Knee osteoarthritis is one of the most common causes of chronic knee pain and stiffness in adults. It happens when the smooth cartilage cushioning the joint gradually breaks down, leading to pain, swelling and difficulty with everyday activities like walking or climbing stairs.
This guide covers what knee OA is, why it develops, how it is diagnosed and which treatments the evidence actually supports — with links to detailed articles on each specific topic.
When to See a Doctor
Most knee osteoarthritis is managed conservatively. Seek prompt medical assessment if you have any of the following, because they suggest something other than, or in addition to, osteoarthritis:
- A hot, red, severely swollen knee with fever — possible joint infection, which is urgent
- Sudden severe pain or swelling after an injury, or inability to bear weight
- A knee that locks, catches or gives way repeatedly
- Pain that is worse at night or at rest, or unexplained weight loss alongside joint pain
- Multiple swollen joints, prolonged morning stiffness beyond an hour, or symmetrical joint involvement — this pattern points toward inflammatory arthritis rather than OA
What Is Knee Osteoarthritis?
Knee osteoarthritis (knee OA) is a degenerative joint disease in which the cartilage covering the ends of the thigh bone (femur), shin bone (tibia) and kneecap (patella) slowly wears away. As this cushioning breaks down, bones can begin to rub together, causing pain, stiffness and structural change in the joint.
Specialists distinguish two main forms:
- Primary knee osteoarthritis: age-related wear without a single clear cause.
- Secondary knee osteoarthritis: OA developing after another problem, such as injury, deformity or metabolic disease.
It is a leading cause of disability worldwide, which is why early diagnosis and active management matter. For how the condition advances over time, see osteoarthritis progression and what slows it down.
Symptoms of Knee Osteoarthritis
Symptoms usually appear gradually and worsen over time rather than starting suddenly.
- Pain: typically worse with activity, walking or stairs, and better with rest.
- Stiffness: especially on waking or after sitting for a long period. Morning stiffness in OA usually eases within 30 minutes.
- Swelling and warmth: from inflammation and excess joint fluid.
- Crepitus: a grinding or crunching sensation on movement.
- Reduced range of motion: difficulty fully bending or straightening the knee.
- Instability: the knee feels weak, wobbly or unreliable.
Everyday tasks such as rising from a chair, squatting or walking distances become more tiring or painful. Pain on stairs specifically is one of the earliest functional complaints. Severity is often described in grades — see knee osteoarthritis stages, grade 1 to 4.
Causes of Knee Osteoarthritis
The core problem is progressive damage to articular cartilage, the smooth tissue allowing bones to glide without friction. Over time the cartilage loses water balance, its proteins break down, and it cracks, thins or wears away entirely.
Primary knee osteoarthritis
- Age-related cartilage wear
- Cumulative joint loading over many years
- Genetic and biochemical changes in cartilage and surrounding bone
Secondary causes
Post-traumatic: previous fractures around the knee, meniscus tears or ligament injuries, and repetitive sports injuries that alter joint mechanics. Injury-related OA can appear decades after the original event.
Structural: congenital malformations, and malalignment such as varus (bow-legged) or valgus (knock-knee) deformity, which concentrates stress on one side of the joint. Malalignment is also what makes certain braces effective — see choosing a knee brace for osteoarthritis.
Metabolic and systemic: rickets and other mineralisation disorders, haemochromatosis (iron overload), chondrocalcinosis (calcium crystal deposits), ochronosis, and endocrine conditions including acromegaly, hyperparathyroidism and hyperuricaemia. Crystal-related joint disease is a distinct problem — see gout: causes, treatment and diet.
Risk Factors
- Older age — risk rises significantly after middle age.
- Sex — women are more affected than men, particularly after menopause.
- Excess body weight — increases load on weight-bearing joints, and adipose tissue also produces inflammatory mediators that damage cartilage. This is why it is the most modifiable risk factor of all.
- Previous joint injury — sports injuries or accidents raise later OA risk even years afterwards.
- Repetitive joint stress — occupations or sports involving frequent squatting, kneeling or heavy lifting.
- Genetics — family history and collagen gene variants predispose to earlier cartilage breakdown.
- Joint deformity — abnormal joint shape or misalignment.
- Metabolic disease — diabetes and haemochromatosis are associated with increased risk.
How Knee Osteoarthritis Is Diagnosed
Diagnosis combines history, physical examination and imaging.
- History — where the pain is, when it began, whether it worsens with activity and eases with rest, previous injury or surgery, and the effect on daily function, work and sleep.
- Examination — joint line tenderness, swelling, bony enlargement, crepitus, restricted flexion or extension, reduced muscle strength and balance deficits.
- X-ray — shows joint space narrowing, osteophytes (bone spurs) and changes in bone density.
- MRI — used selectively to assess cartilage, meniscus or bone marrow changes when the diagnosis is unclear.
- Blood tests — mainly to exclude rheumatoid arthritis or infection rather than to confirm OA.
An important caveat: radiographic severity often does not match the level of pain. Substantial changes can appear on X-ray in people with few symptoms, and severe pain can occur with modest imaging findings. Treatment is guided by symptoms and function, not by the scan alone. Distinguishing OA from inflammatory arthritis matters here — see rheumatoid arthritis versus osteoarthritis.
Treatment Options
Treatment aims to reduce pain, improve function and slow progression. Management starts conservatively and escalates only if symptoms warrant it.
1. Lifestyle and self-management
- Weight management — even modest weight loss meaningfully reduces knee load and pain.
- Low-impact activity — walking, cycling and swimming maintain motion and strength without excessive impact. See swimming and aquatic exercise for knee OA.
- Activity modification — reducing kneeling, deep squatting and heavy lifting that aggravates pain. Practical day-to-day adjustments are covered in living with knee osteoarthritis.
- Heat and cold — heat for stiffness, ice for flare-up pain and swelling.
2. Exercise therapy
A tailored exercise programme is first-line care and has the strongest evidence base of any treatment for knee OA. Core components are quadriceps and hip strengthening, stretching of hamstrings, calves and hip flexors, and balance and proprioception training. Full programme in knee osteoarthritis exercises.
3. Medications
- Topical NSAIDs — often preferred first for knee OA, with fewer systemic side effects.
- Oral NSAIDs — effective for pain and inflammation, but require caution given gastrointestinal, kidney and cardiovascular risk.
- Paracetamol (acetaminophen) — modest benefit; no longer first-line in several guidelines.
- Other agents — duloxetine in selected cases. Long-term opioids are not recommended for osteoarthritis.
There are currently no proven disease-modifying drugs that reliably halt or reverse knee osteoarthritis.
4. Injections
- Corticosteroid — short-term relief during flare-ups, not for frequent or long-term use.
- Hyaluronic acid — evidence is mixed and guidelines disagree. Full breakdown in do hyaluronic acid knee injections work?
- Platelet-rich plasma (PRP) — emerging, higher cost, evolving evidence. See PRP therapy for knee osteoarthritis.
5. Surgery
- Arthroscopy — limited role, mainly where mechanical symptoms from loose bodies or meniscal tears coexist. Not recommended for OA alone.
- Osteotomy — bone realignment in younger patients with malalignment.
- Partial or total knee replacement — replaces damaged surfaces to reduce pain and restore mobility in advanced disease.
Surgical decisions depend on pain, disability, age, comorbidities and imaging, and must be individualised. Cartilage-restoration approaches are discussed separately in the full treatment escalation guide.
Complications
- Chondrolysis — rapid, severe cartilage breakdown with loose debris in the joint. See chondrolysis: symptoms and treatment.
- Osteonecrosis — poor blood supply to bone beneath damaged cartilage, causing collapse.
- Stress fractures — repeated overload on weakened bone.
- Ligament and tendon weakening — chronic instability strains soft tissue and reduces joint stability further.
- Joint bleeding or infection — particularly after invasive procedures, or in people on anticoagulants or immunocompromised.
- Disability and reduced quality of life — advanced OA limits mobility, independence and mental wellbeing.
Knee Osteoarthritis and Fall Risk
Falls are a significant concern because pain, stiffness and muscle weakness all affect balance and gait. A systematic review of adults with knee OA identified impaired balance, quadriceps and lower-limb weakness, multiple comorbidities (such as diabetes or low back pain), and an increasing number of symptomatic joints as key fall risk factors.
Knee pain itself was also identified as a possible risk factor, but the evidence was rated conflicting because studies disagreed. Limited evidence linked knee instability, impaired proprioception and walking-aid use to fall risk. More recent observational work has additionally associated falls with fear of falling, higher body mass index, reduced range of motion and gait impairment.
Practical prevention: quadriceps, hip and ankle strengthening; balance work such as single-leg stance or Tai Chi; treating comorbidities and optimising vision; reviewing medications that cause dizziness; correct use of walking aids; and home safety measures. Detail in knee osteoarthritis and falls.
The Complete Knee Osteoarthritis Guide
Detailed articles on each part of managing knee and hip osteoarthritis:
Understanding the condition
- Knee osteoarthritis stages: grade 1 to 4
- How osteoarthritis progresses and what slows it
- Hip osteoarthritis: symptoms, exercises and surgery
- Rheumatoid arthritis vs osteoarthritis
- Gout: causes, treatment and diet
- Aneurysm osteoarthritis syndrome
Exercise and daily management
- Knee osteoarthritis exercises
- Swimming and aquatic exercise for knee OA
- Living with knee osteoarthritis: daily joint protection
- Knee osteoarthritis and falls
- Best knee brace for osteoarthritis
Treatments and procedures
- Treatment escalation: lifestyle to surgery
- Hyaluronic acid knee injections
- PRP therapy for knee osteoarthritis
- Chondrolysis: symptoms and treatment
FAQs About Knee Osteoarthritis
Knee osteoarthritis is a “wear and tear” joint disease where the cushion between the bones in your knee slowly breaks down, causing pain, stiffness, and swelling. Over time, this can make everyday movements like walking, climbing stairs, or squatting more difficult.
Major risk factors include older age, being female, excess body weight, previous knee injuries, repetitive joint stress, genetics, and metabolic diseases such as diabetes and haemochromatosis. Structural problems such as bow-legs or knock-knees also increase the chance of developing knee OA.
Yes. Adults with knee osteoarthritis have a higher risk of falls due to impaired balance, quadriceps weakness, pain, comorbidities and gait changes. Research has also linked higher body mass index, reduced knee range of motion and fear of falling with greater fall risk.
There is no single best treatment. Guidelines recommend combining weight management, low-impact exercise, physical therapy, pain relief and joint-protection strategies. In advanced cases, injections or knee replacement may be considered when conservative treatment no longer helps.
There is currently no cure that restores normal cartilage. However, early diagnosis and good management reduce pain, improve function, slow progression and help you stay active and independent for longer.
Not necessarily. Radiographic severity often does not match symptom severity. Significant changes can appear on X-ray in people with little pain, and severe pain can occur with modest imaging findings. Treatment is guided by symptoms and function rather than the scan alone.
Sources
- StatPearls — Knee Osteoarthritis (NCBI Bookshelf)
- Centers for Disease Control and Prevention — Arthritis
- Cleveland Clinic — Knee Osteoarthritis
- Arthritis Foundation — Osteoarthritis
- Mayo Clinic — Osteoarthritis diagnosis and treatment
- NHS — Osteoarthritis treatment
- PubMed — Falls risk factors in knee osteoarthritis (systematic review)
Last updated: August 2026 | Related: Lower Back Pain Guide | Exercise and Fitness Guide | How we source figures
Medical disclaimer: This article is for general information and education only. It is not medical advice, diagnosis or treatment. A hot, swollen knee with fever needs urgent assessment. Always discuss treatment decisions, including medication and surgery, with a qualified clinician who knows your history.
