Tsai Andy, Coats Brittany, Kleinman Paul K
Department of Radiology, Harvard Medical School, Boston Children's Hospital, 300 Longwood Ave., Boston, MA, 02115, USA.
Department of Mechanical Engineering, University of Utah, Salt Lake City, UT, USA.
Pediatr Radiol. 2017 Nov;47(12):1622-1630. doi: 10.1007/s00247-017-3921-y. Epub 2017 Jul 18.
The classic metaphyseal lesion (CML) is strongly associated with infant abuse, but the biomechanics responsible for this injury have not been rigorously studied. Radiologic and CT-pathological correlates show that the distal tibial CML always involves the cortex near the subperiosteal bone collar, with variable extension of the fracture into the medullary cavity. Therefore, it is reasonable to assume that the primary site of bone failure is cortical, rather than intramedullary.
This study focuses on the strain patterns generated from finite element modeling to identify loading scenarios and regions of the cortex that are susceptible to bone failure.
A geometric model was constructed from a normal 3-month-old infant's distal tibia and fibula. The model's boundary conditions were set to mimic forceful manipulation of the ankle with eight load modalities (tension, compression, internal rotation, external rotation, dorsiflexion, plantar flexion, valgus bending and varus bending).
For all modalities except internal and external rotation, simulations showed increased cortical strains near the subperiosteal bone collar. Tension generated the largest magnitude of cortical strain (24%) that was uniformly distributed near the subperiosteal bone collar. Compression generated the same distribution of strain but to a lesser magnitude overall (15%). Dorsiflexion and plantar flexion generated high (22%) and moderate (14%) localized cortical strains, respectively, near the subperiosteal bone collar. Lower cortical strains resulted from valgus bending, varus bending, internal rotation and external rotation (8-10%). The highest valgus and varus bending cortical strains occurred medially.
These simulations suggest that the likelihood of the initial cortical bone failure of the CML is higher along the margin of the subperiosteal bone collar when the ankle is under tension, compression, valgus bending, varus bending, dorsiflexion and plantar flexion, but not under internal and external rotation. Focal cortical strains along the medial margins of the subperiosteal bone collar with varus and valgus bending may explain the known tendency for focal distal tibial CMLs to occur medially. Further research is needed to determine the threshold of applied forces required to produce this strong indicator of infant abuse.
经典干骺端病变（CML）与虐待婴儿密切相关，但导致这种损伤的生物力学机制尚未得到严格研究。放射学和CT病理相关性研究表明，胫骨远端CML总是累及骨膜下骨环附近的皮质，骨折向髓腔的延伸程度不一。因此，有理由认为骨破坏的主要部位是皮质，而非髓内。
本研究聚焦于有限元模型生成的应变模式，以确定易发生骨破坏的加载情况和皮质区域。
根据一名正常3个月大婴儿的胫骨远端和腓骨构建几何模型。设定模型的边界条件，以模拟用八种加载方式（拉伸、压缩、内旋、外旋、背屈、跖屈、外翻弯曲和内翻弯曲）对踝关节进行强力操作。
除内旋和外旋外，所有加载方式的模拟均显示骨膜下骨环附近的皮质应变增加。拉伸产生的皮质应变最大（24%），在骨膜下骨环附近均匀分布。压缩产生相同的应变分布，但总体应变较小（15%）。背屈和跖屈分别在骨膜下骨环附近产生高（22%）和中度（14%）的局部皮质应变。外翻弯曲、内翻弯曲、内旋和外旋产生的皮质应变较低（8 - 10%）。最高的外翻和内翻弯曲皮质应变出现在内侧。
这些模拟表明，当踝关节处于拉伸、压缩、外翻弯曲、内翻弯曲、背屈和跖屈状态时，但不是在内旋和外旋状态下，CML初始皮质骨破坏沿骨膜下骨环边缘发生的可能性更高。内翻和外翻弯曲时沿骨膜下骨环内侧边缘的局灶性皮质应变可能解释了胫骨远端局灶性CMLs已知的内侧发生倾向。需要进一步研究以确定产生这种虐待婴儿强烈指标所需的外力阈值。
