Joint aspiration and injection in adults: Indications and technique

INTRODUCTION — 

A needle is inserted into a joint for two main indications: aspiration of fluid (arthrocentesis, for diagnosis or relief of pressure) or injection of medications. In practical terms, most injections into joints consist of a glucocorticoid, a local anesthetic, or a combination of the two.

This topic will review the main indications for arthrocentesis and intraarticular glucocorticoid injection, basic techniques for needle insertion, and the approach to a dry tap. Separate topic reviews related to joint aspiration in adults include the following:

●(See "Intraarticular and soft tissue injections: What agent(s) to inject and how frequently?".)

●(See "Joint aspiration and injection in adults: Complications".)

●(See "Synovial fluid analysis".)

●(See "Musculoskeletal ultrasonography: Guided injection, aspiration, and biopsy of joints and related structures".)

Occasionally, saline is injected into the joint to diagnose a joint injury (ie, saline load test). This is discussed elsewhere. (See "Severe lower extremity injury in the adult patient", section on 'Soft tissue and bone assessment'.)

Evaluation and treatment of bursitis sometimes require bursal aspiration and injection, which are discussed separately. (See "Septic bursitis", section on 'Bursal fluid and tissue samples' and "Knee bursitis" and "Greater trochanteric pain syndrome (formerly trochanteric bursitis)", section on 'Oral NSAIDs or glucocorticoid injection'.)

INDICATIONS AND RELATIVE CONTRAINDICATIONS

Indications for joint aspiration — Arthrocentesis and synovial fluid analysis are important in the evaluation of a patient who has a suspected effusion or signs suggesting inflammation within the joint (see "Monoarthritis in adults: Etiology and evaluation"). The two most important indications for diagnostic arthrocentesis are:

●Suspected septic arthritis – Arthrocentesis is critically important for any patient with concern for septic arthritis, especially when there is lower-extremity arthritis in diabetic or immunocompromised patients or when patients face challenges in returning for follow-up care. Septic arthritis can co-occur with other types of inflammatory arthritis (gout, rheumatoid arthritis), emphasizing the importance of obtaining fluid to look for both infection and crystals [1]. Fluid should be obtained prior to initiation of antibiotics, since synovial fluid cell count can fall by half once antibiotic treatment begins [2]. (See "Septic arthritis in adults" and "Bacterial arthritis: Clinical features and diagnosis in infants and children".)

●Suspected crystalline arthropathy – Arthrocentesis and crystal analysis is also important for patients with concern for a new diagnosis of crystalline arthropathy, including gout and calcium pyrophosphate crystal deposition (CPPD) disease. While findings on advanced imaging (eg, musculoskeletal ultrasound and, particularly, dual-energy computed tomography [DECT]) can be supportive of a crystal diagnosis of both gout [3] and CPPD [4], aspiration with synovial fluid analysis remains the preferred approach to the diagnosis of gout. Crystal confirmation by arthrocentesis done early during an acute gout flare is still more sensitive than DECT scanning [3,4] or ultrasound [5]. (See "Calcium pyrophosphate crystal deposition (CPPD) disease: Clinical manifestations and diagnosis", section on 'Diagnostic evaluation' and "Gout: Clinical manifestations and diagnosis", section on 'Suspected gout flare in patients without established gout'.)

Indications for intraarticular glucocorticoid injection — There are various potential indications for intraarticular glucocorticoid injections. The list below is representative and not intended to be comprehensive, as clinical indications continue to evolve. The evidence to support this varies by type of condition as well as the specific joint being considered and is discussed in more detail in the separate topic reviews:

●Inflammatory arthritis

•Rheumatoid arthritis (see "Use of glucocorticoids in the treatment of rheumatoid arthritis", section on 'Intraarticular therapy')

•Psoriatic arthritis (see "Treatment of psoriatic arthritis", section on 'Limited role of glucocorticoids')

•Spondyloarthritis (see "Treatment of peripheral spondyloarthritis", section on 'Initial therapy')

•Reactive arthritis (see "Reactive arthritis", section on 'Intraarticular glucocorticoids')

●Crystalline arthropathy

•Gout (see "Gout: Treatment of flares", section on 'Intraarticular glucocorticoids')

•CPPD disease (see "Treatment of calcium pyrophosphate crystal deposition (CPPD) disease", section on 'Intraarticular glucocorticoids')

•Basic calcium phosphate crystal arthritis (see "Basic calcium phosphate (BCP) crystal arthritis, including Milwaukee shoulder syndrome", section on 'Milwaukee shoulder syndrome')

●Osteoarthritis

•Overview (see "Overview of the management of osteoarthritis", section on 'Pharmacologic therapy')

•Hand involvement (see "Management of hand osteoarthritis", section on 'Therapies with limited efficacy or of uncertain benefit')

•Hip involvement (see "Management of hip osteoarthritis", section on 'Limited role of intra-articular glucocorticoids')

•Moderate to severe knee involvement (see "Management of moderate to severe knee osteoarthritis", section on 'Limited role of intra-articular glucocorticoid injections')

Relative contraindications — From a technical standpoint, arthrocentesis and intraarticular glucocorticoid injections can be done for most patients by adapting technique or using imaging guidance such as ultrasonography or fluoroscopy in those with challenging anatomy or positioning (eg, joint contracture). (See 'Dry taps' below.)

It is generally safe to perform these injections for patients taking anticoagulation with or without antiplatelet therapy. (See 'Patients on anticoagulation' below.)

Intraarticular glucocorticoid injections should not be done in patients who are suspected of having septic arthritis. A detailed discussion to the approach to septic arthritis is discussed elsewhere. (See "Septic arthritis in adults".)

Other relative contraindications for intraarticular glucocorticoid injections, especially repeated injections, include:

●Patients with rheumatoid arthritis affecting small hand joints where glucocorticoids may cause atrophy of supporting soft tissues that can lead to accelerated joint deformities (see "Management of hand osteoarthritis", section on 'Therapies with limited efficacy or of uncertain benefit')

●Patients with osteoarthritis who did not respond to more than one previous glucocorticoid injection of the same joint

The cost-benefit assessment might also be affected by preexisting avascular necrosis (AVN) in an individual patient, even in joints distant from the one to be injected. Some purported risk factors for AVN are genetic and therefore presumably apply to all the patients joints equally.

In addition, there is limited evidence to suggest that intraarticular glucocorticoids may interfere with cartilage repair in patients with early osteoarthritis. The role of intraarticular glucocorticoid injections for large joints is discussed elsewhere. (See "Management of moderate to severe knee osteoarthritis", section on 'Limited role of intra-articular glucocorticoid injections' and "Management of hip osteoarthritis", section on 'Limited role of intra-articular glucocorticoids'.)

OBTAINING INFORMED CONSENT — 

As with any procedure, providers should obtain a patient's informed consent prior to arthrocentesis and/or glucocorticoid injection. The discussion should provide information about the diagnosis, proposed procedure including risks and benefits, alternative options, and the risks of declining treatment. More information on obtaining informed consent can be found elsewhere. (See "Informed procedural consent".)

We typically discuss the following risks of arthrocentesis with patients, which are detailed elsewhere (see "Joint aspiration and injection in adults: Complications"):

●The possibility of infection and symptoms that should prompt further evaluation (eg, fever, worsening joint pain and swelling, redness or drainage around the injection site). Infection is rare, occurring in approximately 1 of every 1000 to 3000 procedures, and appears to be relatively more common when intraarticular glucocorticoids are used [6,7]. (See "Joint aspiration and injection in adults: Complications", section on 'Infectious complications'.)

●The more common local postinjection flare, which occurs after approximately 5 percent of injections [8] and is easily confused with infection. (See "Joint aspiration and injection in adults: Complications", section on 'Postinjection flare'.)

●Facial flushing, which is seen in up to 10 percent of patients and is rarely associated with a true allergy [8]. (See "Joint aspiration and injection in adults: Complications", section on 'Facial flushing'.)

●Leakage of joint fluid, which occurs rarely and does not necessarily lead to infection, but which should prompt a repeat visit to the clinician. Leakage is particularly likely to occur in two settings: drainage of a popliteal (Baker's) cyst, and aspiration of an interphalangeal joint or cyst over a Heberden's nodule with a larger-bore needle. (See 'Equipment and medications' below.)

Intraarticular glucocorticoids can sometimes cause transient systemic side effects, which are discussed elsewhere. (See "Major adverse effects of systemic glucocorticoids".)

EQUIPMENT AND MEDICATIONS — 

The exact supplies required for a joint arthrocentesis or intraarticular glucocorticoid injection will depend on the size and location of the joint. An overview of supplies can be found in the table (table 1), with more detail on needle and syringe sizes below.

●Needle size – The ideal needle size for most taps is probably 22 gauge; smaller for small joints, such as interphalangeal joints; and larger if the effusion is a large knee collection, if smaller needles have failed, and/or if very viscous pus or synovial fluid is suspected. As an example, popliteal cysts contain highly viscous material and can be safely aspirated with a 20- or 18-gauge needle. However, the site should be bandaged with a pressure dressing since the frequency of leaking and pain are much greater with large needles.

The optimal needle length depends on the depth of the joint and the habitus of the patient. Providers can aspirate most small and medium joints with 1-inch needles. Aspiration of larger joints (eg, shoulder, knee) usually requires 1.5- to 2-inch needles, or longer ones for patients with obesity (eg, 3.5-inch needle for a hip aspiration in a patient with a body mass index of 40 kg/m² or greater). Rarely, even longer needles are required; spinal needles may be used for trochanteric syndrome injections, and the authors have used 10-inch needles under fluoroscopic guidance for hip aspiration.

Providers may benefit from consistently using one needle gauge and one syringe size as much as possible. This strategy helps develop an appreciation for the expected resistance with intraarticular injections so that providers can recognize the higher resistance encountered when the needle tip is misplaced in a tendon. This cautionary higher resistance is easier to perceive with a 22-gauge needle on a 3 mL syringe and more difficult to appreciate with a smaller-bore needle or with a larger syringe (eg, 5 to 10 mL). These larger-sized syringes have more surface area and therefore additional friction between the internal diameter of the syringe and the rubber part of the piston. This extra friction creates a stiff feel that can be difficult to distinguish from the extra resistance added by injecting into tendon substance.

●Syringe size – The 5 mL syringe is often the ideal size. The 3 mL syringe may not create enough vacuum for aspiration, while a larger syringe may create too much suction and may bring debris or a synovial frond into the bevel of the needle, physically blocking aspiration. However, syringe size should be adjusted based on the size of the joint and effusion. A 20 or even 50 mL syringe is standardly used for large joints (eg, shoulder or knee) with large effusions, while 0.5 to 1 mL syringes may be better for small-volume tendon finger joint injections.

Larger syringes may make it more difficult to know when a needle is placed in a tendon instead of the joint space. When a provider misplaces the needle tip in a tendon and attempts to inject fluid, they encounter increased resistance. The same type of increased resistance can be sensed when using larger syringes, since they have more surface area between the plunger and internal surface of the barrel of the syringe and therefore offer more resistance.

●Medications – We prefer the use of single-dose medication vials for local anesthetic and glucocorticoids because of the risk of microbial contamination of multidose vials [9-12]. In settings in which multidose vials of medications are used, we advise meticulous attention to sterile procedure and appropriate storage. Medications used for arthrocentesis and intraarticular injection are discussed in detail elsewhere. (See "Intraarticular and soft tissue injections: What agent(s) to inject and how frequently?".)

ANATOMIC APPROACHES TO SPECIFIC JOINTS

General principles — The site of aspiration is based upon three principles:

●Easy access to the joint capsule with the least obstruction by bone

●Avoidance of neurovascular bundles

●Avoidance of lesions in the overlying tissues (eg, cellulitis, psoriatic plaques)

The preferred anatomic approaches to following specific structures are shown in the accompanying figures, but other approaches can also be used depending on the clinical situation [13].

Needles should always be inserted bevel-up to help enter the skin more easily.

Specific joints

Sternoclavicular joint

●Patient position – The patient is sitting with the arm on the affected side supported.

●Landmarks – The sternoclavicular joint is superficial and can be palpated where the clavicle meets the sternum (figure 1).

●Needle insertion – The needle is inserted perpendicular to the skin at the midpoint of the sternoclavicular joint.

Shoulder

●Anterior approach – The authors use the anterior approach most commonly due to relatively easier access to the shoulder joint capsule for aspiration.

•Patient position – The patient is sitting or slightly reclining, with their affected arm by their side and slightly externally rotated. Ideally, the ipsilateral elbow and forearm are supported. Maximum relaxation of shoulder muscles can be obtained by having the patient support their own arm (ie, use the contralateral hand to hold the wrist or forearm on the affected side), as patients may trust this intrinsic support more than extrinsic support from towels, pillows, or an assistant.

•Landmarks – Important anatomic landmarks include the humeral head, distal clavicle, and coracoid process (figure 2A-B).

•Needle insertion – The needle is inserted perpendicular to the skin, medial to the humeral head, and approximately 1 cm inferior and lateral to the coracoid process (figure 2A-B). It is directed posteriorly and slightly superiorly and laterally. Injecting glucocorticoid in a tendon is painful and can cause tendon rupture; providers should not inject if they encounter increased backpressure while injecting fluid, as this can be a sign that the needle tip is misplaced in a tendon.

●Posterior approach – The posterior approach to shoulder may be especially useful when the patient requires injection but not aspiration and expresses nervousness or is known to be especially pain-sensitive. This approach is theoretically less painful and the patient does not see the needle approach.

The ideal equipment for the posterior approach is different. Providers can use a smaller-gauge needle (eg, 25 or 27 gauge). When using a long 27-gauge needle, the provider may need to thread the needle using sterile gloves to keep the needle from bending off course. It is ideal to use a small syringe (eg, 3 to 5 mL) to increase the ability to detect back pressure, which would suggest injection into tendon substance instead of the joint space.

•Patient position – The patient is sitting upright or slightly forward with their arm slightly internally rotated at their side. As with the anterior approach, maximum relaxation of shoulder muscles can be obtained by having the patient support their own arm (ie, use the contralateral hand to hold the wrist or forearm on the affected side). Again having the patient use the contralateral hand to grip the wrist on the side of the targeted shoulder will give maximum shoulder muscle relaxation.

•Landmarks – Important anatomic landmarks include the humeral head and the posterolateral border of the acromion process, where the bone contour makes something close to a right angle in the plane of the floor with the patient sitting up (figure 3 and picture 1).

•Needle insertion – The provider inserts the needle perpendicular to the skin, at a point lateral to the humeral head and approximately 2 to 3 cm inferior and medial to the posterolateral corner of the acromion process (figure 3 and picture 1). The needle is directed anteriorly towards the thyroid for injections targeting shoulder bursa or tendinopathy, or 15 degrees downward towards the coracoid process for injections targeting the glenohumeral space.

Elbow (ulnohumeral joint)

●Patient position – The patient flexes the elbow to 90 degrees and pronates the forearm. The patient can lie down with their hand beneath their buttock or sit upright or slightly reclined with their palm down or with their arm resting over the back of their chair.

●Landmarks – Important anatomic landmarks include the lateral humeral epicondyle, the radial head, and the tip of the olecranon process of the ulna (figure 4). The radial head may be identified by palpating the elbow while the patient pronates and supinates their forearm, which will rotate the radial head. The needle should always be placed on the lateral side of the elbow to avoid the neurovascular bundle in the cubital tunnel (between the medial epicondyle and the olecranon).

●Needle insertion – The provider inserts the needle perpendicular to the skin and parallel to the radial head, in the soft spot in the center of the triangle created by the above landmarks (picture 2 and figure 5 and figure 6), to a depth of approximately 0.75 to 1 inch (2 to 2.5 cm).

Wrist (distal radioulnar joint)

●Patient position – The patient flexes the wrist and rotates it slightly towards the ulnar side.

●Landmarks – Important anatomic landmarks include the dorsal radial tubercule (Lister tubercle) and the anatomic snuffbox, including the extensor pollicis longus tendon that makes up its ulnar border (picture 3 and figure 7). The extensor pollicis longus tendon can be identified by having the patient extend their wrist and thumb.

●Needle insertion – The provider inserts the needle perpendicular to the skin, at a point distal to the dorsal radial tubercle and ulnar to the extensor pollicis longus (the lateral border of the anatomic snuffbox) (picture 3 and figure 7 and image 1A-C). Providers should avoid the neurovascular structures in the snuff box. If the needle hits bone, the provider should pull it back and redirect it slightly towards the thumb.

Carpometacarpal

●Patient position – The patient should rest the forearm on a supportive surface (eg, a pillow) with their thumb facing up and flexed towards the tip of the fifth finger (figure 8).

●Landmarks – Important anatomic landmarks include the trapezium (greater multangular bone), proximal base of the first metacarpal bone, and anatomic snuffbox, including the extensor pollicis brevis tendon that makes up its radial border.

●Needle insertion – The provider inserts the needle at the base of the first metacarpal bone on the ulnar side of the extensor pollicis brevis tendon (figure 8).

Finger

●Patient position – The patient should have their fingers resting on a supportive surface and have the fingers straight or slightly flexed (figure 9).

●Landmarks – Important anatomic landmarks include the affected metacarpophalangeal or interphalangeal joint.

●Needle insertion – The provider inserts the needle on either side of the joint adjacent to or beneath the extensor tendon mechanism (picture 4 and figure 9). The extensor tendon is not thick enough to be palpated easily but can be assumed to occupy half of the dorsal side of the finger (ie, one quarter of the total circumference of the finger). The needle enters the skin over the medial or lateral aspect of joint line at an angle of approximately 45 degrees above the plane of the hand to avoid the digital artery and nerve.

The target for arthrocentesis is a bulging joint capsule (image 2). However, for injections of medication, the space between the phalanges will often be too tight to admit the needle and the volume of fluid to be injected. Thus, therapeutic injections often aim to infiltrate the injection mixture circumferentially in the tissue planes around the joint line.

Hip — Hip aspiration generally requires image-guided technique. For adults, this is still most often done by an experienced radiology specialist using fluoroscopy. For children, ultrasonographic assessment and sonographically guided needle placement has become a favored approach, and it can be employed for adults with thin to average body habitus hips as well. (See "Evaluation of the child with joint pain and/or swelling", section on 'Joint aspiration' and "Musculoskeletal ultrasonography: Clinical applications".)

Knee — There are many potential positions for knee aspiration and injection, including medial and lateral versions of three anatomical approaches (suprapatellar, parapatellar, and infrapatellar).

Laterality — We usually favor a medial approach regardless of the anatomic approach used. However, the lateral approach may be used initially when patients have an elevated body mass index (BMI) or when ultrasound demonstrates a full lateral gutter.

●Medial approach – The medial approach is often favored because the surface landmarks and shape of the patella are more obvious medially, and it is therefore easier to learn this approach. It may also be easier in patients with significant patellofemoral osteoarthritis, which often preferentially affects the lateral side of this joint compartment. However, using the medial approach with a 1.5-inch needle may fail to reach the joint capsule in patients with elevated BMI (image 3).

●Lateral approach – The lateral approach may work best when the medial approach is unsuccessful and/or when an ultrasound shows that the lateral gutter of the joint space is full. The lateral gutter may be nearly empty even when there is an effusion, meaning that the needle would painfully hit periosteum instead of encountering fluid. This approach may also be helpful for patients with elevated BMI.

Anatomical approaches — We generally use the suprapatellar approach for knee effusions. The parapatellar approach may be useful for small effusions. The infrapatellar approach requires a flexed knee and therefore is not as optimal for fluid aspiration but may be used for intraarticular injection or when the patient uses a wheelchair and cannot tolerate repositioning [14,15].

●Suprapatellar approach – This approach may be the most useful for large knee effusions.

•Patient position – The patient should have their leg lying on a flat surface, with the knee supported by a pillow or towel to slightly flex to 15 to 20 degrees.

•Landmarks – Important anatomic landmarks include the superior and medial borders of the patella (picture 5).

•Needle insertion – The provider inserts the needle at a 45 degree angle relative to the leg, directed slightly posteriorly and inferiorly under the patella, at a point approximately 1 cm superior and 1 cm medial or lateral to the border of the patella (figure 10 and picture 5).

●Parapatellar approach – This approach may be useful for small effusions.

•Patient position – The patient should have their leg lying on a flat surface, with the knee supported by a pillow or towel to slightly flex to 15 to 20 degrees.

•Landmarks – Important anatomic landmarks include the medial or lateral borders of the patella (picture 5).

•Needle insertion – The provider inserts the needle perpendicular to the leg, directed slightly posteriorly and inferiorly under the patella, at a point approximately 1 cm medial or lateral to the border of the patella (picture 6 and picture 5).

When using a lateral parapatellar approach, the window to enter the joint space can be expanded just prior to the arthrocentesis by having an assistant depress the patella on the opposite, medial edge with their thumb, thus lifting the lateral edge of the patella by a centimeter (figure 11). This maneuver also helps push synovial fluid towards the aspiration site. The length of the needle that enters the joint space with this approach may be less than an inch to avoid painfully hitting the periosteum.

●Infrapatellar, seated approach – This approach is used for joint injection without aspiration or for joint aspiration when it is not possible to position the patient with their knee straight (eg, the patient uses a wheelchair and cannot tolerate repositioning). The infrapatellar approach is notably suboptimal for fluid aspiration since fluid will move into the popliteal fossa where there is less pressure from the joint capsule.

•Patient position – The ideal position is for the patient to sit on a chair or examination table with their knee bent at 90 degrees and the affected foot dangling, as this helps to relax the musculature and open the joint space with mild traction. If this is not possible, the patient can remain in their own wheelchair and/or rest their foot on the ground.

•Landmarks – Important palpable anatomic landmarks include the inferior border of the patella, the tibial plateau, and the patellar tendon (picture 5). Providers should identify the soft spot approximately 5 mm below the inferior border of the patella on either side of the patellar tendon.

•Needle insertion – The provider inserts the needle perpendicular to the skin and parallel to the floor at a point in the center of the soft spot approximately 1 inch medial or lateral to the center of the patellar tendon or half an inch from palpable edge of the patellar tendon. The orientation of the needle is 45 degrees from the long axis of the femur. The standard inch-and-a-half intramuscular needle may reach the joint space halfway in but may also need to be fully inserted for patients with a higher BMI.

Debulking — Debulking can be facilitated by using the supine knee extended position where the patient is supine with the knee extended instead of flexed and by applying gentle external compression to the knee effusion [15-17]. However, if a bent knee approach is used, mechanical compression by an experienced provider can increase the amount of aspirated fluid to a level similar to that obtained using when using the supine extended knee position [15,18].

Ankle (tibiotalar joint)

●Tibiotalar approach – The most commonly used approach to ankle arthrocentesis is the tibiotalar approach.

•Patient position – The patient should sit or lie with their leg in front of them, bent at the knee so the dorsum of the foot can rest flat on the surface (figure 12). To palpate for the tibiotalar joint line, flex the patient's foot to 90 degrees and then plantar flex several times through a comfortable range of motion (eg, to 130 degrees). Once the site is marked, let the patient’s foot assume an intermediate neutral position to help relax the musculature.

•Landmarks – Important anatomic landmarks include the medial malleolus of the tibia, the tibialis anterior tendon, and the extensor hallucis longus tendon. The tendons can be readily identified by asking the patient to dorsiflex the ankle and great toe respectively.

•Needle insertion – The provider inserts the needle medial to the tibialis anterior tendon and lateral to the anterior border of medial malleolus, directed posteriorly and cephalad at a 45 degree angle (figure 12). The goal is to direct the needle over the edge of the talus. If the needle hits periosteum before fluid, it is usually because the angle of needle insertion is too high, causing the needle to hit the dome of the talus. The needle can be redirected using a more cephalad angle.

●Subtalar approach – The subtalar joint may be helpful when the tibiotalar approach is unsuccessful.

•Patient position – The patient should sit or lie with their leg in front of them, bent at the knee so the dorsum of the foot can rest flat on the surface (figure 13).

•Landmarks – Important anatomic landmarks include the lateral malleolus of the tibia and the sinus tarsi.

•Needle insertion – The provider inserts the needle immediately beneath the most distal palpable point of the lateral malleolus (approximately 1 finger breadth below the prominence of the lateral malleolus), directed perpendicular to the skin and parallel to the sole of the foot (figure 13).

PREPARING THE SITE

Hair removal — Using a scissor to trim long hairs which may otherwise brush against the shaft of the entering needle may be helpful. Shaving the site has been shown to be of no net value, since shaving exposes more staphylococci by removing the top layer of epidermis and disturbs hair follicles.

Marking the site — After identifying landmarks, we mark the intended procedure site by impressing the skin with a hard object, such as the sterile end of the needle sheath or a ballpoint pen with a retractable writing tip. Impressing the skin should leave a temporary mark that is not affected by subsequent skin preparation.

Skin preparation — To prepare the skin prior to arthrocentesis, we typically use three separate concentric outward spirals with an iodine disinfectant or scrub with a chlorhexidine prep kit [19,20].

The use of these approaches (an iodine-based or chlorhexidine-based scrub) is supported by indirect evidence from their benefit for more common procedures, including blood culture and surgery. We do not perform joint aspiration or injection following skin preparation with alcohol alone. (See "Overview of control measures for prevention of surgical site infection in adults", section on 'Skin antisepsis'.)

NO-TOUCH TECHNIQUE — 

After preparing the site, there is generally no reason to touch the sterilized field, even with a gloved finger. If the initial site chosen seems wrong, a different site should be identified, palpated, and sterilized. This means that sterile gloves are not necessary since the gloved hand will not touch the prepared field. Unsterile clean gloves are mandated as a universal precaution. Proper no-touch technique can reduce the incidence of iatrogenic septic joint to less than 1 in 2000 [6].

The alternative to the no-touch technique is using sterile technique, which requires sterile gloves and draping in addition to sterilization of the aspiration site. A sterile approach may be used in any scenario and is sometimes preferred for patients who are severely immunocompromised or who require sedation for the procedure.

More information about standard precautions for preventing infection and safe injection practices is provided elsewhere. (See "Infection prevention: Precautions for preventing transmission of infection", section on 'Standard precautions' and "Infection control in the outpatient setting", section on 'Safe injection practices'.)

ADMINISTRATION OF LOCAL ANESTHETIC — 

In our experience, using subcutaneous lidocaine and/or ethyl chloride spray (a type of rapidly evaporating coolant) helps to alleviate the pain associated with insertion of the needle through the skin:

●Lidocaine – We inject approximately 0.5 to 2 mL of lidocaine without epinephrine, depending on the joint size, at the anticipated procedure site using a small-gauge needle (eg, 25 to 30 gauge). Lidocaine should be injected along the intended needle track for the arthrocentesis. Lidocaine may cause some temporary burning pain and takes approximately two minutes to take effect.

A potential disadvantage of this technique is that lidocaine and the methylparaben preservatives in lidocaine may both decrease sensitivity of synovial fluid culture if some of the lidocaine is included in the culture sample [21].

●Ethyl chloride spray – We use a short (10 to 15 second) burst of ethyl chloride spray. The spray nozzle should be approximately 12 inches above the surface of the skin. Providers should aim the spray directly at the planned insertion site, rather than swirling the spray over a larger area, to minimize splatter and avoid washing contamination from the periphery of the field towards the intended aspiration site. Spraying for 15 seconds is sufficient for the anesthesia, independent of any freezing effect, and will provide approximately 15 seconds of anesthesia for needle insertion. After the needle tip passes through the C-fiber neurons in the first few millimeters of skin, the needle can then be redirected as required for the arthrocentesis at a more leisurely pace.

While ethyl chloride is nonsterile and is typically applied after the skin preparation, it can be used safely for these procedures, in our experience, as long as the application technique is good. This approach is supported by a small study that found that the use of ethyl chloride spray did not alter the skin sterility when it was applied at mock injection sites following site preparation using 70 percent isopropyl alcohol [22]. The chemical itself is mildly bacteriostatic.

An effort at pain reduction is shown to be cost-effective by several metrics, including reduced need for subsequent procedures [23,24], perhaps because the analgesia facilitates more complete aspiration.

Alternatively, joint aspiration and/or injection can be done without local anesthesia. This technique relies upon a quick, sure puncture through both pain-sensitive structures (skin and joint capsule) with the smallest possible needle. It is best reserved for procedures that are anticipated to be quick and where the patient is well known to the provider (eg, a patient receiving a repeat intraarticular glucocorticoid injection for a knee with osteoarthritis).

JOINT ASPIRATION

Visual inspection of fluid prior to glucocorticoid injection — It is prudent to visually inspect the fluid (not necessarily microscopically), especially prior to injecting glucocorticoid. If synovial fluid is highly turbid or unexpectedly viscous, it should be sent for further testing to evaluate for infection prior to glucocorticoid injection, including Gram stain, cell count, and fluid culture. (See "Synovial fluid analysis" and "Synovial fluid analysis", section on 'Gross appearance'.)

Switching syringes — Syringes may need to be switched if the initial one is full and there is more fluid to be drained, or to facilitate visual inspection of aspirated fluid before injecting glucocorticoid. To change syringes during the procedure, a hemostat can be used to grip the more distal half of the needle hub, which has specially made fins to accommodate this maneuver. Gripping the more proximal round portion of the hub should be avoided, since it may persistently deform the aperture into an oval shape, ruining the airtight connection between the syringe and needle.

Debulking effusions — Patients may benefit from debulking of an effusion, where the provider aspirates as much synovial fluid as possible. Debulking an effusion can reduce pain from stretching of the joint capsule. It can also reduce the risk of chondrocyte damage for patients with septic joints, as neutrophil enzymes and peroxides may adversely affect chondrocyte viability. Finally, it may improve the effectiveness of intraarticular glucocorticoid injections. As an example, in a small randomized trial of patients with rheumatoid arthritis affecting the knee, aspiration followed by glucocorticoid injection was compared with glucocorticoid injection alone; relapse rate was lower among those who had aspiration first (23 versus 47 percent) [25].

Sending synovial fluid studies — Synovial fluid studies should be sent whenever the diagnosis is in question, especially when septic arthritis is being considered. A more detailed discussion of the collection and handling of synovial fluid samples and study interpretation can be found elsewhere. (See "Synovial fluid analysis", section on 'Specimen collection and handling' and "Synovial fluid analysis", section on 'Routine components of synovial fluid analysis'.)

MEDICATION INJECTION — 

If medications are being injected after joint aspiration, the provider uses the same needle and switches from the aspiration syringe to the medication syringe. (See 'Switching syringes' above.)

The techniques above apply for injection of glucocorticoids as well as for injection of the less commonly used hyaluronate viscosupplementation agents into larger joints. The specific medications used for intraarticular injections are detailed elsewhere. (See "Intraarticular and soft tissue injections: What agent(s) to inject and how frequently?".)

WHEN TO USE ULTRASOUND GUIDANCE — 

Ultrasonography can provide additional information that is not readily obtained from physical examination, depending upon the depth of the joint and its complexity. As an example, small-volume knee effusions are more likely to lateralize to the lateral suprapatellar pouch than the medial [26]. Ultrasonography can be used for direct guidance of needle insertion, with concurrent ultrasound visualization of the area for injection, or for indirect guidance, in which the target region is visualized for the purpose of marking the needle insertion site and estimating the depth and direction of needle placement.

We use ultrasound guidance in the following scenarios:

●Aspiration of joints that are deep to the surface (eg, hip, shoulder) or difficult to identify due to body habitus [27]

●Failure to aspirate fluid (a "dry tap") without imaging guidance in a suspected septic joint, since a timely arthrocentesis is required to make a diagnosis

Ultrasound guidance can improve accuracy and is increasingly used even for the more accessible joints, such as knees [28]. However, it may add to the cost of an injection [29] and may be less valuable when the bony landmarks are very close to the surface or when the clinician is highly experienced in arthrocentesis [30]. The utility of ultrasound also depends on both skillful acquisition and interpretation of images.

The use of ultrasound guidance in rheumatology practice continues to evolve and is discussed in detail separately. (See "Musculoskeletal ultrasonography: Nomenclature, technical considerations, and basic principles of use" and "Musculoskeletal ultrasonography: Clinical applications" and "Musculoskeletal ultrasonography: Guided injection, aspiration, and biopsy of joints and related structures".)

DRY TAPS — 

Sometimes synovial fluid cannot be aspirated during arthrocentesis despite needle redirection; this is known as a "dry tap." This problem occurs with surprising frequency when aspirating knees as well as other joints that are more difficult to tap, such as the ankle and shoulder. In the case of a dry tap, we first switch to an alternative anatomic approach. If this is still unsuccessful and a septic joint is suspected, we use ultrasound or fluoroscopic guidance, as both modalities allow for direct visualization of joint anatomy. Ultrasonography is particularly effective in that it may demonstrate small synovial compartmentalized fluid pockets in atypical locations.

Causes of a dry tap — The most common causes of a dry tap include the following:

●Technical failure to enter the joint – This may be from challenges in selecting the insertion site (eg, poorly defined bony landmarks in a person with obesity) or altered anatomy (eg, from prior trauma, surgery, or chronic deforming arthritis).

●Abnormal compartmentalization of joint fluid – Prior trauma or surgery may result in altered joint anatomy or abnormal compartmentalization of joint fluid, rendering standard arthrocentesis difficult. Similarly, anatomic changes due to a chronic deforming arthritis may make arthrocentesis technically challenging.

●Physical blockage of the needle – The needle bevel may be blocked by thickened synovium, plica, fat, debris, or highly viscous fluid [31].

•Thickened synovium – Providers may accidentally place the needle tip into this thickened synovium or mistake the thickened synovium for a joint effusion. Chronically inflamed synovium may undergo subsynovial fat proliferation and become markedly thickened, much more so than is indicated by examination of the surface anatomy (image 4). This condition is referred to as lipoma arborescens in severe cases [32-34].

•Very high viscosity fluid – Highly viscous synovial fluid can be difficult or impossible to remove by smaller-gauge needles, and the provider may need to use a larger-gauge needle (eg, 18 to 20 gauge). In some cases, the distended joint consists of areas of free fluid along with other areas occupied by semisolid gelatinous material too viscous to be withdrawn (image 5) [32,35].

●Small effusion – The effusion may be too small to aspirate successfully.

●Mistaken physical diagnosis – Sometimes there is no effusion present. This can happen in any patient but is more common in those with obesity (image 6).

Some patients have more than one cause for a dry tap, as with lipoma arborescens and a gelatinous effusion (image 7).

Some additional considerations for a dry tap in certain joints include the following:

●Knee

•Misplacement of the needle in a fat pad – The needle may be misplaced in a fat pad depending on which approach is used. When using a medial suprapatellar or parapatellar approach, the needle may encounter a fat pad in the medial aspect of the patellofemoral compartment that can preclude fluid aspiration (image 3). Hoffa's infrapatellar fat pad may also interfere with the medial or lateral infrapatellar approaches.

•Presence of a plica – A commonly invoked, but rarely present, explanation for failed arthrocentesis in the knee is a thickened medial plica (picture 7), which behaves as a dam or valve and obstructs the lumen of the needle (image 8) [36]. Normally, embryonic tissue separating the three knee joint compartments (medial, lateral, and patellofemoral) involutes; failure to do so results in a medial patella plica [37]. Symptomatic inflammation of the plica is rare, as is "dry tap" due to a medial plica. Lateral plicae are very rare [31,32].

●Ankle — A dry tap in a patient with apparent bilateral ankle effusions may be due to a periarthritis without true effusion. This can occur in sarcoidosis and gout. In the latter disorder, a single drop of interstitial fluid expressed from needle puncture wound of an unsuccessful arthrocentesis can be applied to a slide for examination under polarized light.

Unilateral ankle effusions can be crystal-induced "cluster attacks" in which several anatomically adjacent joints are involved. Arthrocentesis may be successful by switching from the tibiotalar joint to the subtalar joint, which can be accessed one finger's breadth below the prominence of the lateral malleolus (figure 13).

Adjusting the approach — In the case of a dry tap, we first attempt a different anatomic approach when one is available (eg, from medial to lateral knee).

For knee effusions, additional helpful maneuvers may include mechanical compression through bracing, wrapping, or manual manipulation by an assistant; these techniques can reduce the incidence of a dry tap by half [16,17].

Obtaining imaging — If an alternative anatomic approach to arthrocentesis is not possible or is unsuccessful, we generally proceed with some form of diagnostic imaging to confirm the presence of intraarticular fluid. Depending on the imaging modality, it can also be used to guide the joint aspiration. However, the absence of a joint effusion on pre-procedure imaging should not preclude an arthrocentesis attempt when it is otherwise clinically indicated. In an observational study of 217 patients who underwent arthrocentesis of a large joint (ie, shoulder, hip, or knee) and pre-procedure imaging, arthrocentesis was successful in 5 of the 17 patients who did not have an appreciable effusion on imaging and identified one case of septic arthritis [38].

The authors prefer ultrasonography, as this is an effective tool for both detecting a joint effusion and facilitating needle placement for arthrocentesis. Ultrasonography can be used for direct guidance of needle insertion or for indirect guidance to mark the needle insertion site and estimate the depth and direction of needle placement. While the availability of ultrasonography is increasing, its use varies widely due to costs of equipment, regulatory and reimbursement policies, and differences in experience and training. The use of ultrasound guidance in rheumatology practice continues to evolve and is discussed in detail separately. (See "Musculoskeletal ultrasonography: Nomenclature, technical considerations, and basic principles of use" and "Musculoskeletal ultrasonography: Clinical applications" and "Musculoskeletal ultrasonography: Guided injection, aspiration, and biopsy of joints and related structures".)

Radiography is useful in confirming a distended joint in the knee and elbow, in particular. However, simple radiographs cannot distinguish simple or complex fluid from thickened synovium. Other imaging modalities, including fluoroscopy, single-energy computed tomography (CT), and magnetic resonance imaging (MRI), can sometimes be used to confirm the presence of a joint effusion as well. (See "Imaging techniques for evaluation of the painful joint".)

Additional clinical considerations regarding specific joints are described below.

●Suspected acute septic prosthetic joint – An acute septic prosthetic joint is an orthopedic emergency, requiring immediate accurate diagnostic tap. If standard arthrocentesis without imaging guidance is unsuccessful, the authors prefer fluoroscopic guidance as the technique of choice. Fluoroscopy allows direct visualization of key landmarks, and the concurrent injection of contrast material absolutely confirms successful intraarticular needle placement. The diagnosis of prosthetic joint infection is discussed in detail separately. (See "Prosthetic joint infection: Epidemiology, microbiology, clinical manifestations, and diagnosis", section on 'Diagnosis'.)

●Shoulder effusions – As with other joints, ultrasound can be used to confirm a glenohumeral joint effusion and guide aspiration. Ultrasound is particularly useful in distinguishing fluid collections that may be limited to the true glenohumeral joint compartment versus those isolated within the more superficial subacromial-subdeltoid bursa. Ultrasound of the shoulder and an approach to an ultrasound-guided aspiration of the glenohumeral joint is presented elsewhere. (See "Musculoskeletal ultrasound of the shoulder", section on 'Sonographic appearance of shoulder pathology' and "Musculoskeletal ultrasonography: Guided injection, aspiration, and biopsy of joints and related structures", section on 'Shoulder joint and subacromial/subdeltoid bursa'.)

●Wrist effusions – The wrist consists of three normally noncommunicating compartments: the distal radioulnar joint (DRUJ), the radiocarpal joint, and the midcarpal joint. Additionally, multiple extensor and flexor tendons with their sheaths cross the wrist superficially. Infectious processes may only affect one of these separate compartments initially, eventually spreading to affect multiple. Due to this complexity, the authors prefer ultrasound in the wrist for detecting and aspirating fluid in the case of suspected infection (image 1C and image 1A and image 1B). Approximately 5 percent of emergency department nontraumatic wrist presentations are due to septic joint [39].

●Hip effusions – Hip effusions are seen well on ultrasound in most adults, as demonstrated in a study promoting the bedside use of joint ultrasound in the rheumatologic setting [40]. Ultrasound is useful for average to thin adults. For heavier patients (eg, significant abdominal obesity or body mass index [BMI] ≥40 kg/m²), and in cases of prostheses, fluoroscopy remains the standard imaging study for the hip requiring arthrocentesis.

Lavage in selected patients — In most cases, we do not perform joint lavage (ie, intraarticular injection of sterile, preservative-free saline followed by reaspiration) for dry joint taps, as this process dilutes the sample and complicates interpretation of synovial fluid studies. However, lavage may be helpful when septic arthritis is suspected in certain joints, including the following:

●Prosthetic joint – If fluoroscopically guided arthrocentesis is unsuccessful for a patient with a suspected acute septic prosthetic joint, culture yield can potentially be improved by careful lavage [41]. The utility of joint lavage in the setting of suspected septic total joints is controversial, with possible increased sensitivity but decreased specificity (higher false positives) [42]. The diagnosis of prosthetic joint infection is discussed in detail separately. (See "Prosthetic joint infection: Epidemiology, microbiology, clinical manifestations, and diagnosis", section on 'Diagnosis'.)

●Sternoclavicular joint – Limited data suggest that image-guided lavage of the sternoclavicular joint may help identify septic arthritis when aspiration is unsuccessful [43].

POST-PROCEDURE CARE AND FOLLOW-UP — 

We advise patients about conservative management after a joint aspiration and/or injection. This guidance is based on the authors' clinical experience and includes:

●Decrease weightbearing for the following 24 to 48 hours.

●Consider applying cold therapy (eg, ice covered in a cloth, cool pack) to the affected area for 20 minutes at a time.

●Use over-the-counter analgesics (eg, acetaminophen, ibuprofen) as needed, unless these medications are otherwise contraindicated. (See "Nonopioid pharmacotherapy for acute pain in adults", section on 'Acetaminophen' and "Nonopioid pharmacotherapy for acute pain in adults", section on 'Nonsteroidal anti-inflammatory drugs'.)

●Keep the area clean. Patients should be advised that they can bathe or shower as per their usual routine.

The timing of follow-up will depend on the diagnosis and acuity. As an example, an intraarticular injection of glucocorticoids for moderate to severe knee osteoarthritis might warrant follow-up in three months, whereas the same procedure for an acute flare of rheumatoid arthritis would require shorter-term follow-up to ensure the patient has responded and does not require additional therapy.

CONSIDERATIONS IN SELECT PATIENTS

Patients on anticoagulation — We generally perform arthrocentesis and injections in patients on anticoagulation with warfarin or direct oral anticoagulants (DOACs) without altering the anticoagulation regimen. For patients who are supratherapeutic on warfarin, an international normalized ratio (INR) of greater than 3.0 to 3.5 is reason to temporarily withhold arthrocentesis, unless a septic joint is suspected. We prefer to use a 22-gauge needle, although larger needles may also be safe for use [44]. (See 'Equipment and medications' above.)

The available data regarding the use of arthrocentesis or injection in patients receiving warfarin or DOACs suggest that these procedures are generally safe [44-49]. A systematic literature review of the risk of serious bleeding complications from arthrocentesis in patients taking long-term oral antagonists identified only four cases of hemorrhage out of 5427 procedures, suggesting that serious bleeding complications in this setting are rare [50]. Studies on specific anticoagulants include:

●Warfarin – A retrospective analysis of arthrocentesis in patients taking warfarin did not find a significant difference in early or late complications of the procedure, including clinically significant bleeding, in patients receiving therapeutic levels of anticoagulation (INR ≥2.0) compared with patients with nontherapeutic levels (INR <2.0) [46]. Only one procedure (0.2 percent) resulted in clinically significant bleeding in the fully anticoagulated group of patients.

●Direct oral anticoagulants – A retrospective review of arthrocentesis in patients taking DOACs did not identify any bleeding complications during the median follow-up period of five days [47]. Almost a quarter of patients were taking a DOAC plus antiplatelet therapy (aspirin or clopidogrel).

Pediatric patients — Joint aspiration and injection in children are discussed elsewhere. (See "Joint aspiration or injection in children: Indications, technique, and complications".)

SUMMARY AND RECOMMENDATIONS

●Indications and relative contraindications – Arthrocentesis and synovial fluid analysis are important in the evaluation of a patient who has a suspected effusion or signs suggesting inflammation within the joint. The two most important indications for diagnostic arthrocentesis are suspected septic arthritis and suspected crystalline arthropathy. Intraarticular glucocorticoid injections should not be done in patients who are suspected of having septic arthritis. (See 'Indications and relative contraindications' above.)

●Equipment – The exact supplies required for a joint arthrocentesis or intraarticular glucocorticoid injection will depend on the size and location of the joint. An overview of supplies can be found in the table (table 1). (See 'Equipment and medications' above.)

●Anatomic approaches to specific joints – The site of aspiration is based upon three principles: easy access to the joint capsule with the least obstruction by bone, avoidance of neurovascular bundles, and avoidance of lesions in the overlying tissues (eg, cellulitis, psoriatic plaques). From a technical standpoint, arthrocentesis and intraarticular glucocorticoid injections can be done for most patients by adapting technique or using imaging guidance such as ultrasonography or fluoroscopy in those with challenging anatomy or positioning (eg, a joint contracture). (See 'Anatomic approaches to specific joints' above.)

●Preparing the site – A scissor is used to trim long hairs that may otherwise brush against the shaft of the entering needle. After identifying landmarks, we mark the intended procedure site by impressing the skin with a hard object, such as the sterile end of the needle sheath or a ballpoint pen with a retractable writing tip. To prepare the skin prior to arthrocentesis, we typically use three separate concentric outward spirals with an iodine disinfectant or scrub with a chlorhexidine prep kit. Subcutaneous lidocaine or ethyl chloride spray (a type of rapidly evaporating coolant) can be used to minimize any pain associated with insertion of the needle through the skin. (See 'Preparing the site' above.)

●Joint aspiration and medication injection – It is prudent to inspect the aspirated fluid visually, especially prior to injecting glucocorticoid. If synovial fluid is highly turbid or unexpectedly viscous, it should be sent for further testing to evaluate for infection prior to glucocorticoid injection. Patients may benefit from debulking of an effusion, where the provider aspirates as much synovial fluid as possible. If medications are being injected after joint aspiration, the provider uses the same needle and switches from the aspiration syringe to the medication syringe. (See 'Joint aspiration' above and 'Medication injection' above.)

●When to use ultrasound guidance – Ultrasonography can be used for direct guidance of needle insertion, with concurrent ultrasound visualization of the area for injection, or for indirect guidance, in which the target region is visualized for the purpose of marking the needle insertion site and estimating the depth and direction of needle placement. In patients requiring aspiration of a joint that is deep to the surface (eg, hip, shoulder) or difficult to identify due to body habitus, we suggest using ultrasound guidance for aspiration (Grade 2C). Ultrasound guidance is also appropriate when aspiration has failed during evaluation of a suspected septic joint. (See 'When to use ultrasound guidance' above.)

●Dry taps – Sometimes synovial fluid cannot be aspirated during arthrocentesis despite needle redirection; this is known as a "dry tap." In the case of a dry tap, we first switch to an alternative anatomic approach. If this is still unsuccessful and a septic joint is suspected, we use ultrasound or fluoroscopic guidance. (See 'Dry taps' above.)

●Patients on anticoagulation – We generally perform arthrocentesis and injections in patients on anticoagulation with warfarin or direct oral anticoagulants (DOACs) without altering the anticoagulation regimen. For patients who are supratherapeutic on warfarin, an international normalized ratio (INR) of greater than 3.0 to 3.5 is reason to temporarily withhold arthrocentesis, unless a septic joint is suspected. (See 'Patients on anticoagulation' above.)