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BackgroundThe biomechanical change during the medial meniscus damage in the process of knee osteoarthritis has not been explored. The purpose of this study was to determine the effect of aggravating medial meniscus degenerative tear on the progress of knee osteoarthritis through the finite-element simulation method.MethodsThe three-dimensional digital model of a total-knee joint was obtained using a combination of magnetic resonance imaging and computed tomography images. Four types of medial meniscus tears were created to represent the aggravating degenerative meniscus lesions. Meniscectomy of each meniscal tear was also utilized in the simulation. The compression and shear stress of bony tissue, cartilage, and meniscus were evaluated, and meniscus extrusion of the healthy knee, postinjured knee, and postmeniscectomy knee were investigated under the posture of balanced standing.ResultsBased on the results of finite-element simulation, the peak shear principal stress, peak compression principal stress, and meniscus extrusion increased gradually as the meniscus tears’ region enlarged progressively (from 7.333 MPa to 15.14 MPa on medial femur and from 6 MPa to 20.94 MPa on medial tibia). The higher stress and larger meniscus extrusion displacement in all tests were observed in the flap and complex tears. The oblique tears also had a biomechanical variation of stress and meniscus extrusion in the knee joint, but their level was milder. Both the peak value of the stress and meniscus displacement increased after the meniscectomy.ConclusionIn contrast to the damaged hemijoint, the stress applied on the healthy lateral hemijoint increased. The change of biomechanics was more obvious with the aggravation of meniscus injury. The advanced degenerative damage resulted in increasing stress that was more likely to cause symptomatic clinical manifestation in the knee joint and accelerate the progress of osteoarthritis. Moreover, we found that the meniscus injury caused higher stress concentration on the contralateral side of the joint. We also discovered that the meniscectomy can lead to more serious biomechanical changes, and although this technique can relieve pain over a period of time, it increased the risk of osteoarthritis (OA) occurrence.The translational potential of this articleIt is clear that the meniscal lesions can cause osteoarthritic knee, but the biomechanical change during the meniscus damage period has not been explored. We have evaluated the variation of stress during the aggravating medial degenerative meniscus tears and the relationship in the process of knee OA through finite-element simulation. This study does favour to obtain a better understanding on the symptoms and pathological changes of OA. It also may provide some potential directions for the prophylaxis and treatment of OA.

BackgroundThe graded porous structures were designed using triply periodic minimal surfaces models to mimic the biomechanical properties of bone. The mechanical properties and bone formation ability were evaluated to explore the feasibility of the design method in bone tissue engineering.MethodsThe scaffolds were designed using a P-surface with different pore sizes. All materials were fabricated using 3D printing technology and the mechanical properties were tested by an electronic universal testing device. The biomechanical properties were then analyzed by finite element method, while the ontogenesis of the material in vivo was examined by implanting the scaffolds for five weeks in pigs.ResultsAccording to the obtained results, the pore size ranged between 100 μm to about 700 μm and porosity were around 49.54%. The graded porous architectures can decrease the stiffness of implants and reduce the stress shielding effect. In addition, these porous structures can stimulate bone ingrowth and achieve a stable interface between implants and surrounding bone tissues after 5 weeks' implantation. The micro-CT results also demonstrated the obviously bone formation around all the porous structures.ConclusionTo sum up, the triply periodic minimal surfaces based graded porous structure is effective in decreasing the stress shielding effect, promoting early osteogenesis and osteointegration. This is the first research to explore the effect of this kind of porous structures on bone formation in vivo where the obtained results supported the previous theoretical research on the application potential in bone tissue engineering.The translational potential of this articlePorous architecture designed using triply periodic minimal surface models can achieve gradually changed pore size and appropriate porosity for bone regeneration. This kind of structure can mimic the Young’s modulus of natural bone tissue, improve the stress transmission capability and dismiss the stress shielding effect. It also can stimulate the early bone integration in vivo and enhance the binding force between bone and implants, which may bring a new design method for orthopaedic implants and their surface structure.

Background: Titanium implants are widely used in orthopedic and dental for more than 30 years. Its stable physicochemical properties and mechanical strength are indeed appropriate for implantation. However, the Bioinertia oxidized layer and higher elastic modulus often lead to the early implantation failure. Methods: In this study, we proposed a simple design of porous structure to minimize the disparity between scaffold and natural bone tissue, and introduced a one-step reaction to form a polydopamine (PDA) layer on the surface of titanium for the purpose of improving osteogenesis as well. The porous scaffolds with pore size of 400 μm and porosity of 44.66% were made by additive manufacturing. The cell behavior was tested by seeding MC3T3-E1 cells on Ti6Al4V films for 15 days. The biomechanical properties were then analyzed by finite element (FE) method and the in vivo osteogenesis effect was accordingly evaluated by implanting the scaffolds for 5 weeks in rabbits. Results: According to the achieved results, it was revealed that the immersion for 40 min with dopamine could significantly improve the cell adhesion. The proposed method for design of porous structure can avoid the stress shielding effect and bone growth inside the PDA coating scaffolds, which were observed at the early stage of bone healing process. Conclusions: It can be concluded that the proposed PDA coating method is effective in promoting early osteogenesis, as well as being easy to operate, and can be helpful in the future clinical application of titanium implants.

Objective The objective of this study is to investigate the biomechanics on the knee components caused by degenerative and radial meniscal tears and resultant meniscectomy. Methods A detailed finite element model of the knee joint with bones, cartilages, menisci and main ligaments was constructed from a combination of computed tomography and magnetic resonance images. Degenerative and radial tears of both menisci and resultant medial meniscectomy were used and two different kinds of simulations, the vertical and the anterior load, mimicking the static stance and slight flexion simulations, were applied on the model. The compressive and shear stress and meniscus extrusion were evaluated and compared. Results Generally, both degenerative and radial tears lead to increased peak compressive and shear stress of both cartilages and menisci and large meniscus extrusion, and the medial meniscal tear induced larger value of stress and extrusion than the lateral meniscal tear. The peak stress and meniscus extrusion further elevated after the medial meniscus meniscectomy. Distribution of stress was shifted from the intact hemi joint to the injured hemi joint with either medial or lateral meniscal tear. Conclusion Our finite element model provides a realistic three-dimensional knee model to investigate the effects of degenerative and radial meniscal tears and resultant meniscectomy on the stress distribution of the knee. The stress was increased in meniscal tears and increased significantly when meniscectomy was performed. Increased meniscus extrusion may explain the mechanism for higher stress on the components of the knee. The translational potential of this article Meniscal tears are the most common damage associated to the menisci, and meniscectomy is often performed to relieve the pain and instability of the knee. The results of our study indicated increased stress on cartilages and menisci, which may lead to early onset of osteoarthritis. This may guide surgeons to preserve more of the meniscus when performing meniscectomy.