AN EMG OPTIMIZATION MODEL OF THE KINETIC DEMANDS ON THE LOWER BACK DURING ASYMMETRICAL GAIT AND LOAD CARRIAGE

Gait asymmetries are associated with a high incidence of lower back pain (LBP). Although there are several causes of gait asymmetry (i.e. amputation, injury, or deformities), lower back kinetic demands have not been quantified and suitably compared due to experimental limitations in these clinical populations. Further, the impact of gait asymmetry on lower back demands during carrying tasks has not been established. This dissertation addressed these issues by artificially and safely inducing gait asymmetry in healthy able-bodied participants during walking and carrying tasks. LBP risk was assessed by L5/S1 vertebral joint force levels estimated with an OpenSim musculoskeletal model of the lower back adapted to incorporate participant-specific responses using an EMG optimization approach. The model was evaluated systematically for force estimate efficacy and sensitivity to input parameters prior to gait asymmetry assessments. Twelve participants performed walking and carrying tasks on a treadmill at individually scaled speeds while kinematics, external kinetics, and muscle activities (EMG) were recorded. Walking conditions consisted of unperturbed symmetrical gait, and asymmetrical gait induced by perturbing the right leg with a 2.54 cm shoe leveler, ~1 kg ankle weight, combined weight and shoe leveler, or a clinical walking boot that restricted ankle joint motion and added mass. Load carrying was performed while holding 7.5% and 15% bodyweight dumbbells in one or two hands during symmetric gait and asymmetric gait induced by the walking boot. The perturbations were successful in producing different degrees of gait asymmetry. However, L5/S1 joint forces were not significantly different between conditions despite unique spatiotemporal asymmetries. This indicates that LBP in those with gait asymmetry may not be due solely to level planar walking. During carrying tasks, gait asymmetry induced by the walking boot increased some metrics of lower back loading. Further, carrying a load in the hand contralateral to the walking boot produced larger forces than when carried on the same side. These results emphasize the importance of evaluating specific sources of gait asymmetry during daily activities other than walking when assessing LBP risk and would encourage more inclusive ergonomic carrying guidelines

Biomechanical risk factors and reduced bone health in lower limb amputees

Bone constantly adapts to its surroundings through the formation and resorption of material, controlled by bone modelling and remodelling. Strains produced by mechanical loading are one factor that drive these processes and thus determine bone health. Lower limb amputees (LLA) adopt an asymmetrical movement pattern to compensate for the loss of a limb, resulting in a change in mechanical loading and subsequently a degradation in bone health. The aetiology of the majority of amputations is vascular diseases, which affect bone health. Therefore, it is not clear whether the asymmetrical loading, or comorbidities cause the degradation in bone health in LLA. Finite element models (FEM) are used to generate strain plots and predict the bone's response to mechanical loading. To understand the relationship between the degradation in bone health and asymmetrical loads in LLAs the asymmetrical loads can be applied to a healthy bone using FEMs, or simulated within a healthy population using restrictive devices. Therefore, the overall aim was to investigate the relationship between asymmetrical loading, as observed in LLA’s, and bone health, through the use of semi-subject specific FEMs and restrictive lower limb devices. Study one established a novel image processing method to convert peripheral quantative computed tomography (pQCT) scan images into binary and segment the tibia. The outer perimeter of the tibia was identified and sectioned to produce landmarks. The outer geometry landmarks were used to morph a base FEM, constructed from open source scan images to create semi-subject tibia FEM. Study two applied subject-specific joint reaction and muscle forces to the semi-subject tibia FEM. The strain plots output from Study two were validated against longitudinal geometrical changes from Study three. Study three, used 3D motion capture, pQCT and dual energy x-ray absorptiometry (DXA) to investigate gait and tibial geometry within a lower limb amputee and able-bodied population across twelve months. The coefficient of variation (CV) for able bodied subjects was less than 10% for ground reaction force (GRF) in level walking and less than 4% for bone total area. Study four, used a rigid foot orthosis and a trans-femoral prosthesis, to restrict able-bodied gait. Results showed participants walked significantly slower (p<0.01) in the restricted conditions, with a longer non-restricted step length (p<0.001). The loading rate and maximum GRF were higher in the non-restricted limb (p<0.05). Larger knee adductor moments were shown in the un-restricted leg in the trans-tibial condition (p<0.05). This thesis presents a novel method of constructing semi-subject specific FEMs from pQCT scans. This can be used to further investigate the link between asymmetrical loading and bone health in LLA's and other populations with asymmetrical gait. The use of restrictive devices allow investigation into LLA's specifically, without the interference of prosthetic variability, or comorbidities

PREDICTIVE SIMULATION OF HUMAN MOVEMENT AND APPLICATIONS TO ASSISTIVE DEVICE DESIGN AND CONTROL

Predictive simulation based on dynamic optimization using musculoskeletal models is a powerful approach for studying biomechanics of human gait. Predictive simulation can be used for a variety of applications from designing assistive devices to testing theories of motor controls. However, one of the challenges in formulating the predictive dynamic optimization problem is that the cost function, which represents the underlying goal of the walking task (e.g., minimal energy consumption) is generally unknown and is assumed a priori. While different studies used different cost functions, the qualities of the gaits with those cost functions were often not provided. Therefore, this dissertation evaluates and examines different cost function forms for dynamic simulation of human walking. The problem of the walking cost function determination was cast as a bilevel optimization, which was solved using a nested evolutionary approach. The results showed cost functions based on a weighted combination of muscle-based performance criteria (e.g., metabolic cost, muscle fatigue), gait smoothness, and gait stability led to better walking solutions compared to any cost functions only based on muscle performance criteria. Further evaluations of the walking cost functions were done in the simulation cases of human walking augmented with assistive devices such as prosthesis and exoskeleton. The simulations of augmented walking were comparable to the experimental results, which suggests the potential of using the simulation approach to address problems of finding assistive device design and control

The effect of prefabricated wrist-hand orthoses on performing activities of daily living

Wrist-hand orthoses (WHOs) are commonly prescribed to manage the functional deficit associated with the wrist as a result of rheumatoid changes. The common presentation of the wrist is one of flexion and radial deviation with ulnar deviation of the fingers. This wrist position Results in altered biomechanics compromising hand function during activities of daily living (ADL). A paucity of evidence exists which suggests that improvements in ADL with WHO use are very task specific. Using normal subjects, and thus in the absence of pain as a limiting factor, the impact of ten WHOs on performing five ADLs tasks was investigated. The tasks were selected to represent common grip patterns and tests were performed with and without WHOs by right-handed, females, aged 20-50 years over a ten week period. The time taken to complete each task was recorded and a wrist goniometer, elbow goniometer and a forearm torsiometer were used to measure joint motion. Results show that, although orthoses may restrict the motion required to perform a task, participants do not use the full range of motion which the orthoses permit. The altered wrist position measured may be attributable to a modified method of performing the task or to a necessary change in grip pattern, resulting in an increased time in task performance. The effect of WHO use on ADL is task specific and may initially impede function. This could have an effect on WHO compliance if there appears to be no immediate benefits. This orthotic effect may be related to restriction of wrist motion or an inability to achieve the necessary grip patterns due to the designs of the orthoses

Use of stance control knee-ankle-foot orthoses : a review of the literature

The use of stance control orthotic knee joints are becoming increasingly popular as unlike locked knee-ankle-foot orthoses, these joints allow the limb to swing freely in swing phase while providing stance phase stability, thus aiming to promote a more physiological and energy efficient gait. It is of paramount importance that all aspects of this technology is monitored and evaluated as the demand for evidence based practice and cost effective rehabilitation increases. A robust and thorough literature review was conducted to retrieve all articles which evaluated the use of stance control orthotic knee joints. All relevant databases were searched, including The Knowledge Network, ProQuest, Web of Knowledge, RECAL Legacy, PubMed and Engineering Village. Papers were selected for review if they addressed the use and effectiveness of commercially available stance control orthotic knee joints and included participant(s) trialling the SCKAFO. A total of 11 publications were reviewed and the following questions were developed and answered according to the best available evidence: 1. The effect SCKAFO (stance control knee-ankle-foot orthoses) systems have on kinetic and kinematic gait parameters 2. The effect SCKAFO systems have on the temporal and spatial parameters of gait 3. The effect SCKAFO systems have on the cardiopulmonary and metabolic cost of walking. 4. The effect SCKAFO systems have on muscle power/generation 5. Patient’s perceptions/ compliance of SCKAFO systems Although current research is limited and lacks in methodological quality the evidence available does, on a whole, indicate a positive benefit in the use of SCKAFOs. This is with respect to increased knee flexion during swing phase resulting in sufficient ground clearance, decreased compensatory movements to facilitate swing phase clearance and improved temporal and spatial gait parameters. With the right methodological approach, the benefits of using a SCKAFO system can be evidenced and the research more effectively converted into clinical practice