Knee Pain Algorithm

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, painful knee with restricted active and passive movement → immediate hospital assessment; urgent aspiration in an appropriate sterile setting. Fever and raised WCC/CRP may be absent and do not exclude it (especially older or immunosuppressed patients, prosthetic joints). Do not inject the joint. Shock or rapid deterioration → 999

Acute limb ischaemia Sudden severe pain + pale, cold, pulseless leg + paraesthesia, weakness or paralysis → 999 immediate vascular emergency; urgency depends on limb viability and neurological status — do not delay transfer for imaging

Fracture with neurovascular compromise Significant trauma + deformity + absent distal pulse or paraesthesia → 999; major knee dislocation with suspected popliteal artery injury is a limb emergency — a palpable pulse does not exclude vascular injury

Compartment syndrome / major trauma Severe pain out of proportion, tense swollen leg after injury, or severe trauma with multiple injuries → 999

Haemarthrosis — acute ligament rupture / fracture Immediate (within about 2h) tense effusion after trauma → ACL rupture, patellar dislocation, fracture or osteochondral injury until proven otherwise → same-day assessment, radiography where indicated (Ottawa Knee Rule) and specialist acute knee pathway; surgery depends on the injury and instability

Deep vein thrombosis Calf and posterior knee pain, swelling, erythema, post-immobility/surgery/travel → same-day two-level Wells pathway (NICE NG158): Wells ≥2 → proximal leg-vein ultrasound within 4 h (if not possible: D-dimer, interim therapeutic anticoagulation and ultrasound within 24 h); Wells ≤1 → D-dimer. Do not diagnose DVT from calf/posterior knee pain alone; consider ruptured Baker's cyst if the DVT pathway is negative

Bone tumour / malignancy Persistent unexplained bone pain or swelling, rest/night pain, limp, systemic features (weight loss) → X-ray. Adults: consider a suspected cancer pathway referral if X-ray suggests bone sarcoma. Children and young people: consider a very urgent direct-access X-ray, and a very urgent referral if it suggests sarcoma (NICE NG12, updated April 2026). Age thresholds are not standalone cancer criteria

Necrotising fasciitis / cellulitis with systemic sepsis Rapidly spreading erythema around knee + fever + disproportionate pain + systemically unwell → 999 (NICE NG253)

Locked knee — acute mechanical block True mechanical locking (fixed inability to extend) after trauma → displaced meniscal tear or loose body; same-day orthopaedics — do not force extension. Distinguish from pseudo-locking due to effusion or spasm

Other same-day assessment New knee effusion without a clear benign explanation; acutely swollen knee on anticoagulants; suspected tibial plateau fracture; sudden severe pain with known malignancy or suspected pathological fracture; cannot straight-leg-raise after injury (suspected quadriceps or patellar tendon rupture) → same-day orthopaedics

Septic arthritis is the most commonly missed serious knee diagnosis in primary care. Untreated bacterial infection rapidly destroys cartilage. Fever and raised WCC/CRP may be absent, particularly in older or immunosuppressed patients and those on steroids — normal results do not exclude it and a high index of suspicion is essential. Haemarthrosis within about 2 hours of trauma suggests ACL rupture, patellar dislocation, fracture or osteochondral injury; a delayed effusion (several hours to 24 h) suggests meniscal or other internal derangement — timing is suggestive rather than diagnostic. The Baker's cyst rupture / DVT mimic is a well-recognised diagnostic trap — follow the DVT pathway first. The distal femur and proximal tibia are common sites for primary bone sarcoma — 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 focused history narrows the differential.

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), varus stress (LCL), dashboard injury (PCL), fall, direct blow to lateral knee (fibular head fracture/LCL), hyperextension (PCL), atraumatic gradual onset (OA, tendinopathy, inflammatory)

Onset & duration

Immediate effusion (within about 2h) → haemarthrosis (ACL injury, patellar dislocation, fracture, osteochondral injury). Several hours to 24h → meniscal or other internal derangement more likely. Insidious → OA, inflammatory arthritis, crystal disease, infection or tumour. Timing is suggestive rather than diagnostic. Ask about progression and weight-bearing ability

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, nail changes / IBD / urethritis or diarrhoeal illness (psoriatic/reactive); previous gout, pseudogout or inflammatory arthritis; fever, rigors, malaise (septic); recent infection, joint injection or penetrating injury; malignancy, weight loss or night pain

Hip & lumbar spine

Ask about hip and lumbar symptoms — both may refer pain to the knee

Functional impact

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

PMH / medications

Previous knee or joint surgery, steroid use (osteonecrosis), anticoagulants / antiplatelets (haemarthrosis risk), immunosuppressants, fluoroquinolone use (tendinopathy), immunosuppression (atypical septic arthritis)

Pain location combined with mechanism often suggests the diagnosis before any examination. The "cinema sign" (anterior knee pain after prolonged sitting) is suggestive of patellofemoral pain but not diagnostic alone. True mechanical locking — the patient cannot actively extend the knee, not just stiffness — suggests a displaced meniscal tear or loose body requiring same-day orthopaedic review; distinguish it from pseudo-locking due to effusion or spasm and from OA morning stiffness. 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 or over, activity-related joint pain, and no morning stiffness or stiffness lasting no longer than 30 min; crepitus may be present (NICE NG226 clinical diagnosis — no imaging unless atypical features or another diagnosis suspected). 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. These are generally clinical diagnoses — ultrasound may help with focal bursal or cystic pathology but is not routinely required

🟢 Inflammatory arthritis

Persistent synovitis: refer for specialist opinion even if CRP, RF or anti-CCP are negative — urgently if small joints, multiple joints or prolonged symptoms (NICE NG100). Rheumatoid arthritis: bilateral, symmetrical, morning stiffness >30 min, recurrent effusions. Psoriatic arthritis: dactylitis, nail changes, skin psoriasis. Reactive arthritis: post-GI/STI, asymmetric. Also ask about inflammatory back pain and uveitis. Gout/pseudogout: acute hot swollen joint, crystal arthropathy — pseudogout particularly common in knee (CPPD); septic arthritis can coexist — crystals do not exclude infection. PMR: bilateral, age >50, shoulder girdle ± hip, raised inflammatory markers — do not diagnose on steroid response alone

🔵 Referred / systemic

Hip OA: medial knee pain with limited hip rotation — always examine the hip. Lumbar radiculopathy: L3/L4 referred to anterior knee — examine lumbar spine and neurology. Vascular: examine pulses and calf. 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 commonly refers pain to the knee, and treating the knee without addressing the hip yields no benefit. NICE NG226 (2022) allows clinical diagnosis of OA without imaging when age 45 or over, activity-related pain, and no morning stiffness or stiffness lasting no longer than 30 minutes — 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. Special tests may support a diagnosis but should not be used in isolation — performance varies with pain, guarding, timing and examiner experience.

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, warmth, skin integrity, psoriatic plaques, scars. Gait and deformity

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. Limited diagnostic value alone — most useful when combined with joint line tenderness and history

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. Perform in any acute haemarthrosis — a negative Lachman does not exclude ACL injury in a painful, swollen knee

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 is non-specific — do not diagnose patellofemoral pain on this test alone; 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). Popliteal swelling, calf swelling and DVT features. Essential after any trauma — a palpable pulse does not exclude vascular injury after knee dislocation

Lachman's test is more sensitive than the anterior drawer for ACL rupture 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. Joint line tenderness plus a positive McMurray's increases suspicion of a meniscal tear, but neither test should be used in isolation. 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 to decide on imaging after acute trauma — it is an imaging decision rule, not a diagnosis or management rule. 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 take four steps both immediately after injury and at assessment (people over 2 years with suspected knee fracture; NICE NG38). Do not use it to avoid imaging if there is deformity, open injury, neurovascular compromise, suspected dislocation, unreliable examination, a high-energy mechanism, or clinical concern despite a negative rule

X-ray knee If indicated

Not routinely required for typical clinical OA. Image for: suspected fracture (Ottawa positive); atypical symptoms; suspected loose body, malignancy, Paget's or another diagnosis — use the local radiology protocol. Weight-bearing views may be helpful for OA assessment but are not mandatory in every case. Skyline view for patellofemoral

Bloods — inflammatory screen

FBC, CRP and/or ESR, renal function, urate (if gout suspected) for: acute hot swollen joint (septic arthritis/gout/inflammatory); blood cultures if febrile or systemically unwell. A normal CRP or WCC does not exclude septic arthritis. 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). Suspected PMR: assess for GCA and exclude mimics before treatment — inflammatory markers, FBC, renal function, liver profile, calcium, ALP, CK and protein electrophoresis where clinically indicated (see Step 6)

Joint aspiration Urgent if septic

Indicated urgently (in hospital, in an appropriate sterile setting) for: hot swollen knee where septic arthritis is possible — systemic features may be absent; consider when gout remains uncertain (NICE NG219). Send: cell count and differential, Gram stain and microscopy, culture and sensitivity, crystals (polarised light: negatively birefringent = urate/gout; positively birefringent = CPPD/pseudogout). Bloody aspirate = haemarthrosis. Straw-coloured = OA/reactive. Turbid = infection/crystal. Finding crystals does not by itself exclude infection

MRI knee 2nd line

Specialist / acute knee pathway imaging — do not delay referral or rehabilitation to obtain it. Indicated for: suspected ACL/PCL or multiligament injury, persistent mechanical symptoms suggestive of a meniscal tear, unexplained persistent knee pain with normal radiographs, osteochondral lesion, suspected osteonecrosis, stress fracture not seen on X-ray, suspected bone tumour. Do NOT arrange MRI for clinical OA — interpret MRI with the clinical findings; incidental meniscal and cartilage abnormalities are common

Ultrasound

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

Suspected DVT

Two-level DVT Wells score (NICE NG158): ≥2 → proximal leg-vein ultrasound within 4 h if possible; if not, D-dimer, interim therapeutic anticoagulation and ultrasound within 24 h. ≤1 → D-dimer pathway. Consider ruptured Baker's cyst and other differentials if the DVT pathway is negative

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 in suitable acute-trauma patients (Stiell 1995, JAMA; NICE NG38). 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 common on MRI in asymptomatic older adults and can lead to unnecessary arthroscopic surgery (which NICE NG226 does not recommend for OA). Transfer for suspected septic arthritis must not be delayed for imaging — aspiration and blood cultures should ideally precede antibiotics, but antibiotics must not be withheld in sepsis or if transfer is significantly delayed (NICE NG253).

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 with haemodynamic compromise. Suspected popliteal artery injury post knee dislocation. Suspected compartment syndrome. Severe trauma with multiple injuries. Septic arthritis with shock, severe sepsis or rapid deterioration. Do not delay transfer for imaging

Same-day urgent

Same-day Suspected septic arthritis → immediate hospital assessment (orthopaedics/rheumatology) for aspiration + IV antibiotics. Include immunosuppressed patients and prosthetic joints. True locked knee (displaced meniscal tear / loose body) → orthopaedics. Cannot straight-leg-raise after injury (suspected quadriceps or patellar tendon rupture) → orthopaedics. Acute traumatic haemarthrosis → same-day assessment, radiography where indicated, then specialist acute knee pathway (BOA: assessment within about 2 weeks with MRI access). Suspected tibial plateau fracture → ED / orthopaedics. Suspected DVT → NICE NG158 two-level Wells pathway. New effusion without a clear benign explanation, acutely swollen knee on anticoagulants, or sudden severe pain with malignancy / suspected pathological fracture → same-day assessment

Suspected cancer pathway

Suspected cancer NICE NG12 (updated April 2026): adults — consider a suspected cancer pathway referral if an X-ray suggests the possibility of bone sarcoma; children and young people with unexplained bone swelling or pain → consider a very urgent direct-access X-ray (within 48 hours), and a very urgent referral (within 48 hours) if it suggests sarcoma. Adults with an unexplained soft-tissue lump that is increasing in size → consider an urgent direct-access ultrasound (within 2 weeks); consider a suspected cancer pathway referral if ultrasound suggests sarcoma, or findings are uncertain and concern persists. Also X-ray persistent unexplained rest/night pain, bony swelling or limp (clinical practice). Age thresholds should not be used as standalone cancer criteria.

Urgent (not same-day)

Suspected persistent synovitis / new inflammatory arthritis (RA/psoriatic/reactive) → rheumatology without waiting for RF, anti-CCP or CRP results; urgent if small joints of hands/feet, multiple joints or prolonged symptoms (NICE NG100; NICE QS33: seen within 3 weeks of referral). PMR suspected → assess for GCA and exclude infection, malignancy, endocrine disease and inflammatory arthritis first; typical PMR may then be treated with prednisolone — do not use steroid response as a diagnostic shortcut. Any visual disturbance, jaw claudication, new temporal headache or scalp tenderness → same-day GCA management and urgent specialist advice. Suspected ACL injury → acute knee pathway for shared decision on rehabilitation vs reconstruction. Tibial plateau fracture confirmed → orthopaedics

Routine orthopaedics

Knee OA: symptoms with substantial impact on pain, function or quality of life, and non-surgical management ineffective or unsuitable — no mandatory waiting period or Oxford Knee Score/KOOS threshold; do not exclude because of age, smoking, comorbidity or obesity (NICE NG226). Meniscal tear with persistent mechanical symptoms (true locking → same-day, above), an unstable or repairable tear, or failed rehabilitation. 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 (rehabilitation first; reconstruction mainly for symptomatic instability). Degenerative meniscal tear without true locking. 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, recurrent or diagnostically uncertain CPPD, seronegative arthropathy, atypical 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 in selected patients only (insoles not routinely offered for OA — NICE NG226)

NICE NG226 (2022) recommends therapeutic exercise as a core OA treatment, tailored to the individual. NICE NG226 (2022) explicitly does not recommend arthroscopic lavage/debridement for OA — this reduces inappropriate surgical referrals. For RA, delay to DMARD initiation risks progressive joint damage, so refer suspected persistent synovitis without waiting for blood results (NICE NG100). PMR should not be diagnosed solely on response to steroids — assess for GCA and mimics first; suspected GCA needs same-day management and steroids must not be delayed.

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, self-management + therapeutic exercise (core first-line): Individualised management plan; physiotherapy referral where needed. Aerobic exercise (swimming, cycling) + strengthening tailored to the person. Weight management where appropriate. Advise: exercise does not damage arthritic joints — this misconception must be actively addressed. Provide written Versus Arthritis (formerly Arthritis Research UK) information

Step 2Analgesia — topical first: Topical diclofenac 1% gel (Voltarol) applied to knee TDS–QDS (NICE NG226: offer a topical NSAID first for knee OA — less systemic risk, particularly in elderly). Paracetamol and weak opioids: do not routinely offer (NICE NG226) — only infrequent short-term use if other options are unsuitable. Avoid strong opioids for OA — not recommended by NICE NG226 (no evidence of long-term benefit, significant harm)

Step 3Oral NSAID (only if suitable, topical inadequate): Use the lowest effective dose for the shortest time. Assess renal function, blood pressure, cardiovascular disease, ulcer history and anticoagulant/antiplatelet use before starting; provide gastroprotection (e.g. PPI) where indicated; review after starting and during continued treatment. Choose drug and dose individually per local prescribing guidance

Step 4Intra-articular corticosteroid injection: Methylprednisolone 40–80 mg + 1% lidocaine — short-term relief (generally around 2–10 weeks) when other treatments are ineffective or unsuitable, or to support therapeutic exercise. No universal annual limit — follow local injection policy and individual risk assessment

Step 5Joint replacement referral: Refer when symptoms have a substantial impact on pain, function or quality of life and non-surgical management is ineffective or unsuitable. Use clinical assessment, not scoring tools; no arbitrary waiting period; do not exclude because of age, smoking, comorbidity or obesity (NICE NG226). Discuss realistic expectations

⚠ NICE NG226: Do NOT offer arthroscopic lavage/debridement for knee OA. Do NOT routinely offer paracetamol or weak opioids, and do not offer strong opioids (topical NSAIDs preferred). Do NOT offer glucosamine, chondroitin or intra-articular hyaluronan. Do NOT routinely offer braces, tape, insoles or supports — consider only in selected patients after assessing benefit and harm.

② Acute Ligament Injury (ACL/MCL)

Grade I–II MCL sprain

Conservative Primary care

Relative protection, early range-of-motion exercise, progressive strengthening and physiotherapy. Temporary bracing only when clinically indicated. Individualise analgesia/NSAID choice and dose — assess renal, GI, cardiovascular, anticoagulant and pregnancy considerations. Graded return to sport

ACL rupture (active patient)

Acute knee pathway Urgent

Specialist knee assessment (BOA: within about 2 weeks of traumatic haemarthrosis) with MRI via that pathway — do not delay referral or rehabilitation for imaging. Prehabilitation to restore full extension and quadriceps strength. Reconstruction is not automatic — mainly for symptomatic instability, particularly in active patients or with repairable meniscal injury; shared decision on rehabilitation vs reconstruction

ACL rupture (older / less active)

Physiotherapy First-line

Neuromuscular rehabilitation programme. Functional brace for ADLs. If persistent instability despite rehab → late orthopaedic referral. Need for surgery depends on instability, activity, associated injury and response to rehabilitation

Meniscal tear

Rehabilitation first Physiotherapy

Degenerative tear without true locking → exercise-based rehabilitation rather than immediate arthroscopy. Refer if true locking, persistent mechanical symptoms, unstable or repairable tear, or failed rehabilitation

Locked knee

Clarify true vs pseudo-locking Same-day

True mechanical locking (fixed inability to extend — displaced meniscal tear or loose body) → same-day orthopaedic assessment; do not forcibly extend. Pseudo-locking from effusion or muscle spasm → treat cause

③ Septic Arthritis (primary care holding management)

Immediate action

Immediate hospital assessment; provide analgesia; do not inject the joint; do not delay transfer for primary-care imaging. Fever, CRP and WCC may be normal. Blood cultures only if this will not delay transfer. Where possible, aspiration and blood cultures should precede antibiotics — but antibiotics must not be withheld solely to obtain an aspirate if the patient is septic, unstable or transfer will be significantly delayed (NICE NG253). In that case: blood cultures if they will not delay treatment, then antibiotics per the local sepsis/antimicrobial protocol (discuss with on-call)

In hospital

Joint aspiration + washout (arthroscopic preferred). IV antibiotics: flucloxacillin 2g QDS (MRSA risk: vancomycin). Duration per organism and microbiology/orthopaedic advice (commonly up to about 2 weeks IV, then oral, to around 6 weeks in total). Orthopaedic follow-up essential

④ Crystal Arthropathy — Gout / Pseudogout (CPPD)

Before labelling an inflamed knee as gout, assess for septic arthritis and CPPD. NICE NG219: offer an NSAID, colchicine or a short course of oral corticosteroid, chosen by renal function, comorbidities, co-prescriptions and patient preference; consider intra-articular or intramuscular corticosteroid if NSAIDs and colchicine are unsuitable or ineffective.

Acute attack (no CI)

Naproxen NSAID

Lowest effective dose for the shortest time, with gastroprotection where indicated; assess renal, cardiovascular, GI and anticoagulant risk. Effective for both gout and CPPD pseudogout. Ice packs. Rest acutely, then mobilise

NSAID unsuitable

Colchicine Alt. 1st line

Dose per current product information / local formulary. Caution: renal impairment, older age and interacting drugs (e.g. macrolides, some lipid-lowering medicines) increase toxicity risk. GI side effects common — warn patient

Both contraindicated

Prednisolone Oral steroid

Short course (dose per local formulary). Check glucose if diabetic. Consider intra-articular or intramuscular corticosteroid if NSAIDs and colchicine are unsuitable or ineffective

Gout — long-term ULT

Discuss ULT with everyone who has had a flare; offer treat-to-target ULT for multiple or troublesome flares, CKD stage 3–5, diuretic therapy, tophi or chronic gouty arthritis. Usually start 2–4 weeks after a flare has settled (can start during a flare if flares are frequent). Start at a low dose and titrate using monthly serum urate to <360 μmol/L, or consider <300 μmol/L if tophi, chronic gouty arthritis or continuing frequent flares despite <360 (NICE NG219). Consider flare prophylaxis when starting ULT, taking renal function and interactions into account. Pseudogout (CPPD) has no equivalent urate-lowering therapy — manage attacks; refer recurrent or diagnostically uncertain CPPD to rheumatology

Next steps: see Osteoarthritis · Gout · Osgood-Schlatter disease

Topical NSAIDs are now the preferred first pharmacological step for knee OA in NICE 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. NICE HTG148 (formerly IPG230, 2007) advises that arthroscopic knee washout alone should not be used for OA, and NICE NG226 (2022) does not recommend arthroscopic lavage or debridement for OA — RCTs have shown no benefit over sham surgery. Prehabilitation to restore full extension and quadriceps strength is important before any ACL reconstruction decision (BOA 2020).

Lifestyle

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

Done

NICE NG226 recommends therapeutic exercise and, where appropriate, weight management as the foundation of knee OA treatment. Tailor advice to the individual and discuss weight sensitively.

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

Quadriceps strengthening Individualised programme (e.g. straight leg raises, wall squats, step-ups) rather than a fixed prescription. Terminal knee extension exercises prevent VMO atrophy. Refer to physiotherapy for supervised programme

Weight management Discuss sensitively where appropriate. Weight loss can improve pain and function — any weight loss may be beneficial, and 10% may provide more benefit than 5% (NICE NG226); no target BMI is required. Refer to weight management services where appropriate

Knee bracing & supports Do not routinely offer braces, tape or supports (NICE NG226). Consider only in selected patients (e.g. knee sleeve, unloader brace, patellar taping for patellofemoral pain) after assessing benefit and harm — refer to physiotherapy for assessment and fitting

Footwear & orthotics Supportive footwear with shock-absorbing soles. Do not routinely offer insoles (NICE NG226); consider only in selected patients after assessing benefit and harm. 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, adequate fluid intake. 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 (group exercise and self-management — evidence-based, free); Pain management principles. Encourage independence and self-efficacy — reduces dependency on healthcare contacts long-term

Weight loss can improve pain and function in people with knee OA who are overweight — NICE NG226 notes that any weight loss may be beneficial and that 10% may provide more benefit than 5%; discuss it sensitively. The ESCAPE-pain programme (Enabling Self-management and Coping with Arthritic Pain through Exercise) is an evidence-based, free, group-based exercise and self-management programme for knee OA (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, discuss urate-lowering therapy (NICE NG219: offer if multiple or troublesome flares, CKD 3–5, diuretics, tophi or chronic gouty arthritis). 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: reassessment — pain, function and quality of life, weight where relevant (scores may help monitoring but are not referral thresholds). If no improvement on steps 1–3, consider corticosteroid injection or expedite physio. Gout on allopurinol: recheck serum urate, eGFR, LFT — dose-titrate using monthly serum urate if above target (<360 μmol/L, or consider <300 if tophi, chronic gouty arthritis or continuing frequent flares; NICE NG219)

6 months

OA: refer for joint replacement consideration (at any point, no fixed waiting period) if substantial impact on pain, function or quality of life and non-surgical management ineffective or unsuitable. 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 deformed knee, numbness, weakness or cold foot (a pulse may still be present). Severe pain with a tense swollen leg after injury (compartment syndrome). Hot swollen knee with fever and feeling very unwell, faint or confused (septic arthritis with sepsis)

Safety-net → same-day GP

Same-day Acute hot, swollen, painful knee, with or without fever (septic arthritis until proven otherwise). Swollen knee while on anticoagulants. Calf or posterior knee swelling (possible DVT). Sudden inability to straighten knee after giving way (acute bucket-handle lock). Can't lift the straightened leg after an injury (possible tendon rupture). Knee pain in patient on immunosuppressants — lower threshold for septic arthritis. New pain, swelling, redness or fever in a knee 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 unexplained weight loss (fever with a painful or swollen knee → same day)

NSAID monitoring

If on regular oral NSAIDs: review renal function, BP and GI symptoms after starting and periodically during continued treatment, per local prescribing guidance. Review indication at every consultation — aim to stop or use topical if possible. NSAIDs can raise BP

Septic arthritis of the knee can present without fever, and CRP/WCC may be normal — 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 of knee replacement; any new onset pain, swelling, or fever in a patient with a knee replacement requires same-day assessment and likely aspiration — avoid antibiotics before specialist assessment unless the patient is septic or transfer is delayed. Regular NSAID use carries a significant renal risk that is frequently under-monitored in primary care: review renal function and blood pressure after starting and during continued use. The Oxford Knee Score (12-item PROM) can help track treatment response, but NICE NG226 advises clinical assessment rather than scoring tools when deciding on referral for joint replacement.