The term elbow dysplasia refers to a group of pathologic processes that occur in the elbow joint of primarily large breed dogs that cause elbow arthritis. The diseases include fragmented medial coronoid process, ununited anconeal process, osteochondritis dessecans of the distal humerus and joint incongruity. The end stage of all these diseases is the same - elbow arthritis. Recent evidence supports a genetic component to the disease but environmental factors also influence development such as rate of growth, nutrition and activity level. Breeds commonly affected include Bernese Mountain dogs, German Shepherds, Rottweilers, Newfoundlands, Saint Bernards, Mastiffs, Springer Spaniels, Australian Shepherds, Chows, Shar-peis and Labradors.

Clinical signs usually begin at 5-7 months and progress with age. Signs include forelimb lameness that worsens after exercise, stiffness after rest or exercise and shifting weight to the opposite limb when sitting or standing. Severity can vary from mild to severe. Evaluation includes gait analysis, orthopedic exam and radiographs of one or both elbows.

Fragmented medial coronoid process (FCP) is the most commonly seen component of elbow dysplasia. The elbow is a complex joint because it is composed of three bones and is responsible for flexion, extension and rotation of the distal forelimb. The elbow is composed of the humerus, radius and ulna bones. Normally the radius bears 80 % of the weight in the forelimb and the ulna is mainly a stabilizing support structure. The proximal ulna is made of the lunar notch, anconeal process proximally and medial and lateral coronoid processes at the distal end of the notch. In a normal elbow the radial head and medial coronoid are at the same level articulating with the humerus with the radial head bearing the majority of the weight. If during development of the elbow there is a disparity in the length of the radius compared to the ulna then a step defect develops between the radial head and the medial coronoid process. This places increased pressure on the coronoid process and leads to fissuring of the bone and fragmentation. Weight bearing becomes painful due to instability of the bone or the presence of a free fragment (pebble in the shoe). The cartilage of the humerus that articulates with the coronoid will often develop an abnormal wear pattern known as a kissing lesion.

The current treatment for FCP is arthroscopic removal of the fragment with or without an ulnar ostectomy to treat joint incongruity. Through 2 small incisions (~1cm) we can insert a small camera and light source into the elbow joint to explore the joint under magnification. Once the FCP is located it is removed from the joint and the remaining bone is shaved away to level the coronoid with the radial head. Joint incongruity can be improved by cutting a small piece of the ulna out to shorten the bone and relieve pressure on the coronoid area. Most dogs are released the day after surgery with very little residual lameness from the surgery itself due to the minimally invasive nature of arthroscopy. They are restricted to leash walks for a few weeks following surgery. In general dogs are more comfortable following surgery but most continue to develop some degree of elbow arthritis in the future which requires medical therapy. These dogs function well as pets but are generally unable to perform as working or sporting dogs.

Osteochondritis Dissecans (OCD) of the distal humerus is a less often seen component of elbow dysplasia. The distal humerus, like all synovial joints is covered in articular or hyaline cartilage. Normally as bones develop the ends of the bones lengthen as cartilage develops into bone (endochondral ossification). During development for an unknown reason (theories include genetics, overnutrition, trauma, or ischemia) a portion of the cartilage does not develop into bone and the cartilage becomes thicker and thicker. As cartilage receives nutrition from the joint fluid and underlying bone, that thickened cartilage becomes unhealthy and can fissure away from the bone forming a cartilage flap. The unstable flap causes pain upon weight bearing and can break free into the joint (joint mouse). The end result is arthritis.

Diagnosis is based on the presence of a defect in the distal humerus on radiographs or the visualization of a lesion during arthroscopy. Treatment is arthroscopic removal of the OCD flap and curettage of the underlying bone. The defect will fill in with fibrocartilage rather than articular cartilage. These dogs are generally more comfortable after surgery but long term prognosis depends on the amount of arthritis already present in the joint.

Ununited Anconeal Process (UAP) is another component of elbow dysplasia that occurs predominantly in German Shepherds but can occur in other large breeds. The anconeal process is located at the caudal aspect of the lunar notch of the ulna. It articulates with the intercondylar fossa of the humerus. This process develops separately from the ulna and normally fuses to the ulna by 4-5 months of age. The cause of the failure to fuse is not clear but is likely related to increased pressure on the AP during growth because of incongruity in the elbow joint. If the radius is slightly longer than the ulna, the humeral condyle is pushed proximally and the anconeal process bears a shearing force that prevents fusion. The anconeal process may be free in the joint or may have a fibrous but unstable connection to the ulna.

Diagnosis is based on the presence of a non fused anconeal process on elbow radiographs in a dog older than 5 months. Treatment options include removal of the process, fixation of the process to the ulna with a bone screw, cutting the ulna to relieve pressure on the process or some combination of the above. As with FCP and OCD of the elbow, surgery is likely to limit development of degenerative arthritis in the joint but a return to normal function is unlikely.