The use of musculoskeletal ultrasound is useful to assist in arthrocentesis and has been shown to have many benefits including greater fluid aspiration and greater novice physician confidence. It does not result in more pain for the patient and takes minimal additional time to perform at the bedside. The reader is referred to an ultrasound technique text for full instruction, but a few important points are included here. Bone will appear hyperechoic and easily differentiated from muscle and subcutaneous tissue. Tendons will appear fibrillar in nature, like a bundle of drinking straws. Joint fluid will appear hypoechoic and dark. The “seagull sign” is a shape that can be seen on most joint images and represents the joint space between the articular surfaces of two opposing bones. It is a V-shaped hypoechoic area surrounded by hyperechoic bone. Once the landmarks are identified, the needle can be inserted with or without ultrasound guidance.
Apply the needle to the syringe and break the resistance. This avoids any sudden and painful movements of the needle within the joint cavity. Stretch the skin over the site where the needle will be inserted. Penetrate the skin briskly with the needle and enter the joint cavity. Gently aspirate synovial fluid to confirm proper needle position within the joint cavity. If bone is encountered, slightly withdraw the needle and re-advance it in a different direction. Grasp the hub of the needle with your finger or a hemostat. Remove the syringe while leaving the needle in place. Attach the syringe filled with the diluted methylene blue onto the needle.
Inject the methylene blue slowly into the joint cavity. There should be no resistance to flow if the needle is within the joint capsule. The injection should not be painful if the needle is within the synovial capsule. Observe the skin wound for extravasation of blue dye while it is being injected into the joint cavity. Remove the needle when the procedure has been completed. Apply a bandage to the skin.
Different joints will accommodate various amounts of injected volume. The knee may allow for 30 mL or more, whereas the finger may accommodate only 1 mL. It is only necessary to inject a minimal amount of dye before extravasation is seen. If the joint capsule is ruptured, a greater amount of fluid can be injected, as it will escape through the breach. In intact joints, the capsule will expand, increasing pressure and resistance to continued injection. There is often visibly swelling of the skin around the injected joint if there is no breach.
Complete a procedure note in the medical record. A sample procedure note is described below:
After informed consent, the skin overlying the_________joint was cleaned and prepped with povidone iodine solution. The skin was anesthetized with (_____mL of_____% lidocaine, ethyl chloride vapor coolant, ice for_____minutes). Using sterile technique, an_____gauge needle was inserted on the (supero-/infero-,medial/lateral/inferior/superior) surface of the joint. It was directed (supero-/infero-,medially/laterally/inferiorly/superiorly). _____mL of fluid was obtained. It was (thin, thick, yellow, clear, straw-colored, bloody, purulent, with debris, without debris). No complications were noted.
The joint was injected with_____mL of sterile saline containing less than 0.2 mL of 1% methylene blue dye. No complications were noted.
Methylene blue joint injection can be reasonably accomplished at any joint. The concern for joint capsule rupture without concomitant obvious need for operative exploration and fixation is rare in joints other than the knee and fingers. The knee is relatively easy to inject while the fingers are more difficult. Arthrocentesis with methylene blue injection in the knee and finger is discussed below. The principles and techniques described below can be used on any synovial joint for which there is concern of a capsule breach and for which the EP feels competent to perform arthrocentesis. Please refer to Chapter 77 for the complete details of joint arthrocentesis.
Patellofemorotibial Joint (Knee) Arthrocentesis, Parapatellar Approach
The knee joint can be injected in a variety of locations and with the knee extended or flexed. Palpate the borders of the patella (superior, lateral, and inferior) and the patellar tendon (Figures 78-4A & B). Identify the midpoint of the lateral or medial border of the patella (Figure 78-4B). Either of these landmarks may be used as the site for needle insertion.
Methylene blue dye injection of the knee. A. Anatomy of the region. B. Palpating the boundaries of the patella. C. Injection of methylene blue using the medial parapatellar approach.
Place the patient supine on a stretcher with the affected knee fully extended.
Needle Insertion and Direction
Insert an 18 gauge needle just below the midpoint of the lateral or medial border of the patella (Figure 78-4C). Direct the needle perpendicular to the long axis of the leg and aimed toward the intercondylar notch of the femur. Advance the needle to a depth of 1 to 2 cm. Inject the methylene blue dye.
Ultrasound Probe Placement
Start with probe placement longitudinally lateral or medial to the patella for a first view of the possible fluid collection. Then change the probe to a horizontal orientation, and rotate the probe like the hand of a clock around the patella 360° to discover the area with the largest anechoic fluid collection.
The easiest site for arthrocentesis is the medial parapatellar region. There are no disadvantages to using the medial parapatellar site. The lateral and medial parapatellar approaches are used with high relative success, most likely due to the large joint space and minimal accessory structures. Studies have demonstrated decreased success of the medial midpatellar approach (56%), relative to the lateral midpatellar (76%-93%) or the infrapatellar (71%-85% lateral and 73%-75% medial) approaches.6,7
Metacarpophalangeal Joint Arthrocentesis
The relatively thin dermal and subcuticular layers over the phalanges often make one wonder about deep soft tissue avulsions or lacerations and the potential involvement of the joint capsule. Injection with methylene blue dye is an ideal method to assess joint capsule integrity. The success rate of arthrocentesis is much lower in the phalangeal joints than larger joints. The overlying ligaments and tendons are more prominent and the synovial capsule is smaller. A failure rate of 15% for finger arthrocentesis was found among skilled surgeons, and as high as 32% among first year residents.8 Successful arthrocentesis was highest in the proximal interphalangeal joint compared to the distal interphalangeal joint or carpometacarpal joint of the thumb.
Identify the metacarpophalangeal (MCP) joint and the extensor digitorum tendon (Figures 78-5A & B). The MCP joint can be located just proximal to the prominence at the base of the proximal phalanx of the finger. Identify the extensor tendon by having the patient extend the finger against resistance.
Methylene blue dye injection of the metacarpophalangeal (MCP) joint. A. Anatomy of the region. B. Palpation of the MCP joint. C. Injection of methylene blue.
Place the patient sitting upright or supine on a stretcher. Pronate the hand and abduct the fingers. Grasp the finger and apply distal traction.
Needle Insertion and Direction
Insert a 22 gauge needle into the dorsal joint space just medial or lateral to the extensor tendon (Figure 78-5C). Direct the tip of the needle toward the center of the joint. Advance the needle to a depth of 0.3 to 0.5 cm. Inject the methylene blue dye.
The application of distal traction often causes a depression to appear on both sides of the extensor tendon. These depressions can be used as landmarks for the site of needle insertion into the joint cavity.
A maximum volume of 1 mL may be instilled into this joint.