A case-cross study of the impact of position on anterior pelvic parameters assessed by ultrasound KONG Fengbei，ZHANG Dirong，SHI Yu，YAO Chunxiao Department of Ultrasonic，Peking University Shenzhen Hospital，Guangdong Shenzhen，China，518036 ABSTRACT Objective To investigate the impact of traditional and modified lithotomy positions on the anterior pelvic parameters evaluated by ultrasound.Methods By two-stage crossover design.A total of 100 patients with pelvic floor ultrasound examination were randomly divided into two groups （50 cases in each group） and obtained required ultrasonic parameters.Group A started from traditional position to modified position，group B started from modified position to traditional position.The success rate and ultrasonic parameters between two positions were compared and analyzed.Results The success rate of maximum Valsalva movement in modified position was higher than that in traditional position （96% vs 90%,P<0.05）； The distance from bladder neck to reference line，posterior angle of bladder and urethral inclination angle were similar between the two positions at rest（P > 0.05）； The bladder posterior angle，bladder neck movement ，urethral rotation angle ，formation rate of urethral funnel obtained in the modified position were higher than those in the traditional position at maximum Valsalva movement （P＜0.05），and the first three parameters were not significantly affected by the experimental sequence （P > 0.05）.Conclusion Body position factors had influence on the evaluation of anterior pelvic parameters.The parameters obtained by modified position were higher than those in the traditional position，so we should pay attention to reasonable analysis in clinical application. KEY WORDS body position，pelvic floor ultrasound，anterior pelvic cavity，lithotomy position，case-cross study