Finger Flexor Tendon Orientation and Location as a Function of Postural Changes of the Wrist and Forearm: The Quantification of Musculoskeletal Loading in Jobs with Deviated Forearms

Forearm pronation/supination is common during manual activities, and has been linked to upper limb disorders in the workplace (Hughes et al. 1997). Forearm deviations from neutral (palm of the hand facing medially) can increase discomfort and forearm musculature activity (EMG) (Khan 2009a; Domizio & Keir, 2010), particularly when combined with wrist postures deviated from neutral. Yet ergonomic tools commonly used to assess the risk of developing distal upper limb disorders (e.g., Strain Index and RULA), often disregard or only minimally account for forearm pronation/supination posture. As a result, the risk of injury may be underestimated. This dissertation first examined methods of measuring pronation in the workplace by testing instantaneous agreement of forearm posture measurements between Inertial Motion Units (Xsens, Netherlands) and a laboratory-based motion capture system (Vicon, UK). Participants turned metallic and non-metallic handles in front of them, in order to quantify the effect of magnetic disturbance and sensor orientation on the Xsens. On average, RMSE errors of 12.6 deg around metal, and 8.6 deg around plastic were observed on instantaneous measures. Higher rotational velocities appeared associated with larger errors. Summarized data revealed smaller discrepancies. Second, this dissertation examined the effect of forearm pronation/supination coupled with wrist flexion/extension on the orientation and location of finger flexor tendons with respect to a radial coordinate system, using MRI of 4 healthy wrists. Pronation/supination caused movement almost exclusively in the frontal plane. Radial tendons exhibited larger angular deviations in pronation, whereas ulnar tendons were nearly straight, and the opposite was observed in supination. Larger angular deviations were thought to increase contact forces within the tunnel in the direction of the bend, which combined with finger movement could increase the risk of tenosynovitis. Finally the results of these studies were combined to measure tendon movement during a repetitive task. The three tendons with the greatest angular movement in the tunnel were: FDP2 (0.16 deg/pronation/supination degree), FDS3 (0.15 deg/ pronation/supination degree), and FDS4 (0.17 deg/ pronation/supination degree).