| The bone defect of knee joint and the status quo of the clinical treatmentThe knee joint disorders significantly affect the function and quality of the patient. Especially, osteoarthritis (OA) which is the most common degenerative joint disease in the elderly population. Each year because of the knee joint disease, the direct cost and related cost related to the operation have reach billions of dollar. The knee OA become increasingly serious social problem. With the rapid development of surgical technology, the knee joint resurfacing technology matured gradually and become effective surgical procedure for the treatment of various end-stage disease of knee joint in the 1980s. More than 50% of knee OA patients with obvious symptoms may make decision of knee replacement in their lifetime. Despite the long-term success rate of total knee arthroplasty has been rising dramatically, the average annual failure rate< 1%, however, with the increase of knee replacements, the knee joint replacement related complications risk is increasing. The bone defects around the knee joint is a common problem for replacement and revision procedures, which affects the effect of revision and long-term stability of prostheses.Bone defect of the knee joint mainly involve primary bone defect and secondary bone defect, which is common in osteonecrosis and infarction, severe osteoarthritis, tibial plateau and femoral condyle fracture complicated by bone defects, and tumor diseases, stress shelter effect, osteolysis, infection, prosthesis loosening after the primary total knee arthroplasty, and intraoperative removal of prosthesis may also lead to iatrogenic bone defect. The key of the treatment is preoperative accurate assessment of the severity and type of the bone defect. The knee joint bone defect classification system mainly Including:Rand classification system, Clatworthy and Gross classification system, Anderson orthopedic institute classification system, etc. Anderson Orthopaedic Institute Classification system (AORI) is the most commonly used classification system in the clinical evaluation of bone defects. Knee joint bone defect repair is one of the most important factors affect joint stability and function, the final purpose of the treatment is to achieve early postoperative full weight-bearing and retain the complete activity as much as possible, and ensure the long-term stability of the prosthesis and maximally keep the patient’s bone volume. Depending on the type and degree of bone defect, there were significant differences in the repair methods. The method of bone defect repair mainly include:bone graft, metal augments, hinged knee and customized knee prosthesis. Allograft reconstruction are commonly used in the treatment of bone defects around the knee joint, the main advantage is that it could achieved the goal of new bone forming and reconstruction. New metal materials the porous tantalum metal (TM),which has been widely used, compared to traditional prosthesis, TM has better biomechanical properties, such as high biocompatibility, high porosity, and low modulus of elasticity similar to those of cancellous bone trabecular, etc. Hinged knee can solve the defects of the knee joint bone and defects result from resection of tumor disease, and the requirements for soft tissue and ligaments that around the knee joint is low, but the rate loosing in the late stage is higher because of its high restriction. Although the customized augment has good anatomical matching and reliable biomechanical properties, but also has many problems such as high cost and long time consuming etc.Rapid prototyping technology and the status quo of applicationRapid prototyping technology(RP), also known as Additive Manufacturing and 3D printing, which is the manufacturing technology through continuous increase cascade of physical materials step by step to produce three-dimensional entity and is the result of combination of high-distinguish technology, high-definition reconstruction,3D model free editing, mechanical and electrical control technology, materials science and chemistry. The basic working principle of rapid prototyping technology and steps include:model building, printing phase and post-processing, according to the different materials and printing process, the RP which including fused deposition molding and free electron beam forming and direct metal laser sintering, electron beam melting, selective laser melting technology and selective thermal sintering.Rapid prototyping technology has been widely used in aviation equipment, precision instruments and other advanced industrial manufacturing, which has been gradually used in medical field. Recent research has showed that the rapid prototyping technology has been successfully used in the organ printing such as bone tissue, ear, trachea, jaw, even print tissues and organs such as stem cells, blood vessels etc. The application of rapid prototyping technology in the medical field mainly includes:first, anatomical model and preoperative preparation, second, individualized customization of implant prosthesis, third, Biological print of tissues and organs, fourth,3D printing of vascularized organ, fifth,3D printing of individualized drug dosage forms and dosing device.The development and status quo of the application of Rapid Prototyping technology in the field of jointIn recent years, with the continuous development of medical imaging technology, the digital transmission and collection of CT and MRI laid a solid foundation for the wide application of 3D printing in the field of joint. Now, RP technique mainly concentrated in the following aspects:1, three-dimensional model and preoperative planning.2, individual prosthesis and plant manufacturing.3, regenerative medicine and bone tissue engineering. The rapid development of three-dimensional printing technology provides a new way of diagnosis and treatment for clinical medicine, improved the traditional operation mode and learning mode, promoting the improvement and popularization of the surgical technique, at the same time, which also make individualized health gradually become a reality, especially in the field of joint surgery,3D printing will bring an revolutionary progress.The research of treatment of defects of the knee joint bone used titanium alloy block manufactured with rapid prototyping based on CT of patientKnee joint bone defect is one of the common clinical problems of knee surgery, and the bone defect treatment is directly related to the stability of the prosthesis and the success or failure of the operation. Usually mild bone defect could be repaired through bone grafting and standardized block, however, the method is not ideal for some serious cases of bone defect. On the one hand, the structural bone grafting has a shortage of blood supply and the absorption of graft, which could led to long-term instability and loosening of prosthesis. Standard block usually has regular geometric shape, while and the shape of bone defect usually irregular, as a result a secondary bone cutting should be conducted to accommodate a standard block, which could make bone defect more severe.Research purposes:1. Based on the patient’s CT image, get three-dimensional model of bone defect by reverse molding, and design the 3D model of the defects of bone block and customized augments.2. Through rapid prototyping technology to process porous titanium alloy entities with mechanical supporting3. With total knee prosthesis to complete revision operation and repair the bone defect, and to evaluate the clinical features of patients and follow-up.4. To explore a new type of individualized treatment technical process to repair bone defect based on porous titanium alloy block with rapid prototyping technologyMethods:Based on the clinical problem and typical cases, we selected a bone defect patient after primary TKA as the research object, and go through the follow steps:1. CT scanning and image data processing, using interactive medical imaging control system-MIMICS software-to deal with CT data.2. Reverse building bone defect with Mimics software, eventually get more exquisite knee 3D model, separate and extract the bone cement placeholder body model, lateral femoral bone defect model and lateral tibia bone defect model.3. Individual block design modeling, respectively export the side of the femur and tibia bone defect model in the.STL form, and then import into computer graphic design software-UG 6.0 software-to design individual block4. Internal bone trabecular structure design and mechanics testing of material.5. Make porous titanium alloy block by rapid prototyping with materials Ti6A14V.6. The implant surgery of Individualized porous titanium alloy block and clinical follow-up.Results:Through processing CT image to design individualized block modeling, ultimately, we attain the CAD models of femoral bone defect filling block and CAD models of tibia bone defect filling augment. The measure data show that the ACCK prosthesis B sized femoral prosthesis and size 2 tibial platform prosthesis which made in Beijing AK company have the best compatibility. By electron beam melting technology (EBM), we printed the customized titanium alloy block with 665 microns diameter,35.77 MPa compressive strength,0.74 GPa elastic modulus and with microporous structure similar to trabecular bone. Finally, following the preoperative planning, we successfully complete knee joint bone defect repair and revision with customized titanium alloy block, the patient’s postoperative HSS score reach 83, and no obvious prosthesis loosening was observed during the follow-up of 18 months.Conclusion:Based on CT data of patients,we print customized porous titanium alloy block which has a high degree of matching with the bone defect of patient through RP technology, which could avoid the traditional operation of secondary bone cutting. The microporous surface design improves the initial stability of the prosthesis at the same time. Microporous bone ingrowth improve the long-term stability of the prosthesis, and the hollow frame structure design make it possible for bone graft, and maximum restore the bone mass. This technology has more technical support and more optimistic clinical expectations.Main innovation and significance:This study is a clinical application research which based on the clinical case, and combined the clinical medicine, engineering materials, computer technology, etc. The purpose of study is to solve clinical problem:1. Individualization of bone defect repair, achieving the high matching between augment and the bone defect,2. Enough mechanical support, in order to maintain the stability of the prosthesis.3. Individual block surface design, which enhanced the initial stability of the prosthesis.4. Microporous design is good for bone ingrowth and long-term stability. Respectively based on the CT data of patient to reconstruct the three-dimensional model, so as to design personalized block to match the bone defect. With low elastic modulus, high porosity and metal bone trabecular structure with good biological fixed performance, the block could achieve the micro combination of trabecular bone and metal, so as to realize biological fixation. Electron beam melting technology make it possible for the control of macro-morphology and microscopic pore size. Finally, repairing of the knee joint bone defect is the key step in revision surgery, adequate preoperative planning and simulation, can improve the matching between the block and the prosthesis, reduce the trial time in the operation. In the process of block design, there is a innovation in detail-the polishing processing on the front of the tibia block, and the main purpose of the design is to reduce the friction of patellar ligament to prevent the patellar ligament rupture. The research is on the clinical exploration stage, and clinical experience and related literature support was rare, and follow-up time is limited, so the clinical effect of the technology should be observed in future, and need further related basic research and research of large-scale clinical trials to evaluate its clinical efficacy. But it can be regarded as new exploration on treatment of bone defect of knee joint. |
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