knee joint cavity paracentesis

Knee joint cavity paracentesis is commonly used to examine the nature of effusion in the joint cavity, or to inject medications into the joint cavity after fluid aspiration.

Procedures

Place the patient in a supine position on the operating table with both lower extremities fully extended.

Perform routine skin disinfection at the puncture site. The operator shall wear sterile gloves and lay a sterile perforated drape, followed by local anesthesia with 2% lidocaine.

Use a 7–9 gauge injection needle. Generally, insert the needle inferomedially into the joint capsule from the lateral side of the quadriceps tendon at the superolateral margin of the patella. Alternatively, perform posterior puncture beside the patellar ligament below the patella to reach the joint capsule.

If medication needs to be injected after fluid aspiration, replace with a new sterile syringe.

Cover the puncture site with sterile gauze and secure it with adhesive tape after the procedure.

Precautions

Strictly sterilize all puncture instruments and standardize operative procedures to prevent secondary infection of sterile joint cavity effusion.

Operate gently to avoid damage to the articular cartilage.

In cases of massive joint effusion, apply appropriate compression and immobilization after aspiration.

Puncture Techniques

Superolateral Patellar Puncture

Location: The junction between the superolateral margin of the patella and the vastus lateralis muscle. Press the depression beneath the vastus lateralis, insert the needle 0.5–1 cm deep along the edge of the fingernail until a breakthrough sensation is felt.

Advantages: This area has sparse nerve distribution with low sensory sensitivity and thin soft tissues, allowing for good tactile feedback and easy patient cooperation.

There is less synovium in this region, so pain is rarely induced. The thin tissue layer at the puncture site enables the needle to reach the joint cavity easily. Adjacent to the suprapatellar bursa, this approach allows fluid in the bursa to be milked downward for thorough aspiration; the needle can also be adjusted upward to directly drain fluid from the suprapatellar bursa.

Inferolateral Patellar Puncture

Location: With the knee flexed at 90°, identify the site 1 cm lateral to the patellar ligament at the inferior margin of the patella (the lateral infrapatellar fossa, visible as a small depression).

Method: Mark the puncture point with a fingernail and disinfect the affected area. Use a 10-gauge needle, keep it parallel to the tibial plateau and angled 45° medially, then insert the needle fully into the joint.

Advantages: The location is easy to identify, and patients experience no pain after intra-articular injection, ensuring good cooperation.

For sodium hyaluronate injection, lateral parapatellar intra-articular injection is recommended. This prevents medication from being injected into the infrapatellar fat pad, which would otherwise cause pain and compromise drug efficacy.

Needle insertion can also be performed at the medial parapatellar space besides the superolateral patellar approach, which also yields satisfactory results. In patients with severe synovial hyperplasia or hypertrophic infrapatellar fat pad, puncture becomes difficult, and repeated irritation of the synovium and fat pad may trigger pain.

Puncture with Patient in Sitting Position (Knees Hanging Down)

Draw a horizontal line and a vertical line crossing the central point of the patella. Draw two angle bisectors at 45° within the first and second quadrants respectively. The intersection of each bisector with the lateral margin of the patella serves as the puncture point.

Conventional Puncture Sites for the Knee Joint

Supine position with the knee fully extended: Select the two intersection points of the superior margin and medial/lateral margins of the patella. Insert the needle at a 45° oblique angle toward the center of the patellofemoral joint.

Knee slightly flexed at approximately 30°: Perform vertical puncture through the medial or lateral joint space below the patella beside the patellar ligament.

For patients with massive joint effusion, perform fluid aspiration via the superolateral patellar approach, followed by sodium hyaluronate injection. Most effusion accumulates in the suprapatellar bursa when there is excessive joint fluid, and the patellofemoral joint space is widened, making the superolateral patellar approach simple for aspiration. However, this method is not ideal for patients without joint effusion.

For patients without joint effusion, adopt the inferolateral patellar (lateral infrapatellar fossa) approach with accurate positioning: flex the knee at 90° and target the area 1 cm lateral to the patellar ligament at the inferior patellar margin. Use a 10 mL syringe needle, keep it parallel to the tibial plateau and angled 45° medially, then insert the needle completely until a breakthrough sensation is perceived. If joint fluid is aspirated, injection can proceed safely.

If no fluid is withdrawn, sodium hyaluronate can still be injected. Smooth injection without pain or distension indicates proper needle placement. If resistance is encountered or the patient complains of pain and distension, advance the needle slightly and adjust its position side to side. Resume injection only when the process becomes smooth and the patient feels comfortable. With proficient operation, accurate positioning and timely adjustment, post-injection discomfort is rare in patients.