This condition affects the subchondral bone of the palmar/plantar aspects of the distal metacarpal/metatarsal condyles and is a common cause of performance-limiting lameness in Standardbred and Thoroughbred racehorses. It is thought to be a stress remodeling response to high-level activity in young racehorses and is associated with lameness referable to the fetlock region. Typically, the lameness improves with a block of the palmar/plantar metacarpal/metatarsal nerves proximal to the fetlock. Intra-articular analgesia of the fetlock joint can have varying results and is less reliable to improve lameness. Radiographic signs may be minimal, and the changes are identified earliest using nuclear scintigraphy, CT, or MRI. Treatment consists of controlled exercise.