I've heard this disease of the canine hip go by a variety of names: "Legg-Calve-Perthes disease," "avascular necrosis of the femoral head" and "aseptic necrosis of the femoral head."
Toy breeds and terriers are most commonly affected, but most any small breed dog of a young age (usually under 12 months) can inherit this disease.
To understand this disease, imagine the ball end of the ball and socket hip joint (the ball portion is made up of the "head" of the leg's femur bone while the socket is the pelvis's purview). When the femoral head (the ball) lacks blood supply due to either trauma or a genetic predisposition to poor circulation here (by far the most common cause), it starts to die. Dying bone can lead to extreme pain for these dogs, as does the collapse of the cartilage that makes up the joint. Because the resulting change in the shape of the bone leads to a poor fit in this ball and socket joint, arthritis (and more pain) inevitably ensues.
Symptoms and Identification
Dogs affected with Legg-Perthes will almost always limp. Some may cry out in pain when the leg is used. Since most dogs stoically refuse to display pain, simple lameness and loss of muscle mass over the affected limb is the most typical sign. Nonetheless, early identification is possible by pressing on the affected area and eliciting a pain response (veterinarians will usually check for this in young, small breed dogs).
X-rays are the most common way we diagnose this disease. Clear evidence may be obtained by observing the lower bone density in the head of the femur (in its earliest stages). As the disease progresses, a flattening of the ball of the femoral head becomes evident. Eventually, severe arthritis serves as the most obvious radiographic sign.
Toy, miniature and small breed dogs are the typical Legg-Perthes patients. The Orthopedic Foundation for America lists the most commonly affected breeds:
Another study quantified the risk of Legg-Calves-Perthes in various dog breeds. Some small-breed dogs such as the Pug and the West Highland White Terrier have a very high risk of Legg-Perthes disease relative to a mixed breed dog.
Surgery is by far the most effective means of treatment in these affected dogs. The procedure typically employed is the FHO (femoral head osteotomy). The idea is to remove the offending bit of bone so the pain is eliminated and the area's adjacent muscles and resulting scar tissue can serve as a "false joint." This works especially well in small dogs because their weight-bearing needs are not so pronounced as in larger ones. In fact, most post-surgical cases begin bearing weight on the limb within 1-2 weeks.
Pain relief can be had through dog-specific pain medication. NSAIDS (aspirin-like drugs) are now available in safer, dog-only preparations. But pain relief alone is rarely recommended for these sufferers. Definitive treatment through surgery is almost invariably the ideal approach.
Though potentially expensive, the FHO is one orthopedic procedure that is relatively easily accomplished. A board-certified veterinary surgeon is always the right choice for best results, but many general practitioners can competently accomplish this surgery at the lower range of the average price: Expect $1,000 to $3,000 depending on your geographic locale and your surgeon's experience/education.
The mainstay of prevention for this genetic disease is the result of responsible breeding practices. Breeders who keep track of their breeding dogs' offspring will be advised of this trait by their owners. But more proactive measures may be even more effective. This involves identifying dogs who may have a lower-grade form of this disease before they bear offspring.
To this end, the Orthopedic Foundation for Animals offers a program to evaluate dogs for Legg-Perthes as early as one year of age. In this case, X-rays are used to grade these dogs as Legg-Perthes-free or not.
J Am Anim Hosp Assoc 2002;38:467-477 Breed Susceptibility for Developmental Orthopedic Diseases in Dogs.