Osteochondritis of the elbow (elbow dysplasia) is not a simple condition to understand nor easy to explain. Osteochondritis is a term used to describe a disorder in growing bone. Elbow dysplasia is really a syndrome in which one or more of the following conditions are present: fragmentation of the coronoid process, ununited anconeal process and osteochondritis dissecans.
Normal bone growth
Many bones in a newborn puppy are not just one piece of bone, but several different pieces of bone with cartilage in-between. This is especially true of long bones of the limbs. As the puppy grows the cartilage changes into bone and the several pieces of a bone fuse together forming one entire bone. For instance, the ulna, a bone in the forearm starts out as 4 pieces of bone that eventually fuse into one.
In osteochondritis, the cartilage between the bony areas fails to turn into bone and often becomes thickened. The cause of osteochondritis may include genetic factors, trauma and nutrition. The signs of this abnormal bone growth usually develop between 6 and 9 months of age, and generally appear as lameness. Osteochondritis is more common in rapidly growing, large breed puppies.
Normal elbow anatomy
In the healthy dog, the elbow joint itself is fairly complicated. The elbow of the dog corresponds to ours anatomically but rests relatively closer to the chest wall then it does in man. The bones that form the joint are the humerus from above the ulna and radius from below. The lower end of the humerus has two rounded knobs (the lateral and medial condyles) on it with a hole between that extends completely through the bone (the supratrochlear foramen). The radius and ulna bones basically act as one bone as they are held tightly together by several ligaments. They move together at all times. The upper end of the ulna has a hook-like process that fits neatly into the supratrochlear foramen of the humerus and a curved ridge called the trochlear notch that fits against and rotates between the medial and lateral condyles. At the base of this notch and on either side of it are the medial and lateral coronoid processes that the condyles of the humerus rest on, therefore supporting the weight of the dog. Finally there is the upper end of the radius that also lies between the coronoid processes of the ulna and it also helps support the weight of the animal as it is transmitted down through the humerus. In the normal dog, all of these surfaces that rub or articulate against each other are perfectly smooth. They are constantly lubricated by the joint fluid that is contained by the capsule that surrounds the joint.
Changes in anatomy resulting in elbow dysplasia
As joints go, the elbow is a fairly complicated one and anything that alters any of the bones or their articular surfaces will affect the ability of the animal to use the leg correctly. There are three common areas of osteochondritis in the elbow. "Elbow dysplasia" is a term used to describe a condition in which one or more of these three areas are affected Actually, most cases will have at least two if not three occurring at the same time. A case may start out with just one anomaly, but as time passes the other changes may occur as a result of the first, or develop independently from genetic programming. There is some controversy today as to which of these changes is most important or if a particular one is an initiator of the syndrome.
Fragmentation of the coronoid process (FCP):Most researchers and clinicians today believe that the first and often initiating change or degeneration in elbow dysplasia is "fragmentation of the medial coronoid process". Remember that the coronoid processes of the ulna articulate with the condyles of the humerus and also bear much of the weight of the dog. Fragmentation means that the bone in this area of the ulna starts breaking up or degenerating, exposing the underlying tissues of the bone. This occurs very early in the life of the dog, often times before six months of age. We see it mostly in the larger breeds such as the German Shepherd, Golden Retriever, Rottweiler, Doberman and the giant breeds. However, as we become better at diagnosing this disorder, it is being recorded in more and more breeds even some of the smaller ones such as the Springer Spaniel, Cocker Spaniel and German Shorthair. It is thought to have strong genetic transmission as it has been found to be passed from generation to generation in certain lines of several breeds.
Ununited anconeal process (UAP): The second lesion associated with elbow dysplasia is "ununited anconeal process". Generally by 20-24 weeks of age the anconeal process should have fused with the ulna. In UAP, the hook, or anconeal process, never attaches correctly to the rest of the ulna as the puppy is developing, but rather floats loose. It is held fairly close to where it should be by ligaments between it and other portions of the bone but it is not solid enough to remain exactly where it should. This leads to joint instability, preventing the humerus and ulna from interacting correctly. Additionally, the loose anconeal process is often caught abnormally between the ends of the ulna and humerus thus irritating and bruising the articular surfaces. Ununited anconeal is commonly found by itself with the elbow dysplasia syndrome. However, when it is discovered in the larger breeds listed above, it is almost always part of the elbow dysplasia syndrome and most of these dogs will also have the fragmentation disorder of the medial coronoid process.
Osteochondritis dissecans (OCD):The last of the three elbow disorders that make up dysplasia is osteochondritis dissecans of the medial condyle of the humerus. Osteochondritis dissecans is also a common problem of the shoulder joint in young, rapidly growing larger breeds. Most authorities believe that osteochondritis of the medial condyle of the humerus this may be secondary or caused by the fragmentation of the bone of the medial coronoid process on the ulna. These two affected areas come together and rest on each other at this site and the first lesion may therefore precipitate the other. In all joints where different bones come together and articulate against each other, the surface of the bone is covered with cartilage. It acts as a cushion, protecting the underlying bone from irritation or damage as the two bones come together. With OCD, a portion of that cartilage loosens from the underlying bone. It may break loose and float free in the joint or remain partially attached to the bone like a flap. In either case this is an extremely painful situation as the lower bony layers are exposed to trauma and the joint fluid.
Symptoms of osteochondritis of the elbow
Patients with elbow dysplasia will usually display an obvious limp, may hold the leg out from the body while walking, or even attempt to carry the front leg completely, putting no weight on it at all. Signs may be noted as early as four months of age. Many affected animals will go through a period between six and about twelve months of age, during which the clinical signs will be the worst. After this period, most will show some signs occasionally but they will not be as severe. As these dogs continue to mature, there will probably be permanent arthritic changes occurring in the joint. This will cause many obvious problems and it may become necessary to utilize oral or injectable medications to make the animal more comfortable. Elbow dysplasia is therefore a life long problem for the affected animals. Some of these patients can be helped with surgery. In some, surgery can even eliminate the problem totally.
Diagnosis of osteochondritis of the elbow
As stated, most affected dogs will have two, and most probably all three of the elbow dysplasia disorders present at the same time. Additionally, a majority of these animals will have both their right and left elbows involved. The symptoms of front leg lameness and pain in the elbow lead us to think about elbow dysplasia as a diagnosis. However, there are other conditions that can affect the front leg of a young dog that will mimic the signs of elbow dysplasia very closely. Therefore, it is necessary to take radiographs (x-rays) of the elbow(s) to verify the diagnosis.
Of the above three, an ununited anconeal process is by far and away the easiest to show with x-rays. However, the fragmentation of the medial coronoid process and the osteochondritis can be very difficult. The dog generally needs to be heavily sedated or anesthetized to obtain good x-rays, since the limb needs to be manipulated and positioned in ways that are often painful. High quality radiographs are a must - it may be necessary to go to a veterinary teaching hospital or referral center where they have the most sophisticated x-ray equipment. In addition, it is usually necessary to have the radiographs sent to an expert veterinary radiologist who can discern the very minor changes that may appear in a dog with osteochondritis. In some cases, the diagnosis of FCP can only be made at the time of exploratory surgery.
Treatment of osteochondritis of the elbow
Treatment of osteochondritis of the elbow varies with what distinct abnormalities are present. Fragmented coronoid process and OCD are often treated medically, without surgery. The young dog is placed on a regular low-impact exercise program (swimming is often preferred). Depending on the severity of the condition however, surgery may be performed to remove the fragmented process or cartilage flap.
United anconeal process is usually treated with surgery in which the ununited process is removed. In some instances, small pins or screws may be used to join the process with the rest of the ulnar bone.
Usually after the dog is 12 to 18 months of age the lameness will have become less severe and some dogs can function very well. The long-term prognosis (outlook) however is guarded. Usually degenerative joint disease (arthritis) will occur as the animal ages, regardless of the type of treatment.
Race Foster, DVM and Marty Smith, DVM