CANINE GENETICS

"Legg-Perthes" is a disintegration of the top of the rear leg bone(s), usually found in smaller dogs as opposed to hip dysplasia in large breeds but it is equally as painful.

LEGG-CALVÉ-PERTHES DISEASE

Fred Lanting © TheDogPlace.org

A disorder sometimes mistaken for hip dysplasia is Legg-Calvé-Perthes disease, perhaps more frequently referred to by the dog fancier as “Legg-Perthes.” This is an aseptic (not infected), developmental necrosis (dying of tissue) of the femoral head and neck, found almost entirely in toy or other small breeds. On radiographs, it often looks as if the bone is “rotting away”, and lameness is the major or only symptom.

It has a history in human medicine, too. In fact, that's where it was first discovered in 1910 by three researchers working independently. Legg, Calvé, and Perthes each saw a flattening of the femoral head (coxa plana) in affected youngsters and thought that trauma was at the heart of its etiology.

Schnelle in the 1930s first saw the disorder in the canine in Wirehaired Fox Terriers, and Moltzen-Nielsen in Germany about the same time saw it mostly in the Wires but also in a few other breeds Since then, puppies of many other small, toy, and miniature breeds between 3 and 10 months of age have been affected.

Symptoms And Diagnosis Of Legg-Perthes

Radiographic (“X-ray”) signs of Legg-Perthes are usually gross and the course and outcome discouraging, since many cases are not referred to the vet or the specialist for diagnosis until the dog has been limping for a long time or the disease has progressed to the point that it becomes a more real problem to the owner. These small dogs put so little weight on their tiny hip joints that they almost can compensate for discomfort by “walking on their forelimbs instead of their four limbs”. Many are “couch potatoes” or spend much time being carried, but even then, picking up an affected dog in a certain manner can put more pressure on the joint than does normal locomotion, so pain at that time is often the stimulus to do something about it. Owners have reported “incredible pain” and constant, progressive discomfort, inability to stay long in any one position, and bone lysis (loss through a process akin to dissolving or consuming) at other areas in the limb distal to the hip (further away, the opposite of proximal).

The earliest radiographic signs, should you look for them before they change, include an increased radiodensity (opacity as seen on the radiograph) in the lateral part of the epiphysis of the femoral header Lateral means the part away from the mid-line or medial; the “outside”. Resorption of necrotic (dying, rotting or decomposing) trabecular bone cells is next accompanied by a lysis (dissolving or being consumed) of bone. These are replacement attempts by the body, similar to the attempt to replace bone that takes place during HD remodeling; eventually there is fracture or collapse, like a frame house riddled by termites. As HD may or may not be concurrent, the congruity of the ball-and-socket coxofemoral joint might still be maintained until collapse. See pictures at the end of this article.

Cause Of Legg Perthes Disease

The most probable cause is a genetic weakness that allows abnormal or inadequate blood supply to the ossifying epiphyses. Those are the ends or caps of long bones that are changing from cartilage in the embryo to bone in the adult. Depending upon breed and particular bone portion, ossification is usually complete by 12 months of age. Compression/pinching of the blood vessels in that area leads to the necrosis (death) of cartilage and bone tissue. One unproven idea was that some of these little dogs have excess and premature levels of androgen and estrogen hormones that influence this process.

Various Treatments For Hip Dysplasia or Legg Perthes Disease

Various treatments have been suggested but the usual one is excision (surgical removal) of the femoral head and neck, again with a similarity to one of the HD operations performed on dogs.

Conservative treatment (as opposed to “heroic measures” such as surgery) has been suggested for those unilaterally limping dogs (lame on only one side and supported well by the other limb) with good congruity and no collapse or deterioration. The dog's worse limb is put into an Ehmer sling for a time, perhaps as much as a couple of months, then the dog is kept in a crate to minimize activity for another few weeks perhaps, during which time the dog is periodically radiographed. If this approach is successful, the resorbed bone is replaced in a normal manner and radiopacity returns, indicating normal bone cells and regained strength. In such cases, aseptic necrosis is halted and then reversed by keeping the dog's weight off the limb. Lameness has been reported to cease in perhaps a quarter of dogs treated conservatively, but much of this estimate depends on owners' reports rather than always being followed up by veterinary examination.

A syndicated column called “To Your Good Health” in the Clarksburg (WV) Telegram of June 30, 1994 included a brief discussion by Paul Donohue, M.D., responding to a reader's request for advice. Her 8-year old child had recently been diagnosed with Legg-Calvé-Perthes disease and she had seen no improvement after 3 months in a brace.

By the way, human infants with HD are put into slings or casts which keep the legs spread apart until the joint begins to strengthen; did you know that people get HD, too? Anyway, Dr. Donohue told her that the Legg-Calvé-Perthes disorder involved a cutting off of the blood supply to the epiphysis (top part of the femur) and that it might take more than a year for the brace to rest the hip enough so that restoration of blood supply can help restore bone there. If unsuccessful after that long a wait, surgery may be needed, he advised. So you see, your dogs are not the only ones at risk for this problem.

Some of us may not have heard of any of our specific breeds diagnosed with Legg-Perthes yet, but that may be because, to many veterinarians, the radiograph looks like hip dysplasia, and it is not sent in to experts for diagnosis and recording of data. On the other hand, I have seen many HD cases mistakenly diagnosed as LCP. If you come across a case of Legg-Perthes in your breed, please report it (accurately, with name and address of person diagnosing it) to the health committee and/or magazine editor of your club.

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