Focus - January 2021

Osteoarthritis (OA) in the cat is a very common condition with 40% of all cats having clinical signs and >90% of cats older than 12 years’ showing radiographic evidence of OA.^1,2 The condition is not exclusive to older cats and clinical studies have shown that even cats as young as two years’ can suffer from OA. However, as a disease, the clinical signs are infrequently recognised by pet owners and the condition is under diagnosed by the veterinary profession, with only 13% of affected cats globally being diagnosed.² As veterinarians, we should be assessing cats for its presence and educating owners to recognise the signs (see Figure 1).  Starting to screen cats as early as seven to 10 years of age will help to establish a baseline of ‘normal’ for that cat and may uncover OA early in the disease. Active screening and early identification can increase the number of impacted cats treated and improve the quality of life of cats suffering from the pain and reduced mobility associated with OA.

What is osteoarthritis?

Degenerative joint disease refers to damage in both the appendicular and axial skeletal systems, with most of the cases diagnosed as osteoarthritis. OA implies a joint problem, primarily associated with degeneration and loss of cartilage and proliferation of bone in the form of osteophytes around the joint. This results in a joint that has a reduced range of motion and one that is undergoing low grade inflammation resulting in varying degrees of pain and swelling of the offending joint(s). It is common in cats where multiple joints are impacted. In cats, OA usually occurs as a primary problem with no easily identifiable underlying cause, but it can also occur secondary to underlying developmental joint disease such as hip dysplasia (see Figure 2) or subsequent to a joint injury such as an intra-articular fracture or luxation. Cats develop osteoarthritis in all their large joints, but particularly the hip, hock and elbow joint^3,4 (see Figure 3). Over 80% of cats older than 12 years of age had axial skeletal changes.⁴ Appendicular skeletal changes are even more common with over 90% of cats of all ages having radiographic changes in at least one joint.³

Veterinarians globally report that decreased agility and reduced mobility are the most common signs reported to them for cats diagnosed with OA. Behavioural changes are also common and usually associated with the cats’ decreased agility and reluctance to move around.^5,6 Cats presenting with behavioural problems can be easy to miss and is another reason to screen all cats for OA around seven to 10 years of age. These findings are in line with published studies on feline OA.

How to diagnose osteoarthritis

Owners may believe that it is normal for their older cat to sleep more and be less active or may only notice more severe signs of OA pain. As veterinarians we need to be aware of the high incidence of OA in cats and not dismiss an owner’s observation that their cat cannot jump as high anymore as being normal for an older cat. If the cat is in pain and unwilling to move around because of osteoarthritis, then it is important to educate owners as to this possibility and to try to intervene to alleviate some of the pain that the cat is experiencing. The good news is, cat owners are interested in learning more about OA in cats. In a global survey, when educated on OA as an extremely common, painful disease that could be treated, 53% of cat owners found the information relevant to their cat, and 39% were motivated to make an appointment with their veterinarian.²

There are some useful questions that we can ask of an owner to identify cats with musculoskeletal problems (see Table 1). Alternatively, the cat owner can be asked to complete a validated questionnaire prior to the consultation and then regularly thereafter to assess response to treatment.^8,9 Asking the pet owner to record their cat via video is also helpful to watch the cat move in their natural environment without the stress of being at the clinic. Early screening allows for a baseline to be set of what is ‘normal’ for that cat. This will help uncover any changes in behaviour or mobility as the cat ages.  

Orthopaedic examination

Performing an orthopaedic examination of a cat can be tricky and often requires patience. There are ‘feline-friendly’ approaches to handling a cat that can be implemented in the practice.^11,12 In a cat that is impossible to examine, this is another opportunity to ask the owner to videotape the cat in its home environment to assess their concerns more fully. Ask them to video the cat doing the things it finds difficult, eg. jumping or climbing stairs. In the more amenable cat, watching it walk around the consulting room and allowing or encouraging it to jump on and off a chair can be helpful to observe if there are any gait abnormalities. Following the visual observation, an examination of the joints is recommended. This is best carried out with an assistant holding the cat gently over its chest. The changes to look for in individual joints are swelling or enlargement, crepitus, decreased range of motion, and pain. However, bear in mind that not all joints will be painful and not all painful joints will have OA. The presence of crepitus, joint thickening and joint effusion has been shown to be predictive of the presence of radiographic degenerative joint disease.³

Confirming the diagnosis

Although the combination of appropriate clinical signs and physical examination findings may lead you to be fairly certain a cat has OA, it is ideal to try to confirm your suspicions by seeing radiographic changes. The primary radiographic change associated with osteoarthritis is the presence of periarticular osteophyte formation, although this is not always present or easily identifiable in every case. It is important to appreciate that osteoarthritis may be present in the absence of obvious radiographic changes. Contrarily, the presence of radiographic changes does not always correlate with clinical signs of OA nor the degree of pain suffered. Occasionally, cats develop excessive periarticular mineralisation and ossified bodies adjacent to their joints, particularly in the stifle joint (see Figure 4).

This article was adapted from a Zoetis technical bulletin: Feline Osteoarthritis, a Common and Painful Disease: Diagnosis, Treatment, New Resources and Future Options.