Hypothesis / aims of study
Incontinence is a major issue after radical prostatectomy; affecting up to 60% of men. Although many men recover within 12 months, some continue to have long terms problems with a major impact on their quality of life. Radical prostatectomy removes smooth muscle of the internal sphincter, which places greater demand on the striated muscles of the pelvic floor to recover continence. “Sphincter insufficiency” is considered to be a major determinant of incontinence after prostatectomy, yet this concept oversimplifies the complex interaction of activity of multiple striated muscles that is required to maintain continence and other factors that challenge continence such as elevated intra-abdominal pressure. A major limitation has been that simultaneous measurement of the multiple muscles that can contribute to continence has been difficult, invasive and unlikely to be viable in clinical practice. Recent work has validated measurement of dynamic motion of pelvic structures using transperineal ultrasound imaging as a measure of activation of the striated urethral sphincter (SUS), puborectalis (PR) and bulbocavernosus (BC) muscles . Initial work has highlighted some differences in men with and without incontinence after prostatectomy .
This study aimed to compare dynamic (activation of SUS, PR and BC muscles) and anatomical (urethral length) features related to urinary continence control between men with and without incontinence after prostatectomy, and between these men and an age-matched group of men with no history of prostate disease or incontinence. The objective was to test the hypotheses that pelvic floor muscle function would be a determinant of why some men recover continence and others do not, and that recovery of continence requires augmentation of muscle function beyond that required to maintain continence in men without prostate disease/surgery. The second aim was to identify the amplitudes of pelvic floor muscle displacement that best discriminate between men with and without incontinence after radical prostatectomy.
Study design, materials and methods
The study included men with incontinence post-prostatectomy (PPI; n=20), continent men post-prostatectomy (PPC; n=23) and a control group with no history of prostate disease or incontinence (CC; n=20). In supported sitting, an ultrasound transducer (Aixplorer, SuperSonic Imagine, France) was placed on the perineum to visualise the urethra, bulb of penis, ano-rectal junction and bladder in a single view. Using this transperineal ultrasound imaging technique we recorded motion associated with contraction of the SUS, PR and BC muscles during maximal voluntary contraction (MVC), sub-maximal voluntary efforts, evoked coughing (inhalation of titrated dose of nebulised Capsaicin) and while performing a bearing down manouevre. Data were stored in video format and frames were exported for analysis with Matlab (The Mathworks, USA). Anatomical landmarks were identified and displacements between rest and contraction were measured for MVC, sub-maximal and bearing down tasks. For analysis of coughing, measures were made at the point of maximum displacement prior to, then after expulsion. Measures were compared between groups using Analysis of Variance and receiver operating characteristics (ROC) were calculated to determine the threshold displacements of pelvic structures that best differentiated PPI and PPC.
Interpretation of results
Men who were continent after radical prostatectomy achieved greater shortening of the SUS, PR and BC muscles than incontinent men during voluntary contractions. Notably, during an evoked cough, men who were continent after radical prostatectomy were able to maintain better bladder support (less PR lengthening) and greater compression of the distal urethra (BC displacement) than was achieved by the control participants with no history of prostate cancer or incontinence. The capacity to shorten the SUS ≥4.1mm and the PR ≥2.4mm best distinguished between PPI and PPC.