The elbow is a complex joint made up of three bones, the humerus in the upper arm and the radius and ulna in the lower forearm. The radius is the weight bearing bone in the forearm, and the top of the radius is flat and supports the humerus. The top of the ulna curves around the humerus to allow the normal movements of the elbow joint.
Elbow dysplasia is a generic term for arthritis of the elbow joint of which there are five major causes: fragmented medial coronoid process, osteochondritis dissecans (OCD), elbow incongruity, ununited anconeal process, and ununited medial epicondyle. Elbow dysplasia is a generic term for developmental abnormalities of the elbow that result in osteoarthritis of the elbow. There are 3 generally accepted forms of elbow dysplasia- not 5. Elbow incongruity, while being related to fragmented medial coronoid in some cases is generally considered to be due to asynchronous growth of the radius and ulna and is not considered by itself elbow dysplasia. Ununited medial humeral epicondyle is extra-articular and therefore no longer considered part of elbow dysplasia. It is more likely an avulsion injury that can happen in young dogs and not a developmental disease.
Whenever your pet is showing signs of a health issue, your first step is to contact your primary care veterinarian. If it is indicated that your pet may have elbow dysplasia or another serious condition, a veterinary specialist is available at an ExpertVet certified hospital.
Fragmented Medial Coronoid Process
The point at the bottom part of the ulna in the elbow that curves around the humerus is called the medial coronoid process. If there is even slight incongruity, or disparity, in the lengths of the radius and ulna during rapid growth, the coronoid process can become traumatized and fragmented. Not all dogs with fragmented coronoids have incongruity present. While incongruity is likely a cause of fragmented medial coronoid- there may be other causes as well that have yet to be defined.
In the case of fragmented medial coronoid process, a small piece of bone breaks off the ulna bone and floats around the inside of the joint. These fragments are almost never completely loose and therefore never float around. The fragment, when it breaks off, makes the humeroulnar articulation and the radioulnar articulation abnormal and potentially unstable and this leads to osteoarthritis of the joint- cartilage wearing and synovitis. This bone fragment irritates the lining of the joint and grinds off the cartilage of the adjacent humerus bone (similar to a pebble in your shoe that is irritating your foot).
The fragmented coronoid process (FCP) must be surgically removed to avoid severe, crippling arthritis. If your pet has exhibited symptoms of this condition, even with early diagnosis and surgery, irreversible damage to the cartilage has already occurred, which makes arthritis inevitable. The ultimate goal of the surgery is thus to minimize the severity of the arthritis that your pet will develop: The earlier surgery can be performed, the less arthritis may eventually develop. There is no evidence that removing the fragment will necessarily change the ultimate outcome of the joint. The hope is that early surgery will slow the progression of the osteoarthritis and make the dog more comfortable. Most, but not all, dogs clinically improve following arthroscopic surgery.