In vivo and ex vivo range of motion in the fire salamander Salamandra salamandra

Abstract

Joint range of motion (RoM) analyses are fundamental to our understanding of how an animal moves throughout its ecosystem. Recent technological advances allow for more detailed quantification of this RoM (e.g. including interaction of degrees of freedom) both in ex vivo joints and in vivo experiments. Both types of data have been used to draw comparisons with fossils to reconstruct locomotion. Salamanders are often used as analogues for early tetrapod locomotion; testing such hypotheses requires an in‐depth analysis of salamander joint RoM. Here, we provide a detailed dataset of the ex vivo ligamentous rotational joint RoM in the hindlimb of the fire salamander Salamandra salamandra, using a new method for collecting and visualising joint RoM. We also characterise in vivo joint RoM used during walking, via scientific rotoscoping and compare the in vivo and ex vivo data. In summary, we provide (1) a new method for joint RoM data experiments and (2) a detailed analysis of both in vivo and ex vivo data of salamander hindlimbs, which can be used for comparative studies.

Spherical frame projections for visualising joint range of motion, and a complementary method to capture mobility data

“…To evaluate the effectiveness of the new spherical frame projection of RoM in the context of anatomical data, we designed a novel rig using motion capture. Our companion paper on the joint RoM of Salamandra salamandra is a case study of these methods (Herbst et al 2022). The general setup of the data collection and data transformation is outlined below; these new methods can be applied to a variety of organisms because the rig components can easily be scaled up or down.…”

“…For our companion paper (Herbst et al 2022 ), we developed a new experimental approach using visual kinematic capture using multiple cameras. We describe the foundations for the application of this approach in this paper, whereas the companion paper provides a case study with real biological data.…”

“…If torque recordings are used, the magnitude of torque load on the joint can be set beneath some maximum limit; then, the space of possible orientations would be swept fully, but prioritising range limits in a systematic manner. We recommend randomising the order of the sequences between trials to balance the bias and minimise tissue strain (see Herbst et al 2022 ).…”

“…For the salamander joints used in our companion paper (Herbst et al 2022 ), a contrastingly simple but sufficiently repeatable method was used. Our method worked on specimens such as salamanders where geometric primitives cannot easily be fit into the morphology of some bones.…”

“…In Rhinoceros software, points were evenly placed along the proximal and distal edges of each bone (Figure 3 ), and lines were fit through these points. The salamander‐specific coordinate systems are described in detail in our companion paper (Herbst et al 2022 ). Our sensitivity studies showed good agreement with other methods and repeatability between users.…”