The Effect of Injection Needle Gauge Size on the Viability of Equine Mesenchymal Stem Cells

Aims Performance horses are at high risk of injury to the superficial digital flexor tendon (SDFT). Studies have shown that autologous mesenchymal stem cells (MSCs) injected into SDFT lesions subsequently result in a significant reduction of re‐injury in National Hunt racehorses; however, recent studies show that only 25% of implanted MSCs survive 24 h post injection. The reason for this loss is unclear but may relate to cell quiescence or injection‐related mortality. We hypothesised that cell viability and mortality is increased with needle gauge. Methods Equine MSCs cultured in vitro were resuspended to a final suspension density of 5 x 105 cells/ml to mimic that used for implantation in clinic. The cell suspension was injected through a 19 gauge, 21 gauge (current practice in clinic) or 23 gauge needle. Mesenchymal stem cells viability and mortality was analysed over a 24 h period post injection using alamarBlue® and Annexin V (apoptosis) assays, respectively. Results There was a 25% reduction in viability (P