by Michele Steed, BVSc
1. Hip Dysplasia (HD)
Dysplasia derives from the Greek `dys’ which means abnormal and `plassein’ which means to form, thus abnormal formation of the hip joint. This abnormal formation causes ill or loose fitting hip joints, which in turn leads to the secondary development of joint disease or osteoarthrosis. The hip joints of pups that eventually develop HD are normal at birth, but the muscles and supporting tissues of the joint don’t develop as well as the skeleton leading to joint instability. The result is a shallower acetabulum (pelvis socket) and a flatter femoral head than normal.
The cause of HD is thought to be multifactorial with genetics, nutrition and environmental conditions all being involved. It is thought that at least 25% of the conditions frequency and severity is genetically controlled, therefore breeding from stock with normal hips (as indicated by hip score) can reduce the occurrence. It is known that nutrition during growth is important in hip development, especially for dogs with a strong genetic background for HD.
A high caloric intake and rapid growth makes HD more severe with an increased incidence and a faster onset, and a low caloric intake makes the disease less severe, with reduced incidence. Also it has been found that dogs with a greater pelvic muscle mass (such as Ridgebacks, Greyhounds) have more normal hip joints than those with a relatively smaller muscle mass. The disease is rare in dogs weighing less than 10 kg, although it does occur.
The signs of the disease are seen in 2 main groups of dog – the young ones, 4-12 months old and the older dogs with chronic disease. In the young ones the signs are caused by partial luxation (dislocation) of the hip joint and small fractures of the rim of the acetabulum. In the older dog the signs are caused by arthritis of the joint. They may have difficulty rising, walking, running, climbing stairs or be lame. They may have a “bunny-hopping” gait when running and show signs of pain or soreness in the hindlegs. In older dogs the shoulder muscles may increase in size in order to compensate from less use of the hindlegs. The disease is diagnosed by palpation of the hip joint for signs of looseness and pain while the dog is awake and under anaesthetic and by X-raying the hip joints under anaesthetic or heavy sedation. The Radiographs can be sent to a panel of Vets in NZ or Australia to be “scored”. This is an objective means of assessing the degree of HD in a dog and is used by breeders as a benchmark for deciding whether or not to breed from their stock. The dog is given a score for the degree of dysplasia for each hip and the maximum possible total is 106. The ideal total is less than 5 and less than 8 is good. The breed average for the RR in NZ (NZVA Scheme, as at 7 March 2001) is 4.9, which is very good. Careful attention to hip-scoring of breeding stock in NZ and only breeding from dogs with low scores has helped to keep the breed average down, however breeders should not become complacent.
OCD – Osteochondrosis dessicans
This is a disease characterized by abnormal cartilage development in affected joints. It is common in many species of animal including dogs, horses and pigs. There is a failure of the lower layers of cartilage of the joint surface or growth plate to mature into bone, resulting in thickened cartilage, which is prone to injury. Sometimes pieces of cartilage may break off into the joint, becoming what is known as “joint mice”. This disease occurs in rapidly growing domesticated animals, particularly in the medium to giant breeds of dog. The cause is related to a combination of genetics, body mass, growth rate, joint congruity, mineral imbalance (too much Calcium) and energy levels. The signs seen are lameness and swelling usually at the elbow, shoulder, hock or stifle. Corrective measures include adjusting the diet, reducing exercise or cage rest and surgery if necessary to remove cartilage fragments.
* Elbow Dysplasia This is a term used to describe the developmental anomalies `ununited anconeal process of the ulna’, `fragmented coronoid process of the ulna’ and `OCD of the medial humeral epicondyle of the elbow’. These are all presumed to be a result of osteochondrosis as above, but have these specific changes as common findings. The cause and signs seen are the same as for the disease OCD, but a screening system is now available with scores given between 0-3 (0=no evidence of dysplasia, 3=severe arthritis) per elbow based on a single radiograph (of each elbow). The dog should be at least 1 year old when the X-rays are taken for scoring and at least 2 years if the dog is to be accredited free of ED (if it has a score of 0 on each elbow). It has been shown that there is a strong hereditary basis for this disease in some breeds.