Improved Accuracy in Optical Motion Capture Measurements Leads to Increased Sensitivity to Kinematic Changes

Clinical optical motion capture allows us to obtain kinematic and kinetic outcome measures that aid clinicians in diagnosing and treating different pathologies affecting healthy gait. The long term aim for gait centres is for subject-specific analyses that can predict, prevent, or reverse the effects of pathologies through gait retraining. To track the body, anatomical segment coordinate systems are commonly created by applying markers to the surface of the skin over specific, bony anatomy that is manually palpated. The location and placement of these markers is subjective and precision errors of up to 25mm have been reported [1]. Additionally, the selection of which anatomical landmarks to use in segment models can result in large angular differences; for example angular differences in the trunk can range up to 53o for the same motion depending on marker placement [2]. These errors can result in erroneous kinematic outcomes that either diminish or increase the apparent effects of a treatment or pathology compared to healthy data. Our goal was to improve the accuracy and precision of optical motion capture outcome measures. This thesis describes two separate studies. In the first study we aimed to establish an approach that would allow us to independently quantify the error among trunk models. Using this approach we determined if there was a best model to accurately track trunk motion. In the second study we designed a device to improve precision for test, re-test protocols that would also reduce the set-up time for motion capture experiments. Our method to compare a kinematically derived centre of mass velocity to one that was derived kinetically was successful in quantifying error among trunk models. Our findings indicate that models that use lateral shoulder markers as well as limit the translational degrees of freedom of the trunk through shared pelvic markers result in the least amount of error for the tasks we studied. We also successfully reduced intra- and inter-operator anatomical marker placement errors using a marker alignment device. The improved accuracy and precision resulting from the methods established in this thesis may lead to increased sensitivity to changes in kinematics, and ultimately result in more consistent treatment outcomes.

Fear of Falling and Balance Confidence in Older Adults with Diabetes Mellitus

Several determinants of fear of falling (FoF) and low balance confidence overlap with the consequences/complications of diabetes mellitus (DM). FoF is strongly associated with low balance confidence, and balance confidence mediates the relationship between FoF and balance and physical function. The purpose of this thesis was two-fold: (1) to examine the prevalence, severity and determinants of FoF in older adults (aged≥65) with DM, and (2) to evaluate the validity of the short version of the Activities-specific Balance Confidence scale (ABC-6) and its association with balance and postural control in older adults with DM. Three separate studies were conducted of older adults with DM (DM-group) and without DM (noDM-group). Study I revealed that although FoF prevalence adjusted for age and sex was not different between-groups, the DM-group had 8.8% fewer participants in the low and 8.4% more in the high Falls-Efficacy Scale International categories when compared to the noDM-group. Higher FoF severity in the DM-group was associated with poor physical performance, being female, fall history and clinical depressive symptoms. Study II provided evidence of convergent, discriminant and concurrent validity of the ABC-6 for use in older adults with DM with and without diabetic peripheral neuropathy (DPN). Notably, the ABC-6 was more sensitive in detecting subtle differences in balance confidence between the DM-group and noDM-group when compared to the original ABC scale (ABC-16), and can be administered in less time. Study III explored balance confidence (ABC-6) and its association with balance and postural control in older adults with DM. Subtle differences in axial segmental control (i.e., lower trunk roll velocity and higher head-trunk correlations) while walking and lower balance confidence were apparent in the DM-group, even in the absence of DPN, when compared to the noDM-group. Balance confidence partially explained the variance in head-trunk stiffening between-groups, and consequently low balance confidence in older adults with DM may contribute to the dependence on postural control strategies that are normally only utilized in high-risk situations. Findings from this thesis will help to guide the development of protocols for screening and intervention recommendations of patient education and targeted rehabilitation programs for older adults with DM.