Effect of sustained experimental muscle pain on joint position sense

Introduction: Joint position sense (JPS) is impaired in clinical musculoskeletal pain conditions, but when this impairment develops in the transition from initial to prolonged pain is not known. Objectives: This study assessed whether progressively developing sustained experimentally induced muscle pain impacts JPS in healthy individuals. Methods: Twenty-eight healthy individuals received injection of nerve growth factor (NGF) into the right extensor carpi radialis brevis muscle on days 0 and 2 to induce sustained pain and hyperalgesia. Wrist JPS was assessed 2 days before day 0 (day 22), before the injection on days 0 and 2, and on days 4 and 14. Joint position sense was quantified as the ability to return the wrist to a neutral position following movements in the direction of radial and ulnar deviation. A 3-dimensional motion analysis system was used to calculate absolute, relative, and joint-angle repositioning errors. Numerical rating scale scores of pain intensity, body chart pain drawings, and pressure pain thresholds (PPTs) were recorded on each day. Results: Compared with baseline, pressure pain thresholds decreased while pain intensity and area increased at day 2 (P , 0.001) and day 4 (P , 0.001) before returning to baseline on day 14 (P . 0.13). Relative to day 0, there was no change in wrist JPS at day 2, 4, and 14 following movements in either target direction (P . 0.05). Conclusion: Despite the presence of sustained muscle pain and hyperalgesia for 4 days at the elbow, no statistical change in wrist joint position error was observed. These findings suggest that pain and hyperalgesia lasting as long as 4 days does not impair JPS.