The Musculoskeletal System

A healthy cats uniquely stunning physical traits – its power, agility and lightning-fast responses to external stimuli – are essentially attributable to its musculoskeletal system. In one way or another, this system is in operation 24 hours a day, whether a cat is hunting prey, escaping from predators, eating, drinking, napping, toying intently with a ball of yarn or digging its claws into your favorite piece of furniture.

Unfortunately, cats are subject to a veritable host of disorders that can impair or totally impede the smooth operations of this impressively complex array of bones, muscles, tendons, ligaments and other tissues. Owners should be aware of the systems basic structure, various functions, and signs of its impairment, such as a noticeably altered gait, an apparent weakness in the joints, and the inability to chew and swallow food easily. As is the case with other feline disorders, says Christine Bellezza, DVM, a consultant at Cornell Universitys College of Veterinary Medicines Feline Health Center, early recognition and diagnosis of a cats musculoskeletal disorder are likely to improve the chances for its successful treatment.

The musculoskeletal system provides shape and support to a cats entire body, from the tip of its nose to the tip of its tail. The feline skeleton – comprising 244 individual bones – supports 500 or so muscles and other soft tissues that effect movement and other bodily processes. These processes are enabled by the instantaneous transmission of electrical signals, largely via the peripheral nervous system, which is made up of nerves that extend, via the spinal cord, from a cats brain throughout its entire body.

Many of this nerve networks functions – such as the movement of an animals leg or the opening and closing of its mouth – are under conscious, voluntary control. Other functions are involuntary, such as those that control the muscles in the digestive tract and the heart. Some feline musculoskeletal problems may therefore stem from what are regarded as essentially neuromuscular disorders.

Among all feline musculoskeletal disorders, the most commonly seen by far are those associated with either arthritic disease or traumatic injury.

• Arthritis comes in a variety of forms, explains Dr. Bellezza, and can be precipitated by wide-ranging factors, including genetically acquired predisposition; congenital malformation; physical trauma; immune system malfunction; and even infectious disease. Most commonly, however, feline arthritis results from the constant wear and tear that the joints experience during the course of a typically active cats daily life. While the sources of the condition vary, they all eventually lead to inflammation within the joints, changes in their anatomical makeup, pain and an inevitable decline in the ability of the associated bones, muscles, tendons and ligaments to function properly.

The most common form of feline arthritis is osteoarthritis, otherwise known as degenerative joint disease. This condition, especially prevalent in geriatric cats, is characterized by the erosion of cartilage, the smooth tissue that protects the ends of bones from rubbing directly against one another within a movable joint. When this protective tissue, for whatever reason, is worn or torn away completely, the bone ends come immediately in contact, and the persistent grinding of bone against bone results in inflammation and pain.

All joints in a cats body can be affected by osteoarthritis, but those that will become most visibly apparent to the owner are the movable joints, most often the shoulders and elbows. But the knees (stifles), the wrists (carpi) and the hips are also frequently affected. The outward signs will vary, depending on which joints are most painful, the extent of damage, and the animals age.

• Trauma, such as results when a cat is hit by a car or falls from a tree, can damage an animals musculoskeletal system in the form of bruises, sprains, dislocated joints or – most seriously – broken bones. Feline fractures occur most frequently in the long bones of the front or hind limbs – the femur, tibia, humerus, radius or ulna. Broken pelvises, jaws and spines may also occur, though less frequently. Fractures can be categorized as either “closed” or “open.” Closed fractures are those in which a broken bone has not penetrated the skin surface, while open fractures are those in which a bone has pushed through the skin and caused damage to the surrounding tissues.

Most broken bones can be successfully repaired by a local veterinarian, the choice of methods depending primarily on which bone is broken and which type of fracture has occurred. A hairline fracture, for instance, may require only the use of bandages or splints, since the bone has not been displaced. Many fractures, however, will require surgery entailing the repositioning of the bone parts and their stabilization with any of a variety of plates, rods, wires or other orthopedic devices.

A host of other feline musculoskeletal disorders may be associated with such underlying causes as neurologic impairment, immune system malfunction, nutritional deficiencies, bacterial infection, blood chemistry abnormalities, cancerous growths and endocrine imbalances. The following examples reflect the vast range of potential conditions:

• Myasthenia gravis, which can be either congenital or acquired, is an autoimmune disease resulting in a defect in the transmission of electrical impulses from the nerve endings to a cats muscles. Clinical signs include progressive muscle weakness and exercise intolerance.
  
  
• Hip dysplasia is a genetically inherited malformation of the ball-and-socket joint that connects an animals rear thigh bone to its hip. Over time, this defect causes the structural components of the joint to become worn and misshapen, resulting in looseness of the entire joint and, eventually, arthritis.
  
  
• Osteogenic sarcoma, a malignant tumor most often found in a cats skull or hind legs, can cause pain, swelling, deformity and lameness. Although this cancer may be treated successfully with limb amputation and chemotherapy, it is likely to prove fatal if it spreads to a cats lungs.
  
  
• Osteomyelitis is a deep bone infection caused by bacteria or other microorganisms that invade a cats body following, for example, an open fracture or a bite wound. The disease may be treated successfully with antibiotics and surgery to remove infected tissue, although it may become a chronic and recurring problem that requires prolonged therapy and more aggressive surgical intervention.

Fortunately, these and other acute and chronic musculoskeletal disorders are relatively rare in cats, especially when compared to the frequent incidence of feline arthritis and bone fractures.