■ To determine if a laceration communicates with the joint space.
■ To relieve pain from hemarthrosis by removing blood from joint space.
CONTRAINDICATIONS
■ Absolute: Infection in the tissues overlying the puncture site
■ Relative: Known bacteremia that may lead to hematogenous spread of
bacteria into the joint
TECHNIQUE
■ 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.
■ Elbow: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 lat-
eral epicondyle and directed medially.
■ Shoulder: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 gle-
noid rim.
■ Knee:The knee can either be fully extended or flexed to 15–20°by plac-
ing a towel under the knee to open up the joint space. The foot is kept per-
pendicular to the floor. An 18-Ga needle is inserted at the midpoint or
superior portion of the patella approximately 1 cm medial to the antero-
medial patellar edge. The needle is directed between the posterior surface
of the patella and the intercondylar femoral notch.
■ Ankle: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 ten-
don and directed into the hollow at the anterior edge of the medial malle-
olus. The needle must be inserted 2 to 3 cm to penetrate the joint space.
■ Studies usually obtained include cell count with differential, crystal analy-
sis, 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.
COMPLICATIONS
■ Infection, bleeding, allergic reaction to local anesthesia
INTERPRETATION OFRESULTS
■ WBC >50,000/mm^3 is highly suggestive of a septic joint. WBC >50,000/mm^3
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/mm^3.
■ 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.
PROCEDURES AND SKILLSIf 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.