Tactile acuity is disrupted in osteoarthritis but is unrelated to disruptions in motor imagery performance

Objective. To determine whether tactile acuity is disrupted in people with knee OA and to determine whether tactile acuity, a clinical signature of primary sensory cortex representation, is related to motor imagery performance (MIP; evaluates working body schema) and pain. Methods. Experiment 1: two-point discrimination (TPD) threshold at the knee was compared between 20 participants with painful knee OA, 20 participants with arm pain and 20 healthy controls. Experiment 2: TPD threshold, MIP (left/right judgements of body parts) and usual pain were assessed in 20 people with painful knee OA, 17 people with back pain and 38 healthy controls (20 knee TPD; 18 back TPD). Results. People with painful knee OA had larger TPD thresholds than those with arm pain and healthy controls (P <0.05). TPD and MIP were not related in people with knee OA (P = 0.88) but were related in people with back pain and in healthy controls (P <0.001). Pain did not relate to TPD threshold or to MIP (P > 0.15 for all). Conclusion. In painful knee OA, tactile acuity at the knee is decreased, implying disrupted representation of the knee in primary sensory cortex. That TPD and MIP were unrelated in knee OA, but related in back pain, suggests that the relationship between them may vary between chronic pain conditions. That pain was not related to TPD threshold nor MIP suggests against the idea that disrupted cortical representations contribute to the pain of either condition.