Articular cartilage has a limited capacity to repair following injury. Early intervention is required to prevent progression of focal traumatic chondral and osteochondral defects to advanced cartilage degeneration and osteoarthritis. Novel cell-based tissue engineering techniques have been proposed with the goal of resurfacing defects with bioengineered tissue that recapitulates the properties of hyaline cartilage and integrates into native tissue. Transplantation of mesenchymal stem cells (MSCs) is a promising strategy given the high proliferative capacity of MSCs and their potential to differentiate into cartilage-producing cells - chondrocytes. MSCs are historically harvested through bone marrow aspiration, which does not require invasive surgical intervention or cartilage extraction from other sites as required by other cell-based strategies. Biomaterial matrices are commonly used in conjunction with MSCs to aid cell delivery and support chondrogenic differentiation, functional extracellular matrix formation and three-dimensional tissue development. A number of specific transplantation protocols have successfully resurfaced articular cartilage in animals and humans to date. In the clinical literature, MSC-seeded scaffolds have filled a majority of defects with integrated hyaline-like cartilage repair tissue based on arthroscopic, histologic and imaging assessment. Positive functional outcomes have been reported at 12 to 48 months post-implantation, but future work is required to assess long-term outcomes with respect to other treatment modalities. Despite relatively positive outcomes, further investigation is required to establish a consensus on techniques for treatment of chondral and osteochondral defects with respect to cell source, isolation and expansion, implantation density, in vitro precultivation, and scaffold composition. This will allow for further optimization of MSC proliferation, chondrogenic differentiation, bioengineered cartilage integration, and clinical outcome.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-014-0432-1) contains supplementary material, which is available to authorized users.

IntroductionThe quality of cartilaginous tissue derived from bone marrow mesenchymal stromal stem cell (BMSC) transplantation has been correlated with clinical outcome. Therefore, culture conditions capable of modulating tissue phenotype, such as oxygen tension and scaffold composition, are under investigation. The objective of this study was to assess the effect of hypoxia on in vitro BMSC chondrogenesis within clinically approved porous scaffolds composed of collagen and hyaluronic acid (HA). It was hypothesized that hypoxic isolation/expansion and differentiation would improve BMSC chondrogenesis in each construct.MethodsOvine BMSCs were isolated and expanded to passage 2 under hypoxia (3% oxygen) or normoxia (21% oxygen). Cell proliferation and colony-forming characteristics were assessed. BMSCs were seeded at 10 million cells per cubic centimeter on cylindrical scaffolds composed of either collagen I sponge or esterified HA non-woven mesh. Chondrogenic differentiation was performed in a defined medium under hypoxia or normoxia for 14 days. Cultured constructs were assessed for gene expression, proteoglycan staining, glycosaminoglycan (GAG) quantity, and diameter change.ResultsIsolation/expansion under hypoxia resulted in faster BMSC population doublings per day (P <0.05), whereas cell and colony counts were not significantly different (P = 0.60 and 0.30, respectively). Collagen and HA scaffolds seeded with BMSCs that were isolated, expanded, and differentiated under hypoxia exhibited superior aggrecan and collagen II mRNA expressions (P <0.05), GAG quantity (P <0.05), and proteoglycan staining in comparison with normoxia. GAG/DNA was augmented with hypoxic isolation/expansion in all constructs (P <0.01). Comparison by scaffold composition indicated increased mRNA expressions of hyaline cartilage-associated collagen II, aggrecan, and SOX9 in collagen scaffolds, although expression of collagen X, which is related to hypertrophic cartilage, was also elevated (P <0.05). Proteoglycan deposition was not significantly improved in collagen scaffolds unless culture involved normoxic isolation/expansion followed by hypoxic differentiation. During chondrogenesis, collagen-based constructs progressively contracted to 60.1% ± 8.9% of the initial diameter after 14 days, whereas HA-based construct size was maintained (109.7% ± 4.2%).ConclusionsHypoxic isolation/expansion and differentiation enhance in vitro BMSC chondrogenesis within porous scaffolds. Although both collagen I and HA scaffolds support the creation of hyaline-like cartilaginous tissue, variations in gene expression, extracellular matrix formation, and construct size occur during chondrogenesis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13287-015-0075-4) contains supplementary material, which is available to authorized users.

BackgroundGlenohumeral instability is a common problem following traumatic anterior shoulder dislocation. Two major risk factors of recurrent instability are glenoid and Hill-Sachs bone loss. Higher failure rates of arthroscopic Bankart repairs are associated with larger degrees of bone loss; therefore it is important to accurately and reliably quantify glenohumeral bone loss pre-operatively. This may be done with radiography, CT, or MRI; however no gold standard modality or method has been determined. A scoping review of the literature was performed to identify imaging methods for quantifying glenohumeral bone loss.MethodsThe scoping review was systematic in approach using a comprehensive search strategy and standardized study selection and evaluation. MEDLINE, EMBASE, Scopus, and Web of Science were searched. Initial selection included articles from January 2000 until July 2013, and was based on the review of titles and abstracts. Articles were carried forward if either reviewer thought that the study was appropriate. Final study selection was based on full text review based on pre-specified criteria. Consensus was reached for final article inclusion through discussion amongst the investigators. One reviewer extracted data while a second reviewer independently assessed data extraction for discrepancies.ResultsForty-one studies evaluating glenoid and/or Hill-Sachs bone loss were included: 32 studies evaluated glenoid bone loss while 11 studies evaluated humeral head bone loss. Radiography was useful as a screening tool but not to quantify glenoid bone loss. CT was most accurate but necessitates radiation exposure. The Pico Method and Glenoid Index method were the most accurate and reliable methods for quantifying glenoid bone loss, particularly when using three-dimensional CT (3DCT). Radiography and CT have been used to quantify Hill-Sachs bone loss, but have not been studied as extensively as glenoid bone loss.ConclusionsRadiography can be used for screening patients for significant glenoid bone loss. CT imaging, using the Glenoid Index or Pico Method, has good evidence for accurate quantification of glenoid bone loss. There is limited evidence to guide imaging of Hill-Sachs bone loss. As a consensus has not been reached, further study will help to clarify the best imaging modality and method for quantifying glenohumeral bone loss.Electronic supplementary materialThe online version of this article (doi:10.1186/s12891-015-0607-1) contains supplementary material, which is available to authorized users.

The pre-Bötzinger Complex (preBötC) inspiratory centre remains active in isolated brainstem-spinal cords and brainstem slices. The extent to which findings in these models depend on their dimensions or superfusate [K + ] and [Ca 2+ ] (both of which determine neuronal excitability) is not clear. We report here that inspiratory-related rhythms in newborn rat slices and brainstem-spinal cords with defined boundaries were basically similar in physiological Ca 2+ (1.2 mM) and K + (3 mM). Hypoglossal nerve rhythm was 1 : 1-coupled to preBötC activity in slices and to cervical nerve bursts in en bloc preparations lacking the facial motonucleus (VII). Hypoglossal rhythm was depressed in brainstems containing (portions of) VII, while pre/postinspiratory lumbar nerve bursting was present only in preparations with > 79% VII. preBötC-related slice rhythms were inhibited in 1.5 mM Ca 2+ solution, whereas their longevity and burst rate were substantially augmented in 1 mM Ca 2+ . Ca 2+ depression of slice rhythms was antagonized by raising superfusate K + to 8-10 mM. This strong extracellular Ca 2+ /K + antagonism of inspiratory (motor) rhythms was also revealed in brainstem-spinal cords without VII, while the inhibition was progressively attenuated with increasing amount of rostral tissue. We hypothesize that depression of hypoglossal rhythm and decreased Ca 2+ sensitivity of preBötC rhythm are probably not related to an increased content of rostral respiratory structures, but rather to larger brainstem dimensions resulting in interstitial gradients for neuromodulator(s) and K + , respectively. We discuss whether block of pre/postinspiratory activity in preparations with < 79% VII is due to impairment of the pathway from preinspiratory interneurons to abdominal muscles

Bone marrow-derived mesenchymal stromal stem cells (BMSCs) are a promising cell source for treating articular cartilage defects. The objective of this study was to assess a protocol that involved autologous transplantation of BMSCs into full-thickness cartilage defects in sheep following isolation, expansion, and a short period (4 days) of chondrogenic priming. The impact of oxygen tension during preimplantation culture was investigated. It was hypothesized that chondrogenically primed BMSCs would produce superior cartilaginous repair tissue relative to control defects, and that culture under hypoxia would yield improved repair tissue in comparison to normoxia. Ovine BMSCs were isolated, expanded to passage 2, seeded within a hyaluronic acid (HYAFF) scaffold, and primed ex vivo in chondrogenic medium for 4 days under normoxia (21% oxygen) or hypoxia (3% oxygen). Full-thickness, 7-mm-diameter articular cartilage defects were created in the femoral condyles of five sheep. Twenty defects were treated with normoxia-cultured, autologous BMSC-seeded scaffolds (eight); hypoxia-cultured, autologous BMSC-seeded scaffolds (eight); cell-free scaffolds (two); or no implants (two). Preimplantation priming was evaluated through gene expression analysis using reverse transcription quantitative polymerase chain reaction. After 6 months, histological assessment was performed on repair tissues with a modified O'Driscoll scoring system and tissue dimension analysis. Priming of preimplantation BMSC-seeded scaffolds in chondrogenic medium for 4 days resulted in significantly increased gene expression of hyaline cartilage-related collagen II and aggrecan relative to unprimed BMSCs (p < 0.05). Defects implanted with chondrogenically primed BMSC-seeded scaffolds developed cartilaginous repair tissues that contained safranin O-positive proteoglycans, and had significantly larger repair tissue areas, higher percentages of defect fill, and improved histological scores than cell-free controls (p < 0.05). Although hypoxic culture improved the preimplantation gene expression profile, a consistent difference in histological scores was not found between normoxia- and hypoxia-seeded BMSC-seeded scaffolds after 6 months (p = 0.90). This study demonstrates in a sheep model that (1) chondrogenic priming ex vivo improves the gene expression profile of BMSCs; (2) chondrogenically primed BMSCs are associated with the development of superior cartilaginous tissue to cell-free controls within cartilage defects; and (3) oxygen tension during preimplantation ex vivo culture does not consistently modulate cartilaginous repair tissue formation following BMSC transplantation into cartilage defects.