Feline joint disease is an enzyme problem wearing a pain mask. Inflamed synovium releases interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha (TNF-alpha) and prostaglandin E2 into a joint that holds only 0.1-1 mL of fluid, and those signals switch on matrix metalloproteinases that digest a cartilage layer 0.2-0.5 mm thick. Non-steroidal drugs block one step of that cascade, which is why they help the pain and do not stop the erosion.
Most cats over 12 years show degenerative changes on X-ray and most of them are not limping, because range of motion goes over 1-3 years, not in a week.
What synovitis actually is
The synovial membrane is 1-3 cell layers thick, thinner than a sheet of paper, and covers everything inside the joint capsule except the cartilage. When it inflames, it swells to 10-20 times that thickness within 24-72 hours, grows new capillaries, and leaks protein-rich fluid into a space that normally holds 0.1-1 mL in the stifle. The joint runs 1-3 degrees warmer than the opposite side; the stretched capsule is the first pain, before cartilage is lost.
Four mediators, one 6-hour window
The sequence is fast and predictable. Within 15-30 minutes of a trigger, bradykinin and substance P sensitize nerve endings. By 2-6 hours, IL-1 beta and TNF-alpha have pushed synovial cells into producing prostaglandin E2 and nitric oxide, and the joint is visibly swollen. Left alone, a single acute flare settles in 3-10 days; repeated flares leave a membrane that stays 2-5 times normal thickness permanently.
IL-1 beta does the structural damage: it tells chondrocytes to stop making type II collagen and start making matrix metalloproteinases, at concentrations in the low nanograms per milliliter, so 0.5 mL of fluid keeps a whole joint degrading.
Enzymes that eat 0.2-0.5 mm of cartilage
Three enzyme families do the cutting: MMP-13 (collagenase 3) cleaves type II collagen, MMP-3 and MMP-9 break down proteoglycans, and ADAMTS-4 and ADAMTS-5 cut aggrecan, the molecule that lets cartilage hold water under load. Aggrecan loss comes first and is reversible; once the collagen scaffold is cut, cartilage does not rebuild. The structure itself is covered in cartilage biology.
Load matters because it drives the enzymes. A cat walking on a normal stifle puts 2-3 times body weight through the joint; a jump from a 1 m surface lands at 4-6 times body weight. For a 4.5 kg cat that is 9-13 kg on landing, roughly 90-130 N, applied in under 200 ms; a 7 kg cat carries about 55% more, and a breed quiz gives the weight range to check against.
Acute pain and chronic pain are different problems
Acute joint pain is nociceptive: a swollen capsule stretches receptors, the cat guards the limb for 3-14 days, and the tissue heals. Chronic pain is maladaptive: after roughly 3 months of ongoing inflammation, spinal and brainstem circuits amplify signals, so the cat hurts with less input. An old cat with modest X-ray changes can therefore jump less than a young cat with a worse-looking joint.
The clinical signature of chronic feline joint pain is subtle and mostly postural: jumps onto surfaces above 40 cm drop out first, the cat stops using the litter tray edge, sits with one hind leg out, and takes 2-4 seconds longer to lie down. Owners typically notice 12-24 months after the process started.
Where NSAIDs land in the cascade
Cell membrane phospholipids become arachidonic acid via phospholipase A2, and cyclo-oxygenase (COX) converts that to prostaglandin H2, then to PGE2, which sensitizes pain receptors and dilates joint vessels. NSAIDs inhibit COX. Meloxicam leans toward COX-2 and is the drug most often licensed for long-term feline use, at 0.1 mg/kg on day 1 then 0.05 mg/kg once daily, with the oral suspension reaching peak blood levels in about 2-3 hours and a half-life near 24 hours in cats.
Two safety numbers matter more than the dose. Never combine two NSAIDs, and leave 5-7 days between stopping one and starting another. Never give an NSAID with a corticosteroid, and stop NSAIDs 2-3 days before planned surgery unless the vet says otherwise. Cats clear these drugs slowly, so the feline dose is roughly half the dog dose per kilogram.
Table: mediator to clinical sign
| Mediator or enzyme | Main source | Effect | Time to peak |
|---|---|---|---|
| Bradykinin, substance P | Nerve endings, synovium | Sensitizes nociceptors | 15-30 min |
| IL-1 beta, TNF-alpha | Synovial macrophages | Swelling, enzyme induction | 2-6 h |
| PGE2 | COX-2 in synovium | Pain, vasodilation, fever | 2-6 h |
| MMP-13 | Chondrocytes | Cuts type II collagen | 24-72 h |
| ADAMTS-4/5 | Chondrocytes | Aggrecan loss | 3-14 days |
What changes the load, not just the pain
Weight is the single most useful lever. A 5% body weight loss in a 5 kg cat removes about 250 g, and at 4-6 times body weight on landing that is 1-1.5 kg less peak load per hind limb. Feeding to a body condition score of 5 out of 9, measured by rib palpation rather than by eye, is the practical target.
Omega-3 fatty acids at roughly 40-90 mg/kg per day of combined EPA and DHA are commonly used alongside NSAIDs; the effect builds over 6-12 weeks, not days, so do not judge it at week 2. Environmental changes with a measurable target help more than most supplements: a 20-30 cm step up to the sofa, a litter box with a 5-8 cm lower rim, and a warmed bed at 20-24 C.
Monitoring thresholds and when to call a vet
Score the cat monthly on 3 things: jump height (can it still reach a 60 cm surface), time to lie down (count seconds), and grooming of the lower back, which stops early. A drop of one jump height band, or 2 or more seconds added to lying down, is a reason to book an exam rather than to wait.
Call a vet within 24-48 hours for: a joint that is hot and swollen for more than 48 hours, refusal to bear weight for more than 24 hours, a fever above 39.5 C, or any cat on an NSAID that stops eating or vomits twice in 24 hours. Stop the drug and call the same day if there is black stool, vomiting, or reduced urine output, because those are the early signs of the gastrointestinal and kidney effects these drugs can cause.
5 things to do this week
- Weigh the cat on the same scale, then set a target of 5% loss over 8-12 weeks if it scores 6/9 or above.
- Measure the three jumps it uses most and add a 20-30 cm step to the highest one.
- Log lie-down time for 3 days; it is the cheapest objective pain marker an owner has.
- Book a vet exam with a mobility questionnaire before starting any NSAID, plus baseline blood work.
- Recheck kidney values and weight 4-6 weeks after starting a long-term NSAID, then every 6-12 months.
Terms mentioned in this article
Frequently asked
Can I give my cat the dog's meloxicam dose?
No. Cats have low glucuronidation capacity and clear these drugs slowly, so the licensed feline dose is roughly half the dog dose per kilogram: 0.1 mg per kg on day 1, then 0.05 mg per kg once daily with the oral suspension. The same reasoning is why two NSAIDs are never combined and 5-7 days are left between products.
If the X-ray shows severe arthritis, does that mean severe pain?
Not reliably. Radiographic change and pain behavior diverge in both directions, because chronic pain after about 3 months is driven by amplified spinal signalling rather than by the joint alone. Judge function instead: jump height, seconds to lie down, grooming of the lower back. Those 3 measures track the cat better than a film does.
Do joint supplements replace an NSAID?
They do not act on the same step. Omega-3 fatty acids at roughly 40-90 mg per kg daily of combined EPA and DHA shift the inflammatory balance over 6-12 weeks and are usually used alongside an NSAID, not instead of it. Weight loss of 5% removes real load from every landing, which no capsule can match.