<qa>  What is the aim of this study?The aim of this study is to find out the optimal technique to perform spinal anesthesia by residents in training. Thus the investigators will compare preprocedural ultrasound-guided paramedian technique using parasagittal oblique view vs preprocedural ultrasound-guided midline technique using transverse median view vs landmark-guided midline technique of spinal anesthesia in the elderly population. Our hypothesis is that both preprocedural US-guided techniques are superior to the conventional landmark-guided midline technique with regard to ease of performance defined as success rate at first attempt, number of puncture attempts, spinal procedure time, and patient satisfaction. 