The Biomechanical Effects Of The Complete Posterior Root Tear Of Medial And Lateral Meniscus On The Knee Joint-a Finite Element Analysis

The meniscus root is defined anatomically as the portion of the meniscus that attachesthe anterior and posterior horn of the meniscus to the central tibial plateau. The meniscus roottears caused by trauma or secondary to degenerative joint changes. Acute root tears generallyoccur in young, active individuals, and the elderly patients more likely suffer from attritionaldegenerative radial tearing. According to the available literature, only posterior meniscal roottear has been reported, and the most of the published literature regarding posterior root tearshas focused on medial meniscal root tears. The medial meniscus is less mobile than the lateralmeniscus and carries more force during weight bearing making it more prone to injury.However, posterior lateral meniscus root tears are injuries that are commonly associated withanterior cruciate ligament tears. In recent years, with technological advances in arthroscopyand magnetic resonance imaging and improved biomechanical studies of the meniscus, therehas been some progress in the diagnosis and treatment of injuries to the roots of the meniscus.However, the biomechanical effect of posterior meniscus root tears on the knee has not yetbecome clear. In this study, we developed a finite element model of the knee joint based onhigh resolution MRI images, and verified the validity of the model. The models of medial andlateral posterior meniscus root tear, anterior cruciate ligament and meniscofemoral ligamentdeficiencies, and total meniscectomy of the medial and lateral meniscus were generated on thebasis of the intact knee model. Finite element analysis (FEA) was performed to investigate thebiomechanical effects of the complete posterior root tears of medial and lateral meniscus onthe knee joint and to providing a theoretical basis for the diagnosis and treatment of meniscalroot tears.Section one: Development and validation of3-D finite element model of knee joint. Theaim of this section is to develop and verify a three-dimensional (3D) computational model ofa knee joint that to be used to predict the biomechanical effect of posterior meniscus root tearson the knee. Numerical data of three-dimensional finite element models of the knee werebased on MRI images of an adult volunteer. The images were processed using MIMICS to construct the knee model consisted of the femur, the tibia and fibula, articular cartilage layers,the menisci and the main ligaments of the knee: anterior cruciate ligament (ACL), posteriorcruciate ligament (PCL), medial collateral ligament (MCL), lateral collateral ligament (LCL)and posterior meniscal femoral ligament(PMFL). The model was refined for finite elementanalysis using Geomagic Studio. Tetrahedral elements were used to mesh the entire model andit was then analyzed in ABAQUS. The material properties of the model were chosen fromvalues identified in the literature. In order to compare the obtained results with previousstudies, a compressive axial load of1000N and an anterior load of134Nwere applied to theFEA model. The results show that we have developed an accurate, relatively complete three-dimensional finite element model of knee joint, including bone tissue, cartilage, meniscus andmajor ligaments. This model was validated using experimental and numerical results obtainedby other authors. The results obtained from our study are in agreement with previouslypublished reports. This validated computational knee model can be used to predict kneebiomechanical mechanics and laid the foundation for further biomechanical study.Section two: Finite element analysis of the complete posterior medial meniscus root tear.The purpose of this section was to determine the biomechanical effect of a complete posteriormedial meniscus root tear (PMMRT) on the knee joint. Based on the pre-established,validated finite element model of knee joint, we simulated different cases for intact knee, acomplete PMMRT, and total meniscectomy of the medial meniscus. Isolated axialcompressive load of1000N and anterior load of134N were applied in all cases to comparetheir contact mechanics, kinematics and knee stability. The results show that the completePMMRT increased the peak contact pressure and stress on the medial compartment undercompressive load and its values approximate to medial total meniscectomy. We also foundincreased contact pressure and stress in the lateral compartment, but it was not obviouscompared to the medial compartment. Significant increases in radial displacement of medialmeniscus, femoral internal rotation, posterior and medial translation, compared with the intactknee, were observed in association with the complete PMMRT. The anterior tibial translationunder the anterior tibial load in knee with tear in the posterior root of medial meniscus waslarger than in the intact knee, but it is smaller than values of total medial meniscectomy. Theresults show that the complete PMMRT leads to deleterious alteration of the loading profilesof the medial joint compartment and results in significant changes in knee joint kinematicsand stability. All these are not conducive to play a normal physiological function of the knee.Section three: Finite element analysis of the complete posterior lateral meniscus root tear. The purpose of this section was to determine the biomechanical effect of a complete posteriorlateral meniscus root tear (PLMRT) on the knee joint. Based on the pre-established, validated,finite element model of knee joint, we simulate different cases for a complete PLMRT, acomplete PLMRT combined with ACL deficiency, and total meniscectomy of the lateralmeniscus. Isolated compressive load of1000N was applied in all cases to compare theircontact mechanics, kinematics and knee stability. The results show that the complete posteriorlateral meniscus root tear increased the peak contact pressure and stress on the lateralcompartment under compressive load, but it is smaller than values of total medialmeniscectomy. The complete PLMRT leads to significant increases in radial displacement oflateral meniscus, femoral external rotation, lateral and posterior translation, compared withthe intact knee. We also found that in the complete PLMRT combined with ACL deficientknee, there were no significant contact profiles alteration compared to the knee with tear inthe posterior root of lateral meniscus. However, there were deleterious alterations of kneekinematics. The complete PLMRT had no significant effect on the anterior tibial translationunder the anterior tibial load. The results show that the complete PLMRT is not functionallyequivalent to total meniscectomy. The posterior root torn lateral meniscus continues toprovide some load transmission and distribution functions across the joint.Section four: Finite element analysis on the function of the posterior meniscofemoralligament on the knee with or without tear in the posterior root of lateral meniscus. Thepurpose of this section was to predict the function of the posterior meniscofemoral ligament(PMFL) on the knee with or without tear in the posterior root of lateral meniscus. In order todetermine the effects of PMFL deficiency on the knee with or without tear in posterior root oflateral meniscus, we used a computer-aided method to artificially remove the PMFL andcompared the contact variables of pre-and post-sectioning. After comparing the contactvariables of before and after removing the PMFL on the knee with or without a tear in theposterior root of the lateral meniscus, our results indicate that the PMFL assists the lateralmeniscus in transmitting a certain amount of stress and load in the lateral compartment of theknee and this effect more obvious in the knee with a torn lateral meniscus. Meanwhile, thePMFL prevents excessive radial displacement of the lateral meniscus with a torn posteriorroot under compressive load.Posterior root tears of meniscus lead to deleterious alteration of the biomechanicalenvironment of knee joint. The presence of double attachment of lateral meniscus posteriorhorn makes the biomechanical consequences of PLMRT different from PMMRT. These findings improve our understanding of the effect of meniscal posterior root tear on thebiomechanics of the knee joint and could guide clinicians in making a diagnosis anddetermining the appropriate treatment plan in this type of injury. In addition, based on thebiomechanical contributions of the PMFL found in this study, we suggest PMFL retention inPCL and meniscal surgery.