Critical-sized bone defects are defined as those that will not heal spontaneously within a patient's lifetime. Current treatment options include vascularized bone grafts, distraction osteogenesis, and the induced membrane technique. The induced membrane technique is an increasingly utilized method with favorable results including high rates of union. Tissue engineering holds promise in the treatment of large bone defects due to advancement of stem cell biology, novel biomaterials, and 3D bioprinting. In this review, we provide an overview of the current operative treatment strategies of critical-sized bone defects as well as the current state of tissue engineering for such defects.

Purpose of Review This review evaluates current clinical literature on the use of platelet-rich plasma (PRP), including leukocyterich PRP (LR-PRP) and leukocyte-poor PRP (LP-PRP), in order to develop evidence-based recommendations for various musculoskeletal indications. Recent Findings Abundant high-quality evidence supports the use of LR-PRP injection for lateral epicondylitis and LP-PRP for osteoarthritis of the knee. Moderate high-quality evidence supports the use of LR-PRP injection for patellar tendinopathy and of PRP injection for plantar fasciitis and donor site pain in patellar tendon graft BTB ACL reconstruction. There is insufficient evidence to routinely recommend PRP for rotator cuff tendinopathy, osteoarthritis of the hip, or high ankle sprains. Current evidence demonstrates a lack of efficacy of PRP for Achilles tendinopathy, muscle injuries, acute fracture or nonunion, surgical augmentation in rotator cuff repair, Achilles tendon repair, and ACL reconstruction. Summary PRP is a promising treatment for some musculoskeletal diseases; however, evidence of its efficacy has been highly variable depending on the specific indication. Additional high-quality clinical trials with longer follow-up will be critical in shaping our perspective of this treatment option.

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Key Points• Hb-conformation-dependent interaction with band 3 protein regulates glycolysis in RBCs.• In hypoxia, HbS disrupts this system, disabling RBC antioxidant defense. Energy metabolism in RBCs is characterized by O 2 -responsive variations in flux through the Embden Meyerhof pathway (EMP) or the hexose monophosphate pathway (HMP). Therefore, the generation of ATP, NADH, and 2,3-DPG (EMP) or NADPH (HMP) shift with RBC O 2 content because of competition between deoxyhemoglobin and key EMP enzymes for binding to the cytoplasmic domain of the Band 3 membrane protein (cdB3). Enzyme inactivation by cdB3 sequestration in oxygenated RBCs favors HMP flux and NADPH generation (maximizing glutathione-based antioxidant systems). We tested the hypothesis that sickle hemoglobin disrupts cdB3-based regulatory protein complex assembly, creating vulnerability to oxidative stress. In RBCs from patients with sickle cell anemia, we demonstrate in the present study constrained HMP flux, NADPH, and glutathione recycling and reduced resilience to oxidative stress manifested by membrane protein oxidation and membrane fragility. Using a novel, inverted membrane-on-bead model, we illustrate abnormal (O 2 -dependent) association of sickle hemoglobin to RBC membrane that interferes with sequestration/inactivation of the EMP enzyme GAPDH. This finding was confirmed by immunofluorescent imaging during RBC O IntroductionSickle cell anemia (SCA) arises from a single amino acid substitution (Glu6Val) in the ␤-globin chain. Although the change to hemoglobin (Hb) is simple and uniform, SCA is characterized by broad differences in clinical manifestation. Phenotype variation in SCA is thought to arise from both environmental and genetic factors (eg, ␤-gene cluster haplotype, degree of HbF expression, or effects of other epistatic genes). The environmental factor that most clearly influences SCA phenotype is hypoxia, which drives sickle Hb (HbS) polymerization and the resulting well-characterized alterations in RBC physiology and the microcirculation. However, the influence of hypoxia on the SCA phenotype appears to be insufficiently explained by HbS polymerization alone. 1 Moreover, we lack a clear mechanistic understanding of the significant oxidative stress complicating SCA, a key feature of phenotype variation, both at rest and in association with hypoxia. 2 Nonpolymerized, solution-phase HbS may promote oxidative stress, even in RBCs under normal physiologic O 2 gradients. 3 Specifically, the low redox potential for heme in HbS 4 and avid binding affinity of HbS for the cytoplasmic regulatory domain of the Band 3 membrane protein (cdB3) 5,6 strongly affect RBC energetics and antioxidant systems [7][8][9] and, notably, do so as a function of RBC O 2 content. Therefore, both the genesis and the disposal of reactive oxygen species are abnormal in SCA, creating a baseline state of oxidative stress, which worsens in hypoxia.In particular, consideration of metabolic control in RBCs suggests O 2 -dependent HbS-cdB3 interaction as a relatively ...

Background The number of Mesenchymal Stem/Stromal Cells (MSCs) in the human bone marrow (BM) is small compared to other cell types. BM aspirate concentration (BMAC) may be used to increase numbers of MSCs, but the composition of MSC subpopulations and growth factors after processing are unknown. The purpose of this study was to assess the enrichment of stem/progenitor cells and growth factors in BM aspirate by two different commercial concentration devices versus standard BM aspiration. Methods 120 mL of BM was aspirated from the iliac crest of 10 male donors. Each sample was processed simultaneously by either Emcyte GenesisCS ® (Emcyte) or Harvest SmartPReP2 BMAC (Harvest) devices and compared to untreated BM aspirate. Samples were analyzed with multicolor flow cytometry for cellular viability and expression of stem/progenitor cells markers. Stem/progenitor cell content was verified by quantification of colony forming unit-fibroblasts (CFU-F). Platelet, red blood cell and total nucleated cell (TNC) content were determined using an automated hematology analyzer. Growth factors contents were analyzed with protein quantification assays. Statistical analyses were performed by ANOVA analysis of variance followed by Tukey’s multiple comparison test or Wilcoxon matched-pairs signed rank test with p < 0.05 for significance. Results Cell viability after processing was approximately 90% in all groups. Compared to control, both devices significantly enriched TNCs and platelets, as well as the CD45−CD73+ and CD45−CD73+CD90+ cell populations. Further, Harvest significantly concentrated CD45−CD10+, CD45−CD29+, CD45−CD90+, CD45−CD105+, CD45−CD119+ cells, and CD45dimCD90+CD271+ MSCs, whereas Emcyte significantly enriched CD45dimCD44+CD271+ MSCs. BM concentration also increased the numbers of CFU-F, platelet-derived growth factor, vascular endothelial growth factor, macrophage colony-stimulating factor, interleukin-1b, VCAM-1 and total protein. Neither system concentrated red blood cells, hematopoietic stem cells or bone morphogenetic proteins. Conclusion This data could contribute to the development of BMAC quality control assays as both BMAC systems concentrated platelets, growth factors and non-hematopoietic stem cell subpopulations with distinct phenotypes without loss of cell viability when compared to unprocessed BM. Electronic supplementary material The online version of this article (10.1186/s12967-019-1866-7) contains supplementary material, which is available to authorized users.