Abstract: Objective To study the clinical value of posterior urethral curvature (PUC) in evaluating bladder outlet obstruction (BOO) caused by benign prostatic hyperplasia (BPH). 
Methods A total of 253 male patients treated in the Department of Urology,the Second Hospital of Hebei Medical University were enrolled in this study. According to presence or absence of lower urinary tract symptoms (LUTS), the patients were divided into LUTS group (n=193) and control group (n=60). The PUC of all enrolled people was collected by pelvic floor ultrasound. The data collected included total prostate volume (TPV), transition zone volume (TZV), transition zone index (TZI), degree of intravesical prostatic protrusion (IPP), prostate urethral angle (PUA), prostatic specific antigen (PSA), international prostate symptom score (IPSS) and urethral length (UL). The maximum urinary flow rate (Qmax) and bladder outlet obstruction index (BOOI) were collected with the urodynamic detector. The sensitivity, specificity and cut-off point of PUC in predicting BOOI were further analyzed by receiver operating characteristic (ROC) curve. Multiple linear regression was used to analyze the impact of TPV, TZV, TZI, IPP, PUA, PUC, UL, PSA, Qmax and IPSS on BOOI. 
Results The mathematical simulation showed that when the PUC angle increased from 0 °to 90 °, the urinary flow rate decreased by 50.9%. When the PUC angle increased from 30 ° to 90 °, the urinary flow rate decreased by 27%. The area under the ROC curve of PUC in diagnosing BOOI was 0.867. The optimal PUC value for diagnosing BOO was 48 °, the sensitivity was 88.1%, and the specificity was 75.8%. Based on comparison between PUC ≤48 ° group and PUC ＞48 ° group, patients with large PUC had larger TPV, TZV, TZI, IPP, PUA, IPSS and lower Qmax (P＜0.05). PUC was significantly correlated with TPV (r=0.268, P＜0.001), TZV (r=0.257, P＜0.001), TZI (r=0.241, P＜0.001), IPP (r=0.305, P＜0.001), PUA (r=0.335, P＜0.001), IPSS (r=0.357, P＜0.001), and BOOI (r=0.154, P=0.014). PUC was negatively correlated with Qmax (r=-0.358, P＜0.001). Multiple linear regression analysis showed that TPV, TZV, Qmax, PUA and PUC were the major influencing factors of BOOI. 
Conclusion In this theoretical model, PUC is negatively correlated with urinary flow rate. PUC is positively correlated with TPV, TZV, TZI, IPP, PUA, IPSS, and negatively correlated with Qmax, which may make PUC a new indicator for evaluating LUTS.

Key words: urinary bladder neck obstruction, ultrasonography, posterior urethral curvatyre