I. Diagnosis and treatment of quadrilateral foramen syndrome The quadrilateral foramen syndrome is a series of clinical syndromes caused by the compression of the posterior spinohumeral artery and axillary nerve at the quadrilateral foramen. The main manifestations are sensory disturbance and limitation of deltoid function in the lateral shoulder arm innervated by the axillary nerve. In 1980, Cahill first described quadrilateral foramen syndrome, and in China, Lu Shibi et al. first reported this syndrome. With the increase of basic and clinical research on this disease, early clinical diagnosis and early treatment have been possible, but the overall understanding of this disease is still insufficient, and clinical misdiagnosis and mistreatment often occur, and most patients lose the opportunity of early diagnosis and treatment. In this paper, we introduce the causes, diagnosis and treatment of this syndrome with a clinical patient as an example. The main causes of quadrilateral foramen syndrome are: 1. Scapular impingement injury can cause contusion to the bones, muscles and tendons around the quadrilateral foramen, resulting in congestion and edema, hyperplasia and scar formation in the damaged tissues, and direct compression of the axillary nerve; 2. Sudden excessive abduction of the shoulder joint, sudden traction and damage to the tissues around the quadrilateral foramen, and scar formation during the repair process, resulting in relative reduction of the quadrilateral foramen and compression of the axillary nerve; 3. Repeated activities cause chronic injury to the axillary nerve by repeated friction in the muscles around the rotator cuff, and the pathological changes are local tissue congestion and edema, resulting in axillary nerve compression. The diagnosis and treatment points of quadrilateral foramen syndrome: 1. History of trauma or repeated activity in the shoulder or posterior axillary area; 2. Paralysis of deltoid and triceps muscle; 3. Sensory impairment of the lateral shoulder skin; 4. Fixed pressure points at the quadrilateral foramen; 5. Electromyography suggests axillary nerve injury, accompanied by reduced elbow extension force when the triceps muscle branch of radial nerve is injured. In the process of clinical diagnosis, those without a clear history of trauma should be differentiated from frozen shoulder and cervical spondylosis, and pressure points at the quadrilateral foramen and electromyography are often helpful for differential diagnosis. Treatment points: Conservative treatment of quadrilateral foramen syndrome includes limb immobilization, local nerve block and needle knife release, deltoid muscle electroacupuncture stimulation, etc. Most mild cases can be cured. If conservative treatment fails to recover after 3 months, surgical exploration should be performed promptly to relieve the symptoms of axillary nerve impingement as soon as possible. Regarding the diagnosis, it should be noted that in the clinical treatment process, since the occurrence of quadrilateral foramen syndrome often coexists with shoulder trauma, it is often the case that only the treatment of shoulder trauma is focused on, while the existence of axillary nerve injury is ignored, which subsequently delays the diagnosis and treatment of this syndrome. The effectiveness of treatment for quadrilateral foramen syndrome is closely related to the degree of damage to the nerve itself and the duration of the disease; the longer the duration of the disease and the more severe the lesion, the worse the outcome.