Data Collection

14 retro-reflective markers were placed on anatomical landmarks on the participant's right foot and shank, in accordance with a previously described multi-segment foot model (Figure 2; Leardini et al., 2007). 3-Dimensional (3D) marker positions were captured using an OMC system (Qualysis Track Manager, Qualysis AB, Gothenburg, SWE) sampled at 250 Hz.

Optical motion capture (OMC) marker placement was performed in accordance with the Rizzoli model (Leardini et al., 2007). Markers are listed in order from proximal to distal, and numbered, to assist with identification. Tibial Markers (Magenta): (1) Lateral Shank (LtS), (2) Medial Shank (MdS), (3) Distal Shank (Shk). Calcaneal Markers (Green): (4) Superior Calcaneal Ridge, (5) Inferior Calcaneal Ridge (ICR), (6) Sustentaculum Tali (ST), (7) Peroneal Tubercle. Navicular Marker (Blue): (8) Navicular (TN). Metatarsal Markers (Purple): (9) First Metatarsal Base (FMB), (10) Second Metatarsal Base (SMB), (11) Fifth Metatarsal Base (VMB), (12) First Metatarsal Head (FMH), (13) Second Metatarsal Head (SMH), (14) Fifth Metatarsal Head (VMH).

A high-speed, BVR method was used to simultaneously record x-ray images of the foot across a capture volume that was in the middle of the OMC space. The BVR system, X-ray Reconstruction of Moving Morphology (XROMM), has been previously documented by Brainerd et al. (2010) and Knorlein et al. (2016) for validation of beaded tracking. This BVR method consisted of two x-ray transmitters paired with two x-ray receivers that were coupled to high-speed cameras. The transmitters emitted x-rays using an exposure of 75 kVp and 100 mA. Lateral-oblique views were obtained by setting the imaging planes at 130° relative to each other about a global vertical axis. A carbon fiber plate (Dragon Plate, AllRed and Associates, Elbridge, USA) was placed in the middle of the capture volume, which allowed for enhanced bone visibility in the x-ray images. Participants landed with their right foot on the plate during each trial. The high-speed camera captured the x-ray images at 250 Hz. BVR data collection was manually triggered just prior to the participant's right foot entering the data collection space and was terminated when the participant's foot was no longer in the field of view. A synchronization signal from the x-ray system was used to trigger the start of the OMC system, which was recorded with a 0.5 s pre-trigger, and a trial duration of 3.0 s.

A computed tomography (CT) scan of each participant's right foot was captured with the participant lying prone with the ankle in a plantarflexed orientation (average resolution: 0.419 mm × 0.419 mm × 0.625 mm, LightSpeed 16, GE Medical Systems, USA). This orientation was chosen to improve the in-plane resolution which aids in the segmentation process. Foot position was maintained during the scan via a custom-made foam support. Two participants received CT scans at a different imaging location (for convenience) and therefore had a different CT protocol (resolution: 0.488 mm × 0.488 mm × 0.312 mm, Optima CT 660, LightSpeed CT, GE Medical Systems, USA). Each bone of the foot was segmented using Mimics17 (Materialize, Leuven, Belgium). The segmentation provided a tessellated 3D surface mesh, as well as, a 3D partial volume for each bone of interest.