Many epidemiological studies have named pinching, deviated wrist postures, and repetitive motion as ergonomic risk factors in the development of carpal tunnel syndrome (CTS). Evidence suggests that hypervascularization of the median nerve and increased intraneural blood flow proximal to the carpal tunnel result in response to ergonomic risk factors (finger pressing and deviated wrist postures). The purposes of this study were to 1) determine the effect of a pinch posture, with and without force exerted by the finger, thumb, or both and 2) determine the effect of repetitive wrist flexion and extension on intraneural blood flow velocity in the median nerve proximal to the carpal tunnel. Eleven healthy and eleven CTS symptomatic individuals participated in this study and completed three components: 15 pinch posture force trials, 3 repetitive wrist motion trials, and 3 static wrist posture trials. Intraneural blood flow was measured using pulse wave Doppler during each trial. Main effects of pinch posture force (F4,80 = 21.397, p < 0.001) and wrist posture (F2,40 = 14.545, p < 0.001) were observed. Trials where force was applied by the finger (2.21 cm/s), thumb (2.22 cm/s) or both (2.34 cm/s) produced higher intraneural blood flow velocities than trials with no force (1.79 cm/s) or relaxed hand (1.89 cm/s). Trials performed in flexion (2.24 cm/s) were greater than neutral (2.06 cm/s) and extension (1.97 cm/s). No interactions or main effects of time were found in response to repetitive wrist motion. These results suggest that at low force levels (6 N) it’s not how the force is applied but rather that the force is being applied that has an effect on the median nerve. Additionally these results suggest that the contribution of repetitive motion to the development of CTS may not be directly to the median nerve. / Thesis / Master of Science (MSc)

<p>Carpal tunnel syndrome (CTS) is one of the most prevalent work-related musculoskeletal disorders of the upper extremity yet its etiology remains elusive. Nerve hypervascularization has been proposed as a pathophysiological change in CTS and can be measured using high resolution sonography of intraneural blood flow. The purpose of this study was to determine the effects of deviated wrist postures and fingertip force on the intraneural blood flow velocity of the median nerve proximal to the wrist crease. Ten participants experiencing the classic symptoms of CTS and nine healthy volunteers were recruited and underwent qualitative assessments (Phalen’s test, Katz hand diagram, Levine’s CTS questionnaire). Intraneural blood flow velocity was measured in five wrist postures (flexion 30°, flexion 15°, neutral, extension 15°, extension 30°) with and without a middle digit fingertip press (0N, 6N). A control (N=9) group and a CTS symptomatic (N=9) group were determined, in addition to a CTS individual (N=1) that required a separate analysis. A significant main effect of force was found (F_1,16= 28.039, p < 0.0005) with the mean peak velocity being greater with force (3.56 cm/s) than without force (2.81 cm/s). Wrist posture had a main effect (F_4,64= 3.163, p < 0.020) with flow velocity as neutral (2.87 cm/s) was significantly lower than flexion 30° (3.37 cm/s), flexion 15°(3.27 cm/s) and extension 30° (3.29 cm/s). There was no significant difference in peak blood flow velocity between the two experimental groups, CTS symptomatic (3.34 cm/s) and control (3.03 cm/s) (F_1,16= 4.121, p < 0.059). The results suggest that both force and non-neutral wrist postures may acutely induce vascular changes previously associated with CTS. The quantification of reactive median nerve hypervascularity should be investigated further as it has potential to be both a reliable diagnostic technique and a non-invasive assessment of CTS risk.</p> / Master of Science in Kinesiology