Knee osteoarthritis
Degeneration of the cartilage lining of the knee joint, causing pain, swelling, stiffness and loss of function. The knee is the most commonly replaced joint in the UK, with over 100,000 procedures annually.
📊 Knee osteoarthritis affects approximately 18% of adults over 45 and is the leading indication for total knee replacement in the UK.
What is knee osteoarthritis?
The knee joint has three compartments: the medial (inner), lateral (outer), and patellofemoral (kneecap) compartments. Osteoarthritis can affect one, two, or all three compartments. Medial compartment osteoarthritis is the most common and causes a varus (bow-legged) deformity. Lateral compartment disease causes a valgus (knock-kneed) deformity. Patellofemoral arthritis causes pain at the front of the knee, particularly on stairs and when rising from a chair.
The KELLGREN-Lawrence grading system (0-4) classifies knee osteoarthritis radiologically. Weight-bearing X-rays are essential to accurately assess joint space narrowing - non-weight-bearing films consistently underestimate the degree of cartilage loss. The Outerbridge classification grades intra-articular cartilage damage at arthroscopy. Varus or valgus deformity, ligamentous laxity, and bone quality are important factors in surgical planning.
Not all knee pain in older adults is osteoarthritis. Meniscal tears, bursitis (Pes anserine, prepatellar), iliotibial band syndrome, and referred pain from the lumbar spine or hip should be considered in the differential diagnosis. MRI is helpful in younger patients or those with atypical presentations to assess soft tissue structures.
Common causes
- Age-related cartilage degeneration
- Obesity - the most modifiable risk factor
- Previous knee injury (meniscal tear, ACL rupture)
- Previous knee surgery (particularly meniscectomy)
- Inflammatory arthritis (rheumatoid, psoriatic)
- Crystal arthropathy (gout, pseudogout)
- Post-traumatic arthritis after intra-articular fracture
Who is at risk? Obesity is the most important modifiable risk factor - each unit increase in BMI increases knee OA risk by approximately 10%. Female sex, age, family history, and previous knee injury significantly increase risk.
Symptoms
Symptoms vary depending on the severity and duration of the condition. Common symptoms include:
- Pain on walking, particularly on stairs, hills, and uneven surfaces
- Stiffness after rest, improving with movement (gelling phenomenon)
- Swelling (effusion) within the joint after activity
- A varus (bow-legged) or valgus (knock-kneed) deformity developing over time
- Crepitus (clicking and grinding) with knee movement
- Reduced walking distance and limitation of daily activities
When to seek help: See your GP if knee pain is limiting your walking, disturbing your sleep, or not responding to simple analgesia. Weight loss (if relevant) and physiotherapy should be tried before referral. Orthopaedic referral is appropriate when these measures are insufficient.
How is it diagnosed?
Your surgeon will take a detailed history and examine the joint. The following investigations may be arranged to confirm the diagnosis:
- Clinical examination - assessment of alignment, range of movement, joint line tenderness, and effusion
- Weight-bearing X-ray - essential; AP, lateral, and skyline (patellofemoral) views
- MRI - for younger patients, atypical presentations, or when soft tissue pathology is suspected
- CT scan - for pre-operative planning in complex deformity cases
Weight-bearing X-rays are mandatory before any surgical discussion. Unicompartmental disease (affecting only one compartment) may be suitable for partial knee replacement. Tricompartmental disease requires total knee replacement.
Treatment pathway
Treatment is tailored to the severity of the condition, your age, activity level, and overall health. Most conditions are treated in a stepwise fashion, starting with the least invasive options.
Conservative management
Weight loss (if BMI elevated), analgesics (paracetamol, NSAIDs), targeted quadriceps strengthening physiotherapy, activity modification, and the use of a walking stick. Knee bracing (unloading brace) can reduce pain in unicompartmental disease.
Intra-articular injection
Corticosteroid injection provides short-term pain relief. Hyaluronic acid injections may offer longer-lasting benefit in selected patients. Not recommended before joint replacement surgery within 3 months due to infection risk.
Unicompartmental (partial) knee replacement
Replacement of one compartment only (usually medial). Smaller operation with faster recovery than total knee replacement. Suitable for isolated single-compartment disease with intact anterior cruciate ligament and correctable deformity.
Total knee replacement (TKR)
Replacement of all three knee compartment surfaces with metal and polyethylene components. Highly effective and durable. Over 90% of implants survive 15 years. Patient satisfaction is slightly lower than for total hip replacement, with some patients reporting residual functional limitations.
Recovery
Recovery after total knee replacement is more prolonged than after hip replacement. Physiotherapy focusing on quadriceps strengthening and range of movement is essential. Swimming and cycling are encouraged from 6-8 weeks. High-impact activities (running, contact sport) are generally not recommended after knee replacement.
- Non-operative management: 3-12 months trial
- After knee replacement: mobilise day 1:
- Walking without aids: 4-6 weeks
- Return to driving: 6-8 weeks
- Full functional recovery: 6-12 months
What results can I expect?
Total knee replacement achieves significant pain relief in over 85% of patients. Approximately 15-20% of patients are dissatisfied with their outcome despite a technically well-performed operation - most commonly due to residual pain or stiffness. Unicompartmental replacement has higher satisfaction rates in appropriately selected patients.
Knee osteoarthritis - understanding your condition
In numbers
Typical activity timelines for this condition. These are approximate and vary considerably between patients. Always follow the specific guidance given by your surgeon and physiotherapist.
| Activity | Typical timeline | Notes |
|---|---|---|
| Stay active | Now | Activity is treatment, not a risk. Low-impact exercise reduces pain and improves function.[2] |
| Lose weight if needed | Ongoing | Weight loss has a substantial effect on knee pain, even small amounts make a measurable difference.[2] |
| Try a knee brace or support | For flares | A simple soft support may help during flares. Custom unloading braces are useful for some patients with predominantly medial OA.[1] |
| Consider an injection | For severe flares | A corticosteroid injection may help short-term but is not for repeated long-term use. Hyaluronic acid injections are not routinely recommended.[2] |
| Discuss surgery | When function is limited | Knee replacement is considered when symptoms substantially limit daily life and other measures are no longer adequate.[5] |
| Drive after TKR | 4-6 weeks after surgery | When you can react and brake safely and bend the knee enough to control the car. Inform your insurer.[7] |
| Return to sport | After TKR: 3-6 months | Walking, cycling, swimming, golf, doubles tennis are usually fine. Running and jumping sports are typically avoided.[8] |
Common concerns from patients with this condition or recovering from treatment, and whether they are expected or worth mentioning to your team.
Your questions, answered
Plain-English answers to the things people most often ask, grounded in UK clinical guidance. Tap a question to open it.
About thisWhat is knee osteoarthritis?
Knee osteoarthritis is gradual wear and thinning of the cartilage that lines the knee joint, along with changes in the bone underneath. It causes pain, swelling and stiffness, and is one of the most common causes of knee trouble as we get older.
SymptomsWhy is my knee stiff in the morning and worse later in the day?
Short-lived morning stiffness that eases within about half an hour is typical of osteoarthritis. Pain often builds with activity through the day and after prolonged standing or stairs. Some swelling and a grinding or creaking sensation are also common.
TreatmentWhat are my options before surgery?
First-line care is exercise to strengthen the thigh and leg muscles, weight management if needed, and simple pain relief. These are recommended by UK guidance for everyone with knee osteoarthritis. Knee replacement is reserved for when symptoms are severe and quality of life is significantly affected despite these measures.
ExerciseWon't exercise damage my knee further?
It will not. Strengthening exercises and low-impact activity reduce pain and improve function, and they are safe even when the joint is worn. Building up the muscles that support the knee protects it, whereas avoiding all activity makes the muscles weaker and symptoms worse.
InjectionsAre steroid injections helpful?
A steroid injection can calm a painful, swollen flare for a few weeks, which can be useful to get you moving again. The effect is temporary and the injection does not slow the arthritis, so it is best used alongside exercise rather than instead of it.
Daily lifeDo braces, insoles or walking aids help?
Some people find a supportive knee sleeve, good cushioned footwear or a walking stick eases their symptoms and confidence. These do not change the arthritis itself but can make day-to-day activity more comfortable. A physiotherapist can advise what is worth trying for you.
OutlookWill I end up in a wheelchair?
That is very unlikely. Most people with knee osteoarthritis stay mobile and independent, and many manage well for many years without surgery. Staying active is the single most effective way to keep the knee working.
When to worryWhat changes should prompt a check?
Get medical advice if the knee becomes hot, very swollen and painful with feeling unwell, if it suddenly locks or gives way, or if you cannot put weight on it. New severe pain after an injury also needs assessing.
- 1.Versus Arthritis: Knee pain and osteoarthritis
- 2.NICE NG226: Osteoarthritis in over 16s, diagnosis and management
- 3.Cochrane Review: Arthroscopic surgery for degenerative knee disease
- 4.National Joint Registry annual report (NJR), hip and knee implant data
- 5.NICE NG157: Joint replacement (primary): hip, knee and shoulder
- 6.British Association for Surgery of the Knee: Patient information
- 7.Royal College of Surgeons of England: Recovering from surgery, driving guidance
- 8.NHS: Knee replacement
- 9.Chartered Society of Physiotherapy: Patient information
References are to UK clinical guidance and patient information from recognised organisations. This page is for general information and does not replace personalised advice from your own clinical team.
Preparing for surgery?
Read our step-by-step guide - what to expect before, during, and after your procedure.
How is it diagnosed?
- ✓Clinical examination - assessment of alignment, range of movement, joint line tenderness, and effusion
- ✓Weight-bearing X-ray - essential; AP, lateral, and skyline (patellofemoral) views
- ✓MRI - for younger patients, atypical presentations, or when soft tissue pathology is suspected
- ✓CT scan - for pre-operative planning in complex deformity cases
Recovery milestones
- ●Non-operative management: 3-12 months trial
- ●After knee replacement: mobilise day 1:
- ●Walking without aids: 4-6 weeks
- ●Return to driving: 6-8 weeks
- ●Full functional recovery: 6-12 months