Noninvasive assessment of in vivo tissue loads to enhance the treatment of gait disorders

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Abstract The long-term goal of this research is to use in vivo muscle-tendon force measurements to enhance the clinical treatment of gait disorders in individuals with cerebral palsy (CP). We have recently shown that the frequency at which a tendon vibrates is dependent on the applied stress. This phenomenon is similar to the tension-dependent vibration seen in guitar strings. Vibration frequency reflects the speed at which transverse, or shear, waves propagate. Hence, it may be feasible to monitor shear wave speed in tendon as a proxy for tissue loading. This study will investigate the potential to measure and interpret shear wave speeds in human tendons. The initial two aims are designed to investigate the validity and robustness of the relationship between shear wave speed and tendon loading. Skin-mounted tensiometers will be designed that induce and track propagating shear waves of micron-scale amplitude. Cadaveric ankle-foot specimens will be tested in aim 1. A robotic gait simulator will drive external foot and internal tendon loading to emulate human walking. Tendon tensions and wave speeds will be simultaneously monitored. Human subjects will be tested in Aim 2. Tensiometers positioned over superficial knee and ankle tendons will monitor wave speeds while subjects perform isometric and isokinetic exertions. Data from aims 1 and 2 will be used to investigate how subject- and tendon-specific geometry can modulate the relationship between tendon wave speed and load. The final two aims will use tensiometers to measure shear wave speeds in the superficial leg tendons during walking. Typically developing children will be tested in Aim 3 to establish a normative database of wave speed patterns over a gait cycle. Individuals with CP who exhibit either equinus (toe-walking) or crouch (flexed knee) will be tested in Aim 4. Tendon wave speed measures will be obtained while subjects are undergoing a standard clinical gait analysis. We will explore clinical utility by performing direct comparisons between shear wave speed data, joint kinetics, EMG signals and clinical interpretations based on traditional gait analysis. The anticipated outcome of this study is a ground-breaking approach to assess in vivo muscle-tendon loads during both normal and pathological gait. Successful completion of the aims could lead to enhanced diagnosis and outcomes assessment of gait disorders.