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Bone Disorders in Cats

By Russell R. Hanson, DVM, DACVS, DACVECC, Professor of Equine Surgery, Department of Clinical Sciences, College of Veterinary Medicine, Auburn University ; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS, Professor and Director, Equine Department, Vetsuisse Faculty, University of Zürich ; Joseph Harari, MS, DVM, DACVS, Veterinary Surgeon, Veterinary Surgical Specialists, Spokane, WA ; Dale A. Moore, MS, DVM, MPVM, PhD, Associate Professor, Veterinary Medical Teaching and Research Center, University of California-Davis ; Sheldon Padgett, DVM, MS, DACVS

Also see professional content regarding osteopathies in small animals.

Bone diseases can be developmental, infectious, nutritional, or due to bone tumors, trauma, or unknown causes.

Developmental Bone Disorders

Developmental bone disorders appear in young animals when the bones do not grow correctly. They may be congenital (present at birth) or occur as the animal grows. Some of the more common causes include hereditary breed characteristics and dietary imbalances.

Osteochondromatosis (Multiple Exostoses)

Osteochondromatosis in young cats is an uncommon disorder characterized by multiple bony growths (known as osteochondromas) that arise from the surface of the long bones, vertebrae, and ribs. Animals may have no signs, and the diagnosis is confirmed by x-rays and physical examination of the growths. If lameness or pain develops, the masses can be surgically removed.

When osteochondromatosis occurs in older cats, it is believed to be caused by infection with the feline leukemia virus. The outlook in these cats is guarded.

Scottish Fold Osteodystrophy

This genetic condition of Scottish Fold cats is characterized by deformities of the bones of the spine (vertebrae), the meta-carpal and metatarsal bones, and the toes due to the development of bony growths. Affected cats are lame, and the bones in question are deformed and swollen. Treatment involves surgery to remove the bony growths. The outlook for recovery is guarded.

Osteomyelitis

Osteomyelitis is inflammation of the bone. The condition is most often associated with bacterial infection, although fungal diseases may also cause osteomyelitis. Factors contributing to infection include an inadequate blood supply to the bone, trauma, inflammation, bone damage, and the spread of an infectious agent through the bloodstream.

General signs of osteomyelitis include lameness and pain. Cats may have pus-filled sores at the wound site, fever, persistent lack of appetite, and depression. X‑rays, laboratory tests, and cultures to identify the source of infection can all help to confirm the diagnosis.

Longterm treatment with antibiotics, either injected or given by mouth, is the usual treatment. Additionally, flushing of the wound; removal of dead, damaged, or infected tissue; and removal of loose implants are recommended. Open or closed wound drainage and bone grafting can also be performed. In cases that persist or recur, limb amputation may be necessary. The outlook for recovery varies based on the severity of the infection and on how long it has remained untreated.

Nutritional Osteopathies

Reduced bone mass, bone deformities, bony growths, fractures, and loose teeth (rubber jaw) are all conditions that can result from nutritional disturbances (Disorders Associated with Calcium, Phosphorus, and Vitamin D in Dogs). These disturbances affect parathyroid hormone function and the metabolism of calcium and vitamins in the body. Specific causes may include an unbalanced diet resulting in an abnormally high level of parathyroid hormone (nutritional secondary hyperparathyroidism) or an abnormally high level of parathyroid hormone causing kidney damage (renal hyperparathyroidism), a deficiency of vitamin D, and excessive intake of vitamin A. Diagnosis is by blood tests, x‑rays, and identification of any underlying nutritional cause. Treatment is aimed at reversing the specific cause. Surgery is rarely needed.

Nutritional secondary hyperparathyroidism refers to a calcium deficiency in cats that are fed an all-meat diet, which is high in phosphates and low in calcium. Over time, this diet causes the parathyroid glands to secrete parathyroid hormone in an effort to restore the normal balance of minerals in the body. Unfortunately, calcium is extracted from the skeleton, leading to thinning and weakening of bones. The condition is seen most often in kittens but may also occur in older indoor cats on an all-meat diet. If treated early with calcium supplementation and a balanced diet, most cats have a good outlook. However, if severe bone deformities have occurred, the outlook is poor.

Hypervitaminosis A is a condition that develops in cats whose diets contain excessive amounts of vitamin A (for example, diets that include a large quantity of liver). Although it is primarily considered a disorder of the nervous system, problems usually start when bony outgrowths form on the vertebrae. These cause deformities, interfere with normal movement, and can lead to nerve damage. The bony outgrowths may also occur in the elbows and other joints of the legs. If treated early (with a balanced diet), some signs may be reversed; however, skeletal changes are generally irreversible and the outlook is guarded.

Bone Tumors

Skeletal tumors can be benign or malignant (cancerous). They can either begin in the bone or spread from other areas of the body. The most common primary bone tumor is osteosarcoma of the radius, humerus, femur, or tibia.

Signs include lameness, bone swelling, and fractures of the bone that are not caused by injury. X-rays of the affected limb can help confirm the diagnosis. Chest x‑rays should be performed to look for any original tumors that may be spreading to the bones. A bone biopsy is required to confirm the diagnosis.

The outlook for recovery is guarded. Untreated animals rarely live more than several months. The recommended treatments are limb amputation and chemotherapy. On average, cats live for 4 years after amputation.

Bone Fractures

Bone fractures are often caused by car accidents, firearms, fights, or falls. Fractures can involve single or multiple breaks in the bone and may be open (also called compound) or closed (see Figure: Fracture types can range from incomplete to compound.). Open fractures have a wound or break in the skin that is associated with the fracture; closed fractures are those that do not produce an open wound. The shape and severity of the fracture depends on the force and type of the trauma (See also Introduction to Emergencies)

Some common sites of fractures in cats include the thigh bone (femur), pelvis, jaws, and tail vertebrae. Signs of fracture are general and include lameness, pain, and swelling. X-rays are useful in determining the type and extent of the fracture. Treatment is based on the type of fracture, the cat’s age and health, the owner’s finances, and the surgeon’s technical expertise.

Incomplete fractures in young, healthy cats can be treated with external splints or casts. Other injuries are treated with bone plates, screws, orthopedic wires, or pins. Bone grafts are frequently used to help healing. Antibiotics are given to keep open fractures from becoming infected. Appropriate pain-relieving medication is used to reduce discomfort.

An incomplete fracture may be treated by a splint or cast.

The outlook for recovery is usually good, depending on the injury and the success of the surgery. Followup care includes x-rays and veterinary checkups to assess how the fracture is healing. Removal of internal implants like bone plates or screws is not necessary unless complications such as stress protection, infection, and soft-tissue irritation develop. Fractures of the vertebrae that lead to damage of the spinal cord have a guarded to poor outlook, although surgical repair is sometimes possible when the damage is not extensive.

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