Impaired Tactile Performance in Patients with Hand Immobilization

Recent studies have provided evidence that training, differential use and alterations in behavior cause plastic reorganizational changes in the human central nervous system. However, no report addressed the issue of how immobilization and thereby sensorimotor restriction caused tactile behavioral changes besides the previously described neural changes in the human motor system. To investigate the implication of a several-week immobilization induced by wearing a cast due to bone fractures of the hand, we tested spatial 2-point discrimination abilities of the healthy and immobilized hand during immobilization. To study the reversibility of the observed behavioral effects, subjects were additionally tested 2 weeks after removal of the cast. Here we found that, in spite of large variations in age and duration of immobilization, the thresholds measured for the index finger of the affected hand were significantly higher than the thresholds of the intact hand, indicating impaired discrimination abilities on the affected hand. Based on these findings, we then asked whether enforced disuse of the affected hand accompanied by restricted tactile acuity in cast patients is closely related to the duration of wearing a cast. We therefore correlated side-to-side differences between both IF with the individual duration of immobilization revealing a strong positive correlation. Accordingly, little impairment of discrimination abilities was associated with short-term immobilization. On the other hand, those subjects with long-term immobilization also had the highest discrimination thresholds and therefore the highest restriction of their affected hand. Retesting of discrimination behavior 2 weeks after removal of the cast indicated the reversibility of the observed effects. We conclude that enforced disuse over several weeks impairs discrimination abilities, whereby the impairment was reversible within 2 weeks. Moreover, functional MRI was performed in cast patients to test not only behavioral but also cortical changes within primary somatosensory cortex (SI) due to several weeks of immobilization.