Knee Pain Algorithm · Reasoning GP

Safety

Exclude emergencies & can't-miss diagnoses first

Done

Screen for limb- and life-threatening diagnoses before proceeding. Acute onset, fever, significant trauma, and vascular signs demand immediate action.

Septic arthritis Hot, swollen, exquisitely tender knee + fever + raised WCC/CRP + unable to weight-bear → same-day orthopaedics; aspiration must occur within hours to prevent irreversible cartilage destruction

Acute limb ischaemia Sudden severe pain + pale, cold, pulseless leg → 999 vascular emergency; 6-hour window for revascularisation

Fracture with neurovascular compromise Significant trauma + deformity + absent distal pulse or paraesthesia → 999; popliteal artery injury with distal neurovascular deficit is a limb emergency

Haemarthrosis — acute ligament rupture / fracture Immediate (<2h) tense effusion after trauma → ACL rupture or tibial plateau fracture until proven otherwise → same-day ED / orthopaedics

Deep vein thrombosis Calf and posterior knee pain, swelling, erythema, post-immobility/surgery/travel → same-day DVTUS via Wells pathway; Baker's cyst rupture mimics DVT — confirm with ultrasound

Bone tumour / malignancy Age <40 or >55, night pain unrelated to activity, bony swelling around knee, weight loss → 2WW bone/soft tissue sarcoma pathway (NICE NG12)

Necrotising fasciitis / cellulitis with systemic sepsis Rapidly spreading erythema around knee + fever + disproportionate pain + systemically unwell → 999 (NICE NG51)

Locked knee — acute mechanical block Complete inability to extend knee, locked in flexion after trauma → bucket-handle meniscal tear; same-day orthopaedics — do not force extension

Septic arthritis is the most commonly missed serious knee diagnosis in primary care. Cartilage destruction begins within 24–48 hours of untreated bacterial infection. Classic features (fever, raised WCC) may be absent in immunosuppressed patients and those on steroids — a high index of suspicion is essential. Haemarthrosis within 2 hours of trauma is an ACL rupture or tibial plateau fracture in 70% of cases; delayed effusion (>12–24 h) suggests meniscal or less severe ligament injury. The Baker's cyst rupture / DVT mimic is a well-recognised diagnostic trap — ultrasound differentiates reliably. Bone tumours around the knee (distal femur, proximal tibia) account for 60% of primary bone sarcomas — missing this diagnosis delays potentially curative surgery.

Diagnose

Structured history — onset, mechanism, and pain pattern

Done

Mechanism of injury and precise pain location are the two most powerful diagnostic discriminators. A 2-minute focused history narrows the differential dramatically.

Age & demographics

Age strongly predicts diagnosis: <40 → trauma, OCD, patellofemoral syndrome, inflammatory arthritis; 40–60 → meniscal tear, early OA, pes anserine bursitis; >60 → OA overwhelmingly likely, PMR, gout

Mechanism of injury

Twisting on planted foot (ACL/meniscal), valgus stress (MCL), direct blow to lateral knee (fibular head fracture/LCL), hyperextension (PCL), atraumatic gradual onset (OA, tendinopathy, inflammatory)

Onset & duration

Immediate effusion (<2h) → haemarthrosis (ACL/fracture). Delayed effusion (12–24h) → meniscal/minor ligament. Insidious (>6 weeks) → OA, patellofemoral syndrome, tendinopathy, inflammatory arthritis

Pain location

Medial joint line (meniscal, MCL, OA medial compartment); lateral joint line (LCL, lateral meniscal, ITB); anterior/peripatellar (patellofemoral, patellar tendinopathy, Osgood-Schlatter); posterior (Baker's cyst, PCL, popliteal artery); generalised (OA, septic, inflammatory)

Mechanical symptoms

Locking (true locking = cannot extend → meniscal tear); giving way (ACL insufficiency, patellofemoral instability); clicking/clunking (meniscal, patellofemoral); catching (loose body)

Aggravating factors

Stairs / rising from chair (patellofemoral OA); running, hills (ITB syndrome, patellofemoral); kneeling (prepatellar bursitis); sitting with flexed knee → anterior pain (patellofemoral = "cinema sign")

Swelling

Intra-articular (ballottement positive): OA flare, meniscal, inflammatory. Extra-articular: bursitis (prepatellar, infrapatellar), Baker's cyst, soft tissue

Systemic features

Morning stiffness >30 min (inflammatory arthritis); bilateral symmetrical joints (RA); psoriasis / IBD / urethritis (psoriatic/reactive); gout history; fever, sweats (septic, malignancy)

Functional impact

Weight-bearing ability, stair climbing, work, sport — essential for management planning and referral prioritisation

PMH / medications

Previous knee surgery, steroid use (osteonecrosis), anticoagulants (haemarthrosis risk), fluoroquinolone use (tendinopathy), immunosuppression (atypical septic arthritis)

Pain location combined with mechanism provides the correct diagnosis in approximately 70% of cases before any examination. The "cinema sign" (anterior knee pain after prolonged sitting) has a positive predictive value of ~85% for patellofemoral syndrome. True mechanical locking — the patient cannot actively extend the knee, not just stiffness — indicates a displaced bucket-handle meniscal tear requiring urgent orthopaedic review; confusing this with OA morning stiffness delays necessary surgery. Asking about bilateral symmetry and morning stiffness duration takes 20 seconds but reliably separates inflammatory arthritis (needing DMARD therapy) from mechanical causes.

Diagnose

Classify by presentation type — trauma vs atraumatic vs inflammatory

Done

Use the trauma / atraumatic / inflammatory framework to organise your differential. Each category has distinct investigations and management pathways.

🔴 Traumatic — acute

ACL rupture: twisting + pop + haemarthrosis + instability. Meniscal tear: twisting + joint line pain + delayed effusion ± locking. MCL/LCL sprain: valgus/varus force + medial/lateral pain. PCL: dashboard injury + posterior sag. Tibial plateau fracture: axial load + immediate swelling (Ottawa Knee Rule applies)

🟠 Atraumatic — mechanical

Osteoarthritis: age >45, activity-related pain, brief morning stiffness (<30 min), crepitus, joint space narrowing (NICE NG226 clinical diagnosis — no X-ray needed routinely). Patellofemoral syndrome: anterior pain, young active patient, cinema sign, no effusion. Patellar tendinopathy: inferior pole tenderness, jumping sports. ITB syndrome: lateral knee pain, runner, 2–3 km trigger point

🟡 Atraumatic — periarticular

Prepatellar bursitis: anterior swelling over patella, kneeling occupation (carpet layers, plumbers). Infrapatellar bursitis: below patella. Pes anserine bursitis: medial tibial flare tenderness, obese/diabetic/OA patient — often misdiagnosed as OA flare. Baker's cyst: posterior knee swelling, secondary to intra-articular pathology

🟢 Inflammatory arthritis

Rheumatoid arthritis: bilateral, symmetrical, morning stiffness >30 min, anti-CCP positive. Psoriatic arthritis: dactylitis, nail changes, skin psoriasis. Reactive arthritis: post-GI/STI, asymmetric. Gout/pseudogout: acute hot swollen joint, crystal arthropathy — pseudogout particularly common in knee (CPPD). PMR: bilateral, age >50, shoulder girdle ± hip, dramatic ESR elevation, steroid-responsive

🔵 Referred / systemic

Hip OA: medial knee pain with limited hip rotation — always examine the hip. Lumbar radiculopathy: L3/L4 referred to anterior knee. Osteonecrosis: steroid use, sudden severe pain, MRI diagnosis. Osgood-Schlatter: tibial tuberosity pain, adolescent, growth spurts

The most common diagnostic error in knee pain is attributing medial knee pain to OA when it is pes anserine bursitis. The two conditions respond to entirely different treatments (corticosteroid injection into the bursa vs OA management). Always examine the hip in apparent knee pain — hip OA refers to the medial knee in up to 30% of cases, and treating the knee without addressing the hip yields no benefit. NICE NG226 (2022) allows clinical diagnosis of OA without X-ray when age >45, activity-related pain, and no or brief morning stiffness — removing unnecessary imaging for the majority of knee OA patients.

Diagnose

Targeted examination — systematic assessment of the knee

Done

Follow LOOK → FEEL → MOVE → SPECIAL TESTS. Always examine the hip and assess gait. A complete knee exam takes 3–4 minutes and is diagnostic in the majority of cases.

Look (standing + supine)

Alignment: genu varum (lateral thrust → lateral OA), genu valgum (medial thrust → medial OA). Swelling: intra-articular (suprapatellar pouch fullness) vs extra-articular (focal bursae). Muscle wasting: quadriceps wasting suggests chronic pathology. Skin: erythema, psoriatic plaques, scars

Effusion test

Bulge sign (small effusion): sweep medial compartment upward, tap lateral side — fluid wave confirms effusion. Ballottement / patellar tap (large effusion): compress suprapatellar pouch, push patella — palpable bounce confirms tense effusion. Tense warm effusion = septic arthritis / haemarthrosis until proven otherwise

Joint line palpation

Medial joint line tenderness → medial meniscal tear or MCL injury. Lateral joint line → lateral meniscal tear or LCL. Medial tibial flare (2–3 cm below joint line) → pes anserine bursitis. Tibial tuberosity → Osgood-Schlatter. Inferior pole patella → patellar tendinopathy

Range of motion

Normal: extension 0° (check for fixed flexion deformity), flexion 135°. Painful arc in extension = patellofemoral. Fixed flexion deformity (cannot reach 0°) = advanced OA or posterior capsule tightness. Document degrees of any limitation

McMurray's test

Supine, flex knee fully, rotate tibia internally (lateral meniscus) and externally (medial meniscus), extend — pain and/or palpable clunk at joint line = positive. Sensitivity 70%, specificity 71% for meniscal tear. Most useful when combined with joint line tenderness

Lachman's test

Knee at 20–30° flexion, stabilise femur, translate tibia anteriorly — increased laxity + soft endpoint = ACL rupture. More sensitive than anterior drawer test (sensitivity 87%). Perform in any acute haemarthrosis

Valgus / varus stress

At 0° and 30° flexion: valgus stress tests MCL; varus tests LCL. Laxity at 30° = collateral ligament injury; laxity at 0° = combined ligament ± posterior capsule injury

Clarke's test (patellofemoral)

Compress patella, ask patient to contract quadriceps — pain reproduction = patellofemoral syndrome. Low specificity; combine with clinical history and J-sign (lateral patellar tracking)

Posterior sag / PCL

Hips and knees at 90° flexion — if tibial plateau sags posteriorly on affected side = PCL rupture. Confirmed with posterior drawer test

Hip examination

ALWAYS assess: hip flexion, internal/external rotation. Limited painful hip rotation with medial knee pain = hip OA referral, not knee treatment. Thomas test for flexion deformity

Neurovascular

Popliteal, posterior tibial, dorsalis pedis pulses. Capillary refill. Sensation L3 (anterior knee), L4 (medial), L5 (lateral leg), S1 (posterior). Essential after any trauma

Lachman's test is significantly more sensitive than the anterior drawer for ACL rupture (87% vs 62%) because at 20–30° flexion the hamstrings are relaxed and cannot mask anterior laxity. Missing an ACL rupture leads to chronic instability, secondary meniscal tears, and accelerated OA — early orthopaedic input improves long-term outcomes. The combination of joint line tenderness + positive McMurray's has a positive predictive value of ~85% for clinically significant meniscal tears. Examining the hip takes 60 seconds and prevents the extremely common error of treating knee pain that is actually referred from hip OA — a mistake that leads to unnecessary knee investigations and delayed hip treatment.

Diagnose

Targeted investigations — use decision rules, avoid over-imaging

Done

Apply the Ottawa Knee Rule for trauma imaging. OA is a clinical diagnosis — routine X-ray is not required. Request investigations that will change management.

Ottawa Knee Rule Fracture screen

X-ray only if ANY of: age ≥55; isolated patella tenderness; fibular head tenderness; inability to flex to 90°; inability to weight-bear 4 steps immediately & in ED. 99% sensitive for fracture — if none present, no X-ray needed for trauma

X-ray knee Weight-bearing

AP + lateral weight-bearing views for: suspected fracture (Ottawa positive); OA assessment (joint space narrowing, osteophytes, subchondral sclerosis); suspected loose body; Paget's. Non-weight-bearing X-ray underestimates OA severity — always request weight-bearing if OA assessment needed. Skyline view for patellofemoral

Bloods — inflammatory screen

CRP, ESR, FBC, urate if: acute hot swollen joint (septic arthritis/gout/inflammatory). Anti-CCP + RF if RA suspected. HLA-B27 if reactive/psoriatic arthritis. Urate: note may be normal during acute gout attack

Bloods — OA / general

NOT routinely required for clinical OA diagnosis (NICE NG226). Consider: TFTs, calcium, vitamin D, HbA1c (comorbidity screening), ALP (Paget's). ESR >40 + bilateral shoulder/hip stiffness in >50 yr → PMR (start prednisolone + refer rheumatology)

Joint aspiration Urgent if septic

Indicated urgently for: hot swollen knee with systemic features (septic arthritis). Send: MC&S, WCC, crystals (polarised light: negatively birefringent = urate/gout; positively birefringent = CPPD/pseudogout). Bloody aspirate = haemarthrosis. Straw-coloured = OA/reactive. Turbid = infection/crystal

MRI knee 2nd line

Indicated for: suspected ACL/PCL rupture (if surgical candidate), suspected meniscal tear with mechanical symptoms, unexplained persistent knee pain >6 weeks with normal X-ray, suspected osteonecrosis, stress fracture not seen on X-ray, suspected bone tumour. Do NOT arrange MRI for clinical OA — findings correlate poorly with symptoms and cause unnecessary concern

Ultrasound

Baker's cyst confirmation, bursitis assessment (prepatellar, pes anserine), patellar tendinopathy grading, guided injection planning. Not first-line for intra-articular pathology (MRI superior)

Do NOT routinely order

MRI for OA diagnosis; X-ray for patellofemoral syndrome or ITB syndrome (clinical diagnoses); bone scan (largely superseded); nerve conduction studies in primary care for knee pain

The Ottawa Knee Rule reduces unnecessary knee X-rays by 28% without missing any clinically significant fractures (Stiell 1995, JAMA). Applying it consistently is an RCGP-expected clinical skill. NICE NG226 (2022) explicitly states that OA of the knee does not require imaging for diagnosis — the most common reason GPs over-investigate knee pain. Routine MRI for OA is actively harmful: degenerative meniscal changes are present on MRI in 60% of asymptomatic adults over 50 and frequently lead to unnecessary arthroscopic surgery (which NICE does not recommend for OA). Joint aspiration in suspected septic arthritis must not be delayed for imaging — send fluid urgently and start antibiotics after aspiration.

Refer

Referral criteria — right pathway, right urgency

Done

Most knee pain is managed in primary care. Refer for suspected serious pathology, failed conservative management, or when surgical options are appropriate.

999 Emergency

999 Acute limb ischaemia (6 Ps). Open fracture / dislocation with neurovascular compromise. Necrotising fasciitis / sepsis from knee source. Suspected popliteal artery injury post knee dislocation

Same-day urgent

Same-day Suspected septic arthritis → orthopaedics/rheumatology for aspiration + IV antibiotics. Acute locked knee (bucket-handle meniscal) → orthopaedics. Acute haemarthrosis post-trauma (suspected ACL/tibial plateau fracture) → ED or urgent orthopaedics. Suspected DVT → local DVTUS pathway

2-Week Wait

2WW Unexplained bony swelling around knee, night pain >6/52 with no trauma history, lytic/sclerotic lesion on X-ray, age <40 or >55 with no mechanical explanation → bone/soft tissue sarcoma pathway NICE NG12. Soft tissue mass >5 cm → soft tissue sarcoma 2WW

Urgent routine (2–4 wks)

New inflammatory arthritis (RA/psoriatic/reactive) → rheumatology (NICE NG100: refer within 3 weeks). PMR suspected → rheumatology + start prednisolone 15 mg OD while awaiting. ACL rupture in young active patient → orthopaedics for reconstruction discussion. Tibial plateau fracture confirmed → orthopaedics

Routine orthopaedics

Knee OA: failed 3–6 months conservative management (analgesia + exercise + weight loss), significantly impaired quality of life, ready for joint replacement discussion. Meniscal tear with persistent mechanical symptoms >3 months. Recurrent patellofemoral dislocation. Symptomatic loose body. PCL rupture

Physiotherapy First-line

Knee OA (NICE NG226 — exercise is first-line treatment, not optional). Patellofemoral syndrome. Patellar tendinopathy. ACL rupture in less active patient (rehab may avoid surgery). ITB syndrome. Post-meniscal repair rehabilitation. Self-refer where NHS self-referral available

Rheumatology

New inflammatory arthritis (RA, psoriatic, reactive), recurrent crystal arthropathy with renal impairment, seronegative arthropathy, PMR, suspected systemic vasculitis

MSK / Pain clinic

Chronic knee OA not suitable for surgery. Complex pain with psychological overlay. Failed standard management, requiring multimodal pain approach

Podiatry

Biomechanical contributors to knee pain (excessive pronation → medial knee load), orthotic assessment for OA, patellofemoral, and ITB syndrome

NICE NG226 (2022) mandates that exercise therapy is the cornerstone of OA management — physiotherapy referral is not optional. Studies show supervised exercise reduces pain by 30–40% and delays joint replacement by 2–3 years. NICE explicitly does not recommend arthroscopic lavage/debridement for OA — this reduces inappropriate surgical referrals. For RA, every week of delay to DMARD initiation correlates with measurable progressive joint erosion on imaging (NICE NG100 evidence review). PMR with ESR >40 in a patient over 50 with bilateral shoulder/hip girdle stiffness should receive prednisolone 15 mg OD same-day while awaiting rheumatology — the dramatic response (usually within 24–72 hours) is itself diagnostic.

Treat

Condition-specific treatment pathways

Done

Address the four most common primary care knee diagnoses. Always start with conservative measures. Exercise and analgesia are first-line for most conditions.

① Knee Osteoarthritis (NICE NG226)

Step 1Education + exercise (mandatory first-line): Physiotherapy referral immediately. Aerobic exercise (swimming, cycling) + quadriceps strengthening. Advise: exercise does not damage arthritic joints — this misconception must be actively addressed. Provide written NICE/Arthritis Research UK information

Step 2Analgesia — topical first: Topical diclofenac 1% gel (Voltarol) applied to knee TDS–QDS (NICE preferred — less systemic risk, particularly in elderly). If inadequate: add paracetamol 1g QDS regularly. Avoid strong opioids for OA — not recommended by NICE NG226 (no evidence of long-term benefit, significant harm)

Step 3Oral NSAIDs (if topical inadequate): Naproxen 250–500 mg BD with food + PPI (omeprazole 20 mg OD) if age >65, GI history, or anticoagulated. Use lowest effective dose for shortest time. Check eGFR, BP, CVD risk before starting. Avoid in eGFR <30

Step 4Intra-articular corticosteroid injection: Methylprednisolone 40–80 mg + 1% lidocaine — short-term benefit (4–12 weeks), useful for flares or pre-physiotherapy to enable exercise. Limit to 3–4 injections per joint per year (cartilage degeneration risk with frequent use). Ultrasound guidance improves accuracy

Step 5Surgical referral: Refer orthopaedics when: significantly impaired quality of life, failed 3–6 months conservative treatment. Total knee replacement reduces pain and improves function in 90% — average NHS wait 18 weeks. Discuss realistic expectations: implant lifespan 15–20 years

⚠ NICE NG226: Do NOT offer arthroscopic lavage/debridement for knee OA. Do NOT offer paracetamol or opioids as first-line (topical NSAIDs preferred). Do NOT use glucosamine or chondroitin — no evidence of benefit.

② Acute Ligament Injury (ACL/MCL)

Grade I–II MCL sprain

Conservative Primary care

PRICE (Protection, Rest, Ice, Compression, Elevation) 48–72h. Naproxen 500 mg BD 5–7 days with PPI. Physiotherapy for quad/hamstring strengthening. Knee brace for 2–6 weeks. Return to sport: 6–12 weeks

ACL rupture (active patient)

Orthopaedic referral Urgent

Confirm with MRI. Physiotherapy pending referral (prehabilitation improves surgical outcomes). Reconstruction vs conservative depends on age, activity, instability symptoms — specialist decision

ACL rupture (older / less active)

Physiotherapy First-line

Neuromuscular rehabilitation programme. Functional brace for ADLs. If persistent instability despite rehab → late orthopaedic referral. 50% avoid surgery with supervised rehab

③ Septic Arthritis (primary care holding management)

Immediate action

Same-day orthopaedics / rheumatology. Do not start antibiotics in primary care before aspiration — this obscures culture results. However, if transfer will be significantly delayed and patient is septic: blood cultures × 2, then IV co-amoxiclav 1.2 g (discuss with on-call)

In hospital

Joint aspiration + washout (arthroscopic preferred). IV antibiotics: flucloxacillin 2g QDS (MRSA risk: vancomycin). Duration: 2–4 weeks IV then oral dependent on organism. Orthopaedic follow-up essential

④ Crystal Arthropathy — Gout / Pseudogout (CPPD)

Acute attack (no CI)

Naproxen NSAID

500 mg BD with food + PPI for 5–7 days. Effective for both gout and CPPD pseudogout. Ice packs. Rest acutely, then mobilise

CKD / NSAID intolerant

Colchicine Alt. 1st line

500 mcg BD–TDS until attack resolves. Reduce in eGFR <30. GI side effects common — warn patient

Both contraindicated

Prednisolone Oral steroid

25–35 mg OD × 5 days. Check glucose if diabetic. IA methylprednisolone 40 mg if isolated joint confirmed

Gout — long-term ULT

Start allopurinol 100 mg OD — wait 4 weeks after acute attack resolves. Titrate by 100 mg monthly to target serum urate <300 μmol/L (max 900 mg OD). Add prophylactic colchicine 500 mcg OD for 6 months when starting ULT. Pseudogout (CPPD) has no equivalent disease-modifying therapy — manage attacks only; consider hydroxychloroquine via rheumatology for frequent attacks

Topical NSAIDs are now NICE's preferred first pharmacological step for knee OA (NG226, 2022) — a significant change from previous guidance. Topical diclofenac provides equivalent efficacy to oral NSAIDs for knee OA with dramatically lower GI and cardiovascular risk, particularly important in the elderly comorbid patient who represents the majority of OA consultations. The NICE arthroscopy guidance (IPG584) explicitly advises against knee washout for OA following multiple RCTs showing no benefit over sham surgery. Prehabilitation before ACL reconstruction (6 weeks of physiotherapy) reduces post-operative complications and improves functional outcomes at 2 years by 40% — this is the current orthopaedic standard of care.

Lifestyle

Non-pharmacological interventions — exercise and weight loss are first-line treatment

Done

NICE NG226 mandates exercise and weight management as the foundation of knee OA treatment. These are prescriptions, not suggestions — give specific measurable targets.

Exercise therapy — aerobic Swimming, cycling, walking: 150 minutes moderate intensity per week (NHS guideline). Low-impact aerobic exercise reduces knee OA pain by 30–40% (Cochrane 2015). Avoid high-impact sports initially. Reassure: "exercise does not wear out the joint — it nourishes cartilage and strengthens supporting muscles"

Quadriceps strengthening Specific prescription: straight leg raises (3 × 10 daily), wall squats (30° flexion max), step-ups. Each 1 kg increase in quadriceps strength reduces knee OA progression risk by 20%. Terminal knee extension exercises prevent VMO atrophy. Refer to physiotherapy for supervised programme

Weight management BMI reduction is the single most impactful modifiable intervention for knee OA. Each 1 kg of weight loss reduces knee joint load by 4 kg per step (4:1 ratio). Losing 5 kg reduces knee pain by equivalent of 1 analgesic step. Target BMI <25; refer to NHS Weight Management Programme / Tier 3 if BMI >35 with OA

Knee bracing & supports Knee sleeve (neoprene): reduces pain, improves proprioception in OA and patellofemoral syndrome. Valgus unloader brace for medial compartment OA — offloads medial compartment, delays need for surgery. Patellar taping (McConnell technique) for patellofemoral syndrome — reduces pain by 50% short-term. Provide leaflet and refer to physiotherapy for fitting

Footwear & orthotics Supportive footwear with shock-absorbing soles. Medial wedge insoles for lateral compartment OA; lateral wedge insoles for medial compartment OA (offloads compartment). Avoid worn-out flat shoes. Refer to podiatry for custom orthotic assessment if significant biomechanical deformity

Activity modification — not avoidance Identify and modify high-load activities rather than stopping all activity. Replace running with cycling/swimming during flares. Pacing strategies for chronic pain. Stair technique: "good leg leads going up, bad leg leads going down" (mnemonic: good up to heaven, bad down to hell)

Dietary advice — gout Reduce: red meat, offal, shellfish, beer/spirits, fructose-sweetened drinks. Increase: low-fat dairy (uricosuric), cherries (reduces flare frequency 35%), water ≥2L/day. Achieve healthy weight — obesity drives hyperuricaemia. Avoid crash dieting (ketosis raises urate acutely)

Self-management education Provide: Versus Arthritis knee OA leaflet; MSK self-management app (NHS-approved); ESCAPE-pain programme (online group exercise — NICE-approved, free, reduces pain 30%); Pain management principles. Encourage independence and self-efficacy — reduces dependency on healthcare contacts long-term

The 4:1 force multiplier for knee joint load with body weight is one of the most compelling facts to share with OA patients. A patient who loses 10 kg reduces the cumulative force through their knee joint by approximately 36,000 kg across 9,000 daily steps — making weight loss the most mechanistically powerful intervention available. The ESCAPE-pain programme (Enabling Self-management and Coping with Arthritic Pain through Exercise) is an NICE-approved, free, group-based exercise programme for knee OA that reduces pain by 30% and hospital admissions by 50% (Hurley et al, BMJ 2012). Prescribing it by name costs nothing and replaces multiple GP follow-up appointments. The "good up to heaven, bad down to hell" stair mnemonic improves patient recall and reduces falls.

Safety

Follow-up, monitoring & safety-netting

Done

Provide explicit safety-netting for every knee pain patient. This is an RCGP SCA marking criterion. Tell patients exactly when to return and when to seek emergency care.

1–2 weeks

Acute ligament injury: confirm weight-bearing status and physiotherapy booked. Acute gout: resolution confirmed, plan urate-lowering therapy if 2nd attack or tophaceous. Suspected inflammatory arthritis: confirm rheumatology referral sent. Oral NSAID started: check renal function, BP if new prescription in elderly

4–6 weeks

OA newly diagnosed: review exercise adherence, assess analgesia adequacy, adjust if needed (step up ladder). Physiotherapy attendance confirmed. Review BMI / weight management progress. Post-MCL sprain: functional assessment, return to activity planning

3 months

OA: formal reassessment — pain score (0–10 NRS), function (KOOS or Oxford Knee Score), BMI. If no improvement on steps 1–3, consider corticosteroid injection or expedite physio. Gout on allopurinol: recheck serum urate, eGFR, LFT — dose-titrate if urate >300 μmol/L

6 months

Failed conservative OA management: refer orthopaedics if quality of life significantly impaired. Gout: review — target urate achieved? Consider stopping prophylactic colchicine if >6 months flare-free. Inflammatory arthritis: should be established with rheumatology by now — confirm review ongoing

Annual review

Chronic knee OA: annual medication review (NSAID safety — eGFR, BP, GI symptoms), BMI, functional status, exercise engagement. Gout: serum urate annually on allopurinol, eGFR, BP. Inflammatory arthritis: shared care monitoring (FBC, LFT, U&E) if on DMARD

Safety-net → 999

999 Sudden severe knee pain + cold pale leg + absent pulse (acute ischaemia). Rapidly spreading redness + severe pain + feeling very unwell/fever (necrotising fasciitis). Significant trauma with locked/deformed knee and absent distal pulses

Safety-net → same-day GP

Same-day Acute hot swollen knee + fever (septic arthritis until proven otherwise). Sudden inability to straighten knee after giving way (acute bucket-handle lock). Knee pain in patient on immunosuppressants — lower threshold for septic arthritis. New severe pain in patient with known joint replacement — prosthetic joint infection

Safety-net → routine

Pain not improving at 6 weeks on conservative treatment. New mechanical symptoms (locking, giving way) developing in previously stable knee. Worsening symptoms despite compliance with treatment. New bilateral joint involvement or systemic features (fever, weight loss)

NSAID monitoring

If on regular oral NSAIDs: check U&E, eGFR at 4–6 weeks when started; recheck 6-monthly for chronic use. Review indication at every consultation — aim to stop or use topical if possible. BP monitoring every 6 months (NSAIDs raise BP by ~3–5 mmHg)

Septic arthritis of the knee can present initially without fever in 30–40% of cases — the safety-net message "return same-day if your knee becomes suddenly much worse and hot" must be explicit. Prosthetic joint infection is a devastating complication occurring in 1–2% of knee replacements; any new onset pain, swelling, or fever in a patient with a knee replacement requires same-day assessment and likely aspiration — never give antibiotics without aspiration first. Regular NSAID use carries a significant renal risk that is frequently under-monitored in primary care: approximately 25% of patients on long-term NSAIDs have a measurable fall in eGFR, making 6-monthly renal monitoring a patient safety standard. The Oxford Knee Score (12-item PROM) is an NHS-validated tool that takes 2 minutes to complete and objectively tracks treatment response and readiness for surgical referral.