Arthrocentesis and
Therapeutic Joint
Injection: An Overview
for the Primary
Care Physician
R. Brian Bettencourt, MD*, Michael M. Linder, MD
Arthrocentesis is a safe and useful primary care procedure. Joint aspiration and
injection can be both diagnostic and therapeutic; it can allow identification and treatment of pathologic agents as well as provide significant pain relief. There are
numerous conditions affecting adults and children that may lead to mono- or polyarticular joint swelling. Causes can range from rheumatic to infectious to idiopathic, and
thorough investigations of each may require specific serologic studies or specialist
consultation. This review provides current and practical recommendations for
evaluation and localized treatment of effusive joint pain by the primary care physician.
INDICATIONS AND CLINICAL EVIDENCE
Multiple indications exist for arthrocentesis. Synovial fluid aspiration may be indicated
in any joint with an effusion, or even in a normal-appearing joint when the diagnosis is
in doubt. There are many causes for joint effusions in adults and children (Table 1).
When evaluating a synovial effusion of unknown origin, aspiration is indicated.1 Arthrocentesis is essential for the diagnosis and management of the acute hot red joint,
which may be a medical emergency secondary to the morbidity and mortality associated with septic arthritis.2
With or without subsequent therapeutic injection, arthrocentesis of a joint effusion
can often provide pain relief. Traumatic injury to a joint may cause hemarthrosis and
effusions ranging from small to large, tense and painful. Aspiration of large traumatic
effusions can ease pain and allow for increased range of motion.
The authors have nothing to disclose.
Family Medicine Residency Program, University of South Alabama, 1504 Springhill Avenue,
Room 3414, Mobile, AL 36604, USA
* Corresponding author.
E-mail address: rbettencourt@usouthal.edu
KEYWORDS
Arthrocentesis Joint Effusion Steroid Injection
Prim Care Clin Office Pract 37 (2010) 691–702
doi:10.1016/j.pop.2010.07.002 primarycare.theclinics.com
0095-4543/10/$ – see front matter 2010 Published by Elsevier Inc.
CONTRAINDICATIONS
Diagnostic arthrocentesis has few contraindications. Periarticular cellulitis or infection
is considered an absolute contraindication to joint aspiration. The concern is that the
joint might be seeded by organisms of the overlying skin infection during percutaneous access. However, if the joint is believed to be the cause of the infection,
diagnostic aspiration should be performed. The attempt should be made through an
area of appropriately prepared uninvolved skin. Joint access through an area of
irregular or disrupted skin, such as in psoriasis, should be avoided because of
increased numbers of colonizing bacteria in these areas.3
Septicemia has been considered a contraindication to arthrocentesis secondary to
the possibility of introducing organisms into the joint space. The morbidity and
mortality associated with a septic joint are substantial. Joints with a high suspicion
for bacterial infection should probably undergo aspiration regardless of the presence
of septicemia. Septicemia may be the initial finding in young children with bacterial
arthritis. The risk of leaving a septic joint improperly treated seems to outweigh the
theoretic risk of seeding.
In patients with bleeding disorders or who are taking anticoagulants, joint aspiration
is contraindicated. Inducing traumatic hemarthrosis is a concern. However, the risk of
significant hemarthrosis after arthrocentesis is low. At least 1 study showed that even
in patients on warfarin therapy with international normalized ratios of 4.5, there was not
an increased risk of significant bleeding.4
COMPLICATIONS OF ARTHROCENTESIS
Generally, the most feared complication of arthrocentesis is iatrogenic infection.
Although there is a lack of recent large studies, iatrogenic infection after arthrocentesis
seems rare but remains a possible complication. In studies in which injection sites were
stained before percutaneous needle access of a joint, investigators were able to arthroscopically identify transferred fragments of the stained skin within the joint in most
cases.5 Although iatrogenic infection seems rare, these findings serve to reinforce
the importance of sound aseptic technique and skin preparation during the procedure.
SYNOVIAL FLUID AND EFFUSIONS
There are numerous causes for joint effusions. The gross appearance of synovial fluid
can provide clues related to the type and degree of joint pathology.
Table 1
Differential of an acute joint with effusion
Infectious Osteoarthritis
Bacterial Rheumatologic
Viral Rheumatoid arthritis
Lyme disease Juvenile idiopathic arthritis
Bacterial endocarditis sequelae Systemic lupus erythematosus
Crystalline disease Spondyloarthropathy
Gout Transient synovitis
Pseudogout (CPPD) Systemic vasculitis
Hydroxyapatite Neoplastic
Hemarthrosis Pigmented villonodular synovitis
Coagulopathy Metastatic disease
Trauma Idiopathic
Data from Refs.1,2,27,28,32–38
692 Bettencourt & Linder
Historically, 1 step in clinical diagnosis has been to assign results of synovial fluid
visual inspection to 1 of 5 categories: normal, inflammatory, noninflammatory, hemorrhagic, or septic (Table 2). Each category can have an association with a specific
disease process.
On visual inspection, inflammatory-appearing fluid may suggest crystalline joint
disease or any number of rheumatologic conditions. Noninflammatory appearing fluid
may be present in joints with osteoarthritis. It is important to remember during clinical
decision making that there can be significant overlap between categories.
Normal synovial fluid is clear, colorless to pale yellow, and highly viscous. Fluid of an
inflammatory source ranges from yellow to greenish yellow and may be white in the
crystalline arthropathies (eg, gout, calcium pyrophosphate dehydrate [CPPD]). Septic
joints can yield greenish, gray, or purulent fluid. Red, rusty, or brownish fluid suggests
hemarthrosis. The viscosity and turbidity of synovial fluid varies with the cause.
Turbidity can be expected to increase with the degree of inflammation.3
Viscosity can be variable. The “string sign” has been used as a subjective examination whereby normally viscous fluid dripped out of a syringe stretches to 3 cm in length
before breaking. Inflammation with release of proteolytic enzymes generally
decreases synovial fluid viscosity. However, septic fluid may show increasing
viscosity with increased purulence.
LABORATORY ANALYSIS OF SYNOVIAL FLUID
Laboratory analysis of synovial fluid is the single most important assessment
technique when investigating an effusion of unclear etiology. It is essential in any
investigation of a suspected septic joint. Synovial fluid analysis also allows for
diagnosis of specific crystalline arthropathies, and helps to determine whether the
cause may be inflammatory or noninflammatory.
For formal study, collected synovial fluid can be divided into 4 aliquots. One of the 4
should be a sterile tube with anticoagulant for bacteriologic studies. One tube with ethylenediaminetetraacetic acid should be sent for routine cytology, and another tube
without anticoagulant should be prepared for crystal search and analysis. The remaining fluid may be reserved for other specialized studies if indicated.5
Often the volume of available fluid for study may be limited. Ruling out a septic
etiology is the primary concern when evaluating an effused joint. In such cases,
laboratory analysis of synovial fluid should include a white blood cell (WBC) count
with differential, Gram stain, and culture.
CYTOLOGY
Normal synovial fluid should be nearly free of cells. Samples indicating an inflammatory cause show increasing numbers of leukocytes, with the WBC cutoff of 2000
cells/mL generally accepted as distinguishing noninflammatory from inflammatory
Table 2
Gross visual inspection of synovial fluid aspirate
Normal Noninflammatory Inflammatory Infectious Hemorrhagic
Appearance Clear to
pale yellow
Clear,
yellow
Cloudy,
yellow
Purulent or
cloudy
Bloody
Viscosity High High Low Variable Variable
Data from Refs.1,2,27,28,32–38
Arthrocentesis and Therapeutic Joint Injection 693
conditions. The widely accepted WBC count defining septic synovial fluid has
classically been greater than 50,000 WBC/mL.6 However, in one recent study of
culture-positive synovial fluid aspirates, 39% had synovial WBC counts of less than
50,000 cells/mL.7 Another similar study found greatly increased likelihood for septic
arthritis with synovial WBC counts equal to or greater than 25,000 cells/mL, but
a polymorphonuclear leukocyte count less than 90% significantly decreased the likelihood of a septic cause. Thus 25,000 cells/mL may be a more accurate threshold if
there is concern regarding septic arthritis.8
Additional information regarding synovial fluid findings can be found in Table 3.
CRYSTAL DETECTION
Synovial fluid analysis is useful in establishing a diagnosis of crystal-induced arthritis.
The CPPD of pseudogout appear as positively birefringent rhomboid crystals under
polarized microscopy. Definitive diagnosis of CPPD generally requires the addition
of characteristic joint findings on imaging. The monosodium urate crystals of gout
are negatively birefringent under polarized light microscopy, and their presence is
diagnostic of gout.
GRAM STAIN AND CULTURE
Studies to evaluate for microbes are essential in the evaluation of an effusion of
unknown cause. The sensitivity of the Gram stain in bacterial arthritis is generally
50% to 70%, with the exception being gonococcal arthritis (perhaps <10%).9,10
Cultures are generally positive in most cases of bacterial arthritis, the exception again
being gonococcal arthritis (<50%).11,12 Even in joint aspirates from patients with
confirmed crystal-induced arthritis, one study reported that 1.5% had concomitant
synovial bacterial infections.13 In the setting of an unexplained joint effusion the synovial fluid investigation should include Gram stain and culture even if the fluid appears
inflammatory.
Table 3
Synovial fluid analysis
Normal Noninflammatory Inflammatory Infectious
Culture Negative Negative Negative Often
positive
WBC/mL <200 <200–2000 200–50,000 >25,000–
50,000
Polymorphonuclear
leukocytes (%)
<25 <25 >50 >50–90
Crystals Negative Negative Positive
or none
None
Associated
conditions
Osteoarthritis Rheumatic diseases,
crystalline
diseases,
spondyloarthropathies,
systemic lupus
erythematosus
Septic
arthritis
Data from Refs.