Dual belt instrumented treadmill

One knee of each participant was imaged at 3T using a Trio Tim Siemens magnetic resonance imaging (MRI) scanner. Sagittal, coronal, and axial plane images were acquired using a double-echo steady-state sequence (voxel size, 0.3 × 0.3 × 1 mm³; flip angle, 25°; repetition time, 17 ms; echo time, 6 ms) and an 8-channel knee coil.^{11 (link),39 (link)} High-speed biplanar radiographs (matrix size, 1152 × 1152 pixels²; frame rate, 120 Hz; pulse width, 1.5 ms) were obtained as participants performed a single-leg jump.^{18 (link),20} Specifically, participants were asked to keep their trunk upright, jump vertically, and land on the same location of the force plate embedded in the treadmill. After several practice jumps to ensure that the participant was able to perform the motion within the field of view, high-speed biplanar radiographs were obtained at a frame rate of 120 Hz as the participant performed the motion. Ground-reaction forces (GRFs) were obtained at a sampling rate of 1200 Hz using an instrumented dual-belt treadmill (Bertec).

Data collection and processing details have been previously published [25 (link)]. Briefly, synchronized biplane radiographs of the knee were collected (100 images/sec for 1.0 sec, maximum 90 kV, 160 mA, 1 ms pulse width) during walking at a self-selected speed (average 1.3 ± 0.2 m/s) on a dual-belt instrumented treadmill (Bertec Corp, Columbus, OH). Two trials were imaged from terminal swing to mid stance and two trials were imaged from mid stance to terminal swing, for each knee. Ground reaction forces (GRF) were recorded from the instrumented treadmill at 1000 Hz. Foot strike and toe off events were denoted using a 50 N threshold in the vertical component of the GRF. Bilateral computed tomography (CT) scans of each participant’s knees were also obtained (0.6 × 0.6 mm in-plane resolution, 1.25 mm slice thickness).

A custom DF system consisting of two x-ray emitters, 12” image
intensifiers, and high-speed cameras [17 (link)]
was positioned around a dual-belt instrumented treadmill (Bertec, Columbus, OH)
(Figure 1). Specimens were placed in
the shared field of view (FOV) (Figure 1).
The image space was calibrated using an acrylic cube with 19 beads [17 (link)].

One static (standing) and three dynamic activities were completed on a dual-belt instrumented treadmill (Bertec Corporation, Columbus, OH, USA), including level walk at a self-selected over-ground walking speed, internal rotation, and external rotation [9 (link), 13 (link), 15 (link), 16 ]. For the static trial, subjects were instructed to stand upright with their feet hip-width apart and pointed forward, but the position of their feet was not strictly enforced by research personnel. The internal and external rotation activities were performed to end range of motion with both feet on the ground, while angular changes were permitted at the ankle and knee joints. The order of the dynamic activities was randomized. One trial of the static activity and two trials of the dynamic activities were collected.

Subjects were imaged simultaneously using an optical motion capture system and DF (Fig. 1). The motion capture system utilized Vicon Nexus software (v1.8.5, Vicon Motion Systems, Oxford, UK) and 10 near infrared cameras to acquire reflective marker positions at 100 Hz. Activities were performed on a dual-belt, instrumented treadmill (Bertec Corporation, Columbus, OH, USA). Reflective markers were placed on the pelvis and thigh to locate bony landmarks and track segment motion [12 ]. Surface markers were placed on the left and right anterior superior iliac spine (ASIS), posterior superior iliac spine (PSIS) and iliac crests (ILC). A cluster of four markers on a rigid plate was strapped to the thigh with Velcro at a proximolateral position. Markers were also placed on the medial epicondyles of the knees and medial malleoli of the ankles to calculate leg length, which was required for predictive HJCs. Three dimensional (3D) skin marker positions were reconstructed and gap-filled in Vicon Nexus software. The Vicon and DF systems were synced temporally with an external trigger and spatially using a calibration cube that contained reflective markers with metal beads at their center [12 ].