Synovial Fluid Crystals

Monosodium urate (MSU) crystals

Needle-shaped
Intracellular, approximate diameter of neutrophil
Strongly negatively birefringent (yellow)
Gout

Calcium pyrophosphate dihydrate (CPPD) crystals

Rhomboid-shaped
Weakly positively birefringent (blue)
Psuedogout
Chondrocalcinoisis (x-ray)
Osteoarthritis

Calcium basic phosphate (CBP) crystals

Small - only identified by electron microscopy
Not birefringent
Clumps of crystals (shiny coins) under LM
Alizarin red stain to detect calcium-containing crystals
Acute inflammatory arthritis (young people)
Milwaukee shoulder (older people)

Calcium oxalate crystals

bipyramidal and envelope shaped
Stain with alizarin red
Primary oxaluria (autosomal recessive)
Kidney failure on hemodialysis

Cholesterol crystals

Very large
Flat and rectangular shaped
Notched corners
Varying birefringence
Rheumatoid arthritis

Corticosteroid crystals

Iatrogenic
Strongly variably birefringent
Polymorphic clumps, rods, or rhomboids
May cause joint pain for several hours

Talc crystals

Iatrogenic
Originate from latex gloves during arthrocentesis
Strongly birefringent
Maltese cross pattern

Free fat

oil-red-O - stains droplets red
osmic acid - stains droplets black
Most likely result of trauma (intra-articular fracture)

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Synovial Fluid Crystals

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