Gracilis muscle dynamic urethral sphincter myoplasty: rat model experience

Dynamic urethral sphincter myoplasty (skeletal muscle urinary sphincter reconstruction) using a neurovascularly intact gracilis muscle was investigated in a rat model.

In female Sprague-Dawley rats, a unilateral gracilis anticus muscle flap was dissected from the medial thigh, preserving the medial muscular insertion, vascular flow, and innervation. This muscle graft was used to completely encircle the urethra and was fixed in position. Urodynamic leak point pressure (LPP) and bladder volume at leakage were measured with cystometry after 1 month, using an 18 gauge catheter placed through the bladder dome with a constant infusion rate of 0.2 ml. per minute. In addition, the effect of electrical stimulation of the gracilis myoplasty (current parameters: 1 to 10 mA, 1 to 60 Hz, 0.05 to 1 msec. duration) on intravesical leak point pressure was noted during cystometry.

The gracilis muscle measured 3.8 +/- 0.3 cm. in length, 0.5 +/- 0.1 cm. in width and 0.2 +/- 0.1 cm. in thickness. Blood flow rates to the grafted and contralateral gracilis myoplasty were similar at 43 +/- 26 and 51 +/- 30 g.cm.3, respectively (p = 0.46). The leak point pressure (LPP) of control, unstimulated gracilis myoplasty and gracilis myoplasty with electrical stimulation were 28 +/- 8, 32 +/- 12, and 85 +/- 27 mm.Hg (p < 0.01). Bladder volumes at LPP in the 3 respective groups were 0.5 +/- 0.2, 0.6 +/- 0.3 and 1.2 +/- 0.6 ml (p < 0.01).

Gracilis myoplasty is not obstructive, as substantiated by unchanged leak point pressure and leak point capacity. Myoplasty with low current stimulation, however, significantly increased LPP and leak point capacity.