Figure 1

Osteochondral lesions in the articular epiphyseal cartilage complex and subchondral bone of the talus. These six macro- and microscopic images of slabs from the tali of different pigs show lesions that are characteristic of each osteochondrosis (OC) score. Together, they illustrate how lesions develops from minor OC (scores 1 and 2) through moderate to extensive OC (scores 3 and 4) and finally to OC dissecans (score 5). Open spaces in the microscopic images are artefacts. Score 0: No lesions in the articular epiphyseal cartilage complex (AECC) and subchondral bone (SCB) (medial distal talus, figure size × 10). Score 1: Minimal focal thickening* of the AECC with necrotic cartilage visible histologically (lateral distal talus, ×4). Score 2: Small focal thickening and necrosis in the AECC with vascular and/or inflammatory** reaction in subchondral bone (medial distal talus, ×10). Score 3: Moderate lesions in the AECC and underlying bone with minor separation (arrows) in the osteochondral junction. Focal chondrocyte clusters* are seen (medial distal talus, ×4). Score 4: Extensive lesions in the AECC and underlying bone where separation (arrows) is visible in both cartilage and subchondral bone (medial distal talus, ×1). Score 5: Osteochondrosis dissecans. Severe lesion with clefts that cut through the surface of the cartilage (arrows) with necrosis in the AECC and involvement of subchondral bone (medial trochlea of the talus, ×1).