Fabulous Feline Orthopedic Oddities #2 – Detection of Osteoarthritis

The fabulous feline rests just a few notches below US politics on a list of polarizing topics for public discussion.  Love ‘em or fear ‘em, the mysterious and all-powerful domestic house cat is a unique creature that has historically been sadly relegated to almost an afterthought in the world of veterinary orthopedics.  In effort to elevate their status, I introduced the first of a series of blog posts on fabulous feline orthopedic oddities in October 2022.  Today, I find myself compelled to share my thoughts and observations about how these clever little creatures so deftly disguise their orthopedic maladies including osteoarthritis (OA).

Unlike dogs who are pack animals and benefit from communicating their health status to others, cats are solitary hunters who derive no benefit from outwardly demonstrating their pain, weaknesses, and limitations.  Thus, cats are, instinctively, very good at hiding their pain. Because of their secretive nature, we must be keen observers in order to detect their OA and other orthopedic problems. It is very apparent that we SHOULD be looking because the prevalence of OA is high in cats. In fact, an estimated 90% of cats over the age of 10 years have radiographic signs of OA, with at least 40% showing clinical signs of pain.^{1, 2}

Now, let me throw you a curve ball … when was the last time you saw a Yorkie on top of a refrigerator?  While that visual image seems preposterous, would you be shocked or mystified if you saw a cat resting and observing their world from such a perch?  Of course not. That is because cats instinctively use vertical space in their environment while dogs are not so compelled.

This observation is important because one of the keys to detection of orthopedic abnormalities in cats is our keen awareness of their normal use of that vertical space in their daily routines. Has there been a change in their use of that vertical space?  A cat may manifest orthopedic pain, not through obvious lameness, but through a subtle change in their favorite elevated resting spots.  Look closely at their new favorite locale compared to the previous site.  Often the original favorite could be accessed by only by a single graceful leap whereas the newly preferred perch permits the cat access to smaller intermediate steps along the way.  Clues to their orthopedic pain can be that subtle!

Other cats will maintain their usual perches but access them differently, so it is only in the careful observation of their movement to/from the elevated site that reveals their malady.  It is helpful for cat owners to think of that slender, athletic cat that they once knew; the one that moved like an elegant jungle cat and could effortlessly defy gravity to access their desired perch in a single jump with no premeditation.  Similarly, they could once be easily compelled to leap nonstop from “on high” to pursue their prey (or more likely food or a toy) without hesitation or the need for intermediate descents toward their ultimate ground level destination.  It is that sleek, effortless, athletic, fluid movement of a jungle cat that characterizes normal orthopedic health and comfort. Subtle disruption of that sort of sleek movement often subtly reveals underlying orthopedic pain.

In preparation for a feline appointment, I frequently instruct my cat owning clients to use their smartphone to shoot for me several video clips of their cat’s ADL’s (activities of daily living). Now, I don’t have time to watch hours of video of cats sleeping in the sun, so I ask my clients to edit the video clips down to a few 10-15 second clips of their cat moving across a well-lit room, going up/down the stairs, and jumping on/off a couch or table. The fundamental question that I ask myself as I observe these clips in preparation for their appointment is “is the cat making these movements as a jungle cat would?”  The cat who uses their front legs to pull themselves up on to a couch is not normal. The cat who, rather than just jumping down to the floor, chooses to crouch down and walk their way along the table leg to reach the floor is not normal. The cat who hesitates halfway down the stairs and always leads with the same front limb is not normal.  Closer examination is warranted when I see these deviations from normal feline movement patterns.

In fact, it is this awareness of normal feline movement and detection of subtle deviations from it that are at the core of the recently published 6 question “Yes/No” screening checklist for detection of DJD in cats.³ This checklist is the basis of several cat owner educational website postings:

https://www.zoetispetcare.com/checklist/osteoarthritis-checklist-cat

https://www.catredflags.com/

While this checklist appears very simple (and it is), such tools are NOT simple to develop, refine and validate.  Painstaking effort was expended by the investigators at NC State University to produce this validated tool that is so very easy for you and me to use.  These tools are very helpful to heighten cat owner awareness of normal and abnormal feline movement patterns.

Other subtle clues of feline orthopedic pain may be less daily activity, less interest in being picked up or otherwise handled, inappropriate eliminations outside of the litter box or changes in hair coat condition.

Any of these observed feline behavioral changes can indicate the need to more closely evaluate for orthopedic abnormalities. While comprehensive veterinary orthopedic assessment of the feline patient is beyond the scope of this posting, the good news is that we’ve got more therapeutic options than ever before to address feline osteoarthritis. Just as a multimodal approach to OA is indicated in dogs (and humans), the same is true for cats. Overweight cats will benefit from weight loss to their ideal weight through a combination of exercise and use of a low-calorie diet. While cats are less inclined than dogs to exercise alongside their owners, the rotating use of new toys, chase games, food puzzles and even exercise wheels can be helpful when encouraging our feline friends to be more active. Of course, pain relief is the therapeutic cornerstone that fosters their willingness to exercise.  Historically, control of inflammation and pain through NSAID inhibition of prostaglandin E₂ has been the main treatment modality. This has been particularly challenging in cats due to their low behavioral tolerance of regular oral administration of these medications as well as the absence (in the USA) of FDA licensure for long term use of any NSAIDs in cats.

Fortunately, there are other novel targets for control of joint inflammation and pain. One such target is the binding up of nerve growth factor (NGF) that circulates in increased concentrations within osteoarthritic joints.  Osteoarthritis pain mediated through NGF binding to tropomysin receptor kinase A (TrkA) on first order sensory neurons can be controlled by use of species-specific therapeutic monoclonal antibodies (mAbs) that bind to NGF.  A new felinized anti-NGF mAb called frunevetmab (Solensia™; Zoetis) has recently been FDA approved for monthly injection to control feline OA pain.  Though there is a high caregiver placebo effect in the treatment of feline OA, this novel therapy demonstrated efficacy as compared to placebo with 77% of cat owners reporting improvement in signs of OA pain when their cats were treated monthly in a 3-month study.⁴

Hopefully, this posting has prompted to you to be more attentive observation of cats’ use of their vertical space (or at least communicating the importance of that to your cat owners).  So, let’s keep a keen eye on how our feline patients are using that space … and please let me know if you happen to spot a Yorkie atop a refrigerator (but only after you’ve safely helped them to the floor … I’ve seen far too many fractured Yorkies in my career … but that’s a discussion for another day).

Ross’ career has spanned both private practice and academia. Along the way, he has been actively engaged in orthopedic training of veterinarians for more than 30 years. Ross is a professor Orthopedics at Colorado State University, Associate Director of Education at the Translational Medicine Institute and a frequent educator at orthopedic courses held here at CSUVetCE and around the world.  If you, too, believe that “what if … thinking” is the key to innovation and advancement beyond that status quo, please get to know us at www.CSUVetCE.com because nothing fuels our passion like rubbing elbows with those who are similarly driven.

Reference Reading & Resources:

1. Slingerland LI, Hazewinkel HA, Meij BP, et al. Cross-sectional study of the prevalence and clinical features of osteoarthritis. Vet J 2011; 187: 304-309.
2. Lascelles BD, Henry JB III, Brown J, et al. Cross-sectional study of the prevalence of radiographic degenerative joint disease in domesticated cats. Vet Surg 2010;39: 535-544.
3. Enomoto J, Lascelles BDX, Gruen ME. Development of a checklist for detection of degenerative joint disease-associated pain in cats. J Fel Med Surg 2020;22: 1137-1147.
4. Gruen ME, Myers JAE, Lascelles BDX. Efficacy and safety of anti-nerve growth factor antibody (frunevetmab) for the treatment of degenerative joint disease-associated chronic pain in cats: a multi-site pilot field study. Front Vet Sci 2021;8; 610028. Doi:10.3389/fvets.2021.610028.

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