Popliteal cysts may be caused by joint injury, inflammatory reaction, adverse irritation and so on. 1. Joint injury: it may be caused by meniscus injury, anterior cruciate ligament injury, etc. Swelling and pain may appear at the injury site, and then popliteal cyst may also be formed. 2. Inflammatory reaction: caused by inflammatory diseases such as knee osteoarthritis, gouty arthritis, rheumatoid arthritis and so on. Due to the stimulation of inflammation, patients may have joint effusion, which may cause popliteal cyst. 3. Adverse stimuli: such as long-distance walking, mountain climbing, long-term standing and other reasons, can make the gastrocnemius semitendinosus muscle capsule expansion, joint fluid into the dilated muscle capsule, thus forming a popliteal cyst. It is recommended that patients with popliteal cysts go to the hospital in a timely manner, do the relevant examinations to clarify the cause of the disease, and then follow the doctor’s instructions for treatment to avoid delaying the condition.