To determine whether motor imagery performance is disrupted in patients with painful knee OA and if this disruption is specific to the location of the pain.
Twenty patients with painful knee OA, 20 patients with arm pain and 20 healthy pain-free controls undertook a motor imagery task in which they made left/right judgements of pictured hands and feet. Accuracy and reaction time of judgements were compared between groups and pain locations (side: left vs right; site: upper vs lower).
Patients with knee pain were less accurate (P < 0.01) than healthy controls, but not different from people with arm pain (all P > 0.11). There were no differences in reaction time between groups (P = 0.64). Further, there was no effect of side or site of pain on reaction time (P = 0.43, 0.54, respectively) and no effect of site of pain on accuracy of left/right judgements (P = 0.12). However, there was an interaction effect of side of pain on accuracy of left vs right images (P = 0.03). If left-sided pain was present, accuracy was lower when images showed left hands/feet than when images showed right hands/feet.
Motor imagery performance is disrupted in patients with knee OA, but is also disrupted in patients with arm pain. Accuracy of left/right judgements is disrupted in a spatially defined manner, raising the important possibility that brain-grounded maps of peripersonal space contribute to the cortical proprioceptive representation.