Vascularization and bone repair are accelerated by a series of gene-activated scaffolds delivering both an angiogenic and an osteogenic gene. Stem cell-mediated osteogenesis in vitro, in addition to increased vascularization and bone repair by host cells in vivo, is enhanced using all systems while the use of the nanohydroxyapatite vector to deliver both genes markedly enhances bone healing.

Gene therapy can be combined with tissue engineering constructs to produce gene-activated matrices (GAMs) with enhanced capacity for repair. Polyethyleneimine (PEI), a non-viral vector, has previously been optimised for high efficiency gene transfer in rat mesenchymal stem cells (rMSCs). The use of PEI to transfect human MSCs (hMSCs) with ephrinB2 is assessed here. Recently a role for the ephrinB2 ligand and EphB4 receptor duo has been proposed in bone remodelling. Herein, over-expression of the ephrinB2 ligand resulted in increased osteogenic differentiation in hMSCs. As ephrinB2 is a cell surface anchored ligand which only interacts with cells expressing the cognate EphB4 receptor through direct contact, we have shown that direct cell-cell contact between two neighbouring cells is responsible for enhanced osteogenesis. In an effort to begin to elucidate the molecular mechanisms at play downstream of ephrinB2 over-expression, RT-PCR was performed on the GAMs which revealed no significant changes in runx2 or BMP2 expression but an upregulation of osterix (Osx) and Dlx5 expression prompting the belief that the mode of osteogenesis is independent of the BMP2 pathway. This select interaction, coupled with the transient gene expression profile of PEI, makes the PEI-ephrinB2 GAM an ideal candidate matrix for a bone targeted GAM.

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Background Many orthopaedic units measure hemoglobin (Hb) levels after primary joint arthroplasty to identify patients with postoperative anemia. With the refinement of surgical techniques, blood loss in primary arthroplasty has decreased. The aim of this study was to investigate the postoperative Hb monitoring and transfusion practices in our own institution after elective hip or knee arthroplasty. Methods We conducted a retrospective audit of all patients who underwent elective total hip or knee arthroplasty in Galway University Hospital between March 1 and June 1, 2019. We recorded when they underwent postoperative Hb testing, whether or not they had a drop of Hb, which would indicate transfusion (<8 g/dL), and whether or not they were transfused. In patients who underwent transfusion, a chart review was performed to establish the presence of factors that would have triggered repeat Hb testing. Results One hundred thirty-six patients underwent elective primary hip or knee arthroplasty in the period. All had a full blood count sent on the first postoperative day. None (0%) had a clinically significant (to < 8g/dL) postoperative Hb drop on day 1. Eighteen (13.2%) patients underwent repeat testing on day 2 or subsequently. Eight (5.9%) exhibited a drop in Hb to less than 8 g/dL, with a mean Hb drop of 4.26 (standard error of the mean ± 0.862, standard deviation ± 0.98), and 5 (3.7%) proceeded to undergo allogenic blood product transfusion. All 5 underwent documented indications for repeat Hb testing. Conclusions There is no evidence for performing routine Hb testing on day 1 after elective hip or knee arthroplasty. We recommend that postoperative Hb testing should only be carried out on patients with additional indications.

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