Tanaka Hidetatsu, Yamako Go, Kurishima Hiroaki, Yamashita Shutaro, Mori Yu, Chiba Daisuke, Chosa Etsuo, Itoi Eiji
Department of Orthopaedic Surgery, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai, 980-8574, Japan.
Department of Mechanical Design Systems, Faculty of Engineering, University of Miyazaki, Miyazaki, 889-2192, Japan.
J Orthop Sci. 2018 Sep;23(5):825-833. doi: 10.1016/j.jos.2018.04.005. Epub 2018 Jun 14.
Supra-acetabular insufficiency fractures (SAIFs) occur in the upper acetabulum and are rare compared with insufficiency sacral, femoral head, or ischial fractures. However, SAIFs are known to occur in low grade trauma, and the underlying mechanism is still remained unclear.
We performed biomechanical analysis using finite element analysis to clarify the mechanisms underlying the development of SAIFs. Patient-specific models and bone mineral density (BMD) were derived from pelvic computed tomography data from two patients with SAIF (unaffected side) and two healthy young adults. The bone was assumed to be an isotropic, linearly elastic body. We assigned Young's modulus of each element to the pelvis based on the BMD, and reported the relationships for BMD-modulus. Clinically relevant loading conditions-walking and climbing stairs-were applied to the models. We compared the region of failure risk in each acetabulum using a maximum principal strain criterion.
The average supra-acetabular BMD was less than that of the hemi-pelvis and femoral head, but was higher than that of the femoral neck and greater trochanter. Greater minimum principal strain was concentrated in the supra-acetabular portion in both the SAIF and healthy models. In the SAIF models, the higher region of the failure risk matched the fracture site on the acetabulum.
Relative fragility causes compressive strain to concentrate in the upper acetabulum when walking and climbing stairs. When presented with a patient complaining of hip pain without apparent trauma or abnormal X-ray findings, physicians should consider the possibility of SAIF and perform magnetic resonance imaging for the diagnosis of SAIF.
髋臼上缘不全骨折（SAIFs）发生于髋臼上部，与骶骨、股骨头或坐骨的不全骨折相比较为罕见。然而，已知SAIFs可发生于低级别创伤，但其潜在机制仍不清楚。
我们使用有限元分析进行生物力学分析，以阐明SAIFs发生发展的机制。根据两名SAIF患者（未受影响侧）和两名健康年轻成年人的骨盆计算机断层扫描数据，建立了患者特异性模型并得出骨密度（BMD）。假定骨骼为各向同性的线弹性体。我们根据BMD为骨盆各单元指定杨氏模量，并报告了BMD与模量之间的关系。将临床相关的负荷条件——行走和爬楼梯——应用于模型。我们使用最大主应变标准比较了每个髋臼的失效风险区域。
髋臼上缘的平均BMD低于半骨盆和股骨头，但高于股骨颈和大转子。在SAIF模型和健康模型中，更大的最小主应变均集中在髋臼上缘部分。在SAIF模型中，较高的失效风险区域与髋臼骨折部位相符。
相对脆弱性导致在行走和爬楼梯时压缩应变集中在髋臼上部。当遇到主诉髋部疼痛但无明显创伤或X线检查结果异常的患者时，医生应考虑SAIF的可能性，并进行磁共振成像以诊断SAIF。
