High incidence of post-dural puncture headache in patients with spinal saddle block induced with Quincke needles for anorectal surgery: a randomised clinical trial. - Schmittner MD; Terboven T; Dluzak M; Janke A; Limmer ME; Weiss C; Bussen DG; Burmeister MA; Beck GC (International journal of colorectal disease, 2010)