It is stated that urinary incontinence in women is caused by at least two different mechanisms. Stress urinary incontinence (SUI) is caused by an increase of the intra-abdominal vertical pressure leading to an opening of the urethra. In contrast, urgency urinary incontinence (UUI) is considered to be caused by uninhibited contractions of the detrusor muscle. It is often reported in literature that the muscle contractions open up the urethra-vesical junction (UVJ) and lead to the involuntary loss of urine. Therefore, UUI is treated by physiotherapy and treatment of the neurological stimulation of the detrusor muscle. SUI, however, is treated by the anatomical replacement of the pubo-urethral ligament.
Analyzing the triggers for losing urine in patients with urge symptoms and incontinence, we observed that there is nearly no involuntary loss of urine in a horizontal body position. 
Therefore we hypothesized that the urge component may also be caused by the upright body position in a way that anatomic changes are leading to the urge sensation and involuntary loss of urine.

413 female patients with urge symptoms and involuntary loss of urine were included. The involuntary loss of urine was classified in “loss of urine in a horizontal body position” and “loss of urine in a vertical body position”. The horizontal body position was represented by lying and sleeping. The vertical body position was represented by an upright body position (standing up out of a sitting position and walking). Furthermore we verified if additional abdominal pressure (coughing/sneezing/laughing) leads to the loss of urine in patients with urge symptoms. After a self-observation period of 4 months the patients were interviewed with our standardized check-list about their daily routine and loss of urine situations.

All 413 patients with the symptoms of an overactive bladder and involuntary loss of urine went to the toilet immediately after the first urge. The patients went to bed between 10pm-11pm and got up between 7am-8am. Therefore all patients had a sleeping period (horizontal body position) between 8 - 12 hours and remained sitting/standing/walking  (vertical body position) between 12-16 hours.
Only 4% of patients (22/413) reported involuntary loss of urine during the horizontal body position, while all other 391 patients (96%) stated that the loss of urine was only in the vertical body position. 
32% of the women (135/413) with involuntary urine loss and urge symptoms stated a loss of urine in case of standing up out of a sitting position, 14% (59/413) while walking and 50% (206/413) while coughing/sneezing/laughing (extra abdominal pressure). 11% (44/413) reported a loss of urine independently of the body position.

Our study demonstrates that only 4% of female patients with urge symptoms and involuntary loss of urine are suffering of incontinence while lying/ sleeping (horizontal body position). It should be noted that an increase of the abdominal pressure in our patients (coughing/sneezing/laughing) was associated with the loss of urine.
We assume that if only the dysfunction of the detrusor muscle is causing the loss of urine in women with urge symptoms, the incontinence must be independent of the body position. Contrary to this, our results show that the majority of evaluated women with urge symptoms have involuntary loss of urine in the upright, vertical position.

We hypothesize that stress urinary incontinence and urge urinary incontinence are expressions of the same pathophysiological defect, namely the premature opening of the urethra-vesical junction (UVJ). As we observed the importance of the upright body position in women with urge symptoms and involuntary loss of urine, we consider the urge incontinence to be mainly caused by anatomical defects. There must be a rethinking of the etiology and treatment of urinary urge incontinence.