Previous studies have shown that bone growth acceleration can occur in many animal species after periosteal resection (removal of a strip of periosteum) with minimum morbidity. This has numerous clinical applications, including treatment of limb length differences. Here we use Second Harmonic Generation (SHG) imaging microscopy to evaluate changes in collagen architecture reflective of the different strains the periosteum may encounter during bone growth. Specifically, we image rabbit tibial periosteum strips at -20%, 0%, 5%, and 10% strains. We first quantify these changes using the SHG creation ratio (Forward/Backward) or the initially emitted SHG directionality to provide information on the fibril level of assembly. The in situ (i.e. physiological) strain had the highest creation ratio compared to the non-in situ strains of -20%, 5%, and 10%, which were shown to be significantly different via RCBD statistical analysis. These trends are consistent with SHG phasematching considerations, where more organized fibrils/fibers result in primarily forward emitted components, which here is the physiological strain. We further use the relative SHG conversion efficiency to assess the tissue structure under strain, where this results from the combination of collagen concentration and organization. The 0% strain SHG conversion efficiency was significantly higher than all other strains, where this is expected as the fibers have the highest local density and organization, and is consistent with the emission directionality results. Importantly, due to the underlying physical process, the label-free SHG imaging modality can non-invasively monitor the effect of treatments for bone growth and other orthopedic disorders.
Rajeev Chaudhary, Matthew Halanski, and Paul J. Campagnola, "Advanced quantitative imaging of musculoskeletal disorders (Conference Presentation)," Proc. SPIE 10063, Dynamics and Fluctuations in Biomedical Photonics XIV, 100630I (Presented at SPIE BiOS: January 30, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2252985.5371893404001.
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