Lucan · Conditions

Knee osteoarthritis

Australian guidance: RACGP Guideline for Knee and Hip Osteoarthritis

1. Definition and epidemiology

Osteoarthritis (OA) is a chronic degenerative joint disease characterised by progressive loss of articular cartilage, subchondral bone remodelling, osteophyte formation, and varying degrees of synovial inflammation. It is the most common form of chronic arthritis in Australia, with an estimated 2.1 million Australians (9% of the population) affected as of 2015. Prevalence increases sharply after age 45, rising to greater than 60% among those aged over 55 years, and the number of Australians affected is projected to reach 3.1 million (12% of the population) by 2030 as rates of obesity and population ageing increase.

2. Pathophysiology

Knee OA results from an imbalance between cartilage matrix synthesis and degradation. Chondrocytes, normally quiescent in mature cartilage, undergo phenotypic changes under mechanical stress, obesity-related metabolic signals, and ageing. These cells upregulate matrix metalloproteinases (MMPs) and aggrecanases that degrade type II collagen and aggrecan, the principal structural proteins of hyaline cartilage. Simultaneously, attempted repair produces abnormal fibrocartilage rather than true hyaline cartilage, and chondrocytes eventually undergo apoptosis leaving areas of full-thickness cartilage loss. Subchondral bone responds by undergoing sclerosis and cyst formation, and marginal osteophytes form at the joint periphery as a reparative response driven by transforming growth factor beta and other mediators. The synovium becomes reactive, releasing interleukin-1 (IL-1) and tumour necrosis factor alpha that further accelerate cartilage catabolism, creating a self-perpetuating destructive cycle. Periarticular muscle weakness, ligamentous laxity, and altered proprioception compound joint instability and accelerate mechanical wear over time.

3. Clinical presentation and diagnostic criteria

The RACGP guideline specifies that a clinical diagnosis of knee OA can be made without further investigations when a person is aged 45 years or older, has activity-related joint pain, has morning stiffness lasting less than 30 minutes, has crepitus on active motion, has bony enlargement, and has no detectable joint warmth. Additional features that may accompany the diagnosis include fixed flexion or varus deformity, joint instability, periarticular or joint-line tenderness, and pain on patellofemoral compression. Risk factors include older age, female sex, obesity (body mass index of 30 or above), prior joint injury, occupation involving repetitive kneeling or heavy lifting, and quadriceps muscle weakness. Red flags warranting consideration of alternative diagnoses include a warm swollen joint, prolonged morning stiffness exceeding 30 minutes, rapid symptom progression, history of trauma, or systemic features such as fever or weight loss.

4. Investigations and AU-specific cutoffs

Knee OA is primarily a clinical diagnosis and investigations are not routinely required. The diagnostic workup should be directed by atypical features or the need to exclude alternative or coexisting conditions.

Plain weight-bearing radiograph of the knee, including anteroposterior and patellofemoral views, may be considered for atypical presentations. Radiographic features include joint space narrowing, subchondral sclerosis, subchondral cysts, and osteophyte formation graded by the Kellgren-Lawrence scale (grade 0 to 4). Note that radiographic changes and meniscal tears are an almost universal finding in older populations and do not necessarily correlate with symptoms.

Laboratory investigations are not required for diagnosis but are ordered when coexisting inflammatory arthritis is suspected. Relevant tests include erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor, anti-cyclic citrullinated peptide antibodies, urate, and full blood count. If a palpable knee effusion is present, synovial fluid aspiration and analysis is indicated to exclude septic arthritis, gout, and calcium pyrophosphate deposition disease. OA synovial fluid typically contains fewer than 2000 leucocytes per mm3.

Magnetic resonance imaging (MRI) is not routinely indicated. It may be useful for atypical presentations or when the clinical diagnosis is uncertain. GP referral for MRI is not reimbursed under the Medicare Benefits Schedule (MBS) for OA, making specialist referral the appropriate pathway when MRI is genuinely needed.

5. Management

The RACGP guideline emphasises active, non-pharmacological interventions as the mainstay of knee OA management, with pharmacotherapy used adjunctively.

Non-pharmacological interventions with strong recommendations include land-based exercise (particularly muscle-strengthening exercises, walking, and Tai Chi) for all people with knee OA regardless of age, disease severity, or pain level; and weight management for those with a body mass index of 25 or above. A minimum weight loss target of 5 to 7.5% of body weight is recommended for overweight and obese patients, with the weight loss combined with exercise for greater benefit.

Conditionally recommended non-pharmacological measures include aquatic exercise or hydrotherapy, a short course of massage therapy or manual therapy (soft tissue and joint mobilisation) as an adjunct to active management, cognitive behavioural therapy (CBT) particularly in combination with exercise, local heat therapy as a self-management strategy, an assistive walking device (for example a cane) where appropriate, and home-use transcutaneous electrical nerve stimulation (TENS).

Arthroscopic procedures including lavage, debridement, meniscectomy, and cartilage repair are strongly recommended against for knee OA unless there is a clinically locked knee as per the Australian Knee Society arthroscopy position statement.

6. Pharmacology and AU PBS notes

Pharmacotherapy is a conditional addition to exercise and lifestyle modification rather than a first-line standalone approach.

Oral nonsteroidal anti-inflammatory drugs (NSAIDs) including cyclo-oxygenase-2 (COX-2) selective inhibitors such as celecoxib (Celebrex) and meloxicam (Mobic, Movalis) are conditionally recommended. These should be trialled at the lowest effective dose for a short period, with monitoring for gastrointestinal, renal, and cardiovascular adverse events. A proton pump inhibitor (PPI) should be co-prescribed when oral NSAIDs are used in patients at elevated gastrointestinal risk. These agents are available on the PBS for symptomatic relief of OA without streamlined authority (general benefit Schedule item).

Topical NSAIDs may be trialled for a short period and discontinued if ineffective, with monitoring for adverse effects. The RACGP guideline notes a neutral recommendation for topical NSAIDs given moderate quality evidence.

Paracetamol (Panadol, Panamax) carries a neutral (conditional) recommendation. It may be reasonable to trial paracetamol for a short period and discontinue use if ineffective, with monitoring for adverse events. It does not carry PBS authority restrictions for OA.

Intra-articular corticosteroid injection (for example methylprednisolone acetate 40 mg) is conditionally recommended for short-term symptom relief. Repeated injections carry potential harm, including risk of cartilage degradation, and should be approached with caution.

Duloxetine (Cymbalta) is conditionally recommended when other forms of pain relief are inadequate. It does not have Therapeutic Goods Administration (TGA) approval for an OA indication and is therefore considered an off-label investigational use. It is not PBS-listed for OA.

Strongly recommended against: oral and transdermal opioids, viscosupplementation injection (hyaluronic acid) for knee OA, doxycycline, strontium ranelate, IL-1 inhibitors, and stem cell therapy. Glucosamine and chondroitin supplements are conditionally recommended against and should not be offered.

7. Complications and monitoring

Progressive structural joint damage leads to worsening pain, loss of mobility, and functional decline. End-stage knee OA produces significant joint pain, swelling, deformity, disrupted sleep, and marked restriction of activities of daily living. This trajectory may ultimately require referral to an orthopaedic surgeon for total knee replacement, which offers the most cost-effective and clinically effective treatment for end-stage disease in appropriately selected patients. Best surgical outcomes are associated with Kellgren-Lawrence grade 3 or 4 radiographic change, well-controlled comorbidities, body mass index between 20 and 30, and good mental health status.

Ongoing monitoring in primary care should include periodic assessment of pain using validated tools such as the Numeric Pain Rating Scale (NPRS) or the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), functional capacity (for example the 30-second chair-stand test and 40-metre fast-paced walk test), weight, muscle strength, adherence to exercise, and any adverse effects of pharmacotherapy. Monitoring for NSAID-related renal function impairment and gastrointestinal harm is particularly important in older patients with comorbidities.

Falls risk should be assessed systematically given that quadriceps weakness, joint instability, and analgesic use each independently increase falls risk in this predominantly older population. Referral to a falls clinic may be appropriate.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.