This degenerative disease is known by a few other names, such as coxa plana, osteochondritis juvenilis, aseptic or avascular necrosis of the femoral head, Perthes Disease or simply Legg’s Disease. The condition is quite painful, as the disfigured joint becomes inflamed and leads to arthritis. It can happen to both male and female cats, usually within the first year of life. The joint will gradually worsen over several months until the limb can no longer support any weight.

The hip joint of a healthy cat is composed of a ball and socket joint. The socket is a part contained in the pelvis called an “acetabulum”, while the ball is made up of the femoral head (the top of the femur bone). Ligaments and cartilage keep the femoral head properly in place, and the smooth shape of the ball provides fluid limb movement to the cat. If the blood supply to this joint is cut off, the head of the femur begins to disintegrate. This occurrence is called ischemia and it leads to the death of the bone and of the surrounding cartilage. The joint is no longer able to function properly due to the misshapen femoral head, which leads to Legg-Calvé-Perthes Disease.

This issue is usually unilateral (one sided), however it can affect both legs, generally starting in one and spreading to the other. Symptoms will increase over time. Early diagnosis can improve the results of treatment. All symptoms to watch for include:

The exact cause of Legg-Calvé-Perthes Disease is not widely understood. What is known is that cats under a year of age seem to be most susceptible to the condition. All known causes are listed below.

Once you have arrived at your appointment with the veterinarian, be sure to provide your cat's full medical history to help with the diagnosis. The vet will perform a complete physical examination of the cat, possibly extending the leg to see if there is a response of pain. The vet may also note a clicking sound as the hip pops out of joint, or a grinding noise from cracked and deformed cartilage. Legg-Calvé-Perthes Disease will have to be differentiated from other hip issues, such as fractures, hip dysplasia and arthritis. 

Full blood work will need to be run including a complete blood count and a biochemical profile to assess the cat's overall health. Urinalysis will also be done to ensure the organs are functioning properly. An x-ray of the hip joint will be needed to show the condition of the hips. A widened space between the femoral head and the pelvic socket may be found, suggesting femoral head deterioration. Fragments of bone may also be present. Abnormal bone density or osteoarthritis may be noted. If the hip is causing the cat great pain, sedation throughout the examination may be required.

If the condition is found at its early stages, or if the case is very mild, the cat may not need surgery. Strict crate rest will be advised in this scenario, with the cat only being allowed out to eliminate waste. Painkillers are often required for the healing process. If this fails or if the condition is too severe, other treatments will be sought.

This is the most common procedure for treating Legg-Calvé-Perthes Disease. During this surgery, the femoral head and neck of the affected limb are removed. A false joint is then formed as fibrous and scar tissue will form around the femur during the healing process. This will recreate the ball of the joint. Only a board certified orthopedic surgeon should attempt this procedure, as leaving any fragments behind will cause health problems to develop in the cat.

Nonsteroidal antiinflammatory drugs (NSAIDS) or corticosteroids may be prescribed to slow bone degeneration in mild cases, especially if an improper hormonal response is causing the issue. 

In both surgical and nonsurgical treatments, physiotherapy is a key part of restoring movement to the affected hip. Ultrasound treatments, laser therapy, hydrotherapy, shockwave therapy, massage therapy, acupuncture and electrical stimulation can all have a positive impact on the cat's recovery.

If your cat has undergone surgery, be sure to follow all postoperative care guidelines from the surgeon. Check the incision site daily to ensure there are no signs of infection developing. Bandages may need to be changed regularly. All activity should be limited while the hip joint heals. Your cat may need to be encouraged to eat after surgery. Warming up aromatic foods can make eating more appealing to your healing feline. Physiotherapy sessions will need to be attended. 

Monthly x-rays will be needed to determine how the hip is healing, and if it is capable of handling weight. The prognosis for cats with Legg-Calvé-Perthes Disease is excellent if they have recovered from surgery. Normal movement and play can often be resumed within months. If you notice any limping or pain in the affected limb, the surgery may have been performed incorrectly and further surgeries or medical therapies may be needed. Supplements that decrease inflammation in the body can be very helpful to a cat who has suffered Legg-Calvé-Perthes Disease. The cat may also be prescribed a diet for weight loss to limit the amount of weight that the hip is burdened with. Cats who have had Legg-Calvé-Perthes Disease should not be bred.