Definition and clinical progress of critical shoulder angle

Abstract

Rotator cuff disease and degenerative osteoarthritis are caused by many factors. Several studies had shown that rotator cuff disease was related to lateral extension of the acromion and glenoid inclination. A new parameter, critical shoulder angle (CSA), which is defined as the angle between a line connecting the superior to the inferior margins of the glenoid and a line connecting the inferior margin of the glenoid to the inferolateral edge of the acromion measured on anteroposterior (AP) shoulder radiographs, is proposed to comprehensively reflect the relationship between abnormal anatomical structure and rotator cuff injury. There is a close relationship between CSA and the injury of rotator cuff and the osteoarthritis of glenohumeral joint: the injury of rotator cuff is often accompanied by a larger CSA (> 35 °), and a smaller CSA (< 30 °) is closely related to the occurrence of glenohumeral arthritis. Therefore, CSA is helpful for the diagnosis of rotator cuff injury and glenohumeral osteoarthritis. Correction of abnormal CSA by arthroscopic lateral acromial osteotomy also provides a new idea for the treatment of shoulder diseases. In this paper, we reviewed the research progress of the angle from five aspects: definition, measurement, biomechanical significance, treatment and ethnic differences.