Dwidmuthe Samir C., Roberts Catherine C., Pinkerman Seth
All India Institute of Medical Sciences, Nagpur
University Medical Center of Southern Nevada
Multidirectional instability (MDI) of the glenohumeral joint is a complex clinical entity characterized by symptomatic, involuntary subluxation or dislocation in 2 or more directions, typically including an inferior component. The condition, first described by Neer and Foster in 1980, highlights the delicate balance between mobility and stability in the human body's most mobile joint; a sophisticated interplay of static and dynamic stabilizers maintains this balance. The static stabilizers include the bony architecture of the glenoid and humeral head, the glenoid labrum, which deepens the socket, the capsuloligamentous complex, and the negative intra-articular pressure. The dynamic stabilizers consist of the muscles surrounding the shoulder joint, including the rotator cuff, the long head of the biceps tendon, and the periscapular musculature, which maintain stability through active concavity-compression and coordinated neuromuscular control. MDI represents a failure of this integrated system, wherein the humeral head translates beyond the physiologic boundaries of the glenoid, resulting in pain, apprehension, and functional disability. Historically, shoulder instability was conceptualized through a dichotomous classification system called TUBS (traumatic, unilateral, Bankart, surgical) and AMBRI (atraumatic, multidirectional, bilateral, rehabilitation, inferior capsular shift). While valuable for introducing the concept of atraumatic instability, this framework is now considered obsolete as it fails to account for the significant clinical heterogeneity and the spectrum of pathology observed in patients with MDI. A substantial portion of patients with MDI have a history of trauma, and many with traumatic instability have underlying ligamentous laxity, blurring the lines of this rigid classification. A modern approach, reflecting a more advanced understanding of the condition, emphasizes the underlying etiological factors. A recent systematic review proposed a more clinically relevant "AB classification," which categorizes patients based on the presence or absence of (A) significant trauma and (B) generalized hyperlaxity. This framework acknowledges that MDI is not a single entity but a heterogeneous condition. This moves the clinical focus from a rigid algorithm to a patient-specific diagnosis, which better guides treatment decisions and helps standardize future research. This shift in thinking, from a simple dichotomy to a multifactorial spectrum, is fundamental to the contemporary management of MDI.
肩关节多向不稳定（MDI）于1980年首次被描述为一种复杂的肩部疾病，其定义为在两个或更多运动平面上存在不稳定。肩关节在提供极大运动范围的方式上独具特色。事实上，它是人体中所有关节里活动度最大的。然而，活动度和稳定性成反比，并且在不稳定发生之前，肩部稳定器之间复杂的相互作用容错空间很小。因此，事实证明，在非凡的生理运动范围和肩部稳定性之间取得平衡是很微妙的。肩部的主要职责是将手定位到空间中。因此，有些活动更倾向于活动度（游泳），而其他活动则更注重稳定性（举重、橄榄球线卫）。肩部稳定性通过动态和静态稳定器来维持。负责关节稳定性的动态结构包括肩袖肌群、肱二头肌长头肌腱和肩胛周围肌肉组织。静态稳定器包括盂肱关节面的一致性、盂唇复合体、盂肱韧带以及关节内产生的负压。一旦肱骨头的运动超出盂唇复合体设定的边界，肩部不稳定就会出现症状。这是静态和/或动态稳定器出现病变的结果。肩部不稳定最初被认为属于两类中的一类。第一类是创伤性单侧伴Bankart损伤需手术治疗（TUBS）。第二类是非创伤性、多向、双侧性，通常对康复治疗或下关节囊移位术（AMBRI）有反应。尽管这两类为MDI提供了一个简单的分类系统，但它们过于简化，不能完全代表病理松弛的全部范围。随着我们对MDI过程的了解越来越多，对原来过于简单的分类进行了修改。
