Dynamic urinary graciloplasty in male goats: a study on histology and urethral pressures

The purpose of this study was to investigate the feasibility of dynamic bulbous urinary graciloplasty with respect to graciloplasty histology and urethral pressures. Two adult male goats underwent a pulled-through bulbous urethral graciloplasty with implant of electrodes and a pulse stimulator. Afterwards, a stimulation protocol was applied to have the fatiguable type II fibers replaced by fatigue-resistant type I fibers. Urethral pressure profilometry as well as analysis of histology was performed afterwards and compared with preoperative biopsies and preoperative recorded urethral pressures. Successful conversion from type II into type I muscle fibers was observed; the percentage of type I fibers increased from 29% to 83%. The percentage of connective tissue increased from 8% to 16%. No stricturing of the bulbous urethra was observed. The urethral pressures before stimulation increased from a mean of 107 cm H2O without stimulation, to 187 cm H2O with stimulation for the two goats. After training, the urethral pressure increased from a mean of 85 cm H2O without stimulation, to 118 cm H2O with stimulation. In male goats, successful dynamic urinary graciloplasty at the bulbous urethra is feasible. The achieved muscle fiber conversion guarantees fatigue-resistance, necessary for a continuous sphincteric muscle contraction. The maximal urethral pressures, however, are lower than those without stimulation.