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

本实验采用10个新鲜冰冻尸体肩关节，探讨下关节囊移位术治疗肩关节多向失稳的机制。从肩部移除所有肌肉，并将肩胛骨固定到定制的肩部固定器上。使用X线平片测量肱骨头相对于关节盂的位置。对肱骨施加0 kg、0.5 kg和1.0 kg载荷。关节囊条件为：1）完整，2）前下关节囊使用夹钳叠瓦状，3）后下关节囊以相同方式叠瓦状。关节内压测量采用压力传感器，关节内压的负值随负荷的增加而增加，呈线性关系。前囊和后囊重叠后也观察到这种情况。囊膜条件之间无显著差异。无论关节囊条件如何，当关节内压力完整时，肱骨头的位置平移小于5 mm。当关节内压力被释放时，肱骨头向后脱位。结论：下关节囊移位术的主要稳定机制是通过减少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.