Estimating ankle joint angle from skeletal geometry: a mechanical model of the calcaneal lever in terrestrial mammals.

IF 2.4 3区 生物学 Q2 MULTIDISCIPLINARY SCIENCES
PeerJ Pub Date : 2025-09-23 eCollection Date: 2025-01-01 DOI:10.7717/peerj.20056
Fumihiro Mizuno, Shin-Ichi Fujiwara
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引用次数: 0

Abstract

Background: The ankle joint angle, typically measured between the tibia and metatarsus, shows only a small range of movement during the stance phase and remains relatively constant within species, but varies across taxa. This variation influences traits such as stride length, posture, and locomotor function. While joint angles are readily observable in living animals, they cannot be directly measured in extinct species, for which only skeletal remains are available. Therefore, estimating ankle joint posture from skeletal geometry is important for reconstructing locomotion in both extant and extinct mammals. In this study, we propose a mechanical model of the ankle extensor apparatus to estimate ankle joint angle from bones and test whether the muscle-lever system aligns consistently with skeletal features across taxa.

Methods: We developed a simplified mechanical model of the ankle extensor apparatus to calculate ankle extensor moment arm defined as the perpendicular distance from the ankle joint center to the muscle force line of action, which was assumed to be parallel to the tibia. To verify the Achilles tendon runs parallel to the tibia across taxa, dissections were performed on cadavers of 24 species in seven orders. We compared observed angle (θ obs) from 26 species of zoo-kept terrestrial mammals, covering various body mass and locomotor modes, with estimated angle (θ est) from skeletal specimens of the same species. θ obswas the mean tibia-metatarsus angle during the stance phase, recorded laterally with a high-speed camera. θ estwas measured on reassembled skeletal specimens as the ankle joint angle that maximized the extensor moment arm in the model. Phylogenetic comparative methods, including phylogenetic ANOVA and PGLS, were applied to analyze relationships among θ obs, θ est, body mass, and locomotor mode based on a time-calibrated phylogeny.

Results: Dissections confirmed the Achilles tendon runs nearly parallel to the tibia across species. Stance phase ankle joint rotations were small. Therefore, θ obs could be considered as representative for each species. Over 85% of the studied species maintained their ankle joint angle at which the mechanical advantage of the calcaneal lever was greater than 0.9. No significant differences in the mechanical advantage of the calcaneal lever were found among locomotor modes or taxonomic orders. A strong positive correlation was observed between θ obs and θ est (ρ = 0.70, p < 0.001).

Conclusion: Our mechanical model could estimate θ est from skeletal morphology that closely match θ obs during stance phase. Despite interspecific variation of θ obs, the mechanical advantage of the calcaneal lever remains within a narrow range, suggesting mechanical optimization of the ankle extensor apparatus across terrestrial mammals. This model informs postural reconstruction in extinct species.

从骨骼几何角度估计踝关节角度:陆生哺乳动物跟骨杠杆的力学模型。
背景:踝关节角度,通常在胫骨和跖骨之间测量,在站立阶段只显示一个小范围的运动,在物种内保持相对恒定,但在不同的分类群中有所不同。这种变异会影响步长、姿势和运动功能等特征。关节角在活着的动物身上很容易观察到,但在灭绝的物种身上却不能直接测量,因为它们只有骨骼残骸。因此,从骨骼几何来估计踝关节姿势对于重建现存和灭绝的哺乳动物的运动是很重要的。在这项研究中,我们提出了一个踝关节伸肌装置的力学模型来估计踝关节与骨骼的角度,并测试肌肉杠杆系统是否与不同分类群的骨骼特征一致。方法:建立踝关节伸肌器的简化力学模型,计算踝关节伸肌力臂,定义为踝关节中心到肌肉力作用线的垂直距离,假设与胫骨平行。为了证实跟腱在不同分类群中与胫骨平行,对7目24个物种的尸体进行了解剖。我们比较了26种不同体重和运动方式的动物园饲养的陆生哺乳动物的观察角(θ obs)与同一物种骨骼标本的估计角(θ est)。θ为高速摄像机横向记录的站立阶段胫骨-跖骨平均角度。θ est作为模型中最大伸肌力臂的踝关节角,在重组骨标本上测量。采用系统发育比较方法,包括系统发育方差分析和PGLS,基于时间校准的系统发育分析了θ obs、θ est、体重和运动模式之间的关系。结果:解剖证实跟腱几乎平行于胫骨跨物种运行。站立阶段踝关节旋转较小。因此,θ obs可以被认为是每个物种的代表性。超过85%的研究物种保持踝关节角度,此时跟骨杠杆的机械优势大于0.9。跟骨杠杆的机械优势在不同的运动方式和分类目之间没有显著差异。θ obs与θ est呈正相关(ρ = 0.70, p < 0.001)。结论:我们的力学模型可以根据与站立阶段θ obs接近的骨骼形态来估计θ est。尽管θ obs在种间存在差异,但跟骨杠杆的机械优势仍然在一个狭窄的范围内,这表明陆生哺乳动物的踝关节伸肌装置存在机械优化。这个模型为灭绝物种的姿势重建提供了信息。
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来源期刊
PeerJ
PeerJ MULTIDISCIPLINARY SCIENCES-
CiteScore
4.70
自引率
3.70%
发文量
1665
审稿时长
10 weeks
期刊介绍: PeerJ is an open access peer-reviewed scientific journal covering research in the biological and medical sciences. At PeerJ, authors take out a lifetime publication plan (for as little as $99) which allows them to publish articles in the journal for free, forever. PeerJ has 5 Nobel Prize Winners on the Board; they have won several industry and media awards; and they are widely recognized as being one of the most interesting recent developments in academic publishing.
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