Table 1

Intrinsic and extrinsic crystals and particles detected in synovial fluid

Extrinsic crystals or particles (introduced from outside)Intrinsic crystals or particles (formed within the joint)
Pathogenic Non-pathogenic Pathogenic Non-pathogenic
Corticosteroid can cause short lived inflammatory episodeFrom air - dust, fungal spores, (lens) tissue fibres, etc; many are birefringentMSUM −vely birefringent needles 1–20 μm. Can form in “beachball” arrayFibrin. Hair-like strands under HP 1000X. Found in many SF
Storage artefacts - Brushite, +vely birefringent rods 10 μm+ in “star-bursts”CPPD +vely birefringent rods/rhomboids. 1–20 μm. Can form “beachballs” Non-birefringent 1–20 μm “broken glass” cartilage in all SF
Larger (100 μm+) birefringent “silk-sheen” cartilage in damaged/arthritic joints.
“Drying-out” SF gives spectacular birefringent particles resembling MSUM, CPPD, etcBCP - submicroscopic, very weakly birefringent. Aggregates 2–80 μm visible if stained.Meniscal fragments = silksheen + fibrillar appearance. Fragments many contain CPPD/MSUM
Ovoid starch granules from gloves, 10–100 μm+ birefringent weak “Maltese cross” NB Mixed crystal populations are commonFragments of fibrillar cruciate ligament - joint injury
Corticosteroids (all strongly birefringent crystals 1–40 μm)CPPD + BCP (often)Fragments of synovium - villi + birefringent fibrous core
MSUM + CPPDRice bodies - aggregates of synovial tissue in RA SF
Lederspan (1–10 μm) resembles CPPDMSUM + cholesterol, etcLipid crystals - 1–30 μm ovoids. Birefringent. Bright “Maltese cross”
Cholesterol 5–40 μm. +vely birefringent notched plates. Lipid globules - non-birefringent (resemble air bubbles)