Canine Elbow Dysplasia
Elbow dysplasia is a term used to describe three different disease processes associated with the abnormal development of the elbow joint during growth. These processes are referred to as osteochondritis dissecans (OCD) of the medial humeral condyle, fragmented medial coronoid process (FCP), and ununited anconeal process (UAP). Although, the cause of elbow dysplasia is not fully understood, it is believed to have mainly genetic and environmental components (such as nutrition, exercise and growth rate).
Lameness is usually first noted around 5-6 months of age. A high incidence of occurrence has been noted in the Bernese Mountain Dog, German Shepherd, Rottweiler, Golden Retriever, and Labrador Retriever. Other breeds affected are the Newfoundland, Saint Bernard, Mastiff, Springer Spaniel, Australian Shepherd , Chow Chow, Shar-Pei, Shetland Sheepdog, and some Terrier breeds. Typically, both elbows are affected. However, unilateral elbow dysplasia is also recognized.
Fragmented Coronoid Process (FCP)
The most common form of elbow dysplasia is the fragmented medial coronoid process of the ulna. The elbow joint is made up of the radial head, responsible for 80% of weight bearing, the medial and lateral coronoid processes of the ulna,which bears the remaining 20%. From about 12 to 20 weeks of age the medial coronoid process undergoes ossification (turning cartilage in bone). FCP is the result of unequal growth rates of the radius and ulna, either individually or together. The joint space between the ulna and humerus is narrower than the joint space between the radius and humerus. The resulting uneven pressure on the medial coronoid process can develop cracks or fragments of the coronoid process. Left untreated these loose bits of bone will lead to pain during movement and arthritis.
Osteochondritis Dissecans (OCD)
Osteochrondrosis is a disruption of the cartilage development in large breed, rapidly growing dogs. As normal growth occurs the cartilage on the end of long bones (humerus, femur) must ossify/calcify or turn into bone. If calcification does not occur properly the cartilage becomes thickened and prevents joint fluid from reaching the other cartilage cells underneath. Without joint fluid these cells breakdown, causing cracks in the cartilage. This defective cartilage does not properly adhere to the mature bone that is already present, disrupting the normal gliding motion within the joint causing pain, lameness and eventually arthritis. During movement these cracks can loosen, forming flaps that can break off and float freely within the joint interfering with normal function. OCD of the elbow occurs on the medial condyle of the distal humerus. Clinical signs include intermittent lameness of one or both front legs and pain on manipulation of the elbow. Diagnosis is made through a physical exam and radiographic visualization of a defect on the humeral head. Once lameness is exhibited medical management is usually unsuccessful and most dogs require surgical removal of the cartilage flap.
Ununited Anconeal Process (UAP)
The anconeal process is a large piece of bone located at the growth plate at the top of the ulna. Normally, in growing dogs, this area will close or fuse between 16-24 weeks of age. An ununited anconeal process is the failure of the anconeus to fuse with the ulna. Instability within the joint leads to damage of the articular cartilage, lameness and arthritis of the elbow joint. Radiographs and a physical exam confirm the diagnosis. Surgical treatment is necessary to correct this condition.
Treatment
Treatment of elbow dysplasia is often a combination of medical and surgical management. The objectives of therapy are to relieve pain and maintain limb function as well as to keep the dog at as normal an activity level as possible. Surgical removal of the fragments is recommended before the development of severe arthritis occurs. While the choice of surgical technique (arthroscopy or traditional surgery) may vary, the results are similar. Unfortunately, this disease is progressive. Improvement is expected, but not normality. Medical therapy consists of weight control, moderate exercise, and antiinflammatory medications. Each case is evaluated for the degree of discomfort and arthritic change before a final treatment choice is selected.
All immature dogs with fragmentation of the coronoid, OCD, or an ununited anconeal process are surgical candidates. Recent studies suggest that, if an ununited anconeal process is detected early enough, an ulnar osteotomy (cutting the ulna) to relieve the stress may allow the process to unite in a normal fashion. Dogs with mild to moderate incongruity and minimal arthritis have the best prognosis. Even dogs with marked incongruity and large lesions benefit from surgery due to the decrease in pain. Dogs that have a combination of an ununited anconeal process and a fragmented coronoid have a poor prognosis.
Mature dogs with mild to moderate arthritis may also be considered for surgery. The objective is to slow the progression of the arthritic change.
References:
Wind, A.P., Elbow Dysplasia, Textbook of Small Animal Surgery
Debra Eldredge et al. Dog Owner's Home Veterinary Handbook
Orthopedic Foundation of Animals, http://www.offa.org/ed_types.html
Southern California Veterinary Specialty Hospital, http://petsurgery.com/elbowdysplasia.html
