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

Abstract

Quantifying joint range of motion (RoM), the reachable poses at a joint, has many applications in research and clinical care. Joint RoM measurements can be used to investigate the link between form and function in extant and extinct animals, to diagnose musculoskeletal disorders and injuries or monitor rehabilitation progress. However, it is difficult to visually demonstrate how the rotations of the joint axes interact to produce joint positions. Here, we introduce the spherical frame projection (SFP), which is a novel 3D visualisation technique, paired with a complementary data collection approach. SFP visualisations are intuitive to interpret in relation to the joint anatomy because they 'trace' the motion of the coordinate system of the distal bone at a joint relative to the proximal bone. Furthermore, SFP visualisations incorporate the interactions of degrees of freedom, which is imperative to capture the full joint RoM. For the collection of such joint RoM data, we designed a rig using conventional motion capture systems, including live audio-visual feedback on torques and sampled poses.Thus, we propose that our visualisation and data collection approach can be adapted for wide use in the study of joint function.

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

“…Here, we summarise the main findings of our study, and how they relate to our initial aims. Aim 1 : We successfully implemented our joint RoM rig and SFP method (Herbst, Eberhard, et al, 2022), capturing a detailed dataset of the hindlimb joint range of motion in S. salamandra including interaction of degrees of freedom. Aim 2 : The SFP approach enabled intuitive comparisons between in vivo (during walking) and ex vivo (ligamentous) ROM data. In the hip, ex vivo FE, LAR and ABAD had similar ranges, whereas in the in vivo salamander, the ABAD range had the lowest excursion (much lower than ex vivo ABAD), followed by LAR (a bit lower range than ex vivo), and a similar FE range to ex vivo. The in vivo hip FE range was slightly biased towards extension rather than flexion, whereas for the ex vivo individuals there was much greater flexion than extension. In the salamander knee, there was a strong correspondence between in vivo and ex vivo FE range, maxima and minima, suggesting that cadaver studies of ROM may give reasonable predictions of the in vivo FE range for this joint. However, the in vivo FE range was shifted (more internal rotation) relative to the ex vivo ranges.…”

“…More details about the applications and benefits of the rig, as well as the new SFP method, can be found in the companion methods paper (Herbst, Eberhard, et al, 2022). Future experiments on salamanders The Rhino and Matlab software-based method of assigning ACSs provided a repeatable alternative to other methods of assigning ACSs and can be adopted using other software.…”

“…We represent the joint RoM using SFPs. SFPs are new visualisations to illustrate the entire rotational pose space, including interaction of degrees of freedom, for a joint (Herbst, Eberhard, et al, 2022).…”

“…Therefore, we measured ligamentous RoM in the salamanders. The ex vivo dataset was collected using a custom rig, and joint RoM was visualised using the new spherical frame projection (SFP) method, which incorporates interaction of degrees of freedom (the effect of the rotations about each axis on the rotational ranges of the other axes) and provides an accurate representation of the real distances between poses (see Herbst, Eberhard, et al, 2022 ).…”

“…The goals of this study were threefold. First, it is a case study using the methodology from Herbst, Eberhard, et al ( 2022 ). Second, we wanted to determine how in vivo hindlimb RoM during walking compares to ex vivo ligamentous joint RoM.…”