Stynes, Siobhan, Snell, Kym IE, Riley, Richard D, Konstantinou, Kika, Cherrington, Andrea, Daud, Noor, Ostelo, Raymond, O'Dowd, John, Foster, Nadine E, "Predictors of outcome in sciatica patients following an epidural steroid injection: the POiSE prospective observational cohort study protocol", BMJ Open, 2023