The nail is a continuous skin appendage. Cells located around the nails, which display coordinated homeostatic dynamics and release a flow of stem cells in response to regeneration, have been identified in mice. However, very few studies regarding human nail stem cells exist in the literature. Using specimens isolated from humans, we detected an unreported population of cells within the basal layer of postnatal human nail proximal folds (NPFs) and the nail matrix around the nail root. These cells were multi-expressing and expressed stem cell markers, such as keratin 15 (K15), keratin 14 (K14), keratin 19 (K19), CD29, CD34, and leucine-rich repeat-containing G protein-coupled receptor 6 (Lgr6). These cells were very similar to mouse nail stem cells in terms of cell marker expression and their location within the nail. We also found that the putative nail stem cells maintained their abundance with advancing age, but cell proliferation and nail growth rate were decreased on comparison of young and aged specimens. To summarize, we found a putative population of stem cells in postnatal human nails located at NPFs and the nail matrix. These cells may have potential for cell differentiation and be capable of responding to injury, and were retained, but may be hypofunctional during aging.

Background: The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are important structures to maintain knee stability. The present study aimed to further enrich understandings of the morphology of the cruciate ligaments and explore the relationship between the diameter of ACL and PCL. Method: This study collected valid MRI samples of 50 male and 50 female normal right knee joints and measured the diameter of each point of the ACL and PCL through the 3D Slicer. Results: The diameter of the ACL in the sagittal MRI of the normal right knee joint was significantly different from the diameter of each point of the PCL. The average diameter of each point of the ACL was larger than the diameter of the corresponding point of the PCL. Males and females had statistical differences in their PCL origin point, PCL midpoint, ACL origin point, ACL midpoint, and ACL insertion point diameters under sagittal MRI examination. The average diameter of males was greater than the average diameter of females at the above corresponding sites. In sagittal MRI scans of the normal right knee joint, we observed that only the origin point of the PCL exhibited a moderate correlation with the midpoint and insertion point of the ACL in terms of their respective diameters. Conclusion: The correlation between diameters of normal ACL and PCL in knee joint MRI was moderate and may help clinicians determine appropriate graft for cruciate ligament reconstruction surgery quickly for severe cruciate ligament injuries.