Matsen Frederick A, Chebli Caroline M, Lippitt Steven B
Department of Orthopaedics, University of Washington, Seattle, Washington, USA.
Instr Course Lect. 2007;56:23-34.
During use of the normal shoulder, the humeral head is centered within the glenoid and the coracoacromial arch. When the shoulder cannot maintain this centered position during use, it is unstable. An unstable shoulder prevents normal function of the upper extremity. Shoulder instability is not the same as joint laxity. Joint laxity is a property of normal joints and allows the shoulder to attain its full range of functional positions. The concavity of the glenoid and the coracoacromial arch along with the passive and active forces that press the humeral head into the glenoid and the coracoacromial arch maintain the head in its centered position. This concavity-compression mechanism is dependent on the integrity of the glenoid and the coracoacromial arch, muscular compression, and restraining ligaments of the shoulder. Loss of any of these elements due to developmental, degenerative, traumatic, or iatrogenic factors may compromise the ability of the shoulder to center the humeral head in the glenoid.
在正常肩部使用过程中，肱骨头位于关节盂和喙肩弓中心。当肩部在使用过程中无法维持该中心位置时，即为不稳定。不稳定的肩部会妨碍上肢的正常功能。肩部不稳定与关节松弛不同。关节松弛是正常关节的一种特性，可使肩部达到其全部功能位置范围。关节盂和喙肩弓的凹面，以及将肱骨头压入关节盂和喙肩弓的被动和主动力量，使肱骨头保持在中心位置。这种凹面 - 压缩机制取决于关节盂和喙肩弓的完整性、肌肉压缩以及肩部的限制韧带。由于发育、退变、创伤或医源性因素导致这些要素中的任何一个丧失，都可能损害肩部将肱骨头定位于关节盂中心的能力。
