9.09 Acute Monarticular Arthritis

agk’s Library of Common Simple Emergencies

Presentation

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.

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