• To obtain synovial fluid for analysis in order to differentiate joint disease caused by crystal-induced arthritis or septic arthritis
  • To determine if an intra-articular fracture is present
  • To determine if a laceration communicates with the joint space.
  • To relieve pain from hemarthrosis by removing blood from joint space.
  • Absolute: Infection in the tissues overlying the puncture site
  • Relative: Known bacteremia that may lead to hematogenous spread of bacteria into the joint
  • Always use sterile technique to prevent infection.
  • Local anesthesia can be used to reduce pain of procedure.
  • Ultrasonography may be used to assess for the presence and location of synovial fluid.


  • The elbow is flexed to 90 with forearm pronated and palm flat on a table.
  • A 22-Ga needle is inserted from the lateral aspect distal to the lateral epicondyle and directed medially.


  • The patient should sit upright with the arm at the side and his or her hand in the lap.
  • A 20-Ga needle is inserted at a point inferior and lateral to the coracoid process and is directed posteriorly toward the glenoid rim.


  • The knee can either be fully extended or flexed to 15-20 by placing a towel under the knee to open up the joint space.
  • The foot is kept perpendicular to the floor. An 18-Ga needle is inserted at the midpoint or superior portion of the patella approximately 1 cm medial to the anteromedial patellar edge.
  • The needle is directed between the posterior surface of the patella and the intercondylar femoral notch.


  • The patient is positioned supine with the foot plantar flexed.
  • A 20- to 22-Ga needle is inserted at a point just medial to the anterior tibial tendon and directed into the hollow at the anterior edge of the medial malleolus.
  • The needle must be inserted 2 to 3 cm to penetrate the joint space.
  • Studies usually obtained include cell count with differential, crystal analysis, Gram stain, bacterial culture and sensitivity analysis, and synovial fluid glucose measurement. Less frequently obtained studies include protein
    measurement, rheumatoid factor analysis, fungal and acid-fast stains, lyme titer, fungal and tuberculous culture, and complement analysis.
  • Infection, bleeding, allergic reaction to local anesthesia
  • WBC >50,000/mm3 is highly suggestive of a septic joint. WBC >50,000/mm3 may be seen with gout. The presence of crystals, the absence of bacteria on Gram stain and culture, and the clinical presentation should help differentiate between septic and crystal-induced synovitis.
  • A high percentage of neutrophils on the differential suggests a septic joint even if WBC <50,000/mm3.
  • Joint fluid-to-serum glucose ratio <50% suggests a septic joint.
  • Crystal analysis: Gout is caused by monosodium urate crystals, which are negatively birefringent. Pseudogout is caused by calcium pyrophosphate crystals, which are positively birefringent.
  • Presence of fat globules in joint fluid indicates presence of a fracture extending into the joint.
  • If you suspect septic arthritis, perform an arthrocentesis. No other test allows you to exclude the diagnosis with confidence.
  • Pseudogout is caused by calcium Pyrophosphate crystals that are Positively birefringent