Randomised clinical trial of pilonidal sinus operations performed in the prone position under spinal anaesthesia with hyperbaric bupivacaine 0.5 % versus total intravenous anaesthesia - Schmittner, Marc; Dieterich, Sven; Gebhardt, Volker; Weiß, Christel; Bussen, Dieter G.; Viergutz, Tim (International journal of colorectal disease, 2013)