Crystal deposits have been observed in equine articular cartilage and
identified by scanning electron microscopy and X-ray diffraction as oc
tacalcium phosphate and calcium pyrophosphate dihydrate. Of 89 equine
fetlock joints examined 10 contained evidence of calcification visible
by eye. It is suggested that the deposition of crystals may be a medi
ator of arthritis in horses and may also cause damage directly.