Calcium pyrophosphate deposition disease (CPPD) - oftenly known as Pseudogout or Chondrocalcinosis, occurs due to deposition of calcium pyrophosphate dihydrate (CPPD) in the joints (in the form of crystals) especially in the articular and fibrocartilage. Inflammation occur due to body's reaction to these crystals. Science don't know why body is creating these crystals but it's probably abnormality in the cartilage cells or connective tissue. The cause of this disease may also be genetic.
This condition causes pain, redness, swelling and heat in the joint (or more joints). Due to cartilage damage and rubbing bones it can cause serious damages to the joint.
Treatments inlude exercises, rest, medications, removing fluid and crystals and as the last solution surgery.

Risk of this kind of Arthritis rises with age, although many people experience presence of CPPD crystals in their twenties but not everyone will have symptoms. CPPD affects knees most oftenly, but it occurs also in ankles, elbows, wrists, hands and shoulders.
It can usually be mistaken with Gout but the difference is in cause of forming crystals which in case of Gout is uric acid, not CPPD.