Does levator avulsion increase urethral mobility?

Objective: It is often assumed that stress urinary incontinence may be due to abnormal pelvic floor muscle function or anatomy. This may be mediated through urethral hypermobility. The aim of the study was to determine the association between major levator ani defects ('avulsion') and urethral mobility. Study design: Three hundred and five women were referred to a tertiary referral service for lower urinary tract and prolapse symptoms between December 2006 and July 2008. All patients had undergone an interview, clinical examination, multichannel urodynamic testing and 4D transperineal ultrasound. Ultrasound volume datasets of 198 women were analysed retrospectively. Tomographic ultrasound imaging was used to diagnose levator avulsion at the time of the original assessment. To determine urethral mobility, data analysis was performed on a desktop PC using proprietary software several months later. The urethra was divided into 5 equal segments with 6 points marked evenly along the urethra from the bladder neck (Point 1) to the external meatus (Point 6) as identified in the mid-sagittal view. Measurements of vertical and horizontal distances from the dorsocaudal margin of the pubic symphysis of these 6 points were taken in the mid-sagittal plane, using volume datatsets obtained at rest and on maximal Valsalva. Mobility vectors of these 6 points were calculated using the formula SQRT ((x _valsalva - x _rest ) ² + (y _valsalva - y _rest ) ² ) and were correlated with levator status using two sample T tests. Results: Levator avulsion was found in 18% of patients (n = 35). Except at the bladder neck which almost reached significance (32.5 mm in those with defects vs. 28.9 mm in those without, P = 0.07), there was no significant association between urethral mobility and avulsion (all P ≥ 0.17). Conclusion: Major levator trauma does not seem to substantially affect urethral mobility, with the possible exception of the bladder neck.