Ectopic Growth Plate

Young dog. Cross-section through the distal femoral metaphysis. Osteochondroma is a developmental anomaly (at least in dogs) that commonly occurs adjacent to the physis. The lesion is essentially a misplaced center of ossification. While some categorize osteochondromas as neoplasms, the young age in which they occur in dogs suggests the hyaline cartilage that initiates everything may be a choristoma (chondrocyte-capped periosteal choristoma). The insets illustrate normal (lower) cortical bone compaction vs uncompacted cortex beneath the mass. Failure of cortical bone compaction suggests this osteochondroma occurred during development of the bone. Some smaller percentage of cortical bone compaction failure could be due to stress shielding. Original digital image courtesy of Steven Weisbrode and OSU CVM.