OCD is an abbreviation of 'osteochondral defect'. The abbreviation is also used of 'osteochondritis dissecans'.
What is an osteochondral defect?
An osteochondral defect is a circumscribed area of joint damage, where the rest of the joint is mostly in good condition, such as might follow from a blow on the knee.
What is osteochondritis dissecans
Osteochondritis dissecans is a particular type of osteochondral defect caused by a failure of blood supply to a small area, which local loosening of a small chunk of bone and cartilage in a similar way
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.