Osteochondritis dissecans (OCD) is a degenerative bone condition in which cracks form in the in the articular cartilage of joints.The cracks lead to pain in the affected joint, as well as movement restriction.

It can affect any joint, but in humans the knee joint is problematic in 75% of OCD cases.

It was first medically described in 1887, and can affect people of any age. It's also found in other mammals; notably pigs, horses, cattle, cat, rats and dogs.

The etiology of osteochondrosis has been intensively researched; however, these efforts have been hampered by confusion regarding the definition of the disease and a lack of understanding of the pathogenesis, particularly regarding the formation of primary lesions.

Source : Vet Pathol 44:429–448 (archived)

It's thought to be linked to problems with blood flow around the joints, and is known to be affected by repetitive physical trauma, as well as by hereditary, endocrine and dietary factors. But the full pathological pathways of this complex condition are unknown.

Note : Osteochondritis dissecans is sometimes abbreviated to OCD, but has no links with Obsessive-Compulsive disorderplugin-autotooltip__plain plugin-autotooltip_bigObsessive-Compulsive disorder

Obsessive–compulsive disorder (OCD) is a mental condition in which a person feels the need to perform certain routines repeatedly (called "compulsions"), or has certain thoughts repeatedly (called "obsessions"). The sufferer is unable to control either the thoughts or activities for more than a short period of time..also known as OCD.