Biomechanics Research Group, Lehrstuhl für Produktentwicklung, Faculty of Mechanical Engineering, Ruhr-University Bochum, Bochum, Germany.
Institute of Geosciences, Division of Paleontology, University of Bonn, Bonn, Germany.
Anat Rec (Hoboken). 2020 Aug;303(8):2177-2191. doi: 10.1002/ar.24311. Epub 2019 Nov 22.
Adaptation of osteology and myology lead to the formation of hydrofoil foreflippers in Cheloniidae (all recent sea turtles except Dermochelys coriacea) which are used mainly for underwater flight. Recent research shows the biomechanical advantages of a complex system of agonistic and antagonistic tension chords that reduce bending stress in bones. Finite element structure analysis (FESA) of a cheloniid humerus is used to provide a better understanding of morphology and microanatomy and to link these with the main flipper function, underwater flight. Dissection of a Caretta caretta gave insights into lines of action, that is, the course that a muscle takes between its origin and insertion, of foreflipper musculature. Lines of action were determined by spanning physical threads on a skeleton of Chelonia mydas. The right humerus of this skeleton was micro-CT scanned. Based on the scans, a finite element (FE) model was built and muscle force vectors were entered. Muscle forces were iteratively approximated until a uniform compressive stress distribution was attained. Two load cases, downstroke and upstroke, were computed. We found that muscle wrappings (m. coracobrachialis magnus and brevis, several extensors, humeral head of m. triceps) are crucial in addition to axial loading to obtain homogenous compressive loading in all bone cross-sections. Detailed knowledge on muscle disposition leads to compressive stress distribution in the FE model which corresponds with the bone microstructure. The FE analysis of the cheloniid humerus shows that bone may be loaded mainly by compression if the bending moments are minimized.
对骨骼和肌肉的适应导致Cheloniidae 科（除了 Dermochelys coriacea 之外的所有现代海龟）的翼状前鳍形成，这些前鳍主要用于水下飞行。最近的研究表明，拮抗张力和弦的复杂系统具有生物力学优势，可以减少骨骼的弯曲应力。使用海龟肱骨的有限元结构分析（FESA）来更好地理解形态和微解剖结构，并将这些与主要的鳍功能，即水下飞行联系起来。对 Caretta caretta 的解剖揭示了前鳍肌肉的作用线，即肌肉在起点和止点之间的路径。作用线是通过在Chelonia mydas 的骨骼上跨越物理线来确定的。对该骨骼的右肱骨进行了微 CT 扫描。基于扫描结果，建立了有限元（FE）模型并输入了肌肉力矢量。通过迭代逼近肌肉力，直到达到均匀的压缩应力分布。计算了两个负荷情况，下冲程和上冲程。我们发现，除了轴向加载外，肌肉包裹（m. coracobrachialis magnus 和 brevis、几个伸肌、m. triceps 的肱骨头）对于获得所有骨横截面的均匀压缩加载至关重要。对肌肉位置的详细了解导致 FE 模型中的压缩应力分布与骨微观结构相对应。对海龟肱骨的有限元分析表明，如果弯矩最小化，骨骼可能主要承受压缩载荷。
