Two Cases of Delayed Flexor Tendon Rupture Decades After Reconstruction

Two patients are presented with late-term ruptures of their flexor tendon grafts 10 and 40 years, respectively, after reconstruction. Both occurred from low-energy mechanisms. Their ruptures were intratendinous and not at the proximal or distal insertions. Electron microscopy demonstrated degeneration and increased matrix deposition. Immunohistology showed viable tenocytes, but no clear vascular organization to the disrupted grafts. Even after clinically successful flexor tendon autograft, tendons may still be at risk of degeneration and rupture a decade or more after reconstruction.

Statistical Assumptions in Orthopaedic Literature: Are Study Findings at Risk?

Background

As orthopaedic surgery becomes more evidence-based, the need for rigorous research has increased. This results in more complex studies that employ more sophisticated statistical analysis, often some form of regression. These statistical techniques require the data to meet certain assumptions for the findings to be considered valid. The purpose of this study is to determine the common regression techniques employed in the orthopaedic surgery literature, and demonstrate how often the assumptions of regression analyses are met and reported.

Methods

Studies published in the Journal of Bone & Joint Surgery (JBJS) in 2017 and 2018 were reviewed. Commentaries, editorials, and systematic reviews were excluded. The statistical analyses performed in each study were documented. When regression analyses were utilized, the article was reviewed for evidence that the necessary assumptions underlying the statistical methodology were assessed and met.

Results

From the 470 studies that were reviewed, the most common statistical test reported was the independent-samples t-test (n=215, 45.7%). Also, 201 studies (42.8%) implemented some form of regression analysis. The most common regression was a logistic regression (n= 106). None of the 201 studies using regression analysis reported meeting all of the necessary assumptions to appropriately use a regression test.

Conclusion

Many recent studies published in JBJS depended on regression analyses to reach their conclusions, but none fully reported the necessary assumptions of these tests. Orthopaedic surgery journals should be more transparent in reporting the methodology of statistical tests, and readers must beware of possible gaps in statistical methodology and critically evaluate the studies' findings.

Cannabinoid Receptor-2 Regulates Embryonic Hematopoietic Stem Cell Development via Prostaglandin E2 and P-Selectin Activity

Cannabinoids (CB) modulate adult hematopoietic stem and progenitor cell (HSPCs) function, however, impact on the production, expansion, or migration of embryonic HSCs is currently uncharacterized. Here, using chemical and genetic approaches targeting CB-signaling in zebrafish, we show that CB receptor (CNR) 2, but not CNR1, regulates embryonic HSC development. During HSC specification in the aorta-gonad-mesonephros (AGM) region, CNR2 stimulation by AM1241 increased runx1;cmyb(+) HSPCs, through heightened proliferation, whereas CNR2 antagonism decreased HSPC number; FACS analysis and absolute HSC counts confirmed and quantified these effects. Epistatic investigations showed AM1241 significantly upregulated PGE2 synthesis in a Ptgs2-dependent manner to increase AGM HSCs. During the phases of HSC production and colonization of secondary niches, AM1241 accelerated migration to the caudal hematopoietic tissue (CHT), the site of embryonic HSC expansion, and the thymus; however these effects occurred independently of PGE2. Using a candidate approach for HSC migration and retention factors, P-selectin was identified as the functional target of CNR2 regulation. Epistatic analyses confirmed migration of HSCs into the CHT and thymus was dependent on CNR2-regulated P-selectin activity. Together, these data suggest CNR2-signaling optimizes the production, expansion, and migration of embryonic HSCs by modulating multiple downstream signaling pathways.

Estrogen defines the dorsal-ventral limit of VEGF regulation to specify the location of the hemogenic endothelial niche

Genetic control of hematopoietic stem and progenitor cell (HSPC) function is increasingly understood; however, less is known about the interactions specifying the embryonic hematopoietic niche. Here, we report that 17β-estradiol (E2) influences production of runx1+ HSPCs in the AGM region by antagonizing VEGF signaling and subsequent assignment of hemogenic endothelial (HE) identity. Exposure to exogenous E2 during vascular niche development significantly disrupted flk1+ vessel maturation, ephrinB2+ arterial identity, and specification of scl+ HE by decreasing expression of VEGFAa and downstream arterial Notch-pathway components; heat shock induction of VEGFAa/Notch rescued E2-mediated hematovascular defects. Conversely, repression of endogenous E2 activity increased somitic VEGF expression and vascular target regulation, shifting assignment of arterial/venous fate and HE localization; blocking E2 signaling allowed venous production of scl+/runx1+ cells, independent of arterial identity acquisition. Together, these data suggest that yolk-derived E2 sets the ventral boundary of hemogenic vascular niche specification by antagonizing the dorsal-ventral regulatory limits of VEGF.

Prostaglandin E2 regulates liver versus pancreas cell-fate decisions and endodermal outgrowth

The liver and pancreas arise from common endodermal progenitors. How these distinct cell fates are specified is poorly understood. Here we describe prostaglandin E2 (PGE2) as a regulator of endodermal fate specification during development. Modulating PGE2 activity has opposing effects on liver versus pancreas specification in zebrafish embryos as well as mouse endodermal progenitors. The PGE2 synthetic enzyme cox2a and receptor ep2a are patterned such that cells closest to PGE2 synthesis acquire a liver fate, whereas more distant cells acquire a pancreas fate. PGE2 interacts with the bmp2b pathway to regulate fate specification. At later stages of development, PGE2 acting via the ep4a receptor promotes outgrowth of both the liver and pancreas. PGE2 remains important for adult organ growth, as it modulates liver regeneration. This work provides in vivo evidence that PGE2 may act as a morphogen to regulate cell-fate decisions and outgrowth of the embryonic endodermal anlagen.