Stress incontinence is reported to occur more commonly in standing than other postures(1), but pelvic floor muscle function is rarely assessed in standing in men after prostatectomy. To better understand the mechanisms of incontinence and recovery after prostatectomy, it is important to investigate the influence of posture (seated vs. standing) on pelvic floor landmark location and displacement caused by contraction of individual pelvic floor muscles in this group.

Thirty-two men recruited for a randomised controlled trial of the efficacy of the pelvic floor muscle training for prevention and treatment of incontinence after prostatectomy underwent an assessment of pelvic floor anatomy and muscle function with transperineal ultrasound imaging at 2 weeks after prostatectomy. The ultrasound transducer was placed in the mid-sagittal plane of the perineum and optimised to visualize the urethra and five anatomical landmarks. Landmarks included the mid-urethra (related to contraction of the striated urethral sphincter (2)), bulb of the penis (for bulbocavernosus (2)), the ano-rectal junction and urethro-vesical junction (for puborectalis (2)) and the pubic symphysis. Participants were instructed to perform three submaximal pelvic floor muscle contractions (effort of 3 out of 10 on a modified Borg scale) in both supported-sitting with the legs straight on a plinth and in standing. Ultrasound data were recorded in video format. 

	Two individual ultrasound frames were exported for analysis from the videos at: (i) rest and (ii) peak displacement of peri-urethral landmarks during the submaximal pelvic floor muscle contraction. The dorsoventral (x) coordinates of the mid urethra and penile bulb, and both the dorsoventral and caudocranial (y) coordinates of the anorectal and urethrovesical junctions with respect to the dorsal pole of the pubic symphysis in the ‘rest’ frame provided measures of pelvic floor anatomy at rest. The change in location of each landmark (i.e. displacement in the x, y and combined [vector] direction) between the ‘rest’ and ‘contract’ frames relative to the pubic symphysis provided a measure of pelvic floor muscle contraction.

	Repeated measures ANOVAs were used to compare the resting location of each landmark between postures, and also the displacement and vector length of landmarks during contraction between postures, as these measures have been shown to be repeatable and related to continence status after prostatectomy.

Analysis of landmark location between postures after prostatectomy revealed that the urethro-vesical junction was located lower (P<0.001) and the anorectal junction (P=0.004), penile bulb (P<0.001) and mid-urethral (P<0.001) landmarks were all located more ventrally at rest in standing than supported sitting. The vector length of UVJ and ARJ (as an estimate of puborectalis length) were both shorter in standing than sitting (P=0.002 and P<0.001). Group average of the location data has been represented in Figure 1. During contraction the data showed greater caudocranial (elevation) motion of the urethrovesical junction (P=0.007) in standing than sitting. Group average, standard deviation and p-values for all comparisons are presented in Figure 2.

The results of this study demonstrate differences in urethral, anorectal and bladder neck position and bladder neck motion with contraction between sitting and standing postures in men after prostatectomy. Some results differ from those in a previous analysis of men prior to prostatectomy (3). The more caudal placement of the urethrovesical junction at rest and greater cranial motion with contraction in standing than in sitting could be explained by greater descent as a result of challenge to support the abdominal contents, and then greater potential for movement with contraction from a lower position. The shorter length of the puborectalis muscle (estimated from vector distance to pubic symphysis) in standing is explained by more ventral location of the landmarks, despite their lower position. This is similar to observations of men before prostatectomy(3). Unlike the pre-operative observations, the mid-urethra and penile bulb are more ventral in standing than sitting after prostatectomy. This difference in mechanics is likely to be explained by changes to pelvic support associated with surgery (e.g. excision of the endopelvic fascia and of the puboprostatic ligaments and suturing/scaring).Greater displacement of the UVJ in standing and sitting after, but not before prostatectomy is also most likely explained by differences in mobility related to disruption of bladder and urethral supporting structures during the procedure.

In men two-weeks after undergoing prostatectomy, puborectalis was observed to be more shortened, the bladder neck lower and the anorectal junction, mid urethra and penile bulb more ventrally located in standing than sitting. The participants also elevated the bladder neck more in standing than in sitting with pelvic floor contraction after prostatectomy. These differences in pelvic floor anatomy and muscle function between postures are most likely explained by surgical factors and are likely to impact the mechanics of the continence mechanism.

Bo K, Finckenhagen HB. Is there any difference in measurement of pelvic floor muscle strength in supine and standing position? Acta Obstet Gynecol Scand. 2003;82(12):1120-4.
Stafford RE, Coughlin G, Lutton NJ, Hodges PW. Validity of Estimation of Pelvic Floor Muscle Activity from Transperineal Ultrasound Imaging in Men. PLoS One. 2015;10(12):e0144342.
Cowley D, Stafford RE, Hodges PW. Influence of body position on dynamics of the pelvic floor measured with transperineal ultrasound imaging in men. Neurourology and urodynamics. 2020:10.1002/nau.24301.