What are the possible complications of osteoarthritis of the knee?

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There can sometimes be rarer complications with osteoarthritis of the knee, including deposits of calcium crystals in your cartilage and cysts forming at the back of your knee.

Osteoarthritis with crystals

Chalky deposits of calcium crystals can form in your cartilage. This is called calcification or chondrocalcinosis. The crystals show up in x-rays and can be seen under a microscope in samples of fluid taken from your joint.

Osteoarthritis tends to become more severe more quickly when crystals have formed. Sometimes the crystals can shake loose, causing a sudden attack of very painful swelling called acute calcium pyrophosphate crystal arthritis (acute CPP crystal arthritis), which has previously been called 'pseudogout'.

Read more about calcium crystal diseases.

Baker’s cysts (popliteal cysts)

Baker’s cysts can form when extra joint fluid is being produced by the joint and some of it becomes trapped in a pouch (hernia) sticking out of the joint lining. They’re often painless, but you may be able to feel a soft-to-firm lump at the back of your knee. Sometimes a cyst can cause aching or tenderness when you’re exercising.

Occasionally a cyst can press on a blood vessel, which can lead to swelling in your leg, or the cyst may burst (rupture) and release joint fluid into your calf muscle, which can be very painful.

A cyst may not need treatment, but if it does the extra fluid can be drawn from your knee using a syringe (this is called aspiration) and a steroid solution can be injected into it.

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