Osteochondritis dissecans is a destructive condition of bone, where blood supply becomes insufficient to a small section of cartilage and its underlying cartilage.
The localised bit of bone may die off and leave a crater, but initially the compromised fragment may not be dead, and it may be possible to fix it back onto the main bone.
Osteochondritis Dissecans: Etiology, Pathology, and Imaging with a Special Focus on the Knee Joint. Bruns J, Werner M and Habermann C. Cartilage. 2018 Oct; 9(4): 346–362.