Experimental Study And Simulation Analysis Of Mechanical Behavior Of Total Knee Articular Cartilage Defect And Repair Under Compression Load

Articular cartilage damage is common in the clinic,since the knee joint bears large amount of exercise,complicated load and high stress due to its main sports pivot and load-bearing tissue of the human.Many studies have found that mechanical factors play an important role in the degradation or repair of articular cartilage.This paper had researched the mechanical properties of knee cartilage in different states from experimental research and simulation analysis.Firstly,the digital image correlation techniques was used to explore the law of strain changes in natural cartilage,artificial cartilage and its junctions in the superficial,middle and deep layers in full-thickness and half-thickness defects models of articular cartilage in vitro repaired by tissue engineering at different compression levels.The result showed that the axial strain(Ex),lateral strain(Ey)and shear strain(Exy)of the repair zone showed significant heterogeneity.Different repair models had different laws of axial strain changes.Both lateral strain and shear strain are significantly different from host cartilage.Due to the implantation of artificial cartilage,the lateral strain and shear strain of the host area,the repair area and the junction area all showed changes in regional characteristics.Secondly,the total knee joint samples were used to establish an experimental model of intact and defect femoral cartilage,to simulate the knee erect state and load it to different loads at different loading rates along the direction of the femoral force line.The contact pressure sensor I-SCAN was inserted between the femoral cartilage and the meniscus of the joint cavity,and the pressure distribution in the contact area and the peak contact pressure,the average contact pressure and the contact area were measured during the loading process.The result showed that different loads and defects will change the mechanical state of the knee joint under different loading rates.For the intact samples,the average contact pressure and peak pressure of the femoral cartilage increased with loading rates while the contact area decreased as the loading rate increased.As for defect samples,not only the stress concentration will occur at the edge of the defects,but the pressure distribution in the joint cavity is different from intact samples.The main bearing area had transferred from the femoral cartilage and meniscus contact area to other contact areas.In addition,the load sharing between the knee cartilage and the meniscus would also change during different loading phases.Thirdly,the total keen joint samples were used to establish defective and repaired articular cartilage experimental models with four different shapes,including circular,square,triangular and trapezoid.Making two kinds of artificial cartilage with high elastic modulus and low elastic modulus to implant into the defects.Medical bio-adhesive was used to bond the artificial cartilage with the host cartilage.The defect samples and the repair samples wereloaded with the same loading scheme.The result showed that total knee cartilage defects and repair will redistribute the pressure distribution throughout the contact area.All shapes of defects in the experiment would produce stress concentrations at the edges,in some cases,it would even reach 3 times or 5 times for the intact samples in the same position.It also produced abnormal pressure distribution in other areas.The stress concentration at the edge had relieved with repairing the defects by artificial cartilage with low compression modulus while the pressure at some of the edges is still larger than that in the intact samples.The artificial cartilage with a high compression modulus bore a large pressure in the repair area and was numerically close to the level of natural cartilage.And the edge stress concentration was basically eliminated.But the pressure distribution in the whole contact area was still slightly different from that in the intact samples.Finally,we established a three-dimensional finite element model of the total knee joint,and made four different femoral cartilage defects in the femoral cartilage and meniscus contact areas,including circular,square,triangular and trapezoid.The finite element simulation analysis of the model had carried out and the result showed that the presence of defects not only significantly change the distribution of pressure and stress in the contact area of the femoral cartilage,but also the mechanical state of the meniscus and tibial cartilage.In addition,stress concentrations can also occur at certain defect edges after loading.In summary,the different mechanical stimulation had effects on the mechanical properties of the knee joint cartilage.Total knee femoral cartilage defect and repair could change the contact pressure distribution in the joint cavity,and even completely change the pressure distribution in the normal physiological state.These will make great impact on knee health and injury treatment.