Validation of an Echidna Forelimb Musculoskeletal Model Using XROMM and diceCT

Abstract

In evolutionary biomechanics, musculoskeletal computer models of extant and extinct taxa are often used to estimate joint range of motion (ROM) and muscle moment arms (MMAs), two parameters which form the basis of functional inferences. However, relatively few experimental studies have been performed to validate model outputs. Previously, we built a model of the short-beaked echidna (Tachyglossus aculeatus) forelimb using a traditional modelling workflow, and in this study we evaluate its behaviour and outputs using experimental data. The echidna is an unusual animal representing an edge-case for model validation: it uses a unique form of sprawling locomotion, and possesses a suite of derived anatomical features, in addition to other features reminiscent of extinct early relatives of mammals. Here we use diffusible iodine-based contrast-enhanced computed tomography (diceCT) alongside digital and traditional dissection to evaluate muscle attachments, modelled muscle paths, and the effects of model alterations on the MMA outputs. We use X-ray Reconstruction of Moving Morphology (XROMM) to compare ex vivo joint ROM to model estimates based on osteological limits predicted via single-axis rotation, and to calculate experimental MMAs from implanted muscles using a novel geometric method. We also add additional levels of model detail, in the form of muscle architecture, to evaluate how muscle torque might alter the inferences made from MMAs alone, as is typical in evolutionary studies. Our study identifies several key findings that can be applied to future models. 1) A light-touch approach to model building can generate reasonably accurate muscle paths, and small alterations in attachment site seem to have minimal effects on model output. 2) Simultaneous movement through multiple degrees of freedom, including rotations and translation at joints, are necessary to ensure full joint ROM is captured; however, single-axis ROM can provide a reasonable approximation of mobility depending on the modelling objectives. 3) Our geometric method of calculating MMAs is consistent with model-predicted MMAs calculated via partial velocity, and is a potentially useful tool for others to create and validate musculoskeletal models. 4) Inclusion of muscle architecture data can change some functional inferences, but in many cases reinforced conclusions based on MMA alone.

Quantitative biomechanical assessment of locomotor capabilities of the stem archosaur Euparkeria capensis

“…the COM position. Each moment was calculated as the shortest distance between two skew lines: the GRF vector from the COP in the foot and the unit vectors from the COM position representing its principal axes ( figure 1 c , d ), and scaled by the two-dimensional projection of that distance onto each axis's plane of rotation [ 71 ], i.e. using its vector components (electronic supplementary material, information S3).…”

Truly dorsostable runners: Vertebral mobility in rhinoceroses, tapirs, and horses

“…However, the research of combined motions raises new methodological problems which can be illustrated by the papers just cited. First, the combined motion is performed by an experimenter via ropes (Panyutina et al, 2013) or sticks (Kambic et al, 2017; Regnault et al, 2021) attached to the subject. This may lead to articular surfaces being less closely articulated than in living animals developing muscle contraction.…”

“…Therefore, the procedure is potentially confounded by disarticulation and consequent aROM overestimation. Second, an additional overestimation of translational amplitudes can come from the use of geometric primitives (e.g., the sphere) for joint structure imitation as in Regnault et al (2021). If the center of a chosen geometric primitive is placed away from the true center of joint rotation, the distance between the two is inevitably recalculated into a translational shift which does not exist in reality.…”

“…For instance, the syndesmological aROM was presented for circumduction (combined flexion-extension and adduction-abduction) in the bat shoulder joint (Panyutina et al, 2013). Among the most methodologically advanced in vitro studies of combined aROM, are recent studies of the turkey's neck (Kambic et al, 2017) and of the echidna's forelimb (Regnault et al, 2021). Combined motions in a joint are interesting because they are often used by animals and, therefore, the interdependencies between ROMs across different DoFs may be important.…”

Computational Modeling of Gluteus Medius Muscle Moment Arm in Caviomorph Rodents Reveals Ecomorphological Specializations

“…Hence, the functioning of this instantaneous muscle moment arm (IMMA) can only be understood by determining its length throughout relevant joint poses. For example, this can be achieved with the help of computational musculoskeletal modeling of scanned bone models ( Charles et al, 2016 ; Regnault et al, 2021 ). However, its technical sophistication and the multivariate nature resulting from the IMMAs’ dependency on complex 3D joint poses over time complicate the analysis of IMMAs in more inclusive, phylogenetically broader datasets.…”