Abstract
Background: The morphological changes of the meniscus affect normal biomechanical functioning of the knee joint and it has been demonstrated as an initiator of knee osteoarthritis(OA). Prevention of meniscal damage or clinical management of the meniscal injury is therefore essential to prevent or delay the underlying tissues from degeneration.Some possible solutions to prevent or clinically manage meniscal injuries include: (1) replacing severely injured meniscus with a synthetic artificial meniscal implant, (2) wearing unloader brace to avoid overloading the affected compartment after meniscal injury or meniscectomy, and (3) clinical management of other damaged/injured tissues (e.g. anterior cruciate ligament (ACL) rupture) that are susceptible to meniscal tissue damage. Important research questions which were left unanswered have restricted the use of these interventions in the clinical setting, and they can be answered through following scientific investigations: (i) biomechanical evaluation of physical characteristics and mechanical properties of a synthetic artificial meniscal implant, (ii) comprehensive biomechanical evaluation of unloader knee brace, and (iii) evaluation of the biomechanical role of the anterolateral ligament (ALL) in ACL deficient knee. Purpose: The main purpose of this thesis was to develop anatomically detailed subjectspecific computational finite element (FE) models of the knee joint to evaluate the biomechanical performance of medical interventions in the knee joint under physiological loading. The specific aims include the following: (a) biomechanical evaluation of material properties of a synthetic artificial meniscal implant, (b) biomechanical evaluation of isotropic and hard core-soft shell composite meniscal implants, (c) biomechanical evaluation of non-anatomical placement of the meniscal implant, (d) comprehensive biomechanical evaluation of unloader knee brace and its alignment angle in the surgically treated knee, and (e) evaluation of the biomechanical role of the ALL in ACL deficient knee to aid in clinical decision-making of the ACL reconstruction strategy. Methods: Four anatomically detailed (one cadaver-specific and three subject-specific computational FE models of the knee were developed in this thesis using joint substructures segmented and reconstructed from magnetic resonance (MR) medical images of the lower limb. A sensitivity analysis of mesh element size was performed on all knee models to optimize the mesh density, which is important to make sure the model estimated values are adequately accurate. Confidence in the ability of the computational models to predict clinically relevant outcomes was established by performing multiple validation checks. The gait pattern of three healthy subjects was captured in the gait and motion analysis laboratory and estimated knee joint forces and moments and quadriceps forces for one complete gait cycle. Models derived from the cadaverspecific FE model, to simulate different clinical scenarios for biomechanical evaluation of (a) material properties of the meniscal implant, were all loaded with a short-term physiological gait load of 1150 N at 0 flexion (full extension). Models derived from subject-specific FE models, to simulate different clinical scenarios for biomechanical evaluation of (b) isotropic and hard core-soft shell composite meniscal implants, (c)non-anatomical placement of the meniscal implant, (d) unloader knee brace, and (e) the role of ALL in ACL deficient knee, were all loaded with corresponding subjectspecific physiological data for one complete gait cycle. The contact mechanics in the affected and contralateral healthy compartments and tibiofemoral kinematics were estimated and compared for each clinical scenario considered. Results: (a) An increase in elastic modulus of the medial meniscal implant significantly increased the peak contact pressure in the medial compartment. The meniscal implant with the elastic modulus of 11 MPa restored normal contact conditions in the medial compartment. (b) Both isotropic and hard core-soft shell composite meniscal implants restored normal knee joint biomechanics, while the hard core-soft shell composite meniscal implant resulted in more reduction of contact stresses in the medial compartment compared to the isotropic meniscal implant. (c) Placement of the meniscal implant in non-anatomical locations adversely affects contact conditions in both medial and lateral compartments and tibiofemoral kinematics. (d) Surgically treated knee with an unloader brace resulted in a greater reduction of total contact force in the affected compartment and vice-versa in the contralateral healthy compartment compared to the unbraced knee. The contact mechanics in both affected and contralateral healthy compartments are sensitive to the brace alignment angle. (e) The combined ACL and ALL deficient knee had no significant change in contact mechanics and tibiofemoral kinematics compared to the ACL deficient knee. Conclusions: This thesis has demonstrated the ability of computational FE models to virtually evaluate the biomechanical performance of medical interventions in the knee joint under physiological loading conditions. FE simulations conducted on models representing meniscal injury and meniscectomy have provided valuable insight into the underlying mechanisms that are responsible for the onset and progression of knee OA. Biomechanical evaluation of physical characteristics and mechanical properties of a meniscal implant resulted in critical findings which can assist in optimizing geometric design, material properties, and implant placement relative to the anatomical position. The study on unloader knee brace has shown that excessive brace valgus alignment angle (8 or over), for a desired clinical outcome, could potentially increase the risk of damaging the articular cartilage in the contralateral healthy compartment and may turn uni-compartmental arthritis into bi-compartmental arthritis. The study on the ALL has delineated its biomechanical function and importance in the knee joint. The study showed that the ALL do not serve as a secondary restraint to joint kinematics and the reported critical findings will provide a basis for clinical decision-making of surgical strategy for treating ACL injuries and new designs for ACL grafts.