I have been hearing a lot about elbow dysplasia recently. What exactly is elbow dysplasia? Are there symptoms I should be watching for in my young dog?
The term elbow dysplasia ("ED") is a general term that is used to describe a developmental degenerative disease of the elbow joint. There are in fact three different etiologies that can create a diagnosis of ED. These etiologies may occur individually or in combination with each other in any one dog. This disease has created considerable confusion and controversy not only on the part of dog owner, but with practicing veterinarians as well as researchers who are studying the problem. While our ability to diagnose ED has improved in recent years, there is still a great deal to be learned about its causes, prevention, and what constitutes appropriate treatment.
ED occurs predominantly in medium or larger breeds of dogs. The Orthopedic Foundation for Animals (OFA) maintains statistics in their elbow registry for many breeds. As of December 31, 1998, ED had been diagnosed by OFA in 87 breeds. Incidences range from 0% in Border Collies up to 47.8% in Chow Chows. The average incidence of the breeds for which at least 75 individuals have been evaluated is 11.11%. Male dogs are more likely to have ED then females, and 20-35% of dogs with ED have it in both elbows.
Dogs with ED may or may not be lame, therefore, using lameness to determine its presence or the breed worthiness of an animal is foolhardy. Dogs with clinical ED typically develop foreleg lameness between the ages of 5 and 12 months of age, however, in some cases the lameness may not be apparent until as late as 5-7 years of age. The lameness may be variable and periodic. Some dogs may demonstrate soreness after rest, improve slightly with activity, but then worsen with increased activity. There may be intervals with no lameness at all. Jumping and sharp fast turns usually exaggerate the lameness. Pain can be elicited by overextending the elbow, and there may be a slight to moderate swelling noticeable when carefully feeling the elbow joint. If both legs are meaningfully affected the lameness may be more difficult to detect. Careful observation would show slight rotation of the top of the paws outwardly, as well as a stiff or stilted movement of the forelegs. There may be a reluctance on the dogs part to land hard on the front legs (e.g. trotting, loping or landing jumps).
For the sake of simplicity the three etiologies resulting in ED will be discussed individually, but it is important to note that there can be considerable overlapping in their presence, their cause and effect. The magnitude of the overlapping has probably not been fully realized at this time.
The anconeal process is a small pyramid shaped piece of bone on the upper end of the ulna. In a young dog it is a piece of cartilage that gradually turns to bone and unites with the rest of the ulna at approximately 4 ½ - 5 months of age. If that union fails to take place we have an ununited anconeal process (UAP). The presence of UAP leads to degenerative joint disease as a result of a decrease in stability within the joint, and an increase in inflammation caused by the chip of bone being free within the joint.
Osteochondritis dessicans (OCD) can occur in many joints, but when it occurs in an elbow it most commonly is on the lower, inner aspect of the humurus (medial humural condyle). In essence OCD is a vertical fracture in the articular cartilage of the humurus, which can lead to a flap of cartilage within the joint. This flap leads to degeneration within the joint as a result of an inflammatory process.
The coronoid process is a small piece of bone on the ulna, which articulates with the humurus. Similar to the anconeal process it starts as cartilage, and gradually turns to bone as it unites with the rest of the ulna. Failure of that fusion to occur or chipping of the area after fusion has occurred, creates a fragmented coronoid process (FCP). Subsequent to FCP degenerative joint disease develops for the same reason as with UAP.
The exact causes of ED have been the subject of considerable controversy. A number of predisposing factors have been identified, and recently some new theories have gained support as probable explanations for the development of ED. The individual etiologies of ED most likely have multiple possible causes.
OCD has at least three possible causes. Heredity certainly plays a role, as we do see a tendency for this problem to occur in family lines, as well as in those breeds that grow rapidly. Trauma within the joint also is a factor, evidenced by the fact that areas commonly affected by OCD are those that typically experience high levels of biomechanical stress. Additionally, animals housed on hard surfaces are more likely statistically to have a higher incidence of OCD. A third cause is a lack of sufficient blood supply to the joint cartilage. The specific cause of this marginal blood supply is not currently understood.
Understanding of the causes of FCD and UAP has experienced a surge in recent years. In addition to the causes listed for OCD, recent research strongly suggest that two factors are playing a major role in the development of these two etiologies. A disparity in the growth rate between the radius and ulna, as well as an abnormal formation of the trochleor notch in the ulna, have been implicated in the development of ED. The elbow joint is a very complex joint that is created by the junction of three different bones. Normally these bones fit and function together with very close tolerances. If the growth rate of the bones is changed, or a structure does not form normally, the tolerances change, enhancing the possibility of damage within the joint. The damage created typically results in either FCP or UAP.
Understanding the symptoms and causes of ED is extremely important if informed decisions are to be made regarding diagnosis, treatment, and prevention of ED. These are the topics that will be covered in the next installment of this column.
Picture credits: Orthopedic Foundation for Animals and Gheorghe M. Constantinescu D.V. M.
Dr. Henry De Boer Jr. practices veterinary medicine at his Pioneer Valley Veterinary Hospital in western Massachusetts. An accomplished competitor in the sport of Schutzhund, his involvement with working dogs dates to the mid 1960's when he began training and handling hunting dogs. In 1984 he became involved with the sport of Schutzhund and has gradually risen to the level of national competitor. Known primarily as a motivational trainer, he also provides training assistance to others to help them achieve their training goals. His wide range of experience lends a unique understanding to the special veterinary problems of working canines and their handlers. Dr. De Boer provides specialized online veterinary services to working dogs and their owners on his innovative web site http://www.workingk-9vet.com Working K9 Veterinary Consultation Services.