Carpal tunnel syndrome is characterized by non-inflammatory fibrosis of the subsynovial connective tissue next to the tendons in the carpal tunnel, suggesting a shear injury owing to repetitive wrist and finger motion at work. I tested the effects of several well-established biomechanical predictors of injury on tendon and subsynovial connective tissue motion and shear in the carpal tunnel. These included non-neutral finger and wrist posture, speed of work, and forceful exertion. A cadaveric paradigm was used to directly measure tendon gliding characteristics, which showed that concurrent exposure to multiple biomechanical risk factors disproportionately increased tendon frictional work (Chapter 2). Given that tendon shear cannot be directly measured in vivo, colour flow ultrasound was used to assess relative motion between tendon and subsynovial connective tissue as a metric of shear potential (Chapter 3 − 5). Healthy participants completed middle finger movements while colour flow ultrasound imaged carpal tunnel structures and optical motion capture recorded finger joint kinematics. From the data, I developed regression equations to predict both tendon and subsynovial connective tissue displacements as a function of finger joint angles, which can be used as an ergonomic method to calculate the relative displacement (Chapter 3). Furthermore, relative motion between tendon and subsynovial connective tissue increased with wrist flexion angle, suggesting a greater susceptibility to shear injury during repetitive work when the wrist is flexed (Chapter 4). Using colour flow imaging, electrogoniometry, and fine-wire EMG, relative displacement was found to increase with tendon velocity and force (Chapter 5). Relative displacements in Chapters 3 to 5 were combined into a prediction model, and further compared to a tendon friction model derived from Chapter 2. The relative displacement model showed an additive relationship with combined physical exposures, including finger and wrist position, tendon velocity, and force (Chapter 6). The relative displacement model was more responsive to lower physical exposures whereas the friction model produced greater overall changes (with higher exposures). While both models infer a greater risk of shear injury due to repetitive and forceful wrist/finger movement, future studies will aim to set protective guidelines based on tendon motion and shear during hand-intensive work. Overall, this thesis showed that tendon friction and relative motion between tendon and subsynovial connective tissue both increased in response to well-established biomechanical risk factors. We propose the current models for use in ergonomics, representing a move towards mechanistic-based injury risk assessment of the wrist and hand. / Thesis / Doctor of Philosophy (PhD)

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京都大学 / 新制・課程博士 / 博士(医学) / 甲第23773号 / 医博第4819号 / 新制||医||1057(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 金子 新, 教授 杉田 昌彦, 教授 松田 秀一 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM