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The human wrist is a vital joint in daily life, and it is subject to injuries and disease. Currently, severe wrist disease is normally treated with wrist arthrodesis, which is normally reliable but results in a fixed wrist incapable of allowing wrist motion. Another method of treating a nonfunctional or severely painful wrist is wrist arthroplasty where the wrist joint is replaced with an implant that allows wrist movement. As of yet, a suitable wrist implant has not been developed, especially for the case of the post-traumatic, young male wrist, and most current wrist implants fail from failure of the bone-implant interface. Through simulation and literature review, it is concluded that implants that restrict axial rotation are bound to fail overtime. With this conclusion, a new wrist implant prototype is designed that incorporates state of the art materials, fluid film lubrication, proper kinematics, a suitable range of motion, and more. This implant contributes several improvements to the field of wrist arthroplasty.

Repetitive manual lifting and whole body vibration (WBV) exposure encountered in manual handling and delivery type jobs lead to muscle fatigue and are documented risk factors for low back disorder (LBD). In order to compensate for muscle fatigue, people in these occupations may adapt their working strategy to prevent an injury. The goal of this dissertation research was to identify the interactive effects of WBV and repetitive lifting exposures on muscle fatigue and changes in lifting mechanics. Study 1 investigated the effects of prolonged repetitive asymmetric lifting task on behavioral adaptations, measures of tissue oxygenation, and spine kinematics during a controlled flexion-extension motion task. Seventeen healthy volunteers repeatedly lifted a box (15% of the participant’s lifting capacity) positioned in front of them at ankle level to a location on their left side at waist level at the rate of 10 lifts/minute for 60 minutes. The results showed that this prolonged lifting task lead to decrease in tissue oxygenation measures and an increase in the level of perceived exertion over time. Behavioral changes with repetitive lifting task included an increase in forward bending motions and velocities in the sagittal and coronal plane. Behavioral measures that increased over time have also been documented to increase the risk of back injury. Study 2 investigated the interactive effects of seated vibration exposure and lifting task precision demands on behavioral and physiological changes experienced during a repetitive lifting task. This study was a 2 x 2 repeated measures design with two levels of vibration exposure and two levels of lifting task precision demands. The initial analyses showed no significant interaction between WBV exposure and task precision demands during the repetitive lifting task. Thus, the data was separately analyzed to understand changes in the physiological and behavioral responses associated with each of these physical factors. Study 2a focused on the changes in the physiological and behavioral responses to repetitive asymmetric lifting activity after seated exposure to a 5 Hz WBV for one-hour. The changes in muscle physiology and behavioral measures replicated the findings from study 1. Following exposure to WBV, participants showed larger spine twisting motion and movement velocity as they performed the lifting task. The larger spine kinematic response indicated these changes would increase the risk of back injury. Study 2b focused on the effect of task precision demands during a repetitive asymmetric lifting task on muscle physiology and behavioral measures. High precision demands resulted in significantly higher movement times, larger sustained twisting motions and lateral bending moments on the spine. These behavioral changes suggest that the risk to low back injury is elevated while performing a repetitive asymmetric lifting activity under high task precision demands. In summary, this research has shown that the risk of low back injury while performing a repetitive asymmetric lifting activity is likely due to changes in the adopted behavior. Moreover, this risk is further elevated when people are exposed to WBV prior to lifting, and when the lifting requires the object be placed in precise location at its destination.

Rigid pavement condition evaluation using dynaflect and falling weight deflectometer measurements