Knee osteoarthritis is the single largest cause of activity limitation in older adults worldwide, and the most common joint disease there is. It is also one of the most misunderstood — usually described as “wear and tear” and “bone on bone”, which describes neither the biology nor the prognosis.
Osteoarthritis is an active process in which the joint’s repair mechanisms are failing. That distinction matters, because a process you can influence behaves differently from damage that is simply done.
What happens in the joint
Articular cartilage is a smooth, low-friction surface covering the ends of the bones. In osteoarthritis, the balance between breakdown and repair shifts:
- Cartilage thins and roughens — the smooth surface develops fissures, then loses coverage
- Subchondral bone remodels — becomes denser and forms cysts; this is where a lot of the pain signals originate
- Osteophytes form — bony spurs at the joint margins, the body’s attempt to redistribute load
- Synovium becomes inflamed — producing effusion, warmth and swelling
- Menisci degenerate — reducing shock absorption and further altering load distribution
Low-grade inflammation is present throughout, which is why the condition responds to anti-inflammatory treatment even though it is not an autoimmune disease.
Risk factors
| Factor | Note |
|---|---|
| Age | Prevalence rises steeply after 50, but is not inevitable |
| Previous knee injury | ACL or meniscal tear, fracture, or dislocation raises risk substantially — often the strongest single factor in younger patients |
| Excess body weight | The strongest modifiable factor. Each kilogram of body weight carries roughly four kilograms of force across the knee during normal activity |
| Quadriceps weakness | Both a risk factor and a treatment target |
| Malalignment | Knock-knee or bow-leg concentrates load on one compartment |
| Occupational loading | Repeated kneeling, squatting, or heavy lifting |
| Genetics | Meaningful contribution, including to cartilage structure |
| Female sex | Higher prevalence after menopause |
Symptoms and how they differ from arthritis
Pain pattern
Pain that is worse with activity and better with rest — stairs, squatting, kneeling, getting out of a car or chair. Morning stiffness, if present, is brief: typically under 30 minutes. This is the key differentiator from rheumatoid arthritis, where stiffness lasts well beyond an hour and pain is worse after rest.
Other features
- Crepitus — grinding or crunching with movement. Common and not by itself a severity marker
- Giving way — often from pain inhibition or a meniscal problem rather than true instability
- Effusion — swelling, particularly after activity
- Locked knee — inability to fully extend; suggests a mechanical block such as a meniscal fragment
- Deformity — progressive varus (“bow leg”) or valgus (“knock knee”) in advanced disease
The imaging problem
This is worth understanding before an X-ray is ordered: radiographic severity correlates poorly with pain. Studies repeatedly show people with dramatic X-rays and no symptoms, and people with near-normal films and severe pain.
X-rays show structural change — joint space narrowing, osteophytes, sclerosis. They do not show cartilage directly, do not measure inflammation, and do not predict how much a given person hurts. MRI is not routinely indicated unless there is a specific clinical question such as a locked knee or suspected occult fracture.
The useful consequence: treatment is aimed at symptoms and function, not at making the film look better. A “bone on bone” X-ray in someone who walks comfortably is a poor reason for surgery.
Treatment, in the order that matters
1. Education and exercise — the most important intervention
Exercise is the treatment with the best evidence base, and its effect on pain is comparable to anti-inflammatory medication. Two components:
- Strengthening, particularly the quadriceps and hip abductors. Stronger muscles absorb load that would otherwise go through the joint
- Aerobic and land-based or aquatic exercise — walking, cycling, swimming, group programmes
Aquatic exercise is genuinely useful when pain limits land-based activity, because buoyancy reduces joint load while allowing resistance training. The single most common failure in management is being told to rest rather than being given a programme.
2. Weight management
For anyone carrying excess weight, this is the highest-value change available. A 5–10% loss produces measurable pain reduction, and the load mathematics mean the benefit is larger than the weight alone suggests.
3. Medication
- Topical NSAIDs — first-line pharmacological treatment. Similar analgesic effect to oral versions with far less gastrointestinal and cardiovascular exposure
- Oral NSAIDs — used at the lowest effective dose for the shortest period, with a gastroprotective agent where risk warrants it. Full cardiovascular, renal and gastrointestinal assessment comes first
- Paracetamol — once recommended first-line; current evidence shows little specific benefit in osteoarthritis and it is no longer preferred
- Duloxetine — an SNRI with specific evidence in osteoarthritis, particularly where pain is persistent and other options are contraindicated
- Stronger analgesics — opioids are not recommended for chronic osteoarthritis; the risk-benefit is unfavourable and tolerance develops
4. Injections
- Intra-articular corticosteroid — provides real but temporary relief, typically weeks. Frequent repeated injections are discouraged given concerns about cartilage effects with repeated exposure
- Hyaluronic acid (viscosupplementation) — evidence is mixed and major guidelines do not recommend it for knee osteoarthritis. It remains in use in some settings; worth asking what the expected magnitude of benefit is
5. Bracing and devices
An unloader brace can shift load away from the affected compartment in someone with malalignment — a non-surgical option that can meaningfully improve walking distance. Shoe insoles and walking aids are legitimate tools rather than symbols of decline.
6. Surgery
- High tibial osteotomy — realigns the leg to unload a damaged compartment. Aimed at younger, active patients, and buys time rather than being definitive
- Arthroscopy — not indicated for osteoarthritis without a mechanical symptom. Trials show debridement and lavage do not outperform sham surgery for arthritic pain. This is one of the most persistently over-performed procedures
- Total knee replacement — for end-stage disease where symptoms limit daily life and conservative treatment has been exhausted. Outcomes are excellent: over 90% report meaningful improvement, implants commonly last 15–20 years or more. Recovery is real work — several months of rehabilitation
A note on supplements
The evidence is disappointing relative to the marketing:
- Glucosamine and chondroitin — the large NIH GAIT trial found no benefit over placebo for knee osteoarthritis across the whole group, with a modest effect in a subgroup with moderate-to-severe pain. Widely sold, weakly supported
- Turmeric/curcumin — some evidence for modest pain reduction, generally short-term
- Omega-3 fatty acids — modest evidence, better established for inflammatory conditions generally
- White willow bark, devil’s claw, collagen — evidence limited and methodologically weak
Supplements are not regulated as rigorously as medicines, so content and purity vary. If something helps, it is worth continuing — but it should not displace exercise, which has far stronger evidence.
Red flags and when to seek help
- A hot, red, markedly swollen joint with fever — emergency. Septic arthritis destroys cartilage within days
- Sudden locking or inability to bear weight after an injury — possible meniscal tear or fracture
- Rapid worsening over days to weeks rather than the usual gradual pattern
- Signs of inflammatory arthritis — prolonged morning stiffness, multiple joints, swelling of hands and feet, fatigue. Requires rheumatology assessment
- Unexplained weight loss or night pain that wakes you — warrants investigation
- Failure of a structured 12-week programme — worth a specialist review to confirm the diagnosis and discuss options
Frequently asked questions
Is walking bad for a knee with osteoarthritis?
No. Impact activity at normal intensities does not accelerate cartilage loss, and walking maintains cardiovascular health, strength and weight. The old advice to avoid loading the joint is now understood to be actively harmful. Pain during activity that settles shortly afterwards is acceptable; pain that escalates over hours suggests the intensity needs reducing.
If my X-ray says bone on bone, do I need a replacement?
Only if your symptoms say so. Severity on imaging and severity of experience diverge substantially. The indication for replacement is pain and functional limitation that has not responded to appropriate conservative treatment — not the appearance of the film.
Can cartilage grow back?
Adult cartilage has very limited capacity for self-repair, and no treatment reliably regenerates it. What can change is everything around it: muscle strength, load distribution, inflammation, weight, deconditioning and pain processing. Those account for most of the improvement people achieve — which is why the treatment list starts with exercise rather than cartilage.
Is running going to ruin my knees?
The evidence does not support this. Recreational runners do not have higher rates of knee osteoarthritis than non-runners, and some studies suggest lower rates — plausibly because of the conditioning and weight maintenance that come with it. Very high volumes with prior injury are a different matter. The stronger risk factor remains inactivity.
Do I have to give up the things I enjoy?
Rarely, and usually only temporarily. The goal of treatment is function, not a clean X-ray. Most people can continue cycling, swimming, walking and much of what they did before, adjusted for load and intensity. What tends to cause decline is stopping altogether.
This article is for general information only and is not a substitute for professional medical advice. See our medical disclaimer.
