Mechanism of Inferior Capsular Shift Procedure for Multidirectional Instability of the Shoulder

我们进行了这项实验研究，探讨下囊移位术稳定多向不稳定肩关节的机制。我们用了10个新鲜的冷冻尸体肩膀。将肩胛骨固定在定制的肩关节固定器上。使用x线平片测量肱骨头相对于关节盂的位置。肱骨下部分别负重0 kg、0 kg、5 kg和1.0 kg。囊体条件为1)完整，2)前下囊用夹钳压瓦，3)后下囊以相同方式压瓦。关节内压力测量使用压力传感器连接到导管充满生理盐水。关节内压力负值随负荷的增加呈线性增加。前后囊叠瓦后也观察到这一点。不同荚膜状态间无显著性差异。当关节内压力完整时，无论关节囊状况如何，肱骨头的位置移位小于5mm。当释放关节内压力时，肱骨头向下脱位。前后囊叠瓦后，肱骨头仍为下半脱位。总之，下囊移位术的主要稳定机制是通过减小关节体积来维持关节内压力。

We performed this experimental study to investigate the mechanism of inferior capsular shift procedure to stabilize the shoulder with multidirectional instability.We used 10 fresh previously-frozen cadaveric shoulders. All the muscles were removed from the shoulder, and the scapula was stabilized to the custom-made shoulder fixator. The position of the humeral head relative to the glenoid was measured using plain roentgenograms. The humerus was loaded inferiorly with 0 kg, 0,5 kg, and 1.0 kg load. The capsular conditions were 1) intact, 2) anteroinferior capsule imbricated using a clamp, 3) posteroinferior capsule imbricated in the same fashion. The Intraarticular pressure was measured using a pressure sensor attached to the catheter filled with saline.The negative value of intraarticular pressure increased with the increase of the load in a linear fashion. This was also observed after imbrication of anterior and posterior capsule. There was no significant difference between the capsular conditions. The position of the humeral head translated less than 5 mm when the Intraarticular pressure was intact regardless of capsular conditions. When the Intraarticular pressure was vented, the humeral head dislocated inferiorly. After the imbrication of anterior and posterior capsule, the humeral head was still inferiorly subluxated.In conclusion, the major stabilizing mechanism of the inferior capsular shift procedure is to maintain the intraarticular pressure by reducing the joint volume.