Joint aspiration or injection in adults: Technique and indications

INTRODUCTION — A needle is inserted into a joint for two main indications: aspiration of fluid (arthrocentesis) for diagnosis or for 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. Occasionally saline is injected into the joint to diagnose a joint injury.

This topic will review the basic technique of inserting a needle into a joint and the main indications for intraarticular glucocorticoid injections. The same techniques apply for injection of the less commonly used hyaluronate viscosupplementation agents into knees, hips, and perhaps shoulders.

The choice of injectable glucocorticoid and whether it should be combined with a local anesthetic, the frequency of injection, and potential complications that can occur are discussed separately (see "Intraarticular and soft tissue injections: What agent(s) to inject and how frequently?" and "Joint aspiration or injection in adults: Complications"). The injection of saline (ie, saline load test), used to diagnose traumatic arthrotomy, is also discussed elsewhere. (See "Severe lower extremity injury in the adult patient", section on 'Soft tissue and bone assessment'.)

INDICATIONS FOR ASPIRATION OR INJECTION — There are a number of indications, both diagnostic and therapeutic, for joint aspiration or injection (table 1). Arthrocentesis and synovial fluid analysis are important in the evaluation of a patient who has an effusion or signs suggesting inflammation within the joint. (See "Monoarthritis in adults: Etiology and evaluation".)

The two most important indications for diagnosis are:

●Evaluation for sepsis in a single inflamed joint, particularly in patients with diabetes who have lower-extremity arthritis or in patients who face challenges in returning for follow-up care. Septic joints may occur more commonly in lower extremities, especially in pediatric patients, adding to the importance of lower-extremity aspiration technique and musculoskeletal ultrasound of lower-extremity joints [1]. Gram stain is incompletely sensitive in septic joints. The false-positive rate of the culture itself, following careful chlorhexidine or iodine preparation, is less than 0.5 percent [2]. Synovial fluid cell count can fall by half if the aspiration of a septic joint takes place after, rather than before, antibiotic treatment begins [3]. However, in joint spaces that are loculated or anatomically compartmentalized, the negative predictive values of aspiration and culture can be unexpectedly poor. Such joint spaces include knees with an established subacute infection as well as joints with several anatomically separated compartments like the shoulder [4] or wrist. (See "Septic arthritis in adults".)

●Initial confirmation of gouty arthritis by polarized light. While findings on advanced imaging (eg, musculoskeletal ultrasound, dual-energy computed tomography [DECT]) can be supportive of a crystal diagnosis of both gout [5] and calcium pyrophosphate crystal deposition [6], aspiration with synovial fluid analysis remains the preferred approach to the diagnosis of gout. Crystal confirmation by arthrocentesis done early during an acute attack is still more sensitive than DECT scanning [5,6] or ultrasound [7]. Centrifuging the synovial fluid sample marginally improves the accuracy of the crystal exam [8] (see "Clinical manifestations and diagnosis of gout", section on 'Diagnosis of a gout flare'). It has been estimated that 5 percent of inflammatory presentations in the emergency department turn out to be combined gout and infection in the same joint at the same time [9]. (See "Septic arthritis in adults", section on 'Diagnosis'.)

The main therapeutic indications for glucocorticoid injections are:

●Injection of joints with inflammatory arthritis (rheumatoid arthritis [RA], spondyloarthropathies), especially when previous injections have lead to near remission for long periods (one to six months). (See "Use of glucocorticoids in the treatment of rheumatoid arthritis", section on 'Intraarticular therapy'.)

●Injection of symptomatic, inflamed soft tissue structures such as the subdeltoid bursa, trochanteric bursa, and tendon sheathing. Soft tissue injections can be curative in some cases. However, short-term pain relief does not ensure a better long-term outcome. (See 'Elbow (lateral epicondyle)' below.)

Weaker indications or uses for injection of glucocorticoid are OA of large weightbearing joints and repetitive injection of small joints of the hands, which can become more deformed if their ligamentous support atrophies due to injection. Injection of the carpometacarpal joint with glucocorticoids was no more effective than placebo (saline) injections in one small double-blind study [10]. In another randomized study of 52 patients, both hyaluronate and glucocorticoid injections improved grip strength and pain in OA of the thumb (trapeziometacarpal) joint [11].

PATIENT EDUCATION — Prior to glucocorticoid injection, the patient should be educated about appropriate postinjection care and possible complications. A survey of about one-quarter of the members of the American College of Rheumatology (ACR) found that 71 percent of rheumatologists ask patients to decrease weightbearing, often for 48 hours, after injection of a weightbearing joint, that 30 percent advise applying ice to the injected joint, and that 29 percent specifically caution about either infection or postinjection flare.

Major components of patient education should include:

●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, measured between 1 in 2034 [12] to 1 in 3500 procedures [13]. (See "Joint aspiration or injection in adults: Complications", section on 'Infectious complications'.)

●Description of the more common local postinjection flare (up to 20 percent in muscular trigger or tender point injections), which is easily confused with infection. (See "Joint aspiration or 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. (See "Joint aspiration or 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 with a needle that is too large (see 'Needle size' below). Likewise, if a larger-bore needle is used to evacuate viscous material in a cyst over a Heberden's node, the patient might be cautioned about leaking from the site.

TECHNIQUE OF ARTHROCENTESIS — A variety of factors must be taken into account when performing arthrocentesis, including needle and syringe size, skin sterilization, and local anesthesia.

Patients who are receiving anticoagulation at therapeutic levels can generally undergo arthrocentesis safely. (See 'Approach to the patient on anticoagulants' below.)

Image-guided approaches may be valuable to assure needle placement when aspirating certain joints, such as the hip [14]. Ultrasound guidance is increasingly used even for the more accessible joints, such as knees and shoulders, and can improve accuracy [15], but it may add to the cost of an injection [11] (see 'Ultrasonography' below). It may be most helpful in cases of "dry tap" in a suspected septic joint (see "Joint aspiration: The dry tap"). Ultrasound guidance may be of less value when the bony landmarks are very close to the surface or when the clinician is highly experienced in arthrocentesis [16].

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 if very viscous pus is suspected. As an example, drainage of a popliteal cyst can be safely performed with a 20 or 18 gauge needle, but the site should be bandaged with a pressure dressing since the frequency of leaking and pain are much greater with large needles. The high viscosity of the material within a popliteal cyst tempts the operator to use a still larger bore needle, a procedure which we do not advise.

The best strategy is to use one needle and syringe size as much as possible. Getting used to the resistance offered by injecting through the same needle and syringe size allows the operator to more immediately and reliably recognize the higher resistance that comes with attempting to inject with the needle tip in tendon substance. This cautionary higher resistance is easier to perceive with a 22-gauge needle or larger and more difficult to appreciate with a smaller bore needle.

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. If, however, a knee effusion or shoulder effusion is of obviously large magnitude, a 20 gauge needle and 20 mL (or even 50 mL) syringe are standard. On the other hand, small-volume tendon sheath injections performed by a subspecialist are often best accomplished with tuberculin-sized syringes.

Removing hair at the aspiration site — Shaving the site has been shown to be of no net value due to exposure of more staphylococci within hair follicles disturbed by the removal of the top layer of epidermis during shaving. It is difficult to imagine a sterile preparation of all surfaces of a long hair shaft. Using a scissor to cut hairs which may otherwise brush against the shaft of the entering needle may be helpful.

Sterile 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 [17,18].

Since arthrocentesis is not life-saving or time-limited, there is generally no reason to touch the previously prepared site with a gloved finger. If the initial site chosen seems wrong, a different site should be identified, palpated, and sterilized. Proper no-touch technique can reduce the incidence of iatrogenic septic joint to less than 1 in 2000 [12].

Two consequences follow from these principles:

●Sterile gloves are not necessary since the gloved hand will not touch the prepared field. Unsterile clean gloves are mandated as a universal precaution, since human immunodeficiency virus (HIV) and hepatitis have grown from synovial fluid.

●Careful initial palpation and marking of the site obviates the need for repeat preparation. Flexing the joint to be sure of the location of the actual articulation helps initial site selection. Marking is done by impressing the skin with a hard object, such as the sterile end of the needle sheath or a ball point pen with a retractable writing tip.

One form of commonly used topical anesthetic, ethyl chloride spray, which is labeled as nonsterile, is typically applied after the skin preparation, although it can be used safely for these procedures in our experience. In a small study that examined the effects of the spray on skin sterility, the use of ethyl chloride spray did not alter the sterility of skin at mock injection sites when it was applied following preparation of the sites with 70 percent isopropyl alcohol [19]. (See 'Local anesthesia' below.)

It is very unlikely that randomized trials will be performed that are of sufficient power to determine the optimal approach to skin preparation before arthrocentesis, given the very low rate of infectious complications (estimated to be 1 in every 2000 to 3000 procedures). 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'.)

Single versus multidose medication vials — We prefer the use of single-dose medication vials rather than multidose vials because of the risk of microbial contamination of multidose vials of glucocorticoids or local anesthetic [20-23]. In settings in which multidose vials of medications are used, we advise meticulous attention to sterile procedure and appropriate storage.

Local anesthesia — An effort at pain reduction is shown to be cost-effective by several metrics, including reduced need for subsequent procedures [24,25], perhaps because the analgesia facilitates more complete aspiration. A bleb of subcutaneous lidocaine or, prior to povidone iodine preparation, a short burst (10 to 15 seconds) of ethyl chloride spray, a rapidly evaporating coolant, may be beneficial and is the most commonly used analgesic technique. In our experience, either approach helps to alleviate the pain associated with insertion of the needle through the skin. Additionally, mixing lidocaine with the glucocorticoid injection may reduce symptomatic postinjection flares, especially with extraarticular injections. Preservative free normal saline can be substituted for local anesthetic to avoid any catabolic effects of the anesthetic itself, low-buffer pH, or preservative additives [26]. Whatever the diluent, dilution of the glucocorticoid helps prevent atrophy of periarticular and subcutaneous soft tissues. (See "Intraarticular and soft tissue injections: What agent(s) to inject and how frequently?", section on 'Should the glucocorticoid be mixed with a local anesthetic?'.)

A two-needle technique with infiltration of the intended needle track with lidocaine before the actual aspiration is probably most effective, but takes more time. Another alternative technique without anesthesia 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 patients well-known to the operator.

Disadvantages of the anesthesia techniques, which limit their use, involve the following theoretical concerns:

●The methylparaben preservatives in lidocaine may decrease sensitivity of synovial fluid culture if some of the lidocaine is included in the culture sample [27]. However, even in the absence of the methylparaben preservative, lidocaine itself has enough antibacterial effect to reduce colony counts in vitro [27].

●Bad technique with the ethyl chloride spray is probably a risk. Spraying from too close creates splatter; while spraying from too far requires adjustment of aim, implying the potential for washing contamination from the periphery of the field toward the center.

●The use of multidose vials, even those with lidocaine plus bacteriostatic agents, does not eliminate all risk of contamination to the degree that single-dose vials do. (See 'Single versus multidose medication vials' above.)

Switching syringes — 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. 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.

Visual inspection of fluid prior to glucocorticoid injection — It is prudent to visually inspect the fluid (not necessarily microscopically) prior to injecting glucocorticoid. In approximately 15 percent of cases, gross inspection prompts a formal study of fluid (culture, white blood cell count, or crystal examination under polarized light). Fluid should be cultured if it has high turbidity or unexpectedly high viscosity, as this can be seen in infection. However, there are many patients in whom the diagnosis is clear, and there is no compelling reason that they cannot be injected directly. (See "Synovial fluid analysis" and "Synovial fluid analysis", section on 'Gross appearance'.)

Debulking effusions — Patients may benefit from debulking of an effusion, where the provider aspirates as much synovial fluid as possible. Gentle manual compression of the joint fluid in a knee increases the yield of fluid and injection efficacy, as does use of the supine knee extended position [28,29]. Although knee aspirations can be successfully done with a flexed knee, the volume of effusion removed in debulking can be maximized in the extended position and by external compression, either manually or pneumatically [30].

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, 191 knees (of 147 patients with rheumatoid arthritis) were randomly assigned to be aspirated or not prior to injection of 20 mg of triamcinolone hexacetonide [31]; relapse of a joint effusion was noted in 23 percent of those who were aspirated versus 47 percent of those who were not (p = 0.001).

Approach to the patient on anticoagulants — We generally perform arthrocentesis and injections in patients on anticoagulation with warfarin or direct oral anticoagulants (DOACs) without altering the anticoagulation regimen. As discussed above, we prefer to use a 22-gauge needle, although larger needles may also be safe for use [32]. (See 'Needle size' above.)

The available data regarding the use of arthrocentesis or injection in patients receiving warfarin or DOACs suggest that these procedures are generally safe [32-37]:

●A systematic literature review of the risk of serious bleeding complications from arthrocentesis in patients taking long-term oral antagonists identified four cases of hemorrhage out of 5427 procedures, suggesting that serious bleeding complications in this setting are rare [38].

●For patients taking warfarin, a retrospective analysis evaluated the safety of 640 arthrocentesis and joint injection procedures in 514 anticoagulated patients [34]. There was no significant difference in early and late complications of the procedure (clinically significant bleeding, procedure-related pain prompting a clinician visit, and joint infection) in patients receiving therapeutic levels of anticoagulation (international normalized ratio [INR] ≥2.0) compared with patients with nontherapeutic levels (INR <2.0). Only one procedure (0.2 percent) resulted in clinically significant bleeding in the fully anticoagulated group of patients.

●For patients taking DOACs, data on the risk of bleeding complications related to arthrocentesis or joint injections come from a retrospective review of 1050 consecutive procedures done at the Mayo clinic over a six-year period [35]. No bleeding complications occurred during the median follow-up period of five days. Of the 1050 procedures, 22 percent were performed in patients receiving a DOAC plus aspirin, and 1 percent were performed in patients on a DOAC plus clopidogrel.

ANATOMIC APPROACHES TO SPECIFIC JOINTS AND BURSAE — The site of aspiration is based upon two principles:

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

●Avoidance of neurovascular bundles

Approaches other than those shown can also be used [39]. These secondary approaches can be employed by the subspecialist who needs to avoid areas of skin with a high density of infecting organisms, such as areas of psoriatic plaque or suspected cellulitis. The preferred anatomic approaches to following specific structures are shown in the accompanying figures.

Knee —  (figure 1)

Ankle —  (figure 2)

Shoulder —  (figure 3)

Wrist —  (figure 4)

Carpometacarpal —  (figure 5)

Finger —  (figure 6)

Elbow —  (picture 1)

Elbow (lateral epicondyle) —  (figure 7)

Subacromial bursa —  (figure 8)

Trochanteric bursa —  (figure 9)

Sternoclavicular joint — The approach to the sternoclavicular joint is discussed elsewhere. (See "Management of isolated musculoskeletal chest pain", section on 'Sternoclavicular osteoarthritis'.)

Hip aspiration — 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 adult hips as well. (See "Evaluation of the child with joint pain and/or swelling", section on 'Joint aspiration' and "Musculoskeletal ultrasonography: Clinical applications".)

DIFFICULT SITES TO ACCESS — Some target sites for needle placement may be difficult to access. The response to "dry taps" and the use of ultrasound guidance are described in detail elsewhere, as indicated below.

Dry taps — The approach to dry taps that is most consistently successful is to switch anatomic approaches (eg, from medial to lateral knee) followed by aspiration with ultrasound guidance if a septic joint is suspected [40] (see "Joint aspiration: The dry tap"). In the case of knee aspiration, mechanical compression from manual manipulation by a separate operator, or by bracing or other wrapping, can reduce the incidence of a dry tap by half [29,30]. Mechanical compression in the hands of an experienced operator can make fluid volume aspirated from a bent knee approach that of aspiration performed on the extended knee supine [28].

Ultrasonography — Ultrasonography may add information to clinician examination, depending upon the depth of the joint and its complexity; it seems to be most useful in the examination of the shoulder and other structures that are difficult to access. As an example, small-volume knee effusions are more likely to lateralize to the lateral suprapatellar pouch than the medial [41]. 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. 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 and aspiration of joints and related structures".)

Transmission ultrasonography, in which the sound source and the receiver are located on opposite sides of the joint, can produce an easily interpreted image like that of conventional radiography and can visualize a distended joint capsule (image 1). This technique, however, is not widely available.

SUMMARY AND RECOMMENDATIONS

●Indications for aspiration or injection – There are a number of indications, both diagnostic and therapeutic, for joint aspiration or injection (table 1). Arthrocentesis and synovial fluid analysis are important in the evaluation of patients who have an effusion or signs suggesting inflammation within the joint. Important indications for synovial fluid analysis include evaluation for a possible septic joint and initial diagnostic confirmation of suspected gouty arthritis. Therapeutic intraarticular or soft tissue injection of glucocorticoids is indicated for a number of disorders. (See 'Indications for aspiration or injection' above.)

●Patient education – Patient education prior to joint injection or arthrocentesis should include a discussion of potential complications, including infection, which is rare; postinjection flare; facial flushing; and leakage of joint fluid. (See 'Patient education' above.)

●Technical factors – A variety of factors must be taken into account when performing arthrocentesis. These include needle and syringe size, which depends upon the region targeted and the potential size of a joint effusion; careful skin sterilization; and local anesthesia, usually with either subcutaneous lidocaine injection or topical ethyl chloride spray. (See 'Technique of arthrocentesis' above and 'Needle size' above and 'Syringe size' above and 'Sterile preparation' above and 'Local anesthesia' above.)

●Patients on anticoagulants – Patients who are receiving anticoagulation at therapeutic levels can generally undergo arthrocentesis safely. (See 'Approach to the patient on anticoagulants' above.)

●Anatomic approaches to specific joints and bursae – The choice of the site of aspiration for a given joint is based upon obtaining easy access to the joint capsule, with the least obstruction by bone, and avoiding neurovascular bundles. The approaches to specific joints and soft tissue sites are shown. (See 'Anatomic approaches to specific joints and bursae' above.)

●Difficult sites to access – Some target sites for needle placement may be difficult to access. The response to "dry taps" and the use of ultrasound guidance are described in detail elsewhere. (See "Joint aspiration: The dry tap" and "Musculoskeletal ultrasonography: Guided injection and aspiration of joints and related structures".)