How should I evaluate and treat swelling above my left lateral knee?

Evaluation and Management of Swelling Above the Left Lateral Knee

Begin with standard knee radiographs (AP, lateral, and tangential patellar views) as your immediate first step to exclude fracture, followed by targeted clinical examination to differentiate between iliotibial band syndrome, Baker's cyst, and deep vein thrombosis. 1

Immediate Diagnostic Algorithm

Step 1: Obtain Radiographs First

• Order knee radiographs immediately (AP, lateral, and tangential patellar projections) before any therapeutic intervention, even if clinical suspicion points toward soft tissue pathology 1, 2
• The lateral view with 25-30 degrees knee flexion is critical for assessing joint effusion and ruling out lipohemarthrosis (indicating occult fracture) 2
• Never perform aspiration or injection before imaging confirmation that excludes fracture 2

Step 2: Urgent Compression Ultrasound if DVT Suspected

• If the patient has unilateral leg swelling with pain behind the knee, compression ultrasound of the proximal deep veins is mandatory to rule out popliteal DVT 3
• Popliteal vein thrombosis presents as swelling behind the knee and is classified as proximal DVT requiring immediate anticoagulation 3
• Start parenteral anticoagulation immediately while awaiting ultrasound if clinical suspicion is high (unilateral swelling, pain, heaviness in extremity) 3
• If proximal ultrasound is positive, initiate treatment immediately without confirmatory venography 3

Step 3: Clinical Examination for Lateral Pathology

For Iliotibial Band Syndrome (most common cause of lateral knee pain in active patients):

• Palpate for tenderness approximately 2-3 cm above the lateral joint line over the lateral femoral epicondyle 4, 5
• Pain typically worsens with repetitive knee flexion-extension activities (running, cycling) 6
• Assess for hip abductor weakness, which predisposes to this condition 4
• Look for history of overtraining or recent increase in activity 4

For Baker's Cyst:

• Ultrasound can differentiate Baker's cyst from DVT and identify loose bodies within the cyst 3
• Palpable fluctuant mass in the popliteal fossa that may extend laterally 3

Treatment Based on Diagnosis

If Iliotibial Band Syndrome Confirmed:

Acute Phase (first 3 days):

• Activity modification with cessation of aggravating activities 4, 5
• Ice application 4
• NSAIDs (oral or topical diclofenac with effect size 0.91 vs placebo) 2
• Corticosteroid injection if severe pain or visible swelling persists >3 days despite initial treatment 5

Subacute Phase:

• Aggressive iliotibial band stretching 4, 5
• Soft tissue therapy for myofascial restrictions 4

Recovery Phase:

• Hip abductor strengthening exercises (gluteus medius focus) 4, 5
• Gradual return to activity with every-other-day program 4
• Avoid hill training initially 4

If Joint Effusion Present Without Fracture:

• MRI without contrast is the next indicated study if radiographs show only effusion or are normal 1, 2
• MRI has 96% sensitivity and 97% specificity for meniscal tears and evaluates ligamentous injuries, bone marrow contusions, and occult fractures 2
• Intra-articular corticosteroid injection provides strong short-term efficacy (effect size 1.27) for pain relief if inflammatory exacerbation confirmed 2

If Popliteal DVT Confirmed:

• Enoxaparin 1 mg/kg SC every 12 hours (BMI <40 kg/m²) or 0.8 mg/kg SC every 12 hours (BMI ≥40 kg/m²) 3
• For severe renal impairment: unfractionated heparin IV 80 units/kg bolus, then 18 units/kg/h adjusted to aPTT 2-2.5x control 3

Critical Pitfalls to Avoid

• Never assume lateral knee swelling is benign without ultrasound confirmation to exclude DVT, especially with unilateral presentation 3
• Approximately one-third of DVT patients are asymptomatic, making imaging essential 3
• Do not withhold anticoagulation for confirmed popliteal DVT—risk of fatal PE outweighs bleeding risks 3
• Avoid premature MRI without recent radiographs (within past year) 1
• Most iliotibial band syndrome patients respond to conservative treatment; surgery is reserved only for refractory cases after exhausting all conservative measures 5, 6
• If corticosteroid injection is performed for inflammatory effusion, counsel that benefit is short-term and does not address structural pathology 2