Levator ani muscle: new physioanatomical aspects and role in the micturition mechanism

The anatomy of the levator ani muscle was studied in relation to the urinary bladder. The study was performed on 23 cadavers by dissection and microscopic examination. The levator ani is funnel-shaped and consists of a transverse portion called the levator plate and a vertical portion called the suspensory sling. The levator plate is a cone and consists of two "lateral masses" and two "crura," with the levator hiatus occupying its anterior part. Three crural patterns could be identified: classic, crural overlap, and crural scissors. The levator crura are connected to the intrahiatal organs by the hiatal ligament; the pubovesical ligament constitutes the anterior part of this ligament. The suspensory sling forms a vertical cuff around the intrahiatal organs, from which it is separated by a "tunnel septum." Its urethral portion ends in multiple fibrous septa, which penetrate the striated urethral sphincter. The levator ani plays an important role in bladder-neck fixation provided by the suspensory sling and hiatal ligament. Levator ani and hiatal ligament subluxation leads to ptosis of the urinary bladder. Furthermore, the present study demonstrates that the urethra is located in the infralevator compartment and is thus protected from the effect of intraabdominal pressure. A chronic increase in intraabdominal pressure leads to levator subluxation and sagging and to urethral exposure to intraabdominal pressure, which seems to interfere with the micturition mechanism. The infralevator location of the urethra might have a bearing on the pathogenesis and treatment of stress urinary incontinence.