Detection of tissue hypoxia. Pimonidazole hydrochloride (Hydroxyprobe™-1 solution; Chemicon) was injected intraperitoneally in Balb/C mice and detected in hypoxic cells immunohistochemically after 24 hours. Most (a), (b) articular chondrocytes and (a) meniscal cells stained positive for this hypoxic marker, whereas osteocytes and other mesenchymal cells were negative. F, femoral condyle; M, meniscus; T, tibial plateau. Bars = 100 μm.