Development of a computational model of knee-ankle-foot complex for foot support design

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Development of a computational model of knee-ankle-foot complex for foot support design


Author: Liu, Xuan
Title: Development of a computational model of knee-ankle-foot complex for foot support design
Degree: Ph.D.
Year: 2013
Subject: Knee -- Mechanical properties.
Foot -- Mechanical properties.
Foot -- Abnormalities -- Diagnosis.
Hong Kong Polytechnic University -- Dissertations
Department: Interdisciplinary Division of Biomedical Engineering
Pages: xvi, 186 leaves : col. ill. ; 30 cm.
Language: English
InnoPac Record:
Abstract: Knee pain and functional impairment are the most common complaints among patients with knee osteoarthritis (OA). Although the causative mechanisms of knee OA are not entirely legible, there are evidences revealing that the initiation and progression of degenerative processes at the knee are associated with joint loadings. The nature of the knee loading is supposed to be altered by a number of conservative intervention strategies, such as foot orthoses. The effects of foot orthoses on knee joint loading rely mainly on experimental measurements. However, due to the experimental design diversity, subject individual differences, and relatively small changes introduced by the orthoses, consistent results have not been achieved. Furthermore, the knee adduction moment (KAdM) was currently employed as a golden index of the knee loading assessment in gait analysis, while leaving the loading distribution pattern inside the joint unknown. Computer modeling, particularly finite element (FE) method gradually manifests its advantage in exploring the biomechanical responses of joint internal structures. Stress/strain distributions on the articulation surfaces predicted by FE modeling could be considered as a more direct index of the knee loading. Thus, whether the foot support reduces relevant knee compartment loading deserves further deliberation through new perspectives. For investigating the joint biomechanics and orthotic performance, an assessment platform was established in this study, including gait analysis, musculoskeletal modeling and FE modeling. Laterally wedged insoles (LWIs) with wedge angles of 0°, 5°and 10° were fabricated for orthotic interventions. Gait analyses were performed to obtain necessary information to drive the musculoskeletal model and to setup FE model. Musculoskeletal modeling was applied to calculate the muscle forces in each LWI condition as FE loading boundary because the external loadings acting on joints must be balanced by muscle forces. To predict the stress, strain, pressure and force in the bony and soft structures, a kneeanklefoot FE model was developed. The model consisted of 30 bony segments, including the distal segment of the femur, patella, tibia, fibula, and 26 foot bones. The knee joint soft structures included the menisci, articular cartilages, and the main ligaments of the knee joint. The established FE model was partially validated through in-vivo plantar pressure and cadaveric tibiofemoral pressure measurements.
From gait analysis, the KAdM peak was reduced by 16.1% and 19.6% in 5° and 10° LWI conditions comparing with the 0° LWI condition, respectively. The decrease in the KAdM during walking was directly related to a decrease of the medial compartment loading at the knee joint. Actually, 5° and 10° LWIs relieved the KAdM prominently during most of the stance phase, which demonstrated the effectiveness of the LWI intervention on redistributing the knee joint loading from the experimentally measured moment level. The musculoskeletal modeling results indicated that the gastrocnemius lateralis force increased while gastrocnemius medialis force decreased in 5° and 10° LWI conditions comparing with the 0° LWI condition, which implicated a strengthening of the lateral muscle group spanning the knee joint triggered by LWI intervention. In FE predictions, with either 5°or 10° LWI, there were significant decreases in stress, strain, contact pressure and force at the medial femur cartilage and the medial meniscus comparing with 0 ° LWI condition, which further demonstrated the effectiveness of LWIs on redistributing knee joint loadings together with the gait analysis results. The predicted maximum loadings on tibiofemoral articulation surface during stance phase appeared at the second GRF peak, which was agreed with the subject specific kinetic data. FE predictions also showed that the 5° and 10° LWIs reduced the lateral collateral ligament (LCL) force comparing with 0° LWIs. The decreasing of the LCL force may be attributed to the increased muscle force spanning lateral side of the knee joint induced by the LWIs. It was suggested that the neuromuscular control made significant contributions to joint loading distributions and LWIs interventions may have positive effects on prevention of the medial knee OA. To our knowledge, there has been no FE model that attempts to incorporate the knee and anklefoot together considering the authentic motion features and muscle loadings. In this study, FE modeling together with experimental studies and musculoskeletal modeling successfully established a useful platform for understanding complicated joint behaviors under different foot supports. Our experimental results and model predictions also provided scientific fundamentals for evaluating and designing effective foot supports.

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