The patient complains of one joint which has become acutely
red, swollen, hot, painful, and stiff.
What to do:
Ask about previous, similar episodes in this or other
joints, as well as trauma, infections, or rashes, and
perform a thorough physical examination looking for evidence
of the same. Ask for a history of gout.
Examine the affected joint, and document the extent of
effusion, involvement of adjacent structures, et cetera. Fluid can often be detected by pressing on one side of the affected joint and at the same time palpating a wavelike fluctuance on the opposite side of the joint.
Cleanse the skin over the most superficial area of the
joint effusion with alcohol and povidone-iodine (Betadine),
anesthetize the skin with 1% plain buffered lidocaine, and aspirate
as much joint fluid as possible through an 18-20 gauge needle,
using aseptic technique throughout. Fluoroscopy may be valuable in guiding needle placement for hip or shoulder joint aspiration.
Grossly examine the joint aspirate. Clear, light yellow
fluid is characteristic of osteoarthritis or mild
inflammatory or traumatic effusions. Grossly cloudy fluid is
characteristic of more severe inflammation or bacterial
infection. Blood in the joint is characteristic of trauma (a
fracture or tear inside the synovial capsule) or bleeding
from hemophilia or anticoagulants.
One drop of joint fluid may be used for a crude string or
mucin clot test. Wet the tips of two gloved fingers with
joint fluid, and repeatedly touch them together and slowly
draw them apart. As this maneuver is repeated 10 or 20
times, and the joint fluid dries, normal synovial fluid will
form longer and longer strings, usually to 5-10 cm in
length. Inflammation inhibits this string formation. This is a non-specific test, but may aid decision at the bed side.
The essential laboratory tests on joint fluid consist of a
Gram stain and culture for possible septic arthritis. (The
presence of urate crystals may sometimes be detected on the
wet prep or Gram stain.)
A joint fluid leukocyte count is the next most useful test
to order. A count greater than 50,000 white cells/mm3 is
characteristic of bacterial infection (especially when most
are polymorphonuclear leukocytes). In osteoarthritis, there
are usually fewer than 2,000 WBCs/mm3, and inflammatory
arthritis (such as gout and rheumatoid arthritis) falls in
the middle range of 2,000-50,000 WBCs/mm3. If there is more fluid, send to the lab for a glucose level, which will be low in infection compared to serum.
Obtain x rays of the affected joint to detect possible
unsuspected fractures, or evidence of chronic disease, such
as rheumatoid, crystal-induced or osteoarthritis.
If there is any suspicion of a bacterial infection (based on fever, elevated ESR, cellulitis, lymphangitis, or the joint fluid results above) start the patient on appropriate antibiotics which will have a high concentration in the synovial fluid. The
most common, and the most devastating, organism requiring
treatment is Staphylococcus aureus, which may be adequately
treated with oral dicloxacillin or cephalexin 500mg q6h, but, since patients with this infection must be very closely followed, it is usually more practical to admit them to the hospital on intravenous antibiotics. In sexually-active patients, look for gonorrhea. In nursing home patients with urinary tract infections there could be gram-negative organizms. In intravenous drug abusers both staph and gram-negatives.
Inflammatory arthritis may be treated with non-steroidal
anti inflammatory medications, beginning with a loading dose
such as indomethacin (Indocin) 50mg or ibuprofen (Motrin)
800mg, tapered to usual maintenance doses.
When joint fluid cannot be obtained to rule out infection,
it may be a good tactic to treat simultaneously for
infectious and inflammatory arthritis.
Splint and elevate the affected joint and arrange for
admission or followup.
What not to do:
Do not tap a joint through an area of obvious contamination such as subcutaneous cellulitis. You may innoculate synovial fluid with bacteria.
Do not be misled by bursitis, tenosynovitis, or myositis
without joint involvement. An infected or inflamed joint
will have a reactive effusion, which may be evident as
fullness, fluctuance, reduced range of motion, or joint
fluid which can be drawn off with a needle. It is usually
difficult to tap a joint in the absence of a joint effusion.
Do not instil local anesthetics in the inflammed joint as an ED procedure. They will mask symptoms transiently without treating the underlying problem.
Do not use NSAIDs when a patient has a history of active peptic ulcer disease with bleeding. Relative contraindications include renal insufficiency, volume depletion, gastritis, inflammatory bowel disease, asthma and congestive heart disease.
Do not start maintenance NSAID doses for an acute inflammation. It will take a day or more to reach therapeutic levels and pain relief.
Discussion
The urgent reason for tapping a joint effusion is to rule out
a bacterial infection, which could destroy the joint in a
matter of days. Beyond identifying an infection (with Gram
stain, culture, and WBC) further diagnosis of the cause of
arthritis is not particularly accurate nor necessary to
decide on acute treatment. Reducing the volume of the
effusion may alleviate pain and stiffness, but this effect
is usually short-lived, as the effusion reaccummulates
within hours. Identification of crystals is essential for the diagnosis of gout or pseudogout, but one acute attack may be treated the same as another inflammatory arthitis and exact diagnosis deferred to follow up.
Infants and young childen may present with fever and reluctance to walk from septic arthitis of the hip or knee, and arthrocentesis may require sedation or general anesthesia.
