Knee osteoarthritis - clinical fact sheet and MCQ

Overview

Knee osteoarthritis (OA) is a chronic degenerative joint disease affecting the synovial knee joint, leading to pain, stiffness, swelling, and reduced mobility. It is one of the most common forms of arthritis and a leading cause of disability worldwide. The condition arises due to the gradual breakdown of cartilage, which cushions the ends of bones, leading to joint space narrowing, osteophyte formation, and inflammation.

The prevalence of knee OA increases with age, affecting about 3.8% of the global population, with higher rates in those over 60 years. In Australia, over 2.1 million people are estimated to have osteoarthritis, and knee OA accounts for a significant proportion of these cases. Women are more frequently affected than men, and the condition is more common in individuals who are overweight or obese.

Knee OA has a substantial impact on quality of life. It can impair walking, climbing stairs, and performing daily activities such as standing from a seated position, getting in and out of vehicles, and engaging in work or leisure. The resulting inactivity can contribute to mental health issues, including anxiety and depression.

Risk factors 

Several factors increase the risk of developing knee OA:

• age: the risk rises sharply after age 45

• gender: women have a higher prevalence, likely due to hormonal and anatomical differences

• obesity: excess body weight quadruples the risk of knee OA, as it increases joint load and systemic inflammation

• genetics: a family history of osteoarthritis increases susceptibility

• previous knee injury: trauma, such as ligament tears, meniscal injuries or menisectomies, and fractures, accelerates joint degeneration

• repetitive joint stress: high-impact sports, heavy lifting, or occupations requiring frequent kneeling or squatting contribute to OA progression

Diagnosis of knee osteoarthritis

Knee OA is primarily a clinical diagnosis based on symptoms and physical examination. Imaging is not required for routine diagnosis but may be used in certain cases.

1. Clinical features

Primary: 

• pain: typically worsens with activity and improves with rest

• stiffness: most noticeable after periods of inactivity, such as in the morning or after prolonged sitting

• swelling: due to inflammation or fluid build-up in the joint

Other: 

• crepitus: a grinding or clicking sensation when moving the knee

• reduced range of motion: difficulty fully bending or straightening the knee

• muscle weakness and instability

2. Imaging and investigations

• X-rays: may be used if alternative diagnoses (eg fractures) are suspected or if symptoms worsen despite treatment

• MRI/CT and ultrasound scans are not recommended for routine diagnosis as they do not significantly alter management

3. Differential diagnoses

Knee OA shares symptoms with several other conditions, making it important to consider alternative or co-existing pathologies.

• Inflammatory arthritis:

• rheumatoid arthritis (RA): typically presents with bilateral knee involvement, prolonged morning stiffness (>1 hour), and systemic symptoms such as fatigue and weight loss. As RA is an autoimmune disease, it often affects multiple joints

• gout: acute onset of severe pain, redness, and swelling due to urate crystal deposition Commonly affects the first metatarsophalangeal joint but can involve the knee

• psoriatic arthritis (PsA): is usually asymmetric and associated with skin and/or nail changes of psoriasis, and/or dactylitis (sausage-like swelling of digits) 

• Traumatic and mechanical disorders

• meniscal tear: presents with locking, catching, or instability. History of twisting injury is common. MRI may be needed for diagnosis
  Note that degenerate meniscal tears can be part of the pathology of knee arthritis

• patellofemoral pain syndrome (PFPS): common in young adults and athletes. Causes anterior knee pain worsened by prolonged sitting or stair climbing

• ligamentous injuries: anterior cruciate ligament (ACL) or medial collateral ligament (MCL) tears cause joint instability and swelling following trauma

• Infection 

• septic arthritis: acute onset of intense pain, swelling, warmth, fever, and systemic symptoms. A medical emergency requiring diagnostic joint aspiration, surgical management and antibiotic treatment

• Other

• osteonecrosis of the knee: common in older adults, presenting with sudden-onset pain without trauma, often affecting the medial femoral condyle

• Baker’s cyst: swelling behind the knee that may rupture, causing calf pain and mimic deep vein thrombosis (DVT)

Management of knee osteoarthritis

Clinical guidelines recommend non-surgical management as the first-line treatment for all patients with knee OA, regardless of disease severity.

1. Education and self-management:

• patients should be informed about OA progression, treatment options, and lifestyle changes that can help manage symptoms

• psychological support, goal setting, and shared decision-making improve self-management outcomes

2. Physical activity and exercise:

• regular exercise is essential in reducing pain and improving function

• strength training, aerobic exercises, and neuromuscular training (eg balance exercises) are effective

• aquatic therapy may be beneficial for those with severe pain or mobility limitations

3. Weight management:

• reducing 5–10% of body weight can significantly improve pain and mobility

• a combined approach of diet and exercise is most effective

4. Pharmacological management:

• first-line treatments:

• NSAIDs (eg ibuprofen, naproxen): provide effective pain relief but should be used cautiously in patients with gastrointestinal or cardiovascular risks. Use the lowest effective dose for the shortest time possible

• paracetamol: less effective than NSAIDs but may be considered for mild symptoms

• intra-articular injections:

• corticosteroid injections can provide short-term relief (up to 3 months). However, long-term use is not supported as repeat injections may cause cartilage damage and further joint deterioration 

• platelet-rich plasma (PRP)is not recommended as it lacks consistent evidence and is costly

• hyaluronic acid injections are not recommended due to inconsistent benefits

• opioids (including tramadol) are not recommended due to high risk of dependence and side effects

Fish oil, chondroitin and glucosamine are not recommended as there is no evidence that they provide benefit.

Surgical management 

Surgery is reserved for severe cases where non-surgical treatments fail to provide relief.

1. Joint replacement surgery:

• total knee replacement (TKR): recommended for patients with severe pain and functional impairment despite optimal non-surgical management

• partial knee replacement (PKR): suitable for localised OA in one part of the knee

2. Arthroscopic surgery:

• not recommended for routine OA management

• may be considered for mechanically symptomatic meniscal tears in select cases

References

Brophy R, Fillingham Y. AAOS Clinical Practice Guideline Summary: Management of Osteoarthritis of the Knee (Nonarthroplasty), Third Edition. J Am Acad Orthop Surg. 2022;30:e721-e729

Australian Commission on Safety and Quality in Health Care. Osteoarthritis of the Knee Clinical Care Standard. Sydney: ACSQHC; 2024.

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