Table 1 Diagnostic criteria for CPP crystal deposition

I

Proof of calcium pyrophosphate crystals by x-ray diffraction or chemical analysis

IIa

Corrected polarization microscopy confirms triclinic and monoclinic crystals showing weak positive birefringence

IIb

Typical calcification image on x-ray

IIIa

Acute arthritis

IIIb

Chronic arthritis

IIIb1

Arthritis in areas where primary OA is usually rare

IIIb2

Narrowing of the joint cleft of the radial carpal joint or patellofemoral joint

IIIb3

Subchondral cyst

IIIb4

Severe progressive degeneration with subchondral bony subsidence and fragmentation with intra-articular radiopaque bodies

IIIb5

Variable osteophyte formation

IIIb6

Tendon calcification

IIIb7

Axial skeletal lesions, subchondral cysts of the epiphyseal and sacroiliac joints, intervertebral disc calcification and vacuum phenomena in multiple vertebral bodies, sacroiliac vacuum phenomena