Modelling osteoarthritis in mice via surgical destabilization of the medial meniscus with or without a stereomicroscope

Aims To evaluate inducing osteoarthritis (OA) by surgical destabilization of the medial meniscus (DMM) in mice with and without a stereomicroscope. Methods Based on sample size calculation, 70 male C57BL/6 mice were randomly assigned to three surgery groups: DMM aided by a stereomicroscope; DMM by naked eye; or sham surgery. The group information was blinded to researchers. Mice underwent static weightbearing, von Frey test, and gait analysis at two -week intervals from eight to 16 weeks after surgery. Histological grade of OA was determined with the Osteoarthritis Research Society Interna-tional (OARSI) scoring system. Results Surgical DMM with or without stereomicroscope led to decrease in the mean of weight -bearing percentages (-20.64% vs-21.4 4%, p = 0.792) and paw withdrawal response thresholds (-21.35% vs-24.65%, p = 0.327) of the hind limbs. However, the coefficient of variation (CV) of weight-bearing percentages and paw withdrawal response thresholds in naked -eye group were significantly greater than that in the microscope group (19.82% vs 6.94%, p < 0.001; 21.85% vs 9.86%, p < 0.001). The gait analysis showed a similar pattern. Cartilage degeneration was observed in both DMM-surgery groups, evidenced by increased OARSI scores (summed score: 11.23 vs 11.43, p = 0.842), but the microscope group showed less variation in OARSI score than the naked -eye group (CV: 21.03% vs 32.44%; p = 0.032). Conclusion Although surgical DMM aided by stereomicroscope is technically difficult, it produces a relatively more homogeneous OA model in terms of the discrete degree of pain be-haviours and histopathological grading when compared with surgical DMM without ste-reomicroscope.