Journal of orthopaedic research : official publication of the Orthopaedic Research Society
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The defining characteristic of the annulus fibrosus (AF) of the intervertebral disc (IVD) has long been the lamellar structures that consist of highly ordered collagen fibers arranged in alternating oblique angles from one layer to the next. However, a series of recent histologic studies have demonstrated that AF lamellae contain elastin- and type VI collagen-rich secondary "cross-bridge" structures across lamellae. In this study, we use optical coherence tomography (OCT) to elucidate the three-dimensional (3-D) morphologies of these translamellar cross-bridges in AF tissues. ⋯ In contrast to previously proposed models extrapolated from 2-D sections, results from this current study show that translamellar cross-bridges exist as a complex, interconnected network. We also found much greater variation in lengths of cross-bridges within the interbundle space of lamellae (0.8-1.4 mm from the current study versus 0.3-0.6 mm from 2-D sections). OCT-based 3-D morphology of translamellar cross-bridge provides novel insight into the AF structure.
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Comparative Study
Population average T2 MRI maps reveal quantitative regional transformations in the degenerating rabbit intervertebral disc that vary by lumbar level.
Magnetic resonance imaging (MRI) with T2-weighting is routinely performed to assess intervertebral disc degeneration. Standard clinical evaluations of MR images are qualitative, however, and do not focus on region-specific alterations in the disc. Utilizing a rabbit needle puncture model, T2 mapping was performed on injured discs to develop a quantitative description of the degenerative process following puncture. ⋯ Population average T2 maps provided a quantitative representation of the injury response, and identified deviations of individual degenerate discs from the pre-injury population. We found that the response to standardized injury was modest at lower lumbar levels, likely as a result of increased disc dimensions. These tools will be valuable for the quantitative characterization of disc degeneration in future clinical and pre-clinical studies.
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Low magnitude high frequency vibration (LMHFV) has been shown to improve anabolic and osteogenic responses in osteoporotic intact bones and during osteoporotic fracture healing; however, the molecular response of LMHFV during osteoporotic fracture healing has not been investigated. It was hypothesized that LMHFV could enhance osteoporotic fracture healing by regulating the expression of genes related to chondrogenesis (Col-2), osteogenesis (Col-1) and remodeling (receptor activator for nuclear factor- κ B ligand (RANKL) and osteoproteger (OPG)). ⋯ Osteoporotic bone had a higher response to LMHFV than normal bone and showed significantly better results as reflected by increased expression of Col-2 and Col-1 at week 2 (p<0.001 for all), larger callus width at week 2 (p=0.001), callus area at week 1 and 5(p<0.05 for all) and greater relative area of osseous tissue (p=0.002) at week 8. This study helps to understand how LMHFV regulates gene expression of callus formation, mineralization and remodeling during osteoporotic fracture healing.
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Heterotopic ossification (HO) is the abnormal formation of bone in soft tissue. Current diagnostics have low sensitivity or specificity to incremental progression of mineralization, especially at early time points. Without accurate and reliable early diagnosis and intervention, HO progression often results in incapacitating conditions of limited range of motion, nerve entrapment, and pain. ⋯ MicroCT could not detect HO until 5 wk. Confocal microscopy confirmed fluorophore localization to areas of HO. These findings demonstrate the ability of a near-infrared optical imaging strategy to accurately and reliably detect and monitor HO in a murine model.
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The goal of soft tissue sarcoma management in the extremities is limb preservation, often combining surgery and external beam radiation. In patients who have undergone this therapy in the thigh, pathologic fracture is a serious, late complication. Non-union rates of 80-90% persist. ⋯ MicroCT demonstrated a lack of callus volume in Disease groups. Heterotopic ossification was observed in some OP-1 treated animals. The ineffectiveness of OP-1 in stimulating fracture union in this model suggests the endogenous repair mechanism has been compromised beyond the capabilities of osteoinductive biologics.