Abstract:
A metal bone supporter for medical bone substitute including a supporter and a connector component which are functionally and structurally designed according to anatomical data and biomechanical data. The titanium alloy powders in the device are able to be scanned, melted and molded through electron beams, to form a cylinder with the strength and elastic modulus similar to cancellous bones of the human body. The supporter component is a porotic spongy body structure with threads on an end, and porous structure forms a rough surface. The connector component is made with a smooth surface and a dense solid mass inside, a thread on an end, and is connected to the supporter component as a removable body. The porous structure enables bone growth, and the device has a high surface friction coefficient, and has a stable structure and mechanical properties are similar to bones.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. §119 to Chinese Patent Application No. 2008-10111686.6, filed May 16, 2008, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to artificial bone material for medical bone transplantation and the preparation of the material, in particular to a metal bone supporter used in the operative therapy of femoral head necrosis for replacing bone grafting to retard the development of the pathological changes. 
     2. Description of Background Art 
     It is well-known that autologous bone, allogeneic bone or artificial bone and other substitutes are required to be implanted into the defective part of the bone during the filling, repairing and other orthopedic treatment for all kinds of bone defects in medical orthopedic trauma and the surgical treatment for necrosis for facilitating the bone at the defective part to regain integrity and continuity, so as to achieve the treating purpose of obtaining normal mechanical property. The therapeutic method is called bone transplantation. Bone defect generally presents at joints, wherein, the incidence rate and disability rate of the bone defect caused by necrosis of femoral head are the highest. According to the statistics, the number of the existing patients with femoral head necrosis, which is a common frequently-occurring disease, is more than 8 million in our country. Pathogenic factors of femoral head necrosis are divided into: traumatic necrosis of femoral head, including fracture of the femoral neck, dislocation of hip joint, acetabular fracture and so on; non-traumatic necrosis of femoral head, comprising many primary diseases, metabolic diseases, diseases induced by alcoholic intemperance and hormonal drugs and so on. The analytical data obtained through scanning, calculating and tracing a plurality of patients with femoral head necrosis via MRI indicates that collapse occurs on the patients whose femoral head necrotic area are more than 43%, no collapse appears on the patients whose necrotic area are less than 25%, and the patients whose the necrotic area are between 25% and 43%, are belong to the potential sufferers of collapse. The only effective therapeutic method for the collapse in relation to necrosis of femoral head is artificial hip joint replacement. In order to prevent collapse, early therapeutic methods for necrosis of femoral head include core decompression, bone grafting, stem cell transplantation and other methods, aiming at decreasing the necrotic range, facilitating the bone healing, preventing the collapse of femoral head and retarding the development of pathological changes. Substitute bone for bone grafting comprises biological artificial bone, including autologous bone or allogeneic bone, wherein, autologous bone, which is provided with great regeneration ability, rapid healing and none immune rejection, is the most reliable bone for implantation. However, for the autologous bone is taken from the patient, the source is limited; in addition, because one more operation is required for taking the bone, not only the treatment time is prolonged, but also the suffer of the patient is increased. Although the source of allogeneic bone is abundant, the original mechanical strength of the bone is decreased and various properties are changed after treatment; moreover, allogeneic bone transplantation is possible of causing the transmission of other diseases, lacking security. Both the autologous bone and allogeneic bone transplantation have the disadvantages of long bone ingrowth and creep substitution period, poor mechanical supporting effect and other factors and limited range of operation indication. In recent years, substitute artificial bone, which is made of composite material as tricalcium phosphate, polylactic acid, pearl powder and sodium chloride, has been used in bone transplantation. However, although being close to the performance of the biological bone, the composite artificial bone still has many problems as unstable therapeutic effect, complicated manufacturing process, great cost, insufficient mechanical property and so on. A significant topic in the field is to solve the difficulty in the treatment of patient at the early stage of femoral head necrosis, such as the reduction of necrotic range, facilitation of bone ingrowth and healing, retardation of the development of pathological changes, prevention of collapse caused by necrosis of femoral head, delay or substitution of hip joint replacement and so on. Therefore, the development of bone substitute, which is characterized in effective defect filling capability, fast bone ingrowth, excellent mechanical effect and low cost, becomes a hot job in the field. 
     SUMMARY OF THE INVENTION 
     The present invention aims to provide a metal bone supporter and the preparation technique thereof. The supporter, which is able to give sufficient spaces for bone ingrowth and the cell structure, is characterized in good biocompatibility, high skin friction coefficient and steady structure, and is similar to the human bone with regard to the mechanical property. The supporter is capable of providing structural support for the necrotic part of the femoral head since the early stage after implantation, and allowing the bone ingrowth, so as to slower the collapse speed of the femoral head necrotic part, accelerate bone healing, and postpone or prevent the need for the hip joint replacement operation. 
     In order to achieve the object, a metal supporter used, which comprises a supporter component and a connector component, is designed in the present invention for medical bone replacement by using the technical solution below. The present invention is characterized in that: the supporter component, which is similar to the human cancellous bone in the aspects of the form, intensity and elastic modulus, is a cylinder made of titanium alloy powders by scanning, melting and molding via an electron beam melting fabrication device; the supporter component surface is a porotic spongy body structure, the axis part is solid, a coarse external surface is formed by a porous structure, the pore diameter is 100-800 micron, and the porosity is 50-80%. The connector component, made by mechanical processing, has a smooth external surface and a compact and solid interior. One end of the connector component is provided with a fixing thread. The supporter component and the connector component are in combined connection forming a whole metal bone supporter after connection. 
     Mechanism and design of the combined connection between the supporter component and the connector component are characterized in that: (1) thread connection between the internal thread and the external thread by direct rotating connection; (2) a fixing bolt is inserted through the center of the supporter component and the connector component for thread connection; (3) based on the operational requirement, the supporter component is used independently. The external surface of one end of the supporter component for independent application is provided with a fixing thread; (4) both the supporter component and the connector component is able to be processed into any other shapes or variant shapes in accordance with the requirements, so as to meet different demands in operation. 
     The processing steps for preparing the metal bone supporter are as follows: 
     a. Carry out the engineering design of function and structure for every component of the metal bone supporter according to anatomical data and biomechanical data; 
     b. Input the information data of the designed supporter component to the computer of an electron beam melting fabrication device, and then carry out layering scanning, high temperature melting, and accumulation for molding; 
     c. Other parts are molded by mechanical treatment according to the design drawings and parameters; 
     d. Each component is sterilized separately as per the process requirements, and sealed and packed for standby. 
     Wherein, the electron beam fusing temperature range in Process Step b is 1800 to 2600° C. 
     The present invention carries out the functional and structural engineering design for each part of the metal bone supporter based on the anatomy data and the biomechanics data, and then lays the design data of the supporter&#39;s supporting component in the electron beam melting fabrication device for forming manufacturing. The operating principle of the forming equipment is: the high-energy electron beam eradiated by the vacuum state electron gun, scans on the evenly laying titanium alloy powder coating in the working chamber after going through the focusing coil and deflecting coil under the control of a computer according to the drawing and data for producing a high temperature of higher than 1800° C. in the target position, so that the metal powders is melted and accumulated by layers for shaping. The remaining parts of the supporter are able to be easily completed by mechanical processing according to the engineering drawings and technical materials. The components are connected by threaded coupling or bolting, so as to finally form the complete metal bone supporter product. 
     With the electron beam melting fabrication device, the metal bone supporter component is made directly from the titanium alloy powders. Thus, the produce time for designing and processing complex implant is reduced. The energy utilization ratio is high and the processing speed is high, reducing the preparation period from the design to the product and ensuring the consistency of the product. The present invention is characterized in that structure and form of the titanium alloy implant are able to be controlled. It is easy to manufacture both the dense implant component and the implant component with different porosities and similar to the cancellous bone as required by the designer. In addition, different density and porosity are able to be realized in different positions of the same implant simultaneously according to clinical requirements, which is good for steady combination of the implant and the human bone. The supporter component of the metal bone supporter has a porosity between 50% and 80%, and its external surface is rough surface with porous structure with high frictional coefficient, enabling bone ingrowth in the pores after implantation for realization of biological fixation, and improvement of the implantation steadiness, meanwhile having the filling function for bone defects and the structural supporting function. Fixation of the fixing thread on the supporting body or the connector can play instant stabilization and support functions after implantation. The connector is an auxiliary component of the metal bone supporter for accurate positioning and implanting the supporting body to the proper location. The connector is provided with compact and solid interior and smooth external surface. Under specific operation conditions, independent application of the supporter component without the connector component is also allowed if required. Human implantation of the present invention belongs to minimally invasive operation, is able to be completed with local anesthesia and clairvoyance. Therefore the suffering of the patient is reduced, the wound healing is fastened, and the recovery after operation is speeded up. 
     For adopting the electron beam fusing preparation process, the metal bone supporter has a high skin friction coefficient, a steady structure, and a mechanical property similar to the mechanical property of the human cancellous bone for immediate stabilization and support after implantation, making up the mechanical function defects of bone grafting and other methods in the early stage. Meanwhile, the implant is similar to the human cancellous bone in form and structure, being propitious to the bone ingrowth and the better stabilization in the long term, reducing the collapse speed of the femoral head necrosis, and postponing or preventing the demand for the hip joint replacement operation, so as to achieve the invention objective. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is the schematic diagram of a first embodiment of the invention showing a direct threaded connection between the supporter component and connector component. 
         FIG. 2  is the schematic diagram of a second embodiment of the invention in which a fixing bolt is provided for connecting the supporter component to the connector component. 
         FIG. 3  is the schematic diagram of a third embodiment of the invention showing independent application of the supporter component. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Details of the invention according to the attached drawing: 
     As shown in  FIG. 1 ,  FIG. 2  and  FIG. 3 , each of the three embodiments of the invention relates to a metal bone supporter for medical bone substitute. The first and second embodiments shown in  FIG. 1  and  FIG. 2  have a supporter component  2  and a connector component  1 . On the other hand, the third embodiment shown in  FIG. 3  has a supporter component  2  without the separate connector component  1  of the embodiments shown in  FIGS. 1 and 2 . The supporter component  2  is a cylinder made of titanium alloy powder by scanning, melting and molding with an electron beam melting fabrication device, and has the strength and elastic modulus similar to cancellous bones of human body; the supporter component  2  is a porotic spongy body structure, of which an axle part is able to be made into solid and the a rough surface is formed by the porous structure. The pore diameter is 100-800 micron, the porosity is 50-80%, the length of supporter component is 20-100 mm and the diameter is 5-15 mm. The connector component  1  used in the first and second embodiments shown in  FIGS. 1 and 2  is made through mechanical treatment, with smooth surface and dense solid mass inside. The length of the connector component  1  is 20-100 mm and the diameter DL of portion P 2  of the connector component  1  is 5-15 mm. The connector component  1  is provided with a continuous cortical bone thread  1   bt  having a diameter DT which is larger than diameter DL. The supporter component  2  is assembled and integrated with the connector component  1  as a metal bone supporter body.  FIG. 1  shows the first embodiment of a thread connecting structure made through direct thread connection of the supporter component  2  and the connector component  1 . An internal thread (not shown) is arranged in a flat head end of the supporter component  2 . As seen in  FIG. 1 , the connector component has a length L, is solid from one longitudinal end to the opposite longitudinal end along the central axis CL thereof, and consists of three portions along the length L thereof, each of which has a different outer diameter. The three portions including a first portion P 1  (having a length La) at the one longitudinal end of the connector component  1 , the first portion P 1  having a continuous spiral-shaped cortical bone thread  1   bt  having an outer diameter DT extending continuously along an entire length La thereof, a second portion P 2  (having a length Lb) directly joined to the first portion P 1 , the second portion P 2  having a smooth, cylindrical-shaped outer surface with an outer diameter DL along an entire length Lb thereof, and a third portion P 3  at the opposite longitudinal end of the connector component  1  so as to be joinable with the supporter component  2 . The third portion P 3  (having a length Lc), which is directly joined to the second portion P 2 , has an outer diameter DS along an entire length thereof, an outer surface of the third portion P 3  having two sections, which include a first section P 3   a  directly joining the second portion P 2 , the outer surface of the first section P 3   a  having a smooth, cylindrical-shape, and a second section P 3   b  directly joining the first section P 3   a , the outer surface of the second section P 3   b  including a small-diameter fixing thread  1   t . The first and second sections P 3   a , P 3   b  of the third portion P 3  of the connector component  1  are able to be fitted into the supporter component  2  in order to connect the supporter component  2  to the connector component  1  to compose the metal bone supporter body. The diameter DT, the diameter DL and the diameter DS have relationships of DT&gt;DL&gt;DS, and La+Lb+Lc=L.  FIG. 2  shows the second embodiment in which the connecting structure of the supporter component  2  and the connector component  1  connected is by means of a fixing bolt  3 . The fixing bolt  3  is inserted through the center (along a central axis CL) of the supporter component  2  and the connector component  1 . A connecting hole (not shown) is arranged in a flat head end of the supporter component  2 , and an internal thread (not shown) matching with the fixing bolt  3  is disposed inside the connecting hole of the supporter component  2 . As seen in  FIG. 2 , the connector component  1  has a length L, is hollow from one longitudinal end to the other longitudinal end along the central axis CL thereof, and consists of three portions along the length L thereof, each of which has a different outer diameter. The three portions include a first portion P 1  (having a length La) at the one longitudinal end of the connector component, the first portion P 1  having a continuous spiral-shaped cortical bone thread  1   bt  having an outer diameter DT extending continuously along an entire length La thereof, a second portion P 2  (having a length Lb) directly joined to the first portion P 1 , the second portion P 2  having a smooth, cylindrical-shaped outer surface with an outer diameter DL along an entire length Lb thereof, and a third portion P 3  (having a length Lc) at the opposite longitudinal end of the connector component  1  so as to be joinable with the supporter component  1 . The third portion P 3  has an outer diameter DS along an entire length Lc thereof, an outer surface of the third portion having a smooth, cylindrical-shape. The third portion P 3  of the connector component  1  is able to be fitted into the supporter component  2  in order to connect the supporter component  2  to the connector component  1  to compose the metal bone supporter body. As in Embodiment 1, the diameter (DT), the diameter (DL) and the diameter (DS) of Embodiment 2 have relationships of DT&gt;DL&gt;DS, and La+Lb+Lc=L. The connector component  1  has a hollow structure having central axis CL, and an end of the fixing bolt  3  passes along the central axis CL, through the connector component  1 , and then is inserted into the connecting hole of the supporter component  2 . Then, the fixing bolt  3  is connected with the internal thread inside the connecting hole of the supporter component  2 , forming a metal bone supporter body. As in the first embodiment shown in  FIG. 1 , the non-connecting end of the second embodiment shown in  FIG. 2  is also provided with a continuous cortical bone thread  1   bt  having a diameter DT which is larger than diameter DL. In each of the embodiments shown in  FIGS. 1 and 2 , the continuous cortical bone thread  1   bt  extends continuously around the smooth, cylindrical-shaped outer surface of the portion P 1 .  FIG. 3  shows the third embodiment of the supporter component  2  for independent use in the metal bone supporter. When the supporter component  2  is in use independently, an external fixation common thread  2   bt  (or a continuous cortical bone thread  2   bt ) is arranged on the flat head end of the supporter component  2 , to fix the supporter component  2  of the metal bone supporter at the required position on bones of the human body. In practical application, the shape of the metal bone supporter can be processed to any other or variant shapes as required. 
     As can be understood from  FIG. 3 , the supporter component  2  of the metal bone supporter is able to be used independently without being assembled with the connector component  1 . As can be seen in  FIG. 3 , supporter component  2  consists of two portions along the length L 1  thereof, each of which has a different outer diameter. The two portions include a first portion P 1  (having a length L 11 ) at one longitudinal end of the supporter component  1 , the first portion P 1  having a continuous spiral-shaped cortical bone thread  2   bt  having an outer diameter DT 2  extending continuously along an entire length L 11  thereof; and a second portion P 2  (having a length L 12 ) directly adjoining the first portion P 1  and extending from the first portion P 1  to the opposite longitudinal end of the supporter component  1 . The second portion P 2  having a cylindrical-shaped outer body with an outer diameter D 2  along the length L 12  of the second portion, except for at the one rounded end  2   e  of the second portion P 2  where the outer diameter decreases. The outer diameter DT 2  of the first portion P 1 , and the outer diameter D 2  of the second portion P 2  have a relationship of DT 2 &gt;D 2 . In addition the total length L 1  of the supporter component  2 , the length L 11  of the first portion, and the length L 12  of the second portion have relationships of L 12 &gt;L 11 , and L 12 +L 11 =L 1 . 
     Processing steps for preparing the metal bone supporter: 
     a. Carry out the engineering design of function and structure for every component of the metal bone supporter according to anatomical data and biomechanical data; 
     b. Input the information data of the designed supporter component to the computer of an electron beam melting fabrication device, and then carry out layering scanning, high temperature melting, and accumulation for molding; 
     c. Other parts are molded by mechanical treatment according to the design drawings and parameters; 
     d. Each component is sterilized separately as per the process requirements, and sealed and packed for standby.