Revised December 2011.

A disorder sometimes easily mistaken for hip dysplasia is Legg Calvé Perthes disease, perhaps more frequently referred to by the dog fancier as Legg Perthes. This is an avascular (pertaining to inadequate blood supply), aseptic (not infected), developmental osteonecrosis (dying of bone tissue) of the femoral head and neck, found almost entirely in toy or other small breeds. It can be described as a localized tissue anemia. On radiographs, it often looks as if the bone is rotting away, and lameness with variable pain 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 (U.S.), Calvé (France) and Perthes (Germany) saw a flattening of the femoral head (coxa plana) in affected youngsters and all first thought that trauma was at the heart of its etiology. They determined that this ischemic osteonecrosis of the femur in children was differentiated from osteomyelitis. Phemister in 1930 found that it occurred also in adults. Schnelle, also in the 1930s but working with dogs, first saw the canine disorder 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, 3 to 10 month-old puppies of many other small, toy, and miniature breeds have been found to be affected.

Phemister concluded that it was an avascular phenomenon rather than an infection and he coined the term cavitation for its unique ability to hollow out bone. This is the same term used to describe a very different and occasional phenomenon when distracting joints during the PennHIP evaluation of laxity. Today LCPD (Legg Calvé Perthes disease) is confirmed to be a disease of ischemia and micro-infarctions of the marrow microcirculation and is known by several different names, including: ischemic osteonecrosis, avascular necrosis, corticosteroid induced osteonecrosis, dysbaric osteonecrosis (when seen in deep sea divers and tunnel diggers with caisson’s disease), and radiation osteonecrosis. Several local and systemic causative or etiologic factors (environmental and genetic) have been implicated. The following list was compiled in a study on a similar jawbone disorder in humans, known as neuralgia-induced cavitational osteonecrosis (NICO).

In 1920 G. V. Black described a progressive death of bone, cell by cell in human jawbones, differing from osteomyelitis and appearing to soften the bone, often hollowing out the cancerous portions of large areas of bony tissue or producing a soft intramedullary mass enclosing small particles of necrotic bone. He called this new disease chronic osteitis, noted its extensive bone destruction, and suggested that the lesion be opened freely, and every particle of softened bone removed until good sound bone forms all the walls of the cavity. If all necrotic bone is removed, generally, the case makes a good recovery.†Black’s Disease, ischemic osteonecrosis of the jaws, was apparently forgotten by the dental profession until the 1970s when a series of reports began to emerge describing an unusual osteomyelitis of the jaws in patients with chronic facial pain; different names were used, including most recently, NICO (neuralgia-inducing cavitational osteonecrosis). Dr. J. E. Bouquot, of the Maxillofacial Center in Morgantown, WV says that its features are seen in ischemic osteonecrosis in other bones, where it is predominantly an aseptic and painful phenomenon. See the paragraphs under CAUSE.


Radiographic (X ray) signs of Legg Perthes are usually gross and 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 normal locomotion, so pain at that time is often the stimulus to do something about it. Owners and vets 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 (further away, the opposite of proximal) to the hip.

Radiographic features in NICO (neuralgia-inducing cavitational osteonecrosis) include:

  1. Poorly demarcated radiolucency or “moth-eaten” appearance as seen on the radiograph,
  2. Irregular vertical trabeculae (a type of bone cell),
  3. A “cotton-wool or ground-glass” radiopacity, sometimes referred to as “ghost marrow,”
  4. Flecks and streaks radiating outward and giving rise to the term “eagle’s nest,”
  5. Soap bubble radiolucency, and more.

These are similar to those in LCPD. The earliest radiographic signs of LCPD, 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 head. 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.

Although NICO and facial neuralgias seem to be associated with more intense pain in the jaws than is experienced in cases of ischemia of many other bones, LCPD in toy breeds is also frequently very painful. The jaws are the only bones with large sensory nerves but there are enough nerves near the femoral head to produce the pain response to the toxins, mediators, and other biochemical products of the disease process. NICO is the second most common form of osteonecrotic disease, affecting more than 68,000 U.S. adults, seen from l6 years of age to as old as 94. As in Legg-Perthes, the disease may “smolder” for years before symptoms are stimulated. In the human jaw, this may be brought on by crown preparation or other dental work, and in dogs, the sudden appearance may result from a small trauma, such as bumping or jumping. In this way, it resembles osteoporosis that can be suddenly manifested by a fall or even a hard sneeze.


The most probable cause of LCPD 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, all normal 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.
More than 80% of NICO patients who failed to improve after their initial surgery had one or more coagulation disorders and other abnormalities, which can all be considered as having genetic origins, as the inability of the body to produce normal biochemical or immunological systems or actions is very often derived from defective genes (wrong chemicals or molecules).


Antibiotics are over-prescribed and administered in most disorders, whether by an M.D. or a veterinarian, but they may temporarily help to diminish the associated pain of NICO in cases with incidental or secondary infections. However, they are very unlikely to effect cure. The abnormal bony tissues in the human maxillary condition (NICO) usually must be surgically removed via decortication and curettage in the case of the jaw, and similarly, complete excision of the femoral head in LCPD. When the abnormal jawbone tissue is removed, the defect frequently heals and pain subsides or disappears. Since such diseases are often merely indicative of underlying systemic disorders, NICO has a strong tendency to recur and/or to develop in additional jawbone sites, often requiring multiple repetitions of the same surgical procedures. We have not seen anything similar in LCPD, probably because the disorders are sufficiently different in genetic and developmental aspects. Also, because in LCPD, we remove the entire portion of affected bone. Thirty percent of NICO’s human patients have recurrence of pain after jaw surgery, but there is nothing like that phenomenon in the canine hip disorder. Dogs that have femoral head excision make a good†recovery in nearly all cases. Not breed-worthy or super-athletic, but able to live a fairly normal life without pain. Various treatments have been suggested for human LCPD, but the usual one is excision (surgical removal) of the femoral head and neck, again with a similarity to the operation performed on dogs. Because humans are bipedal and carry all our (greater) weight through the hips, LCPD is of greater seriousness in humans than in small canine breeds. Fortunately, there are many reports of improvement in surgical operations and follow-up therapy in human hips, so we don’t have to face the same type of surgery that is best for our 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 an incidence, 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. In my opinion, surgery in dogs is almost demanded by the history of the disease in canines, and the results I have seen.

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 saw 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. So you see, your dogs aren’t the only ones at risk for this problem.

Some cases of Legg-Perthes go unreported or misdiagnosed. And some of us may not have heard of any of our specific breeds diagnosed with Legg-Perthes yet, because, to some veterinarians, the radiograph looks like hip dysplasia, and it is not sent in to OFA, or PennHIP for diagnosis and recording of data. I have seen a few cases misdiagnosed by local vets. If you come across a confirmed case of Legg Perthes in your non-toy breed, please report it (accurately, with name and address of person diagnosing it) to the health committee and/or magazine editor of your breed club.

Legg-Perthes is mostly found in Toy breeds. Legg-Perthes; showing necrotic femoral head Legg-Perthes necrosis with HD
Legg-Perthes is mostly
found in Toy breeds.
Legg-Perthes; showing
necrotic femoral head
Legg-Perthes necrosis
with HD