Cheal E J, Hipp J A, Hayes W C
Department of Orthopaedic Surgery, Charles A. Dana Research Institute, Beth Israel Hospital, Boston, Massachusetts.
J Biomech. 1993 Mar;26(3):251-64. doi: 10.1016/0021-9290(93)90363-j.
Between 30 and 70% of almost one million new cancer patients diagnosed each year will develop osseous metastases. Clinicians are faced with the difficult task of determining which patients require prophylactic stabilization to prevent pathologic fracture. The objective of this study was to test the ability of macroscopic finite element models to predict the fracture strength of the proximal femur with a lesion in the femoral neck. Drill hole defects in human cadaver femora were used to simulate lesions that penetrate one cortex of the femoral neck. Based on the first of two series of in vitro experiments, the fracture strength of a femur with a lesion that penetrates either the inferior-medial or superior-lateral cortex of the neck is approximately 45% less than the fracture strength of the paired intact femur; based on the second series, the fracture strength with the inferior-medial lesion is approximately 20% less than the fracture strength with the superior-lateral lesion. A series of three-dimensional finite element models were used to predict the fracture strength for anterior and posterior lesions, as well as the inferior-medial and posterior-lateral lesions tested in vitro. Based on a direct comparison of the strengths predicted by the finite element models to the measured in vitro fracture strengths, the finite element models performed poorly. In particular, the application of an anisotropic strength criterion to the stresses predicted by the models resulted in a considerable underestimation of the percentage reduction in the in vitro fracture strength. This may reflect a fundamental inability of a linear, macroscopic continuum-based analysis to predict accurately the fracture strength of a bone structure as complex as the proximal femur. However, despite this lack of agreement in absolute fracture strength, the general trends for gait and stair ascent loading for the inferior-medial and superior-lateral lesions were consistent with the in vitro data. The greatest reduction in strength was predicted for the inferior-medial lesion, followed by the anterior lesion and then the superior-lateral lesion, and the least reduction in strength was predicted for the posterior lesion. Most importantly, the predicted strength ratio varied considerably as a function of the applied loads. Any metastatic lesions of the femoral neck may be especially sensitive to some particular activity, making it difficult to determine precisely the risk of fracture.
每年新确诊的近100万癌症患者中，有30%至70%会发生骨转移。临床医生面临着一项艰巨的任务，即确定哪些患者需要预防性固定以防止病理性骨折。本研究的目的是测试宏观有限元模型预测股骨颈有病变的近端股骨骨折强度的能力。使用人类尸体股骨上的钻孔缺陷来模拟穿透股骨颈一侧皮质的病变。基于两组体外实验中的第一组，病变穿透颈下内侧或上外侧皮质的股骨骨折强度比配对的完整股骨骨折强度低约45%；基于第二组，下内侧病变的骨折强度比上外侧病变的骨折强度低约20%。使用一系列三维有限元模型来预测体外测试的前侧和后侧病变以及下内侧和后外侧病变的骨折强度。基于有限元模型预测的强度与体外测量的骨折强度的直接比较，有限元模型表现不佳。特别是，将各向异性强度准则应用于模型预测的应力导致对体外骨折强度降低百分比的显著低估。这可能反映了基于线性宏观连续体的分析根本无法准确预测像近端股骨这样复杂的骨结构的骨折强度。然而，尽管在绝对骨折强度上缺乏一致性，但下内侧和上外侧病变在步态和上楼梯负荷方面的总体趋势与体外数据一致。预测下内侧病变的强度降低最大，其次是前侧病变，然后是上外侧病变，而后侧病变的强度降低最小。最重要的是，预测的强度比随施加负荷的函数变化很大。股骨颈的任何转移性病变可能对某些特定活动特别敏感，因此难以精确确定骨折风险。
