Degenerative Arthritis in Cats

Cats

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Degenerative joint disease (DJD), or arthritis, affects cats way more than previously known. One study found that 33.9% of cats aged 6 ½ years had radiographic evidence of arthritis. The prevalence of arthritis in cats increases significantly with age. The most commonly affected joints in this study were the hips and elbows.

In another study (2002), 90% of cats over 12 years of age had evidence of arthritis, most often occurring in the hips, shoulders, elbows, knees and ankles.

Degenerative joint disease (DJD), or arthritis, affects the smooth articular cartilage of the joint, which is the covering of bone in the joints that is responsible for the smooth, non-painful motion of joints. When it becomes worn, raw bone surfaces become exposed and rub together. DJD is the result, causing pain and lack of joint mobility.

DJD can occur over a lifetime of wear or as a result of injury. The soft tissue lining of the joint (synovium) is the first tissue in many animals to be affected in the disease and the subsequent irritation of the joint lining (synovitis) liberates chemical mediators that have been shown to be responsible for cartilage degeneration.

Primary cartilage damage can also initiate a cascade of events that result in further cartilage damage and synovial lining inflammation. This results in a vicious cycle of cartilage degeneration, release of degenerative factors and continued cartilage degeneration.

Normal cartilage is composed of cartilage cells (chondrocytes) and a supporting substance (matrix) that is produced by the cells. DJD involves the derangement of chondrocyte metabolism and subsequent matrix alteration.

What to Watch For

  • Lameness
  • Swollen joints
  • Muscle atrophy
  • Dry crackling sound upon movement of the joint (crepitation)

    Diagnosis

    Diagnostic tests are needed to recognize DJD and exclude other diseases. Tests may include:

  • Complete medical history and physical examination

  • A thorough orthopedic examination. DJD is usually characterized by a slow-onset, waxing and waning lameness pattern of the affected joint. Depending on the length and severity of the disease pain, swelling and grinding may be felt.

  • Radiographs (X-rays) of the suspected joints. These will show evidence of the degenerative process. If the DJD is secondary to a primary problem, evidence of the primary problem is frequently discovered. Occasionally the introduction of contrast material ("dye") into the joint (arthrogram) may uncover a primary problem. Advanced imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI) or bone scan (scintigraphy) is occasionally of diagnostic value.

  • Joint fluid analysis. This test can help differentiate between degenerative joint disease and other causes of more inflammatory joint disease, such as canine rheumatoid and infectious (bacterial, fungal etc.) arthritis.

    Treatment

    Treatment for DJD may include one or more of the following:

  • Medical treatment and weight reduction are often the initial hallmarks toward treatment of DJD. Weight reduction decreases stress placed on the joints and a number of older and newer drugs have been used to alleviate the clinical signs associated with DJD. Nonsteroidal anti-inflammatory drugs (NSAIDS) have been used for years since Bayer marketed acetylsalicylic acid (aspirin) in 1899. All drugs have potential side effects; however, the newer NSAIDs seem to have less side effects than aspirin in animals. Aspirin should not be used in cats. Corticosteroids (cortisone) decrease the inflammation of DJD, although it is a well-established scientific fact that chronic steroid use causes cartilage damage and should not be used for long-term therapy.

  • Surgical treatment of traumatic causes of secondary DJD (such as knee ligament rupture), seem to slow the progression of the degenerative process.

  • Either arthrodesis (fusion) or other arthroplasty (joint replacement or excision) procedures are usually very successful in restoring pain-free range of motion in selected cases of DJD.

    Home Care and Prevention

    After your cat's surgery, follow your veterinarian's specific instruction concerning medications, care and recheck examinations. Limited range of motion and physical therapy exercises are usually beneficial.

    Since some of the developmental orthopedic conditions that result in DJD have some component of inheritability, selective breeding of unaffected animals will help decrease the incidence of the disease in the population as a whole. This can decrease the incidence of many of the congenital orthopedic problems.

    Proper nutrition is also important in order to have a normal weight gain during development.

  • It has been estimated that as much as 20 percent of the feline population over one year of age has DJD. The unifying theme in DJD is degeneration and destruction of articular cartilage – the cartilage looses its elasticity and softening occurs. Fissures can form and result in fibrillation and cell death. The altered chondrocytes release mediators (enzymes and other factors) that cause the cartilage to break itself down in a vicious cycle of degeneration.

    The importance of the anatomy and disease process of DJD becomes meaningful when discussing the action of many of the newer drug therapies. Normal articular cartilage covers the bone on both sides of a joint and provides nearly friction-free motion of the joint. It also provides a "shock absorbing" protection to the joint and associated bones. When the articular cartilage structure is altered, the biomechanical properties of the joint change.

    Normal articular cartilage is made up of cartilage cells (chondrocytes), an extracellular matrix and water. The chondrocytes manufacturer much of the extracellular matrix. The matrix is made up of microscopic fibers called collagen, which provides a structural support for the cartilage matrix and a complex biochemical "goo" called proteoglycan. The chemical chondroitin sulfate makes up much of the proteoglycan.

    The tissue surrounding the joint is called the joint capsule and it contains a thick fluid (hyaluronic acid) that is partly responsible for joint lubrication. The joint capsule becomes inflamed with DJD and the quality of the joint fluid decreases, which causes more changes to the cartilage.

    There are a number of congenital orthopedic diseases that occur in the cat that can lead to DJD at an early age. Many of these are related to the osteochondrosis syndrome:

  • Osteochondritis dissecans (OCD) can occur in the shoulder, elbow, stifle or hock joint in the cat and can cause joint inflammation and secondary DJD at an early age.

  • Fragmented medial coronoid process (FCP) of the elbow produces secondary elbow DJD in cats as young as six months of age.

  • Ununited anconeal process (UAP) can produce severe elbow DJD.

  • Joint trauma can also lead to secondary DJD, including any fracture that involves a joint surface. Joint fractures need to be reduced and stabilized precisely to prevent the occurrence of DJD. Any incongruity during healing will result in degeneration. Hip and elbow fractures occur fairly frequently. A traumatic dislocation of a joint can produce severe DJD if not treated appropriately. Cats are susceptible to ligament injuries, in particular the cranial cruciate ligament (CCL) of the knee, which is the most common injury to the canine stifle. Cranial cruciate rupture causes variable amounts of DJD.

  • Diagnosis In-depth

    Diagnostic tests are needed to recognize DJD and exclude other diseases. Tests may include:

  • A thorough orthopedic examination will revel the presence of joint pain, swelling and tenderness. A careful history will also, many times, tip the veterinarian's suspicion toward a specific primary disease process.

  • Radiographs (X-rays) are usually an essential diagnostic tool. Since the majority of DJD seen in small animals is secondary to some congenital or acquired event, radiographic diagnosis of this inciting cause is important.

  • Contrast studies. Usually the diagnosis of DJD is fairly straightforward, but sometimes, additional views or "stress" views may be necessary. Injecting contrast (dye) into the joint and obtaining a radiograph is seldom necessary. Also, advanced imaging techniques such as CT and MRI are seldom necessary. Bone scans involve injecting a small amount of a radioactive material in the body that would normally accumulate in bone. When a camera is used to record the nucleotide at the joints, an area of increased accumulation may help the clinician detect a subtle area of lameness.

  • Force plate. Although used primarily as a research tool to assess a degree of lameness and response to various treatment modalities, the force plate can be used in the clinical setting to help evaluate the degree of lameness. A plate or mat is placed on the floor and the cat is allowed to make numerous passages across the plate. Sensors in the plate are attached to a computer that analyzes the force each step makes on the plate. There are a number of variables that can occur, but force plate analysis can be helpful.

  • Aspiration of joint fluid. Degenerative joint disease is just one of many types of joint disease that can occur. The other large category of joint diseases is termed "inflammatory." With these diseases, a large amount of white blood cells are attracted to the joint from various disease processes. The most common of these are "autoimmune" diseases where the body recognizes certain portions of an individual's joint to be foreign or abnormal and tries to destroy it. Canine rheumatoid arthritis is an example of this type of arthritis. This type of arthritis is uncommon when compared to DJD. Aspiration of joint fluid can be helpful in determining is the arthritic process is inflammatory (rheumatoid like) or non-inflammatory (DJD).

    Treatment In-depth

    Medical therapy, exercise restriction and loss of excess weight are the hallmarks to medical treatment. Treatment for DJD may include one or more of the following:

  • Nonsteroidal anti-inflammatory drugs (NSAIDs). These drugs primarily inhibit inflammation activity. In particular, NSAIDs they inhibit the synthesis of prostaglandins. While this is good, there is also a major side effect. In the stomach, prostaglandin helps protect the stomach lining from the normal stomach acids. People and animals on some of the early NSAIDs (aspirin, phenylbutazone and ibuprofen) experienced variable gastrointestinal side effects. Examples of newer NSAID's include Deracoxib (Deramaxx®), meloxicam (Mobic® or Metacam®), Carprofen (Rimadyl®), and Etodolac (Etogesic®). These are cyclooxygenase 2 (COX2) inhibitors that specifically act against the pathway directed at the joints but selectively leaves the pathway to protect the stomach (COX1) intact. These drugs are commonly used in dogs but special care is required in cats. Many of the NSAID's have not been tested in cats or cats have been found to be very sensitive. Never give aspirin or any NSAID to your cat without consultation with your veterinarian.

  • Osteoarthritis agents. This slow acting class of drugs help to modulate the progression of DJD. Many of the oral varieties are not regulated by the FDA and fit in the classification of nutraceuticals (vs. pharmaceuticals). The majority of these supplements contain glucosamine and chondroitin sulfate (remember, these are the main chemical substances making up the cartilage matrix). Cosequin contains purified glucosamine, condroitin sulfate and manganese ascorbate. It is hypothesized that, with DJD, the demand for cartilage precursors or building blocks is greater than the body's ability to make them. This results in a diminished repair capacity. This is only theory and no hard scientific evidence illustrates the cartilage cells are nutritionally deprived. A number of studies have shown that these compounds do incorporate in healing cartilage and anecdotal reports are favorable. Many times these compounds are used in conjunction with NSAIDs.

  • Surgical treatment of end stage DJD results in either removal of one side of a joint and allowing a "false joint" to form. Since there is no longer any rubbing of the joint surface, much of the pain is eliminated. This classically was done for hip dysplasia (femoral head ostectomy). Obviously the joint has been de-stabilized, but many smaller animals can accommodate very well.

  • In other joints, surgical fusion of a joint might be helpful. By eliminating the joint surfaces and allowing the joint to fuse in a functional, anatomic position, many cats can have a pain-free existence with adequate mobility.

    Follow-up

    It is extremely important to follow your veterinarian's instructions for pet care, especially if surgery was performed. Rest is usually recommended for three to four weeks postoperatively. Watch any incision your pet has for heat, pain, swelling or discharge.

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