Three-dimensional measurement and analysis of the compressor urethrae and urethra in postpartum women

The position and lines of the compressor urethrae, as well as the different segments and morphological characteristics of the compressor urethrae and urethra have not been systematically characterized. This study thus aimed to quantify the lines, thickness, volume, surface area, and position of the compressor urethrae, as well as the thickness, volume, and surface area in the upper, middle, and lower urethra, in postpartum females via three-dimensional (3D) measurement and analysis methods.

This retrospective study included a total of 90 postpartum women. The 3D models of compressor urethrae and urethra were constructed based on the imaging pictures of these women. The indicators that were analyzed in a 3D plane included volume, surface area, thickness, and diameter lines of the compressor urethrae; the ratio of the compressor urethrae length (CUL) to the urethral length (UL); the distance between the compressor urethrae and the pubic symphysis; the volume, surface area, and thickness of urethra and its different segments; the UL; and the urethral inclination angle (UIA). These indicators were compared between a postpartum-stress urinary incontinence (SUI) group and a control group. Differences in indicators between the segments of urethra were compared. The relationship between related indicators of the compressor urethrae and of the urethra with age was determined.

The length, width, and volume of the compressor urethrae in the control group were 23.24±3.29 mm, 24.61±3.79 mm, and 1.47±0.49 cm³, respectively. The upper, middle and lower regions of the urethral volume in the control group were 2.58±0.59, 2.10±0.32, and 0.84±0.37 cm³, respectively. The volume and thickness of the compressor urethrae, the CUL, and volume of the upper and middle regions of the urethra in the control group were significantly larger than those in the SUI group (P=0.002, P=0.02, P=0.01, P=0.003, and P<0.001, respectively). The volume and surface area of middle urethra were significantly larger than those of the lower urethra (P<0.001 and P<0.001, respectively). The compressor urethrae volume (r=-0.506; P=0.004), compressor urethrae surface area (r=-0.523; P=0.003), middle urethral volume (r=-0.403; P=0.03), and middle urethral thickness (r=-0.629; P<0.001) were negatively correlated with age.

This study provides reference criteria for the volume, thickness, and surface area of different portions of the compressor urethrae and urethra. The upper and middle urethra may be particularly significant to female urinary continence. Meanwhile, strengthening of the compressor urethrae might help treat female urinary continence.