What should I do for a swollen left knee?

Management of a Swollen Left Knee

Begin with plain radiographs (anteroposterior, lateral, sunrise/Merchant, and tunnel views) to exclude fracture, osteoarthritis, osteochondritis dissecans, loose bodies, or tumor before proceeding with any other diagnostic or therapeutic interventions. 1, 2

Initial Diagnostic Approach

Mandatory First Step: Plain Radiographs

• Four essential radiographic views are required: anteroposterior, lateral, sunrise/Merchant, and tunnel views to identify bony pathology, osteoarthritis, chondrocalcinosis, or signs of prior chronic knee injury 1, 2
• Radiographs will detect approximately 80% of significant structural abnormalities including fractures, degenerative changes, and loose bodies that require immediate management decisions 1

History and Physical Examination Specifics

Look for these critical diagnostic clues:

Pain characteristics:

• Night pain or pain at rest suggests infection or tumor 1
• Pain with weight-bearing suggests mechanical loosening or osteoarthritis 1
• Pain worsening with activity suggests inflammatory or structural pathology 1

Physical examination findings:

• Tenderness location (medial vs lateral joint line, tibial tubercle, patella) localizes structural pathology 1, 3
• Effusion presence indicates intra-articular pathology requiring further investigation 1, 3
• Warmth, erythema, and fever indicate acute infection requiring urgent arthrocentesis 1, 3
• Range of motion loss (compare to contralateral side) suggests significant intra-articular pathology 1

Critical Red Flags Requiring Urgent Action

Suspect septic arthritis if:

• Warmth, erythema, fever, or severe pain at rest are present 1, 3
• Never administer intra-articular corticosteroids before excluding infection—this can worsen septic arthritis and lead to joint destruction 2, 4
• Perform urgent arthrocentesis with synovial fluid analysis including cell count, Gram stain, culture, and crystal analysis 3, 5, 4

Suspect deep vein thrombosis if:

• Posterior knee swelling is present—compression ultrasound of proximal deep veins is mandatory to rule out popliteal vein thrombosis, which constitutes a life-threatening emergency requiring immediate anticoagulation 2

Subsequent Imaging Based on Radiographic Findings

If Radiographs Show Joint Effusion or Are Normal

• MRI without IV contrast is the next appropriate study to evaluate meniscal tears, articular cartilage damage, ligament injuries, or bone marrow lesions 1, 2
• MRI accurately depicts effusion extent, synovitis presence, popliteal cyst rupture, and subchondral bone abnormalities 1
• Bone marrow lesions on MRI correlate with increased knee pain, especially in males or patients with family history of osteoarthritis 1

If Radiographs Show Osteoarthritis

• No additional imaging is typically required unless concomitant pathology is suspected (meniscal tear, ligament injury) 1
• Consider MRI if pain is disproportionate to radiographic findings or if mechanical symptoms (locking, catching) suggest meniscal pathology 1

Treatment Algorithm

Non-Pharmacological Management (First-Line for All Patients)

The American College of Rheumatology recommends these as cornerstone interventions: 6

• Exercise therapy including quadriceps strengthening and low-impact aerobic activities should be implemented immediately 6
• Weight management is strongly recommended for overweight or obese patients—even modest weight loss significantly improves symptoms 6
• Activity modification including avoiding symptom-exacerbating activities and using assistive devices (cane, walker) reduces joint loading 6

Pharmacological Management

First-line options: 6

• Topical NSAIDs are preferred for localized knee pain with lower systemic side effect risk 6
• Acetaminophen (paracetamol) is an alternative for pain relief in patients who cannot tolerate NSAIDs 6

Oral NSAIDs (use with caution): 6, 7

• Use at the lowest effective dose for the shortest possible period 6, 7
• Consider proton pump inhibitors for patients at risk of gastrointestinal complications (history of ulcers, concurrent corticosteroid use, age >60, anticoagulant use) 6, 7
• NSAIDs may suppress natural healing processes—use judiciously in acute injuries 1
• Contraindications include: recent heart attack, planned cardiac surgery, aspirin-sensitive asthma, active GI bleeding, severe renal or hepatic impairment 7

When to Refer to Orthopedic Surgery

The American Academy of Orthopaedic Surgeons suggests specialist referral if: 6

• Conservative measures fail to provide adequate symptom relief after 4-6 weeks 6
• Significant functional limitation persists despite appropriate conservative management 6
• Radiographs show severe tricompartmental osteoarthritis with progressive symptoms despite optimal medical management 1
• Mechanical symptoms (true locking, not just stiffness) suggest displaced meniscal tear or loose body requiring arthroscopic intervention 1

Common Pitfalls to Avoid

1. Never perform MRI before plain radiographs—approximately 20% of patients with chronic knee pain undergo unnecessary MRI without recent radiographs 2

2. Never delay compression ultrasound when posterior knee swelling is present—popliteal DVT requires immediate anticoagulation to prevent fatal pulmonary embolism 2

3. Do not assume all knee swelling is osteoarthritis—persistent non-mechanical pain lasting more than a few weeks should raise concern for infection, tumor, or inflammatory arthritis requiring different management 1, 3

4. Avoid prolonged NSAID use without gastroprotection—notable GI complications occur in up to 1% of patients, with risk increasing with duration of use, age >60, concurrent corticosteroids, and anticoagulants 7

5. Do not ignore systemic symptoms—fever, night sweats, weight loss, or multiple joint involvement suggests systemic inflammatory or infectious process requiring different diagnostic workup 1, 3, 4

Monitoring and Follow-up

• Regular reassessment of symptoms and function with adjustment of treatment plan based on response is essential 6
• Patients on long-term NSAIDs require monitoring of hemoglobin, renal function, and liver enzymes 7
• If symptoms persist or worsen despite 4-6 weeks of appropriate conservative management, specialist referral is warranted 6