Recently, the Department of Orthopaedic Surgery of our hospital applied arthroscopy to perform microscopic N-fossa cyst excision and successfully cured a patient with N-fossa cyst. The success of this new procedure launched a new exploration for the minimally invasive treatment of N-fossa cyst and filled the gap in the field of arthroscopy in Gaoming. The patient was an elderly female, a native of Xi’an, Gaoming, who had been squatting for a long time and had been suffering from left knee pain for the past six months, with significant pain from deep squatting. “After careful history and physical examination, Dr. Li Bei, the doctor in charge, determined that the primary cause of the knee pain was injury to the posterior horn of the medial meniscus and the cyst in the N fossa was a secondary symptom, and preoperative MRI proved that the posterior horn of the medial meniscus of the patient’s left knee was torn and a semitendinosus cyst was formed. In the past, conventional surgery was only able to remove the extra-articular N-fossa cyst from the posterior approach, but the primary intra-articular lesion could not be resolved, which was not only traumatic but also had a high recurrence rate. After thorough preoperative preparation, Dr. Li Bei successfully performed an arthroscopic medial meniscus revision + N fossa cyst excision, taking a conventional arthroscopic approach to remove the posterior horn of the medial meniscus and a posterior approach to enlarge the inner opening of the N fossa cyst. Currently, domestic and international studies have shown that 37%-100% of N-fossa cysts can be connected to the joint cavity, and a layer of crease or bundle of bursa is present at the mouth of the access to the knee cavity through a “flap”. The presence of the “valve” allows the fluid to flow in one direction from the joint cavity to the bursa, but not from the bursa into the joint cavity, resulting in a unidirectional flow “valve mechanism” that leads to the creation and persistence of N-fossa cysts, while 70% of N-fossa cysts are associated with damage to the posterior horn of the medial meniscus and 85% are associated with degeneration and damage to the articular cartilage. The key to successful treatment in this patient group is a thorough preoperative examination of the knee joint to adequately assess the intra-articular pathology, as well as proper management of the intra-articular lesion during surgery to re-establish the normal bidirectional passage between the cyst and the joint cavity, while the cyst itself is not the main goal of surgical treatment. The success of this surgery was supported by the MRI room as well as the operating room, and it also provided a new minimally invasive way to treat N-fossa cysts.