skull fixation system, which comprises a skull screw 1 and a connecting piece 2, and the materials are all made of degradable EK30 magnesium alloy. The chemical composition (weight percentage) of the EK30 magnesium alloy is 2.0%-3.2% Nd, 0.15%-0.3% Zn, 0.2%-0.6% Zr, the balance is Mg and other inevitable impurities, and the content of each impurity element is not more than 0.1%.

[0075] As Figure 2As shown, the bottom diameter d1 of the skull screw 1 is 1.4 mm to 1.6 mm, the top diameter d2 of the skull screw 1 is 1.8 mm to 2.2 mm, the ratio of the screw bottom diameter d1 to the screw top diameter d2 is in the range of 70% to 80%, the total length L3 of the screw is 3 mm to 11 mm, the diameter D of the screw head 11 is 2.7 mm to 3.3 mm, the pitch t1 is 0.6 mm to 0.9 mm, the tooth width t2 is 0.05 mm to 0.2 mm, the screw tail 13 has 2 to 3 chip grooves 131, and the screw head is fixed with a cross groove.

[0076] like Figure 4 As shown, the inner diameter d3 of the fixing hole 22 of the two-hole connecting piece 2 is 1.9mm-2.3mm, the outer diameter d4 of the fixing hole is 2.5mm-3.5mm, the length L1 of the two-hole connecting piece 2 is 8mm-20mm, the maximum width L2 of the two-hole connecting piece 2 is 4.0mm-4.4mm, the width L5 of the connecting bridge 21 is 1.8mm-2.2mm, the thickness H is 0.6mm-1.0mm, and the thickness h of the vertical section of the supporting part is 0.12mm-0.3mm. Figure 7 As shown, the structural parameters of the four-hole and six-hole connecting pieces are basically the same as those of the two-hole ones, but the length L1 of the four-hole connecting piece 2 is 15mm to 32mm, and the length L1 of the six-hole connecting piece 2 is 20mm to 40mm. Figure 6 As shown, the gap L4 between the inner hole 222 of the fixing hole of all types of connecting pieces 2 and the skull screw 1 does not exceed 0.3 mm, and L4 is the sum of the gap L41 between the inner hole 222 of the fixing hole of the connecting piece and the left side of the skull screw 1 and the gap L42 between the inner hole 222 of the fixing hole of the connecting piece and the right side of the skull screw 1.

[0077] During skull fixation surgery, after the doctor removes the free skull flap and completes the intracranial surgery, the free skull flap is returned to its original position and fixed using 2 to 6 connecting pieces 2 (different models and sizes of connecting pieces can be selected depending on the situation). Holes are drilled and tapped in advance, and then skull screws 1 are passed through the fixing holes of the connecting pieces to fix the free skull flap.

[0078] The material used to make these skull screws (EK30 magnesium alloy metal rods) has a tensile strength of no less than 230 MPa and a maximum torque of no less than 0.15 N·m. Three beagle dogs were used as an animal model. Each animal was fixed with three connectors (two with two holes and one with four holes) and six skull screws. No screws broke during implantation, and the skull healed well after implantation. No skull screw breakage or premature loosening of the connectors was observed. Complete degradation occurred within approximately 24 months.

[0079] Comparative Example 1:

[0080] A degradable magnesium metal skull fixation system, different from example 1, the bottom diameter d1 of the skull screw 1 is 1.2mm-1.4mm, the top diameter d2 of the skull screw is 1.8mm-2.2mm, and the ratio of the bottom diameter d1 of the screw to the top diameter d2 of the screw is 60%-70%. The technical effect evaluation is that the material (EK30 magnesium alloy metal bar) for preparing the skull screw 1 has a maximum torque not less than 0.10N·m. During implantation, 6 skull screws 1 are implanted in total, of which 2 are twisted and broken, and the broken nails are difficult to remove, and the latter 2 are replaced with the skull screw 1 mentioned in example 1. After 1 month of implantation, it is found that the fixation effect is good, and after 3 months of implantation, it is found that 4 skull screws (small bottom diameter) have 1 broken and come out, and 2 skull screws (large bottom diameter) are fixed well.

[0081] Comparative example 2:

[0082] A degradable magnesium metal skull fixation system, different from example 1, the thickness H of the connecting piece 2 is 0.4mm-0.6mm. The technical effect evaluation is that 3 connecting pieces 2 are implanted during implantation, and after 1 month of implantation, it is found that the fixation effect is good, and after 3 months of implantation, it is found that 1 connecting piece 2 appears loose phenomenon, the skull screw 1 is no longer located at the center of the fixed hole 22 of the connecting piece 2, and the skull screw 1 and the connecting piece 2 appear relative displacement. And after the 3 connecting pieces 2 are taken out for tensile test, it is found that the ratio of the strength of the single connecting piece 2 when it is pulled off to the average value of the result when implanted is 70.2%-75.3%, and the fixation effect is greatly weakened.

[0083] Comparative example 3:

[0084] A degradable magnesium metal skull fixation system, different from example 1, the vertical segment thickness h of the fixed hole support part 223 is 0.10mm-0.12mm. At present, titanium alloy skull connecting piece 2 tends to this design, mainly adopting the idea of low incision, that is, as far as possible to make the highest point of the screw head 11 of the skull screw 1 after implantation and the upper surface of the connecting piece 2 in the same plane, or the highest point of the screw head 11 slightly higher than the upper surface of the connecting piece 2. In this way, after the operation, the patient touches the implanted part with his hand, and there is no obvious foreign body sensation, and the irritation to the scalp is also reduced.

[0085] Technical effect evaluation: 3 connecting pieces 2 are implanted during implantation, and after 1 month of implantation, it is found that the fixation effect is good, and after 3 months of implantation, it is found that 2 connecting pieces 2 appear loose phenomenon, the skull screw 1 is no longer located at the center of the fixed hole 22 of the connecting piece 2, and the skull screw 1 and the connecting piece 2 appear relative displacement. After the 3 connecting pieces 2 are taken out for tensile test, it is found that the ratio of the strength of the single connecting piece 2 when it is pulled off to the average value of the result when implanted is 83.4%-92.3%, and the fixation effect is still maintained.

[0086] Example 2:

[0087] This embodiment provides a high-purity magnesium skull fixation system, comprising a skull screw 1 and a connecting plate 2, both of which are made of biodegradable high-purity magnesium. The chemical composition (by weight percentage) of the high-purity magnesium is no less than 99.99% Mg, with the remainder being other unavoidable impurities, with the content of any individual impurity element not exceeding 0.01%.

[0088] like Figure 2 As shown, the bottom diameter d1 of the skull screw 1 is 2.0 mm to 2.6 mm, the top diameter d2 of the skull screw 1 is 2.6 mm to 3.0 mm, the ratio of the screw bottom diameter d1 to the screw top diameter d2 is in the range of 75% to 85%, the total length L3 of the screw is 4 mm to 11 mm, the diameter D of the screw head 11 is 3.8 mm to 4.5 mm, the pitch t1 is 0.6 mm to 0.9 mm, the tooth width t2 is 0.05 mm to 0.2 mm, the screw tail 13 has 2 to 3 chip grooves 131, and the screw head 11 is fixed with a cross groove.

[0089] like Figure 4 As shown, the inner diameter d3 of the fixing hole 22 of the two-hole connecting piece 2 is 2.7mm-3.1mm, the outer diameter d4 of the fixing hole 22 is 3.8mm-4.5mm, the length L1 of the two-hole connecting piece 2 is 8mm-20mm, the maximum width L2 of the two-hole connecting piece 2 is 5.0mm-6.0mm, the width L5 of the connecting bridge 21 is 2mm-3mm, the thickness H is 1mm-2mm, and the thickness h of the vertical section of the fixing hole supporting portion 223 is 0.2mm-0.4mm. Figure 7 As shown, the structural parameters of the four-hole and six-hole connecting pieces 2 are basically the same as those of the two-hole ones, but the length L1 of the four-hole connecting piece 2 is 15mm to 32mm, and the length L1 of the six-hole connecting piece 2 is 20mm to 40mm. Figure 6 As shown, the gap L4 between the inner hole of the fixing hole 22 of all types of connecting pieces 2 and the skull screw 1 does not exceed 0.5 mm, and L4 is the sum of the gap L41 between the inner hole of the fixing hole 22 of the connecting piece 2 and the left side of the skull screw 1 and the gap L42 between the inner hole of the fixing hole 22 of the connecting piece 2 and the right side of the skull screw 1.

[0090] During skull fixation surgery, after the doctor removes the free skull flap and completes the intracranial surgery, the free skull flap is returned to its original position and fixed using 2 to 6 connecting pieces 2 (different models and sizes of connecting pieces can be selected depending on the situation). Holes are drilled and tapped in advance, and then the skull screws 1 are passed through the fixing holes 22 of the connecting pieces 2 to fix the free skull flap.

[0091] Technical Effectiveness Evaluation: The material used to make this skull screw (high-purity magnesium) has a tensile strength of no less than 150 MPa and a maximum torque of no less than 0.16 N·m. Three beagle dogs were used as an animal model. Each animal was fixed with three connecting plates (two with two holes and one with four holes) and six skull screws. No screws broke during implantation, and healing was excellent after implantation. No skull screws were observed to break or fall out, and no connecting plates were observed to loosen prematurely. Complete degradation took approximately 30 months.

[0092] Comparative Example 4:

[0093] A degradable magnesium metal skull fixation system is different from Example 2 in that the gap L4 between the inner hole of the fixing hole 22 of all types of connecting plates 2 and the skull screw 1 is 0.5mm to 0.7mm.

[0094] Evaluation of technical effects: A total of three connecting pieces 2 were implanted during implantation. One month after implantation, it was found that the fixation effect was good. Three months after implantation, it was found that two connecting pieces 2 were loose, and the skull screw 1 was no longer located in the center of the fixing hole 22 of the connecting piece 2. There was relative displacement between the skull screw 1 and the connecting piece 2.

[0095] Comparative Example 5:

[0096] A degradable magnesium metal skull fixation system is different from Example 2 in that the material of all types of skull screws 1 is replaced with the material EK30 involved in Example 1.

[0097] Evaluation of technical effects: A total of 3 connecting pieces 2 and 6 skull screws 1 were implanted during implantation. One month after implantation, the fixation effect was found to be good. Three months after implantation, it was found that one connecting piece 2 and one skull screw 1 thereon were loose. The skull screw 1 was no longer located in the center of the fixing hole 22 of the connecting piece 2. There was relative displacement between the skull screw 1 and the connecting piece 2, and the screw head 11 had a tendency to break and fall out.

[0098] In the description of this application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0099] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other at will without conflict.

Claims

1. A degradable magnesium metal skull fixation system, characterized in that: It comprises a skull screw (1) and a connecting piece (2), wherein the connecting piece (2) comprises a connecting bridge (21) and fixing holes (22) arranged at both ends of the connecting bridge (21), and the width of the connecting bridge (21) is not greater than the width of the fixing hole (22); The skull screws (1) are correspondingly inserted into the fixing holes (22) of the connecting piece (2), and the number of the skull screws (1) does not exceed the number of the fixing holes (22). The skull screws (1) and the connecting piece (2) are made of pure magnesium or magnesium alloy of the same grade. The bottom diameter of the skull screw (1) is d1, the top diameter of the skull screw (1) is d2, and the ratio of d1 to d2 ranges from 70% to 85%; The thickness H of the connecting piece (2) is 0.6 mm to 2 mm; The fixing hole (22) comprises an outer fixing hole (221) and an inner fixing hole (222); the outer fixing hole (221) and the inner fixing hole (222) are sequentially connected and coaxially arranged; the diameter of the outer fixing hole (221) is larger than the diameter of the inner fixing hole (222); and a fixing hole supporting portion (223) is arranged between the outer fixing hole (221) and the inner fixing hole (222); The fixing hole supporting portion (223) includes an inclined section and a vertical section connected in sequence, one end of the inclined section takes the upper surface (23) of the connecting piece as a starting point, the other end of the inclined section extends toward one end of the vertical section until it is connected to one end of the vertical section, the other end of the vertical section extends in a direction parallel to the central axis (224) of the fixing hole until it is connected to the lower surface (24) of the connecting piece, and the through hole surrounded by the vertical section is the inner hole (222) of the fixing hole; The thickness h of the vertical section is 0.12 mm to 0.4 mm. When the skull screw (1) is inserted into the fixing hole (22), the lower surface (111) of the screw head (11) at the front end of the skull screw (1) fits into the inclined section. When the skull screw (1) is inserted into the fixing hole (22), the clearance between the skull screw (1) and the inner hole (222) of the fixing hole in the radial direction does not exceed 0.5 mm; During the extrusion process, the cross-sectional direction of the metal rod is ensured to be parallel to the cross-sectional direction of the skull screw shank, and the cross-sectional direction of the metal plate is ensured to be parallel to the length / width direction of the connecting piece.

2. The degradable magnesium metal skull fixation system according to claim 1, characterized in that: The skull screw (1) and the connecting piece (2) are both made of one of pure magnesium, magnesium-calcium alloy, magnesium-manganese alloy, magnesium-zinc alloy, magnesium-zirconium alloy, magnesium-yttrium alloy, magnesium-rare earth alloy and magnesium-lithium alloy.

3. The degradable magnesium metal skull fixation system according to claim 1, characterized in that: The top diameter d2 of the skull screw (1) is 1.0 mm to 3.0 mm, and the bottom diameter d1 of the skull screw (1) is 0.7 mm to 2.6 mm; The lower surface (111) of the screw head (11) at the front end of the skull screw (1) is spherical, and the upper surface of the screw head (11) is provided with a slot, a cross slot or a hexagonal slot.

4. The degradable magnesium metal skull fixation system according to claim 3, characterized in that: The diameter D of the screw head (11) is 1.5 mm to 4.5 mm, the length L3 of the skull screw (1) is 3 mm to 12 mm, and the screw tail (13) of the skull screw (1) is provided with 2 to 4 chip removal grooves (131).

5. The degradable magnesium metal skull fixation system according to claim 1, characterized in that: Both ends of the connecting bridge (21) are respectively provided with a pair of fixing holes (22), and the number of the fixing holes (22) does not exceed 6; The width L2 of the fixing hole (22) is 3.0 mm to 6.0 mm, and the length L1 of the connecting piece (2) is 8 mm to 40 mm.

6. The degradable magnesium metal skull fixation system according to claim 1, characterized in that: The outer surfaces of the connecting piece (2) and the skull screw (1) are both provided with one or more layers of gain coating; The gain coating comprises one or more of magnesium fluoride, hydroxyapatite, tricalcium phosphate, magnesium-containing apatite, dibasic calcium phosphate dihydrate, monobasic calcium phosphate, dibasic calcium phosphate, poly(lactic-co-glycolic acid) (PLGA), racemic poly(lactic acid) (PDLLA), poly(L-lactic acid) (PLLA), and polycaprolactone (PCL); The thickness of the gain coating is 0.5 to 50 microns, and the preparation methods of the gain coating include chemical conversion method, thermal spraying method, plasma spraying method and solvent spraying method.

7. The degradable magnesium metal skull fixation system according to claim 6, characterized in that: The skull screw (1) is formed by extrusion of a metal rod, and the cross-sectional direction of the metal rod is parallel to the cross-sectional direction of the screw rod (12) of the skull screw (1); The connecting piece (2) is formed by extrusion of a metal plate, and the cross-sectional direction of the metal plate is parallel to the length / width direction of the connecting piece.

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