Experimental Study No. 8: Stress urinary incontinence results from muscle weakness and ligamentous laxity in the pelvic floor

AIM: To assess the roles of muscle damage and of ligamentous laxity in urinary stress incontinence. PATIENTS AND METHODS: Muscle biopsies (n = 47) were taken from the anterior portion of pubococcygeus muscle during the “tension-free” midurethral slingplasty procedure, an operation which corrects laxity in the pubourethral ligament. There were 38 multiparas with stress incontinence, and 9 nulliparas with mainly urge and frequency. The biopsies were examined blindly for evidence of muscle damage. Surgical cure was blindly assessed by means of a cough stress pad test. RESULTS: The results were correlated only after post-operative assessment. In total, 33 of the 39 patients with stress urinary incontinence were cured. In 17 biopsies of multiparas and in one nullipara the sample consisted only of a fibrous connective tissue scar. Fifteen of these 17 multiparas with stress urinary incontinence were cured postoperatively. Of the 21 biopsies of multiparas containing muscle tissue, 20 showed muscle damage; 18 of these patients were surgically cured; the mean urine loss on cough stress test reduced from 11.3 gm to 0.7 gm. Of the 8 nulliparous patients in this group with muscle tissue in the biopsy, only the biopsies of the four oldest patients showed muscle damage; none lost urine on pre or postoperative pad testing. CONCLUSIONS: Muscle and connective tissue damage are linked abnormalities that together lead to pelvic floor dysfunction and incontinence. Correction of ligamentous laxity can cure incontinence, even when there is muscle weakness.