Avascular necrosis occurs when the bone that makes up the ball portion of the hip is damaged from lack of blood supply. The reasons this occurs are not clear. Since a higher incidence of this disorder is noted in several dog breeds, including terrier breeds, miniature pinscher, poodles and possibly schipperkes, it is assumed that there may be a genetic component to the problem. In Manchester terriers, the genetic component appears to be a strong influence and heritability is pretty high for this problem.
Most of the time the clinical signs of this disease occur in 4 to 11 month old dogs and usually consist of lameness of one leg only. Pain may be mild to very severe. Some dogs have mild forms of this condition and do not require medical care. In other dogs, the condition cause sufficient pain and deformity of the hip joint to require surgical intervention. The disorder can usually be confirmed with X-rays. Atrophy of the muscles of the affected leg is not uncommon. If this is severe it can slow the recovery period considerably and may make medical therapy less likely to work.
Treatment of this condition varies according to the severity of the signs seen. In mild cases, enforced rest may be sufficient to allow healing of the damaged areas to occur. In some cases, immobilization of the affected limb using an Ehmer sling may be beneficial to recovery. Many dogs have advanced cases of this disease by the time they are examined by a veterinarian and medical treatment is not likely to work. In these dogs, excision of the femoral head (ball portion of the hip joint) is often beneficial. Removal of this section of the bone diminishes painful bony contact in the hip joint. Recovery from this surgery can be slow with recovery periods of up to one year sometimes occurring before good use of the affected leg returns. If muscle atrophy is not present at the time of surgery the recovery time is usually much less. Pain relief and anti-inflammatory medications may be beneficial.
There is a stronger tendency to treat this as a medical condition prior to surgery right now. A general rule of thumb is to allow non-surgical therapy a month to show a beneficial response. If one is not seen, surgical repair should be considered more carefully.