Nicholas Yang

Effect of frontal plane tibiofemoral angle on the stress and strain at the knee cartilage during the stance phase of gait

Subject‐specific three‐dimensional finite element models of the knee joint were created and used to study the effect of the frontal plane tibiofemoral angle on the stress and strain distribution in the knee cartilage during the stance phase of the gait cycle. Knee models of three subjects with different tibiofemoral angle and body weight were created based on magnetic resonance imaging of the knee. Loading and boundary conditions were determined from motion analysis and force platform data, in conjunction with the muscle‐force reduction method. During the stance phase of walking, all subjects exhibited a valgus–varus–valgus knee moment pattern with the maximum compressive load and varus knee moment occurring at approximately 25% of the stance phase of the gait cycle. Our results demonstrated that the subject with varus alignment had the largest stresses at the medial compartment of the knee compared to the subjects with normal alignment and valgus alignment, suggesting that this subject might be most susceptible to developing medial compartment osteoarthritis (OA). In addition, the magnitude of stress and strain on the lateral cartilage of the subject with valgus alignment were found to be larger compared to subjects with normal alignment and varus alignment, suggesting that this subject might be most susceptible to developing lateral compartment knee OA.

The Combined Effect of Frontal Plane Tibiofemoral Knee Angle and Meniscectomy on the Cartilage Contact Stresses and Strains

Abnormal tibiofemoral alignment can create loading conditions at the knee that may lead to the initiation and progression of knee osteoarthritis (OA). The degenerative changes of the articular cartilage may occur earlier and with greater severity in individuals with abnormal frontal plane tibiofemoral alignment who undergo a partial or total meniscectomy. In this investigation, subject specific 3D finite element knee models were created from magnetic resonance images of two female subjects to study the combined effect of frontal plane tibiofemoral alignment and total and partial meniscectomy on the stress and strain at the knee cartilage. Different amounts of medial and lateral meniscectomies were modeled and subject specific loading conditions were determined from motion analysis and force platform data during single-leg support. The results showed that the maximum stresses and strains occurred on the medial tibial cartilage after medial meniscectomy but a greater percentage change in the contact stresses and strains occurred in the lateral cartilage after lateral meniscectomy for both subjects due to the resultant greater load bearing role of the lateral meniscus. The results indicate that individual’s frontal plane knee alignment and their unique local force distribution between the cartilage and meniscus play an important role in the biomechanical effects of total and partial meniscectomy.

Protocol for constructing subject-specific biomechanical models of knee joint

A robust protocol for building subject-specific biomechanical models of the human knee joint is proposed which uses magnetic resonance imaging, motion analysis and force platform data in conjunction with detailed 3D finite element models. The proposed protocol can be used for determining stress and strain distributions and contact kinetics in different knee elements at different body postures during various physical activities. Several examples are provided to highlight the capabilities and potential applications of the proposed protocol. This includes preliminary results on the role of body weight on the stresses and strains induced in the knee articular cartilages and meniscus during single-leg stance and calculations of the induced stresses and ligament forces during the gait cycle.

Failure locus of the anterior cruciate ligament: 3D finite element analysis

Anterior cruciate ligament (ACL) disruption is a common injury that is detrimental to an athletes quality of life. Determining the mechanisms that cause ACL injury is important in order to develop proper interventions. A failure locus defined as various combinations of loadings and movements, internal/external rotation of femur and valgus and varus moments at a 25o knee flexion angle leading to ACL failure was obtained. The results indicated that varus and valgus movements were more dominant to the ACL injury than femoral rotation. Also, Von Mises stress in the lateral tibial cartilage during the valgus ACL injury mechanism was 83% greater than that of the medial cartilage during the varus mechanism of ACL injury. The results of this study could be used to develop training programmes focused on the avoidance of the described combination of movements which may lead to ACL injury.

Multi-Axial Failure Models for Fiber-Reinforced Composites

Combined in-phase tension/torsion loading was applied to 8-ply [±45°]4 E-glass/epoxy composite shafts under monotonic and fatigue conditions to determine the effects of multi-axial loading on its failure. A damage criterion for multi-axial monotonic loading was proposed considering the contribution of both normal and shear stresses on the plane of failure. The experimental data showed an excellent agreement with the proposed model for various loading conditions. Several multi-axial fatigue failure models were proposed considering mean and cyclic normal stress and shear stress at the plane of failure, as well as the mean and cyclic normal strain and shear strain at the plane of failure and their capability for predicting the fatigue life of the composite under study was examined. In addition to the fatigue damage model based on the plane of failure, a multi-axial fatigue failure model was proposed considering the mean and cyclic energy in the fatigue experiments. The experimental data showed a reasonably good correlation with some of the proposed damage models.

The Effects of Tibiofemoral Angle and Body Weight on the Stress Field in the Knee Joint

Osteoarthritis (OA) is a degenerative disease of articular cartilage that may lead to pain, limited mobility and joint deformation. It has been reported that abnormal stresses and irregular stress distribution may lead to the initiation and progression of OA. Body weight and the frontal plane tibiofemoral angle are two biomechanical factors which could lead to abnormal stresses and irregular stress distribution at the knee. The tibiofemoral angle is defined as the angle made by the intersection of the mechanical axis of the tibia with the mechanical axis of the femur in the frontal plane. In this study, reflective markers were placed on the subjects’ lower extremity bony landmarks and tracked using motion analysis. Motion analysis data and force platform data were collected together during single-leg stance, double-leg stance and walking gait from three healthy subjects with no history of osteoarthritis (OA), one with normal tibiofemoral angle (7.67°), one with varus (bow-legged) angle (0.20°) and one with valgus (knocked-knee) angle (10.34°). The resultant moment and forces in the knee were derived from the data of the motion analysis and force platform experiments using inverse dynamics. The results showed that Subject 1 (0.20° valgus) had a varus moment of 0.38 N-m/kg, during single-leg stance, a varus moment of 0.036 N-m/kg during static double-leg stance and a maximum varus moment of 0.49 N-m/kg during the stance phase of the gait cycle. Subject 2 (7.67° valgus tibiofemoral angle) had a varus moment of 0.31 N-m/kg, during single-leg stance, a valgus moment of 0.046 N-m/kg during static double-leg stance and a maximum varus moment of 0.37 N-m/kg during the stance phase of the gait cycle. Subject 3 (10.34° valgus tibiofemoral angle) had a varus moment of 0.30 N-m/kg, during single-leg stance, a valgus moment of 0.040 N-m/kg during static double-leg stance and a maximum varus moment of 0.34 N-m/kg during the stance phase of the gait cycle. In general, the results show that the varus moment at the knee joint increased with varus knee alignment in static single-leg stance and gait. The results of the motion analysis were used to obtain the knee joint contact stress by finite element analysis (FEA). Three-dimensional (3-D) knee models were constructed with sagittal view MRI of the knee. The knee model included the bony geometry of the knee, the femoral and tibial articular cartilage, the lateral and medial menisci and the cruciate and the collateral ligaments. In initial FEA simulations, bones were modeled as rigid, articular cartilage was modeled as isotropic elastic, menisci were modeled as transversely isotopic elastic, and the ligaments were modeled as 1-D nonlinear springs. The material properties of the different knee components were taken from previously published literature of validated FEA models. The results showed that applying the axial load and varus moment determined from the motion analysis to the FEA model Subject 1 had a Von Mises stress of 1.71 MPa at the tibial cartilage while Subjects 2 and 3 both had Von Mises stresses of approximately 1.191 MPa. The results show that individuals with varus alignment at the knee will be exposed to greater stress at the medial compartment of the articular cartilage of the tibia due to the increased varus moment that occurs during single leg support.Copyright

Multi-Axial Fatigue Damage Models of Fiber Reinforced Composites

Fiberglass reinforced composites are extensively used in various structural components. In order to insure their structural integrity, their monotonic and fatigue properties under multiaxial stress fields must be understood. Combined in-phase tension/torsion loading is applied to [±45°]4 E-glass/epoxy composite tubes under monotonic and fatigue conditions to determine the effects of multiaxial loading on its failure. Various monotonic and fatigue damage criteria are proposed. These models considered failure mode (failure plane), the energy method and the effective stress-strain method. It is observed for the majority of experiments, the failure initiated at the outer lamina layer at 45° to the tube axis. A damage criterion for multiaxial monotonic loading is proposed considering both normal and shear stress contributions on the plane of failure. The experimental data show an excellent agreement with this proposed model for various loading conditions. Other failure models are currently under investigation utilizing the stresses and strains at the composite laminate as well as stress and strain at the outer lamina layer. Multiaxial fatigue failure models are proposed considering again the plane of failure. Since the plane of the failure is subjected to mean and cyclic stresses (shear and normal) and mean and cyclic strains (shear and normal), the fatigue damage models consider the contributions of these stresses and strains to the fatigue life of the composite tube. In addition to the fatigue damage model based on the plane of failure, a multi-axial fatigue failure model is proposed considering the mean and cyclic energy during fatigue experiments. The experimental data show a good correlation between the proposed damage parameters and fatigue life of specimens with some scatter of the data. Other fatigue failure models are currently under investigation considering the loading frequency and visco-elastic properties of the composite.Copyright

Failure Locus of the Anterior Cruciate Ligament Disruption at 25° Knee Flexion: 3D Finite Element Analysis

Anterior cruciate ligament (ACL) disruption is a common injury that is detrimental to an athlete’s quality of life. Determining the mechanisms that cause ACL injury is important in order to develop proper interventions. This study was conducted to provide insight into the specific knee orientations associated with ACL injuries. A failure locus for the ACL was developed by simulating multiple loading scenarios using a 3-D finite element analysis (FEA) model of the knee. The results indicated varus and valgus were more dominant to the ACL injury compared to femoral rotation. The order of MCL failure, ACL failure, and maximum meniscus stress was also determined with respect to time during loading. The results of this study could be used to develop training programs focused on the avoidance of the described combination of movements, which may lead to ACL injury.© 2010 ASME

The Effect of the Frontal Plane Tibiofemoral Angle on the Stress and Strain at the Knee Cartilage During the Stance Phase of the Gait Cycle

Three-dimensional (3-D) finite element analysis (FEA) knee models were created to determine the effect of the frontal plane tibiofemoral angle on the stress and strain at the knee cartilage during the stance phase of the gait cycle. Knee models of three healthy subjects of different tibiofemoral angles and weight were created from sagittal view magnetic resonance images (MRI) of the knee. The loading conditions were determined from motion analysis and force platform data and a muscle force reduction model. During the stance phase, the subjects exhibited a valgus-varus-valgus knee moment pattern that determined the location and magnitude of the maximum stress and strain in the cartilage on the lateral or medial compartment of the knee. The highest values of the normal stress, Tresca shear stress and normal strain for each subject occurred at 25% of the stance phase of the gait cycle, where the maximum compressive load and varus knee moment occurred. The individual with the varus aligned knee had the largest stress and strain at the medial compartment of the knee compared to the normal aligned and valgus aligned individuals due to the larger varus knee moment exhibited during the stance phase of the gait cycle in the varus aligned individual. The results from the FEA data may be used by health care professional to identify individuals most susceptible to knee osteoarthritis (OA) and assist in developing preventive measure to slow and possibly stop the initiation and progression of OA.Copyright

Method to Determine the Effect of the Frontal Plane Tibiofemoral Knee Angle on the Varus-Valgus Moment at the Knee During Stance and Gait

Osteoarthritis (OA) is a degenerative disease of articular cartilage that affects millions of people [1]. Local biomechanical factors may severely affect initiation and progression of OA due to changes in loading conditions at the cartilage. The frontal plane tibiofemoral alignment effects the varus/valgus moment which could increase the overall loading at the knee. Biomechanical studies have reported that the varus moment is a key determinant in the load distribution at the knee [2, 3] and has been linked to OA progression [4, 5]. A normal knee will have a tibiofemoral angle approximately 7° valgus [6]. Deviation from this angle leads to a knee joint with a varus or valgus condition. In this investigation, a motion analysis procedure was developed to determine the affect of the frontal plane tibiofemoral angle on the force and moment reactions at the knee. The results of these methods could be utilized in a subject specific finite element model to determine the stress and strain at the knee cartilage and to suggest measures to prevent OA.Copyright