Persistent neck pain is a major problem, affecting at least 15.5 million Americans annually. Whiplash injury and the more chronic repetitive stress injury associated with the neck are significant sources of morbidity and disability.
Tissue mechanics and fiber organization for subfailure loading remain poorly understood. The goal of the project is to describe a quantitative and experimentally verified relationship between facet capsule ligament micro-kinematics and the tensile load under subfailure conditions. The integration of structural mechanics, microstructural imaging and modeling of the relationship of these in the context of painful loading will be advance soft tissue biomechanics. The project would provide benefits to not only neck pain sufferers but for a broad range of painful orthopaedic injuries.
The educational component will serve students at different levels (graduate, undergraduate and K-12 students) and promote hands-on and discovery-based learning. The outreach will include high school women in engineering opportunities through a hands-on research and educational program with Penn's Society of Women Engineers Student section.
Persistent pain is a tremendous problem in the United States, with chronic neck pain comprises nearly 30% of these syndromes. Although there is a rich biomechanics literature about ligament failure, prior to this award little was known about those ligament injuries in which dysfunction (i.e. pain) is produced without gross structural failure of the ligament. The facet capsular ligament (FCL) in the spine is particularly susceptible to this type of subfailure mechanical injury. The central hypothesis was that subfailure loading of the FCL can produce microscopic injury under certain loading conditions and permanently alter the fiber organization sufficient to load nerve fibers in the joint but not alter the structural properties of the ligament. This project used novel real-time imaging approaches to determine if, and under which conditions, such microstructural injuries occur. We developed novel methods to integrate with traditional biomechanics methods, validated them and used them to define collagen fiber kinematics upto and during failure. In addition to novel datasets definig macroscopic and microscopic motions and loading for this ligament, this work also defined the tolerance for such tissue micro-injuries for both tensile loading and shear loading - both relevant to real-world loading scenarios for the neck and this ligament. These thresholds provide new metrics for defining injury and for the first time suggest that painful injury can result from loading that is much less severe than that required for gross tissue rupture. Over the entire period of the award these research activities led to many publications in the imaging, biomechanics and modeling communities and also funded several graduate students and undergraduates who were involved in the research. Moreover, the work under this award led to two formalized collaborations - one with a industrial partner to define physiologic conseequences of such loading and another with an academic partner to further develop mathematical models defining the response of the ligament as a whole, the fiber and matrix contributions that comprise the ligament and their relative mechanical responses. In addition, in executing this project there have been many related activities that contribute to the broader impact of the engineering community and academic life of many groups of people. The day-to-day research activities involved students ranging from graduate trainees to college undergraduates to high school students. Hands on laboratories were revised to integrate biomechanical testing in the bioengineering curriculum, and women and high school girls were introduced to engineering opportunities through panels, workshops, visit days and other programs. In addition, several outreach courses were developed during the course of this award, including a new design course for appropriate point of care diagnostics for Sub-Saharan Africa, advances in STEM education at Penn, and more active faculty discussions about engineering education. Moving forward, this project has laid the foundation for additional cutting-edge research to better determine mechanisms by which subfailure tissue loading may lead to pain and permanent disability, in the absence of any gross measures of tissue injury. We are now poised to use those data and our current understanding to more deeply study the microstructural relationships of ligament components, nerve fiber responses and dysfunction - using the imaging methods developed during this award and through the collaborations developed for mathematical modeling.