Background and aim: Human knee joints experience very large loads and motions during regular daily, occupational and sport activities. Consequently, they are at high risk of being exposed to injuries and degeneration. Osteoarthritis and ligament injuries often inflict knee joints causing considerable pain and loss of productivity involving thus significant human and economic costs. Hence, biomechanics of human knee joints has been the focus of many investigations with the primary aim to improve understanding of joint function in normal and perturbed conditions. The existing prevention and treatment programs have been based on such studies.
Material and Methods: Due to inherent costs, limitations, difficulties and ethical concerns associated with in vivo and in vitro cadaveric studies, finite element model studies have been developed as effective, powerful and complementary tools to investigate knee joint biomechanics subject to internal and external mechanical conditions affecting its normal function.
Results: The advantage of finite element method in study of joint biomechanics lies in its robustness to incorporate complex 3D joint geometry, intricate boundary and loading conditions and materials with nonhomogeneous and nonlinear properties.
Conclusion:This article reviews important model studies, presents their relevant results and discusses some of the promising future directions.

Abstract

Background and aim: One of the important health problems in societies, especially among aged population is osteoporosis. Loss of bone density in bone structures is called osteoporosis which increases the risk of fracture due to a decrease of bone stiffness and bone strength. One of the most common sites for osteoporosis-related fractures is the spine. Current assessment of osteoporosis status is based on bone densitometry tools like QCT (Quantitative Computed Tomography) or DEXA (Dual Energy X-ray absorptionmetry). With these methods it is only possible to estimate density regardless of the morphology of trabecular constructing parts (rods and plates). The microstructure of cancellous bone in the vertebrae can be varied based on age, sex, race, etc. The cellular solids theory is a common procedure to model porous materials and we have attempted to present a model parametrical for trabecular bone as a rod like structure based on cellular solids method.

Materials & Methods: In order to model trabecular bone as foam, like what exists in vertebrae core, a finite element code has been written by APDL capability in ANSYS. This parametric code can produce different lattices that can represent various structural and material properties. Then each cubic sample was loaded under compression displacement to failure point to obtain the stress-strain curve. The stress-strain curve is used to calculate mechanical properties of simulated bone model. In order to compare with experimental results, the model has been reconstructed for 6 bone samples were taken from two different vertebrae donors one has 78 years old and the other one has 91 years old then stiffness and strength predictions have been done.

Results: The results have shown that the mechanical properties of experimental results fall between lower and upper limits of model output and it is due to unknown connectivity level for all samples. The model is capable of presenting a band for mechanical properties. Plus the lattices that simulated bone samples taken from cadavers can predict stiffness and strength better than density-based relationships for mechanical properties.

Conclusion: According to the findings of the current study, the strength and stiffness or other mechanical properties of trabecular tissues in vertebrae are highly affected by many parameters like material specification of bone tissue and morphology characteristics like connectivity. It can be concluded that risk of fracture in vertebrae is a function of various factors beyond the bone mineral density that is evaluated by measurements such as DEXA and QCT. This has been shown that our cellular solid model may improve the assessments of mechanical properties of trabecular bone structures.

Keywords: Cellular solids, Risk of fracture, Vertebrae, Trabecular bone, Finite element model

Background and Aim: Researches had shown that the high levels of shear and compression stresses that appear in the articular cartilage after meniscectomy are partly responsible for cartilage pathologies, such as osteoarthrosis . In this study, we probe to determine the stress distribution of the medial and lateral meniscus and to choose the appropriate region of meniscectomy.

Materials and Methods: Biomechanical 3D finite element model of the knee joint was generated from CT-scan images. Mimics modeled the bony structure of knee and Solidworks developed the medial and lateral meniscus.

Results: Under an axial femoral compressive load, the maximal contact stress in the articular cartilage after meniscectomy was about twice that of a healthy joint. The maximal contact pressures took place in the posterior region of the medial meniscus, with average values of 1.622 MPa and in the anterior horn of the lateral menisci with 1.159 MPa.

Results: Critical regions determine the allowed region of menisectomy for surgeon. Not only stress distribution doesn`t change by increasing of body weight or meniscectomy, but also the rate of stress increase after meniscectomy.