Histologic findings and possible causes of osteochondritis dissecans of the knee

Background: The histologic findings of osteochondritis dissecans of the knee vary widely, leading to differences in the interpretation of its origins. Hypothesis: The differences in the histologic findings of osteochondritis dissecans might represent a course of pathologic progression. Study Design: Descriptive laboratory study. Methods: Twelve knees in 11 patients (average age, 16 years) with osteochondritis dissecans of the medial femoral condyle were treated by biological internal fixation. During the surgery, cylinder osteochondral plugs were taken from the center of the osteochondritis dissecans lesion and examined with light microscopy. Results: A complete or partial cleft separated the specimens into 2 parts: basal and fragment sides. The surface of the basal side was covered with dense fibrous or cartilaginous tissue and active bone remodeling was found beneath the surface. In the fragment side, the deep surface was also covered with dense fibrous or cartilaginous tissue and the articular surface consisted of normal articular cartilage. The area between these 2 surfaces could be classified into 3 types: (1) necrotic subchondral trabeculae, (2) viable subchondral trabeculae, and (3) cartilage without bone trabeculae. Conclusion: Based on the histologic findings of this study, the following origins and the pathologic progression of osteochondritis dissecans might be assumed: the initial change in the subchondral area is bone necrosis or subchondral fracture; the necrotic bone is then absorbed and replaced either by viable subchondral trabeculae or cartilage without bone trabeculae. Clinical Relevance: The results of this histologic study provide readers with several insights about the causes and treatment options of osteochondritis dissecans.