Anatomy Msk · Year 1 · from Anatomy Msk
Case 3: Knee Joint Aspiration and Injection
Clinical Image
Source: Wikimedia Commons - Joint Injection - CC BY-SA 3.0
Case Presentation
A 58-year-old man with a history of gout presents with acute onset of severe left knee pain, swelling, and difficulty walking. He reports similar episodes in the past affecting his great toe. Physical examination reveals a tense effusion of the left knee with warmth, erythema, and exquisite tenderness. Range of motion is severely limited by pain. There is no evidence of overlying cellulitis or wound. Given the need to rule out septic arthritis and confirm the diagnosis of acute gout, arthrocentesis is performed. The patient is positioned supine with the knee slightly flexed (15-20 degrees) over a rolled towel to relax the quadriceps. Surface landmarks are identified: the patella, lateral femoral condyle, and lateral tibial plateau. The superolateral approach is selected. The needle insertion point is identified at the superior lateral border of the patella, just posterior to the patella at the junction with the quadriceps tendon. After sterile preparation and local anesthesia, an 18-gauge needle is inserted at this point, directed slightly inferiorly and medially toward the intercondylar notch. The needle enters the suprapatellar bursa (which communicates with the knee joint). A large volume (50 mL) of cloudy yellow fluid is aspirated. Synovial fluid analysis reveals WBC 45,000 with 85% neutrophils, and polarized light microscopy shows negatively birefringent needle-shaped crystals consistent with monosodium urate (gout). Gram stain and culture are negative. He is treated with colchicine and NSAIDs with rapid improvement.
Key Learning Points
- Knee aspiration can be performed via superolateral, superomedial, or lateral mid-patellar approaches
- The superolateral approach enters the suprapatellar bursa, which communicates with the main joint space
- Surface landmarks for superolateral approach: superior lateral border of patella, posterior to quadriceps tendon
- Arthrocentesis is essential for differentiating crystal arthropathy from septic arthritis (both cause acute inflammatory joint)
- Understanding joint anatomy ensures safe needle placement and successful fluid aspiration