Influence of the pre-operative time in upright sitting position and the needle type on the incidence of post-dural puncture headache (PDPH) in patients receiving a spinal saddle block for anorectal surgery. - Schmittner MD; Urban N; Janke A; Weiss C; Bussen DG; Burmeister MA; Beck GC (International journal of colorectal disease, 2011)