不穩定肩關節是指肱骨盂關節的不穩定因其活動度、方向及病因而有不同的表現；過去的文獻常強調重複性"前位"肩關節脫臼的診斷與治療。由於近幾年的努力，發現肩關節的不穩定，包含多種型態(前位、後位、位或混合型)。若未能經術前彾底評估而施予手術，?會漏掉部分病灶，或更加重另一方向的不穩定，時加速關節的退化。為提高手術的成功率，需於術前找出肩關節不穩定的原因、方向及程度。

　　　　　Glenohumeral instability is one of the most complex and challenging areas of shoulder pathology to diagnose and treat. It also encompasses a spectrum of disorders of varying degree, direction, and etiology. Historically, much of the orthopaedic literature has focused on recurrent anterior dislocation. Over the past years, increased attention has been paid to other types of glenohumeral instability. It is now widely recognized that stabilization procedures that may be successful for one type of instability. Careful diagnosis and classification of glenohumeral instabilities will afford the best chance of successful treatment of these disorders.