Reviewed by Dr Vishal Pai
Knee osteoarthritis is wear of the smooth cartilage that covers the ends of the bones in your knee. This page explains what causes it, the symptoms, how it is diagnosed and treated, and when surgery is considered.
At a Glance
- Knee osteoarthritis (OA) is gradual wear of the cartilage in your knee. It is the most common type of knee arthritis.
- It mostly affects people over 50, especially after an earlier knee injury or if you carry extra weight.
- The main symptoms are pain with activity, stiffness, and swelling that comes and goes.
- Most people are treated without surgery. Learning about the condition, exercise and, if needed, weight loss are the core treatments.[1]
What is knee osteoarthritis?
Your knee is where your thigh bone (femur), shin bone (tibia) and kneecap (patella) meet. The ends of these bones are covered with smooth articular cartilage, which lets the joint glide and absorbs load as you walk. In osteoarthritis, this cartilage slowly thins and wears away. The bone underneath thickens and can grow small bony spurs (osteophytes), and the lining of the joint can become inflamed.
Which parts of the knee are affected?
The knee has three parts, or compartments: the inner (medial) side, the outer (lateral) side, and the joint behind the kneecap (patellofemoral). Arthritis can affect one, two or all three. The inner side is the most commonly affected.
How is it graded?
On X-ray, osteoarthritis is usually described as mild, moderate or severe, depending on how much the gap between the bones (the joint space) has narrowed. When the cartilage has worn right through and the bones touch, it is often called “bone on bone” or end-stage arthritis.
What causes knee osteoarthritis?
There is usually no single cause. Things that make it more likely include:
- Getting older. It is uncommon before the age of 45.
- A previous knee injury, such as an ACL injury, a meniscus tear or a fracture into the joint.
- Extra body weight, which increases the load through your knees.
- The alignment of your legs. Being bow-legged (varus) loads the inner side of the knee, and being knock-kneed (valgus) loads the outer side.
- Your genes and family history.
What are the symptoms of knee osteoarthritis?
The main symptom is pain in and around the knee. It is usually worse with activity, such as walking a long way, climbing stairs or getting up from a chair, and eases with rest. As the arthritis advances, pain can also come on at rest or at night. Other symptoms include:
- Stiffness first thing in the morning or after sitting, which usually eases within half an hour.
- Swelling that comes and goes.
- Grinding or creaking when you move the knee.
- The knee feeling weak or giving way.
- Not being able to fully straighten or bend the knee.
- The leg slowly becoming more bow-legged or knock-kneed.
Symptoms often flare up for days or weeks and then settle.
When should you see a doctor?
See your GP or physiotherapist if knee pain is affecting your walking, sleep or daily activities, or has not settled after a few weeks. Seek medical advice sooner if:
- Your knee suddenly swells, locks or gives way.
- You cannot put weight on your leg.
- The pain keeps you awake most nights.
- Your knee is hot, red and swollen, or you have a fever. Seek urgent care.
How is knee osteoarthritis diagnosed?
The diagnosis is usually made from your symptoms and an examination of your knee and the alignment of your legs. X-rays taken while you are standing show how much joint space is left and which parts of the knee are affected. An MRI scan is not usually needed to diagnose osteoarthritis.
How is knee osteoarthritis treated without surgery?
Most people with knee osteoarthritis are treated without surgery. International guidelines recommend three core treatments for everyone: learning about the condition, structured exercise, and weight loss if you are overweight. Other treatments can be added if pain persists.[1] Dr Vishal Pai’s practice is to make sure these have been tried properly before surgery is discussed. You can read more in treating knee arthritis without surgery.
Understanding your condition
Knowing that exercise is safe for an arthritic knee helps you stay active. Physiotherapists run group programs that combine education and exercise, such as GLA:D.
Exercise and physiotherapy
Exercise is the most important treatment. A review of 54 trials found that exercise reduced knee pain and improved function, and the benefit lasted at least 2 to 6 months after the program finished.[2] A physiotherapist can design a program to strengthen the muscles around your knee and hip, improve your balance and keep the joint moving. Walking, cycling and exercise in water (hydrotherapy) are good options.
Weight loss
If you are overweight, losing weight reduces the load on your knees. In an 18-month trial of 454 people with knee osteoarthritis, those who lost about 10% of their body weight through diet and exercise had less pain and better function than those who exercised alone.[3]
Walking aids and braces
A walking stick, held in the hand opposite your sore knee, takes some of the load off the joint. An off-loading brace aims to shift load away from the worn side of the knee.
Pain-relief medicines
Anti-inflammatory gels rubbed onto the knee are a recommended first option. Anti-inflammatory tablets can help with persistent pain, but they have side effects, so use them at the lowest dose for the shortest time, guided by your GP or pharmacist.[1]
Injections
None of the injections used in the knee reverses arthritis, and the evidence for each differs:
- Cortisone (steroid) injection. This can ease pain for a few weeks. In a review of 27 trials, the benefit faded over time, with no evidence of benefit at 6 months.[4]
- Lubricant (hyaluronic acid) injection. Reviews disagree. The largest found the average benefit was too small to notice, with slightly more serious side effects than a placebo injection.[5] Other reviews conclude that it reduces pain for some people.[6]
- Platelet-rich plasma (PRP). This is a concentrate made from your own blood. In an Australian trial of 288 people, PRP worked no better than a salt-water (placebo) injection at 12 months.[7]
Radiofrequency ablation
Radiofrequency ablation uses heat from a fine needle, guided by X-ray or ultrasound, to switch off the small nerves (genicular nerves) that carry pain signals from the knee. It does not change the arthritis itself. In a review of 21 randomised trials with 1,818 people, it reduced knee pain and improved function in the short term, up to 6 months. Whether the benefit lasts longer is less certain.[8]
When is surgery considered?
Surgery is considered only when pain and loss of function still affect your daily life after a good trial of the treatments above, and your X-rays show arthritis that explains your symptoms. Keyhole surgery (arthroscopy) to wash out or trim an arthritic knee is not recommended, because trials show little or no benefit.[9] The main options are a partial knee replacement when only one part of the knee is worn, a total knee replacement when the arthritis is more widespread, and, for some younger, active people with arthritis on one side of the knee, a realignment osteotomy.
Next step
Have your knee assessed
Most knee arthritis is treated without surgery. Dr Vishal Pai can examine your knee, review your X-rays and explain your options, starting with exercise and weight management.
What is the outlook for knee osteoarthritis?
Osteoarthritis cannot be cured, and worn cartilage does not grow back. But it does not always get steadily worse. In a review of 7 studies of 7,747 people, mostly with early or moderate arthritis, pain stayed about the same over the medium term in 85%, improved in 8% and got worse in 7%.[10] Staying active, keeping to a healthy weight and keeping up your exercises are the most reliable ways to control your symptoms.[1][2][3]
References
Show all 11 referencesHide references
- Bannuru RR et al. 2019. OARSI guidelines for the non-surgical management of knee, hip, and polyarticular osteoarthritis. Osteoarthritis and Cartilage.
- Fransen M et al. 2015. Exercise for osteoarthritis of the knee: a Cochrane systematic review. British Journal of Sports Medicine.
- Messier SP et al. 2013. Effects of intensive diet and exercise on knee joint loads, inflammation, and clinical outcomes among overweight and obese adults with knee osteoarthritis: the IDEA randomized clinical trial. JAMA.
- Jüni P et al. 2015. Intra-articular corticosteroid for knee osteoarthritis. Cochrane Database of Systematic Reviews.
- Pereira TV et al. 2022. Viscosupplementation for knee osteoarthritis: systematic review and meta-analysis. BMJ.
- Bruyère O et al. 2025. Effects of intra-articular hyaluronic acid injections on pain and function in patients with knee osteoarthritis: an umbrella review of systematic reviews and meta-analyses of randomized placebo-controlled trials. Maturitas.
- Bennell KL et al. 2021. Effect of intra-articular platelet-rich plasma vs placebo injection on pain and medial tibial cartilage volume in patients with knee osteoarthritis: the RESTORE randomized clinical trial. JAMA.
- Wu LM et al. 2022. Radiofrequency ablation in cooled monopolar or conventional bipolar modality yields more beneficial short-term clinical outcomes versus other treatments for knee osteoarthritis: a systematic review and network meta-analysis of randomized controlled trials. Arthroscopy.
- O’Connor D et al. 2022. Arthroscopic surgery for degenerative knee disease (osteoarthritis including degenerative meniscal tears). Cochrane Database of Systematic Reviews.
- Previtali D et al. 2020. Pain trajectories in knee osteoarthritis: a systematic review and best evidence synthesis on pain predictors. Journal of Clinical Medicine.
- Skou ST et al. 2015. A randomized, controlled trial of total knee replacement. New England Journal of Medicine.
Frequently asked questions
How long can you go with a bone-on-bone knee?
There is no set time, and some people manage well for years. In a trial of people with moderate to severe arthritis who were eligible for a knee replacement, about 3 in 4 of those given non-surgical treatment had not had a replacement a year later.[11] The decision about surgery depends on how much your knee limits your life, not on the X-ray alone.
What is end-stage knee osteoarthritis?
End-stage means the cartilage in at least one part of the knee has worn through, so the bones touch (“bone on bone”) on X-ray. It does not automatically mean you need surgery. Treatment depends on your symptoms and how much they affect you.
Does knee osteoarthritis always need surgery?
No. Most people are treated without surgery, with education, exercise, weight loss if needed and pain relief.[1] Surgery is considered when these have not controlled your pain and the arthritis is advanced on X-ray.
Will a knee replacement get rid of osteoarthritis?
A knee replacement removes the worn joint surfaces and replaces them with metal and plastic parts, so the arthritic surfaces are gone. Most people have much less pain afterwards. A partial knee replacement treats only the worn part, so arthritis can still develop later in the rest of the knee.