Histological and behavioral evaluation. Histological H-E stained appearance of the epiphysis 28 days after intraarticular injection: (A) ipsilateral and (B) contralateral. The scale bars are 2.0 mm. F: femoral condyle; T: tibial condyle, M: meniscus. The histological examination revealed OA-like findings, such as an extensive area of cartilage loss and degeneration, subchondral bone collapse, and moderately well-defined subchondral cystic structure, whereas that of the contralateral knee yielded normal findings. (C) Transverse diameter of the knees. The measured diameter showed significant gradual increase in the ipsilateral knees as the postinjection period passed (P < 0.05). (D) Behavioral profile in the von Frey hairs test. PWT; paw withdrawal threshold. Each point represents the mean value ± S.E. PWT significantly decreased after MIA injection in the ipsilateral limbs from post-injection day 4 and showed a similar tendency to decrease from postinjection day 7 to 28.