A RCT of arthroscopic internal drainage of popliteal cysts with or without cyst wall resection

INTERVENTION: internal drainage group:arthroscopic internal drainage of popliteal cysts without cyst wall resection.;internal drainage with cyst wall resection group:arthroscopic internal drainage of popliteal cysts with cyst wall resection.; CONDITION: popliteal cyst PRIMARY OUTCOME: popliteal cyst disappearing rate at post‐operative 12 months; SECONDARY OUTCOME: Rauschning and Lindgren classification;Lyshom score;pain scores(VAS);Surgery time;Complication rate; INCLUSION CRITERIA: 1: 18‐75 years 2: patients with unicameral popliteal cysts 3: patients who have failed conservative treatment (3 recurrences within 1 year or 2 recurrences within 6 months), or who have a cyst = 3 cm in the smallest diameter with significant clinical symptoms.