Evaluation of Spontaneous Pain in a Monosodium Iodoacetate-Induced Mouse Model of Osteoarthritis Using the Mouse Grimace Scale.

Animal models are critical for elucidating disease mechanisms and pathological outcomes, and for evaluating therapeutic interventions. Osteoarthritis (OA) is a leading cause of chronic pain and disability globally. Clinically, individuals with OA experience both sensory and ongoing pain. However, ongoing pain, as assessed by the Mouse Grimace Scale (MGS), has not yet been evaluated in animal models of OA. This study aims to address this significant knowledge gap. We induced OA by intra-articular injection of monosodium iodoacetate (MIA), while control mice received saline injections. We assessed pain behaviors using the MGS on days 1, 3, 7, and 14 after MIA administration. MIA-treated mice exhibited significantly higher MGS scores than saline-treated controls throughout the study period, indicating ongoing pain-related behavior in the MIA OA model. Furthermore, longitudinal studies showed that this pain is chronic, as seen in people with OA. These findings support the usefulness of the MGS test in the MIA model for studying ongoing pain.