Chapter 77. Arthrocentesis

Arthrocentesis is the insertion of a needle into a joint cavity for the removal of synovial fluid and/or the injection of pharmaceutical agents into the joint cavity. Fluid can be aspirated from almost any joint. Arthrocentesis is used to diagnose and make treatment decisions regarding a joint. Obtaining synovial fluid is safe, simple, relatively pain free, inexpensive, and extremely beneficial to the patient.

Arthrocentesis may be diagnostic or therapeutic. Diagnostically, it is performed to identify the cause of an acute arthritis, to identify an intraarticular fracture, to identify the causes of an effusion, or to give a therapeutic trial of pharmaceuticals. It can also be therapeutic by relieving pain from elevated intraarticular pressure, to drain septic or crystal-laden fluid, or to inject pharmaceuticals. Ultrasound (US)-guided joint aspiration is a supplemental technique that improves several aspects of the arthrocentesis procedure.

Synovial fluid analysis will provide unique and valuable information about the affected joint.32 It is the only method to definitively diagnose or rule out a septic arthritis. The fluid should be analyzed for the presence of crystals. A white blood cell count and differential may help identify the causes of an effusion. A Gram's stain can be quickly performed to identify bacteria in the synovial fluid. Bedside gross analysis of the fluid's physical properties such as clarity, viscosity, and color has been shown to be a reliable clinical predictor of a potentially septic joint.30 A culture of the synovial fluid should be performed to definitively identify any microbiologic pathogen in the joint.

There are several general principles that should be followed when performing an arthrocentesis (Table 77-1). The Emergency Physician (EP) must know the anatomical relationships around the joint. The needle should go around and not through any tendons. Avoid piercing the articular cartilage, which is avascular and may not heal. Do not bounce the needle off the bone, as this is extremely painful for the patient. Insert the needle through the extensor surface of the joint. The synovial cavity is closest to the skin over the extensor surface of the joint. The extensor surface has fewer tendons and ligaments than the flexor surface. Most of the blood vessels and nerves are located on the flexor surface of the joint. Using the extensor surface of the joint for the procedure will avoid potential injury to these structures. Place the joint in slight flexion to maximize the size of the joint cavity. Apply distal in-line traction to the small joints of the wrists, hands, and feet to enlarge the joint cavity. This allows the needle to more easily enter the small joint spaces. Compression of large joints will mobilize peripheral fluid. This is helpful when the volume of synovial fluid is small. Compression may be applied manually or with an elastic bandage.

It is critical to use sterile technique to prevent the infection of a nonseptic joint as well as to ensure the joint fluid is uncontaminated for microbiological cultures. Sterile drapes, sterile gloves, and face masks are not needed to perform the procedure.1–3 It is necessary to wear gloves to prevent transmission of blood-borne diseases to the EP.1,4 The skin should be cleansed and prepped in the usual manner. The needle may then be grasped, with clean gloves, at the hub and inserted. As long as the skin and needle are not handled, sterile gloves are not required. This is sometimes difficult to master if the EP has little practice with the technique of arthrocentesis. It may be better to err on the side of conservatism and use sterile gloves and drapes; particularly with inexperienced EPs and in training situations.

US has been used by Interventional Musculoskeletal Radiologists and Rheumatologists to guide needles for joint injections and aspirations.44,45 US guidance allows these procedures to be performed in a safer manner because the needle is less likely to injure nerves, tendons, and blood vessels. US also allows a comparison with the asymptomatic opposite-side joint. As bedside ultrasonography has become more commonly used in the ED, more EPs are appreciating and reporting on the benefits of its use in guiding arthrocentesis.46–51 Arthrocentesis is commonly performed on the shoulder, elbow, hip, knee, and ankle joints. It may also be performed on other joints. US guidance can be a useful adjunct in all of these procedures.

There are several possible approaches for the use of US-guided arthrocentesis in the ED. Knee arthrocentesis is commonly performed with a high success rate using only the landmark-palpation technique. Many EPs feel comfortable performing this procedure without the routine use of US guidance. Wiler and colleagues compared US-guided versus standard landmark techniques for knee arthrocentesis and found that US guidance did not improve overall success.50 Others may use US guidance in cases anticipated to be difficult, such as small effusions or prior joint surgery. Some EPs feel that US guidance improves the safety of arthrocentesis and thus choose to use it whenever an arthrocentesis is performed. This approach is especially appealing in light of the fact that US is noninvasive and does not add any risk to the procedure.

Arthrocentesis is indicated to evaluate the cause of an arthritis or a joint effusion (Table 77-2).4–7 All patients presenting with an acute monoarthritis or an acute nontraumatic effusion should undergo arthrocentesis when the diagnosis is not clear based upon the history and physical examination. Analysis of the synovial fluid is essential to help differentiate inflammatory from noninflammatory causes of joint disease. Arthrocentesis is the only reliable method to confirm the presence of an infectious agent as the cause of an arthritis. The presence of crystals within the synovial fluid can diagnose gout or pseudogout from other crystal-induced arthritides. Always keep in mind that two or more types of arthritis can coexist in a patient or in a single joint.4

Arthrocentesis may be therapeutic.8 A large effusion, regardless of the cause, stretches the joint capsule, causing pain and limiting range of motion. Removal of the fluid will decrease pain and increase the joint's range of motion. An effusion caused by inflammation or sepsis contains numerous mediators of inflammation. Removal of this synovial fluid will help to relieve the patient's discomfort. The removal of purulent fluid will decrease the number of organisms in the joint cavity and, theoretically, may limit further joint destruction.

Injection of therapeutic agents into nonseptic joints is commonly performed in the Emergency Department (ED). Local anesthetic solutions may be injected to relieve pain. A joint examination after trauma may be limited secondary to pain. Injection of local anesthetic solutions can relieve pain and allow an examination for ligamentous and joint instability. Corticosteroids are injected into joints to control inflammation and arthritis pain. Sometimes, corticosteroids and local anesthetic solutions are combined into one syringe and injected intraarticularly. The local anesthetic provides immediate pain relief and assures the EP of proper needle placement.

Arthrocentesis can be used to diagnose and treat traumatic arthritides. The traumatic event is usually acute, obvious, and followed by joint pain and swelling. Occasionally, the trauma is minimal or remote and not recalled by the patient. A traumatic effusion can be grossly bloody and, if acute, may contain a large amount of red blood cells. The bloody synovial fluid represents an intraarticular fracture or a disruption of an intraarticular structure. An intraarticular fracture may be suspected based on mechanism of injury and yet radiographic findings may be negative. The synovial fluid may then be evaluated for fat globules, which are released from the marrow cavity of the fractured bone, which confirm the presence of an intraarticular fracture.

The temporomandibular joint is a highly specialized joint that has a unique set of problems associated with it. Arthrocentesis can be an easy, minimally invasive, and efficient procedure used to solve some of these issues. Degenerative joint disease and joint lock are two examples of conditions that are amenable to therapeutic arthrocentesis, although much debate still exists concerning efficacy and therapeutic value of this procedure.

There are no absolute contraindications to arthrocentesis. All contraindications are relative. The risks and benefits of the procedure should be evaluated and a decision made with the informed consent of the patient. If a septic joint is suspected, it should be aspirated despite the presence of any relative contraindication. The benefit of the procedure outweighs any relative contraindication when compared to the morbidity of an undiagnosed septic arthritis.

The presence of a suspected or known skin cellulitis, or other infection overlying the joint, is a relative contraindication. A dermatitis or skin lesion overlying the joint should also be avoided. The skin or subcutaneous tissue can harbor organisms that may contaminate the joint when the needle passes through the dermatitis or skin lesion. Often, an alternative site can be found to perform the arthrocentesis and avoid the above obstacles. If the needle is inserted into the joint through any potential or obvious source of infection, antibiotic treatment is required due to the theoretical risk of introducing an infection into the joint cavity.5 In these cases, patients should be admitted for 23 hours of intravenous antibiotics whose spectrum covers skin flora.

Infections after arthrocentesis, in previously sterile joints, have been reported in bacteremic patients.5 It is not clear whether the source of the septic arthritis was from the arthrocentesis or bacteremia coincidentally seeding the joint. It is recommended to avoid arthrocentesis in any patients with bacteremia or sepsis except to rule out a septic arthritis.

Patients may be coagulopathic due to heparin or Coumadin therapy, factor deficiencies, liver dysfunction, or many other causes. When possible, the coagulopathy should be reversed prior to arthrocentesis. Unfortunately, this is not always possible or practical. An experienced EP can safely perform the procedure without reversing the coagulopathy. Use the smallest needle gauge possible (i.e., 22 or 23 gauge) to aspirate the joint fluid. Avoid injury to the articular cartilage by identifying the anatomic landmarks prior to the procedure. Do not bounce the needle off any bony surfaces.

The procedure may be difficult in some patients. In the morbidly obese, it may be difficult to identify anatomic landmarks. The standard needle may be too short to enter the joint cavity. A spinal needle may be required to perform an arthrocentesis in an obese patient. Uncooperative patients require sedation and/or restraint prior to performing the procedure.

A prosthetic joint increases the risk of a septic arthritis. Arthrocentesis is technically more difficult secondary to scar formation and alteration of the normal anatomic relationships. Joints that contain a prosthesis should be aspirated only to rule out a septic arthritis. Arthrocentesis for other reasons, including joint injection, should be referred to a consultant.

Corticosteroids are instilled into joints for a variety of conditions. If the patient has no response to the injection within a few weeks, it may be repeated. If multiple injections cause no improvement, an alternative form of therapy should be explored.9 Multiple injections into a joint increase the risk of complications.

• Clean gloves
• Gauze squares
• Povidone iodine or chlorhexidine solution
• Sterile skin marking pen
• Local anesthetic (injectable, vapor coolant, or ice)
• 25 to 27 gauge needle
• 3 mL syringe
• Needles to aspirate fluid (18/20/22 gauge)
• Syringes to aspirate fluid (1/3/5/10/20/30/60 mL)
• Hemostat
• Specimen tubes
• Culturettes or culture tubes

Optional Equipment

• US machine
• US gel
• US transducers (5 to 10 MHz)
• Sterile US probe covers

Arthrocentesis should be performed with a needle of sufficient bore to allow the aspiration of thick fluid, fluid with debris, or purulent fluid. An 18 to 20 gauge needle is recommended for large joints (i.e., shoulder, elbow, ankle, knee, and hip). A 22 to 23 gauge needle is recommended for all other joints. Using too small a needle makes the procedure technically more difficult and more painful for the patient.

A high-frequency (5 to 10 MHz) linear array transducer is preferred for arthrocentesis and should be used whenever possible.44 If this type of transducer is not available, or if more depth of field is required, a curvilinear array may be used. Cavalier and colleagues reported using color Doppler and a sterile needle guide attached to the transducer when performing US-guided arthrocentesis in children.52 Doppler was used to localize the blood vessels so that they could be avoided by the needle. While Doppler may occasionally provide additional anatomic information, it is not routinely used when performing an arthrocentesis. The use of a needle guide depends on the personal preference of the sonographer.

A complete history and physical examination should be performed prior to the arthrocentesis. The affected joint should be thoroughly assessed. Inspect the skin overlying the joint for breaks, infection, old scars, prior incisions, superficial lesions, or any wounds. Palpate the joint to identify any warmth, tenderness, or effusion. Evaluate the joint for any crepitation, deformity, ligamentous instability, or limitations in motion.

As with any nonemergent procedure, consent should be obtained from the patient or their representative. Ideally, the consent should be documented in the medical record and signed by the patient. Some prefer to note on the patient's chart “indications, risks, and benefits were discussed with the patient” rather than having the patient sign a consent form.4,10 The following is a sample consent for performing an arthrocentesis (which may be written on the medical record and signed by the patient):

Arthrocentesis involves inserting a small needle into your_______joint. The skin is anesthetized prior to the procedure. Ordinarily, the procedure has no significant complications. Occasionally, a patient may experience bleeding into the joint, infection of the joint or skin, pain, bruising, nerve injury, or an allergic reaction to the medications administered. These complications are minimized by the use of sterile technique and proper techniques.

Position the patient based on the specific joint to be aspirated and the approach to be used. Expose the joint and surrounding areas. Identify the anatomic landmarks required for proper needle placement. The landmarks may be difficult to identify on a swollen and tender joint. Compare the “affected” joint to the “normal” joint on the opposite side of the body. Identify the joint and a landmark on the normal joint and transfer this to the affected joint. Clean any dirt and debris from the skin. Scrub the needle insertion site with povidone iodine or chlorhexidine solution and allow it to dry.

Apply anesthesia to the skin and subcutaneous tissue using 1% lidocaine, topical vapor spray, or ice.11 The administration of some form of local anesthesia is recommended but not required.4,12 The most common local anesthetic used is a short-acting injectable anesthetic solution of 1% lidocaine. Do not inject the local anesthetic solution deeper than the subcutaneous tissues. Deep injections may instill anesthetic solution into the joint cavity, which may interfere with the synovial fluid analysis. There is disagreement if the additional needle stick to administer the anesthesia causes as much discomfort as aspiration without any anesthesia. This decision is specific to each patient and EP.

Alternative methods of anesthesia include ice and topical vapor coolants. A sterile drape may be placed over the prepped skin and a bag of ice water placed over the drape. Remove the ice water bag and drape after 5 minutes and perform the procedure. Ethinyl chloride topical vapor coolant may be used as an anesthetic. Spray the solution onto the area of skin in which the needle will be inserted. Apply the spray from 6 in. above the skin. Spray until the skin turns white and frosty. This usually takes 5 to 10 seconds. Immediately perform the procedure, as the anesthesia lasts only 30 to 60 seconds.

The Basic Technique

The general procedure preferred by one of the authors and the editor (EFR) will be described. Some may prefer to insert the needle into the joint space and then attach the syringe. Specifics will be addressed with each individual joint.

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. If bone is encountered, slightly withdraw the needle and re-advance it in a different direction. If no fluid is obtained, reevaluate the joint to determine if an effusion is present, if another site is more appropriate for the procedure, or if another physician may offer a different perspective. For diagnostic aspirations, it is not necessary to aspirate all of the fluid from the joint. Synovial fluid analysis can be performed on 1 to 5 mL of fluid.

If additional fluid is to be removed after the original syringe is filled, or if pharmaceuticals are to be injected into the joint, do not remove the needle from the joint cavity. Grasp the hub of the needle with a hemostat. Remove the syringe and attach the second syringe. Continue to aspirate fluid or inject the desired pharmaceutical. Remove the needle when the procedure has been completed. Apply a bandage to the skin. Transfer the synovial fluid into appropriately labeled tubes or containers. Document the procedure 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/chlorhexidine 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_____% (name of local anesthetic) and/or_____mL of_____%________(name of corticosteroid). No complications were noted.

The Basic US Technique

The acoustic windows used for US-guided arthrocentesis are the soft tissues overlying the joint. The transducer is most commonly oriented across a joint so that the bones on each side of the joint are visualized and the joint space between them. Bone is highly reflective of US waves and the cortex is seen as a bright white echogenic line on the US image. Synovial fluid will be seen as an anechoic line or hypoechoic collection within the joint space. When visualized longitudinally, the needle will appear as a narrow, linear hyperechoic structure with a posterior reverberation artifact (Figure 77-1). When visualized transversely, the needle appears as a small hyperechoic round object.45

The general procedure and technique depend on whether the static or dynamic method is used. Using the static technique, manipulate the US transducer over the joint until the optimal spot for needle entry is found based on fluid accessibility and a needle path that avoids major blood vessels, nerves, and tendons. Mark the skin on the midpoint of each side of the US transducer. Rotate the transducer 90° and repeat the process. Connect the two sets of lines to form an “X” that marks the spot for needle entry (Figure 77-2). Set aside the US transducer, prepare the skin in a sterile manner, and proceed with the arthrocentesis using the standard landmark-based technique.

The dynamic or real-time method is slightly more demanding technically but offers the advantage of allowing visualization of the needle and needle tip.44 Prepare the patient's skin in a sterile manner. Place a sterile probe cover over the US transducer and apply sterile US gel to the skin. Place the transducer over the joint in the appropriate orientation and manipulate it until the synovial fluid is visualized. Inject a local anesthetic agent into the skin and subcutaneous tissue along the projected course of the arthrocentesis needle. In many cases, it is possible to observe the infusion of the anesthetic agent on the US image.44 Advance the needle through the skin and soft tissue and direct it toward the synovial fluid. The needle can be advanced either longitudinally or transversely to the axis of the US transducer. The longitudinal axis allows visualization of the entire needle along its path and is the technique utilized by most EPs. Visualization in the transverse axis allows only one cross-sectional area of the needle to be seen so it can be difficult to identify the needle and its tip. Regardless of orientation, continue to advance the needle until its tip is visible within the synovial fluid. Aspirate the synovial fluid. It is often possible to watch the synovial fluid diminish in size as it is aspirated.

Temporomandibular Joint Arthrocentesis

Landmarks

The landmarks for temporomandibular joint (TMJ) arthrocentesis are found by first drawing a line on the patients face from the corner of the eye to the ipsilateral tragus (canthal-tragus line). Mark the point 10 mm from the tragus along the line and 0.5 mm below the line. This marks the superior compartment. Mark a second point 20 mm from the tragus along the line and 1 mm below the line. This marks the superior compartment.

Patient Positioning

Place the patient sitting upright with their jaw held slightly open.

Needle Insertion and Direction

Use two 21-gauge needles to access the joint space compartments. Insert the first needle at the first mark and advance it into the joint space. Inject 2 to 3 mL of sterile saline to insufflate the joint space. Insert and advance the second needle at the second point and into the joint space. Correct placement is confirmed when the saline flows out the needle.41

Remarks

Arthrocentesis of this joint is a unique solution to a specialized TMJ disorder called closed lock, in which the patient's jaw is felt to be locked and will not open greater than 20 to 25 mm. It is theorized to be the result of small adhesions and nongliding of the intraarticular disk in the TMJ space. Arthrocentesis and subsequent lavage can relieve the symptoms of closed lock.

Joint Injection

Once the two needles are in place in the superior compartment, massive lavage with normal saline or lactated ringers solution can be achieved with the first needle as input and the second needle as output. Continuous fluid can be infused and removed using a 10 mL syringe or attaching IV tubing to each needle.42

Sternoclavicular Joint Arthrocentesis

Landmarks

The sternal end of the clavicle and the suprasternal notch are the landmarks for this joint (Figure 77-3). The joint can be palpated just medial to the sternal end of the clavicle and just lateral to the suprasternal notch.

Patient Positioning

Place the patient supine on a stretcher with their arm hanging over the edge of the table (Figure 77-3A). Abduct the arm 90°. Externally rotate the arm so that the palm faces upward. This position maximally opens the sternoclavicular joint to allow easy access.

Needle Insertion and Direction

Insert a 23 gauge needle through the anterior joint surface and perpendicular to the skin (Figure 77-3B). Advance the needle to a depth of 2 to 5 mm.

Remarks

This joint is often involved with degenerative arthritis. Septic arthritis is commonly seen in intravenous drug abusers who inject drugs into the great vessels; also known as “pocket shooting.” This joint may only contain 0.25 to 0.50 mL of fluid.

Joint Injection

A maximum volume of 1 mL may be instilled into this joint. A maximum dose of 10 mg of corticosteroids may be instilled into this joint.

Acromioclavicular Joint Arthrocentesis

Landmarks

The acromioclavicular (AC) joint is very superficial (Figure 77-4). Palpate the clavicle and move laterally until a prominence is felt. This is the AC joint. Have the patient move their arm to confirm the joint location.

Patient Positioning

Place the patient sitting upright on a stretcher with the affected arm hanging by their side. A weight may be placed in the patient's hand to distract and open the joint space.

Needle Insertion and Direction

Insert a 22 gauge needle through the superior surface of the AC joint and perpendicular to the skin (Figure 77-4). Advance the needle to a depth of 3 to 5 mm.

Remarks

The AC joint is very superficial. It has a dense, thick capsule anteriorly that is lacking on its superior surface. The joint may contain only 0.25 to 0.50 mL of fluid.

Joint Injection

A maximum volume of 1.5 mL may be instilled into this joint. A maximum dose of 10 mg of corticosteroids may be instilled into this joint.

Glenohumeral Joint (Shoulder) Arthrocentesis, Anterior Approach

Landmarks

Palpate the coracoid process of the scapula (Figure 77-5). It will be found below the lateral third of the clavicle. Internally rotate and adduct the humerus. Palpate the groove between the coracoid process and the humeral head. This groove is the landmark for introduction of the needle.

Patient Positioning

Place the patient sitting upright or supine on a stretcher. Flex the elbow 90°. Internally rotate and adduct the arm. In the proper position, the forearm is resting against the patient's abdomen.

Needle Insertion and Direction

Insert an 18 gauge needle perpendicular to the skin and into the groove just lateral to the coracoid process (Figure 77-5B). Aim the needle directly posterior. Advance the needle until a loss of resistance is felt as the joint cavity is entered.

Ultrasound Probe Placement

With the patient positioned as above, place the US probe inferior and lateral to the coracoid process. Rotate the probe so that the marker is cephalad and angled medially toward the patient's head. The curve of the humeral head will appear different than the flat portion of the glenoid, and between these hyperechoic surfaces lies the V-shaped hypoechoic joint space.

Remarks

This approach is the simplest yet most painful of the three approaches. The needle must penetrate the tendons of the coracobrachialis, subscapularis, biceps, and pectoralis major muscles in addition to the very tough anterior joint capsule. The major disadvantage of this approach is the possible (but rare) penetration of the brachial plexus or the axillary vessels with the needle. The patient can view the large needle as it approaches the skin and this may increase their anxiety level. The posterior approach is preferred when using US guidance.44

Joint Injection

A maximum volume of 15 mL may be instilled into this joint. A maximum dose of 30 mg of corticosteroids may be instilled into this joint.

Glenohumeral Joint (Shoulder) Arthrocentesis, Lateral Approach

Landmarks

Identify the acromion process of the scapula (Figure 77-5). A groove can be found just inferior to the lateral surface of the acromion and above the greater tubercle of the humerus.

Patient Positioning

Place the patient sitting upright on a stretcher with the affected arm hanging by their side. A weight may be placed in the patient's hand to distract and open the joint cavity.

Needle Insertion and Direction

Insert an 18 gauge needle into the midpoint of the groove (Figure 77-5A). Direct the needle medially and slightly posterior. Advance the needle to a depth of 2.5 to 3 cm.

Remarks

Immediately below the deltoid muscle is the subacromial bursa. This bursa does not communicate with the shoulder joint. The needle must be inserted 2.5 to 3 cm to ensure the needle is in the shoulder joint and not in the subacromial bursa. The anterior or posterior approach to shoulder arthrocentesis avoids this potential problem.

Joint Injection

A maximum volume of 15 mL may be instilled into this joint. A maximum dose of 30 mg of corticosteroids may be instilled into this joint.

Glenohumeral Joint (Shoulder) Arthrocentesis, Posterior Approach

Landmarks

Identify the spine of the scapula (Figure 77-6). Follow the spine laterally until it turns anterior to become the acromion process. This posterior border of the acromion process is the landmark for this technique. Locate the coracoid process of the scapula, just inferior to the lateral third of the clavicle.

Patient Positioning

Place the patient sitting upright on a stretcher. Place the palm of the hand of the affected shoulder on the anterior surface of the opposite shoulder. The arm and forearm should be held against the chest. This position maximally opens the posterior joint space.

Needle Insertion and Direction

Place the nondominant thumb on the posterior border of the acromion process. Place the nondominant index finger on the coracoid process. Insert an 18 gauge needle 1 to 2 cm below the thumb and parallel to the floor (Figure 77-6). Aim the needle toward the tip of the index finger, approximately 30° medially. Advance the needle to a depth of 2 to 3 cm.

US Probe Placement

Position the patient as described above. Place the US transducer across the posterior aspect of the shoulder in a transverse orientation (Figure 77-7). The marker may be directed medially or laterally. The echogenic cortex of the humeral head is visible along with the adjacent glenoid rim (Figure 77-8). The joint fluid is visible as an anechoic area between these two bony structures (Figure 77-8). Insert and advance the needle from the lateral edge of the US transducer, oriented along the long axis of the transducer, and into the joint fluid.

Remarks

This is felt by some physicians to be the preferred approach to shoulder arthrocentesis. The needle will pierce the deltoid and infraspinatus muscles and avoid the tendons of the rotator cuff. This approach avoids the anxiety associated with the patient observing the large needle and syringe used for the procedure during the anterior or lateral approach. The posterior joint capsule is much thinner and more easily penetrated than the anterior joint capsule. There are no significant neurovascular structures that may be injured from this approach.

Joint Injection

A maximum volume of 15 mL may be instilled into this joint. A maximum dose of 30 mg of corticosteroids may be instilled into this joint.

Humeroradioulnar Joint (Elbow) Arthrocentesis, Lateral Approach

Landmarks

The lateral epicondyle of the humerus, the radial head, and the tip of the olecranon process of the ulna are the landmarks for this joint (Figure 77-9A). Flex the elbow 45° and pronate the hand. Pronation of the hand stretches the radial collateral ligament, moves the radial nerve out of the needle's path, and widens the synovial cavity. Identify the depression between the landmarks. The depression is located proximal to the radial head in the area where no bony structures are palpated.

Patient Positioning

Place the patient sitting upright or supine on a stretcher. Flex the elbow 45° and pronate the hand. This position widens the joint cavity and avoids any neurovascular structures.

Needle Insertion and Direction

Insert a 22 gauge needle perpendicular to the skin and into the depression just proximal to the radial head (Figure 77-9A). Advance the needle to a depth of 0.75 to 2.0 cm.

Remarks

This is the preferred approach for elbow arthrocentesis. It avoids tendons and neurovascular structures, thereby reducing the risk of complications.13

Joint Injection

A maximum volume of 5 mL may be instilled into this joint. A maximum dose of 20 mg of corticosteroids may be instilled into this joint.

Humeroradioulnar Joint (Elbow) Arthrocentesis, Posterior Approach

Landmarks

Identify the top of the olecranon process of the ulna and the triceps muscle insertion into the olecranon process (Figure 77-9B). Find the point just proximal to the top of the olecranon and just lateral to the triceps insertion. This point is the landmark for insertion of the needle.

Patient Positioning

Place the patient sitting upright on a stretcher. Flex the elbow 90° with the hand supinated. The forearm and hand should be resting on a tabletop or on the patient's leg.

Needle Insertion and Direction

Approach the joint from the posterolateral surface with the needle parallel to the radial shaft. Insert a 22 gauge needle perpendicular to the skin at the landmark (Figure 77-9B). Advance the needle to a depth of 1 cm.

US Probe Placement

Position the patient as described above. Place the US transducer along the posterior elbow in a longitudinal orientation, with the marker toward the shoulder (Figure 77-10). This produces an image with the humerus located to the left, the olecranon located to the right, the olecranon fossa at the bottom, and the triceps tendon passing from side to side across the top of the screen (Figure 77-11). Keep the US transducer in the same orientation and slide it laterally to move off the triceps tendon. The joint effusion will be visualized in or adjacent to the olecranon fossa (Figure 77-11). Be sure to avoid the ulnar nerve which passes over the medial epicondyle, by choosing a location as far lateral as possible.33,34 Advance the needle over the superior edge of the US transducer and into the synovial fluid.

Remarks

Potential complications include needle penetration of the triceps tendon or the radial nerve. This approach is reserved for patients in whom the lateral approach is contraindicated.

Joint Injection

A maximum volume of 5 mL may be instilled into this joint. A maximum dose of 20 mg of corticosteroids may be instilled into this joint.

Humeroradioulnar Joint (Elbow) Arthrocentesis, Posterolateral Approach

Landmarks

Identify the lateral surface of the olecranon process of the ulna and the lateral epicondyle of the humerus (Figure 77-9C). Find the indentation just lateral to the olecranon and just distal to the lateral epicondyle. This point is the landmark for the insertion of the needle.

Patient Positioning

Place the patient sitting upright on a stretcher. Flex the elbow 90° with the hand supinated. The forearm and hand should be resting on a tabletop or on the patient's leg.

Needle Insertion and Direction

Approach the joint from the posterolateral surface with the needle parallel to the radial shaft. Insert a 22 gauge needle perpendicular to the skin at the landmark (Figure 77-9C). Advance the needle to a depth of 1 cm.

Remarks

This approach is an alternative when the lateral approach is contraindicated.

Joint Injection

A maximum volume of 5 mL may be instilled into this joint. A maximum dose of 20 mg of corticosteroids may be instilled into this joint.

Radiocarpal Joint (Wrist) Arthrocentesis

Landmarks

Identify the lunate bone (Figure 77-12). Palpate the middle (third) metacarpal and follow it proximally until a rounded bean-like elevation is felt (Figure 77-12A). This is the lunate. Palpate the indentations proximal and distal to the lunate. The indentation proximal to the lunate is the landmark for needle insertion.

Alternatively, identify Lister's tubercle and the extensor pollicis longus (EPL) tendon (Figure 77-12B). Lister's tubercle is a bony prominence in the center of the dorsal aspect of the distal radius. The EPL tendon can be found lateral (radial) to Lister's tubercle. If the EPL tendon is difficult to find, extend the hand and thumb against resistance and it will become prominent. The lunate is the bony prominence distal to Lister's tubercle. The indentation proximal to the lunate is the landmark for needle insertion.

Patient Positioning

Place the patient sitting upright or supine on a stretcher. Pronate the hand with the wrist in slight (e.g., 20°-50°) flexion and ulnar deviation (Figure 77-12A). The palm of the physician's nondominant hand should be holding the patient's palm. Reidentify the lunate with the nondominant thumb.

Needle Insertion and Direction

Insert a 22 gauge needle perpendicular to the skin in the indentation proximal to the lunate (Figure 77-12A). Advance the needle to a depth of 0.75 to 1.25 cm. Alternatively, insert the needle in the indentation just distal to Lister's tubercle and ulnar to the EPL tendon (Figure 77-12B).

Remarks

The preferred, and easiest, method is to identify the lunate and then insert the needle in the indentation just proximal to the lunate.

Joint Injection

A maximum volume of 2 mL may be instilled into this joint. A maximum dose of 20 mg of corticosteroids may be instilled into this joint.

Intercarpal Joint Arthrocentesis

Landmarks

Identify the lunate bone (Figure 77-12). Palpate the middle (third) metacarpal and follow it proximally until a rounded bean-like elevation is felt (Figure 77-12A). This is the lunate. Palpate an indentation distal to the lunate and proximal to the base of the third metacarpal. This indentation is the landmark for insertion of the needle.

Patient Positioning

Place the patient sitting upright or supine on a stretcher. Pronate the hand with the wrist in slight (e.g., 20°-50°) flexion and ulnar deviation (Figure 77-12A). The palm of the physician's nondominant hand should be holding the patient's palm. Reidentify the landmarks with the nondominant thumb.

Needle Insertion and Direction

Insert a 22 gauge needle perpendicular to the skin in the indentation distal to the lunate. Advance the needle to a depth of 0.5 to 1.0 cm.

Remarks

The joints between the carpal bones are all connected to each other (Figure 77-13). Fluid aspirated from one of these joints is representative of all the joints. Likewise, injection of one joint allows the pharmaceutical to be distributed to all the joints.

Joint Injection

A maximum volume of 1.5 mL may be instilled into this joint. A maximum dose of 15 mg of corticosteroids may be instilled into this joint.

Carpometacarpal Joint of the Thumb Arthrocentesis

Landmarks

The base of the first metacarpal and the abductor pollicis longus (APL) tendon are the landmarks for this joint (Figure 77-14). Identify the radial aspect of the base of the first metacarpal. Have the patient rotate the affected thumb to help identify the joint. Identify the APL tendon by extending the patient's thumb against resistance.

Patient Positioning

Place the patient sitting upright or supine on a stretcher. Flex the thumb into the palm with the tip of the thumb touching the fifth metacarpal head. Clench the remaining fingers into a fist (Figure 77-14A).

Needle Insertion and Direction

Insert a 22 gauge needle into the joint space at the radial aspect of the base of the first metacarpal and just lateral (radial) to the APL tendon (Figure 77-14A). Direct the tip of the needle toward the base of the fourth metacarpal. Advance the needle to a depth of 0.5 to 1.0 cm.

Remarks

If difficulty is encountered when inserting the needle, try an alternative thumb position (Figure 77-14B). Flex the first carpometacarpal joint 45° and apply traction to the distal thumb. This in-line traction will enlarge the joint cavity and allow easier access.

Joint Injection

A maximum volume of 1.5 mL may be instilled into this joint. A maximum dose of 10 mg of corticosteroids may be instilled into this joint.

Metacarpophalangeal Joint Arthrocentesis

Landmarks

Identify the metacarpophalangeal (MCP) joint and the extensor digitorum tendon (Figure 77-15A). 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.

Patient Positioning

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 77-15B). 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.

Remarks

The application of distal traction often causes a depression to appear on both sides of the extensor tendon (Figure 77-15B). These depressions can be used as landmarks for the site of needle insertion into the joint cavity.

Joint Injection

A maximum volume of 1 mL may be instilled into this joint. A maximum dose of 5 mg of corticosteroids may be instilled into this joint.

Interphalangeal Joint of the Finger Arthrocentesis

Landmarks

Identify the interphalangeal (IP) joint and the extensor tendon (Figure 77-15A). The IP joint can be located just proximal to the prominence at the base of the middle or distal phalanx of the finger. Identify the extensor tendon by having the patient extend the finger against resistance.

Patient Positioning

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 77-15B). 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.

Remarks

The application of distal traction often causes a depression to appear on both sides of the extensor tendon (Figure 77-15B). These depressions can be used as landmarks for the site of needle insertion into the joint cavity. The joints are small and normally contain almost no synovial fluid. When inflamed or infected, the joint cavity may contain up to 2 mL of synovial fluid.

Joint Injection

A maximum volume of 1 mL may be instilled into this joint. A maximum dose of 5 mg of corticosteroids may be instilled into this joint.

Hip Joint Arthrocentesis, Anterior Approach

Landmarks

Identify the anterior superior iliac spine (ASIS) and the femoral pulse (Figure 77-16). The landmark for insertion of the needle is 2 to 3 cm below the ASIS and 2 to 3 cm lateral to the femoral artery pulse.

Patient Positioning

Place the patient supine on a stretcher with the affected leg internally rotated and the knee slightly flexed.

Needle Insertion and Direction

Insert a 3.5 in., 18 gauge needle at the landmark (Figure 77-16). Direct the tip of the needle posteromedially. Insert the needle at a 60° angle to the skin of the thigh. Advance the needle until bone is encountered. Slightly withdraw the needle and begin aspirating the synovial fluid.

US Probe Placement

Position the patient as described above.49 Place the US transducer over the anterior hip and aligned with the long axis of the femoral neck, with the marker in a superior-medial direction and aimed toward the umbilicus (Figure 77-17).44 The echogenic cortex of the femoral head is visible to the left of the image and the femoral neck to the right. The concave transition between these two areas is the anterior synovial recess.44,49 Synovial fluid will be seen in this recess and tends to displace the joint capsule anteriorly (Figure 77-18).43 Insert the needle from the inferolateral edge of the US transducer and advance it into the synovial fluid.

Remarks

This approach is technically easier and recommended by many authors. A long spinal needle is usually required for this procedure. Use caution as the needle may injure the articular cartilage. This procedure should be performed by an Orthopedist, a Rheumatologist, or a Radiologist under fluoroscopic guidance if US is not available in the ED.

Joint Injection

A maximum volume of 10 mL may be instilled into this joint. A maximum dose of 40 mg of corticosteroids may be instilled into this joint.

Hip Joint Arthrocentesis, Lateral Approach

Landmarks

The greater trochanter is the landmark for this technique (Figure 77-19). Place the patient supine with the affected leg internally rotated. Palpate the greater trochanter.

Patient Positioning

Place the patient supine on a stretcher with the affected leg internally rotated (Figure 77-19A). Identify the greater trochanter and hold it between the thumb and index finger. A second patient position may be used for the alternative approach (Figure 77-19B). Place the patient lying on the unaffected side. Flex the unaffected, lower leg 90°. Fully extend the upper, affected, leg with a pillow supporting the ankle.

Needle Insertion and Direction

Insert a 3.5 in., 18 gauge needle just superior to the superior margin of the greater trochanter (Figure 77-19A). Advance the needle horizontally, parallel to the stretcher, until it contacts the femoral neck. Withdraw the needle 2 to 4 mm and redirect it slightly cephalad. Advance the needle while applying negative pressure to the syringe until synovial fluid enters the syringe. Stop advancing the needle and continue to aspirate the synovial fluid. The alternative technique requires the insertion of the needle perpendicular to the skin and 1 cm proximal to the greater trochanter (Figure 77-19B). Advance the needle until the femoral neck is contacted. Withdraw the needle 2 mm and begin aspirating synovial fluid.

Remarks

In the morbidly obese, the greater trochanter may not be palpable. This approach is technically more difficult than the anterior approach. The advantage of this approach is that the articular cartilage will not be in the needle's path and so avoids injury. This procedure should be performed by an Orthopedist, a Rheumatologist, or a Radiologist under fluoroscopic guidance.

Joint Injection

A maximum volume of 10 mL may be instilled into this joint. A maximum dose of 40 mg of corticosteroids may be instilled into this joint.

Patellofemorotibial Joint (Knee) Arthrocentesis, Suprapatellar Approach

Landmarks

Identify the midpoint of the superolateral or superomedial border of the patella (Figure 77-20A). Either of these landmarks may be used as the site for needle insertion.

Patient Positioning

Place the patient supine on a stretcher with the affected knee fully extended.

Needle Insertion and Direction

Insert an 18 gauge needle through the midpoint of the superolateral or superomedial border of the patella (Figure 77-20A). Direct the tip of the needle toward the intercondylar notch of the femur. Advance the needle to a depth of 1.5 to 3.0 cm.

US Probe Placement

Position the patient as described above. A small roll or towel can be used behind the knee to provide slight flexion. Place the US transducer in a longitudinal orientation superior to the patella, with the probe marker directed toward the patient's head. The cortex of the distal femur is visible as a bright echogenic line to the right of the image and the synovial fluid is visible deep to the quadriceps tendon (Figure 77-21). Keep the US transducer in oriented longitudinally and slowly slide it medially or laterally to move off the quadriceps tendon. Insert the needle from the superior edge of the US transducer in a longitudinal orientation and direct it toward the synovial fluid. Advance the needle into the synovial fluid.

Remarks

The needle enters the suprapatellar bursa and avoids any potential damage to the articular cartilage. The bursa is a direct continuation of the synovial cavity.44 There are no neurovascular structures of significance to injure with this approach. If the knee effusion is minimal, synovial fluid may not be able to be aspirated from this approach. Approximately 10% of the population has a plica completely separating the suprapatellar bursa from the knee joint. If this variation exists in the patient, the bursa fluid will not represent synovial fluid.

Joint Injection

A maximum volume of 10 mL may be instilled into this joint. A maximum dose of 40 mg of corticosteroids may be instilled into this joint.

Patellofemorotibial Joint (Knee) Arthrocentesis, Parapatellar Approach

Landmarks

Identify the midpoint of the lateral or medial border of the patella (Figure 77-20B). Either of these landmarks may be used as the site for needle insertion.

Patient Positioning

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 77-20B). 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.

Ultrasound Probe Placement

Place the US transducer oriented longitudinally, and either lateral or medial to the patella, with the marker directed toward the patients head. Identify the joint fluid. Slowly rotate the US transducer to a horizontal orientation to identify the area with the largest anechoic fluid collection.44 Insert and advance the needle along the superior edge of the US transducer and into the joint fluid.

Remarks

The easiest site for arthrocentesis is the medial parapatellar region. There are no disadvantages to using the medial parapatellar site.

Joint Injection

A maximum volume of 10 mL may be instilled into this joint. A maximum dose of 40 mg of corticosteroids may be instilled into this joint.

Patellofemorotibial Joint (Knee) Arthrocentesis, Infrapatellar Approach

Landmarks

Identify the inferior border of the patella and the patellar tendon (Figure 77-20C). The tendon is a thick band that passes from the inferior border of the patella to the tibial tuberosity.

Patient Positioning

Place the patient sitting upright on a stretcher with the affected knee bent 90° over the edge of the bed and the leg hanging freely and unsupported.

Needle Insertion and Direction

Insert an 18 gauge needle 0.5 cm below the inferior border of the patella at the level of the joint line and just medial or lateral to the patellar tendon (Figure 77-20C). 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 1.5 to 2.0 cm.

Remarks

The weight of the leg helps to open the joint cavity. The risk of injury to the articular cartilage is minimal. This approach was popular in the past but is not often used today. Do not pierce the patellar tendon with the needle.

Joint Injection

A maximum volume of 10 mL may be instilled into this joint. A maximum dose of 40 mg of corticosteroids may be instilled into this joint.

Tibiotalar Joint (Ankle) Arthrocentesis, Anterolateral Approach

Landmarks

Identify the joint cavity, the lateral malleolus, and the extensor digitorum longus (EDL) tendons (Figure 77-22). The joint cavity is located below the distal edge of the fibula and between the bases of the malleoli. Extend the toes against resistance to identify the EDL tendons. Palpate the base of the lateral malleolus.

Patient Positioning

Place the patient sitting upright or supine on a stretcher. The patient can also be placed sitting upright on a stretcher with affected knee bent 90° over the edge of the bed and the foot hanging freely and unsupported. Plantar flex the ankle.

Needle Insertion and Direction

Insert a 22 gauge needle perpendicular to the fibular shaft at the level of the base of the lateral malleolus; midway between the malleolus and the lateral border of the EDL tendon (Figure 77-22A). Advance the needle to a depth of 0.5 to 1.0 cm.

US Probe Placement

Position the patient as described above. Place the US transducer over the anterior tibiotalar joint in a longitudinal orientation, with the marker of the US transducer toward the patient's head (Figure 77-23).44,46 Manipulate the US transducer with a slight rotation until the echogenic cortex of the tibia and talus bones are both visible (Figure 77-24). The tibia is visible to the left of the image and the talus to the right. During the rotation of the US transducer, note the location of the dorsalis pedis artery and the extensor tendons so that they may be avoided when inserting the needle.44 The joint fluid is visible as a hypoechoic area in the V-shaped recess between the tibia and talus (Figure 77-24). Insert the needle at the inferior end of the transducer and advance it into the joint fluid.

Remarks

This approach avoids potential injury to the dorsalis pedis vessels and the deep peroneal nerve.

Joint Injection

A maximum volume of 3 mL may be instilled into this joint. A maximum dose of 20 mg of corticosteroids may be instilled into this joint.

Tibiotalar Joint (Ankle) Arthrocentesis, Anteromedial Approach

Landmarks

Identify the joint cavity, the medial malleolus, and the tendons of the tibialis anterior (TA) and the extensor hallucis longus (EHL) muscles (Figure 77-22). The joint cavity is located below the distal edge of the tibia and between the bases of the malleoli. Extend the great toe against resistance to identify the EHL tendon. Plantar flex the ankle against resistance to identify the TA tendon. Palpate the base of the medial malleolus.

Patient Positioning

Place the patient sitting upright or supine on a stretcher. The patient can also be placed sitting upright on a stretcher with the affected knee bent 90° over the edge of the bed and the foot hanging freely and unsupported. Plantar flex the ankle to use the EHL tendon as the landmark for the procedure. Alternatively, plantar flex the ankle and invert the subtalar joint to use the TA tendon as the landmark for the procedure.

Needle Insertion and Direction

Insert a 22 gauge needle perpendicular to the tibial shaft at the level of the base of the malleolus and medial to the EHL tendon (Figure 77-22B). Alternatively, insert the needle medial to the TA tendon (Figure 77-22C).

Ultrasound Probe Placement

The procedure is exactly as described above for the anterolateral approach.

Remarks

If using the EHL tendon as the landmark, use caution to avoid the dorsalis pedis vessels and the deep peroneal nerve that usually lie immediately lateral to the EHL tendon.

Joint Injection

A maximum volume of 3 mL may be instilled into this joint. A maximum dose of 20 mg of corticosteroids may be instilled into this joint.

Subtalar Joint Arthrocentesis

Landmarks

Identify the tip of the medial malleolus. Palpate the sustentaculum tali of the calcaneus (Figure 77-25). It is approximately 1.5 to 2.0 cm below the tip of the medial malleolus.

Patient Positioning

Place the patient supine on a stretcher with the foot held at a right angle to the leg. Externally rotate the hip until the medial malleolus is pointing upward.

Needle Insertion and Direction

Insert a 22 gauge needle immediately above and slightly posterior to the sustentaculum tali (Figure 77-25). Advance the needle to a depth of 1.5 to 2.0 cm.

Remarks

This is a difficult procedure because the joint space is very small. Fluoroscopy may be required to gain entry into the joint cavity. This procedure is seldom performed in the ED. US is not very helpful due to the small joint space and irregular body surfaces.

Joint Injection

A maximum volume of 1.5 mL may be instilled into this joint. A maximum dose of 20 mg of corticosteroids may be instilled into this joint.

Intertarsal Joint Arthrocentesis

There are no specific landmarks for the many intertarsal joints. Radiographs are required to identify the location of a specific joint. Plain radiographs are often not helpful and fluoroscopic guidance is required. For these reasons, arthrocentesis of these joints is not routinely performed in the ED. Some authors recommend probing the general area of the joint with a needle until it enters the joint cavity. This is extremely painful for the patient and risks injury to the articular cartilage. Therefore, this technique cannot be recommended.

Metatarsophalangeal Joint Arthrocentesis

Landmarks

Identify the metatarsophalangeal (MTP) joint and the extensor tendon. The MTP joint can be located just proximal to the prominence at the base of the proximal phalanx of the toe. Identify the extensor tendon by having the patient extend the toe against resistance.

Patient Positioning

Place the patient sitting upright or supine on a stretcher. Plantar flex the foot. Grasp and plantar flex the toe 15° to 20° and apply distal traction (Figure 77-26A).

Needle Insertion and Direction

Insert a 22 gauge needle into the dorsal joint space and just medial or lateral to the extensor tendon (Figure 77-26B). Direct the tip of the needle toward the center of the MTP joint. Advance the needle to a depth of 0.3 to 0.5 cm.

Remarks

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.

Joint Injection

A maximum volume of 1.5 mL may be instilled into this joint. A maximum dose of 10 mg of corticosteroids may be instilled into this joint.

Interphalangeal Joint of the Toe Arthrocentesis

Landmarks

Identify the IP joint and the extensor tendon. The IP joint can be located just proximal to the prominence at the base of the middle or distal phalanx of the toe. Identify the extensor tendon by having the patient extend their toes against resistance.

Patient Positioning

Place the patient sitting upright or supine on a stretcher. Plantar flex the foot. Grasp and plantar flex the toe 15° to 20° and apply distal traction (Figure 77-26A).

Needle Insertion and Direction

Insert a 23 gauge needle into the dorsal joint space and just medial or lateral to the extensor tendon (Figure 77-26B). The needle should be aimed toward the center of the joint. Advance the needle to a depth of 0.3 to 0.5 cm.

Remarks

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. These joints are small and normally contain almost no synovial fluid. When inflamed or infected, the joint cavity may contain up to 1.5 mL of synovial fluid.

Joint Injection

A maximum volume of 1 mL may be instilled into this joint. A maximum dose of 5 mg of corticosteroids may be instilled into this joint.

A joint may be injected with corticosteroids and/or local anesthetic solution to relieve pain and inflammation. Identify the anatomic landmarks, prepare the patient, and insert the needle as if performing an arthrocentesis. Inject the pharmaceutical(s), remove the needle, and apply a bandage.

Occasionally, synovial fluid may be required for analysis prior to the injection of pharmaceuticals. A prospective randomized study in rheumatoid arthritis patients found that aspirating all the synovial fluid prior to therapeutic steroid injection reduced the risk of relapse, led to better outcomes, and increased symptom relief.40 Identify the anatomic landmarks, prepare the patient, and insert the needle as if performing an arthrocentesis. Aspirate the synovial fluid into the syringe. With the needle still in the joint, grasp the hub of the needle with a hemostat. Remove the original syringe containing the aspirated synovial fluid. Attach a second syringe containing the pharmaceutical(s) to be injected into the synovial cavity. Reaspirate to confirm that the needle tip remained within the synovial cavity. Inject the pharmaceutical(s). While injecting, no resistance should be felt. If resistance is encountered, the needle may have dislodged from the joint cavity. Remove the needle, reinsert it into the synovial cavity, aspirate to confirm proper positioning, and then inject the pharmaceutical(s). After injection, remove the needle and apply a bandage.

The evaluation of a suspected pediatric hip joint effusion requires the consideration of septic arthritis versus a toxic synovitis. Toxic synovitis is the most common cause of hip pain in children and occurs most frequently in ages 3 to 6 years old. It is a nonpyogenic, inflammatory condition of the joint synovium with an unknown etiology. It occurs most commonly in the hip joint and occasionally in the knee joint.

In contrast, septic arthritis is an acute pyogenic inflammation that occurs most commonly in children below the age of 4 years, with a peak incidence between 6 and 24 months of age. Useful studies include serum WBC, ESR, blood cultures, plain films, CT, MRI, and US. The aspiration and analysis of joint fluid being most critical.

US has been shown to be as accurate as MRI in detecting effusions. It is most easily performed using an anterior approach with the US transducer oriented in the sagittal plane and parallel to the femoral neck. An effusion is visible as a convex rather than concave joint capsule that is greater than 5 mm in thickness. Transudates are more often hypoechoic whereas exudates and hemorrhage are usually more hyperechoic.35

Many imaging techniques such as plain film, scintigraphy, MRI or CT are useful to help differentiate these two clinical entities. MRI and CT provide the highest quality information. However, these studies usually require sedation or even general anesthesia in young children due to the long exam times and requirement for no motion. US-guided hip joint arthrocentesis is a useful bedside imaging technique to help solve this problem. US can only detect the presence of a joint effusion. It cannot reliably differentiate between the two entities without further joint fluid aspiration and analysis. US should not be used as a primary means to rule out a suspected septic arthritis.35

There is no special care or precautions required after performing an arthrocentesis. Pain can be relieved with the use of ice, elevation, and nonsteroidal anti-inflammatory drugs. Joint injection, on the other hand, often requires some precautions. Some recommend limiting joint activity for 4 to 8 hours if an anesthetic solution is injected into a joint. An anesthetized joint, especially weight-bearing joints, may be susceptible to further injury when the joint has decreased sensation. Injection of corticosteroids into a joint cavity often requires a period of immobilization. This discussion is beyond the scope of this chapter. The readers should refer to a rheumatology or orthopedic textbook, or the medical literature, for this information.

Complications can occur with joint aspiration and/or injection (Table 77-3). Most of the complications are minor. Significant complications are rare; but they do occur.

Allergic Reactions

Allergic reactions can occur from hypersensitivity to the local anesthetic solution. Symptoms can range from mild itching and urticaria to circulatory collapse and death. Severe allergic reactions are extremely rare but may occur. Taking a thorough history can prevent many allergic reactions. The preservative in the local anesthetic solution is often the cause of the allergic reaction. Local anesthetic solutions containing no preservatives are an alternative. Some authors believe local anesthesia is not required, as the pain of anesthetic injection is equal to performing the procedure without injectable anesthesia.4,12 If one is concerned about a potential allergic reaction associated with local anesthetic solutions, topical ice, or vapor coolant is an acceptable alternative to nothing. A solution of 1% to 2% diphenhydramine can also be used as an injectable local anesthetic agent for the skin and soft tissues. Do not inject diphenhydramine into the joint cavity as this can result in a significant inflammatory reaction and possible crystal deposition.

Cartilage Injury

The articular cartilage can be damaged from improper needle insertion or needle movement within the joint cavity. The actual incidence of cartilage injury is unknown. The cartilage is avascular and injuries do not heal. Damaged cartilage can lead to focal degenerative changes and be a nidus for future infection. Injury to the articular cartilage can be prevented with a few simple steps. Select a site for the procedure and a needle path that avoids the articular cartilage. Aspirate as you slowly enter the joint cavity and stop inserting the needle when synovial fluid enters the syringe. There is no advantage to plunging the needle into the middle of the joint cavity. Avoid needle movement once the joint cavity has been entered. Finally, do not try to completely aspirate all the fluid within the joint cavity.

Dry Tap

A needle inserted into a joint does not always guarantee fluid will be aspirated.14 A dry tap can occur due to improper needle placement, small or absent effusion, mechanical obstruction, or chronic inflammation.

A dry tap can result from improper needle placement. If the needle is not within the joint cavity, no fluid will be aspirated. Slightly withdraw the needle and reinsert it at a different angle. Alternatively, remove the needle, re-identify the anatomic landmarks, and then reinsert the needle.

One of the most common reasons for a dry tap is the lack of an effusion or a small one. It may be difficult on physical examination to determine if an effusion is present. This is especially true if the patient is obese or if a large amount of subcutaneous edema is present. Try using the non-syringe-bearing hand to “milk” fluid toward the needle while aspirating. Alternatively, if a small effusion is suspected, inject a small amount of sterile saline into the joint cavity. Allow the saline to remain for 30 to 60 seconds, then aspirate the fluid.

Synovial fluid may be loculated or inaccessible by the chosen site of needle entry if the joint has been previously injured. Choose an alternate approach or site to enter the joint cavity. This may facilitate synovial fluid aspiration.

Mechanical obstruction can result in a dry tap. Gently move the needle tip to determine if it can move freely. If it does not, it may be caught or embedded in cartilage, periosteum, or synovium. Withdraw the needle 1 to 2 mm and reaspirate. The needle may also be within the intraarticular fat pad. Slightly withdraw the needle and reaspirate. A plica may be obstructing the lumen of the needle. Rotate the needle and reaspirate. If no fluid is aspirated, slightly advance the needle and reaspirate. If still no fluid is obtained, attempt an alternate approach or reconsider if an effusion is present and if the procedure is actually required.31

The synovial fluid itself may be the cause of a dry tap. The presence of purulent fluid or fluid with debris may clog the needle. Remove the needle and repeat the procedure with a larger gauge needle. If the needle clogs during the aspiration, try reinjecting a small amount of the synovial fluid to dislodge the obstruction and then reaspirate. A larger gauge needle may be required to complete the procedure.

Aspiration of synovial fluid from a chronically inflamed joint may be problematic. The synovium may undergo fatty replacement known as lipoma arborescens. Long-standing inflammatory fluid may be resorbed, leaving a thick gelatinous material that is difficult to aspirate. In these cases, arthrocentesis should be referred to the experienced clinician or a consultant.

Hemorrhage

Significant bleeding is extremely rare. External hemorrhage can be controlled with direct pressure over the puncture site. Hemarthroses are usually small, self-limited, and only require observation. If a significant hemarthrosis or external hemorrhage occurs, treatment may be required to reverse the anticoagulant or replace clotting factors. The readers should refer to another source for management of these complications, as a detailed discussion is beyond the scope of this chapter.

Arthrocentesis can be safely performed in patients who are anticoagulated or have a bleeding disorder. The most experienced EP should perform the procedure to limit any potential complications and bleeding. Also reconsider if the procedure must be done immediately in the ED. The only true indication to perform an arthrocentesis in a coagulopathic patient in the ED is to rule-out a septic joint.

Infection

Infection of a sterile joint can occur when the needle penetrates unclean skin, cellulitic skin, infected subcutaneous tissues, or skin lesions. If proper aseptic technique is used, the risk of infecting a sterile joint occurs in less than 1:10,000 arthrocenteses.4 The risk of infection is negligible when the skin is properly cleansed, aseptic technique is used, and the skin is not punctured through an obvious infection or through a skin lesion that may harbor microorganisms.

Hypodermic Needle-Associated Complications

The hypodermic needle can be the source of complications in rare circumstances. The needle may separate from the hub during the procedure and require a minor surgical procedure to recover it.15 The needle tip may be advanced too deep and become embedded in the bony skeleton surrounding the joint. Upon withdrawing the syringe, the needle tip may break off and remain embedded in the bone or the needle may separate from the hub.

Corticosteroid-Induced Complications

Corticosteroid-induced complications can be acute or chronic.3,4,16–18 The most severe acute complication is injection of corticosteroids into an infected joint. A septic arthritis must be ruled out prior to instillation of corticosteroids into a joint cavity. Other local complications include steroid arthropathy, Charcot arthropathy, osteonecrosis, aseptic necrosis, tissue atrophy, tendon rupture, fat necrosis, formation of calcifications, joint instability, intraneural injection, and postinjection flare. Systemic complications include flushing, pancreatitis, posterior subcapsular cataracts, and hyperglycemia. Due to the potential for complications, many clinicians defer corticosteroid injections to the Orthopedist, Rheumatologist, or Sports Medicine consultant.

Vasovagal Reactions

The patient may experience an increase in vagal tone from apprehension, needle phobias, and/or pain. Vasovagal reactions are relatively common and may be associated with light-headedness and/or fainting. To prevent secondary injury to the patient, arthrocentesis should be performed with the patient on a stretcher or in a chair that reclines. These vasovagal reactions are self-limited and only require reassurance.

Hailed as the most valuable test in rheumatology, synovial fluid analysis provides essential diagnostic information for the appropriate management and treatment of urgent and emergent arthritic conditions.4,30 It has been established as a fundamental component to the complete and appropriate work-up of arthritic diseases. With the possibility of potential joint destruction and chronic disability, the role of synovial fluid analysis in the expedient diagnosis and treatment of acute joint disease cannot be overemphasized.

Controversy exists concerning what constitutes the appropriate guidelines for a “routine” synovial fluid analysis.4,19–21,23,24 This controversy arises from multiple issues that include the clinical scenario, physician competency with appropriate arthrocentesis techniques, the sensitivity and specificity of individual tests, the availability and proficiency of laboratories, and cost. Classification schemes have been established based upon gross, microscopic, biochemical, and microbiological analyses. The most traditional and cited classification for synovial fluid is normal, noninflammatory, inflammatory, septic, or hemorrhagic (Table 77-4).4,19,20,24 Despite the controversy that exists with guidelines and classification schemes, it is critical to differentiate between an inflammatory and noninflammatory process, with the intent of expediting the diagnosis and treatment of a possible infectious etiology.4

A detailed discussion of synovial fluid analysis is beyond the scope of this book. A brief discussion of the most essential components that can be performed in the ED will be presented.

Pathophysiology of Synovial Fluid

Synovium refers to the 1 to 3 cell thick structure that lines the joint space and terminates at the articular cartilage margin.19 This structure overlies a highly vascularized subsynovium, both of which are supported by the dense fibrous joint capsule.19 The synovium produces synovia, an ultrafiltrate of plasma that includes hyaluronate. The synovia serves to lubricate, nourish, and clear the metabolic waste of the avascular articular cartilage.20 Synovial fluid has been demonstrated to possess potent bactericidal activity against the most common gram-positive organisms responsible for septic arthritis.28

The synovium has been described as a double barrier in which molecules must pass through the endothelial microvasculature as well as the synovium and its matrix.20 This double barrier is responsible for the retention of plasma protein. In the presence of an inflammatory process, the barrier is disrupted and protein can leak through the synovium. Difficulty arises in the diagnostic interpretation of protein and smaller molecules (i.e., sodium, chloride, urea, urate, and lactate) found in synovial fluid secondary to the effects of damaged endothelial permeability and variable lymphatic drainage.20,23,24

Gross Analysis of Synovial Fluid

The color of synovial fluid varies depending on the amount of protein, blood, and breakdown products of hemoglobin. Normal synovial fluid usually appears clear to a straw or yellow color. Inflammatory and purulent synovial fluid may appear xanthochromic to white. Hemorrhagic synovial fluid is red and must be distinguished from a traumatic arthrocentesis. A traumatic aspiration usually clots and is more than often nonhomogenous.19,20 A hematocrit may be sent on a bloody aspirate to distinguish between a traumatic tap and hemorrhagic fluid. A vein was pierced by the needle (i.e., traumatic tap) if the synovial fluid hematocrit is equal to the serum hematocrit.20

The following synovial fluid properties observed during bedside gross analysis were found to better predict a potentially septic joint when compared to synovial fluid cell count alone.30

The clarity of synovial fluid refers to the amount and type of particles within the fluid. Normal synovial fluid is usually transparent and newspaper print can be easily read through a glass tube containing this fluid.19 Inflammatory and purulent synovial fluid is translucent to opaque secondary to the presence of leukocytes. Opaque fluid can also represent crystals and other particulate matter. Infected synovial fluid cannot be differentiated from noninfected synovial fluid based on gross appearance alone.4

Synovial fluid viscosity is determined by the intactness and concentration of hyaluronate. Viscosity can grossly be assessed by observing a drop of fluid fall from the tip of the needle. The “string” formed will normally be 5 to 10 cm in length.22 In inflammatory and septic synovial fluid, the hyaluronidase is depolymerized and degraded.20 The string formed in these conditions is shorter, or not formed at all, and the fluid falls as a drop. Processes resulting in a significant effusion without inflammation may also dilute hyaluronate without degrading it and result in decreased viscosity. Clotted white blood cells may enhance viscosity in the presence of inflammation.20 EPs must be cautious with their interpretations of viscosity because even quantitative measures often fail to distinguish between inflammatory and noninflammatory states.4

The mucin clot test evaluates the degree of polymerization of hyaluronate.4,19 The mucin clot test is performed by one of two methods. The first method involves mixing the supernatant of a centrifuged specimen with a few drops of glacial acetic acid. The second method involves mixing 1 mL of synovial fluid to 4 mL of 2% acetic acid. A “good” clot consists of a dense white precipitant that indicates a high degree of polymerization and a high viscosity.19 A “poor” clot consists of little to no precipitate and suggests an inflammatory process that has depolymerized the hyaluronate. Controversy exists concerning the subjectiveness of the clot's endpoint.4

Microscopic Analysis of Synovial Fluid

The total leukocyte count, more than any other test, aids in distinguishing between an inflammatory, noninflammatory, and septic process.20 Although a significant overlap may exist, the total leukocyte count can be used to identify synovial fluid as normal, noninflammatory, inflammatory, or septic (Table 77-4). Using this classification scheme, a total leukocyte count of less than 3000 cells/L is considered noninflammatory. A count between 3000 and 20,000 cells/L is considered inflammatory. The range of 20,000 to 50,000 cells/L may be inflammatory or septic. A count greater than 50,000 cells/L is considered septic until proven otherwise. The overlap between categories is considerable and clinicians must be cautious of basing a diagnosis solely on the total leukocyte count. Depending on the acuteness of the inflammation, several arthritic conditions such as gout, pseudogout, and rheumatoid arthritis may yield a significantly elevated total leukocyte count approaching 100,000 cells/L.21 Immunocompromised hosts and some infectious diseases, such as tuberculosis and Neisseria gonorrhoeae, may have lower absolute counts than expected.4

The differential leukocyte count may further aid in distinguishing between inflammatory, noninflammatory, and septic synovial fluid. The cell count and differential (WBC) of the joint fluid is the best diagnostic test for septic arthritis, while the serum ESR and WBC perform poorer in the identification of infection.37 However, using the traditional cut-off value of 50,000 WBC/mm3 lacks sensitivity enough to safely rule-out a septic arthritis.39 Inflammatory processes generally have greater than 70% neutrophils while septic synovial fluid has greater than 90% neutrophils.19 Again, the overlap can be significant depending on the arthritic process and its acuteness. Crystal-induced processes may present with high neutrophil counts, while immunocompromised hosts, fungal infections, and tuberculosis may present with lower neutrophil counts.4,21 In general, a synovial fluid containing greater than 90% neutrophils in the presence of an elevated total leukocyte count should be highly suspicious of a septic process. High eosinophil counts may suggest parasitic infection, allergic reactions, tumor, or Lyme disease.20,23 High monocyte counts may suggest viral infection (e.g., rubella and hepatitis B) or serum sickness.22

Crystal identification is an essential component of synovial fluid analysis. Crystal identification requires the use of a polarized light microscope with higher-powered lenses and oil immersion capabilities. Crystals can be identified based on their shape, size, and birefringence. Birefringence is defined as the crystals' ability to bend the light passing through it into two distinct directions, negative or positive. The light's ability to bend negatively or positively is transformed into a specific color (yellow or blue) under the polarized microscope.19,20 Caution must be taken as artifact and tissue debris can often imitate birefringent material.

Crystal analysis requires an experienced technician and is rarely if ever performed in the ED. Monosodium urate crystals are commonly seen in gout. These crystals are needle-shaped, 2 to 25 μm in length, and have strong negative birefringence. They may clump together in sheets.22,25 Local anesthetic solutions have the ability to dissolve monosodium urate crystals. Therefore, the joint cavity should not be penetrated with the needle when anesthetizing the skin and subcutaneous tissue.21 Calcium pyrophosphate dihydrate crystals are seen in pseudogout. These crystals are rhomboidal or rectangular, 2 to 10 μm in length, and have weak positive birefringence.22,25 These crystals may be more difficult to detect than monosodium urate crystals because of the weaker birefringence. Cholesterol crystals may present in multiple forms and sizes. They are typically flat rhomboidal plates, 5 to 50 μm in length, and have both negative and positive birefringence.22 Artifact “crystals” can be produced by a variety of substances. Corticosteroids can be detected weeks after injection and have variable shapes but no regular geometric form. Maltese crosses are strong birefringent particles that are secondary to multiple compounds such as talc powder, lipids, calcium oxalate, and dust.22

Biochemical Analysis of Synovial Fluid

As discussed previously under the pathophysiology section, difficulty arises with the interpretation of total protein secondary to the effects of damaged endothelial permeability and variable lymphatic drainage.20 In theory, the damage caused by an inflammatory process should increase the permeability of proteins into the synovial fluid. Multiple studies have shown that protein samples were only able to classify synovial fluid into an inflammatory or noninflammatory process in approximately 50% of the cases.23 Furthermore, the total protein count was unable to differentiate among various groups of arthritides, including rheumatoid arthritis and osteoarthritis.4

Theoretically, inflammatory and infectious processes consume glucose and thus lower the level present in synovial fluid. One study has shown that glucose levels were able to classify synovial fluid into an inflammatory or noninflammatory process in less than 50% of cases.23 In 50% of the septic joints analyzed, the glucose level was not significantly decreased. Another study reports glucose analysis having a sensitivity of 20% and specificity of 84% in detecting inflammatory joint disease.24 Synovial fluid glucose levels can vary from serum glucose levels when taken less than 6 hours after oral intake.24 These studies are just a few of many that confirm synovial fluid glucose levels are not reliable to diagnose or rule out a septic joint.

Other biochemical markers have been studied to elicit a marker to differentiate a septic from a nonseptic joint. These include lactate, lactic dehydrogenase, and numerous immunologic and inflammatory mediators. These biochemical markers, at present, are not sensitive or specific to rule out a septic joint. They are not recommended for routine synovial fluid analysis. Bacterial polymerase chain reaction (PCR) techniques with aspirated joint fluid are currently being studied and are theoretically superior tests, able to identify difficult to culture organisms. However, many drawbacks including high false positives due to contamination limit usage until further studies are done.38

Microbiological Analysis of Synovial Fluid

The Gram's stain is an easily performed test that yields rapid results and can lead to the expedient diagnosis and treatment of a septic joint. The Gram's stain has a sensitivity of 50% to 70% for nongonococcal infections and less than 10% for gonococcal joint infections.24 Although the sensitivity of this test is low, the specificity of the Gram's stain approaches 100%. This makes it an essential component of routine synovial analysis. N. gonorrhoeae is identified as a gram-negative intracellular diplococci. Staphylococcus aureus and Streptococcus are responsible for approximately 70% of nongonococcal septic arthritis and can be identified as gram-positive cocci in clusters and gram-positive cocci in chains, respectively.27 Recent studies have identified an increased prevalence of MRSA-associated osteoarticular pathology such as septic arthritis and subperiosteal abscesses.36 These diagnoses should be considered in patients with and without risk factors for community-acquired MRSA infection.36

Bacterial identification is essential when confronted with the possibility of a septic joint. Synovial fluid cultures have a sensitivity of 75% to 95% for nongonococcal bacteria and 10% to 50% for gonococcal bacteria in the absence of previous antibiotic treatment. Difficulty arises from the low sensitivity of cultures for some organisms, culture methods, specimen preparation, and the length of time for some bacteria to grow.24 Recent advances with the use of polymerase chain reaction techniques have shown increased sensitivity and specificity for detecting N. gonorrhoeae.19,26

Minimal quantities of synovial fluid can yield valuable information. Analysis can be performed with as little as two drops of synovial fluid.21 The total leukocyte count, differential leukocyte count, crystal analysis, and Gram's stain can be obtained from the first drop while the second drop can be sent for cultures.21 Unfortunately, few institutions or laboratories can perform synovial fluid analysis with only two drops of fluid.

The specimen may be transported for analysis by one of two methods. First, the syringe with the synovial fluid may be capped and sent to the laboratory. The laboratory technicians will then divide the specimen for analysis. Alternatively, the synovial fluid may be placed into tubes. A new sterile needle, different from the arthrocentesis needle, should be used to place fluid in the test tubes. A needle used for steroid injection should never be used secondary to the formation of a crystal-like substance.4 Synovial fluid for microscopic analysis should be collected in test tubes with and without preservatives. Fluid should be placed in a Culturette or culture bottle for microbiological analysis. Synovial fluid for crystal analysis should be sent in a test tube with liquid heparin (green-topped tube) because EDTA and powdered anticoagulants interfere with crystal identification.21 A red-topped tube containing no preservatives should be used to test for chemistries, serology, and viscosity. A tube with an anticoagulant (purple-topped tube) is used for the cell count, cell differential, and cytology. Prompt examination of fluid specimens is urgent to avoid the following problems: misdiagnosing borderline inflammatory fluids because of decreased WBC counts, not identifying crystals that dissolve with time, or over interpreting findings because of new, artifactual crystals.29

Arthrocentesis is used to diagnose and make treatment decisions regarding a joint. It is a safe, easy, and simple procedure. Arthrocentesis is relatively painless and extremely beneficial to the patient. It may be performed for diagnostic information and/or therapeutic treatment. Analysis of the synovial fluid provides unique and valuable information about a joint. It is the only method to accurately and definitively diagnose or rule out a septic arthritis. Arthrocentesis is indicated to evaluate the cause of an arthritis or a joint effusion. All patients presenting with an acute monoarthritis or an acute, nontraumatic effusion should undergo arthrocentesis when the diagnosis is not clear based upon the history and physical examination.