[Orthopedic Arthroscopy] Common Methods of Knee Joint Aspiration

Knee arthrocentesis is often used to check the nature of the fluid in the joint cavity, or to inject medicine into the joint cavity after removing the fluid. If there is fluid accumulation in the knee joint cavity, joint puncture and drainage are required, or drug injection is required for treatment. Air or contrast agent is injected into the joint cavity, and arthrography is performed to understand changes in articular cartilage or bone ends.

The knee joint capsule, ligaments and tendon attachment points have dense nerve distribution. Many nerve branches penetrate deep into the cartilage, synovium and subchondral blood vessels in the knee joint cavity. Many unmyelinated nerve terminal receptors also co-distribute with vascular courses in the joint capsule, synovium, and joint fat pads.

Causes of knee joint effusion:

1. Injury (sports-related): Knee sprain, meniscus tear, collateral ligament or cruciate ligament injury.

2. Infection (tuberculosis).

3. Rheumatoid arthritis, synovitis.

Position: Supine position, all muscles relaxed.

Joint: Extended or slightly flexed.

Injection point: Around the patella or knee eye.

When joint degeneration, excessive exercise, or trauma occurs, lactic acid, histamine, bradykinin, prostaglandins, and neuropeptides in the joint cavity are activated, causing pain. Simultaneously, a large amount of joint effusion appears in the knee joint cavity, increasing pressure and causing knee swelling.

Patellar Superior Lateral Border Puncture Method

Location: At the junction of the superior lateral border of the patella and the vastus lateralis muscle. Press the depression below the vastus lateralis muscle, insert the needle 0.5-1 cm close to the fingernail, until a feeling of resistance is felt.

Advantages:

1. Few nerve endings, low sensory sensitivity, thin tissue, good feel. Patient cooperation is easier.

2. Less synovial membrane in the joint, less likely to cause pain. Less tissue at the puncture site, easy for the needle to reach the joint cavity. Being close to the suprapatellar bursa allows for downward squeezing of the fluid in the suprapatellar bursa, resulting in more thorough aspiration. Moving the needle upwards allows for direct aspiration of the fluid from the suprapatellar bursa.

Patellar Inferior Border (Lateral Knee Eye) Puncture Method

Location: With the knee flexed at 90°, puncture at the inferior border of the patella, 1 cm lateral to the patellar ligament (lateral knee eye, a small depression can be seen).

Method: After locating the patella with your fingernail, disinfect the affected area. Insert the needle parallel to the tibial plateau at a 45-degree angle inwards, ensuring the needle is fully inserted.

Advantages (Knee-eye):

1. Easier to locate, no pain for the patient after injection. Patient cooperation is easier.

2. Sodium hyaluronate is injected intra-articularly from the lateral side of the patellofemoral joint, avoiding injection into the infrapatellar fat pad, which can cause pain and affect drug efficacy.

3. Injection from the superior lateral aspect of the patella, or from the medial border, also yields good results. If synovial hyperplasia is severe and the infrapatellar fat pad is too thick, needle insertion becomes difficult, potentially causing repeated irritation of the synovium and fat pad, leading to pain.

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Precautions

1. Strict aseptic technique must be maintained for all puncture instruments and procedures to prevent secondary infection from sterile joint effusion. Routine disinfection and draping are performed. Local anesthesia with 2% lidocaine is administered, and the necessary medication is prepared beforehand. The patient should be relaxed during the puncture.

2. Carefully select the puncture site, avoiding blood vessels, nerves, tendons, skin lesions, or superficial areas, and ensuring easy access to the joint cavity. During the procedure, the operator's fingers should not touch the skin or the puncture site. The movements should be gentle, avoiding excessive insertion to prevent damage to the articular cartilage.

3. The needle should be inserted quickly into the skin, gently withdrawing while simultaneously advancing the needle until synovial fluid is observed. If bony obstruction is encountered, slightly withdraw the needle or change the puncture direction slightly, then continue aspiration and needle advancement. If infectious fluid or pus is suddenly found outside the joint capsule during puncture, immediately stop advancing the needle. It is best to first treat the infected soft tissue area with antibiotics. If there is significant purulent discharge, incise and drain the infection site, clearly identifying the extent of the infection and its relationship to the joint cavity; never attempt to enter the joint cavity unnecessarily. After puncture, remove the needle and disinfect the puncture site with iodine.

4. If there is excessive joint effusion, apply appropriate pressure and bandage after aspiration. If the fluid volume is large, aspiration can generally be performed twice a week.

5. Aspiration should be performed while simultaneously advancing the needle. Observe for fresh blood; if present, it indicates a blood vessel has been punctured. Withdraw the needle slightly, change direction, and continue advancing.

6. Repeated intra-articular injections of steroids can cause joint damage. Therefore, no intra-articular steroid injection should exceed three times.

7. In addition to microscopic examination, bacterial culture, and antibiotic sensitivity testing, the aspirated fluid should be carefully observed to preliminarily determine its characteristics and provide timely treatment. Normal fluid is straw-yellow, clear, and transparent. Dark red, old blood often indicates trauma. The presence of fat droplets in the aspirated blood may indicate an intra-articular fracture. Turbid fluid suggests infection; if it is purulent, the diagnosis of infection is certain.

8. Avoid contact with water for 6 hours after the puncture site, and do not apply topical medications for 48 hours. Patients receiving anticoagulation therapy should immobilize the joint for 1-2 days. If necessary, ice packs can be applied near the joint, and an elastic bandage can be wrapped around the joint. Avoid local bathing for 3 days.

How to choose? Lower lateral border of the patella or upper lateral border of the patella

(1) For patients with a large amount of intra-articular effusion, aspiration is performed via the upper lateral border of the patella, followed by injection of sodium hyaluronate. This is because when there is a large amount of intra-articular effusion, the effusion is mostly in the suprapatellar bursa, and the patellofemoral joint space is relatively large, making aspiration via the upper lateral border of the patella easy and allowing for effective aspiration. However, for patients without joint effusion, aspiration via the upper lateral border of the patella is less convenient.

(2) For patients without joint effusion, the patellar inferior margin (lateral knee eye) puncture method is used. It is crucial to accurately determine the location (knee flexed at 90 degrees, 1 cm lateral to the patellar ligament and inferior margin), using an 8-gauge needle, parallel to the tibial plateau, at a 45-degree angle inwards. The needle should be fully inserted; a feeling of emptiness may be felt. Sometimes, aspiration may yield joint fluid; in this case, injection is safe. If no joint fluid is aspirated, sodium hyaluronate can be injected. If the injection is easy, there is no problem. If the injection is difficult, and the patient experiences pain or distension, the needle can be inserted further inwards and moved left and right. If the injection becomes easier and the patient experiences no discomfort, the injection can continue. With skilled operation, correct positioning, and timely adjustments, patients rarely experience post-injection discomfort.