Avascular necrosis of the femoral head is a disease of the hip joints of miniature and toy breeds of dogs, most often in Toy and Miniature Poodles, Yorkies, Lakeland terriers, west Highland white terriers, Jack Russell terriers and miniature pinchers just to name a few. It develops between 4 and 12 months of age. The blood supply to the neck of the femur is inadequate, leading to bone destruction in the hip joint, resulting in a roughened, irregular joint surface. Moving the rear legs causes pain, and the leg muscles weaken and shrink from insufficient use. Occasionally the limbs actually shorten. One or both rear legs may be affected. If only one leg is involved, the dog usually refuses to bear any weight on that limb.

Avascular necrosis is hereditary and probably results from breeding for small body size.

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