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Background
Arthrocentesis, the puncture and aspiration of a joint, is an acknowledged, useful procedure that is easily performed in the emergency department (ED). It has been established as both a diagnostic and therapeutic tool for various clinical situations. When performed properly, the procedure offers a wealth of clinical information and is associated with few complications. In the ED it is difficult to make an accurate assessment of an acutely painful, hot, and swollen joint without performing arthrocentesis.
Indications and Contraindications
The indications for arthrocentesis are listed in Review Box 53.1 .
Infection in the tissues overlying the site to be punctured is generally considered an absolute contraindication to arthrocentesis. However, inflammation with warmth, swelling, and tenderness may overlie an acutely arthritic joint, and this condition may mimic a soft tissue infection. Once convinced that cellulitis does not exist, the clinician should not hesitate to obtain the necessary diagnostic joint fluid. Known bacteremia is a theoretical relative contraindication because infection can spread to the joint; however, this complication should be weighed against the useful information and culture results gained by fluid analysis. Bleeding diatheses are rarely a relative contraindication, and arthrocentesis to relieve a tense hemarthrosis in bleeding disorders such as hemophilia is an accepted practice after infusion of the appropriate clotting factors. There are few data regarding the safety or dangers of arthrocentesis in patients taking anticoagulants or platelet inhibitors. Studies have demonstrated that the risk for iatrogenic hemarthrosis in patients treated with oral anticoagulants is extremely low, even in those who have international normalized ratios (INRs) as high as 4.5. One prospective trial of 32 patients taking warfarin found no complications after athrocentesis. Hence, when necessary, arthrocentesis should be performed in patients taking anticoagulants. The value of reversing a coagulopathy with blood components before the procedure is not proved, and clinical judgment should prevail. Prosthetic joints are at high risk for infection, and arthrocentesis should be avoided whenever possible in this situation. However, if an infected prosthesis is suspected, arthrocentesis should be performed.
Articular Versus Periarticular Disease
Periarticular conditions such as trauma, tendinitis, bursitis, contusion, cellulitis, or phlebitis may mimic articular disease and suggest the need for arthrocentesis. Therefore evaluation of acute joint disease requires that the clinician first determine whether the patient's constellation of signs and symptoms derives from the joint itself or from some other musculoskeletal or periarticular structure. Such a distinction, however, may be difficult, if not impossible to make without analysis of synovial fluid. No specific test or physical finding has high specificity for solving this dilemma; however, some physical findings may prove helpful. A common periarticular structure that can be associated with a joint effusion is a Baker cyst (popliteal cyst).
If the swelling is secondary to joint effusion or inflammation, the entire articular capsule will be inflamed and distended and fluid can often be palpated within the joint. In the knee, this condition must be differentiated from effusion into the prepatellar bursa, where swelling distends the bursa that lies mainly over the lower portion of the patella, between it and the skin. Effusion into the joint occurs posterior to the patella, whereas bursal swelling occurs anterior to it ( Fig. 53.1 ). When considerable articular effusion of the knee is present, the capsule of the joint is distended and an inverted U-shaped swelling of the joint develops. This characteristic shape occurs because the dense patellar ligament prevents distention of the capsule along its inferior border. In addition, with the knee extended a large effusion causes the patella to “float” or lift away from the femoral condyles. Complete extension and flexion are often impossible because of the joint tension produced by the effusion.
Joint effusion causes limited movement of the joint in all directions, with active and passive motion producing pain. The pain arising from a pathologic condition involving a joint may be diffuse or clearly localized to the joint, or it may radiate. Hip pain, for example, frequently radiates into the groin or down the front of the thigh into the knee. Shoulder joint pain commonly radiates into the elbow or the neck. Therefore complete examination of contiguous structures is essential for adequate diagnosis.
In contrast, pain from a periarticular process is often more localized, and tenderness can be elicited only with certain specific movements or at specific points around the joint. In periarticular inflammation, one can often passively lead a joint through a range of motion with minimal discomfort, yet pain is significant when the patient attempts active motion. Crepitus may be elicited with tendinitis, or the pain may be traced along the course of a specific tendon.
Septic Arthritis
Acute monoarticular arthritis is a common problem in emergency medicine. Although acute monoarticular arthritis has many causes, septic arthritis is the one requiring most urgent diagnosis and treatment. Infectious arthritis is still relatively frequent, and suspicion of a septic process in the joint is the first step in appropriate management; confirmation requires arthrocentesis and culture of synovial fluid. In the ED, synovial fluid analysis is the diagnostic test most heavily relied on in making the diagnosis of an acute intraarticular infection. Culture remains the most definitive study, although it is not 100% sensitive. Gram stain may be helpful, but a negative Gram stain does not exclude the presence of a joint infection because not all infected joints have a positive Gram stain. Therapeutic arthrocentesis might need to be repeated when treating a septic joint. Such therapy is usually performed on an inpatient basis.
Infection of a joint occurs by one of several mechanisms: hematogenous spread (bacteremia, infective endocarditis, intravenous drug use) from a contiguous source of infection, direct implantation, postoperative contamination, or trauma. Septic arthritis is typically monoarticular with a swollen, erythematous, and painful joint. The noninfectious differential diagnosis includes crystal-induced arthritis, fracture, hemarthrosis, foreign body, osteoarthritis, ischemic necrosis, and monoarticular rheumatoid arthritis. In addition, osteomyelitis may mimic septic arthritis because of the close proximity of the infected metaphysis to the joint space. In many instances an acutely inflamed joint from gout or other arthritides simply cannot be distinguished from infection clinically. Nonetheless, early diagnosis is essential to prevent complications such as impairment of growth, articular destruction with ankylosis, osteomyelitis, and soft tissue extension.
Because an acutely swollen joint may be indicative of a number of disease entities, a thorough history and physical examination are the cornerstones of evaluation, followed by arthrocentesis ( Fig. 53.2 ). Laboratory findings can be useful in making a diagnosis, as can response to therapy (e.g., the response to empirical antibiotics in gonococcal arthritis is often the only criterion for diagnosis because the organism is difficult to culture from joint fluid). Blood cultures may be positive because joint infections may be due to hematogenous spread. Patients with malignancy (especially leukemia) or those who are immunosuppressed or otherwise debilitated are at particular risk for a septic cause. Infectious arthritis should be considered primarily in these patients, as well as in those with preexisting joint diseases such as rheumatoid arthritis. In general, a swollen joint is not usually injected with corticosteroids until the possibility of infection has been eliminated.
Neisseria gonorrhoeae, Staphylococcus (including methicillin resistant), and Streptococcus are the most frequently identified etiologic agents. N. gonorrhoeae is the most common organism causing septic arthritis in adolescents and young adults. Patients older than 40 years and those with other medical illnesses are more likely to have Staphylococcus joint infections. In children, Staphylococcus, Streptococcus, and Escherichia coli predominate. Haemophilus influenzae was a common cause of pediatric septic arthritis in the past, but widespread use of the conjugate vaccine has reduced H. influenzae infection rates to nearly zero. In neonates, staphylococci, Enterobacteriaceae, group B streptococci, and N. gonorrhoeae are the most likely organisms. Staphylococcal or pseudomonal infections commonly develop in injection drug abusers. Salmonella arthritis is more prevalent in patients with sickle cell disease than in the general population; however, more common organisms still predominate. Prosthetic joints or postoperative infections have high rates of Staphylococcus aureus, Streptococcus epidermidis, Enterobacteriaceae, and Pseudomonas infection.
The prevalence of community-acquired methicillin-resistant S. aureus (CA-MRSA) mandates special attention. Epidemiologic data on the incidence of CA-MRSA septic arthritis are sparse; however, one 2009 study noted that 50% of synovial fluid cultures in suspected septic arthritis ultimately grew MRSA. It would be prudent to consider empirical therapy for MRSA in those suspected of having septic arthritis until the results of culture become available. MRSA-infected joints can be multiple, progress rapidly, and be very destructive of joint tissue and adjacent bone.
Although precise incidence data for nongonococcal septic arthritis have not been established, predisposing factors have been described and include age 80 years or older, diabetes mellitus, rheumatoid arthritis, hip or knee prosthesis, joint surgery, and skin infection. The simultaneous occurrence of gout and septic arthritis is possible, and one should not allow the establishment of a diagnosis of crystal-induced disease to stop a thorough search for infection.
Because N. gonorrhoeae is the most common organism causing septic arthritis, gonococcal arthritis deserves special mention. Disseminated gonococcal infection occurs in 0.5% to 3% of cases of mucosal infection. Gonococcal septic arthritis is more common in women, especially during pregnancy or after menstruation, because women with sexually transmitted gonorrhea infections are more likely to be asymptomatic. The time needed for local infection to disseminate can vary from several days to weeks. Patients will often experience systemic symptoms, including fevers, chills, and malaise, as well as migratory polyarthralgia. Gonococcal tenosynovitis without joint involvement occurs in two thirds of patients. Dermatitis is also present in two thirds-of patients ( Fig. 53.3 ). The most common rash consists of scattered painless, nonpruritic 0.5- to 0.75-cm macules or papules with necrotic or pustular centers, distributed on the extremities and trunk. Eventually, the infection settles into one or two large joints to yield a purulent arthritis. Overt urethritis and vaginitis may be absent or overlooked because of concentration solely on the obvious joint pathology. Hence, it is important to realize that disseminated gonococcal infections can be associated with surprisingly minimal or even absent signs and symptoms of a genital infection source. Some joints may become inoculated through hematogenous spread from anal and oral sites of infection. Even though N. gonorrhoeae –infected joint fluid is usually “septic” in character, the yield of positive synovial fluid cultures has ranged from 25% to 50%. Blood cultures appear to be less helpful as they are positive in only 20% to 30% of cases. Because blood and joint fluid culture has a low yield, it would be prudent to culture all possible sites of gonococcal infection, including anal and pharyngeal sites. The organism can often be identified in asymptomatic genitourinary sites, with cultures from the primary mucosal site being positive in up to 80% of infected patients.
A positive Gram stain is immediately diagnostic of septic arthritis. However, Gram stains are positive in only 71% of gram-positive infections, 40% to 50% of gram-negative infections, and 25% of gonococcal infections. An elevated synovial white blood cell (WBC) count and a reduction in synovial fluid glucose may give confirmatory data. However, the synovial fluid WBC count in gonococcal arthritis is often between 10,000 and 20,000 cells/mm. Although mild leukocytosis and an elevated erythrocyte sedimentation rate may occur, normal laboratory values do not exclude infection.
Hemarthrosis
Isolated nontraumatic hemarthrosis may occasionally be seen by the emergency clinician. An inflammatory reaction may follow intracapsular bleeding, and the proliferative reaction and the hyperplastic synovium formed might predispose patients to recurrent hemorrhage in that joint, especially those with bleeding diatheses. The knee is the most commonly affected joint, followed by the ankle, elbow, shoulder, and hip.
The most common cause of intraarticular hemorrhage in the setting of no or minor trauma is a hereditary clotting factor deficiency such as hemophilia. Hemarthrosis is an infrequent complication of oral anticoagulant therapy but might occur even with prothrombin times within the normal range. Cessation of anticoagulant therapy in these patients must be weighed against the risk for adverse clot formation (e.g., acute cerebrovascular accident). Chronic arthritis does not appear to be a long-term complication in patients with intraarticular bleeding from oral anticoagulant therapy. Hemarthrosis may also be a complication of sickle cell anemia, pseudogout, amyloidosis, pigmented villonodular synovitis, synovial hemangioma, rheumatoid arthritis, and infection.
Management of acute hemarthrosis depends on the cause. Hemarthrosis associated with oral anticoagulant therapy improves only after use of the oral anticoagulant is discontinued and the prothrombin time returns to normal. Hemarthrosis after trauma is a frequent occurrence. It is most common in the knee and often denotes significant internal damage. A massively swollen knee after trauma is frequently seen with knee dislocation (occasionally with spontaneous relocation) and a tear of the anterior cruciate ligament. Intraarticular fractures can cause a significant hemarthrosis.
Distension of the joint by effusion or hemorrhage causes considerable pain and disability. If the fluid is not removed it is partially absorbed, but part of it may undergo organization and result in the formation of adhesions or bands in the joint. This is one argument for drainage of the joint. Some believe that in an otherwise healthy joint that is subjected to a single traumatic event, even a relatively large hemarthrosis will be spontaneously reabsorbed without significant sequelae and therefore presents no pressing need for drainage. Unfortunately, no literature exists to guide the best approach; hence, there is no universal standard of care regarding the need or lack thereof of draining blood from a traumatic joint.
Nonetheless, a large, tense, traumatic effusion is quite painful and its presence precludes proper evaluation of an injured joint. Therapeutic arthrocentesis to drain a symptomatic traumatic effusion is a common and well-accepted practice. The source of blood after trauma is frequently a tear in a ligamentous structure, capsule, synovium, or fracture. Cruciate (especially anterior) ligament injury is the most common cause of significant hemarthrosis after trauma to the knee. A joint effusion that develops 1 to 5 days after trauma may be secondary to a slow hemorrhage or reinjury, but the swelling is often caused by a nonhemorrhagic irritative synovial effusion.
Occasionally, one will diagnose an occult fracture by the presence of lipohemarthrosis, or fat globules in the arthrocentesis specimen ( Fig. 53.4 ). This may be appreciated when the bloody effusion is placed in a clear container (e.g., emesis basin) and held to a light. If the history of trauma is vague, arthrocentesis may be required to differentiate hemorrhage from other causes of joint effusion. An occult tibial plateau fracture is an example in which evaluating for lipohemarthrosis may be of particular value. Following therapeutic arthrocentesis for a hemarthrosis, it may be desirable to inject 2 to 15 mL, depending on joint size, of a long-acting local anesthetic (see Chapter 29 ) into the joint to facilitate examination or provide temporary relief of the symptoms.
Intraarticular Corticosteroid Injections
In 1951 Hollander and coworkers first demonstrated that intraarticular corticosteroid injections are useful for relief of symptoms in patients with severe rheumatoid arthritis. The use of steroids has proved to be a dependable method for providing rapid relief of pain and swelling of inflamed joints, although it is strictly local, usually temporary, and rarely curative. It is easily performed in the emergency setting. Acute gout responds well to joint injection, and this may be preferable in patients who cannot tolerate indomethacin or colchicine.
Corticosteroid injections are most helpful when only a small number of joints are actively inflamed. The most frequently used corticosteroids for intraarticular injection are shown in Table 53.1 . Diminution of joint pain, swelling, effusion, and warmth is usually evident within 6 to 12 hours after injection.
TABLE 53.1
Intrasynovial Corticosteroid Preparations a
From Gray RG, Gottlieb NL: Corticosteroid injections in RA: appraisal of a neglected therapy, J Musculoskelet Med 7:53, 1990. Reproduced by permission.
| PREPARATION | LARGE-JOINT DOSE (mg) | SMALL-JOINT DOSE (mg) b |
|---|---|---|
| Triamcinolone hexacetonide | 20 | 2–6 |
| Triamcinolone acetonide | 20 | 2–6 |
| Methylprednisolone acetate | 40 | 3.5–10.5 |
| Triamcinolone diacetate | 20 | 2–6 |
| Dexamethasone acetate | 5 | 0.5–1.5 |
a Listed in approximate descending order of duration of action.
b The dose will depend on joint size, capsular distensibility, and degree of inflammation.
Though very rare, the most serious complication of this practice is intraarticular infection. Therefore steroids should not be injected into a joint if a joint space infection is suspected. Repeated injections into one joint pose a risk for necrosis of juxtaarticular bone with subsequent joint destruction, instability, and suppression of the hypothalamic-pituitary axis from systemic absorption. Other complications include local soft tissue atrophy and calcification, tendon rupture, intraarticular bleeding, and transient nerve palsy. Transient elevations in blood glucose, as well as erythema, warmth, and diaphoresis of the face and torso, may also occur after intraarticular steroid injections. Acute pain, redness, and swelling 12 to 24 hours after steroid injection can mimic infection, but with this timing it is most likely an inflammatory reaction (steroid flare) to crystal-containing steroid preparation (often methylprednisolone). Deposition of steroid crystals on the synovium might give rise to a transient, self-limited flare-up of synovitis.
It is always important to determine whether local corticosteroid therapy has been used previously, not only to consider the array of clinical conditions associated with steroid use but also because crystalline corticosteroid material can hinder proper interpretation of crystals found in synovial fluid.
Equipment
The materials needed for arthrocentesis include skin preparation solutions (e.g., chlorhexidine); sterile gloves and drapes (optional in some cases); local anesthetic; syringes for injecting local anesthetic and aspirating joint fluid; a three-way stopcock for draining large amounts of fluid; lavender-, red-, and green-topped blood tubes; and various sizes of needles and intravenous catheters (see Review Box 53.1 ).
Depending on the size of the effusion to be drained, a 10-, 20-, or 30-mL Luer-Lok syringe can be used. If a large effusion is suspected, a three-way stopcock between the needle and the syringe allows complete drainage with a single joint penetration. Fluid for cell count should be collected in a lavender-topped tube; however, viscosity, protein, and glucose determinations do not require anticoagulants, and fluid should be placed in a red-topped tube. Though still common practice in many institutions, recent evidence suggests that synovial fluid protein and glucose levels are poor differentiators of noninflammatory and inflammatory effusions and are no longer recommended (see section on Synovial Fluid Interpretation later). Immediately examine fresh synovial fluid in its unadulterated form for crystals. Calcium oxalate and lithium heparin anticoagulants have been reported to introduce artifactual crystals into the fluid. Joint fluid to be analyzed for crystals should be collected in a green-topped tube containing sodium heparin. If culturing for N. gonorrhoeae, the fluid should be immediately placed on proper medium and stored in a low-oxygen environment in the ED.
Ultrasound Box 53.1: Arthrocentesis
Ultrasound offers a significant advantage when evaluating a patient with a complaint of joint pain. In patients with obesity or significant pain, limited physical examination makes the diagnosis of joint effusion difficult. Attempting blind aspiration in these patients may cause significant pain for the patient and frustration for the clinician. Ultrasound allows the physician to thoroughly evaluate the joint space for the presence of effusion and to plan the best approach for aspiration. The initial evaluation of the major joints is discussed hereafter, followed by a general approach to aspiration.
Knee
Although effusions of the knee are frequently diagnosed on physical examination alone and aspirated blindly, ultrasound allows the clinician to distinguish effusion from other conditions that may cause generalized swelling (such as bursitis).
A high-frequency transducer (7.5 to 10 mHz) should be used to allow the greatest resolution. Begin with the indicator pointing toward the patient's head (in longitudinal orientation) over the anterior aspect of the knee and attempt to locate the patella ( Fig. 53.US1 ). The patella can be seen as a brightly echogenic (white) object with posterior shadowing ( Fig. 53.US2 ). Locating the patella is key to distinguishing prepatellar bursitis, which will appear as a dark, fluid-filled collection superficial to the patella, and a joint effusion, which will appear as a dark, fluid-filled collection deep to the patella. Once the patella has been identified, move the transducer medially or laterally to “look under” the patella into the joint space ( Fig. 53.US3 ). Fluid will appear as a dark gray or black collection between the articular surface of the femur and fibula or tibia ( Fig. 53.US4 ). Once this area has been evaluated, move the transducer superiorly to evaluate the suprapatellar bursa, which lies superior to the patella and deep to the quadriceps tendon. The suprapatellar bursa communicates with the joint space and frequently houses a large amount of fluid ( Fig. 53.US5 ).
Shoulder
Either an anterior or posterior approach can be used to evaluate the shoulder. In the anterior approach, place the patient first in a seated position with the elbow adducted and the palm facing up. Then, place the high-frequency transducer in a transverse orientation over the approximate location of the biceps tendon ( Fig. 53.US6 ). The biceps tendon is an extracapsular extension of the joint and will be seen to distend with fluid when a joint effusion is present. A normal tendon can be seen to lie within the biceps groove of the humerus ( Fig. 53.US7 ). When surrounded by fluid, the tendon will be seen to “float” within an anechoic (black) area ( Fig. 53.US8 ).
To evaluate the joint from the posterior approach, place the patient in a seated position with the affected hand on the opposite shoulder to open the joint space. Then, place the transducer at the approximate location of the articulation of the humeral head with the glenoid ( Fig. 53.US9 ). In a normal joint, the humerus can be seen to articulate with the glenoid without any intervening fluid ( Fig. 53.US10 ). When an effusion is present, a dark gray or black collection can be seen medial to the glenoid ( Fig. 53.US11 ).
Ankle
The ankle joint is best evaluated in the longitudinal axis with the transducer placed over the space between the posterior edge of the tibia and the talus ( Fig. 53.US12 ). Slightly plantar-flexing the foot will enable the transducer to “fit” in this space. In a normal joint, the distal edge of the tibia can be seen to articulate with the talus without any intervening fluid ( Fig. 53.US13 ). When an effusion is present, it is seen as a triangular, dark gray or black pocket between the tibia and talus ( Fig. 53.US14 ). Ultrasound can also be used to identify the location of the dorsalis pedis artery before aspiration.
Elbow
The elbow is easily evaluated from the posterior approach. With this approach, place the transducer over the olecranon fossa with the elbow flexed and the lower part of the arm supported ( Fig. 53.US15 ). In a normal elbow the olecranon fossa can be seen as a slight “divot” between the olecranon of the ulna and the humerus ( Fig. 53.US16 ). When an effusion is present, dark gray or black fluid can be seen to distend this space ( Fig. 53.US17 ).
Hip
The hip joint is unique in that physical examination may suggest the presence of an effusion, but direct confirmation is difficult with traditional examination techniques. Ultrasound will easily confirm the presence of an effusion. To evaluate the hip joint, select a low-frequency transducer (3 to 5 mHz) initially because of the depth of the joint. In very thin patients, the distance from the skin to the joint may be small enough to allow the use of a high-frequency transducer. Align the transducer in a slightly oblique axis (mimicking the orientation of the femoral neck) along the inguinal area. It may be helpful to aim toward the umbilicus. Look for the femoral neck and head. They will appear as brightly echogenic outlines in the expected shape of the bones ( Fig. 53.US18 ). Once the femur has been identified, look for the joint capsule. It will appear as an arcing, hyperechoic line superficial to the bones ( Fig. 53.US19 ). In a normal hip there will be very little tissue between these two structures. There may be a small amount of anechoic or hypoechoic fluid present in this space in a normal hip, and correlation with the unaffected side will aid in evaluation. In the presence of a significant effusion, a large anechoic or hypoechoic fluid collection will be seen between the femoral neck and the capsule ( Fig. 53.US20 ).
Aspiration
Once the joint in question has been evaluated, the optimal site for aspiration can be planned. In contrast to the traditional, blind aspiration technique, the use of ultrasound may suggest an alternative approach. Ultrasound will enable the clinician to map the best approach to the effusion. Once this approach has been clarified, one of two techniques can be applied. The site can be marked and the aspiration can then proceed blindly under sterile conditions. In other cases it may be preferable to perform the tap under direct ultrasound guidance. In these circumstances the needle is inserted either from the transverse or from the long-axis approach and guided directly into the joint space.
General Arthrocentesis Technique
Joint fluid may be obtained even when there is little clinical evidence of an effusion. Although one may aspirate successfully at the point where the joint bulges maximally, certain landmarks are important. The most crucial part of arthrocentesis is defining the joint anatomy by palpating the bony landmarks as a guide. First, select a puncture site and an approach to the joint. Avoid tendons, major vessels, and major nerve branches. In most instances the approach is via the extensor surfaces of joints because most major vessels and nerves are found beneath the flexor surfaces. In addition, the synovial pouch is usually more superficial on the extensor side of a joint. Ultrasound may be particularly helpful in locating small effusions.
Use aseptic technique, including the use of sterile gloves and instruments, to avoid infection. Do not attempt arthrocentesis if there is a definite or suspected infection overlying the joint. Allow antiseptic preparation solution to dry for several minutes because the bactericidal effects of iodine are both concentration and time dependent. Remove the iodine solution with an alcohol sponge to prevent transference of iodine into the joint space, which can lead to an inflammatory process. Although the utility of draping is unproved and it may obscure the site, a sterile perforated drape may be placed over the joint.
With appropriate local anesthesia, arthrocentesis should be a relatively painless procedure; without anesthesia, it may be quite painful and distressing to the patient. The synovial membrane itself has pain fibers associated with blood vessels, and the articular capsule and periosteum are richly supplied with nerve fibers so both are very sensitive. The articular cartilage has no intrinsic pain fibers. It is important to have the patient relax during the procedure. Tense muscles narrow the joint space and make the procedure more difficult, often necessitating repeated attempts or resulting in inadequate drainage. Distraction of the joint may enhance the target area, especially in areas such as the wrist and finger joints. Traction not only increases the chance of entering the joint but also lessens the chance of scoring the articular cartilage with the needle.
To best accomplish anesthesia, infiltrate the skin down to the area of the joint capsule along the entire route of needle penetration. Use a local anesthetic agent such as 1% or 2% lidocaine (Xylocaine [AstraZeneca, Cambridge, United Kingdom]) via a 25- to 27-gauge needle. For extremely painful joints, a regional nerve block is appropriate.
Use the landmarks described in “ Specific Arthrocentesis Techniques ” later in this chapter. Take care not to bounce the needle off bony structures as a means of finding the joint space because this may cause unnecessary pain. However, in contrast to earlier beliefs, striking bone with the arthrocentesis needle is unlikely to damage articular cartilage. Attach an 18- to 22-gauge needle or intravenous catheter and needle set of suitable length to an appropriately sized syringe. Insert the needle at the desired anatomic point through the skin and subcutaneous tissue into the joint space. Use the largest needle that is practical to avoid obstructing the lumen with debris or clot. Large joints, such as the knee, can accommodate large effusions, so it is suggested that one use a 30- to 60-mL syringe because it may be difficult to change a syringe when the needle is within the joint cavity ( Fig. 53.5 ). A three-way stopcock placed between the needle and the syringe is an option for draining large effusions ( Fig. 53.6 ). If the syringe must be changed during the procedure, grasp the hub of the needle with a hemostat and hold it tightly while the syringe is removed. The authors prefer to use only a rigid needle and not a flexible catheter to perform arthrocentesis; however, a sturdy catheter is used by some clinicians. If an intravenous catheter and needle set is used, remove the needle while leaving the outer atraumatic plastic catheter in the joint space. Then attach the syringe to the catheter for aspiration. Manipulation of the joint or catheter can now occur with little threat of tissue injury.
Aspiration of synovial fluid and easy injection and return of fluid indicate intraarticular placement of the needle tip. As a general rule, try to remove as much fluid or blood as possible. If the fluid stops flowing, it indicates that the joint has been drained completely, the tip of the needle has become dislodged, or debris or clot is obstructing the needle. In this case, slightly advance or retract the tip of the needle, rotate the bevel, or lessen the force of aspiration. Never reintroduce a needle through a plastic catheter that has been left in the joint. Occasionally, reinjecting a small amount of fluid into the joint space confirms placement of the needle and may clear the needle. If fluid flows freely back into the joint and is easily reaspirated, one has probably removed all the fluid. If resistance is met, the needle has probably been jarred from the joint space and is lodged in soft tissue. In some instances, minor changes in position produced by flexion or extension of the joint may allow the fluid to flow more freely. Scraping or shearing the articular cartilage with the needle should be avoided. One should enter the joint in a straight line and avoid unnecessary side-to-side motion of the needle.
Send synovial fluid for studies as indicated by the clinical situation. Studies usually obtained include cell count with differential, crystal analysis, Gram staining, and bacterial culture and sensitivity analysis. Synovial protein, glucose, and lactate dehydrogenase determinations have been shown to be unreliable in distinguishing noninflammatory from inflammatory and infectious causes and are no longer recommended. Less frequently obtained studies include rheumatoid factor analysis, lupus erythematosus cell preparation, viscosity analysis, mucin clot, fibrin clot, fungal and acid-fast stains, Lyme titer, fungal and tuberculous culture, and synovial fluid complement analysis. If the arthrocentesis is performed for the relief of hemarthrosis, the fluid need not be sent for analysis. One should be selective in ordering tests. There is no need to order a large battery of tests routinely on all fluids. If the volume of fluid collected is low, Gram stain, culture, and examination of the “wet preparation” under regular and polarizing microscopy have the highest priority. Prompt examination of specimens should be performed to avoid misdiagnosing borderline inflammatory fluids, missing crystals that dissolve with time, or overinterpreting the findings because of new artifactual crystals that appear over a prolonged time.
Complications
Significant complications are rare with arthrocentesis but include the following:
- 1.
Infection. Skin bacteria may be introduced into the joint space during needle puncture. Nevertheless, infection occurs rarely because the bacteria are either quickly cleared or not viable. One can further limit this complication by maintaining rigorous sterile technique and avoiding insertion of the needle through obviously (or possibly) infected skin or subcutaneous tissue. Various studies report the incidence of infection after routine arthrocentesis to be in the range of 1 in 10,000. However, in immunocompromised patients, particularly those with rheumatoid arthritis, the incidence is higher (1 in 2000 to 10,000 aspirations). Joint aspiration in the presence of bacteremia was discussed previously. Acute pain, redness, and swelling 12 to 24 hours after steroid injection can mimic infection but is most likely an inflammatory reaction (steroid flare) to the steroid preparation (often methylprednisolone).
- 2.
Bleeding. Bleeding with subsequent hemarthrosis is rarely a complication, except in patients with a bleeding diathesis. In those with a bleeding diathesis such as hemophilia, arthrocentesis should be delayed until clotting competence has been enhanced by infusing specific clotting factors. In general, spontaneous bleeding into a hemophiliac patient's joint is an indication for replacement of clotting factors. Occasionally, a small quantity of blood may be aspirated along with synovial fluid. This happens most often when the joint is nearly emptied. A small amount of blood-tinged fluid is generally the result of nicking a small synovial blood vessel and is usually inconsequential.
- 3.
Arthrocentesis and joint injections in patients receiving chronic warfarin therapy, with a therapeutic INR, were shown to be safe by Ahmed and Gertner, without an increased risk of bleeding complications. In this study of 456 procedures in patients on chronic warfarin therapy, there was no statistically significant difference in the overall complication rate between patients with an INR of 2.0 or greater and patients with an INR less than 2.0. Of note, 103 of 456 procedures (22.5%) were safely performed in patients with an INR greater than 3, with the highest INR being 7.8.
- 4.
Allergic reaction. Hypersensitivity to the local anesthetic can usually be prevented by thorough history taking. Facial and torso flushing associated with corticosteroid injection may represent an idiosyncratic reaction to preservatives in the steroid preparation. Fainting during the procedure is not uncommon and most often the result of vasovagal influences. To help prevent this, perform the procedure with the patient lying down whenever possible.
- 5.
Corticosteroid-induced complications. See earlier section on Intraarticular Corticosteroid Injections .
Specific Arthrocentesis Techniques
Arthrocentesis of the hip is generally performed by an orthopedic surgeon under fluoroscopic, ultrasound, or magnetic resonance imaging, or computed tomography guidance and is not discussed here. If available, fluoroscopy or ultrasound can also be used to guide aspiration of other joints, but these imaging adjuncts are not generally required. For small joints, application of traction is often very helpful in obtaining fluid. While applying continuous suction to the aspirating syringe, walk the needle over palpated bone until the joint is entered or fluid is obtained. However, it may be quite difficult to obtain fluid from small joints in the hand and foot, so the clinician must often treat empirically. If only one drop of fluid is obtained from small joints, it is best to send it for culture.
First Carpometacarpal Joint ( Fig. 53.7 )
Landmarks.
The radial aspect of the proximal end of the first metacarpal is the arthrocentesis landmark for this joint. Locate the abductor pollicis longus (APL) tendon by active extension of the tendon.
Position.
Oppose the thumb against the little finger so that the proximal end of the first metacarpal is palpable. Apply traction to the thumb to widen the joint space between the first metacarpal and the greater multangular (trapezium) bone.
Needle Insertion.
Insert a 22- to 23-gauge needle at a point proximal to the prominence at the base of the first metacarpal on the palmar side of the APL tendon.
Comments.
Degenerative joint disease commonly affects this joint. Arthrocentesis is moderately difficult. The anatomic “snuffbox” (located more proximally and on the dorsal side of the APL tendon) should be avoided because it contains the radial artery and superficial radial nerve. A more dorsal approach may also be used.
Interphalangeal and Metacarpophalangeal Joints ( Fig. 53.8 )
Landmarks.
The landmarks are located on the dorsal surface. For the metacarpophalangeal joints, palpate for the prominence at the proximal end of the proximal phalanx. For the interphalangeal joints, palpate for the prominence at the proximal end of the middle or distal phalanx. The extensor tendon runs down the midline.
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