OCD is found in all large breeds that experience rapid growth, and is therefore sometimes (until now not often) seen in the Leonberger.
OCD is a condition where an area of cartilage dies and falls into the associated joint.
 It sometimes revives and grows to form a loose lump called a "joint mouse."
This rubs on the joint, causing swelling, pain and limping. It is treatable with surgery. There are a variety of causes for the condition.
Some national breed clubs advise the dogs to be x-rayed before breeding.