The quadrilateral foramen is located below the glenohumeral joint and contains the axillary nerve as well as the posterior rotator humeral artery. The quadrilateral foramen is bordered by the lesser trochanter on the superior border, the greater trochanter on the inferior border, the triceps tendon on the medial wall, and the humerus on the lateral wall. Quadrilateral foramen syndrome means that the axillary nerve and the posterior spinohumeral artery within it are compressed, resulting in a range of symptoms. Although the incidence of this disorder is low, it is important to differentiate patients who present with symptoms: The typical causes of QSS are: fibrosis of the quadrilateral foramen area, resulting in a fasciculation sensation and limited abduction and external rotation. Periglenoid labral cysts, especially those resulting from tears of the inferior glenoid labrum are by far the most frequent of our findings. Tumors, hematomas. Clinical symptoms: QSS symptoms are usually seen in young patients aged 25-35 years with no significant history of trauma. The pain is an intermittent dull ache presenting in the postero-lateral region of the shoulder joint, which can be exacerbated by activity and can be induced by performing abduction and external rotation movements. The pain is usually located in the quadrilateral foramen area, posterior to the cusp of the lesser trochanter. It may be accompanied by atrophy and loss of muscle strength of the lesser circular muscle and deltoid muscle, and numbness of the limb may occur in the axillary nerve distribution area. The diagnosis of QSS is difficult and many patients are misdiagnosed and mismanaged for many years before they are found to have QSS, which can be confused with impingement syndrome and subacromial hypertension. Investigation: MRI can show atrophy of the lesser trochanter and also indicate the presence of periglenoid labral cysts, tumors, or hematomas. MRI suggests a typical tear of the inferior glenoid labrum with cysts. Treatment: For patients with non-significant symptoms, such as only mild force weakness and MRI exams that do not suggest a significant tear, rehabilitation would be appropriate, and the symptoms can usually be effectively relieved after a few months. However, if there is significant muscle weakness and dysfunction, we recommend that you undergo shoulder arthroscopy to repair the glenoid labral tear and remove the cyst. Prognosis: Patients basically recover completely. However, the length of time varies, depending on the severity of the condition, and it usually takes 6-12 months to recover.