BACKGROUND:The human sacroiliac joint (SIJ) in vivo is exposed to compressive and shearing stress environment, given the joint lines are almost parallel to the direction of gravity. The SIJ supports efficient bipedal walking. Unexpected or unphysiological, repeated impacts are believed to cause joint misalignment and result in SIJ pain. In the anterior compartment of the SIJ being synovial, the articular surface presents fine irregularities, potentially restricting the motion of the joints. OBJECTIVE:To clarify how the SIJ articular surface affects the resistance of the motion under physiological loading. METHODS:SIJ surface models were created based on computed tomography data of three patients and subsequently 3D printed. Shear resistance was measured in four directions and three combined positions using a customized setup. In addition, repositionability of SIJs was investigated by unloading a shear force. RESULTS:Shear resistance of the SIJ was the highest in the inferior direction. It changed depending on the direction of the shear and the alignment position of the articular surface. CONCLUSION:SIJ articular surface morphology is likely designed to accommodate upright bipedal walking. Joint misalignment may in consequence increase the risk of subluxation.

中文翻译：

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骶髂关节运动阻力的实验表征

背景：人体骶髂关节（SIJ）在体内处于压剪应力环境下​​，关节线几乎与重力方向平行。SIJ 支持高效的双足行走。意外或非生理性的重复撞击被认为会导致关节错位并导致 SIJ 疼痛。SIJ 的前室是滑膜，关节面呈现细微的不规则性，可能限制关节的运动。目的：阐明 SIJ 关节面如何影响生理负荷下的运动阻力。方法：根据三名患者的计算机断层扫描数据创建 SIJ 表面模型，然后进行 3D 打印。使用定制设置在四个方向和三个组合位置测量剪切阻力。此外，通过卸载剪切力研究了 SIJ 的可重定位性。结果：SIJ的抗剪强度在下方向最高。它根据剪切方向和关节面的对齐位置而变化。结论：SIJ 关节表面形态可能旨在适应直立双足行走。关节错位可能会增加半脱位的风险。