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 urinar y bladder. The study was performed on 23 cadavers by dissection and microsc opic examination. The levator ani is funnel-shaped and consists of a transv erse portion called the levator plate and a vertical portion called the sus pensory sling. The levator plate is a cone and consists of two "lateral mas ses" and two "crura," with the levator hiatus occupying its anterior part. Three crural patterns could be identified: classic, crural overlap, and cru ral 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 in trahiatal organs, from which it is separated by a "tunnel septum." Its uret hral portion ends in multiple fibrous septa, which penetrate the striated u rethral 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. Fur thermore, the present study demonstrates that the urethra is located in the infralevator compartment and is thus protected from the effect of intraabd ominal pressure. A chronic increase in intraabdominal pressure leads to lev ator subluxation and sagging and to urethral exposure to intraabdominal pre ssure, which seems to interfere with the micturition mechanism. The infrale vator location of the urethra might have a bearing on the pathogenesis and treatment of stress urinary incontinence.