ABSTRACT
Objective To investigate the influence of internal and external sphincter loss synergy on stress distributions and urine flow rates of lower urinary tract organs and tissues. Methods Based on collodion slice, the geometric model of the lower urinary tract was reconstructed, and finite element model of the lower urinary tract with muscle active force was established. Through fluid structure coupling simulation, the changes of tissue stress and urine flow rate were simulated under four conditions: normal contraction of internal and external sphincter, total loss of muscle active force and single loss of muscle active force for internal and external sphincters at the end of urination. Results The urethral stress changes in normal contraction of internal and external sphincter muscles were the same as the clinically measured urethral pressure changes. Compared with normal contraction, when the internal sphincter lost its muscle active force alone, stress of the internal sphincter and the urethra of the prostate was reduced by 33.6% and 13.8%, and flow rate of urine in this position was also reduced. When the external sphincter lost its muscle active force alone, the urethral stress of the external sphincter and external urethra was reduced by 59.5% and 24.03%, respectively. When the internal and external sphincter lost muscle active force, stress of the internal sphincter, the prostate, the external sphincter and the external urethra were reduced by 38.77%, 18.6%, 63.58%, 29.74%, respectively, and flow velocity in the corresponding position was also reduced. Conclusions Internal and external sphincter loss synergy resulted in the difference of tissue stress and urine flow rate. The results can provide the theoretical basis for surgical treatment of urinary incontinence caused by sphincter.