Clinical synthesis based on the most recent international guidelines: NICE NG226 (2022), ACR/Arthritis Foundation (2019), OARSI (2019), the OPTIKNEE consensus (2022) and 2023-2026 data.

How is this condition defined, who is affected and what are the risk factors?

• Age: the dominant non-modifiable risk factor. Radiographic prevalence doubles between the ages of 40-49 (13%) and 60-69 (35%), with a clear acceleration after 65 (Cui 2020).⁵
• Obesity: the most powerful modifiable factor. A BMI ≥ 30 multiplies the risk of symptomatic knee osteoarthritis by about 2.7.⁵ Beyond the purely mechanical effect (overloading), obesity sustains a low-grade systemic inflammation through the adipokines (leptin, resistin), illustrating the « metabolic syndrome meets OA » concept developed by Zhuo 2012.⁷
• Knee trauma: anterior cruciate ligament (ACL) injury is the major post-traumatic risk factor. The OPTIKNEE 2022 systematic review and meta-analysis (Whittaker, BJSM) consolidates an OR of 4 to 6 for knee osteoarthritis after ACL injury, and an OR of around 6 after meniscectomy.⁸ This is post-traumatic knee osteoarthritis (PTOA), which typically affects young people (15-20 years after the injury).
• Female sex and hormonal factors: a consolidated OR of about 1.7. The post-menopausal fall in oestrogens widens the differential.⁵
• Genetic predisposition: documented familial aggregation (OR ≈ 1.4), with several identified loci (GDF5, MCF2L, ASTN2) accounting for about 40% of the heritability of knee osteoarthritis.²
• Occupational activity: jobs involving squatting, frequent stair climbing and the handling of heavy loads (farming, construction, manual handling) multiply the risk by about 2.3.²
• Frontal-plane malalignment: varus (bow legs) accelerates medial knee osteoarthritis; valgus (knock knees) accelerates lateral knee osteoarthritis. A major biomechanical driver of progression.²

What happens in the body and how does knee osteoarthritis progress naturally?

• Cartilage catabolism : breakdown of the extracellular matrix (type II collagen, aggrecan) by proteolytic enzymes (MMP-13, ADAMTS-5), under the influence of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α).²
• Low-grade synovitis : the synovial membrane, long regarded as a « bystander », is in fact a central player. Robinson et al. 2016 (Nat Rev Rheumatol) reconceptualised osteoarthritis as a « low-grade inflammatory disease », in which intermittent synovitis sustains cartilage degradation and pain.⁹ Contrast-enhanced MRI finds synovitis in 50 to 90% of symptomatic osteoarthritis patients.
• Subchondral bone remodelling : sclerosis, osteophytes, marrow lesions (« bone marrow lesions » on MRI) correlated with pain and prognosis.²
• Muscle weakness and atrophy (mainly quadriceps) is both a cause and a consequence: a progressive loss of dynamic knee stability, which amplifies joint loading.
• Central sensitisation 🧠: a subgroup of osteoarthritis patients develops central neuroplastic changes that amplify pain. The Arendt-Nielsen 2018 review (Eur J Pain) consolidates the evidence for central sensitisation present in about 30% of knee osteoarthritis patients, which explains the discordance between unremarkable imaging and intense pain.¹⁰
• Metabolic systemic inflammation : in obese patients, the metabolic syndrome (insulin resistance, dyslipidaemia, hypertension) creates a pro-inflammatory context that worsens the disease independently of mechanical load (the « metabolic OA » concept, Zhuo 2012).⁷

Which questions should you ask to understand the patient and their history?

• First, activity-related knee pain, relieved (at least partly) by rest;
• First, morning stiffness in the knee that is absent or short-lived (< 30 minutes).¹

• Characterising the pain : site (medial / lateral / anterior / posterior / diffuse), intensity (0-10 numeric scale), quality (mechanical, inflammatory, neuropathic-like), functional impact (stairs, prolonged walking, squatting, prolonged sitting, the classic « jelly sign » pattern on long car journeys).⁴
• Temporal pattern : start-up pain, brief morning limbering-up, pain after periods of inactivity, post-exertion pain within 24h (« exercise-induced flare »).
• History of trauma : ACL injury, meniscectomy, intra-articular fracture, to be sought systematically in order to identify post-traumatic knee osteoarthritis (PTOA), often overlooked in young people. The OPTIKNEE 2022 consensus explicitly recommends routine follow-up of patients after ACL injury (Whittaker 2022 BJSM).⁵
• Comorbidities : obesity (calculate BMI), diabetes, metabolic syndrome, other joint involvement (hands, hip, spine), cardiovascular disease (important when planning exercise).
• Drug history : NSAIDs, analgesics, previous injections, viscosupplementation, opioids (to be avoided according to ACR 2019).²
• Psychosocial factors : kinesiophobia (fear of movement), catastrophising, depression, expectations of treatment, beliefs about the disease (« my cartilage is wearing out », « I will end up in a wheelchair »…). These factors strongly predict chronicity and treatment failure (Kanavaki 2017).⁶
• Personal goals : return to a specific activity (hiking, sport, work), symptom tolerance, the patient's values (essential for shared decision-making).

Which clinical tests should you perform and which other conditions must be ruled out?

• Inspection : frontal-plane alignment (varus / valgus), muscle bulk (quadriceps atrophy, wasting of vastus medialis), swelling / effusion (patellar tap, ballottement), skin appearance (redness, warmth, which suggests infection or inflammation).
• Palpation : tenderness of the joint lines (medial, lateral), of the patella, of the pes anserinus (insertion of the sartorius, gracilis and semitendinosus tendons 5-7 cm below the medial joint line, looking for an associated bursitis, common in medial knee osteoarthritis) and of the iliotibial band.
• Range of motion : flexion (normal ≥ 135°), extension (normal 0°, or even +5° of hyperextension), looking for a flexion contracture (limited extension, a major biomechanical factor).
• Crepitus : audible / palpable on passive mobilisation or with active movement (stair climbing, squatting), common in knee osteoarthritis but not very specific.
• Functional tests : the 30-second chair stand test, the Timed Up and Go (TUG), the 40 m walk test, stair ascent and descent, the functional outcome tools recommended by OARSI.³
• Muscle strength : assessment of the quadriceps (dynamometer if possible, otherwise the MRC scale), the iliopsoas and the hip abductors (gluteus medius weakness accentuates dynamic varus).
• Ligament stability : Lachman, anterior drawer, varus / valgus stress, McMurray, to rule out an associated ligament or meniscal injury.
• Distal neurological assessment : sensation, reflexes (knee jerk, ankle jerk), to rule out referred L3-L4 radicular pain.

• Pes anserine bursitis : pain localised 5-7 cm below the medial joint line, at the insertion of the sartorius/gracilis/semitendinosus tendons. Frequently associated with medial knee osteoarthritis (coexisting in up to 75% of cases in some series). Typical case: an obese woman with medial knee osteoarthritis and pain aggravated by stair climbing and prolonged sitting. Reference: case PMC 9674038 (2022).
• Isolated patellofemoral pain syndrome : anterior retropatellar pain, the cinema sign (pain when sitting for long periods with the knees bent), Clarke's test. More common in the active young adult, it can coexist with early patellofemoral osteoarthritis in adults aged 40+.
• Degenerative meniscal lesion : very common (asymptomatic in 60% of people aged 50+), to be correlated with symptoms. Meniscectomy is not recommended in the absence of true mechanical locking (ESSKA consensus).
• Crystal arthritis : gout (hyperuricaemia, podagra), chondrocalcinosis (meniscal calcification). An acute flare with a red, hot, painful knee.
• Septic arthritis : an emergency, with a red, hot, tense, febrile, exquisitely painful knee. Immediate joint aspiration.
• Peri-articular tendinopathies : quadriceps, patellar (jumper's knee), iliotibial band (TFL syndrome).
• Bone conditions : subchondral insufficiency fracture (common in the osteoporotic older adult, see PMC 9975902 2023), condylar osteonecrosis, osteosarcoma (in the young), bone metastasis (older adult with a relevant history).
• Referred pain of extra-articular origin : hip disease (anterior thigh pain referred to the knee, always examine the hip!), L3-L4 radicular pain, entrapment neuropathy (saphenous).

Should patients with knee osteoarthritis be classified, and what is gained by doing so?

• Targeted treatment direction : a « central sensitisation » patient will respond better to pain education + CBT + graded exercise than to an intensive strengthening programme, which can sustain catastrophising. Conversely, a « biomechanical » patient will benefit mainly from quadriceps and neuromuscular strengthening.
• Personalised follow-up : a « metabolic » phenotype calls for coordination with the GP, the dietitian and sometimes the diabetes specialist.
• A sharper prognosis : « central sensitisation » and « metabolic » patients have the least favourable functional prognosis without multidisciplinary intervention (Deveza 2017).⁸

Where do you start? What is the recommended hierarchy of interventions?

• 1. Patient education : dismantling mistaken beliefs (« my cartilage is wearing out », « I must not push it »), a modern explanation of knee osteoarthritis as a whole-joint disease that behaviour can modify, managing expectations, building independence. Caneiro 2020 (BJSM) proposes 3 major narrative shifts: (1) « osteoarthritis is not an inevitability », (2) « moving does not destroy, moving protects », (3) « surgery is neither unavoidable nor always the answer ».⁶
• 2. Tailored physical exercise (land-based or aquatic): the central pillar, with a high level of evidence (Cochrane Fransen 2015, GRADE high quality).⁴ Validated structured programmes: GLA:D (Good Life with osteoArthritis in Denmark, Skou & Roos 2017) rolled out in 11+ countries, and ESCAPE-pain (Enabling Self-management and Coping with Arthritic Pain through Exercise, Hurley), which combines education and supervised group exercise over 6 weeks (10-12 sessions).⁷,⁸
• 3. Weight management in patients who are overweight or obese: the target is ≥ 10% loss of body weight, a minimum threshold beyond which the benefit keeps growing: in the dose-response analysis of the IDEA trial, patients who lost more than 20% reported about 25% less pain than those in the 10-20% group (Messier 2018).⁹ This intervention is synergistic with exercise: combining weight loss + exercise gives the best functional outcomes.⁹

What is the place of exercise, and is there a superior approach?

• Combined programme : strengthening (≥ 2 times a week, at tolerated intensity), aerobic work (walking, cycling, swimming: 150 min a week in total), neuromuscular control (balance, proprioception).
• Initial supervision for 8-12 weeks then transition to structured self-management. The Holden 2023 IPDMA (Lancet Rheumatol) confirms that the effects of exercise are independent of age, BMI, radiographic severity and sex: exercise works for every patient.¹¹
• Aquatic exercise : a sound alternative where weight-bearing is not tolerated or comorbidities are present, with efficacy comparable to land-based exercise for pain and function (Dong 2018, Medicine Baltimore).¹²
• Validated structured programmes : GLA:D (Skou & Roos 2017), 2 education sessions + 12 supervised neuromuscular exercise sessions over 6 weeks, deployed in more than 11 countries with an international registry;⁷ ESCAPE-pain (Hurley), 6 weeks, 12 group sessions combining education and functional exercise, economically validated for health services.⁸

Manual therapies and technologies: how effective are they really?

• TENS (transcutaneous electrical nerve stimulation) : a modest, transient effect on pain, superior to placebo in the Cherian et al. 2016 meta-analysis (J Knee Surg) but with high heterogeneity and low to moderate quality of evidence.¹⁴ It may be offered as a home self-management tool, but it is not recommended for routine use by the major guidelines.
• Therapeutic ultrasound : the Dantas et al. 2021 meta-analysis (Braz J Phys Ther) concludes that there is a small, short-term effect on pain and function, with a very low quality of evidence (GRADE very low) linked to risk of bias and to heterogeneity.¹⁵ NICE NG226 and ACR 2019 do not recommend its routine use.¹,²
• Bracing / taping / orthoses : ACR 2019 issues a conditional recommendation for patellar taping in patellofemoral knee osteoarthritis and for orthoses (knee brace, insoles) in patients with malalignment.²
• Acupuncture : OARSI 2019 issues a conditional recommendation; ACR 2019 also recommends it conditionally. A modest effect, heterogeneous from one patient to another.²,³

Beyond the physical: how do you educate the patient and address psychological factors?

• The nature of the disease : a whole-joint disease, modifiable, not simple wear and tear; moving protects, it does not destroy.
• The mechanisms of pain : pain neuroscience education (PNE), particularly useful in patients with central sensitisation.
• The health behaviours : the importance of regular physical activity, weight management, sleep and stress management.
• The beliefs and expectations : deconstructing « the cartilage is wearing out », « I must move less » and « surgery is inevitable ».

• Graded exposure to the feared movement, within a reassuring framework.
• PNE education to deconstruct the pain = damage association.
• Self-monitoring of symptoms, to reassure the patient about tolerance to exertion.
• Working with a psychologist specialising in cognitive behavioural therapy (CBT) if the picture is severe or resistant.

How do you make the patient an active participant in their own recovery through self-management?

• TPE : the Du et al. 2011 meta-analysis confirms that structured self-management programmes produce small to moderate effects on pain and disability in the long term.⁴ TPE must include: an explanation of the nature of knee osteoarthritis (a whole-joint disease, modifiable, not simple wear and tear), deconstruction of mistaken beliefs (« I must move less », « moving wears the cartilage out »), an explanation of pain mechanisms (Pain Neuroscience Education), management of inflammatory flares, and the place of regular physical activity. The Caneiro 2020 review proposes a new narrative in 3 steps: (1) recognise the mistaken beliefs, (2) replace them with evidence-based messages, (3) equip the patient for lasting self-management.⁵
• Self-efficacy 🧠 : the belief in one's own capacity to carry out a task or to manage a situation. In knee osteoarthritis, this means giving the patient the confidence to move despite the pain and to manage flares. The structured programmes GLA:D (Skou 2017) and ESCAPE-pain (Hurley) combine education, supervised group exercise and behavioural support, with documented improvement in self-efficacy and in function at 3, 6 and 12 months.⁶,⁷

When and how do you plan a safe return to sport and to daily activities?

1. Phase 1: pain control and restoration of basic function. Reduce pain and inflammation. Restore a full joint range (≥ 130° flexion, full extension). Activate the stabilising muscles (quadriceps, hamstrings, glutes, gastrocnemius). Low-impact exercise preferred: stationary bike, swimming, aqua-aerobics, progressive walking. Criterion for moving to phase 2: pain ≤ 3/10 on exertion, range ≥ 130° flexion, ability to go up and down stairs without major pain.
2. Phase 2: progressive retraining and increasing load. Progressive mechanical load: the principle of progressive mechanical loading, stimulating tissue adaptation without an excessive inflammatory reaction. Intensified strength work (resistance ≥ 60-70% 1RM if tolerated). Functional exercises approaching the target movements (squats, lunges, moderate jumping according to the goal). Golden rule : monitor the knee's response in the 24 hours after exertion (pain, swelling). If there is a flare → reduce the load by 20-30% for the next session, without giving up. Criterion for moving to phase 3: quadriceps strength ≥ 80% of the uninvolved side (dynamometer), symmetrical functional tests (single leg squat, Y-balance test).
3. Phase 3: return to the specific activity and prevention strategy. Full return to the target activity (sport, work, leisure) only if the functional tests (strength, balance, neuromuscular control) are satisfactory. Long-term maintenance plan : ≥ 2 strength sessions a week + 150 min a week of aerobic activity in total. Intelligent management of the total load (frequency × intensity × duration), with possible application of the ACWR concept (acute:chronic workload ratio) borrowed from sports medicine.

Analysis of a « classic » case: from assessment to resolution

• Mean age 65, 73% women;
• Mean BMI 33.7 kg/m² (class I-II obesity);
• Radiographic knee osteoarthritis, Kellgren-Lawrence grade 2-3;
• Mean WOMAC pain 7.1/20 (0-20 scale, lower = better);
• 6-minute walk distance: 460 m (reduced versus healthy people).

• Mean weight loss: 10.6 kg (loss ≥ 10% in 70% of patients);
• WOMAC pain reduction: −51 % (versus −37% for the Diet-only group, −28% for the Exercise-only group);
• WOMAC functional improvement: +45 % ;
• Walking speed: +15 % ;
• Reduction in inflammatory markers (plasma IL-6: −20%).²

The diagnostic challenge: when knee osteoarthritis mimics another condition

A complex case

When should you refer, and to which other health professionals?

• 🟡 Kinesiophobia that is high (Tampa Scale TSK-11 ≥ 30): graded exposure + PNE + collaboration with a psychologist
• 🟡 Catastrophising about pain (Pain Catastrophizing Scale PCS ≥ 30/52): CBT + PNE recommended (Coronado 2018 JOSPT)
• 🟡 Depression / anxiety : HADS or PHQ-9 assessment, referral to the general practitioner ± psychiatrist
• 🟡 Low self-efficacy : structured programmes such as GLA:D or ESCAPE-pain
• 🟡 Severely mistaken beliefs about the disease: reinforced therapeutic education, the Caneiro 2020 narrative

• General practitioner / rheumatologist : red flags, diagnostic doubt, pharmacological management, significant comorbidities
• Orthopaedic surgeon : conservative failure ≥ 3-6 months, refractory pain, major functional impact, indication for a joint replacement
• Nutritionist / dietitian : overweight or obesity (target loss ≥ 10%), metabolic syndrome, associated diabetes
• Psychologist specialising in chronic pain : severe kinesiophobia, high catastrophising, depression or anxiety, failure of simple therapeutic education
• Podiatrist : static foot disorder, orthotic insoles (conditional according to ACR)
• Occupational therapist : adapting the home or the workstation, assistive devices (handrail, walking stick)
• Adapted physical activity coach : transition after supervised care, long-term maintenance

How do you measure outcomes and overcome the barriers to implementation?

• 📚 Targeted continuing education : webinars, themed study days, certifications (GLA:D, ESCAPE-pain, PNE)
• 🛠 Technology integration : practice software with built-in PROMs, exercise prescription apps
• 👥 Leadership and workplace culture : reflective practice, evidence-based case discussion, audits
• 📖 Accessible resources : PEDro database, Cochrane Library, BJSM podcasts, JOSPT clinical practice guidelines
• 🤝 Communities of practice : journal clubs, professional networks (SFRE, SFP, OARSI, AAOMPT)
• 🔄 Shared decision-making : integrate the patient's values and preferences (Caneiro 2020 narrative shift)⁴