Apparatus and procedure

We collected kinematic data from both the intact hand (left hand) and the affected hand (right hand). The participant was comfortably seated in front of a table. Two columnar bars (with a diameter of 5 cm and height of 10 cm and 30 cm, respectively) were placed on the table. The tips of the bars represented the start and goal points, respectively. The start bar was placed 20 cm away from the participant and the goal bar was located 30 cm further from the start bar (i.e., 50 cm away from the participant). Both bars were aligned with the sagittal body-midline axis. The participant was required to first pinch the tip of the start bar with her thumb and index finger, which was oriented in an anteroposterior direction (starting position), and then moved her hand from the start position to reach and pinch the tip of the goal bar (goal position). The participant was asked to repeat this sequential-movement process 10 times at a comfortable pace. We first obtained kinematic data for both the intact and affected hands and then repeated the measurement of kinematic data from the affected hand after inducing a regional intravenous nerve blockade (Bier block: 1% lidocaine at 20 mL for the affected forearm) that alleviated pain. Creating an intravenous nerve blockade using lidocaine is known to be an effective treatment for severe pain, allodynia, and edema.16 This treatment had an immediate analgesic effect on the patient. Using the nerve blockade enabled us to compare motor control between pain and painless conditions and thus ascertain whether pain contributed to abnormal motor control in the affected limb. In order to minimalize the effect of hemostasis during intravenous nerve blockade, kinematic data in pain alleviation condition were measured in about half an hour after the release of tourniquet. The kinematic data comprised reaching trajectories that were captured using a magnetic measurement system with six degrees of freedom (3 SPACE FASTRAK; Polhemus Inc.). This system generated a hemispherical electromagnetic field with a radius of 76 cm, which is sufficiently large to measure upper limb movement. The system measured the three-dimensional position and orientation of sensors that were attached to the tips of the index fingers and thumb and to the lateral epicondylus of the wrist. The location of the sensors in the field was collected at a sampling rate of 40 Hz and the data were stored on a personal computer.