Abstract
PURPOSE: Functional magnetic resonance imaging (fMRI) visualizes hemodynamic responses associated with brain and spinal cord activation. Various types of pain have been objectively assessed using fMRI as considerable brain activations. This study aimed to develop a pain model in cynomolgus macaques undergoing knee surgery and confirm brain activation due to resting pain after knee surgery. METHODS: An osteochondral graft surgery on the femoral condyle in the unilateral knee was performed on four cynomolgus macaques (Macaca fascicularis). Resting pain was evaluated as changes in brain fMRI findings with a 3.0-T MRI scanner preoperatively, postoperatively, and after postoperative administration of morphine. In the fMRI analysis, Z-values >1.96 were considered statistically significant. RESULTS: Brain activation without stimulation after surgery in the cingulate cortex (3.09) and insular cortex (3.06) on the opposite side of the surgery was significantly greater than that before surgery (1.05 and 1.03, respectively) according to fMRI. After the administration of morphine, activation due to resting pain decreased in the cingulate cortex (1.38) and insular cortex (1.21). CONCLUSION: Osteochondral graft surgery on the femoral condyle can lead to postoperative resting pain. fMRI can reveal activation in pain-related brain areas and evaluate resting pain due to knee surgery.