Osteoarthritis in Cats

Osteoarthritis (OA) is the inflammation and subsequent breakdown of the primary components of the joint, including cartilage, joint capsule, and underlying/surrounding bone. Inflammation in the joint causes damage and, ultimately, erosion of the protective layer of cartilage in the joint. The underlying bone is exposed as cartilage is worn away, resulting in a lack of shock absorption in the joint. The inner lining of the joint capsule surrounding the joint responds by inflammation in the form of synovitis and, ultimately, fibrosis (scarring). The joint capsule lining produces the fluid that lubricates the joint and keeps the cartilage, ligaments, and structures within the joint healthy. As the joint capsule becomes inflamed and fibrotic, it causes the joint fluid to become thin and watery, providing less lubrication and cushion for the joint. Pain from osteoarthritis is linked to cartilage damage, bone exposure, friction, bony change, and inflammation within the joint.

OA can develop due to a primary problem with the joint (excess force, instability, trauma, or abnormal shape) or may develop through wear-and-tear activities of daily life. The primary cause of OA often cannot be identified in cats and the disease is less understood than dogs.

Affected Joints

• Hip
• Stifle (knee)
• Tarsus (ankle)
• Elbow

Older cats or obese cats are most commonly affected due to increased risk factors.

Clinical signs

• Stiff movement
• Reluctance to play or jump
• Limping
• Reluctance to stand to use the scratching post
• Hiding or being less interactive

Risk Factors

• Genetic Predisposition. There are no genetic factors in feline patients that have been shown to be associated with the onset of osteoarthritis.
• Age. As cats age, the cartilage in joints changes composition and is less able to repair areas of damage, resulting in cartilage breakdown and inflammation.
• Obesity. Being overweight or obese has been linked to the worsening of osteoarthritis in animals and humans. Diet restriction in dogs has been shown to decrease the incidence of osteoarthritis in the hips, elbow joints, and shoulder joints. In humans, obesity has been linked to increased load on the joint and altered alignment, resulting in more joint damage and breakdown.
• Gender. An association of osteoarthritis with gender has not been studied in dogs and cats.
• Injury or trauma. Injury to a joint causes joint damage and early onset of osteoarthritis. Types of injuries could include fractures, luxations (dislocations), and cruciate tears in stifles (knees).
• Developmental bone diseases. Developmental diseases that cause abnormal weight distribution in joints, such as elbow dysplasia, or an abnormal joint surface, such as osteochondrosis, will predispose the joint to the development of osteoarthritis.

Orthopedic exam

• Examination of the bones and joints will often result in pain in the manipulation of the joints, grinding of the joint during range of motion, limited range of motion in joints, and swelling of the joints. Patients will often limp or have a stiff gait. 

Radiographs (x-rays)

• Radiographic changes are apparent in up to 90% of cats, but only 50% will be clinically affected by their osteoarthritis. 
• Radiographs of a joint with osteoarthritis can show: 
  • Osteophytes 
    • bony outgrowths around the joint associated with cartilage breakdown
  • Enthesiophytes 
    • mineralization where ligaments attach to the bones
  • Effusion 
    • fluid or swelling in the joint
  • Soft tissue swelling
  • Subchondral sclerosis 
    • Increased mineralization of the bone around the joint due to exposure and overload
  • Mineral inside the joint
  • Bone cysts

Joint fluid analysis

• Joint fluid from a joint with osteoarthritis will show an increase in white blood cells called monocytes.

Other imaging modalities

• MRI. Evaluates soft tissues like ligaments, tendons, and joint capsules. Limited in the ability to evaluate cartilage. 
• CT. Evaluates bone structures within the joint. 
• Scintigraphy. This imaging uses a marker that binds to hydroxyapatite in bone and can target areas of the skeleton with high bone turnover (break down and remodeling) but is not specific for arthritis. 
• Arthroscopy. This involves using a camera within the joint to evaluate the joint surface. This is the gold standard for cartilage evaluation. Feline patients are sometimes too small for this type of imaging.

A multimodal approach is recommended to treat OA in cats. The basis of this approach is to use a combination of therapies that improve comfort and quality of life. It is important to note that all treatment decisions are made based on individual patients and in discussion with the pet owner and surgeon.

• Weight management. Overweight cats are more likely to show signs of lameness or pain associated with OA. Weight loss through controlled feedings or foods formulated for weight loss may improve your cat’s comfort.
• Nonsteroidal anti-inflammatory drugs While these medications (such as meloxicam and robenacoxib) are effective for treatment of acute pain, potential toxicity deters many veterinarians from long-term use, especially if your cat has kidney disease. Research regarding safety and dosing of these medications for OA in cats is ongoing.
• Adjunctive drug therapy Medications such as gabapentin, amantadine, and tramadol are being increasingly investigated for use in treating chronic pain in cats. There is some evidence to support the use of these medications, but it is not conclusive. Your veterinarian may help you decide if one of these medications could be helpful for your cat.
• Dietary supplements. Supplements such as omega-3 fatty acids, glucosamine, and chondroitin are usually well tolerated by cats but may or may not be helpful in reducing signs of OA.
• Environmental modifications. Using steps and ramps and providing soft bedding may improve your cat’s quality of life.
• Physical rehabilitation. This area is just beginning to be investigated in cats and includes different exercises and modalities, such as low-level laser therapy, therapeutic ultrasound, and massage.
• Immunomodulation. Frunevetmab (Solensia) is a monoclonal antibody (cat-specific protein) designed to recognize and attach to a protein called Nerve Growth Factor (NGF), decreasing pain associated with osteoarthritis. It is administered once a month as an injection.
• Joint injections. Injections into the joint can relieve pain by decreasing inflammation, aiding with joint healing, or providing cushion. Some types of joint injections available are steroid injections, platelet-rich plasma, hyaluronic acid, and osteo-cushion technology. The efficacy of this treatment requires further investigation.
• Surgical techniques. Surgery for OA is less common in cats than dogs but may be very helpful in certain cases. Surgical options include joint replacement and arthrodesis (fusion of a painful joint).