Histopathological features according to the Osteoarthritis Research Society International grade and staining method.

<p>Slides from the (A) patellofemoral joint and (B) tibiofemoral joint were stained with hematoxylin and eosin and safranin O. Grade 1, surface intact; grade 2, surface discontinuity; grade 3, vertical fissures; grade 4, erosion; grade 5, denudation and reparative tissue surface present; and grade 6, deformation and osteophyte formation. Scale bar = 1 mm (grades 1–5) and 2 mm (grade 6).