Altering visual feedback during reaching: no mitigating effect on pain for individuals with complex regional pain syndrome, but visuomotor adaptation is preserved.

Introduction: Complex regional pain syndrome (CRPS) is often associated with pain-related fear of movement, and virtual reality has been proposed as a potential rehabilitation intervention to overcome this issue. Therefore, this cross-sectional study aimed to test whether altering the visual feedback (VF) on movement could mitigate pain and promote movement. Methods: Fifteen participants with upper-limb CRPS and 15 age- and gender-matched pain-free participants undertook a target reaching task in the Kinarm exoskeleton, with two VF conditions being tested (Per Exposure: GREATER or SMALLER VF; two separate sessions), preceded and followed by reaching movements without VF (Pre-/Post-Exposure). Proprioception was assessed with a Limb Position Sense task, and a Movement Accuracy outcome was derived from the Pre-Exposure reaching movements. Results: Contrary to our hypothesis, pain intensity was not influenced by VF conditions but increased over Time (p < 0.001). Analyses performed on kinematics data showed that participants displayed visuomotor adaptation both Per Exposure, and Pre-/Post-Exposure to altered VF (VF condition*Time: p < 0.001). Per Exposure analyses revealed that CRPS participants tended to adapt their Movement Length to a lesser extent than pain-free participants (Group*VF condition: p = 0.048). Pre-/Post-Exposure analyses revealed that CRPS participants consistently performed larger movements than pain-free participants (p = 0.002). Both groups performed similarly for the Limb Position Sense task, but CRPS participants displayed significantly larger errors for Movement Accuracy, suggesting impaired proprioceptive integration in the CRPS group. Discussion: These findings support the idea that visuomotor adaptation is preserved in CRPS and can be used to promote movement.