Thesis (M.S.)--University of Delaware, 2008. / Principal faculty advisor: Irene S. Davis, Dept. of Physical Therapy. Includes bibliographical references.

The human foot contributes significantly to the function of the whole lower extremity during standing and locomotion. Nevertheless, the foot and ankle often suffer injuries and are affected by many musculoskeletal and neurological pathologies. The overall aim of this thesis was to evaluate gait parameters and muscle function change due to foot and ankle injury, malalignment and co-contraction. Using 3D gait analysis, analytical analyses and computational simulations, biomechanical consequences of gait impairment at the ankle and foot were explored in ablebodied persons and in patient groups with disorders affecting walking. We have characterized gait patterns of subjects with ankle fractures with a modified multi-segment foot model. The inter-segmental foot kinematics were determined during gait in 18 subjects one year after surgically-treated ankle fractures. Gait data were compared to an age- and gender-matched control group and the correlations between functional ankle score and gait parameters were determined. It was observed that even with fairly good clinical results, restricted range of motion and malalignment at and around the injured area were found in the injured limb. Moment-angle relationship (dynamic joint stiffness) - the relationship between changes in joint moment and changes in joint angle - is useful for demonstrating interaction of kinematics and kinetics during gait. Ankle dynamic joint stiffness during the stance phase of gait was analyzed and decomposed into three components in thirty able-bodied children, eight children with juvenile idiopathic arthritis and eight children with idiopathic toe-walking. Compared to controls, the component associated with changes of ground reaction moment was the source of highest deviation in both pathological groups. Specifically, ankle dynamic joint stiffness differences can be further identified via two subcomponents of this component which are based on magnitudes and rates of change of the ground reaction force and of its moment arm. And differences between the two patient groups and controls were most evident and interpretable here. Computational simulations using 3D musculoskeltal models can be powerful in investigating movement mechanisms, which are not otherwise possible or ethical to measure experimentally. We have quantified the effect of subtalar malalignment on the potential dynamic function of the main ankle dorsiflexors and plantarflexors: the gastrocnemius, soleus and tibialis anterior. Induced acceleration analysis was used to compute muscle-induced joint angular and body center of mass accelerations. A three-dimensional subject-specific linkage model was configured by gait data and driven by 1 Newton of individual muscle force. The excessive subtalar inversion or eversion was modified by offsetting up to ±20˚ from the normal subtalar angle while other configurations remain unaltered. We confirmed that in normal gait, muscles generally acted as their anatomical definitions, and that muscles can create motion in many joints, even those not spanned by the muscles. Excessive subtalar eversion was found to enlarge the plantarflexors’ and tibialis anterior’s function. In order to ascertain the reliability of muscle function computed from simulations, we have also performed a parametric study on eight healthy adults to evaluate how sensitive the muscle-induced joints’ accelerations are to the parameters of rigid foot-ground contact model. We quantified accelerations induced by the gastrocnemius, soleus and tibialis anterior on the lower limb joints. Two types of models, a ‘fixed joint’ model with three fixed joints under the foot and a ‘moving joint’ model with one joint located along the moving center of pressure were evaluated. The influences of different foot-ground contact joint constraints and locations of center of pressure were also investigated. Our findings indicate that both joint locations and prescribed degrees-of-freedom of models affect the predicted potential muscle function, wherein the joint locations are most influential. The pronounced influences can be observed in the non-sagittal plane. Excessive muscle co-contraction is a cause of inefficient or abnormal movement in some neuromuscular pathologies. We have identified the necessary compensation strategies to overcome excessive antagonistic muscle cocontraction at the ankle joint and retain a normal walking pattern. Muscle-actuated simulation of normal walking and induced acceleration analysis were performed to quantify compensatory mechanisms of the primary ankle and knee muscles in the presence of normal, medium and high levels of co-contraction of two antagonistic pairs (gastrocnemiustibialis anterior and soleus-tibialis anterior). The study showed that if the co-contraction level increases, the nearby synergistic muscles can contribute most to compensation in the gastrocnemius-tibialis anterior pair. In contrast, with the soleus-tibialis anterior co-contraction, the sartorius and hamstrings can provide important compensatory roles in knee accelerations. This dissertation documented a broad range of gait mechanisms and muscle functions in the foot and ankle area employing both experiments and computational simulations. The strategies and mechanisms in which altered gait and muscles activation are used to compensate for impairment can be regarded as references for evaluation of future patients and for dynamic muscle functions during gait. / QC 20120514

Background and Objectives: The foot comprises of active contractile and passive connective tissue components, which help maintain stability and facilitate movement during gait. The role of age- or pathology-related degeneration and the presence of fat within muscles in foot function and pain remains unclear. The existence of fat has to date not been quantified or compared between individuals according to age, sex, side or subregion. Materials and Methods: 18 cadaveric feet (mean age 79 years) were sectioned sagittally and photographed bilaterally. Fat in the plantar muscular space of the foot (PMSF) was quantified through the previously validated manual fat quantification method, which involved observing photographs of each section and identifying regions using OsiriX. Fat volume and percentage was calculated using a modified Cavalieri’s method. Results: All feet had fat located within the PMSF, averaging 25.8% (range, 16.5–39.4%) of the total PMSF volume. The presence of fat was further confirmed with plastination and confocal microscopy. Conclusions: These findings suggest that fat within the PMSF is a consistent but highly variable finding in elderly cohorts. Fat within the foot muscles may need to be considered a norm when comparing healthy and non-healthy subjects, and for therapeutic interventions to the foot. Further work is required to understand in detail the morphological and mechanical presence of fat in the foot, and compare these findings with pathological cohorts, such as sarcopenia. Additionally, future work should investigate if fat may compensate for the degeneration of the intrinsic muscles of the foot, with implications for both the use of orthotics and pain management.