Structure and Function of the Skeleton in Cats
Mucopolysaccharidosis VI is a genetic defect in the metabolism of connective tissue that causes secondary changes in bone. It usually affects Siamese cats and causes them to have a broad, flat face. They are often lame and may have trouble walking.
What Are Some Diseases of the Skeleton?
Congenital diseases. Certain congenital and developmental bone diseases occur in the cat, but are usually uncommon. Examples include the following:
Osteodystrophy is a rare inherited disorder of Scottish fold cats. Bony deformities develop in the toes, tail and bones of the wrist and ankle.
Multiple cartilaginous exostoses are abnormal proliferations of bone in certain areas, such as the long bones, ribs and vertebrae. They occur in young adult cats and may cause lameness and discomfort.
Osteomyelitis. Osteomyelitis is an inflammation of bone that is usually caused by a bacterial infection. Infections of the bone may also arise with certain fungal infections and in the presence of bone implants, such as bone plates and pins.
Nutritional disorders. Disorders that cause abnormalities in the circulating levels of calcium, phosphorous and certain vitamins can adversely affect bones. Examples include:
Rickets is severe weakening of the bone due to calcium deficiency or imbalances in the diet. It arises most often in young cats fed an all meat diet. In kittens it causes lameness, deformities and fractures of the bone.
Chronic kidney failure affects bone by altering the amount of phosphorus and vitamin D in the body. The bones become soft, thin and weak.
A deficiency in vitamin D in the diet, or low conversion of vitamin D in the body from a lack of exposure to sunlight, can seriously affect the development of bone. Lameness, bony deformities and fractures may occur.
Excessive vitamin A in the diet of cats causes deformities to develop in bones. Excessive levels of this vitamin are most likely to occur when the cat is fed a diet that contains predominantly liver and milk. Lameness, weakness, and reluctance to move are common signs.
Trauma. Trauma to bones is perhaps the most common skeletal disorder encountered in the cat, especially outdoor cats. Cats that are injured through falls, automobile accidents and fights can experience a variety of bony fractures and dislocations.
Cancer. Neoplasia or cancer of bone is uncommon in the cat. Tumors may arise within the tissues of the bone or may invade bones from the surrounding soft tissues. Cats are most prone to cancers of the bone marrow, such as lymphosarcoma. Cancers of cortical and cancellous bone are more rare in the cat.
What Types of Diagnostic Tests Are Used to Evaluate the Skeleton?
Physical examination and palpation of bones. The initial evaluation of the skeleton involves a thorough examination, with palpation of the bones and joints. The animal may be observed in the examination room for signs of lameness and abnormalities in gait.
Radiography. Cortical and cancellous bone, and some forms of cartilage show up very well on plain x-rays. For this reason, plain x-rays are an important tool in evaluating the skeleton. Some x-rays may be taken with the animal awake and sedated, while other x-rays may require that the animal be completely anesthetized.
Routine laboratory tests. A complete blood count and biochemistry profile may be taken to look for signs of infection and abnormalities in circulating levels of calcium and phosphorus. These tests are also helpful to detect other disorders that may affect the bones, such as kidney disease, anemia and leukemia.
Special laboratory tests. If an infection of bone is suspected, then samples may be collected for bacterial and fungal cultures. Serologic tests for fungal diseases may also be submitted. Occasionally the levels of vitamin D, vitamin A and parathyroid hormones are measured in the blood.
Bone biopsy. Identification of the type of bone disease present may require a bone biopsy. This is especially true in cases of congenital and developmental bone diseases, osteomyelitis and tumors of bone.
Bone marrow biopsy. Biopsy of the bone marrow cavity is done via passage of a needle into the red bone marrow of one or more bones and aspiration of a sample of the bone marrow. The bone marrow sample is then sent to a veterinary pathologist for microscopic examination.
Advanced imaging techniques. CT and MRI are very useful in examining bones and their adjacent soft tissues, such as cartilage, ligaments, and tendons. Radioisotope bone scans are also helpful in some cases. To arrange these tests often requires that your cat be referred to a veterinary orthopedic specialist or a veterinary radiologist.
Chest x-rays. Chest x-rays may be taken to look for evidence of infection or tumors that have spread to the lungs and to identify abnormalities in the ribs or vertebrae of the chest.