| Part oneEffect of Penetrating Injury by Different Absorbable PDLLA Rod onthe Development of Growth Plate:an Experiment Study.BackgroundEpiphyseal fractures account for approximately 25% of pediatric fracture. The traditional internal fixation for epithyseal fracture is to use metallic pins, which are ideal material in terms of strength, durability and biocompatibility. However, metallic materials also have some drawbacks such as stress-shielding, metal erosion, mutagenesis and second operation to remove the pins. Biodegradable internal fixation materials were investigated in the 1960s, with the hope to find better alternatives to metal materials for internal fixation, which should satisfy the need for internal fixation on the one hand, can be biodegraded, do not accumulate in the body and have no toxicity. In this study, absorbable PDLLA rods of different diameters were implanted into the distal femoral epiphysis at different angles on the experimental leg and no internal fixation PDLLA rods were inserted on the control leg, in order to study the effect of PDLLA on bone and cartilage development, so as to provide theoretic basis for the application of absorbable PDLLA rods in the internal fixation of epiphyseal fractures. ObjectiveTo investigate the effect of absorbable PDLLA rods implanted into the distal femoral epiphysis on the development of epiphysis, so as to provide theoretic basis for the application of absorbable PDLLA rods in the internal fixation of epiphyseal fractures. MethodsThree different rods (1 mm, 2 mm and 3.2 mm in diameter and 25 mm in length) weredriven into drill holes of equal bore in the intercondylar and medial condylar 45° on the right distal femoral epiphysis in 72 5-week-old Japanese white rabbits. The identical procedure was performed on the left femur, but the drill was empty. The animals were sacrificed at 6, 12 and 24 weeks, and the percentage of injured growth plates, bone length measurements, gross observation, radiographic measurement of femora condyle angles, tetracycline fluorescence labeling, histology sections, ground section and scanning microscopy were performed to evaluate the development of epiphyseal plate. Resultsl.The percentages of injured growth plates were 1.39±0.09% and 3.33±0.92% for 1 mm rods in intercondylar and medial condylar 45° of the distal femoral epiphysis, 7.44±1.26% and 1.42±0.10% for 2 mm rods, and 3.62±0.18% and 10.15±0.49% for 3 mm rods.2. There was no significant difference in the length between the right and left femur in each group after 6, 12 and 24 weeks. The lmm and 2mm groups did not cause a permanent growth disturbance, but the 3.2 mm group did.3. X-ray film revealed that most rabbits showed genu valgus, similar to the changes in femora length. There was no significant difference between the right and left femur in each group after 6, 12 and 24 weeks.Conclusions1. Epiphyseal plate retardation secondary to a penetrating injury from Kirschner wire is related to the percentage of the injured area. Destruction of 7% or more of the cross section area of the growth plate will result in retarded bone growth.2. The 1 mm and 2mm in diameter drill holes will not cause a permanent growth disturbance whether left empty or filled with a PDLLA rod. But the 3.2 mm hole did. The PDLLA itself does not cause any disturbance of the growth in a rabbit femur. Part two:Repair of Rabbit Growth Plate Defects with Tissue-engineering Cartilage:Compound of Autologous Bone Marrow Mesenchymal Stem Cells and Biological ScaffoldBackgroundEpiphyseal plate injury due to trauma, infection, tumor and development disturbance may cause severe growth arrest because of the bony bridge between the epiphysis and metaphysis, earlier closure of epiphyseal plate and limb length discrepancy and angular deformity. Traditional treatments for bony bridge include resecting the bone bar and setting an interpositional material such as fat and bone cement, and they are only effetive for less then 30% growth plate defects. Recently, tissue engineering techniques have provided many new alternatives for treatment of growth plate injury. In this experiment, rabbit bone marrow-derived mesenchymal stem cells were isolated and cultured in vitro, then induced to differentiate into chondrocytes under three-dimension condition and serum-free medium; and transplanted the cultured cartilage into growth plate defects. It may provide the appropriate cartilage necessary to restore growth potential and prevent transphyseal bone bridge formation. It is a promising way for clinic treatment of growth plate defects. Objectives1. To explore the behavior of MSCs which were isolated from rabbit bone marrow in vitro and investigate the feasibility of MSCs as seed cells of tissue engineering.2. To study the feasibility and application value of MSCs as seed cells in tissue engineering, which were induced to differentiate into chondrocyte.3. To construct tissue-engineering cartilage ,MSCS were seeded on the biological scaffold—poly-DL-lactic acid and cultured under three-dimension condition.4. To investigate the feasibility of repairing the growth plate defects with the compound of tissue engineering cartilage.Methods1. MSCs were extracted from rabbit bone marrow and purified, then cultured in vitro.They were observed under phase-contrast microscope and the growth curve was drawn accordingly.2. MSCs were induced to differentiate into chondrocytes first under serum-free medium contain TGF-Pi and dexamethsone in monolayer culture, then under three-dimension condition with PDLLA and IGF-1 .3. The compound were implanted into the growth plate defects of proximal tibial of 8-weeks rabbits. After 4, 8 and 16 weeks, gross observation, X-ray filem, histologic examinations were performed to evaluate the efficiency.Results1. MSCs which were in low abundance proliferated when cultured in vitro and cell survival rates were 90%~95%.2. After being induced to differentiate into chondrocyte, there was much toluidine blue metachromasia matrix around the cell by toluidine blue staining.3. The rabbits tibia had no marked deformities after 4 weeks of operation, and histologic examination revealed that the defects were filled with cartilage. After 16 weeks, the experiment group had minor deformities, and histologic examination showed near closure of growth plates. On the contrary, the control side showed severe deformities and growth plates were closed.Conclusion1. The success in MSCs culture in vitro will be useful for repairing cartilage and skeletal tissue defects by tissue engineering technique in the future.2. MSCs can be induced to differentiate into chondrocytes under three-dimension condition and serum-free medium.3. PDLLA was a sponge-like porous structure and MSCs showed high level of proliferation. PDLLA was a good carrier for cartilage tissue engineering.4. Transplantation of cultured cartilage into growth plate defects may replace growth plate tissues, maintain normal growth of limbs and prevent developmental deformity. And it is a promising way for clinic treatment of growth plate defects.
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