Assistant Professor University of Delaware, United States
Introduction: Understanding force transmission in muscle-tendon-units (MTUs) is essential in studying the biomechanics of human motion. Relatively little work has been done to study force transmission and stretch in the iliotibial (IT) band. The IT band is a complex structure of connective tissue with proximal origins at the tensor fasciae latae and gluteus maximus with a distal insertion on the tibia at Gerdy’s tubercle.1 The specific function of the IT band is poorly defined, however it is understood to be important in bipedal locomotion as well as knee and hip stabilization. 2,3 Prior work studying IT band mechanics has focused on inverse dynamics approaches. 4,5 However inverse dynamics relies on assumptions that can give inaccurate readings of force transmission due to indirect sensing methods used to approximate load in the tissue of interest. In this study, we aim to non-invasively measure stress in the IT band using shear wave tensiometry.6 A shear wave tensiometer is a wearable biomechanical sensor that consists of a mechanical actuator, which taps on the skin to induce a shear wave through underlying soft tissues, and two mini uniaxial accelerometers, which detect downstream displacement of the tissue caused by the shear wave. The goal of this study was to implement shear wave tensiometry to quantify loading patterns in the IT band during walking, jogging, and functional movements.
Materials and
Methods: A cohort of healthy young adult participants (N=18, 10M/8F, 26 ± 4 years) were recruited for this study approved by the University of Delaware IRB. Analysis was performed on each subject’s dominant leg. For motion analysis, reflective tape was placed on the dominant leg at 8 positions of anatomic interest. The distal IT band (~4 cm proximal to the knee) was identified via palpation and a shear wave tensiometer was secured over the region of interest. Participants completed the following tasks while shear wave tensiometry collections were performed: walking (3 mph) and jogging (5 mph) trials on a fixed speed treadmill, and a series of functional movements. Cyclic shear wave speed data measured with the tensiometer was extracted and averaged using a custom MATLAB code. The raw mean stride for walking and jogging were overlaid for comparison. Jogging and all functional exercises were normalized to the average maximum wave speed during walking for each subject. Markerless motion capture was performed in Kinovea based on video captured during all functional tasks to evaluate joint kinematics. In addition, ultrasound images of the distal IT band were acquired and analyzed for cross sectional area in ImageJ. All normalized shear wave speeds were reported as mean ± standard deviation. Statistical analysis includes comparison between normalized peak shear wave speed within participants and between tasks using repeated measures ANOVA.
Results, Conclusions, and Discussions: Shear wave speed in the IT band varied across the gait cycle in both walking and jogging, as seen for a representative subject in Figure 1. In walking, shear wave speed reached a maximum during midstance, while jogging shear wave speeds were temporarily lower during midstance and between periods of increased tissue tension occurring from foot strike to midstance and midstance to toe off. Comparisons of walking and jogging reveal higher wave speeds in many subjects during walking compared to jogging, which is surprising given the increased ground reaction forces expected in running compared to walking.7 Figure 2 shows representative wave speed patterns across functional exercises. During balance testing, a contralateral reach yielded the highest IT band wave speeds. Hip hinge exercises show that hip flexion/extension (RDL) seemed to elicit the most stretch in the IT band. During combined hip and knee hinge exercises, split squats resulted in the greatest increase in tissue tension, likely due to the flexed position of the knee while maintaining an upright posture. Both isolated knee hinge exercises yielded similar IT band loading responses. When looking across the entire population (Table 1), a higher degree of variability was seen in combined hip and knee hinge exercises and hamstring curls compared to the other tasks. Tissue stretch in the IT band is dependent on both muscular activation and the postural changes in the knee and hip joint due to its origins. Functional movements that target various ranges of motion show the impact of knee and hip range of motion on changing wave speed. This study aimed to evaluate loading of the IT band during walking, jogging, and functional movements using tensiometry. This approach yielded cyclic data for walking, jogging, and functional movements. However, the resulting wave speeds showed high variability across subjects due to the anatomic complexity of the IT band. Ongoing analysis of kinematic data and structural assessment may help elucidate the variability within our study population. The use of shear wave tensiometry to evaluate IT band loading opens the door for continued research into athletic and injured subject populations in the future.
Acknowledgements (Optional): We would like to acknowledge the Delaware Center for Musculoskeletal Research. Funding for this study provided by the University of Delaware Research Foundation.
