Knee osteoarthritis assessment and treatment

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Knee osteoarthritis is a clinical syndrome, not an X-ray finding. Ask about load pain, start-up stiffness, swelling, giving way, true locking, stairs, chair rise, sleep, walking, work and desired activity. Establish tempo, inflammatory symptoms, trauma, previous meniscal or ligament surgery and episodic hot attacks. Clarify whether giving way reflects pain and quadriceps inhibition or true ligament instability. Background radiographic change is common and must not explain a new acute red-flag presentation automatically.

Observe gait and varus or valgus alignment, inspect swelling and scars and palpate joint lines and patellofemoral margins. Test active and passive extension and flexion, effusion, patellar tracking, quadriceps strength and collateral and cruciate stability. Examine the hip and lumbar neurological system when pain pattern or local findings do not match. Document distal pulses and calf findings. A fixed block differs from pain-limited movement and changes urgency.

Diagnose clinically in the typical NICE group and avoid routine imaging. Obtain weight-bearing AP, lateral and skyline or other alignment views for atypical symptoms, major deformity, surgical planning or a competing structural diagnosis. Radiographic joint-space loss, osteophytes, sclerosis and cysts support anatomy but correlate poorly with pain. MRI is not routine and frequently finds age-related meniscal changes that do not require surgery. Use MRI for a specific locked-knee, occult lesion or diagnostic uncertainty question.

Exercise is the central intervention: progressive quadriceps and hip strengthening, aerobic activity, range and neuromuscular work matched to function. Supervision can establish technique and confidence. Explain that early discomfort is compatible with adaptation and that long-term adherence drives benefit. Activity modification should retain movement rather than prescribe avoidance. A walking stick, pacing and workplace changes may help. Consider a brace only when instability or abnormal load is clearly present and an aid will support activity.

For overweight or obesity, offer respectful sustained weight-management support. Any loss is likely to help; NICE notes that 10% is likely more beneficial than 5%. Explore food access, medicines, sleep, mood and mobility limits and consider appropriate services. Do not make improvement or referral conditional on achieving an arbitrary number. Manual therapy can accompany exercise but is not a stand-alone treatment. Do not offer acupuncture, dry needling, glucosamine or electrotherapy in place of core care.

Offer a topical NSAID first for knee osteoarthritis. If ineffective or unsuitable, an oral NSAID can be considered at the lowest effective dose for the shortest time, with a proton-pump inhibitor and review of gastrointestinal, renal, hepatic and cardiovascular risks, anticoagulation and pregnancy. Do not routinely offer paracetamol or weak opioids; use only infrequently for short-term rescue when all other options are contraindicated, not tolerated or ineffective. Strong opioids should not be offered.

Corticosteroid injection can provide temporary relief for roughly two to ten weeks and may create an opportunity to progress exercise. Exclude infection and discuss hyperglycaemia, bleeding and rare septic arthritis. Recurrent large effusions require diagnostic reconsideration rather than automatic reinjection. NICE advises against hyaluronan injections. Arthroscopic lavage or debridement is not treatment for uncomplicated osteoarthritis; a separate true locked-knee lesion requires its own pathway.

Refer for knee replacement assessment when pain, stiffness, deformity or reduced function substantially affects quality of life and non-operative treatment is ineffective or unsuitable. Do not rely on a numerical scoring threshold. Optimise anaemia, diabetes, smoking, weight, medicines, skin and dental issues through shared decisions without unjustified delay. Discuss total versus partial replacement where isolated compartment disease makes both options suitable. Maintain strengthening, analgesic safety and deterioration surveillance during waiting.

Key points

Use NICE's clinical pattern: age at least 45, activity-related joint pain and no or no more than 30 minutes of morning stiffness; do not routinely image a typical presentation.
Assess gait, alignment, effusion, extension and flexion, joint lines, patellofemoral tracking, quadriceps strength, ligament stability and hip and neurovascular sources.
Therapeutic exercise and supported weight management are core treatment; discomfort can initially increase, but regular progressive strengthening and aerobic work improve pain and function.
Offer a topical NSAID for knee osteoarthritis. If ineffective or unsuitable, consider a short oral NSAID with risk review and gastroprotection.
Paracetamol and weak opioids are not routine; reserve infrequent short-term use for when other options cannot be used or have failed, and do not offer strong opioids.
Consider intra-articular corticosteroid for approximately 2 to 10 weeks of relief when other medicines are unsuitable or to support exercise; do not offer intra-articular hyaluronan.
Bracing and insoles are not routine unless instability or abnormal biomechanical loading is present and exercise alone is insufficient; walking aids can improve confidence and unloading.
Refer for replacement when symptoms substantially affect quality of life despite ineffective or unsuitable non-surgical care, without using numerical scores, age, BMI or smoking alone to block referral.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Whole-joint ageing

Cartilage, menisci, subchondral bone, synovium, ligaments and muscle undergo interacting structural and inflammatory change with age.

Mechanical loading

Higher body weight, occupational knee loading, malalignment and muscle weakness alter compartment stress and symptom burden.

Previous injury

Meniscal tissue loss, cruciate injury, intra-articular fracture and recurrent instability substantially increase later post-traumatic knee osteoarthritis risk.

Biological susceptibility

Genetic factors, metabolic health and inflammatory signalling influence why similar structural findings produce different symptoms and progression.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Cartilage and meniscal failure
Loss of load distribution increases focal contact stress and reduces smooth movement, particularly in medial tibiofemoral and patellofemoral compartments.
2
Subchondral response
Bone sclerosis, cysts and marrow lesions contribute to load pain and may fluctuate independently of apparent cartilage loss.
3
Synovial fluctuation
Intermittent synovitis and effusion cause variable swelling, inhibition and stiffness rather than a steadily linear course.
4
Osteophyte and alignment change
Marginal bone formation, capsular restriction and compartment collapse alter coronal alignment and progressively reduce knee extension or flexion.
5
Quadriceps inhibition
Pain and effusion suppress muscle activation, causing weakness, instability sensation and further loss of shock absorption.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Typical mechanical syndrome

Activity pain, brief start-up stiffness, crepitus and gradually reduced movement in an adult over 45 supports clinical diagnosis.

Effusion-driven inhibition

Fluctuating swelling with quadriceps weakness and giving-way sensation may reflect synovitis rather than ligament rupture.

Compartment pattern

Medial joint-line load pain and varus or anterior stair pain and crepitus can indicate tibiofemoral or patellofemoral predominance.

True locked knee

A fixed loss of extension after a mechanical event suggests displaced tissue and requires urgent knee assessment rather than routine OA management.

Inflammatory or septic pattern

Prolonged stiffness, intense warmth, systemic illness or severe passive pain redirects investigation toward aspiration and inflammatory causes.

Referral-level disease

Night disturbance, restricted walking and failed core care justify surgical assessment even when radiographic grading appears modest.

Red flags requiring action

A hot swollen knee with systemic illness or severe passive-movement pain requires urgent aspiration and septic-arthritis treatment sequencing.
A true locked knee that cannot fully extend after an acute mechanical event needs urgent soft-tissue knee assessment rather than routine physiotherapy alone.
Traumatic inability to bear weight, focal bony tenderness or deformity requires fracture assessment before a degenerative pathway.
Calf swelling, absent pulses, foot coolness or new neurological deficit requires vascular and thromboembolic assessment and must not be labelled referred osteoarthritis pain.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line clinical diagnosisFirst stepFirst line
Why
Recognise a typical syndrome and establish functional baseline.
Interpretation and limitations
Document pain pattern, brief stiffness, alignment, range, effusion, strength and alternative sources; routine imaging is unnecessary.
02
Weight-bearing radiographs when indicated
Why
Define compartment, alignment and surgical anatomy.
Interpretation and limitations
Films support planning but should not be used to invalidate substantial symptoms or impose a referral threshold.
03
Aspiration for acute effusion
Why
Exclude infection and identify crystals when the knee is unexpectedly hot or swollen.
Interpretation and limitations
Send cell differential, Gram stain, cultures and crystals; crystals or negative Gram stain do not alone exclude sepsis.
04
MRI for a defined mechanical question
Why
Identify displaced meniscus, occult fracture or other lesion when examination warrants it.
Interpretation and limitations
Avoid MRI for routine degenerative pain because incidental tears can lead to low-value surgery.
05
Blood tests for competing disease
Why
Assess infection, inflammation or malignancy when suggested.
Interpretation and limitations
FBC and CRP are not routine OA tests and normal results cannot rule out early septic arthritis.
06
Pre-replacement assessment
Why
Measure deformity, fitness, expectations and modifiable risk.
Interpretation and limitations
Combine standing radiographs and clinical assessment and avoid numerical-score-only selection.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Crystal or septic arthritis

An abrupt hot effusion requires urgent aspiration because gout, calcium-pyrophosphate disease and destructive bacterial infection can overlap clinically.

Meniscal tear

Joint-line pain, catching and true locking after a twist may indicate displaced tissue, though degenerative MRI tears are often incidental.

Inflammatory arthritis

Prolonged morning stiffness, several swollen joints and systemic features prompt detailed inflammatory examination, blood testing and specialist review.

Referred hip or spine pain

Hip restriction, groin symptoms, radicular features or a normal local knee examination suggest another pain generator.

Osteonecrosis or tumour

Sudden severe focal condylar pain, night symptoms or destructive change requires targeted imaging beyond routine osteoarthritis care.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01CoreExercise, weight and education firstFirst stepThe clinical pattern is typical and no urgent competing diagnosis is present.

1Agree meaningful goals and prescribe progressive knee and hip strengthening, aerobic activity and range work.
2Offer sustained weight support when relevant and address walking aids, pacing and participation barriers.
3EscalationOffer topical NSAID and escalate cautiously only when function remains limited.
4Review function, adherence, adverse effects and diagnostic fit at an agreed interval.

02Acute changeExit the degenerative pathwayThe knee becomes hot, fixed, traumatically non-weight-bearing or neurovascularly abnormal.

1Use sepsis and aspiration sequencing for a hot effusion and obtain urgent fracture imaging after trauma.
2Refer a true locked knee for urgent soft-tissue knee assessment.
3Assess calf, pulses and neurological function when swelling or distal symptoms occur.
4Do not allow old radiographs to override the new clinical syndrome.

03ReplacementRefer from quality-of-life impactSymptoms substantially limit life and appropriate non-surgical care has failed or is unsuitable.

1Discuss replacement benefits, persistent-pain possibility, complications, recovery and alternatives.
2Refer without arbitrary score, age, smoking, comorbidity or BMI exclusion.
3Optimise health and home support while maintaining exercise and analgesic review.
4For isolated medial disease, support a balanced total-versus-partial replacement discussion when both are suitable.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Provides local analgesic and anti-inflammatory effect with less systemic exposure than an oral NSAID.

Topical NSAID

Offer a licensed topical NSAID preparation for the painful knee at the product's adult frequency, typically applied three or four times daily depending on formulation, for a time-limited trial with review of function and skin tolerance.

Check NSAID hypersensitivity, broken skin, pregnancy and concurrent NSAID use; systemic absorption still matters in severe renal, gastrointestinal or cardiovascular risk, and handwashing and product-specific dosing should be explained.

May reduce pain enough to restore exercise, sleep and mobility when local treatment is insufficient.

Oral NSAID plus proton-pump inhibitor

If topical treatment is ineffective or unsuitable, use one oral NSAID at the lowest effective licensed dose for the shortest period and co-prescribe gastroprotection such as omeprazole 20 mg orally once daily while the NSAID continues when appropriate.

Assess ulcer, bleeding, kidney, liver and cardiovascular risk, frailty, blood pressure, anticoagulants, antiplatelets and pregnancy; never combine oral NSAIDs and stop during dehydration or acute renal deterioration.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Loss of mobility

Pain, flexion loss and quadriceps weakness limit walking, stairs, transfers and independent self-care and can accelerate physical frailty.

Varus or valgus progression

Compartment collapse and ligament attenuation progressively increase deformity, instability, bone loss and technical complexity of later knee replacement.

Falls and cardiovascular decline

Prolonged activity avoidance reduces balance, lower-limb muscle reserve and cardiovascular fitness while reinforcing pain-related fear and social withdrawal.

Medicine toxicity

Long-term or poorly monitored NSAID and opioid exposure can cause renal, gastrointestinal, cardiovascular, cognitive, falls and dependence-related harm.

Replacement-related risk

Knee arthroplasty carries infection, thrombosis, stiffness, instability, persistent pain, peri-prosthetic fracture, component loosening and future revision risk.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Track chair rise, stairs, walking, sleep, work and chosen activity goals rather than X-ray grade alone.
Review quadriceps strength, extension, effusion and falls and progress exercise instead of repeating a static programme.
Monitor topical skin effects and oral NSAID blood pressure, renal, gastrointestinal and cardiovascular harm.
Reassess large recurrent effusion, true locking, rest pain or rapid deformity for another diagnosis.
Support weight and metabolic risk without delaying indicated referral through arbitrary targets.
During surgical waiting, maintain fitness, skin care, analgesic safety and home and postoperative planning.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

MRI tears are common

Degenerative meniscal signal frequently accompanies ageing and does not prove that arthroscopy will improve osteoarthritis pain.

Giving way may be muscle inhibition

Effusion suppresses quadriceps activation and creates instability sensation without a primary ligament rupture.

Topical really is first

NICE specifically offers topical NSAID for knee osteoarthritis before exposing the whole body to oral toxicity.

An injection should buy activity

Use temporary corticosteroid relief to progress exercise or decisions, not to defer reassessment indefinitely.

Symptoms can outrun radiographs

Substantial disability deserves treatment and referral even when structural grading is not dramatic.

A hot knee resets probability

Background osteoarthritis and crystals do not protect a patient from simultaneous septic arthritis.

11Common pitfallsFrequent interpretation and management errors.

01
Diagnosing from radiographs without examining alignment, effusion, strength, hip and neurovascular findings.
02
Ordering MRI for routine degenerative pain and over-treating an incidental meniscal tear.
03
Advising prolonged rest and allowing quadriceps weakness and cardiovascular decline.
04
Using recurrent opioids or NSAIDs without functional benefit and toxicity review.
05
Injecting an unexplained hot effusion before excluding infection.
06
Blocking replacement referral with a score or arbitrary BMI rather than individual assessment.