EFFECT OF WRIST POSTURE AND FINGERTIP FORCE ON MEDIAN NERVE BLOOD FLOW VELOCITY

Abstract

<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>