What is the appropriate examination and management approach for a patient presenting with knee effusion and suspected arthritis?

Knee Examination for Effusion and Arthritis

Clinical Examination for Knee Effusion

Clinical examination is the primary method for detecting knee effusion and suspected arthritis, with imaging studies used to confirm the diagnosis and assess severity. 1

Physical Examination Techniques

• Inspection: Look for visible swelling around the knee joint
• Palpation: Assess for tenderness, particularly at joint lines
• Specific tests for effusion:
  • Ballottement test: Push the patella against the femur and release; a "floating" sensation indicates effusion
  • Bulge sign: Milk fluid from medial to lateral aspect of knee, then tap the lateral side and watch for a fluid wave on the medial side
  • Patellar tap: Push the patella posteriorly and feel for a "tapping" sensation against the femur

The ballottement test combined with patient-reported swelling provides the best diagnostic value for detecting effusion (LR+ of 3.6) 2.

Distribution of Effusion

Fluid tends to collect maximally in the lateral suprapatellar pouch when the knee is extended, which is important to consider during examination and aspiration 3.

Imaging Studies

Initial Radiographic Assessment

• Weight-bearing radiographs are the most appropriate initial imaging study for suspected arthritis 4
• Standard views should include:
  • Bilateral anteroposterior (AP) views
  • Lateral view of the affected knee
  • Patellofemoral (sunrise/Merchant) view
  • Tunnel view

Weight-bearing radiographs better demonstrate joint space narrowing and malalignment compared to non-weight-bearing views 4.

Radiographic Findings in Arthritis

• Joint space narrowing
• Osteophyte formation
• Subchondral sclerosis
• Soft tissue calcifications

Advanced Imaging

• MRI is not indicated as an initial investigation but may be appropriate when:
  • Radiographs are normal but symptoms persist
  • Concomitant pathology is suspected (meniscal tears, ligament injuries)
  • More accurate cartilage assessment is needed 1
• Ultrasound can be useful to:
  • Confirm suspected effusion
  • Guide joint aspiration
  • Detect synovial pathology and increased blood flow (power Doppler) 1

Joint Aspiration (Arthrocentesis)

Joint aspiration should be considered when:

1. Crystal arthropathy is suspected
2. Infection needs to be ruled out
3. Therapeutic drainage is required

Ultrasound or fluoroscopic guidance can facilitate aspiration 1.

Synovial Fluid Analysis

• Color and clarity: Cloudy fluid suggests infection or inflammation
• Cell count: >2,000 WBC/mm³ suggests inflammatory arthritis
• Crystal analysis: For gout (monosodium urate) or pseudogout (calcium pyrophosphate)
• Culture: To rule out infection

Management Approach

Initial Management

1. NSAIDs for symptomatic relief after evaluating gastrointestinal, renal, and cardiovascular risk 1
2. Paracetamol/Acetaminophen as an alternative when NSAIDs are contraindicated 1

For Confirmed Inflammatory Arthritis

• Early referral to rheumatologist ideally within 6 weeks of symptom onset 1
• Disease-modifying antirheumatic drugs (DMARDs) should be started early in patients at risk of persistent or erosive disease 1
• Methotrexate is considered the anchor drug for persistent inflammatory arthritis 1

For Osteoarthritis

• Intra-articular corticosteroid injections for acute exacerbations, especially with effusion 1
  • Provides short-term relief (1-3 weeks)
  • More effective in patients with effusion
• Hyaluronic acid injections may be considered for knee osteoarthritis 1

Common Pitfalls to Avoid

1. Relying solely on one physical examination test - Combining self-reported swelling with the ballottement test improves diagnostic accuracy 2

2. Missing bilateral assessment - Always compare the affected knee with the unaffected knee 5

3. Overlooking systemic causes - Consider systemic inflammatory conditions, crystal arthropathies, and infection in the differential diagnosis

4. Delaying referral - Early referral to a rheumatologist (within 6 weeks) is recommended for patients with inflammatory arthritis 1

5. Inadequate imaging - Weight-bearing radiographs are essential for proper assessment of joint space narrowing in osteoarthritis 4