Functional brain effects of hand disuse in patients with trapeziometacarpal joint osteoarthritis: executed and imagined movements

The human trapeziometacarpal (TMC) joint has a crucial evolutionary importance as it permits rotation and opposition of the thumb to the other fingers. In chronic TMC joint osteoarthritis (i.e., rhizarthrosis), this motor ability, essential for pinching, grasping, and manipulating objects, may become difficult or impossible due to intolerable pain. Here, we assess whether patients with rhizarthrosis show signs of abnormal brain representation of hand movements. To this end, we studied 35 patients with rhizarthrosis, affecting predominantly one of the two hands, and 35 healthy subjects who underwent both behavioural and fMRI measures of brain activity during overtly executed or imagined thumb-to-finger-opposition movements. The patients with rhizarthrosis were slower than controls both in motor execution and imagination. In the patients, correlation between the motor execution and imagination times was preserved, even though such correlation was less strong than in normal controls. The fMRI measures showed reduced activation in the hand primary motor and dorsal premotor cortex for the patients only during explicit movements. This was true for both hands, yet more so for the most affected hand. No significant differences were seen for the motor imagery task. These results show that an orthopaedic disorder that reduces patients' motoric repertoire in the absence of any neurological impairment is sufficient to induce neurofunctional changes in the cortical representation of hand movements. The substantial preservation of motor imagery with its neural counterparts distinguishes the neurological patterns of rhizarthrosis from those of complete immobilization or amputation suggesting that motor imagery may be used to boost motor recovery in rhizarthrosis after surgical treatment.